INTRODUCTION.

Chemistry is defined, by Dr Black, to be "the study of the effects produced by heat and by mixture, in all bodies, or mixtures of bodies, natural or artificial, with a view to the improvement of the arts, and the knowledge of nature:" or, according to the definition proposed by the learned editor of his lectures, "chemistry is the study of the effects of heat and mixture, with the view of discovering their general and subordinate laws, and of improving the useful arts."

Fourcroy has defined "chemistry to be that science which teaches the knowledge of the intimate and reciprocal action of all the bodies in nature on one another." To this definition it has been objected, that it requires much explanation, that the terms reciprocal and intimate action not being readily understood, would need new definitions to explain them, and that it embraces more than what strictly belongs to the science of chemistry. When motion is communicated, or taken away by the collision of different bodies, the action between these bodies is intimate and reciprocal; but the study of this action belongs to mechanics, and not to chemical science.

Perhaps no definition of chemistry has yet been given which is of sufficient logical precision to be entirely free from objection. The object of chemistry, however, admits of no ambiguity. It is the province of natural history to arrange and distribute natural bodies into classes and orders, each being accurately characterized, so that the objects which it includes may be readily recognized and distinguished by easy marks of reference. Mechanical science is employed about the external properties of bodies, and their effects on each other, the force and measure of which are subject to calculation; but it is the object of chemistry to discover the component parts of bodies, to examine the properties and uses of the combinations formed, either naturally or artificially, from these simple substances, and to observe and trace the laws by which these combinations take place.

Sect. I. Division of Natural Knowledge.

When we consider the immense and endless variety of objects which present themselves to the eye, it must appear, at first sight, impossible to acquire even a general knowledge of their qualities and properties. And, indeed, the longest life, with the most vigorous mind and the most indefatigable industry, would be greatly inadequate to the task of examining every individual object. Hence it is, by a law of the human mind, that we arrange the objects of our investigations into certain classes, the individuals of which are found to possess certain general properties. These are again subdivided into other classes with additional discriminative marks; and these last are still farther subdivided, till we arrive at the individual; and, if the arrangement be correct, this must possess all the characteristic marks of reference to the general and subordinate divisions of that class of objects to which it belongs. In this way the mind is aided in its investigations, and the communication of knowledge is facilitated and improved. Thus it is the province of natural history to arrange the objects which come under our observation, and to history describe them with such precision and accuracy as they may be easily distinguished from each other. It may be considered as a descriptive view of the material world in a state of rest or inaction, without taking into account the motions or mutual action of bodies on each other. It is the first successful step in the progress of knowledge.

But the operations of nature are seldom at rest. Natural Change succeeds change, new combinations are formed, and new productions make their appearance. The primary planets revolve round the sun as their centre; the secondary planets, or the moons, attracted by the primary, perform similar revolutions; the air of the atmosphere presses on the surface of the earth with a certain force; a stone, when unsupported, falls to the earth in a course directed towards its centre; water deprived of a certain portion of heat becomes solid, and appears in the form of ice; when combined with a greater portion of heat than what is necessary to retain it in the fluid state, it assumes the form of vapour, ascends into the atmosphere, is there by certain processes robbed of its heat, and re-appears in the form of rain; or, when a greater portion is abstracted, takes that of snow or hail, and falls to the earth. A seed is put into the ground; and if heat, air, and moisture be applied, it germinates and springs up; and with the addition of light, if the operation of the same agents be continued, it becomes a new plant, puts forth leaves and flowers, and produces seeds similar to that from which it sprung.

Now to determine what are these changes, to observe the laws by which such changes are effected, and to ascertain the measure and quantity of the effect produced, belong to that department of knowledge which is included under the general term natural philosophy or physics. But of these changes or motions, some are obvious and palpable; others entirely elude our senses. We see a stone descend to the earth; and experience informs us, that it falls with a force in a certain proportion to its weight and the height from which it fell. The peculiar change or motion which takes place when water assumes the solid form, when a fluid undergoes the process of fermentation or when a combustible body is burned, is altogether imperceptible. These motions are too minute to be recognized. The effect is produced before we can discover the change.

Thus natural philosophy divides itself into two great branches. The objects of the first are the sensible changes or motions which are observed in the material world; and the consideration of these objects is, properly speaking, natural philosophy or physics. The second great branch, which is employed in discovering the the laws, and appreciating the effects, of the insensible motions of bodies, constitutes the science of chemistry (A).

Sect. II. Of the Object and Importance of Chemistry.

The importance and extensive utility of this science must appear obvious to those who have at all considered the subject. But for the sake of others who are yet unacquainted with it, we shall take a general view of the objects which it embraces, and the advantages to be derived from the study of chemistry, whether in explaining many of the striking operations of nature, or in improving the arts of life.

The most wonderful effects, after frequent repetition, become familiar, and cease to produce any emotion in the mind. It is on this account that many of the most striking appearances of nature pass unheeded as trifling occurrences, and are unnoticed by common observers. Had we been always accustomed to the rigour of winter, and never known the genial warmth of spring, or experienced the ripening summer's heat, the astonishing changes effected by the return of these seasons could not fail to fill us with admiration. These changes are of such universal influence, that they are limited to no department of nature. Their beneficial effects are felt in the inanimate as well as in the animated creation. The same power which is seen in the gay profusion of the vegetable tribes, restores to a new existence myriads of animals, whose vital functions had been suspended. The air, the earth, the waters, swarm with life.

The principal agent in the production of these changes is heat; an agent, the most powerful and irresistible in its operations, unlimited in its effects, and extensive in its importance and utility. This agent, therefore, acting so powerfully in chemical operations, becomes an essential object of chemical science. Closely connected with heat is light, which is also a powerful agent in many of the processes of nature. This, too, is necessarily a subject of chemical investigation, not less curious and interesting. Such, indeed, is the universal importance of light and heat in all the processes of nature, that no change takes place, no new combination is formed, or new product makes its appearance, in which the one or the other, or both, are not evolved or absorbed.

In the knowledge of the constitution of the atmosphere, in investigating the changes to which it is subject, the variations of temperature, winds, dew, rain, hail, and snow, chemistry is our principal, our only satisfactory guide. These remarkable changes are to be considered as immense chemical operations, and can only be explained by chemical laws.

But in the midst of the infinite variety of objects from which man must derive the means of his comfort, his happiness and his luxuries, the means, it might be added, of his very existence, chemistry affords him the most important aid. Whether his researches be carried into the mineral, the vegetable, or the animal kingdoms, the study and cultivation of chemical science become essentially requisite for the successful progress of his investigations.

Of the importance of chemistry to the mineralogist, minerals, the limited and unsettled state of this science previous to the improvements of modern chemistry, is a convincing proof. In mineralogy, the knowledge of chemistry is not only necessary in detecting and discriminating the various substances of which the globe which we inhabit is composed, in separating and purifying these substances, but also in preparing and accommodating them to the numerous purposes of life.

Of the knowledge which we possess of the vegetable kingdom, chemistry furnishes a very large share. It is from this science that we derive the means of tracing the progress of vegetation, of illustrating the peculiar functions of plants, and discovering the compounds which are formed from a few simple principles, the nature and properties of these compounds, and their relative proportions, which exhibit an immense variety of new productions, many of them of the utmost importance to man, on account of their nutritious qualities, or indirectly useful to him by affording nourishment to those animals which he employs as food. Hence the advantage of applying chemical knowledge to agriculture, in determining the nature of the soil fit for the reception of plants, their proper food, and the mode of supplying it in the preparation of manures. With these objects in view, chemistry holds out incalculable advantages in the improvement of many departments of agriculture and rural economy, many of which, from the rapid and successful progress of the science, there is room to hope, may be soon obtained.

Nor is the application of chemical science to the economy of animals less limited in its importance and utility. It not only contributes to the means of decomposing animal matters, and of exhibiting and examining separately the constituent parts of animal substances; but also serves to explain in some measure many of the essential functions of the living animal body: such are digestion, respiration, secretion, which, so far as matter is concerned, and the changes which it undergoes, are to be considered as true chemical processes, and can only be investigated by chemical principles. But it is here necessary to observe, that the functions of the living vegetable or animal cannot be wholly accounted for from the nature of chemical action, without taking into consideration the existence of the vital principle, which counteracts and regulates the operation of chemical agents, aids and promotes the beneficial effects of those that are useful to its health and growth, and resists and destroys those that are hurtful.

The utility of chemistry in medicine is too obvious to require much illustration. Such, indeed, is its importance that it is now universally received and acknowledged as one of the essential branches of medical education. So far as the principles of chemistry can be applied in investigating the nature of the functions

(A) For this view of the division of natural knowledge, we are indebted to the Introductory Lectures of Professor Robinson of Edinburgh. of the animal body in a state of health, or can be employed in accounting for the irregular action of these powers, whether excessive or deficient, which indicates a deranged state of the functions, and constitutes disease; its relation to medicine must be considered close and intimate. But the medical art comprehends more than a bare knowledge of the structure and functions of the animal body. It also includes an accurate knowledge of the substances employed as remedies, of their nature and properties as simple substances, and their new qualities and effects under new combinations. This knowledge can only be acquired by the study of chemistry, which is indebted to medicine for some part of its progress as an art, in the discoveries which were accidentally made by the rude and uncertain experiments of medical practitioners in the early ages, to ascertain the sensible qualities and salutary effects of the remedies which they employed.

Chemistry, by its rapid progress in modern times, has amply repaid these advantages, and in the hands of the intelligent and accurate observer, has greatly contributed to give more rational and simple views of medical science.

In considering the application of chemistry to the improvement of the arts of civilized life, a wide field of contemplation opens to our view. So extensive indeed are its influence and importance, that in most of the arts, many of the processes, in some all that are employed, depend on chemical principles. Barely to mention some of these arts will afford ample illustration of its extensive utility. In the art of extracting metals from their ores, in purifying and combining them with each other, and in forming instruments and utensils, whether for useful or ornamental purposes, almost all the processes are purely chemical. The essential improvements which modern chemistry has introduced in the manufacture of glass and porcelain show its importance and utility in these arts. Nor has it contributed less by the application of its principles to the arts of tanning, soapmaking, dyeing, and bleaching. All the processes in baking, brewing, and distilling, most of the culinary arts, and many others in domestic economy, are chemical operations. In short, wherever, in any of the processes of nature or of art, the addition or the abstraction of heat takes place; wherever substances in combination are to be decomposed or separated; wherever the union of simple substances is wanted, and new compounds are formed, there effects are produced which can only be explained and understood by chemical principles.

From this view of the extensive application of chemical science in explaining many of the operations of nature, and in elucidating many of the processes of the arts of life, those who have not considered the objects which it embraces will be enabled to judge of the importance of this study.

But however much we may be interested in observing and admiring the changes and effects produced by chemical action, if we extend our views, and consider

(B) According to some it is derived from the word kema, which was supposed to be a book of secrets given to the women by the demons. Others derive it from Cham the son of Noah, from whom Egypt took the name of Chemie, or Chamie. Sometimes the origin of the word is ascribed to Chemmis, a king of the Egyptians; and They prepared alum, sea-salt, and sal ammoniac; and besides working in gold and copper, they possessed many other processes in metallurgy. The extraction of oils, and the preparation of wine and vinegar, were well known; and they were also acquainted with the art of dyeing silk by means of mordants.

Fewer traces of chemistry are found among the Greeks, although they derived the knowledge of many of the arts from Egypt. The ancient philosophers of Greece, as Pythagoras, Thales, and Plato, were more devoted to the cultivation of mathematical and astronomical knowledge, than the physical sciences. Some chemical arts, however, were not unknown to this people. The alloy of metals formed at Corinth has been much celebrated. Cinnabar was employed in some parts of Greece. Typhius knew the art of tanning leather; Plato has described the process of filtration; Hippocrates was acquainted with that of calcination; Galen speaks of distillation per descensum, and the word embic is mentioned by Dioscorides a long time before the Arabic particle al was prefixed to it. According to Athenaeus, there was a manufactory of glas established at Lesbos. Democritus of Abdera prepared and examined the juices of plants; Aristotle and Theophrastus treated of stones and of metals.

The Phoenicians are spoken of as being acquainted with the making of glas, and the celebrated Tyrian purple was found among this people. They were also skilled in the working of metals and other mineral substances. The Persians are said first to have distinguished the metals by the names of the planets, which they retained for many centuries.

Among the Chinese, if we may believe their histo-Chinese, many chemical arts were known from the earliest ages: they were acquainted with nitre, borax, alum, gunpowder, verdigris, mercurial ointments, sulphur, and colouring matters; nor were the arts of dyeing linen and silk, paper-making, manufacturing of pottery and porcelain, unknown. They were skilled in the art of alloying metals, and in the working of ivory and of horn. From the early knowledge which the Chinese possessed of these arts, they have been supposed by some to have been a colony from Egypt.

The wars in which the Romans were almost constantly engaged, and the spirit which prompted them to military affairs, gave them neither time nor taste to cultivate and improve the arts of peace. Chemistry, therefore, appears to have been little known among that people. Petronius indeed speaks of malleable glas, which was presented to Caesar; and the same, or a similar fact, is mentioned by Pliny with regard to Tiberius. But this art, it appears, was long known before the time of the Romans.

To us it may appear somewhat singular, that chemistry, now of such universal importance to mankind, should be indebted, in some measure, for its origin as an art, and for some part of its progress, to one of the least noble or generous of the human passions. Yet, in its early dawn, it was cultivated by men who were instructed

and sometimes to the Greek word χυτός, which signifies liquid, because the art was at first applied in the preparation of liquids; and sometimes to the Greek verb κεῖνος "to pour out," because chemistry is the art of fusing metals. fligated by avarice to prosecute and study it. About the 10th century, or perhaps earlier, a set of men arose, and continued to flourish till the 16th, who assumed, by way of distinction, the name of alchemists, that is, the chemists, because they considered themselves, on account of the knowledge they possessed, more highly favoured than the rest of mankind. It was natural enough for men who observed the remarkable changes produced by chemical action, to be struck with the effects; and overlooking the variations and differences in the result of their operations, which were the consequences of partial or inaccurate observation, to flatter themselves that their power over the substances on which they operated, was only limited by their wishes. Hence, perhaps, originated all the extravagances and follies, similar indeed to those of speculators and projectors of every age, with which the history and works of the alchemical writers are filled. Many of the alchemists, it is not improbable, were the dupes of their own ignorance and credulity; but many more, there is little doubt, took advantage of the ignorance and barbarity which prevailed in the dark ages, during which period they chiefly flourished, and imposed on the weaknesses and credulity of mankind.

It was one of the first principles among the alchemists, that all metals are composed of the same ingredients, or, that the substances which enter into the composition of gold, are found in all metals, but mixed with many impurities, from which, by certain processes, they might be freed. The great, the constant object of all their labours and researches was the discovery of a substance possessed of the wonderful property of converting the baser metals into gold, which, on account of its scarcity and durability, is more valued and esteemed than the other metals, which are more abundant, and generally more useful. This celebrated substance was denominated the philosophers' stone; and those who were so singularly fortunate as to accomplish this great discovery, or those to whom it was imparted by others, were regarded, as might naturally be expected, as the peculiar favourites of heaven. When they were in possession of this grand secret, they were ranked among the highest order of alchemists, and then assumed the name of adepts; and thus initiated, they professed themselves masters of the enviable secret of transmuting or changing metals of inferior value, into gold.

But the adepts never seem to have thought of enriching themselves by their great discoveries. They were too generous to monopolize the wealth of the world. They accordingly offered their services to others, and liberally proposed to communicate the fruit of their labours for a moderate reward. The ambitious man to procure riches, that he might increase his power, and the opulent man to add to his wealth, eagerly sought after, employed, and encouraged them in the prosecution of their extravagant schemes. They were therefore kept in the pay of princes, to fill and repair their exhausted treasuries, and of great men who aspired after boundless wealth. These flattering hopes, it may well be supposed, were never realized. The rich prospect fled before them, and the golden prize which they often supposed was just within their reach, eluded their eager grasp. The magnitude of the plan, however, fired the imagination, and produced something like conviction in the mind, of the possibility, and even certainty, of obtaining the object of all their wishes and all their labours. With unabating ardour, with unexampled fidelity, they pursued their researches, persuading themselves and their employers, that they were on the point of being soon in possession of unlimited wealth.

But the alchemists beholding man by anticipation possessed of immense riches, saw that something more was requisite, that he might be secured in the uninterrupted enjoyment of them. Experience fatally taught them, that the feeble frame of man was liable to the pains and languor of disease; that gold and silver could neither prevent the fit of a fever, nor give to the possessor the blessings of constant health. Thus another most desirable object was held up to view, and deluded their distempered minds into the false hope of attaining it. This was the famous panacea, or universal medicine, which was to cure all diseases; and not only to cure, but absolutely to prevent their occurrence. Thus fortunate in the enjoyment of vast riches; thus blest with unbroken health, the desires of man were yet unsatisfied. Another seeming evil still remained, which was naturally to be dreaded as the destroyer of this fancied scene of apparently perfect felicity. The melancholy reflection, that it was limited by the short span of human life, roused the alchemists again into exertion, and produced new efforts of ingenuity in their labours, to secure to man exemption from the common lot of mortality. In imagination they had discovered the means of prolonging life at pleasure to an indefinite length, of rescuing man from the grave, and of making him immortal upon earth.

Such were the extraordinary views and pursuits of the alchemists. The exact period of the origin of this study is unknown; nor can it now be ascertained what progress it had made, or indeed whether it was at all cultivated among the ancients. Julius Firmicus Maternus is the first historian who mentions this study as well known in his day; and the period when he flourished was about the beginning of the 4th century. A subsequent author, Æneas Blaesus, who lived in the following century, also makes mention of it; and Suidas defines the term by informing us, that it is the art of making gold and silver. Diocletian, he says, prohibited all chemical operations, during his persecution of the Christians, that his subjects might not be inflamed to acts of rebellion against him by the formation of gold. In some places where gold is washed down in minute particles, by brooks and rivulets from the mountains, it is customary to suspend the skins of animals in the water, by which means the particles containing the gold are detained; a circumstance from which the fabulous story of the golden fleece probably derived its origin. Suidas, however, who flourished in the 10th century, is not entitled to any high degree of credit, especially as the ancient authors are wholly silent as to the subject of alchemy.

It is from the physicians of Arabia that we obtain the most satisfactory evidence concerning alchemy. Avicenna, who lived in the 10th century, is said to have written on this subject, according to one of his own disciples, who likewise takes notice of rose-water and some other chemical preparations; and in the 12th century we find the cultivating an acquaintance with the chemists recommended to physicians. Another Arabian writer says, that the method of preparing rose-water, &c., was at that time well understood. These proofs of the existence of alchemy among the Arabsians, and particularly from the particle Al prefixed to it, have induced some to conclude, that the doctrine of the transmutation of metals first originated with the Arabsians, which the crusades were instrumental in introducing into Europe, as well as the rapid conquests of the Arabsians in Europe, Asia, and Africa. At that period Europe was in a state of the utmost barbarity, owing to the incursions of the northern nations; but some of the sciences, among which alchemy was comprehended, were happily revived by the Arabsians; and about the middle of the 17th century, the extravagance of such as were the professors of alchemy arrived at its greatest height.

It appears that the alchemists began to be established in the west of Europe, as early as the ninth century; and between the eleventh and fifteenth centuries, this study was in its most flourishing state. Among the principal alchemists who flourished during this period, and who were distinguished for their discoveries and writings, were Albertus Magnus, Roger Bacon, Arnoldus de Villanova, and Raymond Lully. They all lived in the 13th century. Albertus Magnus was a Dominican monk of Cologne, and was regarded by his contemporaries, no doubt on account of his studies, as a magician. He was born in the year 1205, and died in 1280. He left numerous works, one of the most curious of which is a treatise entitled De Alchimia, which exhibits a distinct view of the state of chemistry at the time he lived. Roger Bacon, another monk, was born in the county of Somerset in England in 1214, and died in 1294. He was celebrated for many ingenious inventions and discoveries in chemistry and mechanics. Among these are mentioned the camera obscura, the telescope, and gunpowder. His works discover astonishing sagacity and acuteness, and, considering the age in which he lived, are composed with no small degree of elegance and conciseness. Some of them, however, bearing the character of the times, are mythical and obscure. Arnoldus de Villanova, was a native of Languedoc in France, and was born about the year 1240. He has mentioned the mineral acids, and joined to his chemical studies extensive knowledge in medicine. His writings are distinguished by all the obscurity of the alchemical authors. Raymond Lully, whose reputation raised him to the rank of adeps, was born at Barcelona in 1235. He wrote on strong waters and metals. His last will and testament is one of the most celebrated of his writings; and these are not less obscure than those of his contemporaries.

About the end of the 14th century, Basil Valentine, a German Benedictine monk, was the first who formally applied chemistry to medicine. He was the original discoverer of many of the virtues of antimonial medicines; and in his celebrated treatise on antimony, entitled Cursus triumphalis Antimonii, are found many preparations which have since been announced to the world as new discoveries. About the same time lived Isaacus Hollandus, whose works have been greatly recommended by Boerhaave.

In the beginning of the 16th century arose Paracelsus, one of the most extraordinary men who ever lived. Paracelsus was born in 1493, near Zurich in Switzerland. Of a bold and enterprising spirit, he despised the common rules of conduct by which men are usually guided. By this means he raised his reputation to a great height; he became an enthusiast in chemistry, and in the application of substances prepared by chemical processes to the cure of diseases. He was the first public teacher of chemistry in Europe, having been appointed to deliver lectures on that subject in the city of Basle; but his restless spirit did not permit him to remain long in this situation. In two years he was involved in a quarrel with the magistrates, from whom he had received his appointment, and he left the city. Despising the common principles of medical practice, and having performed some wonderful cures by the use of opium and mercury, he thought he had discovered the universal medicine, and promised immortality to himself and to his patients. But while he thus made such flattering promises, his own fate was a sad proof of the futility and absurdity of his doctrine. For after an almost uninterrupted course of debauchery, having wandered a great part of his life from place to place, he died at an inn in Salzburg, in the 48th year of his age.

A great number of medical practitioners, in the course of the 16th century, adopted and propagated the principles of Paracelsus. Among the most distinguished of these was Van Helmont, a man of considerable genius, who was born in the year 1577. Many of the followers of Paracelsus were greatly devoted to the study of chemistry; and this, with the absurd and unprincipled conduct of their matter, tended not a little to bring the views and speculations of the alchemists into disrepute. Chemistry, now freed from the trammels of alchemy, consisted only of a number of detached, unconnected facts. To bring these facts together in one point of view, and to arrange them into classes, so that the knowledge of them might be applied to useful purposes, and to those objects to which future researches might be advantageously directed, were now wanted. This task was accomplished by Boccheri, who distinguished himself by the extent of his views, in a work entitled Physica subterranea, which was published at Frankfort in the year 1669. This was the first dawn of chemical science, and the publication of Boccheri's work formed an important era in the history of its progress.

In taking a retrospective view of the progress of discoveries in chemistry, previous to the publication of Boccheri's work, we find that a great number of important facts had been discovered and collected. To the class of acids, the sulphuric, the nitric, and the muriatic, were added; the alkalies were better known, and the volatile alkali was obtained from sal ammoniac by Basil Valentine, by decomposing it by means of soda or potash; the sulphate of potash prepared in three or four different ways, received as many different names; the nitrate of potash was called nitre, a name which was formerly applied to soda; Sylvius discovered the muriate of potash, which he denominated digestive salt; and Glauber, the sulphate of soda, to which he gave the name wonderful salt, though better known by the name of Glauber's salt, by which it is still distinguished. Some of the earthy salts began to be known about this period, and among others the muriate of lime, which received the name of fixed sal ammoniac.

The earths themselves were also better known; lime water was prepared, and some of the alkaline sulphurates were pointed out and examined.

The properties of some of the metallic salts were studied and examined; the nitrate of silver, under the name and form of crystals of Diana, and of lapis infernalis; the muriate of silver, under that of luna cornea. The two muriates of mercury were described, and employed for various purposes. The red precipitate, arcanum corallinum, faccharum saturni or sugar of lead, the butter of antimony, and the powder of algaroth, were either discovered, or their properties more attentively investigated and ascertained.

During this period also, the distinction was made between the brittle and the ductile metals. Bismuth, zinc, antimony, and even arsenic itself, were obtained in a metallic state. A number of oxides, some metallic dyes, fulminating gold, turpith mineral, the saline precipitates of mercury, or the mercurial oxides of different colours, minium and litharge, colcothar, the saffron of Mars, and diaphoretic antimony, were discovered, and their preparation sufficiently described.

During this period, the preparation of oils by distillation commenced, and the distinction was made between volatile and empyreumatic. Others were discovered, and the spirit of wine was well known by the same name, alcohol, which it at present bears.

But however extravagant it may seem to us, the history of the alchemists is instructive, as it affords a useful lesson to moderate our expectations in the pursuit of knowledge, and to restrain them within the bounds which the Almighty has prescribed as the range of our investigations; for of the knowledge and of the power of man, as well as of that of the natural elements, he has probably fixed the limits, and said, Hitherto shalt thou come, but no farther. This history is instructive also, as it presents a singular and extraordinary feature in the history of mankind; but it is immediately useful to our present purpose, as it shows us the commencement of chemical researches. It is true, chemistry in the hands of the alchemists, like every other department of knowledge during the dark ages, was involved in mystery, and the knowledge of it communicated in a barbarous jargon, to be understood only by the initiated, and scarcely to be deciphered and comprehended at the present day, with the affluence of the extensive knowledge of chemical facts which we now possess. But notwithstanding the extravagance of the objects they pursued, the means they employed were useful to the progress of chemistry. By their incessant labours, discovery was added to discovery, facts were multiplied on facts, but these were unaccompanied with any regular train of research or reasoning.

But notwithstanding these important discoveries, it may appear surprising that they were not more numerous. The alchemists had laboured incessantly in chemical pursuits for near a thousand years, and with all the zeal and ardour of enthusiasts; the labour of whole lives was exhausted, and immense fortunes were dissipated in endeavouring to obtain the grand object of all their researches. Considering the long period during which they flourished, and the numbers who were employed in these pursuits, there is indeed room for wonder, that they bequeathed to the first scientific inquirers so small a stock of chemical knowledge. But the spirit which prevailed among the alchemists was directly hostile to the free communication and accumulation of knowledge. The prominent feature of the character of the alchemists was secrecy. This indeed was closely connected with the nature of the object, to attain which all their pursuits and inquiries were directed; and strongly was this impressed upon their minds, that they believed, or pretended to believe, that the dreadful wrath of heaven would fall on him who should presume to disclose to any, but to the initiated, the secrets of the art. That spirit which arose from motives of avarice and self-conceit, became at last one of the leading principles of their conduct. With so great, so important an object in view, as the discovery of the means of putting themselves in possession of unlimited wealth, it is little to be wondered at, if they should carefully conceal from the world, and even from each other, the steps in the progress which led to the accomplishment of this end. Thus, all their processes were carried on in private, all their discoveries were kept secret. In their pretended communication of knowledge with each other, they employed certain signs and figures, and assumed a mysterious mode of writing, that they might be understood only by adepts, and might be totally unintelligible to the rest of mankind.

Considering this spirit, and the character which distinguished the alchemists, it was scarcely to be expected that they should reveal to the world, either by speech or writing, discoveries which most of them probably believed were to be of such vast benefit to themselves. And in this view, we should rather be surprised that any of their processes were ever made known. But here vanity, and even avarice, probably had considerable influence in calling forth what they pretended was an account of their attainments and discoveries. Some of the alchemists, perhaps by means of trick and imposture, had acquired a high reputation for knowledge, and had imposed a belief on many, that they were actually in possession of the philosopher's stone. They were therefore sought after, and often received great rewards for their labour, in proving the effects, or trying the success of this wonderful agent. To be thus employed was perhaps the object of many in the publication of their works. But, at the same time, they cautiously avoided revealing their knowledge, by employing mysterious and metaphorical language. Thus we may account for the impenetrable obscurity and numerous absurdities which characterized their writings.

In this view, therefore, of the character of the alchemists, it is not to be expected that the store of chemical facts could be very ample from their labours. And indeed, considering the caution with which they concealed and carried on all their processes, it is not improbable that many important discoveries were never announced by the first observers; for the very appearance of any thing new or unexpected, would flatter their hopes that they had advanced another step toward the attainment of their objects, and that the next would would put them in full possession of it. Thus, such a discovery would be held inviolably secret, and in this way it might be lost for ever.

We have already mentioned, that the work of Beccher gave the first scientific form to chemical knowledge. This appeared about the middle of the seventeenth century, when the light of knowledge began to spread over Europe, and chemistry received its share. The facts which had been accumulated by the labours of the alchemists, and to which Beccher had given a systematic form, were still farther methodized and extended by his pupil Stahl. Indeed, so much was done by the latter, in simplifying and improving the theory of his master, that it was afterwards denominated from his name the Stahlian or phlogistic theory. This theory was then received and adopted by all chemists, and continued to flourish for more than half a century.

After the middle of the seventeenth century, the establishment of philosophical societies in Europe greatly contributed to the diffusion of knowledge. It was about this time that the academy of sciences was established in France, and some of its members rose high in reputation by their experiments and discoveries in chemistry. The royal society of London was also founded about the same period; but its members, after the example of Newton, were more occupied in mechanical philosophy, and paid less attention to chemical science. It was not, however, entirely overlooked. Newton himself threw out some important hints, and took some general views of chemical phenomena; Boyle, along with his researches in mechanical philosophy, prosecuted the study of chemistry; and the experiments of Hooke and Mayow, on the nature of combustion and respirable air, discover a high degree of sagacity and skill in their investigations.

Towards the middle of the eighteenth century, the study of chemistry became general, and even fashionable, in France. Before this time Homberg, Geoffroy, and Lémery, had distinguished themselves by their chemical experiments and discoveries. Among these Geoffroy is still deservedly celebrated for his invention of the tables of chemical affinities, an ingenious method of exhibiting, at one view, the principal results of experiments in this science. These tables were afterwards improved by several chemists, but especially by Rouelle, Wenzel, and Bergman.

But the discovery of Dr Black formed one of the most important eras in the history of this science, and gave a new and unexpected turn to the views of chemists. It was the object of Dr Black's researches to discover the cause of the remarkable change which a piece of limestone undergoes when it is calcined or burnt, and to point out the reason of the great difference of the properties of this substance in its different states; and his investigations were crowned with success. For, in the year 1755, he ascertained that these changes were owing to the combination or separation of a peculiar kind of air, different in its properties from the air of the atmosphere. When this air is combined with lime, it is in the mild state, or the state of limestone: when this air is driven off, which is the process of calcination or burning, the limestone has changed its properties; it is reduced to the caustic state, and has lost considerably of its weight; and this loss of weight, Dr Black proved, was exactly equal to the weight of the air which had been driven off. To this air Dr Black gave the name of fixed air; because, when united to the lime and other substances, with which it enters into combination, it is in a fixed state. This discovery, one of the most important in chemistry, opened a new field for investigation; for it had not been once suspected, that aerial substances formed combinations with solid bodies.

From this time, the progress of chemistry was rapid and brilliant. Facts and discoveries were daily multiplied, and a spirit of enthusiasm for the study burst forth, and was diffused far and wide. In the year Other imp. 1774, Dr Priestley, who had contributed largely to important discoveries in the stock of chemical knowledge, discovered pure or coveries vital air, and that this air only was fit for the purposes of respiration and combustion. In the year 1781 Mr Cavendish, another ingenious English chemist, proved that water is not a simple element, but that it is composed of pure or vital air, and inflammable air; or, in chemical language, of oxygen and hydrogen.

But, previous to this time, two chemists had appeared in Sweden, had distinguished themselves by their zeal, ingenuity, and indefatigable industry, and had merited and obtained the highest reputation for the valuable discoveries which they had made in chemical science. Those who are at all acquainted with the history of chemistry, need not be told, that these celebrated names are those of Bergman and Scheele; names which will not be forgotten, as long as modesty, candour, and truth, are honoured and respected among mankind.

In the mean time, the French chemists were not idle. The celebrated Lavoisier, in conjunction with some of his philosophical friends, confirmed, by the most decisive experiments, the truth of Mr Cavendish's discovery of the composition of water, which was now received and adopted by almost every chemist. The same unfortunate philosopher, whose bright career was cut short by the horrors of the French revolution, had, previous to the time alluded to, enriched chemical science with many valuable and important facts. He had greatly contributed to overthrow the phlogistic theory, by a series of accurate experiments and observations on the calcination of metals. It had now become a question, whether metals, during the process of calcination, gave out any substance; that is, whether they contained any phlogiston; and Lavoisier incontrovertibly proved, that metals cannot be calcined, excepting in contact with pure air, and that the calx thus obtained was, in all cases, exactly equal to the weight of the metal, and the quantity of air which had disappeared.

Chemistry, by its rapid and unexampled progress, had now so far extended itself, and had accumulated so large a body of facts, that the barbarous, unmeaning, and arbitrary language which the alchemists employed to veil their mysteries, and part of which had been adopted and imitated in language equally obscure and arbitrary by the earlier chemists, rendered it extremely difficult to be acquired or understood. This was loudly and justly complained of, but the difficulties in the way of remedying it seemed almost insurmountable. The French chemists, however, undertook the arduous task, and completely succeeded in their labours. these illustrious philosophers we are indebted for the present language of chemistry, which is so constructed, that every word, and every combination, has an appropriate meaning, and is intended to express the nature and composition of the substance which is represented. It is to this improvement in its language, that we are to ascribe the facility and precision with which the knowledge of chemistry can now be communicated, and which has undoubtedly contributed greatly to its general diffusion and cultivation. And if there be any ground for hope of its future progress, from distinguished talents, ardent zeal, and unceasing industry, those who are now engaged in the study of this science give fair promise of a rich harvest.

Sect. IV. Of the First Principles of Bodies, and of the Methods of Studying and Arranging them.

1. According to the ancient philosophers, all matter consisted of four principles or elements. These were fire, air, water, and earth; and this opinion, with certain modifications, seems to have universally prevailed. But the discoveries of modern chemistry have proved, that three of these elements, at least, are compound substances. Fire is a compound of light and heat; air is composed of oxygen and azotic gases; and water consists of oxygen and hydrogen.

The alchemists, not satisfied with this division of the principles of bodies, adopted another, which was more appropriate to the nature of their labours and experiments, and was better calculated to explain the appearances with which they were acquainted. The elements of all bodies, according to their theory, were salt, sulphur, and mercury; and these were long known among the alchemists by the appellation of the trivium prima. These principles were admitted by all the alchemical writers till the time of Paracelsus, who also adopted them, and added two more to the number. These five elements or principles are thus characterized. Every thing came under the name of salt which was soluble or rapid; all inflammable substances were called sulphur; and every volatile substance, which flies off without burning, was called mercury or spirit. What was liquid and insipid was called phlegm or water; every thing that was dry, insipid, fixed, and insoluble, was called earth, or copul mortuum. The two last, which were added by Paracelsus, are the water and earth of the ancients. According to the original theory of the alchemists, all bodies may be decomposed by fire, and resolved into their three constituent principles. The mercury or spirit, during the process of combustion, escapes in the form of smoke; the sulphur is inflamed; and the salt, which was supposed to be the fixed principle, remains behind.

But Beccher, whom we have already mentioned as the founder of chemical science, perceiving the vague and unsettled notions of the alchemists, with regard to the principles of bodies, generalized and simplified still more, the chemical facts which were then known. According to his theory, all bodies consisted of earth and water. Under the former he included everything that was dry, and under the latter, whatever was humid. He admitted three earthly principles, namely, the fusible earth, the inflammable earth, and the mercurial earth. The first was the principle of dryness, of insusibility and hardness. The fusible earth, combined with water, composed an acid, which was called the universal acid, because all other acids owed their properties to it. The inflammable earth was considered as the principle of combustibility; and the mercurial earth was the principle of volatility. The fusible and the mercurial earths, with water, compose common salt; and the inflammable earth, with the universal acid, forms sulphur. The metals were composed of these three earths in equal proportions. When the mercurial earth was in small proportion, the compound was stone; when the fusible was in greater proportion, the compound was precious stones; and the compounds are the colorific earths, when the inflammable earth is in the greatest, and the fusible in the smallest proportion.

This theory of Beccher was considerably modified by his pupil Stahl. The inflammable earth of Beccher seems to have been changed by him into the principle of inflammability or fixed fire, which he distinguished by the name of phlogiston. He admitted the universal acid, but rejected the mercurial earth. The number of elements in the theory thus modified by Stahl, amounted to five. These were, air, water, phlogiston, earth, and the universal acid.

This mode of considering the elements of bodies, or their first principles, and of admitting such arbitrary and erroneous distinctions, is justly banished from chemical science. All substances are supposed to be simple, which have not been decomposed, without regard to their primitive elements or principles, the knowledge of which is, perhaps, beyond the reach of human power ever to arrive at.

2. To acquire the knowledge of those properties of bodies, investigation of which is properly included under the chemical science, two methods are employed: The one is the method of analysis or decomposition; the other is that of synthesis, or composition. By the one, the different simple substances of which compound bodies consist, are separated, and their properties individually examined; by the other, the simple substances are combined together, and the properties of the new compound are considered and investigated.

Different kinds or modes of analysis have been admitted and described by chemical writers. Some bodies, when exposed to the action of heat and air, undergo a total separation of their component parts. This is called spontaneous analysis. Thus, some minerals, and all vegetable and animal matters, when they are deprived of life, in favourable circumstances slowly separate into their component parts; and in the same way the principles of which some liquids are composed, react on each other, and spontaneously separate, which gives an opportunity of investigating the nature of these substances.

Analysis by fire operates by the accumulation of caloric in bodies; and by the power which it has of separating their particles to favour their examination. But this instrument of analysis is to be considered only as one of the means which should concur with many others, to throw light on the real composition of bodies. For it will afterwards appear, that the different quantities of caloric accumulated in bodies, have the greatest effects in giving different results, and changing the order of decomposition.

Another mode of analysis is by means of re-agents. This is conducted by placing the compound body which is to be examined, in contact with various substances, which have the power of separating its constituent parts. It is here that the genius and science of the chemist appear most conspicuous; for every substance in nature, and all the products of art, become valuable instruments in his hands, to ascertain the nature, and to examine the properties, of the substances which come under his examination. The different means of analysis which chemists have employed, to arrive at the knowledge of compound bodies, have been deemed of such importance and utility, that chemistry has been called the science of analysis.

Synthesis, or composition, is the union of two or more simple substances. This union, from whence results a new compound, has become an important step in arriving at the knowledge of the properties of bodies, and in forming a number of products useful in the arts, and necessary to our wants; and thus it is considered by chemists as in some measure the inverse of the method of analysis, as the perfection of their art, and one of the great instruments of their operations. The method of synthesis or composition, considered as a chemical process to acquire the knowledge of the intimate and reciprocal action of bodies, is in reality more frequently employed than that of analysis; and the name of the science, if we were to regard these two methods, should rather be called the science of synthesis than the science of analysis. In all cases of complicated analysis, the operations are synthetic. Compounds of an inferior order are formed, but more numerous than the first compounds which were subjected to analysis or examination.

But besides, there are many bodies which have never yet been decomposed. It is only by composition or synthesis, that is, by combining them with others, and by examining the nature of the compounds which are formed by this combination, that their chemical properties can be investigated.

However various the operations of chemistry may be; however numerous and different from each other the results which are obtained; they may all be referred to analysis or synthesis, and be regarded either as combinations or decompositions; and to these two general methods, all our operations may be limited.

3. It must be universally allowed, that it is of vast importance, in acquiring or communicating knowledge, to have a clear view of the objects of our studies; and this becomes the more necessary, as the facts in any science are accumulated, and the objects which it comprehends become more numerous. In many of the arrangements of chemical knowledge which have been proposed to the world, the objects of this science have been clasped together according to certain resemblances in one or two points, while they are totally distinct in all others. But an arrangement which is founded on the properties and characters of substances which have not been fully ascertained and generally admitted, must tend to obstruct, rather than facilitate the acquisition of science. If, for instance, the objects of chemical knowledge are to be arranged according to their combustibility or incombustibility, the nature of the process of combustion should be fully understood, and the effects of combustion on the substances to be clasped in this way, clearly established. If all this has not been previously attended to, the principles of the arrangement must be false, and must unavoidably lead to error. As a proof of the truth of our remarks, the same substance has been considered by one chemist as a combustible body, while it is arranged by another among the class of combustibles; and even by the same chemist it is said to be combustible at one time, and incombustible at another, according to the theory which then prevails.

Without pursuing any method of arrangement founded on particular theories or systems, we shall content ourselves, in the following treatise, to lay before our readers a full view of the present state of chemical science; and in arranging the great body of facts of which the science consists, we shall observe the two following rules. 1. To introduce the substances to be examined according to the simplicity of their composition; and, 2. According to their importance as chemical agents. The plan which we propose to pursue, in treating of these different classes of bodies, is, 1. To consider their properties as simple substances, and, 2. The combinations which they form with those which have been already described. By this method of arrangement, and by following out this plan, we hope to have less anticipation and repetition than in most other systems which have yet been proposed. But we wish not to think too confidently of our own labours. We shall probably be considered by the world as the worst judges in this case; and we are not too selfish to submit to the opinion of those to whom it is addressed, to whose candour and impartiality we implicitly trust. We may however observe, that this arrangement has been found extremely convenient for teaching the science; and we hope that our readers will find it equally so in acquiring the knowledge of it.

According to the principles which we have stated, the following table exhibits a view of the order which we shall observe in this treatise. In the present state of chemical science, and in its application to explain the phenomena of nature, or to improve the arts of life, the whole may be conveniently arranged into twenty chapters.

I. Affinity. II. Light. III. Heat. IV. Oxygen Gas. V. Azotic Gas and its Combinations. VI. Hydrogen, &c. VII. Carbure, &c. VIII. Phosphorus, &c. IX. Sulphur, &c. X. Acids, &c. 1. Sulphuric, 2. Nitric, 3. Muriatic, 4. Oxymuriatic, &c. &c. XI. Inflammable Substances. 1. Alcohol, 2. Ether, 3. Oils. XII. Alkalies, 1. Potash and its combinations. 2. Soda, &c. 3. Ammonia, &c. XIII. Earths. 1. Lime and its combinations. 2. Barytes, &c. 3. Strontites, &c. 4. Magnesia, &c. 5. Alumina, &c. 6. Silica, &c. 7. Yttria, &c. 8. Glucina, &c. 9. Zirconia, &c.

XIV. Metals. 1. Arsenic and its combinations. 2. Tungsten, &c. 3. Molybdena, &c. 4. Chromium, &c. 5. Columbium, &c. 6. Titanium, &c. 7. Uranium, &c. 8. Cobalt, &c. 9. Nickel, &c. 10. Manganese, &c. 11. Bismuth, &c. 12. Antimony, &c. 13. Tellurium, &c. 14. Mercury, &c. 15. Zinc, &c. 16. Tin, &c. 17. Lead, &c. 18. Iron, &c. 19. Copper, &c. 20. Silver, &c. 21. Gold, &c. 22. Platina, &c.

XV. The Atmosphere.

XVI. Waters. 1. Sea water. 2. Mineral waters.

XVII. Minerals. 1. Component parts. 2. Analysis.

XVIII. Vegetables. 1. Functions. 2. Decomposition. 3. Component parts.

XIX. Animals. 1. Functions. 2. Decomposition. 3. Component parts.

XX. Arts and Manufactures. 1. Soaps. 2. Glazes. 3. Porcelain. 4. Tanning. 5. Dyeing. 6. Bleaching.

In the above arrangement, the first chapter treats of affinity, or the laws of chemical action. In the two following chapters, the properties of light and heat are detailed. These are considered as material substances; but their properties can only be known in combination with other bodies, as they have never been found in a separate state. Oxygen, azote, and hydrogen, which are considered as the basis of oxygen, azotic, and hydrogen gases, are treated of in the 4th, 5th, and 6th chapters; but these substances, as well as light, intro and heat, are not cognizable by our senses. They are known in a state of combination, the aeriform or gaseous state, when they are combined with caloric, or the matter of heat. The three following substances, carbon, phosphorus, and sulphur, which are the subjects of the 7th, 8th, and 9th chapters, are considered as simple, because they have never been decomposed. They can be exhibited in the solid state. Two of them being very abundantly diffused in nature, and entering into an immense number of combinations with other bodies; and the third, namely, phosphorus, possessing very singular properties, it becomes of great importance that they should be early known.

The acids are treated of in the 10th chapter. They are naturally arranged in this place, because the constituent parts of some of the most important are derived from the substances which have been already treated of. But the properties of the classes of acid bodies ought also to be early known, because they are the most powerful instruments of analysis in the hands of the chemist. Indeed such is their importance in his investigations, that in many of them he can scarcely proceed a single step without their aid.

The bodies treated of in the 11th chapter, namely, alcohol, ether, and oils, under the head of inflammable substances, are properly introduced, because the nature and properties of the substances which enter into their composition have been previously examined; because one of them is the result of a chemical action between the acids and alcohol; and because some of them are employed as chemical agents. In the 12th, 13th, and 14th chapters, the properties and combinations of the alkalies, earths, and metals, are detailed. Excepting one, these three classes of bodies are simple, uncompounded substances. Many of them have long been the subjects of chemical investigation, and they afford some of the most important and interesting chemical researches. They are first to be treated of as simple substances; and next, as they enter into combination with the different classes of bodies which are already known, particularly with that of the acids, forming the numerous classes of alkaline, earthy, and metallic salts, most of which are of vast importance, not only as objects of chemical research, but also of extensive utility in the arts of life.

In the six following chapters, our chemical knowledge is to be applied in explaining the appearances of nature, so far as they are supposed to depend on chemical action. The 15th chapter treats of the chemical changes and combinations which take place in the atmosphere. The waters, as they are found on the earth; the different ingredients with which they are impregnated; the nature and quantity of these ingredients, and the methods of discovering and ascertaining them, form the subject of the 16th chapter. The 17th chapter is employed in giving a view of the component parts of mineral productions, and in describing the methods of analyzing or separating the parts which enter into their composition. The functions of vegetables and animals, or those changes which take place in them in the living state, which seem to be dependent on chemical action; the changes which they undergo by spontaneous analysis, or separation into their constituent parts, and the nature and properties of these elements, will be the subject of discussion in the 18th and 19th chapters. The 20th chapter, in which chemical science is applied to the improvement of arts and manufactures, is not one of the least important and interesting; and a full view of this part of the subject would exhaust the whole of the useful detail of chemical knowledge. But, in the following treatise, it is not proposed to enter at full length into the different branches of the arts and manufactures, but only to give a slight view of their general principles, so far as they depend on chemistry, referring for the particular discussion of each to the different heads under which they will be found arranged in the course of the work.

**CHAP. I. OF AFFINITY.**

Before we enter into the detail of those changes which take place by the action of bodies upon each other, producing compounds which are possessed of totally different properties, and thus exhibiting the characters of chemical action, it is necessary to take a view of the circumstances in which these changes are effected, or, in other words, the laws of combination or chemical affinity.

The term affinity, which is the expression of a force by which substances of different natures combine with each other, seems to have been pretty early employed by chemical writers. Barchufen, it would appear, is among the first who employed it, and thus characterizes it: "Arctam enim atque reciprocum inter se habent affinitatem." It was afterwards brought into more general use, and its application more precisely defined by Boerhaave*. His words are remarkable. "Particulae solventes et solutae, se affinitate fusa nature colligunt in corpora homogenea." And to explain his meaning still more clearly, he adds, "non igitur hic etiam actiones mechanicæ, non propulsiones violentæ, non inimicitæ cognitandæ, sed amicitia." To avoid the metaphorical expression affinity, Bergman proposed the term attraction; and to distinguish chemical attraction, which exists only between particular substances, from that attraction which exists between all the bodies in nature, he prefixed the word elective. The word affinity, however, is now generally adopted, and employed by all chemists.

The different tendency of bodies to combine with each other, or the relative degree of affinity which exists between them, could not long be overlooked by those whose attention was occupied in observing chemical changes. And to explain this difference of action, a maxim of the schoolmen was adopted; *finitum venit ad finitem.* The same doctrine was held by Becker, that substances which were capable of chemical combination, possessed a similarity of particles. Other attempts were made to explain chemical action, by considering solvents as consisting of points, finer or coarser, which were mechanically disposed to enter into the pores of certain substances which they were capable of holding in solution. But Stahl, as appears from his works, rejected the notion of mechanical force, and attributes the power of solvents to contact, or to the attraction of cohesion. "Combinationes qualunque non alter fieri, quam per arcetam appositionem." And afterwards, he speaks still more precisely when he says, "non per modum cunei, neque per modum incurvis, in unam particulam separandam, sed potius per-

modum apprehensionis, seu arctæ applicationis;" and then he adds, "eft inde rationi quam maxime confen- tanum, quod effectus tales potius arctiore unione fol- ventis cum solvente contingant, quam nuda et simplici formalis instrumentali divisione."

Having made this important step in the consideration of chemical action, the experiments and observations of the sagacious chemist led him to conclude that a combination between two substances, once formed, could not be destroyed, without effecting a more intimate union of one of the constituent parts with some other substance.

The next step in the method of observing and studying chemical affinity was made by Geoffroy the elder, who collected the scattered facts, to determine the force or measure of their degrees of union, and to establish rules of analysis and composition. His first table of affinity was presented to the Royal Academy of Sciences at Paris in the year 1718. This consisted only of 17 columns which were but imperfectly filled up, and exhibited rules which have been mostly changed; but with all its errors, it ought to be considered as one of the first guides in medical knowledge.

The first material improvement in Geoffroy's table was made by Gellert, professor at Freyberg. In his *Chemia Metallurgica*, published in 1750, there is a new table of affinity, which extends to 28 columns. At the bottom of each column there is a list of substances with which the body at the head of the column had no action. Rudiger, in the year 1756, inserted a table of affinity in his system of chemistry, in which he reduced the number of columns to 15. In this table he placed the fixed alkalies and lime parallel with each other, and before ammonia, the column of acids. He pointed out also with a good deal of accuracy, in a final very separate table, those substances which refuse to combine without some intermediate substances.

The next important addition to the knowledge of affinities, was made by M. Limbourg. In his table the number of columns was extended to 33. This table was the fullest and most accurate of any that had yet appeared. He had justly observed that zinc, of all metallic substances, should be placed at the head in the column of acids, and that even in the dry way it precipitated them all. He asserted that lime and the caustic alkalies acted by affinity on animal matters; and besides, he stated some cases in which a change took place in the order of affinities, by a change of temperature, or by the volatility of one of the substances.

This subject, the importance of which was sufficiently obvious, was now assiduously investigated by many men. The number of tables was multiplied, and the system of affinity more fully established. But the greatest improvement which it had hitherto received, was made by the celebrated Bergman, in his dissertation on elective attractions, published in the Transactions of the Royal Society of Upsal, in the year 1775. These tables, editions of which appeared in 1779 and 1783, have been justly regarded as striking instances of the sagacity and industry of the author. The affinities of 59 substances are ascertained with great accuracy; and the distinction between those that take place in the moist and dry way, is particularly stated, as well as the distinction between simple and compound affinities. affinities, which has led to the explanation of a great number of apparent anomalies. Since the time of Bergman, this subject has been prosecuted by many of the most distinguished philosophical chemists. Among these we may mention the industrious and indefatigable Kirwan of our own country; and among the French philosophers, Morveau, and more especially Berthollet, distinguished for his skill and sagacity, who has lately, in his researches concerning the laws of affinity, opened a new field of enquiry, corrected many former errors, and pointed out some new laws in this interesting and important subject.

All bodies with which we are acquainted, are influenced by a certain force, by which they are attracted, or drawn towards each other. A stone, when it is unsupported, falls to the ground; the planets are attracted by the sun; two polished plates of metal, of glass, or of marble, when brought into close contact, adhere with a certain force; a piece of wood or stone requires a considerable degree of force to separate the particles, or to draw it asunder; and lime and sulphuric acid enter into such close combination, that it requires an equal degree of force to overcome that combination, or to separate the particles from each other. Whatever may be the nature of these attractions, or the cause of these different combinations, or whether they are to be ascribed to the same universal law pervading matter, as some have supposed, they have been described by philosophers under different names. The attraction which exists between all bodies in the solar system, was denominated by Newton, by the general term attraction; and he demonstrated that this uniform and universal law was precisely the same as the law of gravitation, or the descent of heavy bodies towards the earth; and that this attraction was an essential property of all matter; that the minute particles, in proportion to their bulk, were equally influenced with the largest masses; that the same power which retained the planets in their orbits, gave form to the drops of rain.

We have said, that these different forces or attractions have been distinguished by different names. That attraction which is exerted between two polished surfaces brought into contact, has been called adhesion. When particles of the same nature are attracted or held together, the expression of the force by which this is effected, has received the name of cohesion, homogeneous affinity, or the attraction of aggregation; but when dissimilar particles, or the particles of two substances of different qualities, combine together, the force or attraction which is here exerted has been called heterogeneous affinity, the attraction of composition, or, strictly speaking, chemical affinity. In the three following sections, we propose to give an account of the opinions and doctrines which have been held by philosophers with regard to the nature and force of these attractions. Of the two first we shall only take a short view; but shall enter more fully into the detail of the latter, namely, chemical affinity, which more strictly belongs to our present subject.

Sect. I. Of Adhesion.

By adhesion, then, is to be understood, that force which retains different substances in contact with each other. Thus, water adheres to the finger, which is said to be wet, and mercury brought into contact with gold, adheres with great force. Adhesion takes place, either between two solids, as marble or glass; or between solids and fluids, as when water rises in capillary tubes; or between two fluids, as water and oil. In an experiment made by Dr Delaguliers, he observed, that two plates of glass, of one-tenth of an inch in diameter, adhered with a force equal to 17 ounces. The adhesion of two fluids has been proved by the experiment of Lagrange and Cigna, as that of oil and water, between which it was formerly supposed there existed a natural repulsion; and the experiments on capillary attraction, and particularly the ascent of water between two pans of glass, which was ascertained by Dr Brook Taylor, have established the attraction between solids and fluids.

This adhesive force, or the cause of this attraction, has been differently accounted for by philosophers. According to a dissertation on the weight of the atmosphere, published in 1682 by James Bernoulli, he ascribes the resistance which two polished pieces of marble opposed to their separation to the pressure of the air; and in proof of this, he states as a fact, that the two plates could be easily separated in vacuo. But it has been supposed that he had either never attempted to verify this fact, or that the experiment had been accompanied by some fallacy. From the experiments made by Dr Taylor, he concluded that the intensity of the adhesive power of surfaces might be measured by the weight which was required to separate them. About the same time Mr Hawking proved by experiment, that the adhesion of surfaces and capillary attraction were not to be ascribed to the pressure of the atmosphere, as Bernoulli had supposed; but Lagrange and Cigna, after having proved the adhesion between oil and water, thought that it was owing to a different cause from that of attraction. They supposed that it was occasioned by the pressure of the air, and that the opinion of Dr Taylor was not well founded. Such were the opinions held by philosophers on this subject, when Morveau, in the year 1773, was led to institute a series of experiments on adhesion, which he exhibited at Dijon. By these experiments he proved, that this attraction was not owing to the pressure of the air, but entirely to the attraction of the two substances between themselves. To prove this, a polished plate of glass was suspended from the arm of a balance, and placed in contact with a surface of mercury. The weight necessary to separate the two surfaces was equal to nine gros and some grains. The whole apparatus was placed under the receiver of an air-pump, which was exhausted of the air as much as possible. It required exactly the same force to separate the surfaces. The same disk of glass brought into contact with pure water, adhered to it with a force equal to 258 grams; but from the surface of a solution of potash, it required only a force of 210 grams. This inequality of effects with equal diameters, and in the inverse order of the respective densities, seemed not only to be decisive in favour of Dr Taylor's method, but appeared to point out the possibility of applying it to the calculation of chemical affinities. For the force of adhesion being necessarily proportional to the points of contact, and the sum of the points of contact not varying in the adhesion of a fluid and a solid with equal surfaces, but by the figure of their constituent parts, the difference of the results points out to us precisely a cause analogous to that which produces affinity, the force of which it becomes easy, in these circumstances, to measure and compare.

To ascertain the accuracy of this method, plates of the different metals, of an inch in diameter, and of equal thicknesses, perfectly round, and well polished, were procured. They were furnished, each with a small ring in the centre, to keep them suspended parallel to the horizon. Each of the plates was suspended in turn to the arm of an assay balance, and exactly counterpoised by weights in the opposite scale. Thus balanced, the plate was applied to the surface of mercury in a cup, by sliding it over the mercury in the same manner as is practised for silvering mirrors, to exclude the whole of the air. Weights were then put into the opposite scale, till the adhesion between the plate and the mercury was broken. In each experiment fresh mercury was employed. The following table exhibits the results of these experiments.

| Metal | Grains | |----------|--------| | Gold | 446 | | Silver | 429 | | Tin | 418 | | Lead | 397 | | Bismuth | 372 | | Zinc | 204 | | Copper | 142 | | Antimony | 126 | | Iron | 115 | | Cobalt | 8 |

In considering the remarkable differences, it must appear that the pressure of the atmosphere has no influence, since its effects must have been precisely similar; nor do they depend on the difference of polish on the surface; for a plate of iron, simply smooth and filed, adheres more strongly than a plate of the same diameter which has received the highest polish. Nor are these differences owing to the difference of density; for in this case silver should follow lead; cobalt would adhere with a greater force than zinc, and iron greater than that of tin. On the contrary, the order of their densities is reversed. What then is the order in which the adhesion of these different substances takes place? It is precisely, says Morveau, the order of affinity, or the degrees of the greater or less solubility of the metals for mercury. Gold, of all the metals, attracts mercury most strongly; but mercury dissolves neither iron nor cobalt, and therefore they are placed at the bottom of the list. This correspondence, he farther observes, cannot certainly be the effect of chance, but that it clearly depends on the general property of matter called attraction. This property which is always the same, and always subject to the same laws, produces very different effects, according to the different distances between the particles occasioned by the variety of elementary forms; and that thus it may be possible to estimate the force of chemical affinity by the force of adhesion. In the present case, for instance, the real affinities which tend to combine mercury with gold, silver, zinc, and copper, may be expressed by the above numbers 446, 429, 204, and 142.

Achard of Berlin, convinced by Morveau's experiments, of the accuracy of Dr Taylor's method, saw its importance in chemistry; and having examined the principle, made a great number of applications of it, which he published in 1780. The result of these observations, if accurately obtained, can alone guide us in estimating the points of contact by adhesion, and by calculating the points of contact, to ascertain the figure of the particles which touch, and the resulting affinities. Three essential conditions are necessary for Requisites:

1. That the solid body whose adhesion with a fluid is to be estimated be so suspended as to be in a horizontal position, and that the force employed to detach it, should always act in a line which forms a right angle with the surface of the fluid. 2. That there be no air interposed between the surface of the solid and the fluid; and, 3. That the weights employed as a counterpoise may be added, especially towards the end, in very small quantity, not more than a quarter of a grain each; and to avoid any sudden jerk, they should be placed gently in the scale.

The first point which he wished to ascertain was, whether the difference of atmospherical pressure, the temperature remaining the same, caused any difference in the adhesion of surfaces. For he found that the adhesive force between a plate of glass and distilled water was the same at all pressures, but the uniformity of the results varied when he operated at different degrees of temperature, while the elevation of the barometer continued the same; and he found that this variation did not arise from the different temperatures of the surrounding air, but from that of the water. When the fluids are colder, the adhesion is the stronger; and the reason is obvious: as they contain more matter under the same volume, they ought to present a greater number of points of contact in the same space; and since the force of the adhesion is in proportion to the number of the points of contact, it ought to increase when the fluids are condensed by cold, and to diminish when they are rarefied by heat. Achard did not stop by observing these variations of the force of adhesion between glass and water heated to different temperatures; he subjected them to calculation, to verify his observations, and render their application easy to all degrees. The following table exhibits the force of adhesion by observation, and also by calculation. He proceeded on the following data.

Let \( x \) be the temperature of the water, \( y \) the corresponding adhesion, \( b \) its coefficient, and \( a \) the constant force. We have then the equation \( x = a - bx \). To find the value of \( a \) and \( b \), he employed two observations; the one in which water at 104° of Sulzer's thermometer, adhered to the glass dish with a force equal to 80 grains, and the other in which water at 56° adhered with a force equal to 89 grams. Proceeding from these two terms \( 104 = a - 80b \) and \( 56 = a - 89b \), we have \( a = 530 - \frac{48}{9}y \); and from thence are deduced the corresponding values of \( x \) and \( y \) for all the adhesions of glass to water at any temperature. Such are the data from which, and the corresponding experiments, Achard formed The table which exhibits the adhesive force of a glass disk of 1½ inch in diameter, to water at different temperatures; and showing the difference of the results.

**Table I.**

| Degrees of Sulzer's Therm. | Degrees of Fahrenheit Therm. | Adhesion by Experiment. | Adhesion found by Calculation. | Difference. | |---------------------------|-------------------------------|-------------------------|-------------------------------|-------------| | 95 | 141.687 | 81.25 grs. | 81.55 | -0.3 | | 90 | 135.914 | 82.5 | 82.5 | 0 | | 85 | 130.141 | 83.75 | 83.43 | +0.34 | | 80 | 124.368 | 84.5 | 84.37 | +0.13 | | 75 | 118.595 | 85.75 | 85.31 | +0.46 | | 70 | 112.822 | 86.0 | 86.25 | -0.25 | | 65 | 107.049 | 87.25 | 87.18 | +0.07 | | 60 | 101.276 | 88.5 | 88.12 | +0.38 | | 55 | 95.503 | 89.0 | 89.06 | -0.06 | | 50 | 89.730 | 90.25 | 90.2 | +0.25 | | 45 | 83.957 | 90.75 | 90.93 | -0.16 | | 40 | 78.184 | 92.0 | 91.87 | +0.13 | | 35 | 72.411 | 92.75 | 92.81 | -0.04 | | 30 | 66.658 | 93.75 | 93.73 | +0.02 | | 25 | 60.865 | 94.5 | 94.68 | -0.18 | | 20 | 55.092 | 95.75 | 95.62 | +0.13 | | 15 | 49.319 | 96.25 | 96.56 | -0.31 | | 10 | 43.546 | 97.5 | 97.5 | 0 |

The temperature being supposed to continue the same, if this principle be well founded, the force of adhesion of any given body with water, ought not only to increase or diminish according to the extent of surface, but these differences ought to be as the difference of the surfaces.

If then \( p \) be the force with which a disk of glass whose diameter is \( a \), adheres to water, and \( y \) the force of adhesion of another disk, whose diameter is \( b \), we shall have the proportion \( a^2 : b^2 :: p : y \) and \( y = \frac{b^2}{a^2}p \).

To verify the order of this progression, either with water or other fluids, Achard employed disks of glass from 1½ to 7 inches in diameter, having first ascertained their force of adhesion with these fluids, by the number of grains which were necessary to overcome it. He afterwards calculated the same by the above equation. The following Table exhibits the results of experiment and of calculation, which if the procedure be free from error, correspond as nearly as could be expected.

**Table II.**

The force of adhesion between glass disks of different diameters, and different kinds of fluids, determined by experiment and calculation.

| Diam. of the disk | Distilled water | Alcohol | Liquid ammonia | Solution of potash | Oil of turpentine | Linseed oil | |-------------------|----------------|---------|---------------|--------------------|------------------|------------| | Inches | Experim. grs. | Calcul. grs. | Experim. grs. | Calcul. grs. | Experim. grs. | Calcul. grs. | Experim. grs. | Calcul. grs. | Experim. grs. | Calcul. grs. | | 1.5 | 364. | 216. | 328. | 420. | 240. | 268. | | 1.75 | 494.5 | 49.5 | 294.25 | 294. | 447. | 446. | 571. | 571. | 326.5 | 363.25 | 364. | | 2. | 647.25 | 647. | 384. | 582. | 583. | 746. | 746. | 425. | 426. | 475. | 476. | | 2.25 | 818.75 | 819. | 457.5 | 457. | 738. | 738. | 945. | 945. | 539. | 540. | 604. | | 2.5 | 1010. | 1011. | 600. | 912. | 911. | 1167. | 1166. | 667. | 666. | 744. | 744. | | 2.75 | 1223.5 | 1223. | 725. | 726. | 1103. | 1102. | 1410.75 | 1411. | 806. | 806. | 901. | | 3. | 1457. | 1456. | 863.25 | 864. | 1311. | 1312. | 1680.5 | 1680. | 961. | 960. | 1072. | | 3.25 | 1709. | 1708. | 1015. | 1014. | 1538.25 | 1539. | 1970. | 1971. | 1126.5 | 1126. | 1259. | | 3.5 | 1981.5 | 1982. | 1177. | 1176. | 1786. | 1785. | 2287. | 2286. | 1305.75 | 1306. | 1458.5 | | 3.75 | 2257. | 2257. | 1350. | 1350. | 2049. | 2050. | 2624.5 | 2625. | 1500. | 1500. | 1675.5 | | 4. | 2587. | 2588. | 1538. | 1536. | 2332. | 2332. | 2986. | 2986. | 1707. | 1706. | 1905. | | 5. | 4044. | 4044. | 2399. | 2400. | 3645. | 3644. | 4665.8 | 4666. | 2666. | 2666. | 2977. | | 6. | 5824.5 | 5824. | 3455.5 | 3456. | 5248.25 | 5248. | 6721. | 6720. | 3839.5 | 3849. | 4289.25 | | 7. | 7926.25 | 7927. | 4703. | 4704. | 7143. | 7143. | 9146. | 9146. | 5227. | 5226. | 5836. |

Achard Achard also instituted a series of experiments with different solid substances, formed into disks of equal diameters, and applied to the surface of different fluids. The following table shows the results of these experiments; but from these results it appears, that the force of adhesion does not depend on the specific gravity, either of the solid or the fluid; nor does it correspond with the order of chemical affinities. But besides, some of the results cannot be admitted as perfectly legitimate, on account of the chemical action which would necessarily take place when some of the substances were brought into contact; as some of the metals would be acted on by the acids, and others by the solutions of metallic salts.

### Table III

The force of adhesion of different solids, in disks 1.5 inch in diameter, with water and other fluids, at 70° Fahrenheit's thermometer, determined in grains.

| Solids | Distilled water | Sulphuric acid | Concentrated vinegar | Alcohol | Acetite of lead | Acetite of copper | Deliquated potash | Liquid ammonia | Sulphuric ether | Oil of turpentine | Oil of almonds | |-------------------------|-----------------|----------------|----------------------|---------|----------------|------------------|------------------|---------------|----------------|------------------|---------------| | Specific gravity | | | | | | | | | | | | | Plate-glass | 91 | 115 | 87 | 54 | 98 | 96 | 105 | 82 | 54.5 | 60 | 66 | | Rock crystal | 90 | 112 | 86 | 52 | 98.75 | 95 | 103 | 80 | 53 | 58.5 | 66 | | Green oriental jasper | 96 | 120.5 | 96.25 | 99.8 | 88.5 | 91 | 122 | 85.5 | 84 | 56.5 | | | Gypsum | 80 | 199.75 | 78 | 46.5 | 87.25 | 85 | 93 | 71 | 48 | 52.5 | 56.5 | | Sulphur | 96.5 | 123 | 92.5 | 58 | 107 | 101.5 | 110.5 | 86 | 57.5 | 64 | 69 | | Yellow wax | 97 | 120.5 | 92.75 | 56.5 | 106.5 | 103 | 111 | 88 | 59 | 64 | 71 | | Ivory | 90 | 114 | 90 | 92 | 84 | 86 | 113 | 80 | 77.5 | 52 | | | Horn | 84 | 104.75 | 85 | 83.75 | 76.25 | 81 | 106 | 74.5 | 73 | 48.75 | | | Iron | 93.5 | 116 | 88 | 56 | 104 | 98.25 | 108 | 83.5 | 55.5 | 61 | 68 | | Copper | 96.5 | 123 | 92 | 57.25 | 106 | 102 | 112 | 87 | 58 | 62.5 | 68.5 | | Tin | 94.5 | 91 | 55.5 | 103.5 | 100 | 108.5 | 86 | 54.75 | 61 | 67 | 72 | | Lead | 100.25 | 129.25 | 98 | 59 | 111 | 107 | 115 | 91.5 | 61 | 67 | 72 | | Brass | 99 | 124 | 96 | 59 | 110 | 103.5 | 114 | 90 | 60 | 65 | 70.5 | | Zinc | 96 | 90.25 | 57 | 106.25 | 102 | 110 | 85.75 | 56.75 | 61.25 | 69 | |

From all these observations, then, we may conclude, that the force of adhesion between different bodies is altogether independent of the pressure of the air; that it varies according to the number of points of contact of the touching surfaces; and that it is probably owing to the same cause as the force of affinity. It appears also, that the force of adhesion between solids and fluids is in the inverse ratio of the temperature indicated by the thermometer, and the direct ratio of the squares of their surfaces; that different solids adhere with different degrees of force to the same fluid; but still it must be allowed, that experiments and observations are yet wanting, to derive any advantage from the results of adhesive force which have been obtained, in the cultivation of chemical affinities.

### Sect. II. Of the Attraction of Aggregation.

That force which is inherent in the particles of matter, by which they are held together, and form masses, is called cohesion; and when particles of the same kind are united together, it is denominated the attraction of aggregation, or homogeneous affinity. It is probably the same in kind with that which we have already considered. Chemistry.

Affinity. Considered, but differing in degree. Thus, it requires a much greater force to separate the particles of a mass of marble, than two polished surfaces of the same substance brought into contact.

As the force of cohesion opposes itself to chemical action, so that the chemist in his researches is obliged to destroy or overcome it; it becomes a matter of considerable importance to be able to estimate it. This force is very different in different bodies. A very great force is necessary to overcome the power of cohesion among the particles of an iron or gold wire, while a small degree of force can separate the particles of a piece of wood or stone. To ascertain this force, experiments have been made by different philosophers, and particularly by Mutchtenbroeck, on that of the cohesion of solid bodies. A rod of the substance whose cohesive force was to be estimated, was suspended perpendicularly, and weights attached to the lower extremity. The weight necessary to destroy the cohesive force of the particles of matter in the rod, or to tear it asunder, was considered as the measure of that force. The following are the results of his experiments made on different substances. The substances employed were rods of an inch square, and the numbers in the table indicate pounds avoirdupois.

Metals.

| Steel, bar | 135,000 | | Iron, bar | 74,500 | | Iron, cast | 50,100 | | Copper, cast | 28,600 | | Silver, cast | 41,500 | | Gold, cast | 22,000 | | Tin, cast | 4,440 | | Bismuth, | 2,900 | | Zinc, | 2,600 | | Antimony, | 1000 | | Lead, cast | 860 |

Alloys of Metals.

| Gold 2 parts, silver 1 part, | 28,000 | | Gold 5, copper 1, | 50,000 | | Silver 5, copper 1, | 48,500 | | Silver 4, tin 1, | 41,000 | | Copper 6, tin 1, | 55,000 | | Brass, | 51,000 | | Tin 3, lead 1, | 10,200 | | Tin 8, zinc 1, | 10,000 | | Tin 4, antimony 1, | 12,000 | | Lead 8, zinc 1, | 4,500 | | Tin 4, lead 1, zinc 1, | 13,000 |

Woods.

| Locust tree, | 20,100 | | Jujeb, | 18,500 | | Beech and oak, | 17,300 | | Orange, | 15,500 | | Alder, | 13,900 | | Elm, | 13,200 | | Mulberry, | 12,500 | | Willow, | 12,500 | | Ash, | 12,000 | | Plum, | 11,800 | | Elder, | 10,000 | | Pomegranate, | 9,750 |

Lemon, | 9,250 | Tamarind, | 8,750 | Fir, | 8,330 | Walnut, | 8,130 | Pitch pine, | 7,656 | Quince, | 6,750 | Cypress, | 6,000 | Poplar, | 5,500 | Cedar, | 4,880 |

Bones.

| Ivory, | 16,270 | | Bone, | 15,250 | | Horn, | 8,750 | | Whalebone, | 7,500 | | Tooth of sea-calf, | 4,075 |

Various opinions have been entertained of the nature of this cohesive force. According to Newton, as we have already observed, it is properly essential to all matter, and the cause of the variety observed in the texture of different bodies. "The particles," says he, "of all hard homogeneous bodies which touch one another, cohere with a great force; to account for which some philosophers have recourse to a kind of hooked atoms, which, in effect, is nothing else but to beg the thing in question. Others imagine that the particles of bodies are connected by rest; that is, in effect, by nothing at all; and others by confining motions, that is, by a relative rest among themselves. For myself, it rather appears to me, that the particles of bodies cohere by an attractive force, whereby they tend mutually towards each other: which force, in the very point of contact, is very great; at little distances is less, and at a little farther distance is quite insensible."

"If compound bodies," Dr Desaguliers observes, "be so hard as by experience we find some of them to be, and yet have a great many hidden pores within them, and consist of parts only laid together; no doubt those simple particles which have no pores within them, and which were never divided into parts, must be vastly harder. For such hard particles gathered into a mass, cannot possibly touch in more than a few points; and therefore much less force is required to sever them, than to break a solid particle whose parts touch throughout all their surfaces, without any intermediate pores or interfaces. But how such hard particles only laid together, and touching only in a few points, should come to cohere so firmly, as in fact we find they do, is inconceivable; unless there be some cause by which they are attracted and pressed together. Now, the smallest particles of matter may cohere by the strongest attractions, and constitute larger, whose attractive force is feebler: and again, many of these larger particles cohering, may constitute others still larger, whose attractive force is still weaker; and so on for several successions, till the progressions end in the largest particles, on which the operations in chemistry, and the colours of natural bodies, do depend; and which, by cohering, compose bodies of a sensible magnitude."

A theory, which possesses great ingenuity and plausibility, has been proposed by Bozovich, to account for cohesive attraction; and some suppose, that it is on immaterial immaterial means or powers that this attraction, according to this theory, depends. Dr Hutton seems to think, that Dr Priestley applies it in this view, in the following passage, in which he attempts to solve some difficulties with regard to the Newtonian doctrine of light. "The easiest method," says Dr Priestley, speaking of this subject, "of solving all difficulties, is to adopt the hypothesis of Mr Bofcovich, who supposes that matter is not impenetrable; as has perhaps, been universally taken for granted; but that it consists of physical points only, endowed with powers of attraction and repulsion, in the same manner as solid matter is generally supposed to be: provided, therefore, that any body move with a sufficient degree of velocity, or have a sufficient momentum to overcome any powers of repulsion that it may meet with, it will find no difficulty in making its way through any body whatever; for nothing else will penetrate one another but powers such as we know do in fact exist in the same place, and counterbalance or overrule one another. The most obvious difficulty, and indeed almost the only one, that attends this hypothesis, as it supposes the mutual penetrability of matter, arises from the idea of the nature of matter, and the difficulty we meet with in attempting to force two bodies into the same place. But it is demonstrable, that the first obstruction arises from no actual contact of matter, but from mere powers of repulsion. This difficulty we can overcome, and having got within one sphere of repulsion, we fancy that we are now impeded by the solid matter itself. But the very same is the opinion of the generality of mankind, with respect to the first obstruction. Why, therefore, may not the next be only another sphere of repulsion, which may only require a greater force than we can apply to overcome it, without disordering the arrangement of the constituent particles, but which may be overcome by a body moving with the amazing velocity of light?"

According to the theory of Bofcovich, the first elements or atoms of matter are indivisible, unextended, but simple, homogeneous, and finite in number. They are dispersed in one immense space, in such a manner, that any two or more may be distant from each other any assignable interval. This interval may be indefinitely augmented or diminished, but cannot entirely vanish. Actual contact of the atoms is therefore impossible, seeing that the repulsive power which prevents the entire vanishing of the interval must be sufficient to destroy the greatest velocities by which the atoms tend to unite. The repulsive power must encircle every atom, must be equal at equal distances from the atoms, and, moreover, must increase as the distance from the atoms diminishes. On the contrary, if the distance from the atoms increases, the repulsive power will diminish, and at last will become equal to nothing or vanish; then, and not till then, an attractive power commences, increases, diminishes, vanishes. But the theory does not stop here; for it supposes, that a repulsive power succeeds to the second or attractive, increases, diminishes, vanishes; and that there are several alternations of this kind, till at the last an attractive power prevails; and though diminishing sensibly, as the squares of the distances increase, extends to the most distant regions of our system. All the varieties of cohesion, Bofcovich has shown, may be satisfactorily accounted for from the diversity of size, figure, and density of the cohering particles.

Bodies exist in three different states, which are quite distinct from each other; in the solid state, the liquid, and in the state of elastic fluid. Solidity, he supposes, is the consequence of the irregular figure of the particles, and their great deviation from the spherical form, by which free motion among them is prevented. And thus, in solid bodies, the motion of one particle is followed by that of the whole mass; or if the motion of the whole mass requires a greater force to effect it than what is necessary to destroy the cohesion of the particles, the latter takes place. The diversity in solids arises from the various degrees of force in the limits of cohesion.

The particles of fluid bodies, according to Bofcovich, are spherical, and their forces are more directed to their centres than to their surfaces; by which motion is freely allowed when any force is applied. Fluids, he supposes, are of three kinds: one in which the particles have no mutual power, as sand and fine powders; one in which they have repulsive power; such are the elastic fluids, as air; and the third in which they have an attractive power, as water, mercury, &c. And these three kinds are produced by the primary differences in the particles which compose them.

There is a class of bodies which are intermediate between the solids and fluids; the nature of which may be explained on the same principles. These are the viscid substances, the particles of which attract each other more strongly than the fluids, but not so strongly as the solids. In these bodies the particles deviate so far from the spherical form, as to produce a certain resistance among each other, and to impede their relative motion.

According to this theory, chemical phenomena may be traced to the same principle, namely the law of the forces and the differences in the particles which thence arise. Solution, for instance, is thus explained. The particles of some solid bodies have a less attraction for each other than for the particles of some fluids, and consequently when these are applied to each other, the particles of the solid separate, and combine with those of the fluid; and thus a mixture of the two is formed. But the separation of the particles of the solid can only take place so long as the particles of the fluid are in the sphere of their attraction; and when either of them get beyond it, or when the attraction of the mixture thus formed becomes equal to the attraction of the particles of the solid for each other, no farther solution takes place, and the fluid is said to be saturated. But if, into this mixture, another solid, whose particles have a greater attraction for the fluid, be introduced, the fluid will leave the former solid and combine with the particles of the latter. The particles of the former will fall to the bottom, or what is called precipitation takes place.

Substances which are dissolved, may not only be obtained again by precipitation, but also by slowly attracting part of the fluid in which they are dissolved. This is called evaporation, and the solid bodies which are thus slowly formed, generally assume some regular shape, and are denominated crystals. As the fluid is removed, the particles come gradually into the sphere of the attractive power of each other, and thus attain to some limit of cohesion, when the fluid which kept them them asunder is removed. But when a solid is obtained by precipitation, the fluid is suddenly removed from between the particles, which are consequently left beyond the sphere of attraction of each other, and do not therefore assume any regular form. And thus it will follow, that the more slowly the process of evaporation goes on, the more regular will be the crystals which are formed; and this corresponds with experiment and observation.

Thus, solid bodies are found, either in irregular masses, or assume regular forms by crystallization; and the same substances which are capable of assuming regular figures, uniformly affect the same form; subject, however, to certain variations from particular circumstances. No bodies can assume the form of crystals, excepting such as can be reduced to the fluid state. This, as is well known, is the usual method of crystallizing salts. The substances to be crystallized are dissolved in water, which is then slowly evaporated; and as the bulk of the fluid is diminished, the particles gradually come nearer to each other, combine together, and form crystals. These crystals, which are at first small, receiving the addition of other particles, become larger, and fall to the bottom by their gravity.

Some saline bodies which are very soluble in hot water, are dissolved but in small proportion in cold water. Hot water, which is saturated with any of these salts, is no longer capable of holding them in solution when it cools. The particles then gradually approach each other, and arrange themselves according to certain determinate forms, or in other words, they crystallize. Many of the saline bodies which crystallize in this manner, when they assume the solid form, combine with a considerable portion of water, which is called the water of crystallization. But on the other hand, there is another class of saline bodies which assume regular forms according to a different law. Being equally soluble in hot and in cold water, they cannot be crystallized by cooling the fluid in which they are dissolved, but by diminishing its quantity; and this is effected by continuing the application of heat; that is, by the process of evaporation. Salts which are crystallized in these circumstances, contain but a small quantity of water of crystallization. This is the case with common salt, which is crystallized by boiling the fluid which holds it in solution.

Many substances assume regular forms which are not soluble in any liquid. Such, for instance, is the case with metallic substances, and with glaas, as well as some other bodies. To crystallize substances of this nature, they must be subjected to fusion, and thus by combining with caloric, they are reduced to the liquid state, and the particles being separated from each other, are left at liberty to arrange themselves into regular forms, or to crystallize, and by slow and gradual cooling, the crystals are obtained more perfect.

But what is the cause that the particles of bodies, in these circumstances, arrange themselves in this manner? or what is the cause of the same bodies in the same circumstances assuming regular figures? According to some of the ancient philosophers, the elements of bodies consisted of certain regular geometrical figures; but it does not appear that they employed this theory to explain crystallization. The regular figure of crystals was ascribed by the schoolmen to their substantial forms; while others supposed that it was owing merely to the aggregation of the particles, without, however, explaining the reason of this aggregation, or of the regular figures which it formed.

According to Newton, and the theory of Boscovich which we have quoted, the particles of bodies which are held in solution by a fluid, are arranged in regular order, and at regular distances. When the force of cohesion between the particles and the fluid is diminished, it is increased between the particles themselves; they therefore separate from the fluid, and combine together in groups, which are composed of the particles nearest to each other. If it be supposed, that the particles which compose the same body have the same figure, the aggregation of any determinate number of such particles will produce similar figures. According to the ingenious theory of the abbé Hauy, the integrant particles always combine in the same body in the same way; they attach themselves together by the same faces or the same edges; but these faces and edges are different in different crystals. And although the same substances are observed to crystallize in a great variety of different forms, yet they all contain what Hauy calls the primitive form, or have it within them as a nucleus; and this nucleus or primitive figure may be extracted by careful mechanical division. If then who all the figure of crystals is owing to the figure of the integrant particles, and to the peculiar mode of their arrangement in combination, these particles, when they are left at full liberty, as is the case when they are dissolved in a fluid, will combine in the same way, and thus the crystals of the same body will always exhibit similar forms.

In prosecuting this subject, Hauy found that all the primitive forms of crystals which he had observed, might be reduced to five; namely,

1. The parallelopiped. 2. The tetrahedron. 3. The octahedron. 4. The regular six-sided prism. 5. The dodecahedron, terminated by equal rhombs. 6. The dodecahedron, with triangular faces, composed of two pyramids, united base to base.

But the nucleus or primitive form of a crystal, he observes, is not the last term of its mechanical division. It may be subdivided parallel to its different faces, and sometimes also in different directions. If the nucleus or primitive form be a parallelopiped, which cannot be subdivided, but in a direction parallel to its faces, as takes place in carbonate of lime, it is obvious that the integrant particle or molecule is similar to the nucleus itself. And he has found by experiment, that the figure of the integrant particles of all crystals may be the reduced to the three following. These are,

1. The tetrahedron, or the simplest of all pyramids. 2. The triangular prism, or the simplest of all the prisms. 3. The parallelopiped, or the simplest of the solids, which have their faces parallel.

From these primitive forms, the difference of size, proportion, and density of the different particles of bodies, he supposes, may account for all the differences of attraction which take place in simple aggregation and composition of bodies. The integrant particles sometimes Chemistry sometimes unite by their faces, and sometimes by their edges, in forming the primitive crystals; and this accounts for the different figures of the primitive crystals, which are composed of integrant particles of the same form. But bodies when they are crystallized, do not always exhibit the same primitive form. The deviations from this, and the varieties of forms which are produced, are called by Haüy secondary forms. In some salts, for instance, the primitive form is the octahedron; but in deviating from this form, they assume, when crystallized, that of the cube or the dodecahedron.

These secondary forms seem to depend sometimes on variations in the ingredients which compose the integrant particles of particular bodies, the solvent in which the crystals are formed, or the different decrements of the laminae of the erytals. But for a full view of this ingenious theory, see Crystallization.

Sect. III. Of the Attraction of Composition.

Bodies which are composed of particles of the same nature cohere with a certain force, as in the particles of water or of mercury, and those of wood or of metal; and this force, we have seen, acts with very different degrees of intensity. In the two former, the water and the mercury, it is comparatively weak, but in the two latter it is very powerful.

But the dissimilar particles of bodies also enter into combination; and thus combined, form homogeneous substances, whose particles cohere with very great force; and wherever these combinations take place, the force of cohesion between the particles of each of the bodies must be destroyed or overcome, before the new combination can take place. Thus a piece of marble is dissolved in muriatic acid; but before this can take place, the force of cohesion which exists between the particles of the marble must be overcome; or, in other words, the force of attraction between the particles of muriatic acid and the particles of the marble is greater than that between the particles of marble themselves. This attraction then which exists between the particles of substances of a different nature, has been called the attraction of composition, heterogeneous affinity, or more properly chemical affinity.

This attraction, or this affinity, does not exist between the particles of all bodies. Thus there is no affinity between a piece of marble and water, as is the case between marble and muriatic acid; and it is said that there is no affinity between oil and water, because the particles of the one do not enter into combination with those of the other.

Chemistry may be said to be the history of affinities, as it consists in the detail of the numerous and various compositions and decompositions which take place among natural bodies. Without attending to the phenomena which arise from affinity, the chemist could carry on no process, either of synthesis or analysis; for it is by means of their affinities that the chemical nature of bodies can be discovered.

In taking a general view of the phenomena which depend upon chemical attraction, the changes or events which are the results of this action, have been divided into certain classes, and from their being constant and uniform, they have been characterized by the name of laws of chemical affinity. These may be considered as chemical axioms which are the principles or foundation of the science, and therefore it is necessary that they should be well understood, before we enter into the detail of the facts which it embraces.

The celebrated Fourcroy, whose indefatigable labours and extensive views in chemical science will always be admired and valued, has arranged the facts which depend on chemical affinity under ten different heads, which he has denominated the laws of affinity. In illustrating this interesting part of chemical science, we shall observe the same arrangement.

First Law.

Chemical affinity takes place only between bodies of a different nature, or between dissimilar particles.

This law, when considered as a law of chemical affinity, may be regarded as negative; for when the particles of bodies of the same nature combine together, it is by the force of cohesion, and therefore comes under that species of affinity called the attraction of aggregation. No chemical action has taken place; no new compound is formed; which are the characteristics of chemical affinity.

But as an instance of the effect of chemical affinity between two bodies of a different nature, we may refer to the experiments above alluded to, of the combination which takes place between a piece of marble and muriatic acid; for by mutual action between these two bodies the marble has disappeared, and the acid has totally changed its properties. The compound, which is the result of this combination, proves that the heterogeneous bodies have entered into intimate union with each other.

Chemical affinity may act between two bodies, and a combination take place, when these bodies are totally uncombined with all others. In this case the combination is produced by the force of affinity between the two bodies; but when one or both of these bodies is in a state of combination with others, the bodies which are said to have the greater affinity for each other, do not entirely combine together, and leave the bodies with which they were first in combination. Suppose A and B are two bodies which have an affinity for each other, and are in a state of combination; and suppose C is a third body which has a stronger affinity for the body B than the affinity which exists between A and B. Now, the body C having a greater affinity for the body B than what exists between the compound body AB when it is brought into circumstances where the force of that affinity can be exerted, the compound body AB will be decomposed, that is, the body C will combine with the body B, and will leave the body A. It was formerly supposed by chemical philosophers, that this decomposition was complete; that is, as in the case stated above, the affinity between C and B being greater than the affinity between A and B, the body C, when in sufficient quantity, abstracted every particle of the body B from its combination with the body A. But the experiments and observations of the sagacious Berthollet have placed this matter in a new light. This will be best illustrated by detailing some of the experiments by which this ingenious The sulphuric acid has a very strong affinity for the earth called barytes, forming with it a compound which is insoluble either in hot or cold water. Sulphuric acid also has an affinity for potash, but it is much weaker than that which exists between the acid and barytes; yet the potash, although possessed of the weaker affinity, abstracts part of the sulphuric acid from the barytes, and combines with it. This is proved by Berthollet in the following experiment.

1. He took equal quantities of pure potash, and sulphate of barytes (E), and boiled them together in a small quantity of water. According to the views of former chemists with regard to chemical affinity, no decomposition should take place, because the affinity between the sulphuric acid and the barytes was stronger than that between the acid and the potash. But from the result of this experiment it appears, that the sulphate of barytes was partially decomposed by the potash, and that the sulphuric acid was divided between the two bases; that is, between the barytes and the potash.

2. The oxalic acid has a greater affinity for lime than for potash; but if oxalate of lime, that is oxalic acid combined with lime, be boiled along with potash in a small quantity of water in the proportion of one part of the oxalate of lime to two of the potash, a partial decomposition of the oxalate of lime will take place, part of the oxalic acid is abstracted from the lime, and combines with the potash.

3. One part of phosphate of lime was boiled together in a small quantity of water with two parts of potash. The phosphoric acid has a greater affinity for lime than for potash; but from this experiment it appeared that the phosphate of lime was partially decomposed, and part of the phosphoric acid having combined with the potash, formed the new compound, phosphate of potash.

From these experiments Berthollet observes, that the bases which are supposed to form the strongest combinations with the acids may be separated from them by others whose affinities are supposed to be weaker, and that the acid divides itself between the two bases. Where a small quantity only of the decomposing substance is employed, the effect is not perceptible; but if a large quantity be employed, as in one of the above experiments, if the sulphate of barytes had been treated with successive portions of potash, it would have been ultimately and almost entirely decomposed; for the weaker affinity of any body is made up by increasing the quantity of that body.

Bergman has remarked, that if five times as much of the decomposing substance be employed as is sufficient to saturate the base, a decomposition will be effected, which may be considered as total, because the opposing substance retains so small a part of that with which it was combined, that it may escape the observer's notice, and be considered as an evanescent quantity. But the above experiments shew, that a similar decomposition could be produced, if the reverse of the experiment which Bergman recommends had been attempted.

When one substance acts on another in combination with a third, the subject of combination divides itself between the two others, not only in proportion to the energy of their respective affinities, but also in proportion to their quantities. The two substances which act on the combination may be considered as opposing forces acting on the subject of combination, and sharing it between them in proportion to the intensity of their action; and this intensity may be estimated by the quantity of the substance and the energy of its affinity. The effect, therefore, must increase or diminish as the quantity increases or diminishes. Thus it appears that elective affinity in general does not act as a determinate force by which one body can completely separate another from a combination; but that in all compositions and decompositions produced by affinity, there is a partition of the subject of the combination between the two bodies, the energy of whose affinities is opposed, and the proportions of this partition depend not solely on the difference of energy in the affinities, but also on the difference of the quantities of the bodies; for it has been observed that an excess of the quantity of the body whose affinity is the weaker, compensates for the weakness of affinity.

**Second Law.**

Chemical affinity takes place only between the ultimate particles of bodies.

The attraction of aggregation or cohesion which is exerted between the integrant particles of bodies, is opposed to the action of chemical affinity. For, as in the case just mentioned, of the combination that takes place between a piece of marble and muriatic acid, the force of cohesion between the particles of the marble must be overcome before chemical action begins, and a new compound can be formed. The new compound consists of the constituent particles of the two bodies, which are now intimately united by the force of affinity which exists between them.

**Third Law.**

Chemical affinity takes place between several bodies.

It is not merely compounds consisting of the particles of two bodies, that are formed by chemical affinity, for we shall find that there are numerous instances of three or four substances entering into chemical combination. Alum, a well known substance, is a compound of three substances which have entered into chemical union. These are, sulphuric acid, alumina or pure clay, and potash. The same thing happens also in all those compounds which are called triple salts, which consist, like alum, of three different substances;

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(d) The reader, it is hoped, will find no difficulty in understanding the general reasonings on this subject; but he will be able to comprehend it fully, after the substances whose affinities are given as examples, are treated of in detail in their proper places.

(e) This is the compound of sulphuric acid and barytes, according to the new chemical nomenclature, the principles of which will be afterwards explained. but the most remarkable instances of the effects of chemical affinity on several bodies are observed in the alloys of some of the metals. The temperature at which the metals are fused is generally pretty high, but an alloy of some of them may be brought to a state of fusion at a low temperature. This is the case with the alloy of bismuth, lead, and tin, which may be melted at the temperature of boiling water, which is far below the fusing point of any of the uncombined metals, and shows by this change of their properties, that a chemical union has been effected.

Fourth Law.

That chemical affinity may take place between two bodies, it is necessary that one of them be in the liquid or fluid state.

The solution of a solid body in a fluid, may be considered as the destruction of the cohesion of its particles, and their equal diffusion in that fluid. It is the combination of the particles of the solid with those of the fluid; and the compound still possesses the characteristic physical properties of the fluid. Thus, in the first place, the force of cohesion between the particles of a solid body is destroyed, by its solution in a fluid; which force must always be overcome before a new compound can be formed by the action of chemical affinity. But, 2dly, The particles of a body dissolved in a fluid are in their ultimate, or at least very minute, state of division; by which means the points of contact between the particles of the body held in solution, and those of any other with which it may combine, are greatly multiplied; and thus the operation of chemical action between these particles is greatly extended.

Many familiar processes are examples of the effects of solution, as sugar dissolved in water; common salt in the same fluid; or the experiment mentioned above, of marble in muriatic acid. In the process of making glass we have another example of the same nature. The two substances which enter into the composition of glass are in the solid state. These are siliceous earth or sand, and an alkali. But to effect the combination of the two solids, one of them is brought to the fluid state by the application of heat. The alkali first melts, and in the state of fusion the sand or siliceous earth combines with it, and forms an uniform compound, which is glass.

But Berthollet has shown, that the solubility of bodies has a very great influence in modifying the action of chemical affinity. For, he observes, when a body is in some degree soluble, its action is composed of that of the part dissolved and of that of the part which has retained its solidity. It follows that its action does not increase in proportion to the quantity employed. Lime, for instance, acts by the part dissolved, and by that which remains solid; but it is probably the dissolved part which contributes principally to the effect produced. If the quantity of lime employed in an experiment be doubled, without increasing the quantity of the liquid, the quantity of lime dissolved will rather be diminished than increased, because a part of the liquid is absorbed by the lime which has been added.

If an insoluble combination can become soluble by being deprived of a part of its composition, the inconvenience of insolubility is easily removed. Thus it is when the phosphate of lime is acted on by an acid. The part of it which is within the sphere of action is instantly converted into an acidulous phosphate, and the other part successively, until both the opposed substances be reduced to a liquid state.

"When an eliminated substance becomes insoluble, the precipitate which is formed retains a portion of the substance with which it was combined, in proportion to the individual forces which acted in the moment of the precipitation. The operation is no farther influenced by this portion, so that the quantity of the precipitating body adequate to the precipitation is all that is necessary until the end of the operation. But the case is different when the eliminated substance assumes the liquid state, for then the resistance increases according to the progress of the decomposition; and hence it follows, if a substance nearly insoluble be opposed to a combination, and its action be consequently only partial, whilst the substance eliminated remains liquid, that the decomposition must be quickly stopped, whatever may be the force of the affinities. Because it has been already shown that the decomposing action depends not merely on the affinities, but also on the relative quantities in action. When the phosphate of potash was decomposed by means of lime, the operation was necessarily stopped as soon as the sulphuric acid was entirely divided between the potash and lime, in proportion to their respective affinities, and to the quantity of each which had acted on the *Berthollet's Researches*.

But fluids in the elastic state, or the state of gas, Elastic produce effects which are contrary to those of the force fluids of cohesion; and thus modify in a different manner the effects of the particular affinity of each substance. Elasticity acts, either by the removal of some substances from the action of others, or by diminishing their proportion within the sphere of action. But if all the substances in action be in the elastic state, this effect will not follow, because then they all exist in a similar condition. When a substance, on separating from an intimate combination, assumes the state of gas, it becomes elastic, and then it can oppose no further resistance to the decomposing action. And thus it appears that substances of this nature do not act by their mass. A complete decomposition can then be effected by the decomposing substance, and no greater quantity of it is required than what would have been necessary to form the compound by direct combination. Thus, carbonic acid, which is an elastic fluid, may be disengaged from its combination by another substance whose affinity for the base may be less, because that other substance can act by its mass, and can therefore overcome the affinity of the carbonic acid by its successive action. But if the whole of the carbonic acid is to be expelled, the decomposing substance must be used in greater quantity than what is just necessary to produce saturation.

The action which takes place when concentrated Example. sulphuric acid is poured on dry common salt, that is, both substances being as much as possible deprived of water, affords a good illustration of the effect of the elasticity of one of the substances. Common salt is composed of muriatic acid and soda. The affinity of the sulphuric acid for soda is greater than that of muriatic acid. When, therefore, the sulphuric acid is poured on the common salt, it combines with the soda, and the affinity of the muriatic acid is diminished. It consequently assumes the gaseous state, and acts no longer by its mass. But if a solution of common salt in water be employed, or a diluted acid, then the muriatic acid may be retained in the water, and in this case it can act by its mass.

When, therefore, a substance is in the state of gas, its elasticity is to be considered as a force opposed to the affinity of liquid substances. When the elasticity of gaseous substances is diminished, as happens by compression, they then combine in greater quantity with liquids. When water is brought into contact with carbonic acid, which is in the state of gas, it does not become saturated with that acid, because the elasticity of the gaseous acid opposes the dissolving power of the water; and before its dissolving force is exhausted, the two forces are balanced. But when the opposing elastic force is diminished, as by compression, the dissolving power of the water continues its action, and thus it is more fully saturated with the acid.

Fifth Law.

When bodies combine together, they undergo a change of temperature.

In all bodies there exists a certain quantity of caloric, or the matter of heat; but when any change takes place in the nature or constitution of any body, its power of retaining that portion of caloric is also changed. During these changes heat is either given out or absorbed; and this increase or diminution of temperature becomes obvious to our senses, or may be measured by the thermometer.

The effects of this variation of temperature will be greater or less, in promoting or retarding the action of chemical affinity, according to the change which takes place on the substances which are decomposed, or according to the state of the compound which is formed. When there is a great elevation of temperature, in consequence of the heat produced by the combination of substances, it is necessary to attend to the difference of volatility of which the substances are susceptible by that elevation of temperature. If the substances are not all in the liquid state, or if one of them only be soluble, the effect of heat is to favour their mutual action; because the force of cohesion, which acts even between the particles of bodies in the liquid state, is thus diminished. If the expansion by heat of the one of two substances be greater than that of the other, the more expanded substance acquires a greater degree of elasticity, and this, as has been already observed, must be considered as a force opposing the affinity which existed between the two bodies.

In chemical combinations, according to this law, the temperature changes; and it is either increased or diminished, according to the nature of the combination which is effected. This will be best illustrated by an example or two.

1. When lime is flaked, that is, when water is thrown upon burnt lime, a great elevation of tempera-

(f) The explanation of this phenomenon will be given, when we come to treat of heat. It is indeed one of the characteristics of chemical affinity, that there be a total change in the properties of the substances which enter into combination. This change takes place in the sensible qualities of many of the compounds, and some of these, as an illustration of this law, may be mentioned.

1. Changes of colour. The colour of lead is a bluish white, but when it combines with oxygen it assumes a bright yellow or red colour, in proportion to the quantity of oxygen. Cobalt, which is of a gray colour, when combined with oxygen becomes of a fine blue; and copper, which is red, combined in the same way, exhibits a green colour.

2. Changes in smell. 1. The smell of muriatic acid is highly pungent; ammonia, or the volatile alkali, is not less so; but when these two are combined, forming nitrate of ammonia, or sal ammoniac, the new compound is perfectly inodorous. This last is a remarkable instance of two highly volatile and odorous substances becoming fixed in the compound, and destitute of smell, and thus exhibiting a total change of their properties.

2. The smell of sulphur and of potash is scarcely perceptible in the uncombined state; but when they are united together, and moistened with water, a most fetid and offensive odour is emitted.

3. Changes in taste. 1. The taste of sulphur is nearly insipid; and oxygen, which is one of the component parts of the atmosphere, is not only innocent, but necessary for the existence of animals; but when these two enter into union, the compound formed, which is sulphuric acid, is one of the most corrosive substances.

2. Sulphuric acid, which is sour and corrosive, forms a combination with soda, which is also of a corrosive nature; the result, which is Glauber salt, or sulphate of soda, is a compound of a bitter nauseous taste, but possessing none of the properties of its component parts.

SEVENTH LAW.

The force of chemical affinity, is estimated by the force which is necessary to separate the substances which enter into combination.

In treating of cohesion, or the attraction of aggregation, it was stated, that the method employed by philosophers to estimate that force, was to measure the opposite force, or that which was necessary to overcome the cohesive force. Thus, the weight attached to the lower extremity of a metallic wire perpendicularly suspended, which was just sufficient to tear it asunder, is considered as the measure of its power of cohesion. But it will appear from what follows that this law must be adopted with considerable modification.

In estimating the force of chemical affinity, various methods have been proposed by different philosophical chemists. It was thought by Wenzel, that the time which one body required to dissolve another, might be considered as the measure of the force of affinity between these two bodies; but it must appear from what has been already said, that the time of solution must depend greatly on the cohesive force of the body which is to be dissolved, and the nature of the compound which is formed; so that from these deviations, no certain measure can be obtained from this method.

According to some, the measure of the force of chemical affinity may be estimated by the difficulty of separating the substances which have entered into combination; or, by taking the compound ratio of the facility with which they are combined. But as no method has been invented to ascertain either the one or the other, which are the necessary previous steps in the method proposed, it is impossible, in this way, to estimate the force of chemical affinities.

Observing the effects of the union and abstraction of calorific, in the operations of chemical affinity, Lavoisier and Laplace, in a memoir published in 1783, proposed this as the method of estimating the force of affinity. But it seems scarcely possible to measure the force of chemical affinity between two substances by the degree of temperature which is required to overcome the force of cohesion; or, as this degree of temperature has no measurable proportion with the force of chemical affinity, it can afford no data for estimating this force. And this quantity being variable and unknown, a fixed term is wanting to form a scale of comparison.

We have already mentioned, in treating of adhesion, the experiments of Dr Taylor on the adhesion of surfaces, and the experiments and conclusions of Moreau and Achard on the same subject. From these Moreau has proposed to deduce a method of estimating the force of chemical affinities. But for an account of this, we refer the reader to the first section.

A different method has been proposed by Mr Kirwan's son, in his experiments and observations on the attractive powers of mineral acids*. He observes, that the principal end which he had "in view was, to ascertain and measure the degrees of affinity or attraction that subsist between the mineral acids, and the various bases with which they may be combined; a subject of the greatest importance, as it is upon this foundation that chemistry, considered as a science, must finally rest; and though much has been already done, and many general observations laid down on this head, yet so many exceptions have occurred, even to such of these observations as seem to have been most firmly established, that not only a variety of tables of affinity have been formed, but many very eminent chemists have been induced to doubt whether any general law whatsoever could be traced."

"The discovery of the quantity of real acid in each of the mineral acid liquors, and the proportion of real acid taken up by a given quantity of each basis at the point of saturation, led me unexpectedly to what seems to me the true method of investigating the quantity of attraction which each acid bears to the several bases to which it is capable of uniting. For it was impossible not to perceive,

1st, That the quantity of real acid necessary to saturate a given weight of each base, is inversely as the affinity of each base to such acid.

2dly, That the quantity of each base requisite to saturate a given quantity of each acid, is directly as the affinity of each acid to such base.

Thus, 100 grs. of each of the acids require for their saturation, a greater quantity of fixed alkali than of calcareous calcareous earths, more of this earth than of volatile alkali, more of this alkali than of magnesia, and more of magnesia, than of earth of alum; as may be seen in the following table.

Quantity of base taken up by 100 grs. of each of the three acids.

| Potash | Soda | Lime | Ammonia | Magnesia | Alum | |--------|------|------|---------|----------|------| | Sulphuric acid | 215 | 165 | 110 | 90 | 80 | 75 | | Nitric acid | 215 | 165 | 96 | 87 | 75 | 65 | | Muriatic acid | 215 | 158 | 89 | 79 | 71 | 55 |

"As these numbers," Mr Kirwan observes, "agree with what common experience teaches us concerning the affinity of these acids with their respective bases, they may be considered as adequate expressions of the quantity of that affinity. Thus, the affinity of the sulphuric acid to potash, that is, the force with which they unite to each other, is to the affinity with which the same acid unites to lime, as 215 grs. to 110; and to that which the nitric acid bears to lime, as 215 to 96."

But to this method of Mr Kirwan objections have been made by Morveau and Berthollet. It is stated that the essential principle of the force of affinity being in the direct ratio to the quantity of base, is not fully established. According to the experiments of Morveau, a quantity of sulphuric acid containing 100 grs. of real acid, required for saturation 201 grs. of crystallized carbonate of potash; a quantity of nitric acid which contained 100 grs. of real acid, required 302 grs. for saturation; and a quantity of muriatic acid containing 100 grs. of real acid, required no less than 905 grs. of the same salt for saturation. From these experiments it appears, that Mr Kirwan's calculations are erroneous, or that the principle on which he has proceeded is false; for equal quantities of real acids require for saturation different quantities of potash; and besides, the quantity of base required is in the inverse ratio to the force of affinity, which is the reverse of Mr Kirwan's principle.

Mr Kirwan, however, has acknowledged the force of these objections, and has deduced the proportion of real acid in the nitric and sulphuric acids, from less exceptionable principles. His table, therefore, which expresses in numbers the strength of affinities, is considered as the most correct which has yet been published; and his general principle, that the quantity of base required to saturate a given quantity of real acid, is the expression of the force of affinity between the acid and the base, seems to receive additional confirmation in proportion to the progress of chemical knowledge.

Mr Kirwan has corrected the quantity of base taken up by 100 parts of sulphuric, nitric, muriatic, and carbonic acids, as will be seen in the following table:

| 100 pts. | Potash | Soda | Ammonia | Barytes | Strontites | Lime | Magnesia | |----------|--------|------|---------|---------|------------|------|----------| | Sulphuric | 121.48 | 78.32 | 26.05 | 200 | 138 | 70 | 57.92 | | Nitric | 117.7 | 73.43 | 40.35 | 178.12 | 116.86 | 55.7 | 47.64 | | Muriatic | 177.6 | 136.2 | 58.48 | 314.46 | 216.21 | 118.3| 89.8 | | Carbonic | 95.1 | 149.6 | | 354.5 | 231.+ | 122 | 50 |

But according to the experiments and observations of Berthollet, as the force of affinity varies in proportion to the mass of any body, no method, however accurate in other respects, will afford a certain rule for estimating the force of chemical affinity.

Eighth Law.

Bodies have different degrees of affinity for each other.

On the different force of affinity which exists between different bodies, depend many of the most important operations in chemistry; and it is by multiplying the objects of this law, that chemical science can be improved and extended.

Affinities have been divided into two kinds, simple affinity, and compound affinity; or simple elective attractions, and double elective attractions.

Simple affinity.—The first of these includes all those combinations which directly take place between two bodies, or when muriatic acid and lime are combined together. It is also a case of simple affinity, or single elective attraction, when to a solution which contains two substances, there is added a third which produces the separation of one of the dissolved bodies. This takes place when potash is added to the solution of lime in muriatic acid. The potash has a stronger affinity for the muriatic acid than the lime; it therefore separates the acid from the lime, combines with it, and remains in the solution. The lime thus separated from its combination, appears in the solid form, and falls to the bottom. This is called a precipitate.

In practical chemistry precipitates are distinguished into several kinds. It is said to be a real or true precipitate when the body which is disengaged from the combination falls to the bottom, as in the case above, where the lime fell to the bottom, after being separated from the muriatic acid. A false precipitate is when the new compound which is formed falls down, as when sulphuric acid is added to any solution of lime; for the compound being insoluble, it appears in the form of a precipitate. A precipitate is said to be pure when the body which has been decomposed, can be formed again from the separated constituent parts; and impure... when this cannot be effected; that is, probably, when the decomposition has not been complete. It sometimes happens when a body which consists of two substances, is decomposed by means of a third, that the disengaged substance assumes the elastic form. This is the case when muriate of ammonia is decomposed by quicklime. The muriatic acid which is in combination with the ammonia, unites with the lime, for which it has the greater attraction; and the ammonia is set free, and is instantly volatilized.

**Compound affinity.**—But there are substances which cannot be decomposed when a third substance is presented. The affinity of the two substances A and B in combination, may be so much stronger than the affinity of a third C for either A or B, that no decomposition will take place when the body C is presented to the compound of A and B. Suppose the two substances A and B are held united with a force equal to 12, and the force of affinity between the body C and B is equal only to 8, it is obvious that no change can be effected, because the force of affinity between C and B cannot overcome the cohesive force that exists between A and B. But if a fourth body D is presented to the compound A and B, and acts with a force on the body A equal to 6, while the body C acts on B with a force equal to 8, it is evident that the combined action of these two forces will overcome the force of affinity between A and B, which was supposed to be equal to 12, because the measure of a force equal to 14 is greater than one equal to 12; and in this way the decomposition of the body A and B is effected by the united action of two other bodies, which would not have succeeded had any one been presented to it singly. From this double action a decomposition of this kind is called a **double elective attraction**, a name given by Bergman, or a case of compound or complex affinity, as it has been proposed to be denominated by later chemists.

Bergman invented a method of exhibiting these attractions, as in the following diagram.

### Nitrate of Potash

| Potash | Nitric acid | |--------|-------------| | Sulphate of potash | Nitrate of silver |

### Sulphate of Silver

In this example the substances to be decomposed are placed on the right and left sides of the diagram. These are the sulphate of potash, composed of sulphuric acid and potash on the left side; and the nitrate of silver, which consists of nitric acid and the oxide of silver. When these compounds are combined together, a decomposition is effected by the mutual affinities between the constituent parts of the compounds. Thus the sulphuric acid in combination with the potash, forms a new compound with the oxide of silver, and the nitric acid in combination with the silver, forms a new compound with the potash; because the sum of the force of affinities between the nitric acid and the potash, and the sulphuric acid and the oxide of silver, is greater than the sum of the affinities between the sulphuric acid and the potash, and the nitric acid and the oxide of silver; and thus an exchange of principles takes place, and the new compounds are represented at the top and bottom of the diagram, namely the nitrate of potash and the sulphate of silver.

Mr Elliot in the year 1782 proposed, as an improvement on Bergman's method, to represent the force of these attractions by numbers. The same case in Mr Elliot's method is represented in the following diagram.

### Nitrate of Potash

| Potash | Nitric acid | |--------|-------------| | Sulphate of potash | Nitrate of silver |

### Sulphate of Silver

As it is thus represented, the sulphuric acid and the potash are supposed to act with a force equal to 9; and the nitric acid and the oxide of silver attract with a force equal to 2. The affinity of the potash for the nitric acid is equal to 8; and the affinity between the sulphuric acid and the oxide of silver is equal to 4. But \(9 + 2 = 11\), and \(8 + 4 = 12\); consequently the sum of the affinities between the nitric acid and the potash, and the sulphuric acid and the oxide of silver, exceeds the sum of the affinities between the nitric acid and the oxide of silver, and the sulphuric acid and the potash, and thus a decomposition is effected.

But "in all decomposition," says Mr Kirwan, "we two forces must consider, first, the powers which resist any decomposition, and tend to keep the bodies in their present state; and secondly, the powers which tend to effect a decomposition and a new union. The first I shall call quiescent affinities, and the second, divellent."

"A decomposition will always take place when the sum of the divellent affinities is greater than that of the quiescent; and on the contrary no decomposition will happen when the sum of the quiescent affinities is superior to, or equal to that of the divellent: all we have to do, therefore, is to compare the sums of each of these powers. Thus, if the solutions of sulphate of potash and nitrate of lime be mixed together, a double decomposition will take place." This may be illustrated by the following diagram.

### Nitrate of Potash

| Potash | Nitric acid | |--------|-------------| | Sulphate of potash | Nitrate of lime |

### Sulphate of Lime

The The affinities between the nitric acid and lime, and between the sulphuric acid and the potash, which taken together amount to 311, are the quiescent affinities. The affinities of the sulphuric acid and the lime, and of the nitric acid and the potash, are the divalent affinities which are opposed to the first. But the amount of the latter is equal to 325; that is, the combined affinities of the substances which tend to form a new combination, and thus they overcome the force of the resistance of the quiescent affinities, as 325 exceeds 311.

Another example will serve to make this decomposition by double or compound affinity still more familiar.

Muriate of potash.

| Muriatic acid | Potash | |---------------|--------| | 36 | + | | Barytes | Carbonate of potash | | | 45 |

Carbonate of barytes.

In this case a solution of muriate of barytes is mixed with a solution of the carbonate of potash. The affinity of the muriatic acid for the barytes, and that of the potash for the carbonic acid, are the quiescent affinities which are opposed to any decomposing force. But on the contrary, the affinity of the muriatic acid for the potash, and that of the barytes for the carbonic acid, are the divalent affinities. The quiescent affinities are only equal to 45, while the sum of the divalent affinities is equal to 46; the latter must therefore prevail. The former combinations are broken, and instead of muriate of barytes, and carbonate of potash, we obtain muriate of potash and carbonate of barytes, which latter is insoluble, and is therefore precipitated.

But Berthollet has shown that the force of affinity is not constant and uniform, but is greatly influenced by the quantity and the state of saturation. As, for instance, when two bases act in opposition on an acid, the acid divides its action in proportion to their respective masses. If there be two acids instead of one, and no separation take place, either by precipitation or crystallization, both acids will act equally on both bases, in proportion to their masses. If each of the acids be previously combined with a base, and the solutions of their salts be mixed, the sum of the reciprocal forces will be the same as before. No muriate of potash or sulphate of lime will be formed; but there will be a combination of potash, of lime, of sulphuric and muriatic acid, which will have the same degree of saturation as before the mixture. And hence it happens, that when two salts are mixed together, the mutual decomposition of which would produce combinations of very different proportions, the separation of the component parts, which should result from such decomposition, is not perceptible. No change of bases therefore takes place.

The force of cohesion causes the separation which takes place by precipitation or crystallization. A similar effect is produced by the same cause, in the action of complex affinities. If a solution of sulphate of potash be mixed with muriate of lime, dissolved in a small quantity of water, the lime brought into contact with the sulphuric acid, will be more powerfully influenced by the force of cohesion, than the potash. This is therefore to be considered as an additional force to those which pre-existed, and determines the combination of the sulphuric acid with the lime, and the precipitation of the new compound.

In all decompositions effected by compound affinity, the prevailing affinity has been ascribed to those substances which have the property of precipitating, or of forming a salt which can be separated by crystallization. Thus the knowledge of the solubility of salts which may be formed in a liquid, will point out those substances which are least soluble, and therefore most apt to precipitate. To these substances chemists formerly ascribed the strongest affinity.

Lime, magnesia, stonites, and barytes, form insoluble salts with carbonic acid. When therefore, any of these substances are mixed with alkali, pounds of lime carbonates, an exchange is produced, from which result the formation and precipitation of an earthy carbonate. The compound of sulphuric acid and barytes forms an insoluble salt. When, therefore, a solution of a sulphate is mixed with that of a salt of barytes, a precipitation of sulphate of barytes, which is insoluble, will be effected. The sulphate of lime has also but little solubility, and consequently it is much disposed to precipitate. Lime therefore decomposes all the soluble sulphates. But the sulphate of lime being much more soluble than the sulphate of barytes, the salts of barytes, which are more soluble than the sulphate of lime, decompose it.

There are other circumstances which tend to change the action of compound affinities. This action is greatly influenced by the greater or less solubility of salts. But the solubility of salts is varied by temperature. In estimating the result of compound affinities, therefore, the degree of temperature must be considered and taken into the account. To give an instance of this effect, nitrate of potash mixed with muriate of soda, crystallizes at a low temperature. During the evaporation the muriate of soda is separated. No change of bases will take place, because the nitrate of soda is somewhat more soluble when cold, than nitrate of potash; and muriate of potash is more soluble when hot, than muriate of soda.

The action of complex affinities may also be changed by the formation of a triple salt which precipitates; but if the solubility of the combination be known, the resulting compounds, may also be foreseen.

According to the theory of Berthollet, all substances in the liquid state exert a reciprocal action. In a solution of sulphate of potash and muriate of soda, these two salts are not diluted, nor do they become so, until some extraneous cause produces their separation. Sulphuric and muriatic acids, potash and soda, are contained in the liquid. To ascertain what combinations are produced by the force of crystallization, he made the following experiments.

"Experiment 1.—A mixture was made of equal parts of nitrate of lime and sulphate of potash; after the preparation..." paration of the sulphate of lime formed in the commencement, and of which no further mention shall be made in the following experiments, the liquid was evaporated, and nitrate of potash and sulphate of lime were alone obtained by successive operations. Yet, after the last evaporation, some crystals of sulphate of potash were obtained; there was but a small residue of uncrystallizable liquid, in which carbonate of soda and nitrate of barytes produced precipitations; whence it appears that it consisted of a small quantity of sulphuric acid and lime, and very probably of a larger portion of nitrate of potash.

"The quantity of sulphate of lime which precipitated during this evaporation, was much greater than what could be dissolved in an equal quantity of water; whence it appears that its solubility was augmented by the action of the other substances.

"Experiment 2.—Two parts of sulphate of potash, and one of nitrate of lime, yielded, by the first evaporation, sulphate of potash and sulphate of lime; and by the following, nitrate of potash with the two sulphates, the proportions of which continued to diminish until the salts ceased to crystallize: only a few drops of uncrystallized liquid remained, in which no precipitate was formed on adding to it some carbonate of soda, but this effect was produced by the nitrate of barytes; whence it appears probable that the liquid consisted of sulphate of potash, and a small proportion of nitrate of potash.

"Experiment 3.—Two parts of nitrate of lime, and one of sulphate of potash, yielded by the first evaporation a small quantity of sulphate of lime, and on cooling, some nitrate of potash; by the succeeding evaporations nothing but nitrate of potash was obtained. After the last, however, some crystals of sulphate of lime were perceptible on the surface of the liquid. Though the residue, which was abundant, was repeatedly put to evaporate and cool, no crystallization was effected. This uncrystallizable residue, treated with alcohol, yielded an abundant precipitate, in the solution of which in water no precipitate could be produced by nitrate of barytes; whence it appears that it contained no sulphuric acid, and that it was composed of pure nitrate of potash. What had been dissolved in the alcohol was nitrate of lime, with a small proportion of nitrate of potash: the uncrystallizable residue consisted, therefore, of nitrate of potash and nitrate of lime.

"It appears that the sulphate of lime was rendered much less soluble in this than in the preceding experiments; and that the action of nitrate of lime prevented a considerable quantity of the nitrate of potash from crystallizing.

"Sulphate of lime was necessarily formed in these three experiments, because its component parts were in contact; and the insolubility of the compound formed by them, occasioned its precipitation to a certain extent.

"In the first and second experiments, the sulphate of lime was rendered much more soluble than it naturally is, by the action of the substances in solution; but in the third experiment, its solubility was not perceptibly increased, for this reason, probably, that the nitrate of lime and nitrate of potash, which existed in the uncrystallizable liquid, had mutually saturated each other so much as to diminish their action on the sulphate of lime.*

From these considerations, he deduces the theory of uncrystallizable residues: which the succeeding observations tend to confirm.

"Saline substances exert a mutual action, which augments their solubility; as has been proved by the experiments published by my learned colleague Vauquelin. This reciprocal action varies in different salts; it was once supposed that the solubility of the nitrate of potash was not augmented by the action of earthy salts; and yet it is augmented more by them than by any others.

"There must be, doubtless, in this respect, some difference arising from the nature of the salts, in the effect which they produce; but this difference is, in general, very trifling, compared to that resulting from the force of crystallization.

"Experiment 4.—A mixture of equal parts of nitrate and sulphate of potash, yielded by evaporation, and successively, according to their solubility, sulphate of potash and nitrate of potash, without leaving any uncrystallizable residue; but having made a similar experiment with a mixture of nitrate and sulphate of soda, each of which has but a feeble tendency to crystallize, and nearly an equal degree of solubility, there was separated by crystallization but a small portion of the sulphate of soda, the other parts of the mixture continuing in the liquid state, incapable of being crystallized by any means. Muriate of soda and sulphate of alumine, submitted to the same treatment, were perceived to become more soluble; but they were totally separated in the end by alternate evaporation and cooling.

"It appears, then, that substances which are endowed with an active tendency to crystallize, though rendered more soluble than they naturally are, separate however in the order of their insolubility, without leaving any, or very little, uncrystallizable residue.

"But when a mixture consists of salts which have but a weak tendency to crystallize, their mutual action counteracts that tendency, so that a large portion of uncrystallizable liquid remains: this effect is still more complete when the mixture contains a substance naturally uncrystallizable, as in the third experiment, in which there was an excess of nitrate of lime, the action of which excess on the nitrate of potash rendered a great part of it uncrystallizable."†

From this it appears, Berthollet observes, that the formation of salts obtained by crystallization, depends on the proportions of the substances which act on each other; and combinations may be formed which vary from the proportions of the substances employed, or the stage of the operation; that is, from the proportions which continue in action, when the combinations which might take place are not ended with a force of cohesion sufficient to withdraw them from the sphere of action.

Ninth Law.

Affinity is in the inverse ratio of saturation.

In most of the combinations which take place between bodies, there exists a certain determinate proportion towards the portion of the quantity of the substances which form part of the compound. On this indeed depend the constancy and and permanency, both of natural and artificial compounds. It is to this uniformity and permanency that their characteristic properties are owing; for when the proportions in compound bodies vary, although the constituent parts be of the same nature, yet the properties of the compound are greatly changed. Thus, in a case already mentioned, the different proportions of oxygen with lead, different compounds are produced; with a smaller proportion of oxygen, the resulting compound is yellow, but with a greater it is red.

As there are certain limits to the proportions in which bodies combine together, beyond which they cannot pass, these are called the points of saturation; and when two bodies, in uniting together, have reached this point, they are said to be saturated, or the one body is said to be saturated with the other: in other words, the change has taken place, and a new compound is formed. When, for instance, a salt is dissolved in water, as common salt, the water combines only with a certain proportion; and whatever quantity of salt is added beyond this proportion, it falls to the bottom undissolved. The reason of this is, that the particles of the salt are held together by their affinity for each other; that is, by the force of cohesion. Now, before any combination can be effected between the particles of the salt and the water, this force must be overcome. The force of affinity, therefore, between the water and the particles of salt, is greater than that between the particles of salt themselves, and thus they are separated and dissolve in the water; but this force of affinity between the water and the salt is limited; and when it has arrived at its utmost limit, the action between the two bodies ceases. The two forces which were opposed to each other; that is, the force of affinity between the water and the salt on the one hand, and the force of cohesion between the particles of the salt on the other, are balanced. The water in this case is said to be saturated with salt.

In a sense somewhat similar, the word neutralization has been employed. When to an acid there is added the solution of an alkali to a certain point, they combine together, and form a compound, in which the properties of the acid and of the alkali totally disappear. They are then said to have neutralized each other; and hence the name of neutral salts, which has been given to these compounds.

Some bodies, it would appear, enter into combinations with others, only in one determinate proportion, and some in two proportions, and these proportions are denominated their maximum and minimum of saturation; that is, the smallest and greatest proportions in which they combine with each other. There is another set of bodies which combine in any proportion between the highest and the lowest points, while a fourth set combine only in certain determinate proportions between these points.

Now, from these observations, let us endeavour to illustrate the meaning of this law, by attending to what takes place in the different combinations of bodies with each other. A smaller quantity of salt dissolved in a given quantity of water, is held in combination by a greater force of affinity, than a greater quantity; because this force is to be estimated by the affinity which exists between the salt and the water, and its mass. The nearer, therefore, it comes to the maximum or highest point of saturation, the weaker is the affinity between the water and the salt; and in approximating to this point, this force is gradually diminished.

When two bodies combine together in two different proportions, or what are called the maximum and minimum points of saturation, the force of affinity is greatest between the two bodies at the lowest point. Suppose that two bodies, A and B, can enter into combination with each other, in two different proportions. Suppose the quantity of A is = 20 grs. and the first portion of B which combines with it is = 10 grs.: it is evident from this combination, that part of the force of the affinity of A is exhausted, but still it combines with another portion of B; suppose this is = 5 grs. and then it has reached its highest point of saturation, or the maximum. But as the last portion of B, which combined with A, is retained in the compound by the force of affinity in A, which remained after its combination with the first portion of B, it is obvious that this force must be greatly diminished, and therefore the last portion of B will be most easily separated from its combination with A; and this accordingly is found to hold in all cases.

Tenth Law.

Between two compound bodies which are not acted on by compound affinity, decomposition may take place, if the affinity of two of the principles for a third be greater than that which unites this third to one of the two first, although, at the moment of action, the union between the two first does not exist.

This is called disposing or predisposing affinity, because no change takes place without the influence or affinity action of a third body on some of the compounds; for it is this action which operates the formation of the compound, and the decomposition of another compound, without the formation of the first. To have a clear conception of this disposing affinity, let us suppose that there are two compounds AB and CD; the affinity of whose constituent parts, that is, the affinity between A and C, and the affinity between B and D, is not greater than the affinity which exists between AB and CD. In this case, it is obvious that no decomposition can be effected by compound affinity, because the sum of the slightest affinities exceeds the sum of the divalent; but if the force which tends to combine B and C together, added to that which tends to unite the compound BC to D, be greater than the force of cohesion between the compounds AB and CD, the result of this action will be a decomposition, the formation of a new compound BCD, and the separation of the first component part A.

Water is composed of two substances, which have received the names of oxygen and hydrogen. Sulphur has no direct action on water. This shows that the affinity between sulphur and any of the constituent parts of the water, is not so great as the affinity of the oxygen and hydrogen for each other; but if sulphur be united with an alkali, the water is decomposed by this combination, although there is an affinity between the alkali and the oxygen. The sulphur combines with the oxygen of the water, and forms sulphuric acid. It is this attraction which favours the decomposition of the water, and is therefore called a predisposing affinity.

Such then are the phenomena of chemical action, which have been observed and clasped together. The knowledge of the laws of affinity, and the knowledge of chemistry, may be regarded as synonymous terms, because it is by the observation of the laws by which the changes that take place among bodies by chemical affinity are produced, that this science can be improved and extended. The detail of chemical science, therefore, may be regarded as the history of affinities. We therefore proceed, in the following chapters, to examine the properties of those bodies, the knowledge of which belongs to chemical science; the changes which take place by the action of affinity, and the new compounds which are the result of these changes; and, at the same time, to point out some of their applications and uses.

**CHAP. II. OF LIGHT.**

Light and heat, which are to be treated of in this and the succeeding chapters, are highly interesting, not only as curious subjects of speculation, but as acting a very important part in the changes which are constantly going on among natural bodies. Indeed no change happens, in which the one or the other, and sometimes both, is not either absorbed or extricated.

Light, of which we are now to treat, is the principal agent in many chemical processes; and this, as well as the astonishing velocity of its motions, and the properties which it has of penetrating and traversing substances with which it comes in contact, render it an object worthy of great attention.

Light, if it could be defined, is too familiar to every one to require any definition. It is by the light of the sun, or that which proceeds from burning bodies, that we are informed of the presence of objects; or the rays of light proceeding from these bodies, and entering the eye, produce the sensation of vision. We have no certain knowledge concerning the nature of light. Various conjectures, however, have been made, and various theories have been proposed, with regard to it. Two of these we shall only mention. According to Des Cartes, Huygens, and some other philosophers, all space is filled up with a very subtle fluid, and this fluid is agitated or put in motion by the sun, or burning bodies. This motion consists of vibrations or undulations, which, extending themselves and reaching the eye, render the bodies which have produced these motions visible.

The other theory is that of Newton and his followers. According to this theory, light is supposed to be a real emanation from luminous bodies; that is, a subtle fluid, consisting of peculiar particles of matter which are constantly separating from luminous bodies, and, by entering the eye, excite the sensation of light, or the perception of the objects from which it proceeds, or those from which it is reflected. This theory, which has been deduced from a great number of facts and observations, was established by Newton by mathematical demonstration. If then it be admitted, that light is a subtle fluid, consisting of minute particles, several consequences follow, which require explanation, with regard to the size, the velocity, and the momentum of these particles. In what follows, we shall consider light with regard to its physical properties; its chemical properties, or the effects it produces on bodies with which it enters into combination; and, lastly, the sources from which it is obtained.

**SECT. I. Of the PHYSICAL PROPERTIES of LIGHT.**

1. One of the most astonishing properties of light is its velocity. It has been observed by astronomers, that the eclipses of the satellites of the planet Jupiter appear to take place sooner, when that planet is nearest to the earth, and later when Jupiter is on the opposite side of his orbit from the earth. Roemer, a Danish astronomer, in attempting to account for this apparent anomaly, proved that it was owing to the difference of time which the particles of light required, to pass through the semidiameter of Jupiter's orbit; and from this he demonstrated, that the particles of light move through one half of the diameter of the earth's orbit in about eight minutes. This discovery of Roemer has been fully confirmed by the theory proposed by Dr. Bradley, to account for the aberration of the light of the fixed stars. From these data it has been computed, that light moves with the velocity of 295,000 miles in a second—a velocity of which the human mind can form no distinct conception. But in comparing this velocity with that of a cannon ball, it may be observed, that light passes through a space in about eight minutes, which a cannon ball with its ordinary velocity could not traverse in less than thirty-two years!

2. From the remarkable velocity of light, may be inferred the extreme minuteness of its particles. The very minute force with which moving bodies strike, is in proportion to their masses, multiplied by their velocities. If, therefore, the one or the other, or both, be increased, the striking force is proportionally augmented; and consequently, if the particles of light were not extremely small, their excessive velocity would be highly destructive. Indeed, were they equal in bulk to the two millionth part of a grain of sand, this impulse would not be less than that of sand shot from the mouth of a cannon.

The minuteness of the rays of light may be also demonstrated from the great facility with which they penetrate and pass through transparent solid bodies. In moving through such bodies, light seems not to suffer the smallest diminution of its velocity. If there is nothing to obstruct the rays of light which proceed from a candle, it will fill the whole space within two miles around, almost instantaneously, before it has lost any sensible part of its substance.

3. When a ray of light falls on a polished substance in a perpendicular direction, it is thrown back in the same direction; but when a ray of light falls on the same body obliquely, it returns from the surface on the opposite side of a perpendicular line drawn from the point on which the ray falls, and at an equal distance from that perpendicular. The angle which the ray of light forms with the perpendicular as it falls, is equal to the angle which it forms with the same line, when it is thrown back. The first angle is called the angle of incidence, and the second the angle of reflection. Hence the optical law, that the angle of incidence is equal to the angle of reflection. When the rays of light fall obliquely on polished surfaces, they are reflected before they touch these surfaces, which is supposed to be owing to a repulsion between the particles of light and the particles of the polished body. But when rays of light fall obliquely on a transparent substance, as a plate of glass, they pass through to the other side, and then return to the same surface, and are reflected.

4. When a ray of light is admitted into a dark room, through a small hole, it forms a luminous spot on any object opposite to that from which the light proceeds; and if the blades of two knives are placed on opposite sides of the hole, having their planes parallel to the plane of the window shutter or paneboard through which the ray passes, when the edges of the knives are brought near each other, the rays of light are drawn from their former direction towards the edges of the knives, and the luminous spot appears enlarged. This is called the inflection of light. A similar effect is produced by nearly shutting the eyes, and looking at a candle. The rays of light appear to proceed from it in various directions; for the light, in passing through the eye-lashes, is inflected, and is divided into separate beams, diverging from the luminous object.

5. A ray of light passing from one medium to another, moves on in the same direction; as, for instance, when light passes from air to water, or from water into air. But if a ray of light passes in an oblique direction from one medium to another, it is bent from its former course, and then moves on in a new direction: this is called the refraction of light. A straight rod, which is introduced obliquely into a vessel of water, appears bent at the place where it touches the surface of the water. This is owing to the refraction of the rays of light passing from the rarer medium of the air to the denser medium of the water.

When the light passes into a medium of greater density, as for instance from air into water, it is refracted or bent towards the perpendicular; but when it passes from a denser into a rarer medium, as from water into air, it is refracted from the perpendicular. The measure of the quantity of this refraction is estimated by the density of the medium; with this exception, however, that if the medium be a combustible substance, the refractive power is then found to be greater. It was from the observation of this law of the refraction of light, that the conjecture which was thrown out by Newton, of the combustible nature of water and the diamond, which has been verified by the discoveries of modern chemistry, occurred to the mind of that sagacious philosopher.

6. When a ray of light is admitted through a small hole, and received on a white surface, it forms a luminous spot. If a dense transparent body be interposed, the light will be refracted, in proportion to the density of the medium; but if a triangular glass prism be interposed, the light is not merely refracted, but it is divided into seven different rays. The ray of light no longer forms a luminous spot, but has assumed an oblong shape, terminating in semicircular arches, and exhibiting seven different colours. This image is called the spectrum, and, from being produced by the prism, the prismatic spectrum. These different coloured rays appearing in different places of the spectrum, shew that their refractive power is different. Those which are nearest the middle are the least refracted, those which are the most distant, the greatest. The order of the seven rays of the spectrum is the following: red, orange, yellow, green, blue, indigo, violet. The red, which is at one end of the spectrum, is the least, and the violet, which is at the other end, is the most refracted.

Sir Isaac Newton found, if the whole spectrum was divided into 365 parts, the number of the parts occupied by each of the colours to be the following:

| Colour | Parts | |----------|-------| | Red | 45 | | Orange | 27 | | Yellow | 48 | | Green | 60 | | Blue | 60 | | Indigo | 40 | | Violet | 80 |

These different coloured rays are not subject to farther division. No change is effected upon any of them by dividing them farther refracted or reflected; and, as they differ in refrangibility, so also do they differ in the power of inflexion and reflexion. The violet rays are found to be the most reflexive and inflexible, and the red the least.

7. Light, it is well known, seems to suffer no interruption in passing through some bodies; such are glass or water: but it is interrupted in its passage through other bodies, as a piece of wood or stone. The first set of bodies are called transparent, and the other opaque. The density of water or of glass is greater than that of a piece of wood. It cannot therefore be owing to the density of the latter, or the closeness of the particles which compose it, that the transmission of light is prevented. In the explanation which has been given by Newton, it is supposed that the particles which compose transparent bodies, are of equal density, and are uniformly arranged: but in opaque bodies he supposes the particles are of unequal density, or are not uniformly arranged. From the uniform arrangement and equal density which, according to this explanation, are supposed to exist in transparent bodies, the light passing through them moves in a straight line, because it is equally attracted by the particles of the body. But in the latter (the opaque bodies) the opacity, attraction between light and the particles of the body is unequal; its direction is constantly changing, till at last it is entirely interrupted.

8. Dr Herschel, who has made some interesting discoveries concerning light and heat, found that the illuminating power of the different rays was different. From the observations which he made on this subject, he says, that "with respect to the illuminating power assigned to each colour, we may conclude, that the red-making rays are very far from having it in any eminent degree. The orange possesses more of it than the red, and the yellow rays illuminate objects still more perfectly. The maximum of illumination lies in the brightest yellow, or palest green. The green itself is nearly equally bright with the yellow; but from the full deep green the illuminating power decreases." creases very sensibly; that of the blue is nearly upon a par with that of the red; the indigo has much less than the blue; and the violet is very deficient.*

Sect. II. Of the Chemical Properties of Light.

1. From the properties of light which have now been detailed, it appears that it is subject to the universal law of attraction, as well as other bodies; but it is also found to enter into chemical combination with many substances. These substances, it has been discovered by experiment, after being for some time exposed to the light, and carried into a dark place, appear luminous. It is found, however, that this property is lost when they are kept in the dark, and they do not recover it till after they have been again exposed to the light. Some substances possess this property in a greater degree than others. One which was discovered by Mr Canton, who made a number of experiments on this phosphorescent light, as it has been called, is prepared by the following process. He took some oyster-shells and calcined them, after which they were reduced to powder, and the purest part of them was put through a fine sieve. Three parts of this powder were mixed together with one part of the flower of sulphur; the mixture was put into a crucible, and firmly pressed to the bottom, which was then exposed for an hour to a red heat. It was then removed from the fire, and when it cooled, the purest parts of the mixture were scraped off, and put up in a well-closed phial. This is called Canton's pyrophorus. When this is exposed to the light for a short time, it becomes so luminous that objects may be distinctly perceived in the dark, by the light which it emits. It loses the property, however, by being kept in the dark, but recovers it again when it is exposed to the light. And, after being kept in the dark for some time, the light from the pyrophorus becomes feeble, or is nearly extinct, but it may be revived or increased by plunging the phial into hot water. But, if the whole of the light has been separated previous to the application of heat, no further application can cause it to emit light, till it has been exposed to a luminous body. Thus it appears that light enters into combination with other bodies, and that it afterwards leaves them without having undergone any perceptible change.

2. If a quantity of purple-coloured fluate of lime (Derbyshire spar) be reduced to coarse powder, and exposed to heat in a dark place, it emits a great quantity of coloured light; but when this light which has been in combination with the spar is once expelled, it does not recover its property of shining in the dark, as in the case of Canton's pyrophorus.

It has been supposed by some, that the light, emitted by these substances is the consequence of slow combustion; but many of the substances which have this property are not combustible, and none of the changes which take place during this process have been observed. In some cases it would appear that the light which is given out is different from that to which they were exposed, and which they must have absorbed. In some of the pyrophori, the blue rays were observed to have a greater effect, and the light which was emitted was of a red colour.

3. Light, it is well known, is given out by a number of animal and vegetable matters, when the process of putrefaction commences. In this case it seems to constitute one of their component parts. This particularly happens to fish of different kinds, as the herring and the mackerel; and to this is supposed to be owing the phosphorescent light of the sea, which appears when the water is broken and agitated. These phenomena were observed by Mr Boyle and Dr Beale, both in the flesh of quadrupeds and fishes, and earlier by Fabricius ab Aquapendente and Bartholin in the flesh of quadrupeds. Experiments were made on the same subject by Mr Canton, whom we have already mentioned, and more lately by Dr Hulme. From the experiments of the latter he concludes, that this light is a constituent principle of marine fishes; that it is incorporated with their whole substance, making a part of it, in the same manner as any other constituent principle; that when this spontaneous light is extinguished by some substances, it may be again revived; that the quantity of light emitted is not in proportion to the degree of putrefaction, but, on the contrary, the greater the putrefaction, the less is the quantity of light emitted.

For the sake of those who may wish to repeat these experiments, we shall detail the following made on the herring and mackerel, in the words of the author.

The Flesh of Herring (G).

(1.) "A fresh herring was split, or divided longitudinally by a knife, into two parts. Then about four drams of it, being cut across, were put into a solution, composed of two drams of Epsom salt or vitriolated magnesia, and two ounces of cold spring water drawn up by the pump. The liquid was contained in a wide-mouthed three-ounce phial, which was placed in the laboratory. Upon carefully examining the liquid, on the second evening after the process was begun, I could plainly perceive a lucid ring (for the phial was round) floating at the top of the liquid, the part below it being dark; but, on shaking the phial, the whole at once became beautifully luminous, and continued in that state. On the third evening, the light had again risen to the top; but the lucid ring appeared less vivid, and, on shaking the phial as before, the liquid was not so luminous as on the preceding night.

(2.) The same experiment was repeated. On the second night, the liquid, being agitated, was very luminous; on the third, not so lucid; and on the fourth the light was extinguished.

(3.) With sea salt or muriated natron half a dram, and two ounces of water. On the second night, the liquid, when agitated, was dark; on the third, lucid; on the fourth very luminous; on the fifth, it began to lose light; on the sixth, it continued to decrease; and on the seventh it was quite gone. Neither the liquid, nor the herring, had contracted any putrid smell.

(4.) With

(g) The quantity used in each experiment was about four drams. (4.) With sea water two ounces. On the second night, dark; on the third, fourth, and fifth, luminous; on the sixth, nearly extinct; and on the seventh, totally. The piece of herring, when taken out and examined, was remarkably sweet.

Roe of Herring (H).

(5.) With Epsom salt two drams, and water two ounces. On the second night, the liquid was pretty luminous; on the third and fourth, still luminous; and on the fifth its light was extinct.

(6.) With Glauber's salt or vitriolated natron, two drams to two ounces of water. On the second night, when the phial was shaken, as usual in all these experiments, the liquid was pretty luminous; on the third, less so; and on the fourth the light was scarcely visible.

(7.) With sea water two ounces. On the second night dark; on the third, the liquid was moderately luminous; on the fourth and fifth, it had extracted much light; and on the seventh it was still shining. After this process both the roe and the sea water remained perfectly sweet.

The Flesh of Mackerel.

(8.) With Epsom salt two drams, and water two ounces. On the second night, the liquid was finely illuminated; on the third, a similar appearance; on the fourth, a diminution of light; on the fifth, it continued lucid in a small degree; and on the sixth the light was extinguished.

Roe of Mackerel.

(9.) With Epsom salt two drams, and water two ounces. On the second night, the liquid, when agitated, was exceedingly bright; on the third, the same; and on the fourth and fifth, still lucid.

Dr Hulme found that some substances have the power of extinguishing this light. It was quickly extinguished when mixed with water alone, with water impregnated with lime, carbonic acid gas, or sulphurated hydrogen gas; by fermented liquors and ardent spirits; by the acids, both concentrated and diluted; by the alkalies when dissolved in water; by many of the neutral salts, as the solutions of common salt, Epsom salt, and sal ammoniac. It was also extinguished by infusions of chamomile flowers, of long pepper, and of camphor, made with boiling hot water, but not used till quite cool.

When the substances emitting this light were placed in a freezing medium, the light was in a short time quite extinguished; but when exposed to a moderate degree of temperature, it was revived. A moderate degree of heat increased this light, but it was extinguished by a high temperature, and no luminous appearance could again be discovered.

4. When all the rays of light are reflected from any body, that body is said to be white; but when all the rays are absorbed, the body which absorbs them is said to be black: but experience informs us, that different bodies absorb and reflect different rays. Thus, if a body absorb all the rays excepting the yellow, that body is said to be of a yellow colour; or if a body reflect the red rays, while the others are absorbed, it is said to be red. Thus the colour of the body is characterized by the colour of the ray which is reflected; or, which is the same thing, this is the cause of colouring bodies.

5. One of the most singular effects which is observed in the combination of light with bodies, is its power of reducing the oxides of the metals. Some of these, as, for instance, the red oxide of lead, when exposed to the light of the sun, lose some of their weight. The oxide of gold may also be reduced in the same way, and the white salts of silver become black, and the oxide is reduced; and when that process is going on, oxygen gas is emitted, which, it would appear, has been separated by the action of light. Some of the rays are found to have a greater effect than others. Scheele, who made a set of experiments to ascertain the difference of effect of the different-coloured rays in blackening the muriate of silver, discovered that the violet ray was the most powerful in reducing the oxide of silver.

It was formerly the general opinion, that the colorific rays of light were the cause of the reduction of the oxides of the metals; but the experiments and observations of Meiss Bockman and Ritter in Germany, and of Dr Wollaston in England, prove that the muriate of silver is more strongly and rapidly darkened by rays of the sun which have been more refracted than the violet rays; for it appeared that the muriate was affected in a space lying beyond the violet light. These rays, therefore, have not the property of giving light, nor do they produce any sensible degree of heat; and thus it appears that there are three different sets of rays; namely, rays which illuminate, rays which warm without giving any light (1), and rays which produce a chemical action on bodies, but which give neither light or heat. From the consideration of these curious and interesting experiments, it has been very naturally supposed, that the chemical actions dependent on solar rays are owing to the invisible rays which were refracted beyond the violet rays; and that the colorific rays have no share in these actions: for it has been observed, that the effect of the different colours increases with their refrangibility; and that the whole is owing to the invisible rays which increase in number or quantity as they approach to the violet ray, and are in greatest quantity at a certain distance beyond it.

6. The absorption of light by plants produces another remarkable effect. It has been long known, that, caused by the green colour of the leaves of plants is produced by plants, the light of the sun. Experiments were first made to ascertain this fact by M. Dufay and some others of the French academicians. The subject has been farther prosecuted and extended by Senebier of Geneva. When seeds are sown in a dark place, they vegetate,

(h) The quantity used in each experiment was about four drams.

(i) These will be particularly mentioned in the next chapter. getate, and the plant grows with considerable luxuriance; but it never has any green colour as long as the light is excluded; the leaves continue white; and this happens although air be freely admitted. When the plant in this state is exposed to the light, the green colour begins to appear, and the plant assumes its ordinary habit. It may be added, that while the plant remains white, it contains but a small quantity of combustible matter, and it has but little taste. When it assumes the green colour after its exposure to the light, it acquires its natural taste, and the ordinary quantity of combustible matter. It is upon this principle that the art of blanching celery and other garden plants depends; by heaping up the earth about the stems the light is excluded, and thus they are deprived of any pungent taste, and become white and tender (k).

Sect. III. Of the Sources of Light.

1. The principal source of light is the sun. It has been a question of more curiosity than utility, what is the cause of the sun constantly emitting light, and what are the means of repairing that waste? By calculations it is supposed, that there ought to issue from one square foot of the sun's surface in one second, \( \frac{1}{20} \) part of a grain of matter, to supply the consumption of light; that is, at the rate of little more than two grains a day, or about 4,752,000 grains, or 670lb. in 6000 years, which would have shortened the sun's diameter about 10 feet, if it was formed of matter of the density of water only.*

But at the time this calculation was made, the discoveries of Herschel, of the constitution of the sun, were not known. The body of the sun, according to the observations of this philosopher, is not luminous, but opaque; and the light which was supposed to come from his surface, proceeds from a luminous atmosphere which surrounds that body; and there are probably forms means by which the waste that is constantly going on, is repaired. The light which comes from the stars is of the same nature with that of the sun.

2. Another source of light are burning bodies. In combustion, all cases of burning, light is emitted. This light, therefore, must have been in combination with some of the substances which are employed in these processes.

3. But when bodies, without undergoing the process of combustion, are heated to a certain temperature, they emit light: and it would appear, from experiments which have been made upon the subject, that all bodies which are not decomposed before they arrive at the proper temperature, begin to give out light, exactly at the same degree of heat. Iron heated to 635°, according to Sir Isaac Newton's experiments, becomes visible in the dark; at 752° it shines brightly; and becomes luminous in the twilight at 884°. The temperature is above 1000° when it shines in broad daylight. A red heat, according to the experiments of others, commences at the temperature of 800°, and when a body reaches the proper degree of heat, it appears luminous, independent of the air. Mr T. Wedgwood, who made a number of experiments on this subject, found that a piece of iron wire became red hot when immersed in melted glass. Air, therefore, is not necessary to the shining of ignited bodies.

It was also ascertained by Mr Wedgwood, that a piece of red-hot metal continues to shine for some time after it has been removed from the fire, which proves that constant accretions of light or heat are not necessary for the shining of ignited bodies. But if the red-hot metal be strongly blown upon, it instantly ceases to shine, and thus, it appears, when the temperature is diminished, it ceases to give out light †.

(k) This is remarkably illustrated by the following observations of Professor Robison. "Having occasion in autumn 1774, to go down and inspect a drain in a coalwork, where an embankment had been made to keep off a lateral run of water, and, crawling along, I laid my hand on a very luxuriant plant, having a copious, deep-indentated, white foliage, quite unknown to me. I inquired of the colliers what it was. None of them could tell me. It being curious, I made a sod be carried up to the daylight, to learn from the workmen what sort of a plant it was. But nobody had ever seen any like it. A few days after, looking at the sod, as it lay at the mouth of the pit, I observed that the plant had languished and died, for want of water, as I imagined. But looking at it more attentively, I observed that a new vegetation was beginning, with little sproutings from the same stem, and that this new growth was of a green colour. This instantly brought to my recollection the curious observations of M. Duray; and I caused the sod to be set in the ground and carefully watered. I was the more incited to this, because I thought that my fingers had contracted a sensible aromatic smell by handling the plant at this time. After about a week, this root set out several stems and leaves of common tanin. The workmen now recollected that the sods had been taken from an old cottage garden hard by, where a great deal of tanin was still growing among the grass. I now sent down for more of the same stuff, and several sods were brought up, having the same luxuriant white foliage. This, when bruised between the fingers, gave no aromatic smell whatever. All these plants withered and died down, though carefully watered, and, in each, there sprouted from the same stocks fresh stems, and a copious foliage, and produced, among others, common tanin, fully impregnated with the ordinary juices of that plant, and of a full green colour. I have repeated the same experiment with great care on lovage (Levisticum vulgare), mint, and caraways. All these plants thrive very well below, in the dark, but with a blanched foliage, which did not spread upwards, but lay flat on the ground; in all of them there was no resemblance of shape to the ordinary foliage of the plant; all of them died down when brought into daylight; and the stocks then produced the proper plants in their usual dress, and having all their distinguishing smells.

From such experiments, I thought myself entitled to say that the sun's rays not only produced the green facula of plants, but also the distinguishing juices, and particularly the essential oils. The improvements which have been made in chemical science since that time, have, I think, fully confirmed my conjecture." Black's Lett. i. 533. From the experiments of Mr Wedgwood, it appears that the gases do not become luminous, even at a higher temperature. He took an earthen-ware pipe of a zig-zag form, and placed it in a crucible filled up with sand. The ends of the pipe were left uncovered. To one end was attached a pair of bellows, and to the other a globular vessel with a lateral bent pipe, to let out air, but exclude the external light, and having a neck in which was inserted a circular plate of glass. The crucible, with the sand and the part of the pipe contained in it, was heated to redness. The eye was fixed in the neck of the vessel, which was then observed to be perfectly dark within. A stream of air was then directed through the tube from the bellows, but this air which passed through the red-hot tube, was not luminous. A small strip of gold was then fixed into the orifice of the tube opposite to the eye, and after two or three blasts, it became faintly red; which shows, that though the air was not luminous, it was equal in temperature to what is called red heat. Dr Darwin made an experiment of the same kind, and with a similar result. The heated air was altogether invisible; but when a bit of gold was introduced, it acquired a bright glow in a few seconds.

4. Light is also emitted by attrition and percussion. In the experiments which were made by Mr Wedgwood, on the attrition of bodies, he found that different coloured rays were emitted; sometimes it was a pure white light, as from the diamond; sometimes of a faint red, as from blackish gun flint; and sometimes of a deep red, as from unglazed white biscuit earthenware. But this effect produced by attrition, may perhaps be considered as the same with that of percussion. It is a familiar circumstance, that sparks of light are emitted, when two hard bodies, as, for instance, two quartz stones, are smartly struck against each other; and it appears that light is emitted, or sparks given out, when these bodies are treated by percussion or attrition, even under water; and they seem equally luminous in atmospheric air, oxygen gas, carbonic acid, or hydrogen gases. The emission of this light is accompanied with a peculiar smell, which varies in different bodies. The smell appears to be strongest where the friction is greatest; it has no dependence on the light produced by attrition, because it is often very strong when no light is emitted. Rock crystal, quartz, and other hard bodies, also emit this smell under water.

When flint and steel are struck smartly together, a spark is produced which will communicate fire to combustible substances. This spark has been found to be a particle of the iron which is driven off, and which catches fire as it passes through the air. It is to be considered as a case of combustion, and quite different from what happens when two stones are rubbed or struck against each other.

The matter driven off, when stones of quartz are struck against each other, consists of small, black, friable bodies, which leave a black stain when rubbed on paper, and, when examined with a magnifying glass, have the appearance of being fused. The light is produced, in these cases, by the substances struck together having been red hot. Some have supposed that they are a combination with oxygen; while others, who have probably examined them more accurately, assert that they are pieces of the quartz surrounded with a quantity of black powder; and having been raised to a very high temperature, set fire, in their passage through the air, to the combustible bodies that are floating in it.

CHAP. III. OF CALORIC.

The word heat in common language has two different meanings. When we say that we feel heat, it plainly must mean the sensation of heat excited in the body; but when we say that the fire or a stone is hot, it means that the power of exciting the sensation of heat in us, exists in the stone or fire. The one is the cause, and the other is to be considered as the effect. The heat of the stone or fire is therefore the cause of the sensation of heat in the body. Thus the word heat is generally employed to express both the sensation, and the cause of that sensation. To prevent any ambiguity in the use of these terms, the word caloric has been adopted in the new chemical nomenclature, to signify that state or condition of matter by which it excites in us the sensation of heat; and in this sense it is now to be employed.

The nature and effects of caloric or heat are highly interesting, as curious subjects of speculation; but the knowledge of them is of the utmost importance in the study of chemical phenomena, because no change takes place, no decomposition is effected, and no new compound is formed, without the agency of caloric.

SECT. I. Of the Nature and Properties of Caloric.

Two opinions have been maintained by philosophers concerning the nature of caloric. According to one opinion, it is supposed to be a peculiar subtle fluid, of a highly elastic and penetrating nature, which is universally diffused. According to the other opinion, it depends on a peculiar tremor or vibration which exists among the particles of heated bodies.

Among the first who seem to have adopted the latter opinion, was the celebrated Bacon. In his treatise, De forma calidi, which he proposed as a model of scientific investigation, he enumerates all the facts which were then known concerning heat; and after a cautious consideration of these facts, he concludes, that motion is heat. The facts on which he founded this opinion, were derived from some of the most familiar methods by which heat is produced in bodies. A blacksmith can make a rod of iron red hot by striking it smartly with a hammer; the heavy parts of machinery, by friction upon each other, and the axles of the wheels of carriages, when heavily loaded, sometimes take fire. A fire may be kindled by the friction of two pieces of dry wood; and the branches of trees strongly rubbed against each other by the violence of a storm, have set fire to thick forests. From the observation and consideration of these facts, this eminent philosopher was led to conclude, that heat is the effect of mechanical impulse. Since the time of Bacon, this theory has had many followers, and even at the present day it is maintained by some philosophers.

But the theory which supposes caloric or heat to be a distinct material substance, is now more generally adopted. It was first supposed by those who favoured this theory, that this peculiar matter was chiefly characterized by the great elasticity, or repulsive power, power, of the particles among each other; but besides this property, Dr Cleghorn supposed that it possessed another, namely, that while its particles have a strong repulsion for one another, they are attracted by other kinds of matter, with different degrees of force. But whatever opinion may be formed of the nature of caloric, after we have investigated its properties and effects, we shall probably find, that the phenomena which it exhibits will be easier understood, and more satisfactorily accounted for, on the supposition that it is a distinct substance.

1. The rays of light and caloric accompany each other as they proceed from the sun, or from burning bodies. It is therefore supposed that they move with the same degree of velocity; and if, this be the case, the velocity of the rays of caloric must be equal to 200,000 miles in a second. An experiment made by Mr Picet proves the great velocity of the rays of caloric. Two concave mirrors, the one of tin, and the other of gilt plaster, 18 inches in diameter, were placed at the distance of 69 feet from each other. A thermometer was placed in the focus of the latter, and a heated bullet of iron in the former. When the bullet was placed in the focus, a thick screen, which was a few inches from the face of the metallic mirror, was removed. The thermometer instantly rose, so that the time which caloric requires to move through the space of 69 feet, cannot be estimated. And indeed, if caloric, as is most probable, moves with the velocity of light, the time that it passes the distance of 69 feet, or even 69,000 feet, is by far too minute to be measured by our instruments; so that no conclusion whatever with regard to the measurement of its velocity, can be drawn from this experiment.

2. From the extreme velocity of caloric, and from its being equal to that of light, it is concluded that its particles are equally minute. From the accumulation of caloric in bodies, and particularly from one striking effect which this accumulation produces, namely, expansion, it was natural to suppose that bodies having received this addition, acquired an increase of weight. Experiments have therefore been made to ascertain this effect. Boerhaave weighed a mass of iron of 5 lb. weight, while it was red hot, and afterwards repeated the same experiment with other metals, but found no variation, either in the hot or cold bodies, but what he could account for from the errors of the balance. Mutchefbrook supposed that heat is ponderous, or produced by a ponderous substance; and Buffon thought he had proved, by his own experiments, that a body is heavier when it is hot than when it is cold; but when similar experiments were repeated, particularly by Dr Roebeck and Mr Whitehurst, with very nice and delicate balances, the bodies which were weighed appeared heavier cold, than when they were hot. This seems to be owing to the rarefaction of the air surrounding that scale in which the heated body is placed; the pressure of which is therefore less than that of the air over the other scale. From more recent experiments, and particularly one made by Dr Fordyce, it appears that bodies become heavier, but in a very small degree only, not by the increase, but by the diminution of temperature. When the whole quantity of 1700 grs. of water was frozen, it was found to be, when carefully weighed, 4/3ths of a grain heavier than it had been when fluid. At this time the thermometer applied to the vessel which contained the frozen water, stood at 10°; but when it was allowed to remain till the thermometer rose to 32°, it weighed only 4/3ths of a grain more than when fluid, and at the same temperature. But other experiments prove, that the addition of caloric to bodies produces no sensible change on ful. their weight. This seems to be placed beyond a doubt by the accurate experiments of Lavoisier, which were made with a view of ascertaining whether the weight of bodies is altered by heating or cooling them; but he found no difference.

In the year 1787, Count Rumford repeated the experiment of Dr Fordyce with the greatest care; and varying it in every possible way to avoid error, the results led him to conclude, that there is no sensible difference in the weight of bodies, either by the addition or abstraction of caloric.

3. Caloric agrees with light in another of its peculiar properties; this is its repulsive power, or the tendency of its particles to separate from each other. The particles of caloric, therefore, can never be supposed to cohere.

4. As the rays of light are reflected by polished surfaces, so it is found that the rays of caloric have the same property. The Swedish chemist Scheele discovered, that the angle of reflection of the rays of caloric is equal to the angle of incidence. This has been more fully established by Dr Herschel. Some very interesting experiments were made by Professor Picet of Geneva, which proved the same thing. These experiments were conducted in the following manner. Two concave mirrors of tin, of nine inches focus, were placed at the distance of twelve feet two inches from each other. In the focus of the one was placed the bulb of a thermometer, and in that of the other a ball of iron two inches in diameter, which was just heated to as not to be visible in the dark. In the space of five minutes the thermometer rose 22°. A similar effect was produced by substituting a lighted candle in place of the ball of iron. Supposing that both the light and heat acted in the last experiment, he interposed between the two mirrors a plate of glass, with the view of separating the rays of light from those of caloric. The rays of caloric were thus interrupted by the plate of glass, but the rays of light were not perceptibly diminished. In nine minutes the thermometer sunk 14°; and in seven minutes after the glass was removed, it rose about 12°. He therefore justly concluded, that the caloric reflected by the mirror, was the cause of the rise of the thermometer. He made another experiment, substituting boiling water in a glass vessel in place of the iron ball; and when the apparatus was adjusted, and a screen of silk which had been placed between the two mirrors removed, the thermometer rose 3°; namely, from 47° to 50°.

The experiments were varied by removing the tin mirrors to the distance of 90 inches from each other. The glass vessel, with boiling water, was placed in one focus, and a sensible thermometer in the other. In the middle space between the mirrors, there was suspended a common glass mirror, so that either side could be turned towards the glass vessel. When the polished side of this mirror was turned towards the glass vessel, the thermometer rose only 4/3ths of a degree; but when the other side, which was darkened, was... was turned towards the glass vessel, the thermometer rose 3°.5. And in another experiment performed in the same way, the thermometer rose 3° when the polished side of the mirror was turned to the glass vessel, and 9° when the other side was turned. These experiments show clearly, that the rays of caloric are reflected from polished surfaces, as well as the rays of light.

5. Transparent bodies have the power of refracting the rays of caloric, as well as those of light. They differ also in their refrangibility. So far as experiment goes, the most of the rays of caloric are less refrangible than the red rays of light. The experiments of Dr Herschel shows, that the rays of caloric, from hot or burning bodies, as hot iron, hot water, fires and candles, are refrangible, as well as the rays of caloric which are emitted by the sun. Whether all transparent bodies have the power of transmitting these rays, or what is the difference in the refractive power of these bodies, is not yet known.

6. The light which proceeds from the sun seems to be composed of three distinct substances. Scheele discovered, that a glass mirror held before the fire, reflected the rays of light, but not the rays of caloric; but when a metallic mirror was placed in the same situation, both heat and light were reflected. The mirror of glass became hot in a short time, but no change of temperature took place on the metallic mirror. This experiment shows that the glass mirror absorbed the rays of caloric, and reflected those of light; while the metallic mirror, suffering no change of temperature, reflected both. And if a plate of glass be held before a burning body, the rays of light are not sensibly interrupted, but the rays of caloric are intercepted; for no sensible heat is observed on the opposite side of the glass; but when the glass has reached a proper degree of temperature, the rays of caloric are transmitted with the same facility as those of light. And thus the rays of light and caloric may be separated.

But the curious experiments of Dr Herschel have clearly proved, that the invisible rays which are emitted by the sun, have the greatest heating power. In these experiments, the different coloured rays were thrown on the bulb of a very delicate thermometer, and their heating power was observed. The heating power of the violet, green, and red rays, was found to be to each other as the following numbers:

| Colour | Heating Power | |----------|---------------| | Violet | 16 | | Green | 22.4 | | Red | 55 |

The heating power of the most refrangible rays was least, and this power increases as the refrangibility diminishes. The red ray, therefore, has the greatest heating power, and the violet which is the most refrangible, the least. The illuminating power, it has been already observed, is greatest in the middle of the spectrum, and it diminishes towards both extremities; but the heating power, which is least at the violet end, increases from that to the red extremity: and when the thermometer was placed beyond the limit of the red ray, it rose still higher than in the red ray, which has the greatest heating power in the spectrum. The heating power of these invisible rays was greatest at the distance of ½ inch beyond the red ray, but it was sensible at the distance of 1½ inch.

Dr Herschel's experiments have been varied, and still farther confirmed by a set of experiments by Sir H. Englefield, the results of which were the following:

| Thermometer in the blue ray rose | in 3' from 55° to 56° | |----------------------------------|----------------------| | Thermometer in the green | in 3' from 54° to 58° | | Thermometer in the yellow | in 3' from 56° to 62° | | Thermometer in the full red | in 2½' from 56° to 72° | | Thermometer in confines of the red | in 2½' from 58° to 73½° | | Thermometer quite out of visible light | in 2½' from 61° to 79° |

The thermometer used in these experiments had its bulb blackened with Indian ink.

In the following experiments, three thermometers were employed; one had a naked ball, one was whitened, and the other was blackened. They were exposed to the sun's rays till they became stationary, when the thermometer with the

| Thermometer | Temperature | |-------------|-------------| | Naked ball | 58° | | Whitened ball | 58° | | Blackened ball | 63° |

In other experiments which were made afterwards, the results were,

| Thermometer | Temperature | |-------------|-------------| | Black thermom. rose | in 3' from 58° to 61° | | Whitened thermom. | in 3' from 55° to 58° | | Blackened thermom. | in 3' from 59° to 64° | | White thermom. | in 3' from 58° to 58½° | | Black thermom. | in 3' from 59° to 71° | | White thermom. | in 3' from 57½° to 60½° |

In this last experiment, where the thermometer was carried into the faint-red light, it sunk quickly; and rose again as quickly, when carried into the dark focus; but when carried into the dark on the other side of the red light, it sunk very rapidly, and did not appear to receive any heat at all.

Thus it appears, that the rays of caloric and the rays of light are different: for these experiments clearly show, that there are rays which produce heat, but give no light, and rays which give light, but produce no heat. It was formerly mentioned, that there is another set of rays which give neither light nor heat, but whose existence has been fully demonstrated by the remarkable effect which they produce in reducing the metallic salts and oxides. The light which is emitted from the sun then consists of three distinct sets of rays, which... which have been fully recognized by their different degrees of refrangibility and their different effects. The heating rays are in the smallest degree refrangible; the rays which have the greatest effect on the metallic oxides are the most refrangible, and the coloured rays are in an intermediate degree. The invisible rays beyond the red extremity of the spectrum, which are least refracted, have the greatest heating power; the invisible rays beyond the violet end, which are most refracted, have the greatest power in reducing the metallic salts or oxides, and the rays in the middle of the spectrum have the greatest illuminating power.

Sect. II. Of the Effects of Caloric.

The effects of so powerful an agent as heat must be very considerable; and these effects are found to be different in different bodies, or as it is more or less accumulated in these bodies. One general effect is, that the accumulation of heat enlarges, and its abstraction proportionally diminishes, the bulk of all bodies. When this accumulation is continued in some bodies, they change their condition from the state of solid to that of liquid; and, when the accumulation is still greater, liquid bodies are reduced to the form of vapour. These effects, certainly curious and interesting of themselves, are of the utmost importance in the phenomena of nature and in the processes of art; and the knowledge of the laws which have been deduced from these remarkable changes, enables us to explain many natural appearances, and to improve many of the arts of life.

1. Of Expansion.

1. One of the most general effects of heat, it has been observed, is the expansion of bodies; that is, when caloric is accumulated in any body, it is enlarged in bulk; and, when that quantity of caloric is abstracted, there is a corresponding contraction. Experience teaches us, that this effect of caloric is invariable and uniform in all the simpler kinds of matter. In some bodies, however, there are seeming exceptions to this general rule. In these bodies, when the temperature rises a little above, or falls a little below a certain point, they are subject to irregular variations of their bulk; but these irregularities are limited to a few bodies, and to certain states of temperature of these bodies; for when they are exposed to equal variations of heat, above or below the temperature at which these irregularities are observed, the general law of expansion uniformly holds. The expansion of all bodies by heat, therefore, and their corresponding contraction by the abstraction of caloric or by cold, may be considered as one of the most general facts in chemical science.

2. There are many familiar instances of the expansion of bodies by means of caloric, and this can be proved by very simple experiments. We shall mention an example of this effect on bodies in the solid, and the gaseous state.

(1.) If a rod of metal, as of iron, of an inch in diameter, and six or eight inches long, and the same body thickness through its whole length, be exactly fitted to pass through a hole in a plate of the same metal, and to be admitted lengthwise within the projecting edges of a ruler while it is cold; the same rod, when it is made red hot, will be found to have enlarged in bulk so much, that it will not fall between the projecting parts of the ruler, nor will it pass through the hole; but when it is cooled, or reduced to its former temperature, it again contracts, and returns precisely to its former dimensions.

(2.) As an example of a liquid, whose bulk is enlarged by the accumulation of caloric, fill the body of a glass vessel which has a long slender neck with spirit of wine. On the application of heat the liquid in the body of the vessel is expanded, and rises in the neck; and when the heat is abstracted, and the liquid returns to its former temperature, it is again contracted, and returns to its former bulk. This experiment is most conveniently performed by immersing the body of the vessel in hot water.

(3.) The expansion of a body in the gaseous state by the accumulation of caloric, is shewn by the following experiment. Let a quantity of air be confined in a bladder, but not in such quantity as that the bladder shall be fully distended with it. If the bladder is exposed to heat, the confined air expands, and the bladder is fully distended; but when it is again cooled, the air resumes its former bulk, and the bladder its original flaccid state.

Thus it appears, that all bodies expand by heat, uniformly in contrast by cold, and the quantity of this expansion is uniformly the same in the same bodies, when exposed to the same temperature. But this quantity is found to differ greatly in different kinds of matter, by the same increase or diminution of their heat. In solid bodies it is least, in liquids it is greater, but in elastic fluids greatest of all; and in different kinds of solids, liquids, and elastic fluids, this difference is very considerable. The ratio at which this expansion takes place in different bodies, can only be ascertained by experiment; and as the knowledge of this is a matter of great consequence in many of the arts, experiments have been made with this view by different philosophers (L).

The expansion of gaseous bodies, we have said, is but very greatest, that of liquids least, and that of solids least of all, by being exposed to the same degree of heat, which will appear from the following proportions.

\[ \begin{align*} 100 \text{ cubic inches of Atmospheric air,} & \\ \text{Water, Iron,} & \\ \text{from } 32^\circ \text{ to } 112^\circ & \\ \text{increased to} & \\ & \left\{ \begin{array}{l} 137.5 \text{ cubic inches.} \\ 104.5 \\ 100.1 \end{array} \right. \end{align*} \]

Vol. V. Part II.

See experiments on this subject by Mr Elliot, Phil. Trans. vol. xxxix. and by Mr Smeaton, ibid. vol. xlvi. 4. This expansive effect of heat will enable us to account for the cracking or breaking of vessels which are made of brittle substances, by its sudden application or abstraction. This is particularly the case with those substances which have little flexibility, as cast iron, glass, or earthenware; and accidents of this kind most frequently happen in vessels made of these materials. If, for instance, heat be suddenly applied to a glass vessel of considerable thickness, its external surface to which it is first applied expands more than the internal parts; the consequence must therefore be, that they are separated or drawn asunder, and the vessel is split or broken.

5. One of the best illustrations of this expansion by heat and contraction by cold on solid bodies, is in the application of iron hoops to carriage wheels. The hoop which has been intended for the wheel is made of rather smaller dimensions than exactly to fit it. It is then made red hot, and while it is thus expanded, it is applied to the wheel. It is suddenly cooled by throwing cold water upon it, when it contracts, and returning to its former dimensions, is strongly fastened on the wheel.

The unequal contraction at the same degree of temperature, which is observed among solids, liquids, and aeriform substances, also takes place among solids themselves. Thus, different metallic substances, at the same temperature, are found to expand and contract very unequally.

6. Advantage has been taken of this unequal contraction of metallic substances, to remedy those defects and imperfections of delicate instruments, which are occasioned by the contraction and expansion of the substances employed in their construction, when exposed to different temperatures. These inconveniences were most felt in instruments which were employed for the measurement of time, where great accuracy was required. The spring of a watch and the pendulum of a clock being subject to the same law of contraction and expansion by heat and cold, in these changes, necessarily caused variations, in proportion to the extent of the effect. But as different metals were observed to expand unequally by the same temperature, this was applied to the construction of those parts of the instrument on which the accuracy of its indications depends. The equable measurement of time, for instance, by a clock, depends on the length of the pendulum always continuing the same. If it is subject to variations in length by expansion or contraction, there will also be variations in the rate of its motions; for when the pendulum is lengthened by heat, the clock goes slower; and when it is shortened by cold, it goes faster. It becomes therefore an object of great importance, that these instruments should go at an equable rate in all temperatures; but this can only be effected by having the pendulum so constructed, that it shall neither lengthen by heat, nor contract by cold. This is done by constructing a pendulum in the following manner.

"From the point of expansion A (fig. 1. Plate CXLII.) a rod or thick wire, AB, of the less expandible metal, must hang down a certain length. At the lower end it must have a stud, or crook piece, BC, strongly fastened, and projecting a little to one side. On the projecting part, C, of this crook piece, must be erected a pillar, CD, of the more expandible metal. Calor. To the top of this pillar, another crook and projecting piece, DE, must be strongly fastened; and, from this last, must again hang down another rod or wire, EF, of the first metal, having the ball of the pendulum at its extremity. And now, if the height of the pillar CD be one-third of the length of the two rods taken together, the pendulum can neither be lengthened by heat nor shortened by cold. For by the expansion of the pillar, the pendulum is shortened, or the ball is raised nearer to the point of suspension, because the upper end D of the pillar is more raised by its expansion, than the lower end C is depressed by the expansion of AB; and, on the other hand, by its contraction, the pendulum is lengthened, or the ball is lowered: but, while this happens, the two rods, by their expansion or contraction, produce a contrary effect; and the quantity of expansion or contraction is the same in the rods that it is in the pillar, the greater length in the rods compensating for the greater expansibility of the pillar. The consequence therefore must be, that the length of the pendulum, that is, the distance between the point of suspension and the ball, cannot be varied by heat or cold. Accordingly, the clocks made for the use of astronomers, have pendulums constructed upon this principle, in which pillars of the more expandible metals are employed to counteract the expansion of the other parts of the pendulum-rod."

7. There are, however, some remarkable instances which are seeming exceptions to this general law of water's expansion. This is the case with those bodies which freeze from the liquid to the solid state; as for instance, creel water, when it assumes the solid form. Cloze vessels which are filled with water, are burst when it freezes. In an experiment made by Mr Boyle, a brass tube three inches in diameter, which was closed with a movable stopper, was filled with water; when the water was frozen, it raised a weight equal to 74 lb. with which the flopper was loaded. In an experiment by the Florentine academicians, a hollow brass globe, the diameter of whose cavity was an inch, was burst by freezing the water with which it was filled. Muffchenbeck has computed the force necessary to produce this effect, by estimating it equal to a pressure of 27,720 lbs. weight. But the most remarkable experiments to prove the expansive force of ice, were made with plugs by Major Williams in Canada, in the years 1784 and 1785. The iron plugs with which iron bombshells filled with water were closed up by driving them strongly with a hammer, were thrown out to a great distance by the force of the congelation of the water; and when the plugs were so firmly secured as to resist this force, the shell itself was burst.*

8. To the same expansive force in the congelation of water, the bursting of water-pipes, the splitting of trees and of rocks, is to be ascribed, which not unfrequently happens when the water which has been collected in their cavities or fissures, is frozen. The stones of the pavement are also raised and loosened by the freezing of the water in the earth in which they are imbedded, which is thus increased in bulk, and exerts its expansive force.

9. Attempts have been made to discover the cause of this astonishing effect. According to some, it is owing owing to the extrication of the air which water holds in combination in a dense, nonelastic state. When the water is freezing, part of the air afflues the elastic form, and separates from it; but when the surface of the water is covered with ice, no more air can make its escape. It is then confined, and forms those numerous cavities which are observed in ice. In consequence of these cavities, a mass of ice must be of greater bulk than the water previous to congelation, and cannot therefore be contained in the same space: But another cause, which is perhaps the most probable, has been assigned for this increase of bulk, and consequent expansive force. Liquids which on cooling become solid, and afflue a regular form, are always found to increase in bulk. Water, when it passes from the liquid to the solid state, has a strong tendency among its parts to arrange themselves in a determinate manner. They assume the form of prismatic crystals, which cross each other at angles of $60^\circ$ and $120^\circ$. In this way the increase of bulk, and the expansive force of water when it is consolidated, are accounted for.

10. Some metallic substances, particularly cast iron, are observed to enlarge in bulk, when they pass from the fluid to the solid state, in the same way as water. To this increase of bulk in cast iron when it cools, are owing the sharpness and distinctness of the lines in the ornamental figures on grates and furnaces which are made of this metal. The metal is introduced into the mould while it is fluid, or in a state of fusion, and increasing in bulk as it cools, the minute cavities of the mould are more accurately filled. This increase of bulk, as in the case of water when it becomes solid, is also ascribed to a determinate arrangement of the parts of the metal, or to crystallization.

11. On the expansive property of bodies depends the contraction of the thermometer, which is employed for the measurement of the relative temperatures of bodies. The invention of this instrument is generally ascribed to Sanctorio, an Italian physician, who lived about the beginning of the 17th century, although it is said by some, that thermometers were made by Drebel, a Dutch physician, and that they were common in Holland, and even in England, before Sanctorio was known in these countries.

In the thermometer of Sanctorio, the expansive power of air was employed to measure the temperature. His thermometer is constructed in the following manner. A tube of glass of 18 inches or two feet in length, open at one end, is blown into a ball at the other. When the ball is heated, the air within is expanded, and while the air is thus expanded, if the open end of the tube be immersed in a vessel filled with any coloured fluid; as the internal air cools, and is diminished in bulk, the liquid will rise in the tube by the pressure of the external air on the surface of the liquid in the vessel. A scale of equal degrees was then applied to the whole length of the tube, and the thermometer was constructed. To ascertain the heat of any body, as for instance the hand, it was applied to the ball, and if this temperature was greater than the medium in which the apparatus was placed, the internal air was rarefied, and consequently depressed the surface of the coloured liquid in the tube. The number of degrees of this depression was observed and compared in different experiments.

As, for instance, the difference of temperature of the Imperial body at different periods, to ascertain which, it is said, it was employed by the inventor. But the inaccuracy of this instrument will be obvious; when we consider that it depended, not only on the pressure, but also on the temperature of the atmosphere.

This defect in the air thermometer was remedied by improved Mr Boyle, and by the Florentine academicians, nearly at the same time; and they thought of employing other fluids. The first that was used was spirit of wine, which contracting and expanding more than water at the same temperature, and not being liable to be frozen by cold, was found to be much more convenient. Quicksilver was some time afterwards employed in the same way. The ball of the glass, and part of the tube, was filled with the fluid, when the open extremity of the tube was closed. When heat was applied to the ball, the fluid within expanded, and contracted by cold, without being influenced by the pressure of the atmosphere, as in Sanctorio's thermometer. But still this thermometer was very imperfect, for want of determinate points in the scale, by which different thermometers might be compared together. This was first pointed out by Sir Isaac Newton, and after various improvements, it was brought to its present state of perfection.

The method of constructing Fahrenheit's thermometer, which is now in general use in this country, is the following: A small ball is blown on the end of a glass tube, of a uniform width throughout. The ball and part of the tube are then to be filled with quicksilver which has been previously boiled to expel the air. The open end of the tube is then to be hermetically sealed (m). The next object is to construct the scale. It is found by experiment, that melting snow or freezing water is always at the same temperature. If, therefore, a thermometer be immersed in the one or the other, the quicksilver will always stand at the same point. It has been observed, too, that water boils under the same pressure of the atmosphere at the same temperature. A thermometer, therefore, immersed in boiling water, will uniformly stand at the same point. Here there are two fixed points from which a scale may be constructed, by dividing the intermediate space into equal parts, and carrying the same divisions as far above and below the two fixed points as may be wanted. Thus, thermometers constructed in this way may be compared together; for if they are accurately made, and placed in the same temperature, they will always point to the same degree on the scale.

The fluid that is now generally employed is quicksilver, and it is found to answer best, because its expansions are most equable. The freezing point of Fahrenheit's thermometer is marked $32^\circ$, and the reason of this is said to have been, that this artificer thought

(m) This is done by heating the end of the tube with the flame of a lamp, and by closing it while the glass is softened. thought that he had produced the greatest degree of cold by a mixture of snow and salt; and the point at which the thermometer then stood in this temperature, was marked zero. The boiling point in this thermometer is $212^\circ$, and the intermediate space between the boiling and freezing points is therefore divided into $180^\circ$. This is the thermometer that is commonly used in Britain.

There are three other thermometers employed in different countries of Europe, which differ from each other in the number of degrees between the freezing and boiling points.

Reaumur's thermometer is generally used in France before the revolution, and is still employed in different countries on the continent. The freezing point in this thermometer is marked zero, and the boiling point $82^\circ$. To convert the degrees of Reaumur's thermometer to those of Fahrenheit, the following is the formula:

$$\text{Ream} \times \frac{9}{4} + 32 = \text{Fahr.}$$

This gives the corresponding degrees on Fahrenheit's scale.

The thermometer of Celsius has the space between the freezing and boiling points divided into $100^\circ$. The boiling point is $100^\circ$, and the freezing point zero. This thermometer is used in Sweden. The thermometer centigrade, now used in France, has the scale divided in the same way. To convert the degrees of this thermometer into those of Fahrenheit; Cel. $\times \frac{9}{5} + 32 = \text{Fahr.}$

In Delisle's thermometer, which is used in Russia, the space between the boiling and freezing points is divided into $150^\circ$; but the degrees are reckoned downwards. The boiling point is marked zero, and the freezing point $150^\circ$. To reduce the degrees of this thermometer under the boiling point to those of Fahrenheit, Del. $\times \frac{6}{5} - 212 = \text{Fahr.}$ and above the boiling point, Del. $\times \frac{6}{5} + 212 = \text{Fahr.}$

Such then are the principles and mode of construction of the thermometer; an instrument which has been of the utmost importance in enabling us to discover many of the properties and effects of caloric, as by it only we can ascertain with accuracy the relative temperatures (N).

12. It has been an object of considerable interest and importance to ascertain the quantity and rate of expansion in bodies. Among solid bodies the quantity of expansion is very small, so that a nice apparatus is necessary to ascertain it. But it appears that the ratio of this expansion is equable, or nearly so. The results of experiments made by Mr Smeaton and some other philosophers upon this subject, will be seen in the following table.

| Temperature | Platina. | Antimony. | Steel. | Iron. | Cast Iron. | Bismuth. | Copper. | Cast Brass. | Brass Wire. | |-------------|----------|-----------|--------|-------|------------|----------|---------|------------|-------------| | 32° | 120,000 | 120,000 | 120,000| 120,000| 120,000 | 120,000 | 120,000 | 120,000 | 120,000 | | 212° | 120,104 | 120,130 | 120,147| 120,151| 123,428 | 121,500 | 122,571 | 120,204 | 120,000 | | White heat | | | | | | | | | |

| Temperature | Tin. | Lead. | Zinc. | Hammered Zinc. | Zinc 8. Tin 1. | Lead 2. Tin 1. | Brass 2. Zinc 1. | Pewter. | Copper 3. Tin 1. | |-------------|----------|----------|--------|----------------|----------------|----------------|------------------|---------|-----------------| | 32° | 120,000 | 120,000 | 120,000| 120,000 | 120,000 | 120,000 | 120,000 | 120,000 | 120,000 | | 212° | 120,298 | 120,344 | 120,355| 120,373 | 120,123 | 120,301 | 120,247 | 120,274 | 120,218 |

The rate of the expansion of glass, which is a matter of considerable importance, has been ascertained by M. de Luc, and is exhibited in the following table:

| Temperature | | |-------------|----------| | 32° | 100,000 | | 50 | 100,006 | | 70 | 100,014 | | 100 | 100,023 | | 120 | 100,033 | | 150 | 100,044 | | 167 | 100,056 | | 192 | 100,069 | | 212 | 100,083 |

13. The expansion of liquid bodies is greater than that of solids, but it is not equable with equal additions of temperature. It has been observed, that those liquids which are most readily brought to the state of vapour, or whose boiling point is lowest, expand most. With the same given temperature, the expansion of water is greater than that of mercury, and the expansion of alcohol is greater than that of water. The boiling point of water is lower than that of mercury, and the boiling point of alcohol is lower than that of water; from which it would appear, that the expansion of liquids is nearly in the inverse ratio of their boiling temperatures, and this expansion seems to increase with the temperature; that is, the nearer a liquid is to that point of temperature at which it boils, the greater is the degree of expansion by the addition of caloric; and the farther it is from the boiling temperature, the smaller is the increase of bulk by the addition of caloric. The following table exhibits the ratio of expansion of several liquids, as they have been ascertained by different philosophers.

---

(n) For measuring high degrees of temperature, the pyrometer of Wedgwood is employed, which will be described under the earth alumina. ### Table of the Rate of Expansion of different Liquids from 32° to 212°

| Temp. | Mercury | Linseed Oil | Sulphuric Acid | Nitric Acid | Water | Oil of Turpentine | Alcohol | |-------|---------|-------------|----------------|------------|-------|------------------|---------| | 32° | 100000 | 100000 | — | — | — | — | 100000 | | 40 | 100081 | — | 99752 | 99514 | — | — | 100539 | | 50 | 100183 | — | 100000 | 100000 | 100023| 100000 | 101105 | | 60 | 100304 | — | 100279 | 100486 | 100091| 100460 | 101688 | | 70 | 100406 | — | 100558 | 100990 | 100197| 100993 | 102281 | | 80 | 100508 | — | 100806 | 101530 | 100332| 101471 | 102890 | | 90 | 100610 | — | 101054 | 102088 | 100694| 101931 | 103517 | | 100 | 100712 | — | 101317 | 102620 | 100908| 102446 | 104162 | | 110 | 100813 | — | 101540 | 103196 | — | 102943 | — | | 120 | 100915 | — | 101834 | 103776 | 101404| 103421 | — | | 130 | 101017 | — | 102097 | 104352 | — | 103954 | — | | 140 | 101119 | — | 102320 | 105132 | — | 104573 | — | | 150 | 101220 | — | 102614 | — | 102017| — | — | | 160 | 101322 | — | 102893 | — | — | — | — | | 170 | 101424 | — | 103116 | — | — | — | — | | 180 | 101526 | — | 103339 | — | — | — | — | | 190 | 101628 | — | 103587 | — | 103617| — | — | | 200 | 101730 | — | 103911 | — | — | — | — | | 212 | 101835 | — | 107250 | — | 104577| — | — |

14. It has been proved by experiment that all gaseous bodies undergo the same expansion, with the same addition of heat. This has been ascertained by the ingenious experiments of Mr Dalton and M. Gay Lussac. The increase of bulk of some elastic fluids from 32° to 212°, as determined by the latter, will be seen in the following table:

- Atmospheric air 100 parts, increased 37.50 - Hydrogen gas 37.52 difference + 0.2 - Oxygen gas 37.48 difference - 0.02 - Azotic gas 37.49 difference - 0.01 *

In other experiments he found, that the expansion of the vapour of water and of ether corresponded with the expansion of other gases; and he remarks, that this property of the equable dilatation of the vapour of ether and water, and the gases, with the same degrees of temperature, depends not on the peculiar nature of the vapour and gases, but solely on their elastic state.

Mr Dalton's experiments show that the expansion of air is very nearly equable. It appears, however, that the rate of expansion diminishes as the temperature increases. The expansion from 55° to 132°, which includes 77°, was 167 parts; but the expansion from 132° to 212°, the next 77°, was only 18 parts, which was nine parts less than the first. The same philosopher observes, that the results of several experiments which he made upon hydrogen gas, oxygen gas, carbonic acid gas, and nitrous gas, correspond with those on atmospheric air, not only in the total expansion, but in the gradual diminution of it in ascending. Small differences were observed, but they never exceeded five or eight parts in the whole amount 325; and differences to this amount, he adds, will take place in common air, when not freed from aqueous vapour, which, he says, was the situation of his fictitious gases.

2. Of Fluidity.

1. We have now seen the effects of caloric in expanding bodies, when it is accumulated in them, state. When a solid body, as a piece of iron, is exposed to a high temperature, it is enlarged in bulk; and when the additional quantity of caloric with which it had combined is withdrawn, it returns to its former dimensions; but when still greater additions are made to most bodies, it is not merely a change of bulk that takes place, but a total change of their properties.

All matters exist, either in the state of solid, of liquid, or in the state of vapour. Most bodies, by the addition or the abstraction of caloric, are convertible from one of these states into another. Let us take water for an example. Ice is water in the solid state. When a mass of ice has received a proper quantity of caloric, it assumes the liquid state; and, when this liquid has received another portion of caloric, it is changed into the state of vapour. But if the vapour is deprived of a certain portion of caloric, it returns to the state of liquid or that of water; and when this water is deprived of another portion of caloric, it becomes solid, or is converted into ice.

Thus it appears, that a solid body may be converted into a liquid by means of caloric; and that a liquid may be converted into an elastic fluid by the same means. This seems to be a general law, to which there are but few exceptions. Some bodies may be converted into all the three states, as water; others, as spirit of wine, exist only in the fluid state, and there are some solid bodies which are not convertible into the state of liquid; but these exceptions are so few; that it has been supposed the same effect would follow, were... were these bodies exposed to a proper degree of temperature.

2. The temperature at which these changes are effected in invariably the same in the same body. Thus, a mass of ice is converted into the state of liquid or of water, when it is exposed to a temperature above $32^\circ$; and water, when it is raised to the temperature of $212^\circ$, affirms the state of vapour or of steam. But although this temperature is constant in the same bodies, it varies greatly in different bodies. Thus, spirit of wine and ether are converted into vapour at a very low temperature, while mercury and the fixed oils, to undergo this change, require a temperature far above that which is necessary for the conversion of water.

3. Some bodies are instantaneously converted from the solid to the liquid state. Thus ice, when the temperature is raised, passes immediately from the solid to the fluid state. Other bodies undergo a gradual change. They first become soft, as in the instance of melting wax, and pass through the different degrees of softness, till at last they become perfectly fluid.

4. It may perhaps now seem surprising, that phenomena which were so familiar should have existed so long without the true explanation of the changes which bodies undergo, in passing from the solid to the liquid or vaporous state, or from the fluid to the solid state. The want of instruments to measure accurately the relative degrees of temperature at which these changes take place, might perhaps be one cause of the unsuccessful investigations of philosophers on this subject. But even after the invention and improvement of the thermometer, it was long before the secret, and we may add, simple cause of these wonderful effects, was fully ascertained. It was reserved for the sagacity of Dr Black to give the true explanation. The era of the discovery of this law, of such universal application to the phenomena of nature, may be regarded as one of the most important in the history of chemical science. Dr Black was always distinguished for caution and precision in all his views; and as the progressive steps by which this celebrated philosopher was led to ascertain the true cause of fluidity afford us a fine example of simple and elegant investigation, we shall detail the experiments by which it was established in his own words.

5. After stating that the cause of fluidity which had been formerly given was unsatisfactory, and inconsistent with the phenomena, he observes that "these phenomena, when attentively considered, shew that fluidity is produced by heat, in a very different manner from that which was commonly imagined; a manner, however which, when understood, enables us to explain many particulars relating to heat or cold, which appeared, in the former view of the subject, quite perplexing and unaccountable.

"Fluidity was universally considered as produced by a small addition to the quantity of heat which a body contains, when it is once heated up to its melting point; and the returning of such body to a solid state, as depending on a very small diminution of the quantity of its heat, after it is cooled to the same degree; that a solid body, when it is changed to a fluid receives no greater addition to the heat within it than what is measured by the elevation of temperature indicated after fusion by the thermometer; and that, when the melted body is again made to congeal, by a diminution of its heat, it suffers no greater loss of heat than what is indicated also by the simple application to it of the same instrument.

"This was the universal opinion on this subject, so far as I know, when I began to read my lectures in the university of Glasgow, in the year 1757. But I soon found reason to object to it, as inconsistent with many remarkable facts, when attentively considered; and I endeavoured to shew, that these facts are convincing proofs that fluidity is produced by heat in a very different manner.

"I shall now describe the manner in which fluidity appeared to me to be produced by heat, and we shall then compare the former and my view of the subject with the phenomena.

"The opinion I formed from attentive observation of the facts and phenomena, is as follows: When ice, absorbed for example, or any other solid substance, is changing into a fluid by heat, I am of opinion that it receives a much greater quantity of heat than what is perceptible in it immediately after by the thermometer. A great quantity of heat enters into it, on this occasion, without making it apparently warmer, when tried by that instrument. This heat, however, must be thrown into it, in order to give it the form of a fluid; and I affirm, that this great addition of heat is the principal and most immediate cause of the fluidity induced.

"And, on the other hand, when we deprive such a fluid body of its fluidity again, by a diminution of its heat, coming a very great quantity of heat comes out of it, while it is assuming a solid form, the loss of which heat is not to be perceived by the common manner of using the thermometer. The apparent heat of the body, as measured by that instrument, is not diminished, or not in proportion to the loss of heat which the body actually gives out on this occasion; and it appears from a number of facts, that the state of solidity cannot be induced without the abstraction of this great quantity of heat. And this confirms the opinion, that this quantity of heat, absorbed, and as it were, concealed in the composition of fluids, is the necessary and immediate cause of their fluidity.

"To perceive the foundation of this opinion, and the inconsistency of the former with many obvious facts, we must consider, in the first place, the appearances observable in the melting of ice, and the freezing of water.

"If we attend to the manner in which ice and snow prove melt, when exposed to the air of a warm room, or the melting of ice when a thaw succeeds to frost, we can easily perceive, freezing that however cold they might be at the first, they are soon heated up to their melting point, or begin soon at their surface to be changed into water. And if the common opinion had been well founded, if the complete change of them into water required only the further addition of a very small quantity of heat, the mass, though of a considerable size, ought all to be melted in a very few minutes or seconds more, the heat continuing incessantly to be communicated from the air around. Were this really the case, the consequences of it would be dreadful in many cases; for, even as things are at present, the melting of great quantities of snow and ice occasions violent torrents, and... and great inundations in the cold countries, or in the rivers that come from them. But, were the ice and snow to melt as suddenly as they must necessarily do, were the former opinion of the action of heat in melting them well founded, the torrents and inundations would be incomparably more irresistible and dreadful. They would tear up and sweep away every thing, and that so suddenly, that mankind should have great difficulty to escape from their ravages. This sudden liquefaction does not actually happen; the masses of ice or snow melt with a very slow progress, and require a long time, especially if they be of a large size, such as are the collections of ice, and wreaths of snow, formed in some places during the winter. These, after they begin to melt, often require many weeks of warm weather, before they are totally dissolved into water. This remarkable slowness with which ice is melted, enables us to preserve it easily during the summer, in the structures called ice-houses. It begins to melt in these, as soon as it is put into them: but, as the building exposes only a small surface to the air, and has a very thick covering of thatch, and the access of the external air to the inside of it is prevented as much as possible, the heat penetrates the ice-house with a slow progress, and this, added to the slowness with which the ice itself is disposed to melt, protracts the total liquefaction of it so long, that some of it remains to the end of summer. In the same manner does snow continue on many mountains during the whole summer, in a melting state, but melting so slowly, that the whole of that season is not a sufficient time for its complete liquefaction.

"This remarkable slowness with which ice and snow melt, struck me as quite inconsistent with the common opinion of the modification of heat, in the liquefaction of bodies.

"And this very phenomenon is partly the foundation of the opinion I have proposed; for if we examine what happens, we may perceive that a great quantity of heat enters the melting ice, to form the water into which it is changed, and that the length of time necessary for the collection of so much heat from the surrounding bodies, is the reason of the slowness with which the ice is liquefied. If any person entertain doubts of the entrance and absorption of heat in the melting ice, he needs only to touch it; he will instantly feel that it rapidly draws heat from his warm hand. He may also examine the bodies that surround it, or are in contact with it, all of which he will find deprived by it of a great part of their heat; or if he suspend it by a thread, in the air of a warm room, he may perceive with his hand, or by a thermometer, a stream of cold air descending constantly from the ice; for the air in contact is deprived of a part of its heat, and thereby condensed and made heavier than the warmer air of the rest of the room; it therefore falls downwards, and its place round the ice is immediately supplied by some of the warmer air; but this, in its turn, is soon deprived of some heat, and prepared to descend in like manner; and thus there is a constant flow of warm air from around, to the sides of the ice, and a deficiency of the same in a cold state, from the lower part of the mass, during which operation the ice must necessarily receive a great quantity of heat.

"It is, therefore, evident that the melting ice receives heat very fast, but the only effect of this heat is to change it into water, which is not in the least sensibly warmer than the ice was before. A thermometer, applied to drops or small streams of water, immediately as it comes from the melting ice, will point not indifferently to the same degree as when it is applied to the ice itself, or, if there is any difference, it is too small to deserve notice. A great quantity, therefore, of the heat, or of the matter of heat, which enters into the melting ice, produces no other effect but to give it fluidity, without augmenting its sensible heat; it appears to be absorbed and concealed within the water, so as not to be discoverable by the application of a thermometer.

"In order to understand this absorption of heat into the melting ice, and concealment of it in the water, more distinctly, I made the following experiments.

"The plan of the first was, to take a mass of ice, and an equal quantity of water, in separate vessels, of the same size and shape, and as nearly as possible of the same heat, to suspend them in the air of a warm room, and, by observing with a thermometer the celerity with which the water is heated, or receives heat, to learn the celerity with which it enters the ice; and the time necessary for melting the ice being also attended to, to form an estimate, from these two data, of the quantity of heat which enters the ice during its liquefaction.

"In order to prepare for this experiment, I chose first two thin globular glasses, four inches diameter, and rimmed very nearly of the same weight: I poured into one of them five ounces of pure water, and then set it in a mixture of snow and salt, that the water might be frozen into a small mass of ice. As soon as frozen, it was carried into a large empty hall, in which the air was not disturbed or varied in its temperature during the progress of the experiment; and in this room the glass was supported, as it were, in mid air, by being let on a ring of strong wire, which had a tail affixed from the side of it five inches long, and the end of this tail was fixed in the most projecting part of a reading desk or pulpit: And in this situation the glass remained until the ice was completely melted.

"When the ice was thus placed, I set up the other globular glass precisely in the same situation, and at the distance of 18 inches to one side, and into this I poured five ounces of water, previously cooled, as near to the coldness of melting ice as possible, viz. to 33°, and suspended in it a very delicate thermometer, the bulb of which being in the centre of the water, and the tube being so placed, that without touching the thermometer, I could see the degree to which it pointed. I then began to observe the ascent of this thermometer, at proper intervals, in order to learn with what celerity the water received heat, stirring the water gently with the end of a feather about a minute before each observation. The heat of the air, examined at a little distance from the glasses, was 47° of Fahrenheit's scale.

"The thermometer assumed the temperature of the water in less than half a minute, after which, the rise of it was observed every five or ten minutes, during half an hour. At the end of that time, the water was grown warmer than at first, by 7° degrees; and the temperature... temperature of it had risen to the 40th degree of Fahrenheit's scale.

"The glass with the ice was, when first taken out of the freezing mixture, four or five degrees colder than melting snow, which I learned by applying the bulb of the thermometer to the bottom of it; but after some minutes, it had gained from the air those four or five degrees, and was just beginning to melt, which point of time was then noted, and the glass left undisturbed ten hours and a half. At the end of this time, I found only a very small and spongy mass of the ice remaining unmelted, in the centre of the upper surface of the water, but this also was totally melted in a few minutes more; and, introducing the bulb of the thermometer into the water, near the sides of the glass, I found the water there was warmed to the 40th degree of Fahrenheit. From this it appears, that when a considerable part of the ice was melted, and the quantity of water around it was increasing, the heat was not transmitted through this water to the remaining ice altogether so fast as it was received by the water; which is easily understood, if we consider that the distance between the remaining ice and the external surface of the vessel through which the heat entered, was gradually increasing, and that heat always requires time to pass through bodies, or to be communicated from one part of them to another.

"It appears, therefore from this experiment, that it was necessary that the glass with the ice receive heat from the air of the room during 21 half-hours, in order to melt the ice into water, and to heat that water to the 40th degree of Fahrenheit. During all this time, it was receiving the heat, or matter of heat, with the same celerity (very nearly) with which the water-glass received it during the single half-hour in the first part of the experiment. For, as the water received it with a celerity which was diminishing gradually during that half-hour, in consequence of the diminution of difference between its degrees of heat and that of air; so the glass with the ice also received heat with a diminishing celerity, which corresponded exactly with that of the water-glass, only that the progression of this diminution was much more slow, and corresponded to the whole time which the water surrounding the ice required to become warmed to the 40th degree of Fahrenheit. The whole quantity of heat, therefore, received by the ice-glass during the 21 half-hours, was 21 times the quantity received by the water-glass during the single half-hour. It was, therefore, a quantity of heat, which, had it been added to liquid water, would have made it warmer by $40 - 33 \times 21$, or $7 \times 21$, or 147 degrees. No part of this heat, however, appeared in the ice water, except 8 degrees; the remaining 139 or 140 degrees had been absorbed by the melting ice, and were concealed in the water into which it was changed.

"The communication of heat to the melting ice was easily perceived, during the whole time of its exposition, by feeling the stream of cold air which descended from the glass.

"This experiment was an analysis of the manner in which ice is melted by the heat of the air in ordinary circumstances.

"But another obvious method of melting ice occurring to me, in which it would be still more easy to perceive the absorption and concealment of heat, and this was the action of warm water.

"When hot and cold water are mixed together, the excess of heat contained in the hot water is equally peripherally distributed in an instant through the whole mixture, and raises the temperature of it according to the greatness of the excess of temperature, and the proportion which the hot water bore to the cold. If the quantities of hot and cold water are equal, the temperature is the middle degree between that of the hot and that of the cold. No part of the heat disappears on this occasion, so far as we can perceive, but the intensity of it only is diminished, by its being diffused through a larger quantity of matter. It was, therefore, obvious, that if a quantity of heat is absorbed, and disappears in the melting of ice, this would easily be perceived when the ice is melted with warm water.

"To make this experiment, I first froze a quantity of water in the neck of a broken retort, in order to have a mass of ice of an oblong form.

"At the same time I heated a quantity of water, nearly equal in weight to the ice, in a very thin globular glass, the mouth of which was sufficiently wide to take in the piece of ice. The water was heated by a small spirit of wine lamp applied to the bottom of the glass; it was also stirred with the end of a feather, and a thermometer hung in it.

"While the water was heating, the mass of ice was taken out of the mould in which it had been formed, and was exposed to the air of a temperate room, until it was perceived to be beginning to melt over the whole of its surface.

"I then put a woollen glove on my left hand, and taking hold of the ice, I wiped it quite dry with a linen towel, laid it in the scale of a balance on a piece of flannel, and hastily counterpoised it with sand in the opposite scale, that I might examine the weight of it afterwards; and I immediately plunged it into the hot water, and extinguished the lamp at the same time. The lamp being small, the heat of the water had been increasing very slowly, and had almost ceased to increase; and being examined immediately before I put the ice into it, the temperature was found to be just 190 degrees. The ice was all melted in a few seconds, and produced a mixture, the temperature of which was 53 degrees.

"The weight of the ice, when put into the hot water, was seven ounces three drams and a half. The weight of the glass, with the whole mixture in it, was 16 ounces, seven drams, and seven grains. The weight of the glass alone was nearly one ounce.

"In considering this experiment, we may overlook quantities less than half a dram, or 30 grains, and reckon the quantities of the different articles by the number of half-drams in each.

Thus the weight of the ice was 119 half-drams.

| Hot water | Mixture | Glass alone | |-----------|---------|-------------| | 135 | 254 | 16 |

"The melting of the ice was affected, not only by the heat of the hot water, but also by that of the glass. And, by other experiments, I learned that 16 parts of hot glass have more power in heating cold bodies," bodies, than eight parts of equally hot water; we may therefore substitute, in place of the 16 half-drams of warm glass, eight half-drams of warm water, which, added to the above quantity of warm water, make up 143 half-drams.

"The heat of this warm water was 190 degrees, that is 158 hotter than the ice; and if this heat had abated in the mixture only in consequence of the quantity and coldness of the ice, and if nothing had happened when the ice was put in, but merely a communication of this heat, and an equal diffusion of it through the mixture, the temperature of the mixture should have been 158, viz. the excess of heat in the warm water, multiplied by 143, the quantity of the warm matter, and divided by 262, the quantity of the whole, which gives 86.

"The mixture should have been 86 degrees warmer than melting ice; but it was found only 21 degrees warmer. Therefore a quantity of heat has disappeared, which, if it had remained in a sensible state, would have made the whole mixture and glass warmer by 65 degrees than they were actually found to be. But this quantity of heat would be sufficient for increasing, by 143 degrees, the heat of a quantity of water, equal in weight to the ice alone. It was, however, absorbed by the ice, without in the least increasing its sensible heat (o).

"The result of this experiment coincides sufficiently with that of the former; the difference is not greater than what may be expected in similar experiments, and might arise from the accident of the central parts of the mass of ice being colder than the surface, by one or two degrees.

"I have, in the same manner, put a lump of ice into an equal quantity of water, heated to the temperature 176, and the result was, that the fluid was no hotter than water just ready to freeze. Nay, if a little sea salt be added to the water, and it be heated only to 166 or 170, we shall produce a fluid sensibly colder than the ice was in the beginning, which has appeared a curious and puzzling thing to those unacquainted with the general fact.

"It is, therefore, proved that the phenomena which attend the melting of ice in different circumstances, are inconsistent with the common opinion which was established upon this subject, and that they support the one which I have propounded."

6. These experiments shew clearly and incontrovertibly, that the conversion of ice into water is owing to the absorption of a certain portion of caloric; and that the quantity of caloric absorbed is equal to what would have raised the temperature of a body which remained unchanged, as for instance water, 140°. These 140° therefore, have disappeared, (for no increase of temperature is indicated by the thermometer), have been absorbed by the ice, and are necessary to reduce it to the liquid state. This portion of caloric which had thus disappeared, Dr Black called latent heat, because in this state of combination its presence was not indicated by the thermometer. By others this has been called the caloric of fluidity.

7. In the progress of these investigations, experiments were made on other substances, which clearly shewed that their fluidity is owing to the same cause. Other bodies experimented were made on wax, tallow, spermaceti, sulphur, alum, nitre, and some of the metals, the same thing. The late ingenious Dr Irvine, the pupil of Dr Black, who essentially assisted him in many of his experiments, ascertained the quantity of caloric which was necessary for the fluidity of the following substances; which, when compared with that of ice, will shew that the quantity of the caloric of fluidity increases with the temperature at which the body is converted into the liquid state.

| Substance | Temperature | |--------------|-------------| | Spermaceti | 148° | | Bees wax | 175° | | Tin | 500° |

8. Dr Black farther observes on the operation of this cause, that there is reason to think, that not only the fluidity of bodies, but even the softness of such as are rendered pliable by heat, depends on a quantity of the same heat combined with them, in the form of latent heat; and that the malleability and ductility of metals depend upon the same cause. For, while they are extended under the hammer, they become warm, and in some cases very hot; but at the same time they become rigid, and are no longer malleable. They have lost their toughness and softness. To restore this, they must be annealed or made hot in the fire, and allowed to cool. Thus, they recover their malleability, of which they may be again deprived by a second hammering.

9. The temperature at which solid bodies begin to be converted into the liquid state, is always constant; and till they are raised to this temperature, no change takes place. Water in the solid state, or ice, always remains unchanged till it is placed in a temperature constant above 32°. This point, which is called the melting point, is constant in the same body, but is very different in different bodies. The following table exhibits the melting point of a number of solid bodies.

| Substance | Temperature | |--------------|-------------| | Lead | 594° | | Bismuth | 576° | | Tin | 442° | | Sulphur | 212° | | Wax | 142° | | Spermaceti | 133° | | Phosphorus | 100° | | Tallow | 92° | | Oil of anise | 50° | | Olive oil | 36° | | Ice | 32° | | Milk | 30° | | Vinegar | 28° | | Blood | 25° | | Oil of bergamot | 23° | | Wine | 20° |

(o) "These two experiments, and the reasoning which accompanies them, were read by me in the Philosophical Club, or Society of Professors and others in the University of Glasgow, in the year 1762." Oil of turpentine, 14° Sulphuric acid, 36 Mercury, 39 Liquid ammonia, 46 Ether, 46 Nitric acid, 66

3. Of Vapour.

1. If, after a mass of ice is converted into water or the liquid state, the application of heat be continued to that water, it undergoes other changes, and exhibits very different phenomena. If the temperature be raised sufficiently high, the water becomes agitated with an intense motion, and if it is supplied with a sufficient quantity of caloric, the whole of the water is diffused. This agitation of the water, it is well known, is called, in common language, boiling.

2. As solid bodies which are capable of being converted into the liquid state by an increase of caloric, have a certain determinate temperature, so many of those bodies which are capable of assuming the form of an elastic fluid, undergo this change, only when they are raised to a certain temperature. Some liquids, indeed, assume the form of vapour at all temperatures, which is the case with water, with volatile oils, spirits of wine and ether. This change is called spontaneous evaporation; but there are others which remain fixed and unchanged till the temperature is raised to that point at which they boil. Boiling is nothing else but the rapid conversion of the liquid into vapour. The heat being applied to the bottom of the vessel which contains the liquid, the particles at the bottom first assume the elastic form; and as they rise through the liquid, cause it to be violently agitated. This boiling point, under the same pressure, is always the same in the same liquid; and however strong the heat that may be applied, or however long it may be continued, the temperature of the liquid, in open vessels, never rises above this point. The boiling point of water, for instance, is 212°, and it never becomes hotter; on the contrary, if the same heat be continued, the whole is diffused, and converted into vapour.

Table showing the boiling point of several liquids.

| Substance | Temperature | |--------------------|-------------| | Ether | 98° | | Ammonia | 140° | | Alcohol | 176° | | Water | 212° | | Muriat of lime | 230° | | Nitric acid | 248° | | Phosphorus | 554° | | Oil of turpentine | 560° | | Sulphur | 570° | | Sulphuric acid | 590° | | Linseed oil | 600° | | Mercury | 660° |

3. But this boiling point is found to vary considerably, and this variation depends on the pressure on the surface of the liquid. When the pressure is diminished, liquids boil at a lower temperature; but when this pressure is increased, they require a higher temperature to produce boiling. Water boils at a low temperature on the top of a high mountain, or in the vacuum of an air pump, where the pressure is greatly diminished; but when it is confined in close vessels, as in Papin's digester, the temperature may be raised to 300° or 400° without boiling.

4. The general law which was discovered by Dr. Law Black, of the conversion of solids into liquids, was also extended by him to account for the change of liquids into elastic fluids. This was proved by the following experiments.

"Experiment 1.—I procured (says Dr. Black) some cylindrical tin-plate vessels, about four or five inches diameter, and flat-bottomed. Putting a small quantity of water into them, of the temperature 50°, I set them upon a red-hot kitchen table, that is, a cast-iron plate, having a furnace of burning fuel below it, taking care that the fire should be pretty regular. After four minutes, the water began sensibly to boil, and in twenty minutes more, it was all boiled off. This experiment was made 4th October 1762.

"Experiment 2.—Two flat-bottomed vessels, like the former, were set on the iron plate, with eight ounces of water in each, of the temperature 50°. They both began to boil at the end of three minutes and a half, and in eighteen minutes more, all the water was boiled off.

"Experiment 3.—The same vessels were again supplied with 12 ounces of water in each, also of the temperature 50°. Both began to boil at the end of six minutes and a quarter, and the water was all boiled off from the one in 28 minutes, and from the other in something more than 29.

"I reasoned from these experiments in the following manner: The vessels in the first experiment received 162 degrees of heat in four minutes, or 40½ degrees each minute. If we, therefore, suppose that the heat enters equally fast during the whole ebullition, we must suppose that 810 degrees of heat have been absorbed by the water, and are contained in its vapour. Since this vapour is no hotter than boiling water, the heat is contained in it in a latent state, if we consider it only as the cause of warmth. Its presence is sufficiently indicated, however, by the vaporous or expansive form which the water has now acquired.

"In experiment second, the heat absorbed, and rendered latent, seems to be about 820.

"In the third experiment, the heat absorbed seems to be somewhat less, viz., about 750. The time of rising to the boiling heat, in experiment third, has nearly the same proportion to that in experiment first, that the quantities of water have. The deficiency, therefore, in the heat absorbed, has been probably only apparent, and arising from irregularity in the fire. Upon the whole, the conformity of their results with my conjecture was sufficient to confirm me in my opinion of its justice. In the course of further experiments made both by myself and by some friends, and in which the utmost care was taken to procure a perfect uniformity in the heat applied, the absorption was found extremely regular, and amounted at an average to about 810 degrees.

"There are other cases where this absorption appears in a much more singular manner. I put into a very proof strong phial, about as much water as half filled it, sealed and corked it close. The phial was placed in a sand-pot, which was gradually heated, until the sand and phial were several degrees above the common vapour..." porific point of water. I was curious to know what would be the effect of suddenly removing the pressure of the air, which is well known to prevent water from boiling. The water boiled a very short while, but the ebullition gradually decreased, till it was almost insensible. Here the formation of more vapour was opposed by a very strong pressure, proceeding from the quantity of vapour already accumulated, and confined in the upper part of the phial, and from the increased elasticity of this vapour, by the increase of its heat. When matters were in this state, I drew out the cork. Now, according to the common opinion of the formation of vapour by heat, it was to be expected that the whole of the water would suddenly assume the vaporous form, because it was all heated above the vaporific point. But I was beginning by this time to expect a different event, because I could not see whence the heat was to be supplied, which the water must contain when in the form of vapour. Accordingly, it happened as I expected; a portion only of the water was converted into vapour, which rushed out of the phial with a considerable explosion, carrying along with it some drops of water. But, what was most interesting to me in this experiment was, that the heat of what remained was reduced in an instant to the ordinary boiling point. Here, therefore, it was evident, that all that excess of heat which the water had contained above the boiling point, was spent in converting only a portion of it into vapour. This is plainly inconsistent with the common opinion; that nothing more is necessary for water's existing in a vaporous form under the pressure of the atmosphere, than its being raised to a certain temperature. The experiment makes it more probable, that if the influx of heat could at that instant have been prevented, it would have remained in the form of water, although raised, in a very sensible degree, above the boiling temperature.

"I was anxious to learn whether the heat which disappeared in this experiment was in an accurate proportion to the quantity of vapour produced, or the quantity of water that had disappeared. But the drops of water that were hurled along by the explosion without being converted into vapour, made it impossible for me to ascertain this with any tolerable accuracy, although I repeated the experiment several times.

"This experiment was afterwards made by my friend Mr Watt, in a very satisfactory manner. His studies for the improvement of his steam-engine, gave him a great interest in every thing relating to the production of steam. He put three inches of water into a small copper digester, and, screwing on the lid, he left the safety-valve open. He then set it on a clear fire of coals, and after it began to boil and produce steam, he allowed it to remain on the fire half an hour, with the valve open. Then, taking it off the fire, he found that an inch of water had boiled away. In the next place, he restored that inch of water, foreworded on the lid, and set it on the fire; and as soon as it began to boil, he shut the safety-valve, and allowed it to remain on the fire half an hour as before. The temperature of the whole was many degrees above the boiling point. He took it off the fire, and set it upon ashes, and opened the valve a very small matter. The steam rushed out with great violence, making a shrieking noise for about two minutes. When this had ceased, he shut the valve, and allowed all to cool. When he opened it, he found that an inch of water was consumed.

"It is reasonable to conclude from this experiment, that nearly as much heat was expended during the blowing of the steam pipe, as had been formerly expended in boiling off the inch of water. For, before opening the valve, the temperature was many degrees above the boiling point, and all this disappeared with the vapour. The same inference may be drawn from the time that the digester continued upon the fire with the valve shut, because we may conclude that the heat was entering nearly at the same rate during the whole time. It is plain, however, that the experiment is not of such a kind as to admit of nice calculation; but it is abundantly sufficient to show that a prodigious quantity of heat had escaped along with the particles of vapour produced from an inch of water. The water that remained could not be hotter than the boiling point, nor could the vessel be hotter, otherwise it would have heated the water, and converted it into vapour. The heat, therefore, did not escape along with the vapour, but in it, probably united to every particle, as one of the ingredients of its vaporous constitution. And as ice, united with a certain quantity of heat, is water; so water, united with another quantity of heat, is steam or vapour."

The following experiment made by the late Dr Irvine of Glasgow, at the desire of Dr Black, and recorded by the latter, is a still farther confirmation of the general fact of the conversion of liquids into elastic fluids, by combining with caloric.

"Five measures (each containing 4 lb. 5 oz. and 6 dr. avoirdupois) of water, of the temperature 52°, were poured into a small still in the laboratory. The fire had been kindled about 40 minutes before, and was come to a clear and uniform state. The still was set into the furnace, and, in an hour and 20 minutes, the first drop came from the worm; and in three hours and 45 minutes more, three measures of water were distilled, and the experiment ended. The refrigeratory contained 38 measures of water, of which the temperature, at the beginning of the experiment, was 52°. When one measure had come over, the water in the refrigeratory was at 76°. When two had come over, it was at 100°; and when three had come over, it was at 123°.

"In this experiment, the heat, which emerged from three measures of water, had raised the temperature of the water in the refrigeratory from 52° to 123°, or 71°. Now 3 is to 38 as 71 to 899°, and the heat would have raised the three measures 899° degrees in its temperature, if this had been possible without converting it into vapour. The heat of the vapour from which this emerged, was 212°, or 160° more than that of the water. Taking this from 899°, there remains 739°, the heat contained in the vapour in a latent state.

"But this must be sensibly less than the truth. During the experiment, the vessels were very warm—the head of the still as hot as boiling water, and the refrigeratory gradually rising from 52°, which was within a degree or two of the temperature of the air of the laboratory, to 123°. A very considerable portion of the latent heat of the steam must have been carried off by..." the air in contact with a considerable surface, some of which was exceedingly hot. A great deal must also have been carried off in the steam which arose very sensibly from the water in the refrigeratory, towards the end of the experiment. Mr Irvine also observed, that, during the distillation, the temperature of the water which ran from the worm was about 11° hotter than the water in the refrigeratory. The steam, therefore, at a medium, was not 16° hotter than the water which ran from the worm, but 12°, its mean temperature being about 87°. This consideration alone will make the latent heat of the steam not less than 774 degrees, without any allowance for waste.

"Some comparison may also be made between the heat expended in the production of the steam, and that which emerges during its condensation. The time which elapsed during the raising of the temperature of the five measures of water from 52° to 212°, that is 160°, was one hour and 20 minutes, or 80', and 22' elapsed during the boiling off of three measures. Therefore, since 80 is to 225 as 160 to 450, as much heat was expended as would have raised the five measures 450° in temperature. This would have raised three measures 750° above the boiling heat already produced. This gives 750 for the latent heat of the steam, besides what was unavoidably lost by communication to the ambient air, and what was expended in heating the vessels."

In some experiments made by Mr Watt, who also assisted Dr Black in conducting these invaluable experiments, it appears that the latent heat of steam is from 900° to 950°. This he discovered by observing the quantity of caloric which was absorbed by the water in its conversion into steam or vapour, and the quantity given out, when that vapour returned to the state of water.

The value of the latent heat of steam, estimated by the experiments of M. Lavoisier, amounts to more than 1000°.

Thus is this general law established, that all liquids are converted into elastic fluids, by combining with a certain portion of caloric. This portion of caloric is not indicated by the thermometer, and is therefore said to be latent heat, as we already mentioned; but when the elastic fluid returns to the liquid state, it again becomes sensible, and precisely the same quantity is extricated which was absorbed.

It is an object of some importance to ascertain the elastic force of vapour, and the ratio of the increase of this elasticity by increase of temperature. The elasticity of vapour which is formed by a liquid boiling in the open air, is equal to the pressure of the atmosphere; and it has been ascertained by the experiments of Mr Dalton and of M. Gay-Lussac, that the elasticity of all elastic fluids is the same with that of the vapour of water, with the same increase or diminution of temperature from the boiling point. If then, the boiling point of any liquid be known, the elasticity of its vapour may be discovered, by comparing it with the elasticity of the steam of water, the same number of degrees above or below the boiling point. In the following table, constructed by Mr Dalton from his experiments and calculations, the elasticity of the vapour of water is given for every temperature from 40° to 325°. To find the elasticity of the vapour of ether at 40° below its boiling point, which is 98°, take 40° from 98°, there remains 58, and the same number from 212°, the boiling point of water, there remains 172°, opposite to which number in the table is 12.73, which is the elasticity of the steam of water at 172°, and also the elasticity of the vapour of ether at 58°.

**Table of the Force of Vapour from Water in every temperature, from that of Congelation of Mercury, or 40° below Zero of Fahrenheit, to 325°**

| Temp. | Force of Vap. in inches of Mercury | Temp. | Force of Vap. in inches of Mercury | Temp. | Force of Vap. in inches of Mercury | |-------|-----------------------------------|-------|-----------------------------------|-------|-----------------------------------| | -40° | .013 | 41° | .273 | 88 | .128 | | -30° | .020 | 42° | .283 | 89 | .132 | | -20° | .030 | 43° | .294 | 90 | .136 | | -10° | .040 | 44° | .305 | 91 | .140 | | | | 45° | .316 | 92 | .144 | | 0 | .064 | 46° | .328 | 93 | .148 | | 1 | .066 | 47° | .339 | 94 | .153 | | 2 | .068 | 48° | .351 | 95 | .158 | | 3 | .071 | 49° | .363 | 96 | .163 | | 4 | .074 | 50° | .375 | 97 | .168 | | 5 | .076 | 51° | .388 | 98 | .174 | | 6 | .079 | 52° | .401 | 99 | .180 | | 7 | .082 | 53° | .415 | 100 | .186 | | 8 | .085 | 54° | .429 | 101 | .192 | | 9 | .087 | 55° | .443 | 102 | .198 | | 10 | .090 | 56° | .458 | 103 | .204 | | 11 | .093 | 57° | .474 | 104 | .211 | | 12 | .096 | 58° | .490 | 105 | .218 | | 13 | .100 | 59° | .507 | 106 | .225 | | 14 | .104 | 60° | .524 | 107 | .232 | | 15 | .108 | 61° | .542 | 108 | .239 | | 16 | .112 | 62° | .560 | 109 | .246 | | 17 | .116 | 63° | .578 | 110 | .253 | | 18 | .120 | 64° | .597 | 111 | .260 | | 19 | .124 | 65° | .616 | 112 | .268 | | 20 | .129 | 66° | .635 | 113 | .276 | | 21 | .134 | 67° | .655 | 114 | .284 | | 22 | .139 | 68° | .676 | 115 | .292 | | 23 | .144 | 69° | .698 | 116 | .300 | | 24 | .150 | 70° | .721 | 117 | .308 | | 25 | .156 | 71° | .745 | 118 | .316 | | 26 | .162 | 72° | .770 | 119 | .325 | | 27 | .168 | 73° | .796 | 120 | .333 | | 28 | .174 | 74° | .823 | 121 | .342 | | 29 | .180 | 75° | .851 | 122 | .350 | | 30 | .186 | 76° | .880 | 123 | .359 | | 31 | .193 | 77° | .910 | 124 | .369 | | 32 | .200 | 78° | .940 | 125 | .379 | | 33 | .207 | 79° | .971 | 126 | .389 | | 34 | .214 | 80° | 1.00 | 127 | .400 | | 35 | .221 | 81° | 1.04 | 128 | .411 | | 36 | .229 | 82° | 1.07 | 129 | .422 | | 37 | .237 | 83° | 1.10 | 130 | .434 | | 38 | .245 | 84° | 1.14 | 131 | .447 | | 39 | .254 | 85° | 1.17 | 132 | .460 | | 40 | .263 | 86° | 1.21 | 133 | .473 | | | | 87° | 1.24 | 134 | .486 | ### Table Continued

| Temp. | Force of Vap. in inches of Mercury | |-------|-----------------------------------| | 132° | 5.00 | | 136° | 5.14 | | 137° | 5.29 | | 138° | 5.44 | | 139° | 5.59 | | 140° | 5.74 | | 141° | 5.90 | | 142° | 6.05 | | 143° | 6.21 | | 144° | 6.37 | | 145° | 6.53 | | 146° | 6.70 | | 147° | 6.87 | | 148° | 7.03 | | 149° | 7.23 | | 150° | 7.42 | | 151° | 7.61 | | 152° | 7.81 | | 153° | 8.01 | | 154° | 8.20 | | 155° | 8.40 | | 156° | 8.60 | | 157° | 8.81 | | 158° | 9.02 | | 159° | 9.24 | | 160° | 9.46 | | 161° | 9.68 | | 162° | 9.91 | | 163° | 10.15 | | 164° | 10.41 | | 165° | 10.68 | | 166° | 10.96 | | 167° | 11.25 | | 168° | 11.54 | | 169° | 11.83 | | 170° | 12.13 | | 171° | 12.43 | | 172° | 12.73 | | 173° | 13.02 | | 174° | 13.32 | | 175° | 13.62 | | 176° | 13.92 | | 177° | 14.22 | | 178° | 14.52 | | 179° | 14.83 | | 180° | 15.13 | | 181° | 15.43 | | 182° | 15.86 | | 183° | 16.23 | | 184° | 16.61 | | 185° | 17.00 | | 186° | 17.40 | | 187° | 17.80 | | 188° | 18.20 | | 189° | 18.60 |

### Sect. III. Of the Motion of Caloric.

1. It appears that the motion of caloric, when it is not interrupted, is equal in velocity to that of light. When therefore it is emitted by one body, it moves on equal to with this velocity till it is received by another. This has been called the transmission or radiation of heat. This radiation or separation of heat from any body, arises from the force with which it is connected with that body being diminished; that is, when a greater quantity of caloric is accumulated in that body than it can contain. The experiments of Dr Herschel shew, that refracted heat is radiated, refracted and reflected, in the same manner as light. The reflection of caloric has also been proved by the experiments of Mr Picquet formerly mentioned. But caloric is communicated from one body to another by direct contact of these bodies.

2. It is well known that a cold body brought into contact with a warm body, in a certain time becomes heated; but this does not take place instantaneously; and the time necessary for one body to receive caloric from another, or for the different parts of the same body to acquire the same temperature, varies according to the nature and state of these bodies. This is called the conducting power of bodies.

3. But as different bodies have different degrees of affinity for caloric, or contain different proportions of it, it must be separated or absorbed with greater or less facility. The motion of caloric therefore, in these different circumstances, will be considerably varied in its celerity. This may be proved by direct experiment. If one extremity of two substances of different properties, as, for instance, a rod of iron and another of wood, be put into the fire, and the hand brought into contact with the other extremity, the rod of iron will soon be heated too much for the hand to bear, while the rod of wood will not have its temperature greatly increased. This shews, that there is a smaller quantity of caloric carried through the wood; or, in other words, the iron is a better conductor than the wood.

4. All solid bodies are conductors of caloric, but they possess this power in very different degrees. Those bodies which conduct caloric with facility are called good conductors, but those through which it passes. passes with difficulty, or very slowly, are said to be bad conductors. The motion of caloric from one body to another, or through the same body, is not altogether in proportion to their densities, as might be supposed from the instance of the communication of caloric through wood and iron, just mentioned. Caloric is conducted very slowly through a more porous substance, such as a mat of cork, of wool, of feathers, or furs. It is on account of the slowness with which heat is conducted in these substances, that some of them are employed in the colder seasons of the year, or in cold countries, as materials for clothing. The heat being slowly conducted through such substances, they prevent the heat of the body from being dissipated, or cut off the communication between the warm body and the cold air. And thus we see a wise provision of nature, in furnishing all animals which are inhabitants of the colder regions of the earth, with a thick covering of fur or feathers. According to the experiments of Count Rumford, the conducting power of fur, feathers, silk, and wool, diminishes in proportion to the fineness of their texture.

Metallic substances are the best conductors of caloric; but among the metals it would appear that there is considerable variety in their conducting power, and this is not in proportion to their density, as appears from the experiments of Dr Ingenhouz on the following metals, which are set down in the order of their conducting power:

*Journal de conducing power*.

Phys. 1739.

Silver, Gold, Copper, Tin, Platina, Iron, Steel, Lead.

A set of experiments were made on the conducting power of different woods, by Professor Mayer of Erlangen, of which the following are the results, comparing the conducting power of water:

| Wood | Conducting Power | |------------|------------------| | Water | 10.0 | | Ebony | 21.7 | | Crab apple | 27.4 | | Ash | 38.0 | | Beech | 32.1 | | Hornbean | 32.3 | | Plum tree | 32.5 | | Female oak | 32.6 | | Pear tree | 33.2 | | Birch | 34.1 | | Oak | 36.3 | | Pitch pine | 37.5 | | Alder | 38.4 | | Pine | 38.6 | | Fir | 38.9 | | Lime tree | 39.0 |

The experiments of Guyton show that the conducting power of charcoal is to that of fine sand nearly in the proportion of 2 to 3.

5. Fluid bodies, as well as solids, are conductors of caloric; but they are found to conduct it so slowly, that it was at first supposed they did not possess this fluid power at all, that is, that the caloric was not conducted from particle to particle in fluids, similar to what happens in solid bodies. This opinion seemed to be supported by the nature and constitution of fluids, in which the particles have free motion among each other, so that when one set of particles acquire an additional quantity of caloric, their specific gravity is necessarily diminished, and they naturally change place with those other particles of the fluid which have been less heated and are consequently heavier. These different appearances which were observed in the heating of fluids led Count Rumford, who made many ingenious experiments on this subject, to conclude, that fluids are heated, or conduct caloric, in a different manner from solids. In a spirit of wine-thermometer, which was placed in a window to cool, he observed the fluid in the tube in rapid motion. There were two currents going in different directions, the one ascending, and the other descending. The descending current occupied the sides of the tube, and the ascending current the middle. The currents were owing to the change in the specific gravity of the particles, which being heated became lighter, and rose to the top; the heavier particles at the same time descended. The particles which ascended having reached the sides or top of the tube, gave out their caloric, became specifically heavier, and again fell to the bottom. The motion of the currents was considerably increased by the application of a cold body to the sides of the tube. The count also repeated the experiment with linseed oil, and also with water, in the latter of which he dissolved potash, to bring its specific gravity to that of amber, small pieces of which he introduced, to observe the currents more distinctly. These experiments were followed with the same result. When the temperature was increased or diminished, the currents were let in motion, and only ceased when the temperature became equal to the surrounding bodies.

In prosecuting this subject, the count made other experiments, to ascertain how far the heating or cooling of fluids is affected by a difference of fluidity. The thermometer which he employed in these experiments, has a copper bulb and a glass tube, and it was filled with linseed oil. This was placed in the centre of a brass cylinder, and the space between the sides of the cylinder and the thermometer, was 0.25175. The thermometer being secured, the cylinder was filled with 2276 grs. of pure water, and held in melting snow, till the thermometer fell to 32°. It was then immersed in boiling water, and the thermometer rose from 32° to 200° in 597". The caloric which raised the thermometer must have been communicated to it through the water in the cylinder. The experiment was then varied, by boiling 192 grs. of starch in the water in the cylinder. The thermometer now required 1109" to rise from 32° to 200°. The same experiment was repeated by mixing 192 grs. cider down with the same quantity of water, and also with a quantity of stewed apples. The result of these experiments will be seen in the following tables.

*Ramf.*

*Elay 7.* Time the Caloric was in passing into the Thermometer.

| Temperature | Through the Water and Starch | Through the Water and Eider down | Through stewed Apples | Through pure Water | |-------------|-----------------------------|---------------------------------|----------------------|-------------------| | Therm. rose from 32° to 100°, in seconds | 1109 | 949 | 1096½ | 597 | | Therm. rose 80°, viz from 30° to 110°, in seconds | 341 | 269 | 335 | 172 |

Time the Caloric was in passing out of the Thermometer.

| Temperature | Through the Water and Starch | Through the Water and Eider down | Through stewed Apples | Through pure Water | |-------------|-----------------------------|---------------------------------|----------------------|-------------------| | Therm. fell from 300° to 40°, in seconds | 1548 | 1541 | 1749½ | 1032 | | Therm. fell 80°, viz from 160° to 80°, in seconds | 468 | 460 | 520 | 277 |

The substances which were added to the water in these experiments, by diminishing its fluidity, had the effect of retarding the internal motions or currents by which the caloric is conducted through fluids. Thus, when starch was mixed with water, it required nearly double the time to raise the thermometer to the same degree, as with pure water. From these and from other experiments, Count Rumford concluded, that fluid bodies are heated in a different manner from solids; that caloric is not communicated through fluids from particle to particle, but that all the particles individually come in contact with the heating body, and this is supposed to be the cause of the currents which are observed during the heating of the fluids.

5. Fluids no doubt acquire great part of their temperature in this manner; but it has been clearly proved by the experiments of others, that they are also conductors of caloric exactly the same way as solid bodies, but in an inferior degree. This has been established in the most satisfactory manner by the experiments of Dr Thomson * and Mr Murray †, which were published in Nicholson's Journal; and also by another set of experiments by Mr Dalton, which were published in the Manchester Memoirs ‡. By these experiments it is demonstrated, that fluids conduct caloric from the surface downwards; which could not be the case, were it only communicated through them by the ascending currents of particles, in the way Count Rumford supposed; but they are worse conductors of caloric than solids; that is, it passes through them much more slowly.

Sect. IV. Of the Distribution of Caloric.

If a number of bodies be exposed to different temperatures, and then be all placed in the same temperature, or brought into contact with each other, they acquire in a certain time the same temperature. Thus, if one body be raised to the temperature of 200°, another to that of 100°, and a third to All bodies the temperature of 60°; and if these three bodies be placed in the temperature of 80°, they all indicate, in some temperature, the same temperature. The bodies which were at the temperature of 200° and 100° are reduced medium, to 80°, and the temperature of the body at 60° rises to the same. This is called the distribution, or the equilibrium of caloric. To whatever degree bodies are heated or cooled, they all acquire in time the temperature of the surrounding medium, as it is indicated by the thermometer. It may therefore be received as a general law, that all bodies which communicate freely with each other, and are subject to no inequality of external action, acquire the same temperature.

1. Bodies are deprived of caloric, not only by radiation from their surfaces, but it is also conducted by Radiation those bodies with which the heated body comes in contact, and this depends greatly on the nature of the surrounding cold body. The experiments of Professor Piclet and Count Rumford, however, shew, that radiation is not the only cause. By those of the former it appeared, that hot bodies suspended in the vacuum of an air pump, cooled more slowly than in the open air; and by those of the latter, the cooling was still slower in the Torricellian vacuum.

2. The time requisite for the heating or cooling of bodies depends much on their conducting power. A Good conductor which is a good conductor of caloric cools ductors much more rapidly than a bad conductor. Mercury cools water heated to the same temperature cool in very rapidly, different times; the mercury cools more than twice as fast as the water in the same circumstances. The time of the cooling of fluids has been considered as nearly in the inverse ratio of their conducting power.

3. This equal distribution of caloric was attempted to be explained by Boerhaave, Mulchenbroeck, and Distribu- others, by supposing that there is an equal quantity of caloric in every equal measure of space, however that space might be filled up with different bodies, and that the bodies floated, as it were in this caloric. From this equal distribution of caloric in space, they concluded that there was an equal quantity of caloric in all bodies, because, whatever was the density or different circumstances of bodies, they always indicated the same temperature to the thermometer. A cubic foot of gold, and a cubic foot of air, according to this theory, contained the same quantity of caloric.

Professor Piclet gave another explanation of this phenomenon. He supposed that the accumulation of caloric in a body increased the repulsive force between its particles, by the diminution of the distance between them. By the action of this repulsive force, the particles are driven off in all directions. This repulsion continues to act till it is opposed by a new force, which is the force of repulsion between the particles of caloric separated from another body; and, till these two forces acquire the same intensity, the particles of caloric continue to separate from the hotter body. When the two forces are balanced, the bodies are of the same temperature. Thus, if two bodies of different temperatures... temperatures are brought into contact with each other, the repulsive force of the particles of caloric in the hotter body is the greatest, and therefore the particles tend to separate from each other; but the repulsion between the particles of the colder body being less, they come nearer each other. The caloric from the hotter body continues to separate, and to enter the colder body, till the two forces exactly balance each other, and then the temperature is the same *. But this theory, with all its simplicity and ingenuity, being unsatisfactory in accounting for the equilibrium of temperature, has been given up, even by its author.

4. Another theory has been proposed by M. Prevost, professor of philosophy at Geneva. "Accustomed" says he, "for a long time, to consider this subject in a different view from what had been formerly taken of it, I endeavoured to draw the attention of naturalists to this investigation, in a memoir on the equilibrium of caloric †, and in my researches on heat ‡. In these works, I believe it was first proposed to substitute a moveable equilibrium in place of the immovable equilibrium, the existence of which had been generally admitted.

"On this hypothesis, it is equally easy and satisfactory to account for the reflection of cold, as for that of heat. I consider it indeed a characteristic of its truth; for these two facts being of the same kind, the theory that will account for the one, is applicable to the other. Before I proceed to state in a few words the principle of this theory, I may premise, that I had the satisfaction of seeing it adopted by M. Picquet and others, who are well qualified to judge of it.

"Caloric is a dilute, agitated fluid: each particle of free caloric moves with immense velocity; one particle moves in one direction, and another particle moves in another, so that a heated body gives out caloric rays in all directions; and these particles are so far separated from each other, that two or more currents may cross each other, as is the case with light, without mutual disturbance in their course. Conceiving this to be the constitution of caloric, if we suppose two contiguous spaces in which it abounds, there will be continual changes between these spaces. If in the two spaces caloric abounds equally, the exchanges will be equal; there will be an equilibrium. If one of the spaces contain more caloric than the other, the exchanges will be unequal. The coolest will receive more particles of caloric than it gives out, and after a sufficient time, the continual repetition of these changes will restore the equilibrium §.

"From these principles may be deduced all the laws of the increase and diminution of temperature. Let us suppose a body placed in a medium hotter than itself, and that this medium has a constant temperature. We may consider the caloric of the medium as composed of two parts, the one equal to that of the body, and the other equal to the difference of the two. With regard to the first, the exchanges are equal; between the body and the medium there is an equilibrium. The excess of the heat of the medium may then only be considered; and relatively to this excess the body is absolutely cold. Let us suppose that in one second the body receives \( \frac{1}{2} \) of this caloric; at the end of the first second the excess will be no more than \( \frac{1}{2} \): the \( \frac{1}{2} \) of this new excess will pass into the body during the next second; and the excess will be reduced to \( \frac{1}{2} \) of \( \frac{1}{2} \); and in pursuing this, at the end of the third second, the excess will be \( \frac{1}{2} \), and so on; so that, conformably to the observed law, the times increase in arithmetical progression, and the differences decrease in geometrical progression. In the same way may be easily deduced the law of the cooling of a body placed in a medium colder than itself. And thus the true theory of heat, founded on facts totally different from those by which Richmann established this law, necessarily leads us to it *."

Sect. V. Of the Quantity of Caloric in Bodies.

We have now treated, in the former sections, of the effects of caloric, of its motion, and of its diffusion in bodies; we are next to consider the quantity of caloric which these bodies contain. This subject has occupied the attention and speculations of many philosophers. In these speculations, two objects were kept in view, the one to ascertain the whole quantity of caloric which a body contains, and the other the quantity of caloric necessary to raise different bodies to the same temperature. This last is usually called specific caloric.

1. Of Specific Caloric.

1. If one lb. of water at the temperature of 100° is mixed with another lb. of water at the temperature of 50°, they will very soon acquire the same temperature, which will be the mean of the two temperatures. The pound of water at 100° will give out 25°, and the pound of water at 50° will receive 25°, which brings both to the temperature of 75°.

2. But if we take one pound of water at 100°, and one pound of mercury at 50°, the temperature, after mixing the water and the mercury, will not be 75°, the medium temperature in the former case. On the contrary, when the mixture is made, the temperature will be found to be 88°. The water, therefore, has lost only 12°, and the mercury has gained 38°. If this experiment be reversed, and one pound of water at 50° be mixed with a pound of mercury at 100°, the temperature of the mixture will be found to be only 62°; so that in this case the mercury has given out 38°, and the water has received only 12°. In this experiment, therefore, it appears clearly, that different quantities of caloric are necessary to increase or diminish the temperature of different bodies; for, the quantity of caloric which raises water 12°, raises mercury no less than 38°. This quantity of caloric which bodies require to raise them to the same temperature, is called specific caloric.

3. "It was formerly a common supposition," says Dr Black, "that the quantities of caloric required to increase the heat of different bodies by the same number of degrees, were directly in proportion to the quantity of matter in each; and, therefore, when the bodies were of equal size, the quantities of caloric were in proportion to their density. But very soon after I began to think of this subject, in the year 1760, I perceived that this opinion was a mistake, and that the quantities of heat which different kinds of matter must receive, to reduce them to an equilibrium with one another, or to raise their temperature by an equal num- ber of degrees, are not in proportion to the quantity of matter in each, but in proportions widely different to this, and for which no general principle or reason can yet be assigned.* This difference was first pointed out by Dr Black, which he states in the above observations, and he distinguished it by the term capacity of bodies for heat. Dr Black's method, which is given by Professor Robison, is the following.

"Dr Black estimated the capacities, by mixing the two bodies in equal masses, but of different temperatures; and then stated their capacities as inversely proportional to the changes of temperature of each by the mixture. Thus, a pound of gold, of the temperature 150°, being suddenly mixed with a pound of water, of the temperature 50°, raises it to 55° nearly; therefore the capacity of gold is to that of an equal weight of water as 5 to 95, or as 1 to 19; for the gold loses 95°, and the water gains 5°.

"It will be most convenient to compare all bodies with water, and to express the capacity of water by unity, or to call it 1. Let the quantity of the water be W, and its temperature w. Let the quantity of the other body be B, and its temperature b. Let the temperature of the mixture be m. The capacity of B is

\[ \frac{W \times m - w}{B \times b - m} \]

or when the water has been the hotter of the two, the capacity of B is

\[ \frac{W \times w - m}{B \times m - b} \]

In other words, multiply the weight of the water by its change of temperature. Do the same for the other substance. Divide the first product by the second. The quotient is the capacity of the other substance, that of water being accounted 1 + (p)."

4. This subject was still farther prosecuted by other philosophers, particularly by Dr Irvine of Glasgow, Dr Crawford of London, and Professor Wilcke of Stockholm.

The method which was employed by Dr Crawford was similar to that of Dr Black. Two substances, which were of different temperatures, were uniformly mixed; the change of temperature produced on each was observed, and this was considered as inversely proportional to its specific caloric.

Mr Wilcke has ascertained the specific caloric of many metals, by a set of very ingenious experiments, which were conducted in the following manner. The metal which was the subject of the experiment, was first accurately weighed. The quantity employed was generally a pound. It was then suspended by a thread, plunged into a vessel of tin plate filled with boiling water, and allowed to remain till it reached a certain temperature indicated by the thermometer. A quantity of water at the temperature of 32°, exactly equal in weight to the metal, was put into another vessel of tin plate. The metal was then immersed in this vessel, and suspended in it so as to be kept free from the sides and bottom. The temperature, at the moment when the metal and water were reduced to the same, was observed. The specific caloric of the metal was then deduced by calculation from the change of temperature. He first calculated what the temperature would have been, if a quantity of water of equal weight with the metal, and of the same temperature, had been added to the ice-cold water. The following is the process.

Let M be a quantity of water at the temperature C, m another quantity at the temperature c, and let their common temperature after mixture be x; according to a rule demonstrated long ago by Richman,

\[ x = \frac{MC + mc}{M + m} \]

In the present case the quantities of water are equal, therefore M and m are each = 1; C, the temperature of the ice-cold water, = 32; therefore

\[ \frac{MC + mc}{M + m} = \frac{32 + c}{2} \]

Now c is the temperature of the metal. Therefore if 32 be added to the temperature of the metal, and the whole be divided by 2, the quotient will express the temperature of the mixture, if an equal weight of water with the metal, and of the same temperature with it, had been added to the ice-cold water instead of the metal.

He then calculated what the temperature of the mixture would have been, if, instead of the metal, a quantity of water of the same temperature with it, and equal to the metal in bulk, had been added to the ice-cold water. As the weights of the ice-cold water and the metal are equal, their volumes are inversely as their specific gravities. Therefore the volume of ice-cold water is to a quantity of hot water equal in volume to the metal, as the specific gravity of the metal to that of the water. Let M = volume of cold water, m = volume of hot water, g = specific gravity of the metal, 1 = specific gravity of water; then

\[ m : M :: 1 : g; \text{ hence } m = \frac{M}{g} = (M \text{ being made } = 1) \]

Substituting this value of m in the formula,

\[ \frac{1}{g} \]

(p) "These experiments require the most scrupulous attention to many circumstances which may affect the result. 1. The mixture must be made in a very extended surface, that it may quickly attain the medium temperature. 2. The stuff which is poured into the other should have the temperature of the room, that no change may happen in the pouring it out of its containing vessel. 3. The effect of the vessel in which the mixture is made must be considered. 4. Less chance of error will be incurred when the substances are of equal bulk. 5. The change of temperature of the mixture, during a few successive moments, must be observed, in order to obtain the real temperature at the beginning. 6. No substances should be mixed which produce any change of temperature by their chemical action, or which change their temperature, if mixed when of the same temperature. 7. Each substance must be compared in a variety of temperatures, lest the ratio of the capacities should be different in different temperatures.

"When all these circumstances have been duly attended to, we obtain the measure of the capacities of different substances for heat," Black's Lect. vol. i. p. 506. \[ \frac{MC + mc}{M + m} = x, \text{ in which } M = 1 \text{ and } C = 32, x \text{ will be } \frac{32x + c}{g + 1}. \text{ Therefore if the specific gravity of the metal be multiplied by } 32, \text{ and the temperature of the metal be added, and the sum be divided by the specific gravity of the metal } + 1, \text{ the quotient will express the temperature to which the ice-cold water would be raised by adding to it a volume of water equal to that of the metal, and of the same temperature with it.} \]

He then calculated how much water at the temperature of the metal it would take to raise the ice-cold water the same number of degrees which the metal had raised it. Let the temperature to which the metal had raised the ice-cold water be \(N\), if in the formula

\[ \frac{MC + mc}{M + m} = x, x \text{ be made } N, M = 1, C = 32, m \text{ will be } \frac{N - 32}{c - N}. \text{ Therefore if from the temperature to which the ice-cold water was raised by the metal } 32 \text{ be subtracted, and if from the temperature of the metal be subtracted the temperature to which it raised the water, and the first remainder be divided by the last, the quotient will express the quantity of water of the temperature of the metal which would have raised the ice-cold water the same number of degrees that the metal did.} \]

Now \(\frac{N - 32}{c - N}\) expresses the specific caloric of the metal, that of water being \(= 1\). For (neglecting the small difference occasioned by the difference of temperature) the weight and volume of the ice-cold water are to the weight and volume of the hot water as \(1\) to \(\frac{N - 32}{c - N}\), and the number of particles of water in each are in the same proportion. But the metal is equal in weight to the ice-cold water, it must therefore contain as many particles of matter; therefore the quantity of matter in the metal must be to that in the hot water as \(1\) to \(\frac{N - 32}{c - N}\). But they gave out the same quantity of caloric; which, being divided equally among their particles, gives to each particle a quantity of caloric inversely as the bulk of the metal and water; that is, the specific caloric of the water is to that of the metal as \(1\) to \(\frac{N - 32}{c - N}\) (r).

It will now be proper to give a specimen or two of his experiments, and the calculations founded on them, as above described.

### Gold. Specific Gravity 19.040.

| Number of experiments | Temperature of the metal | Temper. to which it would have been raised by a quantity of water equal in weight and heat to the metal | Temper. to which it would have been raised by water equal in bulk and temperature to the metal | Denominator of the fraction \(\frac{N - 32}{c - N}\) | |-----------------------|-------------------------|-------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------|--------------------------------------------------| | 1 | 163.4° | 38.3° | 97.7° | 38.555° | | | | | | 19.857 | | 2 | 144.5 | 37.4 | 88.25 | 37.58 | | | | | | 19.833 | | 3 | 127.4 | 36.5 | 79.7 | 36.68 | | | | | | 20.500 | | 4 | 118.4 | 36.05 | 75.2 | 36.15 | | | | | | 20.333 | | 5 | 103.1 | 35.6 | 65.75 | 35.42 | | | | | | 18.750 | | 6 | 95 | 34.45 | 63.5 | 35.06 | | | | | | 19.000 |

Mean 19.712

---

(r) All these formulas have been altered to make them correspond with Fahrenheit's thermometer. They are a good deal simpler when the experiments are made with Celsius's thermometer, as Mr Wilcke did. In it the freezing point is zero; and consequently instead of 32 in the formula, 0 is always substituted. ### Chemistry

#### Lead. Specific Gravity II. 456.

| Number of experiments | Temperature of the metal | Temper. to which the metal raised by water at 32° | Temper. to which the water would have been raised by water equal in weight and heat to the metal | Temper. to which the water would have been raised by water equal in bulk and temperature to the metal | Denominator of the fraction | |-----------------------|--------------------------|-------------------------------------------------|-------------------------------------------------|-------------------------------------------------|-----------------------------| | 1 | 186.8 | 38.3 | 109.4 | 44.425 | 23.571 | | 2 | 181.40 | 37.85 | 106.7 | 43.473 | 24.538 | | 3 | 165.2 | 37.4 | 98.6 | 42.692 | 23.666 | | 4 | 163.4 | 37.4 | 97.7 | 42.548 | 23.333 | | 5 | 136.4 | 36.5 | 84.2 | 42.344 | 22.200 | | 6 | 131 | 36.05 | 81.5 | 39.947 | 24.700 | | 7 | 126.5 | 36.05 | 79.25 | 39.585 | 22.333 | | 8 | 107.6 | 35.15 | 69.8 | 38.339 | 23.000 | | 9 | 94.1 | 34.7 | 63.05 | 36.985 | 22.000 |

Mean 23.515

It is needless to add, that the last column marks the denominator of the specific caloric of the metal; the numerator being always 1, and the specific caloric of water being 1. Thus the specific caloric of gold is $\frac{1}{19.712}$. In exactly the same manner, and by taking a mean of a number of experiments at different temperatures, did Mr Wilcke ascertain the specific caloric of a number of other bodies.*

5. With the same view, to ascertain the specific caloric of bodies, a simple and ingenious apparatus was contrived by Lavoisier and La Place. This instrument is called a calorimeter, or measure of heat. Its principles and construction are the following:

"If, after having cooled, says Lavoisier, any body to the freezing point, it be exposed in an atmosphere of 88.25°, the body will gradually become heated, from the surface inwards, till at last it acquire the same temperature with the surrounding air. But, if a piece of ice be placed in the same situation, the circumstances are quite different; it does not approach in the smallest degree towards the temperature of the circumambient air, but remains constantly at 32°, or the temperature of melting ice, till the last portion of ice be completely melted.

"This phenomenon is readily explained; as, to melt ice, or reduce it to water, it requires to be combined with a certain portion of caloric, the whole caloric attracted from the surrounding bodies is arrested or fixed at the surface or external layer of ice which it is employed to dissolve, and combines with it to form water; the next quantity of caloric combines with the second layer to dissolve it into water, and so on successively till the whole ice be dissolved, or converted into water, by combination with caloric; the very last atom still remaining at its former temperature, because the caloric could never penetrate so far, while any intermediate ice remained to melt, or to combine with.

"Upon these principles, if we conceive a hollow sphere of ice at the temperature of 32° placed in an atmosphere of 54.5°, and containing a substance at any degree of temperature above freezing; it follows, That the heat of the external atmosphere cannot penetrate into the internal hollow of the sphere of ice; and, That the heat of the body which is placed in the hollow of the sphere cannot penetrate outwards beyond it, but will be stopped at the internal surface, being continually employed to melt successive layers of ice, until the temperature of the body be reduced to 32° by having all its superabundant caloric above that temperature carried off to melt the ice. If the whole water, formed within the sphere of ice during the reduction of the temperature of the included body to 32°, be carefully collected, the weight of the water will be exactly proportioned to the quantity of caloric lost by the body, in passing from its original temperature to that of melting ice; for it is evident that a double quantity of caloric would have melted twice the quantity of ice. Hence the quantity of ice melted is a very exact measure of the proportional quantity of caloric employed to produce that effect, and consequently of the quantity lost by the only substance that could possibly have supplied it.

"I have made this supposition, of what would take place in a hollow sphere of ice, for the purpose of more readily explaining the method used in this species of experiment, which was first conceived by M. de la..." Place. It would be difficult to procure such spheres of ice, and inconvenient to make use of them when got; but, by means of the following apparatus, we have remedied that defect.

"The calorimeter is represented in Plate CXLII., fig. 2. The capacity or cavity is divided into three parts, which, for better distinction, I shall name the interior, middle, and external cavities. The interior cavity \( f f f f \), into which the substances submitted to experiment are put, is composed of a grating or cage of iron wire, supported by several iron bars; its opening or mouth \( LM \), is covered by the lid \( HG \), fig. 3, which is composed of the same materials. The middle cavity \( b b b b \), fig. 2, contains the ice which surrounds the interior cavity, and which is intended to be melted by the caloric of the substances employed in the experiment. The ice is supported by the grate \( mm \) at the bottom of the cavity, under which is placed the sieve \( nn \).

"In proportion as the ice contained in the middle cavity is melted, by the caloric disengaged from the body placed in the interior cavity, the water runs through the grate and sieve, and falls through the conical funnel \( c c d \), fig. 2, and the tube \( xy \), into a receiver. This water may be retained or let out at pleasure, by means of the stop-cock \( u \). The external cavity \( aa a a \), fig. 2, is filled with ice, to prevent any effect upon the ice in the middle cavity from the heat of the surrounding air, and the water produced from it is carried off through the pipe \( ST \), which flows by means of the stop-cock \( r \). The whole machine is covered by a lid made of tin, and painted with oil colour, to prevent rust.

"When this machine is employed, the middle cavity \( b b b b \), fig. 2, and the lid \( GH \), fig. 3, of the interior cavity, the external cavity \( aa a a \), fig. 2, and the lid which covers the whole, are all filled with pounded ice, well rammed, so that no void spaces remain, and the ice of the middle cavity is allowed to drain. The machine is then opened, and the substance submitted to experiment being placed in the interior cavity, it is instantly closed. After waiting till the included body is completely cooled to the freezing point, and the whole melted ice has drained from the middle cavity, the water collected in the receiver is accurately weighed. The weight of the water produced during the experiment is an exact measure of the caloric disengaged during the cooling of the included body, as this substance is evidently in a similar situation with the one formerly mentioned as included in a hollow sphere of ice. The whole caloric disengaged from the included body is stopped by the ice in the middle cavity, and that ice is preserved from being affected by any other heat by means of the ice contained in the cover and in the external cavity. Experiments of this kind generally last from 15 to 20 hours, but they are sometimes accelerated by covering up the substance in the interior cavity with well drained ice, which hastens its cooling.

"It is absolutely requisite that there be no communication between the external and middle cavities of the calorimeter, otherwise the ice melted by the influence of the surrounding air, in the external cavity, would mix with the water produced from the ice of the middle cavity, which would no longer be a measure of the caloric lost by the substance submitted to experiment.

"When the temperature of the atmosphere is only a few degrees above the freezing point, its heat can hardly reach the middle cavity, being arrested by the ice of the cover, and of the external cavity; but, if the temperature of the air be under the degree of freezing, it might cool the ice contained in the middle cavity, by causing the ice in the external cavity to fall, in the first place, below 32°. It is therefore essential that this experiment be carried on in a temperature somewhat above freezing: Hence, in time of frost, the calorimeter must be kept in an apartment carefully heated. It is likewise necessary that the ice employed be not under 32°, for which purpose it must be pounded, and spread out thin for some time, in a place where the temperature is higher.

6. Tables of the specific caloric of bodies have been given by Dr Crawford, Mr Kirwan, Bergman, Gadolin, and Meyer. The following are the results of their investigations.

**Table of the Specific Caloric of various Bodies, that of Water being = 1.000.**

| Bodies | Specific Gravity | Specific Caloric | |-------------------------|------------------|-----------------| | **I. Gases.** | | | | Hydrogen gas | 0.000094 | 21.4000 | | Oxygen gas | 0.0034 | 47.4900 | | Common air | 0.00122 | 1.7900 | | Carbonic acid gas | 0.00183 | 1.0459 | | Steam | | 1.5500 | | Azotic gas | 0.00120 | 0.7036 | | **II. Liquids.** | | | | Water | 1.0000 | 1.0000 | | Carbonate of ammonia | | 1.851 | | Arterial blood | | 1.030 | | Cows milk | 1.0324 | 0.9999 | | Sulphuret of ammonia | 0.818 | 0.9940 | | Venous blood | | 0.8028 | | Solution of brown sugar | | 0.8600 | | Nitric acid | | 0.844 | | Sulphate of magnesia | | 0.844 | | Water | | 0.832 | | Common salt | | 0.8167 | | Water | | 0.779 | | Tartar | | 0.765 | | Water 237.3 | | 0.759 | | Solution of potash | 1.346 | 0.734 | | Sulphate of iron | | 0.728 | | Water | 2.5 | | | Sulphate of soda | | | | Water | 2.9 | | | Oil of olives | 0.9153 | 0.710 | | Ammonia | 0.997 | 0.7080 |

*Table* ### Table continued.

| Bodies | Specific Gravity | Specific Caloric | |---------------------------------------------|------------------|------------------| | Muriatic acid | 1.122 | 0.6800 | | Sulphuric acid | 0.6631 | | | Water | 0.649 | | | Alum | 0.6181 | | | Lime | 0.646 | | | Nitre | 0.8371 | 0.6021 | | Alcohol | 1.840 | 0.5968 | | Nitrous acid | 1.355 | 0.576 | | Linseed oil | 0.9403 | 0.528 | | Spermaceti oil | 0.5000 | | | Oil of turpentine | 0.9910 | 0.472 | | Vinegar | 0.3870 | | | Lime | 0.3346 | | | Mercury | 13.568 | 0.3100 | | Distilled vinegar | 0.1030 | |

### III. Solids.

| Bodies | Specific Gravity | Specific Caloric | |---------------------------------------------|------------------|------------------| | Ice | 0.9000 | | | Ox-hide with the hair | 0.787 | | | Lungs of a sheep | 0.769 | | | Lean of ox-beef | 0.7400 | | | Pine | 0.408 | 0.65 | | Fir | 0.447 | 0.60 | | Lime | 0.408 | 0.62 | | Pitch-pine | 0.495 | 0.58 | | Apple tree | 0.639 | 0.57 | | Alder | 0.484 | 0.53 | | Oak | 0.531 | 0.51 | | Ash | 0.631 | 0.51 | | Crab-apple | 0.603 | 0.50 | | Rice | 0.5050 | | | Horse beans | 0.5020 | | | Duft of the pine tree | 0.5000 | | | Peafe | 0.4920 | | | Beech | 0.692 | 0.49 | | Hornbeam | 0.690 | 0.48 | | Birch | 0.608 | 0.48 | | Wheat | 0.4770 | | | Elm | 0.646 | 0.47 | | Female oak | 0.668 | 0.45 | | Plum tree | 0.687 | 0.44 | | Ebony | 1.054 | 0.43 | | Barley | 0.4210 | | | Oats | 0.4160 | | | Pitcoal | 0.2777 | | | Charcoal | 0.2631 | | | Chalk | 0.2564 | | | Rust of iron | 0.2500 | | | White oxide of antimony washed | 0.2270 | | | Oxide of copper nearly freed from air | 0.2272 | | | Quicklime | 0.2199 | |

### Table Continued.

| Bodies | Specific Gravity | Specific Caloric | |---------------------------------------------|------------------|------------------| | Stoneware | | 0.195 | | Agate | | 0.195 | | Crystal | | 0.1929 | | Cinders | | 0.1923 | | Swedish glass | | 0.187 | | Ashes of cinders | | 0.1885 | | Sulphur | | 0.183 | | Flint glass | | 0.174 | | Rust of iron nearly freed from air | | 0.1666 | | White oxide of antimony | | 0.1666 | | Ditto | | 0.1402 | | Ashes of the elm | | 0.1369 | | Oxide of zinc nearly free from air | | 0.1264 | | Iron | | 8.786 | | Brass | | 8.358 | | Copper | | 8.784 | | Sheet iron | | 0.1099 | | Oxide of lead and tin | | 0.102 | | Gun-metal | | 0.1100 | | White oxide of tin nearly free from air | | 0.0990 | | Zinc | | 7.154 | | Ashes of charcoal | | 0.0981 | | Silver | | 10.001 | | Yellow oxide of lead nearly free from air | | 0.0680 | | Tin | | 7.380 | | Antimony | | 6.107 | | Gold | | 19.040 | | Lead | | 11.436 | | Bismuth | | 9.861 |

### 2. Of the Absolute Quantity of Caloric.

1. Such then are the different methods which have been proved, to ascertain the relative quantities of caloric which are necessary to reduce bodies to the same temperature. Attempts have also been made to discover the temperature of absolute privation, and thus to ascertain the whole quantity of caloric which a body contains.

The first attempt made with this view, was by the late Dr Irvine's method invented to ascertain the real zero, or the absolute quantity of caloric which a body contains, is founded on the uniformity of the specific caloric of bodies at all temperatures. And taking it for granted that the specific caloric of bodies is always the same whatever be the temperature, the whole quantity, or the absolute quantity, will be proportional to the specific caloricity of bodies. Having discovered the ratio between the absolute calorificities of bodies, and the difference between two abso-rictive calories, the whole quantity in any body might be found by calculation. But either the data on which the theorem proceeds are wrong, or the experiments which have been made with the view of applying it to... the estimation of the absolute quantity of caloric have been very inaccurately conducted, the results varying so much from each other. According to Dr Irvine's own experiments and calculation, the real zero with regard to ice would be $1228^\circ$ below $0^\circ$; but according to Dr Crawford's it is $1500^\circ$. Mr Kirwan makes it $1318^\circ$ below $0^\circ$ in a comparison of the specific caloric of water and ice. Lavoisier and La Place fix it at $3426^\circ$ below $0^\circ$, from the result of experiments on a mixture of water and quicklime. But in other experiments by the same philosophers, there is a great variation in the result. Four parts of sulphuric acid, and three parts of water, mixed together, give a result for the real zero equal to $726^\circ$ below $0^\circ$; and four parts of sulphuric acid, and five of water, give it only equal to $2598^\circ$ below $0^\circ$. Professor Robison, speaking of the specific and absolute quantities of heat in bodies being supposed to be proportional, observes that "this opinion is just, only on the supposition that the measures obtained by experiments and calculation are constantly the same, whatever the temperatures may be in which the experiments are made. Dr Irvine's ingenious method of discovering the temperature of absolute privation, evidently presupposes this constancy of specific heat; or, if they are not constant, it supposes that we know the whole law of variation. Now, both of these assumptions are highly improbable. In none of the progressions of natural operations that we are acquainted with do we find this constancy. It is much more analogous to other phenomena, to suppose that, in the temperatures near to that of absolute privation, the quantities of heat necessary for producing equal elevation gradually diminish, and this, perhaps, without end, like the distance of the hyperbola from its asymptote. It is equally probable that the law of diminution may be different in different substances. This will cause the measures of specific heats to change their proportions continually; and therefore the specific capacities observed in temperatures, all of which are far removed from that of the entire absence of heat, give us no means of obtaining the proportions of the accumulated sum of all the heats which have been received into the substances. It follows from this, that even although it should be granted to Dr Irvine, that the heat which emerges, in mixing vitriolic acid and water, or in the freezing of water, is the difference between the absolute heat of the mixture, or the ice, and the absolute heats of the substances before mixture, or of the water before freezing, still we cannot ascertain those absolute heats, or the temperature of no heat.

Accordingly it appears, that it has been only in a very few cases that Dr Irvine found a tolerable coincidence of his determination of this extreme cold; and the determination by means of mixtures differed enormously from those obtained by means of congelation; and still more from those obtained by means of the condensation of vapour *."

2. Mr Dalton has proposed another hypothesis for determining the real zero, or the absolute quantity of caloric in bodies. He observes that the remarkable fact of the quantity of expansion of elastic fluids being the same in the same circumstances, shews, that it depends solely upon heat: "whereas the expansion in solid and liquid bodies seems to depend upon an adjustment of the two opposite forces of heat and chemical affinity, the one a constant force in the same temperature, the other a variable one, according to the nature of the body; hence the unequal expansion of such bodies. It seems therefore that general laws respecting the absolute quantity and the nature of heat, are more likely to be derived from elastic fluids than from other substances.

In order to explain the manner in which elastic fluids expand by heat, let us assume a hypothesis that the repulsive force of each particle is exactly proportional to the whole quantity of heat combined with it, or in other words to its temperature reckoned from the point of total privation: then since the diameter of each particle's sphere of influence is as the cube root of the space occupied by the mass, we shall have

$$\sqrt{\frac{1}{1000}} : \sqrt{\frac{1}{1325}} (10 : 11, nearly) :: \text{the absolute quantity of heat in air of } 55^\circ : \text{the absolute quantity in air of } 212^\circ.$$

This gives the point of total privation of heat, or absolute cold, at $1547^\circ$ below the point at which water freezes. Dr Crawford deduces the said point, by a method wholly different, to be $1532^\circ$. So near a coincidence is certainly more than fortuitous.

The only objection I see to this hypothesis is, that it necessarily requires the augmentation of elastic fluids for a given quantity of heat to be greater in the higher temperatures than in the lower, because the cubes of a series of numbers in arithmetical progression differ more the larger the numbers or roots: but it has just been shewn that in fact an augmentation of a contrary kind is observed. This refers us to the consideration whether the mercurial thermometer is an accurate measure of the increments of heat: if it be, the hypothesis fails; but if equal increments of heat cause a greater expansion in mercury in the higher than in the lower temperatures, and that in a small degree, the fact noticed above, instead of being an objection, will corroborate the hypothesis. Dr Crawford determines the expansions of mercury to be very nearly in proportion to the increments of heat: M. de Luc makes them to be less for a given quantity of heat in the lower than in the higher part of the scale; and in a ratio that agrees with this hypothesis. Now as every other liquid we are acquainted with is found to expand more in the higher than in the lower temperatures, analogy is in favour of the conclusions of De Luc, that mercury does the same."

The different methods which have been proposed by philosophers to determine the real zero, or the absolute quantity of caloric in bodies, and the want of coincidence between the results of the experiments and calculations founded on these methods, shew us, at least, that the subject is attended with great difficulty and uncertainty. Perhaps the present state of our knowledge does not furnish us with the means of removing the difficulty. Some fortunate discovery is still needed to guide our steps in the solution of this problem.

3. Having thus considered the relative and absolute quantities of caloric in bodies, and the methods which have been proposed for ascertaining these quantities, it may be necessary to state in what sense, or with what limitations, the term cold is to be employed. When we leave a room at the temperature of $60^\circ$, and go into the air in a frosty day at the temperature of $32^\circ$, we say that it is cold; or when the hand is held in water at the temperature of $100^\circ$ for a few minutes, and then suddenly plunged into water at the temperature of $45^\circ$, the latter is said to be cold. This, however, is merely an expression of the sensation excited in the body, which depends solely on the abstraction of its heat. This may be proved by the following experiment. If three quantities of water are taken, the first at the temperature of $32^\circ$, the second at the temperature of $50^\circ$, and the third at the temperature of $100^\circ$. Immerse the right hand into the water at the temperature of $100^\circ$, and the left into the water at the temperature of $32^\circ$. Let them remain for a minute, and then suddenly plunge both hands into the water at the intermediate temperature of $50^\circ$; the right hand will feel cold, and the left hand warm; and thus different sensations are produced by the same body at the same time and at the same temperature. But this depends entirely on the previous state of the hands, and on the abstraction or subtraction of caloric; and this seeming paradox is easily explained by what has been said on the equal distribution of caloric. The right hand which was placed in the water at the temperature of $100^\circ$ absorbed caloric, because the temperature of the water is above that of the body. This excites the sensation of heat; but when the same hand is placed in the water at the temperature of $50^\circ$ it is deprived of caloric, because the surrounding medium is far below its temperature; and thus the sensation of cold is produced. But from the left hand, placed in the water at $32^\circ$ caloric is subtracted, which gives the sensation of cold, and the same hand placed in the water at $50^\circ$ receives caloric, and this entering the body, excites the sensation of heat.

Thus, then, the term cold is merely expressive of the relative temperature of two bodies. In common language the word cold is sufficiently intelligible; but in the present view of the doctrine of caloric, it can have no other precise meaning, than to express the absence of a quantity of heat.

Observing the remarkable effects which were produced on fluids by the abstraction of caloric, it is not at all surprising that the phenomena which were not observed with great accuracy, should be ascribed rather to the addition of some new body, than to the abstraction of one which was formerly in combination. Hence originated the hypothesis which supposed the existence of the frigorific particles of Le Mairan and Munchenbroek, which prevailed till the effects of caloric were developed by the discoveries of modern chemistry. They were led to this hypothesis of the entrance of extraneous matter into water when it is converted from the fluid into the solid state, from observing the increase of bulk which takes place. These frigorific particles, to which all the effects of cold were ascribed, it was imagined, had some resemblance to nitre. This opinion probably arose from the circumstance of a great degree of cold, or diminution of temperature, being produced by dissolving nitre in water. The frigorific particles were supposed to be constantly floating in the air, and by mixing with liquid bodies, as water, converted them into solids, by acting the part of wedges, which prevented the free motion of the particles among each other.

The experiments of Professor Piclet, in which cold seems to be reflected, still give some support to this opinion. Two concave mirrors of tin were placed at the distance of $10\frac{1}{2}$ feet from each other; a glass vessel full of snow was placed in the focus of the one, and an air thermometer in that of the other. The thermometer sunk several degrees, but when the snow was removed, it rose again; and when a greater degree of cold was produced on the snow, by pouring an acid upon it which dissolved it rapidly, the thermometer fell several degrees lower. At first sight it appears, that cold has been given out by the snow, and this cold reflected by the mirrors occasioned the fall of the thermometer. The explanation of this fact is not without difficulty. As the rays of caloric are emitted by all surrounding bodies, the temperature of the thermometer is probably kept up by some of these rays. Suppose when the thermometer is placed in the focus of one of the mirrors, so that it stands at the same temperature that it would do when brought into contact with any other of the surrounding bodies; and that this temperature is partly owing to the rays of caloric which are passing off from those bodies: if then there is any interruption of these rays, the temperature of that body, as the thermometer, must be diminished. This is probably what takes place when the temperature of the thermometer in the focus of one of the mirrors falls, by placing a cold body in the focus of the other. To make this a little plainer, suppose the temperature of the thermometer is kept up by $100$ rays of caloric; when a cold body is placed in a proper situation, as in the focus of the opposite mirror; if any number of these rays be absorbed by the cold body, it must consequently fall in temperature.

But although the explanation be not altogether satisfactory, it affords no proof of the existence of frigorific particles. Were we even to admit this hypothesis, it would not probably affect us much in the explanation.

4. Great degrees of cold are produced, by mixing together those substances which dissolve rapidly. The reason of this will appear by recollecting what has been said of the abstraction of caloric when a solid body is converted into a fluid. Mixtures to produce artificial cold, are generally made of the neutral salts dissolved in water; of diluted acids and some of the neutral salts; and of snow or pounded ice with some of these salts. A great number of experiments were made upon this subject by Mr Walker *; also by Professor Lowitz of * Phil. Petersburgh †; by Foureroy and Vauquelin ‡; and Transf. by Guyton §. The following table exhibits the results of these experiments.

| Table of Freezing Mixtures. | |-----------------------------| | Mixtures. | Thermometer sinks. | | Parts | From $50^\circ$ to $10^\circ$ | | 1. Muriate of ammonia 5 | Nitre 5 | | Water 16 | From $50^\circ$ to $4^\circ$ | | 2. Muriate of ammonia 5 | Sulphate of soda 8 | | Nitre 5 | Water 16 |

* Phil. Petersburgh †; by Foureroy and Vauquelin ‡; and Transf. by Guyton §. ### Table of Freezing Mixtures continued.

| Mixtures | Thermometer limits | |----------|-------------------| | Nitrate of ammonia | From 50° to 4° | | Water | | | Nitrate of ammonia | From 50° to 7° | | Carbonate of soda | | | Water | | | Sulphate of soda | From 50° to 3° | | Diluted nitric acid | | | Sulphate of soda | From 50° to 10° | | Muriate of ammonia | | | Nitre | | | Diluted nitric acid | | | Sulphate of soda | From 50° to 14° | | Nitrate of ammonia | | | Diluted nitric acid | | | Phosphate of soda | From 50° to 12° | | Diluted nitric acid | | | Phosphate of soda | From 50° to 21° | | Nitrate of ammonia | | | Diluted nitric acid | | | Sulphate of soda | From 50° to 8° | | Muriatic acid | | | Sulphate of soda | From 50° to 3° | | Diluted sulphuric acid | | | Snow | From 52° to 0° | | Common salt | | | Snow or pounded ice | From 0° to -5° | | Common salt | | | Snow or pounded ice | From -5° to -18° | | Common salt | | | Muriate of ammonia and nitre | | | Snow and diluted nitric acid | From 0° to -46° | | Potash | From 32° to -51° | | Snow | | | Snow or pounded ice | From -18° to -25° | | Common salt | | | Nitrate of ammonia | | | Snow and diluted nitric acid | | | Potash | From -10° to -56° |

When any of these substances are to be employed as freezing mixtures, the salts should be used fresh crystallized, and reduced to fine powder; and it will perhaps be found most convenient to observe the proportions which are set down in the table. Suppose it is wanted to produce a degree of artificial cold equal to -50°, which is the temperature produced from 32° by the 20th freezing mixture. The substances employed, namely, the muriate of lime and the snow, must be previously cooled down to the temperature of 32°, or any degree below it. This may be done by placing them separately in the 11th freezing mixture, the sulphate of soda and diluted sulphuric acid, which reduces the temperature from 50° to 3°; or in the 12th freezing mixture of snow and common salt, which reduces the temperature from 32° to 0°. The materials thus cooled down, are then to be mixed together as quickly as possible, when, if the experiment succeed, the temperature will fall from 32° to -50°, as in the 20th freezing mixture. The vessels which are employed for these processes should be very thin, and made of the best conductors of heat. Vessels of tin plate answer the purpose, and when acids are to be used, they may be lined with wax, which will secure them sufficiently against their action. They should be of no larger dimensions than just to contain the materials.

### Sect. VI. Of the Sources of Caloric.

We are now to consider the means by which caloric may be evolved, or rendered sensible. This is a subject of great importance, both as a curious investigation, and as a useful and necessary application in chemistry and the arts of life. According to the different sources from which caloric is derived, or the means which are employed for its evolution, these may be reckoned five in number; namely, percussion, friction, mixture, the sun, combustion; and we shall consider them in the order in which they have been named. First Source of Caloric,

Percussion.

The production of heat by striking together flint and steel, is a well known fact. The same thing also takes place when many other hard bodies are struck against each other. Fires are frequently kindled by making a piece of iron red-hot by percussion, which is effected by striking it smartly with a hammer. In most of the cases in which caloric is evolved by percussion, this evolution is ascribed to the condensation of the particles of the body struck. This has been observed to take place, both in elastic fluids and liquids.

1. The sudden condensation of air alone, has been found to produce a change of several degrees in the thermometer. In some experiments by Dr Darwin, the condensed air from an air-gun, thrown on the bulb of a thermometer, uniformly sunk it about 2°. This shews that the condensed air had given out some of its caloric; for during the operation of condensing it, the apparatus became sensibly hot.

Mr Dalton's experiments on the condensation and rarefaction of air, show that an increase of temperature of 50° is produced, by admitting air into an exhausted receiver; and when the equilibrium is restored to condensed air, 50° of cold is produced. The suddenness of the fall and rise of the thermometer is very remarkable in these cases; and from this circumstance, Mr Dalton conjectures, that the real change of temperature of the air or medium, was much greater than the thermometer indicated; but that the inequality existed only for a few seconds. From these experiments, therefore, it appears that caloric is evolved during the condensation, and absorbed during the rarefaction of air.

A considerable rise in temperature takes place, when different gases unite together, and are condensed. Muratic acid gas and ammoniacal gas, when combined together, form a solid salt; and during this combination a great quantity of caloric is evolved.

2. To the same cause is ascribed the caloric which is evolved by the percussion of hard bodies. This is particularly the case with metallic substances. They acquire a considerable increase of density by hammering; and during this process caloric is evolved. A piece of iron, it has been observed, becomes red-hot when it is smartly struck with a hammer on an anvil; and it acquires a considerable increase of density. Before hammering, the specific gravity of iron is 7.788; after it is hammered it increases to 7.840. In some other metals the increase of density is still more remarkable. Before hammering, platinum is only 19.5; and after hammering, its specific gravity is increased to 23.0. As a proof that the heat is evolved by condensation, iron, which has been once heated by hammering, cannot be subjected to the same process till it has been again exposed to heat. It has become so brittle that it flies to pieces under the strokes of the hammer.

3. It is perhaps more difficult to account for the calorific and light which are emitted by incombustible substances; as, for instance, in the case of two quartz incombustible stones struck against each other, which has already been alluded to in treating of light. The particles of these bodies which were struck off by percussion, are found, on struck examination, to be in a state of fusion; and it would appear that this is a case in which light and caloric are emitted without oxygen having any share in the action, as supposed to happen in all cases of combustion.

In some observations on the appearances produced by the collision of steel with hard bodies, made by Mr Davy, he mentions that Mr Hawkbee showed*, that no sparks could be produced in vacuo; a faint light was only perceived. Mr Davy thinks that the vivid sparks obtained from steel in the atmosphere, are owing to the combination of the small abraded and heated metallic particles with oxygen; but it has been doubted, whether the faint luminous appearance, when the experiment is made in vacuo, be owing to the light produced by the fracture and abrasion of the particles of the flint, or only partly to this cause, and partly to the ignition of the minute filaments separated from the steel. When a fine and thin flint, which is easily broken, is used for the collision in vacuo, the light is more vivid, than when a thick one is employed. From this he concludes that the particles of steel are rendered luminous in consequence of combustion. This opinion was proved by the following experiment.

A thin piece of iron pyrites (fulphuret of iron) was inserted in a gun-lock in place of the flint. By collision in the atmosphere it gave vivid sparks, chiefly white, but sometimes mixed with a few red sparks. The same experiment was repeated when the apparatus was introduced into the exhausted receiver of an air-pump; but no light whatever appeared.

Mr Davy further observes, that bodies which are supposed to become luminous by being struck or rubbed together in the electric vacuo, under water, or in gases that do not contain oxygen; such bodies, for instance, as fluors and carbonate of lime, siliceous stones, glass, sugar, and many of the compound salts, are both electrics per se and phosphorescent substances; so that the flashes they produce are probably occasioned, partly by electricity and partly by phosphorescence. In some cases, however, by the collision of very hard, stony bodies, which are bad conductors of heat, there may be an actual ignition of the particles. This seems to be countenanced by various facts. Mr T. Wedgwood found, that a piece of window-glass, when brought into contact with a revolving wheel of grit, became red-hot at its point of friction, and gave off luminous particles, which were capable of inflaming gunpowder and hydrogen gas†; and we are informed, Mr Davy adds, by a late voyager (s), that the natives of Oonalashka light their fires by striking together two pieces of quartz over dry grass, Second Source of Caloric,

Friction.

1. A great quantity of caloric is also given out by friction. The intensity of the heat produced by friction depends on many circumstances, and varies chiefly in the ratio of the time employed and the nature and surface of the bodies which are rubbed together. When the bodies rubbed are combustible, as two pieces of dry wood, they may be inflamed; but when they possess combustibility in a low degree, or are altogether incombustible, the temperature may be raised to high as to communicate a degree of heat sufficient to set fire to combustible bodies. Greater difficulty still attends the explanation of the phenomena of the evolution of caloric by friction than by the percussion of hard, incombustible bodies. In this case there can be no increase of density by the friction in many instances, for caloric is evolved by rubbing together two pieces of wood, or rubbing the hand on a piece of soft cloth where increase of density can scarcely be supposed. Nor can the increase of temperature by friction be accounted for by the diminution of the specific caloric of the bodies which are rubbed together; for Count Rumford, who made some interesting experiments on this subject, could not discover any change in this respect, and supposing that this change had taken place, it would not be sufficiently great to account for all the heat produced. In one of these experiments he took a brass six-pounder, cast solid, and rough as it came from the founders; fixed it horizontally on the machine fixed for boring, and caused its extremity to be cut off; and by turning round the metal in that part, a solid cylinder was formed 7½ inches in diameter, and 9½ inches long. This when finished remained joined to the rest of the metal by a small cylindrical neck 2½ inches in diameter, and 2½ inches long. This short cylinder was bored with a horizontal borer used in boring cannon. Its bore which was 3½ inches in diameter, instead of being continued through its whole length 9½ inches, was only 7½ inches in length. A solid bottom of 2½ inches in length was thus left. A blunt steel borer was pressed against the bottom of the bore of the cylinder with a force equal to 10,000 lb. avoirdupois; and the cylinder was turned round by horses at the rate of about 32 times in a minute. To prevent the dissipation of the heat, the cylinder was covered up with thick flannel. At the beginning of the experiment the temperature of the air and of the cylinder was 60°. At the end of 3½ hours it had made 960 revolutions, a mercurial thermometer was introduced into the hole made to receive it in the side of the cylinder, and the mercury rose to 130°. When the borer was removed, and the metallic dust or scales taken out of the bottom of the cylinder, it was found to amount to 837 grs. As the weight of this dust amounts to no more than ¼ th part of that of the cylinder, it must have given off 948° to raise the temperature of the cylinder 1°, and consequently it must have given out 66,360° of heat in the course of the experiment.

2. But to determine whether the air of the atmosphere had any part or not in the generation of this air-heat, by one decisive experiment, he contrived the following, in which it was impossible for it to produce any effect whatever. The apparatus was inclosed in a wooden box, which was made water-tight, and being filled with water, completely excluded the external air. The quantity of water employed was 18.77 lb. avoirdupois or 2½ wine gallons, and the temperature at the commencement of the experiment was 60°. The machine was put in motion, and moved at the same rate as in the former experiment. At the end of an hour the temperature was 107°; in half an hour more, it rose to 178°, and at the end of two hours and 30' from the beginning of the experiment the water actually boiled. By Count Rumford's calculation the caloric generated by friction in this experiment, and accumulated in two hours and 30', would have heated ice-cold water 180°, or caused it to boil. From the results of his computation it appears, that the quantity of caloric thus generated equably, was greater than that produced equably in the combustion of nine wax-candles, each ½ of an inch in diameter, burning with clear bright flames for the same length of time.

Reflecting on these experiments, Count Rumford returns to the question, What is heat? Is there any Rumford such thing as an igneous fluid? And after stating that the quantity of caloric thus generated could neither be motion furnished by the particles of the metal, detached from the solid masses, nor by the air, nor by the water, because it must have received its heat from the apparatus, he concludes, that caloric is not a material substance, but only a peculiar kind of motion produced among the particles of matter.

3. The experiments of Professor Pictet also prove, that the caloric generated by friction is not owing to the combination of oxygen with any of the bodies. He contrived an apparatus which could be introduced into the receiver of an air-pump. By means of this apparatus, a piece of adamantine spar was rubbed against a fleck cup in the open air. A thermometer friction which was fixed in the inside of the cup, did not rise owing to when the apparatus was set in motion, although abundance of sparks were produced. When the apparatus was placed in an exhausted receiver, and the experiment repeated, a phosphoric light, but no sparks, appeared, nor was the thermometer any way affected; but when a smaller brass cup was employed, and a piece of brass rubbed against it in the open air, the thermometer was not affected till the motion ceased, and then it rose 0.3°. The caloric, it would appear, was carried off as it was generated, by the motion of the air. When the same experiment was repeated in... in vacuo, the thermometer rose 1.2°, and it began to rise as soon as the friction commenced. When a piece of wood was made to rub on a wooden cup, the thermometer rose 2.1°, and in vacuo 2.4°.

These experiments, therefore, are sufficiently conclusive to prove that the caloric evolved by friction is not derived from the atmosphere; but still the question recurs, What is its origin? No satisfactory answer can be given to this question, if it cannot be resolved, as some have supposed, by having recourse to the agency of electricity; and, considering the similarity of the effect of caloric and electricity in heating and cooling bodies, in producing the expansion and fusion of metallic substances, in effecting the actual combustion of inflammable matters, and that in other respects the one can be substituted for the other, it is not at all improbable that electric matter, which is generated in great abundance by friction, may be the chief agent in the evolution of caloric by the friction of bodies on each other.

4. In some observations on spontaneous inflammations by Bartholdi, he mentions the experiments which were repeated by D. Palcani, for obtaining fire by the friction of two pieces of wood, in which he gave to one of the rubbing pieces the form of a tablet, and to the other that of a spindle or cylinder; and as the results of some of these experiments are of importance to show what attention ought to be paid to the choice of wood, in the construction of machines and instruments where there is considerable friction, we shall state the following.

| Cylinders | Tablet | Duration | Effect | |-----------|--------|----------|--------| | Boxwood | Box | 5' | Sensible heat. | | do | Poplar | 5 | do | | do | Oak | 5 | do | | do | Mulberry | 3 | Considerable heat and smoke. | | do | Laurel | 2 | do | | do | Poplar | 2 | do | | do | Ivy | 2 | do | | Ivy | Box | 3 | do | | do | Walnut | 3 | do | | Olive | Olive | 3 | do | | Mulberry | Laurel | 2 | Considerable heat, smoke, and blacknesses. | | Ash | Oak | 5 | Sensible heat. | | do | Fir | 5 | do | | Peartree | Oak | 5 | do | | Cherry | Elm | 5 | do | | Plumtree | Appletree | 5 | do | | Oak | Fir | 5 | do |

When the experiment was changed, and a cylinder of one of the kinds of wood was rubbed between two tablets of the other; as, for example, a cylinder of poplar between two tablets of mulberry wood, the increase of the rubbed surfaces which were in contact with the air, produced a temperature much more considerable; and almost the whole of the kinds of wood enumerated above, took fire.

The effect of friction also varies according as the woods employed of the same kind are rubbed in the direction of the fibres, or when the fibres cross each other. In the first case the friction and heat generated are much more considerable than in the second.

Third Source of Caloric,

Mixture.

1. It is one of the characteristics of chemical action change of to produce a change of temperature. This happens in consequence of the increase or diminution of bulk of mixture by the bodies which have been the subject of combination, or a total change of their state and properties. Thus it has been established as a general law in chemical science, that all bodies which pass from the solid to the fluid state, absorb a quantity of caloric; and all bodies which pass from the fluid to the solid state, give out caloric. This law, therefore, will enable us to account for those changes which take place by the mixture of different bodies. In the course of the detail of chemical science on which we are about to enter, we shall have frequent opportunities of pointing out the effects of this law. At present we shall only mention a few instances in which caloric is evolved by mixture, or chemical action.

2. When two substances in the state of gas enter into union, and form a solid or liquid body, caloric is evolved.

a. Ammoniacal gas and muriatic acid gas, when they are mixed together, instantly combine, and form a solid salt, at the same time giving out a quantity of caloric.

b. When oxygen gas and nitrous gas are mixed together, they combine and form a liquid, and at the moment of union, give out caloric.

3. When two liquids are mixed together, and if the density of the mixture be greater than the mean of the two liquids, caloric is evolved during the combination.

a. When alcohol or spirits of wine and water are mixed together, the density is greater than the mean of the two liquids; caloric, therefore, is given out during the mixture.

b. A much greater degree of heat is produced by mixing together sulphuric acid and water. If four parts of sulphuric acid be combined with one part of water, the density of the mixture is much greater than the medium density of the two liquids, and accordingly the quantity of caloric evolved is sufficient to boil water.

4. A great quantity of caloric is also given out when a fluid body combines with a solid. We have an instance of this in the flaking of lime.

a. When water is thrown upon quicklime, it instantly disappears; for part of it combines with the lime, and becomes solid; and thus passing from the liquid to the solid state, it gives out caloric.

b. If a quantity of sulphuric acid be poured upon quicklime, the caloric evolved is sufficient to raise part of the sulphuric acid into vapour.

5. Were we to reverse these experiments, and state cold productions of caloric being absorbed during the mixture of bodies, we should observe the operation of the same law, in the case of solid bodies becoming fluid, producing a great degree of cold. But it appears that fluid, the production of cold by the solution of salts in water is owing to the water which is in a previous state... of combination with one of the salts, and thus water passing from the solid to the liquid state, must absorb caloric, and therefore produce cold. The salts which are most proper for this purpose, contain a great proportion of water in the composition; for if the same salts are deprived of water by exposing them to heat, the same effect by no means follows. On the contrary, when they are dissolved in water in this state, heat is produced, because they combine with a portion of the water for which they have a strong affinity, and this water passing from the liquid to the solid state, gives out its caloric.

6. A considerable quantity of caloric is also generated in other mixtures, in which the fermentation and putrefaction of animal and vegetable substances takes place. During these processes the substances which are held in solution enter into new combinations, and their chemical properties are totally changed. While this change is going on, there is a gradual and constant evolution of caloric.

It is an artificial heat of this kind, which is generated by animal and vegetable matters, and on account of its uniformity and constancy is employed for promoting vegetation; as when horse dung and tanner's bark are used in making hot beds; or for the hatching of eggs, a practice which has been long in use in Egypt.

Fourth Source of Caloric;

The Sun.

1. But the greatest source of light and heat in the planetary system is the sun. When treating of light we mentioned a speculation of philosophers about the great and constant waste of light, which the sun, although a body of immense magnitude, must sustain. But since the nature and constitution of the sun were discovered by Dr Herschel, these speculations fall to the ground. According to these discoveries, the sun is not, as was formerly supposed, an immense globe of fire, in which the materials composing it were continually wasting by combustion; but a solid opaque body, similar to the other planets, and surrounded by a very dense atmosphere, in which are observed two kinds of clouds. The lower region of clouds is similar to those in the atmosphere of the earth. The uppermost region of clouds is luminous, and from this proceed the light and heat which were supposed to come from the body of the sun. This luminous region, it appears from Dr Herschel's observations, in consequence of changes which seem to be constantly going on in it, exhibits different degrees of splendour, diminishing greatly the quantity of light and heat which are emitted at other times. To these variations he attributes the difference of temperature in different seasons, and the consequent abundance or deficiency of crops.

2. It is a familiar observation, that dark-coloured clothes, as black for instance, are much warmer than those which are of a lighter colour. The observation and the practice founded upon it are correct, although the reason is only obvious to the philosopher. The rays of light, and also probably those of caloric, are reflected in greater proportion by white bodies, than by those which are of a deeper colour. The sun's rays enter the opaque body, and combine with it, and thus increase the temperature. These rays are permitted to pass through transparent bodies, which are very little affected by them; but combining with opaque bodies they heat them, and the deeper the colour of the body, the greater is the increase of temperature.

3. But this has not been left to the uncertainty of common observation. Experiments were made by Dr Franklin, and before him by Dr Hooke, to ascertain this curious point. Pieces of cloth of different colours were placed upon snow, and exposed to the light of the sun. The colours were white, red, blue, black; and it was found that the darkest coloured pieces acquired most heat, because they sunk deepest in the snow, and this was in proportion to the darkness of the colours.

Mr Davy made a similar experiment, to determine the correspondence between the increase of repulsive motion in bodies from the action of light and dark colours.

"Six similar pieces of copper, (t) of equal weight, size, and density, were thus coloured, one white, one yellow, one red, one green, one blue, and one black. A portion of a mixture of oil and wax, which became fluid at about 76°, was placed on the centre of each on the inferior side. They were then attached to a board painted white, and so placed with regard to the sun, that their upper surfaces were equally exposed to the light. Their inferior surfaces, to which the cerate was attached, were equally deprived of light and heat, that is, they were so exposed, that there could be no mistake with regard to the repulsive motion generated in them by the action of light. The changes of temperature in them, from the action of light, took place in the following order. The cerate on the black plate began to melt perceptibly before the rest, the blue next in order, then the green and the red, and lastly the yellow. The white was scarcely at all affected; the black was in a complete state of fusion." It appears, therefore, from these experiments that caloric enters bodies in different proportions; and in the greatest proportion in the darkest coloured bodies.

It appears too, that those bodies which absorb most light, acquire the greatest degree of temperature when exposed to the sun's rays. This has been demonstrated by the experiments of Wedgwood, Cavallot, and Picet.

The former took two pieces of phosphorescent marble, one of which was blackened, and placed them on a hot iron. No light appeared from the blackened marble, but the other exhibited its usual phosphorescence. Upon a second exposure, the piece which was not blackened gave a faint light; the blackened one, as before, gave none at all. When the black was wiped off, and both pieces were again placed upon the heater, no light appeared either from the one or the other. This experiment shows, that the phosphorescent property was nearly destroyed without any visible light having appeared. But both pieces of marble before being heated, must have contained the same quantity of

(t) Each an inch square, and two lines thick. of light and heat, and therefore the light from the blackened piece must have been absorbed by the black colour.

In Cavallo's experiments (u), the bulb of a thermometer was painted black, and exposed along with other thermometers to the sun's rays. The difference of temperature between the blackened thermometer and the other sometimes amounted to 10°; that is, the blackened thermometer indicated a temperature 10° higher than the other; but this difference was not constant; for it varied according to the brightness of the sun, and the density and temperature of the atmosphere. Considerable variations were also observed, from the difference of colours which were employed, and from the difference of polish of the surface of the plate.

The same thing was observed when the thermometers were exposed to strong daylight. The thermometer whose bulb was blackened indicated the highest temperature.

In an experiment by Professor Picquet, two thermometers, one of which had its bulb blackened, when they were kept in a dark place, indicated the same temperature. These experiments prove the close connection between light and caloric; for the greater the proportion of light absorbed by any body, the higher is the temperature of that body. And when the light is totally excluded, as in the last mentioned experiment of Picquet, the temperature is the same.

But it has been shown that there is a very great difference in the heating power of the different rays of light. It appears, from the experiments of Dr Herschel, that this heating power increases from the middle of the spectrum to the red ray, and is greatest beyond it, where the rays are invisible. Hence it is inferred that the rays of light and caloric nearly accompany each other, and that the latter are in different proportions in the different coloured rays. They are easily separated from each other, as, when the sun's rays are transmitted through a transparent body, the rays of light pass on seemingly undiminished, but the rays of caloric are intercepted. When the sun's rays are directed at an opaque body, the rays of light are reflected, and the rays of caloric are absorbed and retained. This is the case with the light of the moon, which, however much it be concentrated, gives no indication of being accompanied by heat.

It has also been shown that the different rays of light produce different chemical effects on metallic salts and oxides. These effects increase on the opposite direction of the spectrum, from the heating power of the rays. From the middle of the spectrum towards the violet end, they become more powerful; and produce the greatest effect beyond the visible rays.

From these discoveries it appears, that the solar rays are of three kinds: 1. Rays which produce heat. 2. Rays which produce colour; and, 3. Rays which deprive metallic substances of their oxygen. The first set of rays is in greatest abundance, or are most powerful towards the red end of the spectrum, and are least refracted. The second set, or those which illuminate objects, are most powerful in the middle of the spectrum; and the third set produce the greatest effect towards the violet end, where the rays are most refracted.

6. The solar rays pass through transparent bodies transparently without increasing their temperature. The atmosphere, for instance, receives no increase of temperature by transmitting the sun's rays till these rays are reflected from other bodies, or are communicated to it by bodies which have absorbed them. This is also proved by the sun's rays being transmitted through convex lenses, producing a high degree of temperature when they are concentrated, but giving no increase of temperature to the glass itself. By this method, the heat which proceeds from the sun can be greatly increased. Indeed, the intensity of temperature produced in this way is equal to that of the hottest furnace. This is done either by reflecting the sun's rays from a concave polished mirror, or by concentrating or collecting them, by the refracting power of convex lenses, and directing the rays thus concentrated on the combustible body. See BURNING GLASS.

Fifth Source of Caloric,

Combustion.

It was impossible for men whose attention was directed to the phenomena of nature, long to let pass un-observed the singular appearances which are exhibited striking in the combustion or burning of bodies. Indeed the changes produced on bodies by this process, the astonishing effects which follow, and the importance of the process itself, could not fail to excite great interest and attention.

As combustion is one of the principal sources of heat, it has long occupied the attention of men in general, both as to the means of its improvement, and application in the arts of life, and in the discovery of a theory or explanation which will account for the phenomena. But the want of success in this branch of philosophical investigation, even at the present day, casts shadows that the subject is attended with great difficulty.

When a piece of iron is exposed to a high temperature, it becomes red hot, and when it is removed from between the heating body, it continues for some time to give out light and heat. But when it is suffered to cool, it returns to the same state in which it was before it was burning, heated, having undergone no perceptible change. When a piece of wood is burnt, it also gives out light and heat, but during this process it is totally changed. Great part is dissipated, and nothing remains but a small quantity of ashes.

When a piece of sulphur is exposed to a temperature between 300° and 400°, it takes fire and burns; gives out

(u) The hint of these experiments, he says, was taken from the account of an experiment in a volume of the Philosophical Transactions, made with a thermometer whose bulb was painted black, and exposed to the rays of the sun. The experiment alluded to was made Dr Watson, bishop of Landaff. Philosophical Transactions, 1763, p. 49. out heat and light, and during this process the sulphur has acquired new properties, or has entered into new combinations.

When a metallic substance, zinc, for instance, is exposed to a certain temperature, it also undergoes a very great change, during which heat and light are also given out. The zinc is changed to a light flocculent substance, but most other metals are reduced to the form of powder (x).

Now, none of these changes can be effected without the presence of atmospheric air, or rather without the presence of oxygen gas, which is one of its constituent parts, and that part of it which is necessary for the process of combustion. In all cases where combustion takes place, oxygen gas disappears or changes this process; light and heat are emitted, and the combustible body has changed its properties. Such are the phenomena of combustion, so far as observation and experiment have gone; but still the difficulty remains, to discover what there is to be ascribed to the different agents which are necessarily concerned in this process, in the changes which are effected. It is now universally agreed, that oxygen gas, or its base, is fixed in the combustible body during the process of combustion, and that the caloric which is necessary to retain the oxygen in the state of an elastic fluid being emitted during the change, is the source of the heat which is given out by burning bodies. But what is the source of the light? Is it emitted by the oxygen gas along with the caloric in its change from the fluid to the solid state? Or has it been a constituent part of the combustible body which is separated during combustion? Of this different opinions have been entertained by philosophers, and the question in a great measure still remains undecided. Let us now consider the different theories which have been proposed to account for these phenomena.

1. In the early dawn of chemistry, when the scattered facts were first collected, and it began to assume a scientific form, attempts to explain this process were soon made. Beccher was the first who gave any consistent form to a theory of combustion. Before his time, sulphur was considered as the universal inflammable principle; but he rejected this opinion, considering sulphur as an inflammable substance, containing the principle of inflammability, but not that principle itself. This theory was improved and extended by Stahl, who gave this principle the name of phlogiston (y), from which the theory is called the phlogistic, and from his own name the Stahlian theory. This principle was supposed to exist in all inflammable bodies, and to be the same in them all. The diversity which is observed among them, in external appearance and other properties, is owing to the other principles or elements of which they are composed, and with which the common principle of inflammability, or phlogiston, is combined. Inflammation or combustion, with the several phenomena that attend it, is supposed to depend on a gradual separation and dissipation of this principle; and this being once separated, what remains of the body is no longer combustible, but is similar to other kinds of matter. This principle is represented as a dry substance, of an earthy nature, composed of particles which move more than all others are disposed to be affected with a very swift whirling motion. When the particles of a body are agitated with this motion, the body becomes hot, is ignited, or undergoes combustion according to its violence. The heat and the light which are emitted during combustion, depend upon a peculiar motion of the particles of matter; phlogiston, which is supposed to be contained in all combustible substances, being most disposed to assume this motion.

2. But before this time a different theory was proposed by Dr Hooke, who published an account of it in 1665, in a work entitled Micrographia; and, in the year 1676, in another work called Lampas. According to this theory, the air of the atmosphere is the universal solvent of all combustibles. This solution takes place when the temperature of the combustible body is sufficiently raised, and during the violence of its action the heat is emitted. This dissolution of inflammable bodies is a substance inherent in the air, which is like, if not the very same with, that which is fixed in saltpetre. During this dissolution of bodies, part unites with the air and escapes; and part, after being mixed with it, forms a coagulum or precipitation, some of which being light, is carried away, while another part which is heavier remains behind.

Some time after, an account of the same theory was published by Dr Mayow, with some additional experiments, in a work entitled De Sal-nitro et Spiritu Nitro-aëreo. The nitro-aërial particles, or the spiritus nitro-aëreus of Mayow, was the same as the universal solvent of Hooke. According to Mayow, this spiritus nitro-aëreus consists of minute particles, from the motion of which it is produced, and when the motion is more rapid, not only heat but light also is extricated. The following abstract of the theory of Dr Hooke, with Professor Robison's observations, will not, we hope, be unacceptable to our readers.

"This theory, to opposite, as Dr Black observes, to the theory of Stahl, is not so recent as is generally imagined. It was seen in all its extent and importance by Dr Robert Hooke, one of the greatest geniuses, and most ardent inquirers into the operations of nature, who figured during the latter half of the 17th century, a period full of great discoveries.

"Dr Hooke proposed this theory in considerable detail in his Micrographia, published in 1665; and in his Lampas, published in 1676; and he makes it an important doctrine in his treatise on Comets, and in many pages of his Cutlerian Lectures. He promises to take it into serious consideration, and to publish a full exhibition of it. The allusions made to it in his lectures, make it evident that he had continued to make some defunct additions to his first conceptions. His Lampas contains a most accurate explanation of flame, which

(x) To these substances was formerly given the name of calx or calcus, but in the present chemical nomenclature they are denominated oxides.

(y) This principle was also called terra secunda, or terra inflammabilis. which cannot be surpassed by any performance of the present day.

"In the Micrographia he states the theory in the following words:

"1. The air in which we live, and breathe, and move, and which encompasses and cherishes all bodies, is the universal solvent of all sulphurous (synonymous, at that time, with inflammable) bodies.

"2. This action it performs, not till the body be sufficiently heated, as we observe in other solutions.

"3. This action of dissolution produces the great heat which we call fire.

"4. It acts with such violence as to agitate the particles of the diaphanous body air, and to produce that elastic pulse called light.

"5. This action, or dissolution of inflammable bodies, is performed by a substance inherent in, and mixed with the air, that is like, if not the very same with, that which is fixed in saltpetre.

"6. In this dissolution of bodies by the air, a part of the body uniting with the air, is dissolved or turned into air, and escapes and flies about.

"7. As one part is thus turned into air, so another is mixed with it, but forms a coagulum, or precipitation, some of which is so light as to be carried away with the air, while other groser and heavier matters remain behind, &c., &c. This latter article is frequently employed in other parts of his writings, and is sometimes called a groser compound, mixed with matters terrene, and originally insoluble in air, and incombustible.

"Can anything more be wanting to prove that this is the same with the modern theory of combustion? Nothing but to shew that this coagulum contained the air which had formed it, by shewing an increase of its weight, or by separating it again. But the eager mind of Hooke, attracted by every appearance of novelty, was satisfied with the general notion of a great subject, and immediately quitted it in chase of some other interesting object. Had he not been thus led off by a new pursuit, this wonderful man would not only have anticipated, but completed many of the great discoveries of the last century. It was a bold conception, and only a vigorous mind could entertain it for a moment, that the vast heat of combustion was contained in a few grains of air. Yet this was his opinion, as appears by the explanation which he gives, in various meetings of the Royal Society, and in his lectures on comets, of the deflagration of combustible bodies with saltpetre, and of fiery motion.

"In the treatise called Lampas, he observes that this his treatise, published eleven years before, had been very favourably received, and that he had not seen any valid objection offered to it. It was in this interval that Dr Mayow at Oxford published his book de De Sal-Nitro et Spiritu Nitro-aereo, in which he holds precisely the same doctrine; but his exhibition of it is obscure, complicated, and wavering, mixed with much mechanical nonsense, of wedges, and darts, and motions, &c., according to the fashion of the times. Hooke's conception of the subject, on the contrary, is clear, simple, and steady. The only addition made by Mayow are some observations on the increase of weight observed in the preparation of diaphoretic antimony, &c. Hooke, explaining at a meeting of the Royal Society, some tricks of the plumbers' workmen, who called the litharge which formed on the surface of the melted lead drops, and took it with them as their perquisite, says expressly that they can make drops of the whole, and that it is more than the lead by all the air which was its menstruum. But Mayow wrote on the subject expressly, and it appears in the title of his book. He is remembered, while Hooke is forgotten, because no one would think of looking into the Micrographia for chemical information. The theory comes in by chance, to explain the indestructibility of charcoal in close vessels by heat. Mayow also made many very ingenious experiments on the air which had contributed to inflammation, and has anticipated both the manipulations and the discoveries of modern pneumatic chemistry."

"But in the progress of chemical science, the existence of the imaginary principle of phlogiston began to be called in question. It had been observed, and being proved by experiment, that substances became inflammable merely by being exposed to the light of the sun, and in this way having acquired the principle of inflammability, it was supposed to be the same as light. This opinion of phlogiston being light fixed in bodies, which was the first improvement or modification of the theory of Stahl, was adopted by Macquer and other chemists.

"In the progress of discovery, this theory was still farther modified. The introduction of pneumatic chemistry, and the accuracy and precision which it gave to the experiments and researches of chemists, enabled them to ascertain, with greater certainty, the changes which take place on bodies after being subjected to combustion, as well as on the air in which they are burnt. Some of these changes were observed by Dr Priestley, whose indefatigable labours contributed essentially to the extension of chemical science. He found, by experiment that the air in which combustibles had been burnt, was afterwards unfit for the support of flame, and equally so for the breathing of animals. He ascribed this change which the air had suffered to its combination with the phlogiston which had separated from the burning body during the process of combustion. He considered air as necessary to combustion, because having a strong affinity for phlogiston, it attracted it during the process, and combined with it; and by this combination the air was contaminated and rendered unfit for further combustion, or for animal respiration. But still the difficulty remained to account for the heat and light which are extricated during this process.

"According to Dr Crawford, the caloric and light which appear during combustion, exist in the air in which the body is burnt; and during the process the phlogiston combines with the air, from which at the same time the light and caloric are separated.

"Soon after Mr Kirwan proposed another opinion, phlogiston which was pretty generally adopted by chemical philosophers. According to this opinion, hydrogen and oxygen are the same; that it exists as a constituent part in all combustibles, separating from them during combustion, and combining with the oxygen of the air.

"In the year 1777, Scheele published a work, Scheele's which was entitled Chemical Experiments on Air and Hypothesis. Heat, according to him, consists of a certain quantity..." quantity of oxygen united with phlogiston. Radiant heat, which moves in straight lines, is composed of oxygen combined with a greater proportion of phlogiston; and light, of oxygen combined with a still greater quantity.

7. But the labours and discoveries of the French chemists gave a new turn to chemical science. The unfortunate Lavoisier, who had devoted his time and his fortune to chemical pursuits, had long directed his attention to the phenomena of combustion, and after an extensive series of experiments, distinguished for their accuracy and precision, he established the general law, that oxygen combines with the burning body in all cases of combustion; and thus, he was enabled satisfactorily to account for the phenomena of combustion without phlogiston, the existence of which had never been proved.

8. The principles of this theory are the following. No combustion can take place without the presence of oxygen, for it is the combination of the combustible body with oxygen. The oxygen of the atmosphere, which is in the state of an elastic fluid, exists in combination with caloric and light; and during the combustion, that is, the combination of the oxygen with the combustible body, the caloric and light are separated.

9. This theory accounts for the phenomena of combustion in the more limited acceptation of this term, some of which is merely the combination of oxygen with a combustible body, without any extrication of caloric and light. Thus, oxygen combines with some metallic substances and other bodies, without any perceptible emission of light or heat. This is called oxidation, and the product of this combination is denominated an oxide. In all cases of combustion oxygen combines with the combustible body. Indeed this is so essential that no combustion can take place without it; but in the more extensive signification of the term combustion, it is understood, not merely to mean the combination of oxygen with the combustible body, but also to be accompanied with the extrication of heat and light. According to the theory of Lavoisier, the caloric and light which appear during combustion, are given out by the oxygen gas. It is the separation of that quantity of caloric which is necessary to retain the base of this gas, or oxygen, in the form of an elastic fluid. When, therefore, the temperature of a body is sufficiently raised, the affinity between oxygen and this body becomes greater than that which exists between the oxygen, and the caloric and light. The oxygen therefore combines with the combustible body, and the caloric and light are separated.

This theory is applicable to the explanation of the phenomena of combustion, in the more limited meaning of that term; and it is partially applicable to explain the phenomena in its more extensive meaning. But when it is considered, that the process of combustion goes on between two solids, one of which contains oxygen in its combination, as, for instance, sulphur and nitre, difficulties arise in accounting for the heat and light, when the oxygen which combines with the combustible body, is in the solid state.

To remove these difficulties, and to explain the appearances, the theory of Lavoisier has been greatly modified, or new theories proposed.

10. With this view a theory has been proposed by Brugnatelli. This theory supposes that oxygen exists in combination with bodies, in two states. In the one state it is entirely deprived of its caloric and light, and in the other, it retains great part of the caloric and light, even in its combined, concrete state. It is simply called oxygen in the first case, when it is deprived of its caloric and light; in the latter it is denominated thermoxigen, when the caloric and light are combined with it in the concrete state. Thermoxigen, then, is a compound of oxygen and caloric in the concrete state. This caloric is different from that which holds the thermoxigen in the state of gas, and it is in the same relation to thermoxigen gas, as water is to crystallized salts. This thermoxigen only enters into the composition of acids, when it is deprived of its concrete caloric. But it combines with the metals in the state of thermoxigen; that is, united with the concrete part of caloric. Metallic substances, therefore, are denominated thermoxider.

In its union with metals, thermoxigen is either previously formed, or is in its nascent state, during the combination. In the latter case, the caloric which is disengaged by the chemical action, or that which is applied to assist the combination, furnishes the necessary portion for the formation of the thermoxide; that is, the combination of oxygen containing caloric in its concrete state, with a metal. Thus it is, that some metals require the application of heat for their solution in concentrated acids.

The base of pure air is in the state of thermoxigen, in its combination with water. The metals, therefore, which have a stronger affinity for it than for hydrogen, the other component part of water, readily combine with it, without the aid of external heat, in acids diluted with this fluid. Gaseous thermoxigen always gives out caloric, when it passes from the elastic to the concrete state; but as thermoxigen requires little caloric for its expansion, little is separated when it is condensed. We shall only add the author's explanation of the difference between atmospheric air and those substances which have the same constituent parts in different proportion. The difference between atmospheric air and nitrous gas, he supposes, is ascribed to the proportion of the constituent principles, and consequently, according to this hypothesis, the atmospheric air might be converted into nitrous gas, by augmenting the proportion of oxygen gas, or by diminishing that of the azotic gas. But the difference between these two gases, according to the theory of Brugnatelli, consists in this, that in atmospheric air the azotic gas is combined with thermoxigen gas; but in nitrous gas, the azotic gas is combined with simple oxygen.

11. This theory, notwithstanding its ingenuity, is regarded by some merely as a plausible hypothesis, which is little supported by facts. We shall therefore hope to leave it to the consideration of our readers, and proceed to state the principles of another, which is proposed to be substituted in place of the Lavoisierian theory, in explaining the phenomena of combustion. In this theory, it is supposed that the oxygen gas which is absorbed during combustion, furnishes the caloric, while the combustible body gives out the light which previously existed in it as a component part. In proof of of this theory it is stated, that some bodies give out, during combustion, a greater quantity of light than others, even where the quantity of oxygen absorbed is less; that the colour of this light varies according to the nature of the combustible; and that vegetables which grow in the dark contain no combustible matter, being deprived of the light which is essentially necessary for its formation. This theory, which Gren calls the theory of fire and combustion, is distinctly detailed by him in the following words:

"I take here the word fire in the usual sense of common language, and understand by it that light which is combined with free caloric. Combustion is the extraction of fire with and by the decomposition of oxygen gas. Take the example of phosphorus. On its combustion two new products, the phosphoric acid and fire, arise from phosphorus and oxygen gas.

"In order that the theory of combustion be admissible, it must explain every circumstance by which this phenomenon is accompanied, and be in contradiction with none of them. It, besides, must not be inconsistent with any other fixed invariable law of nature.

"According to the antiphlogistic system, a combustible body is such as is possessed of the power of attracting, in a certain temperature, the oxygen of vital air more strongly than it is attracted by the caloric. Besides, in that system, oxygen gas does not merely consist of oxygen and caloric, but it likewise contains light, in a fixed state, as a constituent part.

"If, therefore, phosphorus, at the temperature requisite to its inflammation, be brought into oxygen gas, it robs the latter of its oxygen, and makes with it phosphoric acid; whilst the caloric and the basis, or matter of light, previously latent in the gas, are restored to liberty; and, combining together, produce the fire which flies off. Thus the oxygen gas is decomposed.

"A new body, the phosphoric acid, is now generated; and, because in many cases an acid is produced by the combustion of inflammable matters, this circumstance has induced modern chemists to denote the basis of vital air by the words acidifying principle, or oxygen; not on the ground that it is supposed to be four of itself, but because it forms an acid only when combined with an acidifiable basis, as in our experiment with phosphorus. And it is on this account that, in this system, combustion has likewise received the name of oxygenation. But in the case (very often occurring) where the combustible matter imbites oxygen, yet without becoming thereby an acid, the product is called oxide (also denominated half-acid), and the process termed oxidation.

"Since the combustible substance takes up the ponderable basis of oxygen gas, and hence, according to this system, both the caloric and light are imponderable, it is thereby accounted for, why the residue of an burnt matters, the phosphoric acid, for instance, acquires an increase of weight equal to that portion of vital air which was decomposed.—If the inflammable substance be saturated with oxygen, it is rendered incapable of decomposing more oxygen gas, and the combustion is ended.

"When the combustion is performed in atmospheric air, it is then the azotic, either mingled or mixed with the oxygen gas, that prevents these phenomena from going on with the same vivacity as in pure oxygen gas; and likewise, as the azotic gas is not affected or acted on by the inflammable body, it is left as the residue of the atmospheric air.

"Hence, by that system, the combustion of phosphorus in oxygen gas is effected by a simple affinity, a case of the principle of fire is not in the combustible body, but in the oxygen gas.

"However, from what I have stated of the composition of light, I cannot help thinking, that in combustion a double affinity takes place; and to explain this by double theory I shall select the example of phosphorus. That substance consists of the basis of light, called by me phlogiston, and making a constituent part of all combustible bodies united to a peculiar body, the phosphoric-radical.—Oxygen gas is a compound of oxygen and caloric.

"Now, when phosphorus is heated in this gas, and by this means the force of attraction between the phlogiston and the phosphoric-radical is sufficiently weakened, so that the attractive power between the radical of phosphorus and the oxygen may prevail, then the act of combustion ensues. The phosphoric basis attracts the oxygen, while the phlogiston of the phosphorus is attracted by the caloric of the oxygen gas. Thus, by virtue of this double affinity, two new compounds, the phosphoric acid and fire, arise from the two former combinations, phosphorus and oxygen gas.

"When the radical of phosphorus, and in general of any combustible body, has absorbed too much oxygen, that it is saturated with it, the combustion is arrived at its highest degree; and in the same manner it is ended, at the moment when all the quantity of oxygen gas, capable of being decomposed, is exhausted. By this it is explained, why, in a given volume of oxygen gas, only a certain quantity of phosphorus, and in general of every other combustible matter, can be consumed by fire.

"The increase of weight in the residue of the burnt substance is, in this phlogistic, or rather eclectic system, likewise explained by the excess of oxygen; and the caloric and basis of light are likewise supposed to be both imponderable. The remaining azotic gas, not being acted upon by the combustible matter, is merely the residue of the atmospheric air.

"Those that wish to be impartial, must allow that the light, in the antiphlogistic system, acts a part quite out with-superfluous; that it may be thoroughly set aside without oxygen, without impairing the system; that by this system those phenomena cannot be explained, where light issues from combustible bodies without any access of vital air, (some instances of which will hereafter be given (z)); that the influence of light upon the growth and thriving of plants, upon the changes of their mixture during..." ing vegetation, and upon the alteration in the mixture of many other bodies, is by far too great, to allow oxygen gas to be considered as its only reservoir. Finally, it must be granted (an important point) that the antiphlogistic system does in no way explain the incidents preliminary to the process of combustion; and that it affords no argument to show why a certain degree of heat is necessary, in order that the combustible body be inflamed.*

11. Such then are the general facts with regard to combustion, and such are the theories which have been proposed, to account for the phenomena exhibited in this process. Three states or modifications have been distinguished in the act of combustion, namely, ignition, inflammation, and detonation.

a. Ignition, properly speaking, is rather a preliminary step, than a part of the process of combustion itself. A metallic substance, for instance, may become red hot when exposed to a certain temperature; but when it is cooled, it returns without change to its former state. In this case caloric and light are given out, but the body undergoes no farther change. There is no absorption of oxygen, which is one of the ordinary phenomena of combustion. But, with an increase of temperature, this also is effected, and the whole phenomena of combustion are exhibited; namely, the union of oxygen with the combustible body, and the emission of light and heat.

b. The second state or modification of combustion is called inflammation. This depends on the nature of the combustible body, owing partly to its strong affinity for oxygen, and partly to the slight affinity which exists between the particles of the combustible body. We have examples of this in the burning of sulphur or phosphorus, or a candle in the open air, or in oxygen gas.

c. Detonation is another modification of combustion. It is a rapid and instantaneous inflammation, accompanied with explosion. This arises from the sudden formation of a vacuum, by the change of elastic fluids into the liquid state, or by the sudden evolution of elastic fluids from the solid state. Of the first we have an instance in the composition of water by the inflammation of oxygen and hydrogen gases, which is attended with a violent explosion, great condensation, and the extrication of light and heat. Of the evolution of elastic fluids from solid bodies, we have a good instance in common gunpowder, from which an immense volume of elastic vapour is instantaneously extricated, which, by its expansive force being suddenly exerted, produces the explosion, and the irresistible effects of this powerful agent.

12. All inflammable substances, Dr Black observes, are changed, during combustion, into one or more principles. From the combustion of some substances, as sulphur and phosphorus, an acid is obtained. From the combustion of others, as hydrogen with oxygen, water is the product; and in the case of metals, they are reduced to the state of oxide; or calx, as it was formerly called. After the combustible substance has been subjected to the process of combustion, it is totally changed in its properties, and it can no longer exhibit the phenomena of combustion.

Such then are the general properties and effects of light and heat, two of the most powerful agents, and of the most extensive influence, in all the changes and combinations which take place among bodies, by chemical action. In many properties they resemble each other, but are totally different from all other kinds of matter. These bodies, possessed of a repulsive power among the particles of each other, are attracted by other bodies, and combine with them; and these combinations produce the most astonishing effects, giving new forms to matter, and inducing innumerable changes, which may be considered as constituting the principle and essence of some of the most sublime operations of nature, and many of the most important processes of art.

Connected with light and heat in many of their obvious properties, and also in many of the changes which they produce upon bodies, are electricity and galvanism; and with electricity at least, if not also with galvanism, the magnetic power possesses some common properties; and especially if some of these are to be considered, as some have supposed, only as modifications of the same substances which we have treated of, the discussion of these subjects would be properly introduced here; but, according to the nature and arrangement of this work, each will be fully detailed under its proper head. See ELECTRICITY, GALVANISM, and MAGNETISM.

CHAP. IV. OF OXYGEN, AND OXYGEN GAS,

1. Oxygen gas, or its base, oxygen, is one of the most important agents in the chemical phenomena of importance, or in the processes of art. There is indeed scarcely a single process in which this substance has not some share. Its nature and properties, therefore, ought to be early known.

Oxygen gas is one of the discoveries of modern chemistry. It was discovered by Dr Priestley in the year of our Lord 1774, and from him it received the name of dephlogisticated air. It was afterwards denominated highly respirable air. From Scheele, who discovered it in 1775, it received the name of empyreal air. It was called vital air by Condorcet; and Lavoisier gave it the name of oxygen gas, by which it has since been generally distinguished.

2. Oxygen gas is most easily obtained by the following process: a. Take a quantity of the substance called manganese; introduce it into the iron bottle A, fig. 3, to the neck of which apply the bent tube B, which is made to fit it exactly, and unite them together at the joining CD (A). The bottle, thus prepared, is to be exposed

(a) The tube which answers this purpose sufficiently well, is composed of pipe clay and linseed oil well beaten together, and reduced to the consistence of glaziers putty. This is neatly applied to the joining, and if allowed to remain for eight or ten hours before it is exposed to the heat, it will afterwards bear the highest temperature. exposed to the heat of a furnace, or to that of an open fire. As soon as the heat is applied, the atmospheric air within the bottle is driven off; and, as the bottle becomes red hot, the quantity of air which passes over, is greatly increased. Let the end of the tube connected with the bottle be introduced under the shelf in the pneumatic trough, and the bubbles of air will pass through the water, and may be received in jars filled with water, and inverted over the opening in the shelf.

b. Oxygen gas may also be obtained by treating what is called in chemistry the red oxide of mercury, in a similar manner.

c. This gas may be also readily procured by introducing into a glass retort, a quantity of the same substance (manganese) reduced to powder, adding an equal weight of sulphuric acid, and applying a moderate heat.

d. Or it may be obtained from the substance called niter or saltpetre, exposed to a red heat, in an earthen or coated glass retort.

3. In all these methods of obtaining this gas, it is unnecessary to mention, that it must be received in the pneumatic apparatus, in the same way as has been directed for procuring it from the manganese, exposed to heat in the iron vessel; and in whatever way it is obtained, the chemical change which takes place in these processes, is thus explained. Oxygen gas consists of two ingredients, the one, which is called its base, and the other caloric, or the matter of heat. In the manganese, this base is supposed to be combined with the metallic substance; and when this substance is exposed to a sufficient temperature, the oxygen, having a greater attraction for caloric than for the metal, combines with it, and passes off in the state of gas. The same change takes place, when the process for obtaining the gas, by means of the red oxide of mercury, is employed. When the sulphuric acid, which is in the state of liquid, is added to the manganese, it combines with it, and becomes solid. But no liquid substance can become solid, without being deprived of the caloric necessary to retain it in the state of fluidity. The caloric which retained the sulphuric acid in the liquid state, combines with the oxygen of the manganese, affirms the fluid or gaseous form, and makes it escape. This is an example of double affinity. The sulphuric acid unites with the manganese, and forms a solid; while the caloric combines with the base of oxygen, and appears in the form of oxygen gas.

4. Oxygen gas, thus obtained, possesses many of the properties of common air. It is colourless, invisible, elastic, and may be indefinitely expanded or compressed.

Oxygen gas possesses neither taste nor smell; its specific gravity, according to Mr. Kirwan, is to that of water as 0.00135 to 1.0000. Being therefore 740 times lighter than its bulk of water, its weight to atmospherical air is in the proportion of 1193 to 1000; or 100 cubic inches of oxygen gas weigh 34 grs., while the same measure of atmospherical air weighs only 31 grs., the temperature being 60°, and the barometer being at 30 inches. According to Mr. Davy's experiments, 100 cubic inches of oxygen gas weigh 35.05 grs.

Water does not sensibly absorb oxygen gas. But by means of strong pressure, it may be made to combine with, and to retain in solution, half its bulk of the gas. The water thus impregnated, is not sensibly different from common water in taste or smell, but it is said to have proved an useful remedy in some diseases.

Combustible substances burn with greater brilliancy and rapidity in oxygen gas than in common air. Indeed, it is owing to a certain quantity of the former, that the process of combustion goes on in the latter, and when the oxygen gas is exhausted, the process is interrupted. If a jar or phial is filled with this gas, and a lighted candle introduced into it, it burns with greater splendour, and produces a greater degree of heat, than in a similar vessel filled with common air. If the candle be blown out, and while the snuff is red hot, it is introduced into a vessel filled with oxygen gas, it re-kindles with a slight explosion, and burns with the same splendour. A candle in a vessel filled with oxygen gas burns much longer than in the same quantity of atmospherical air.

Oxygen gas is essentially necessary for respiration. No animals breathing animal can live in any air which does not contain some proportion of oxygen gas. And the experiments of Dr. Priestley and others prove, that animals live a much longer time in oxygen gas than in an equal bulk of atmospherical air. The experiments of Count Morozzo fully establish this fact. Into a vessel filled with common air, and inverted over water, he introduced a number of sparrows, and observed the effects. The following are the results of his experiments:

| Sparrow | Time (minutes) | |---------|---------------| | First | 3 | | Second | 3 | | Third | 1 |

The experiments were repeated by filling the same vessel with oxygen gas, and he obtained the following results:

| Sparrow | Time (minutes) | |---------|---------------| | First | 23 | | Second | 10 | | Third | 30 | | Fourth | 10 | | Fifth | 30 | | Sixth | 47 | | Seventh | 27 | | Eighth | 30 | | Ninth | 22 | | Tenth | 21 |

Two sparrows were then put together; the one lived for an hour, but the other died in about 20 minutes.

5. Oxygen combines with a great number of bodies, and forms compounds with them. It is always present in combination. In examining with its properties, it is always as a compound; and therefore, its properties are only cognizable to our senses in that state.

When oxygen combines with metallic substances, they acquire new properties, and this combination in chemical language is denominated an oxide. Combined with many other substances, the nature of the substance is also changed, and the compound exhibits new properties. One of the most remarkable of these is the taste of the compound substance, which is often sour or acid; and because this circumstance was observed to be one of the most frequent and most remarkable... markable which attend its combinations, the name of oxygen, or acidifying, was invented by Lavoisier. Oxygen gas is also necessary for the germination of the seeds of plants; but as the processes of vegetation advances, it is given out in great abundance by the leaves during the day. By this means the great waste of oxygen gas in the processes of combustion and respiration is fully repaired, and the balance between its consumption and supply is preserved.

6. The following is the order of its affinity for the substances with which it enters into combination.

OXYGEN— Charcoal, Titanium, Manganese, Zinc, Iron, Tin, Uranium, Molybdena, Tungsten, Cobalt, Antimony, Hydrogen, Phosphorus, Sulphur, Azote, Nickel, Arsenic, Chromium, Bismuth, Lead, Copper, Tellurium, Platina, Mercury, Silver, Oxide of arsenic, Nitrous gas, Gold, Muriatic acid, White oxide of manganese, White oxide of lead.

CHAP. V. OF AZOTIC GAS.

1. Azotic gas was examined by Mr Scheele, the celebrated Swedish chemist, in 1776; and his experiments proved, that it is a fluid possessed of peculiar properties. It seems, however, to have been known to Dr Rutherford of Edinburgh, as early as the year 1772, as appears from his thesis published in that year, in which he speaks of the effects of combustion and respiration on the atmosphere.

2. There are various methods by which this gas may be obtained. a. The process recommended by Berthollet is the following: Take a quantity of muscular flesh, or the fibrous part of the blood, which has been well washed. Cut the flesh into small bits; introduce it into a retort, or a matrix to which a ground tube has been adapted. Pour over it diluted nitric acid, expose it to a heat of about 100°, and place the beak of the retort or the end of the tube in the pneumatic apparatus, that the gas which comes over may be received in proper vessels. The gas thus obtained, is azotic gas. b. If sulphuric or potash be exposed to the air of the atmosphere, inclosed in a bell-glass, over water; or, if sulphuric iron be formed into a paste with water, and treated in the same way, and allowed to remain for some days, the quantity of air within the glass is greatly diminished, in consequence of part having been absorbed; and what remains is azotic gas. c. When the air of the atmosphere is inclosed in the same way, and exposed to the action of phosphorus, it also suffers diminution, part being absorbed. Azotic gas only remains.

3. Azotic gas, like common air, is invisible and elastic, and may be indefinitely condensed and dilated. Its specific gravity is less than that of atmospheric air. It is estimated by Mr Kirwan at 0.00120, which is in the proportion of 985 to 1000; but according to Lavoisier's experiments, it is to atmospheric air as 942.6 to 1000, which makes its specific gravity only 0.00115.

This gas is unfit for combustion. If into a jar or phial, filled with azotic gas, a lighted candle be introduced, it is immediately extinguished.

This gas is also extremely noxious to animals, and is therefore totally unfit for respiration.

4. No attempts which have yet been made, have succeeded in decomposing azote, or the base of azotic gas. It must therefore be admitted among the number of simple substances. It has never been obtained in a separate state. It is therefore when it is combined with caloric, that is, in a gaseous state, that we are acquainted with its properties; and from its being unfit for respiration, it derived its name. Some chemists have indeed considered it as a compound substance. Dr Priestley supposed that it consisted of phlogiston and oxygen gas. On this account he called it phlogisticated air. According to the Stahlian theory, the process of combustion is the separation of phlogiston from the burning body. Oxygen gas, having a strong affinity for phlogiston, combines with it during the combustion, and is even supposed to contribute to the separation of the phlogiston, by its affinity for it. And when this air is saturated with phlogiston, the process of combustion is at an end. The air that remains after this process is azotic gas. This theory, when first announced by Dr Priestley, was pretty generally received; but future experiments soon demonstrated, that the quantity of air in which a combustible body was burnt, diminished both in bulk and in weight; and therefore proved that the air, instead of receiving any addition, was on the contrary deprived of something.

Achard, about the year 1784, concluded, from some experiments which he had made, that azotic gas consists of water and fire. This theory has been supported by Wetzlumb, and more lately by Wiegleb. According to the experiments on which these chemists rest the truth of their theory, azotic gas is always the result when steam is made to pass through red-hot earthen, or even metallic tubes; but a series of very accurate experiments, instituted by the associated Dutch chemists, clearly proved that no azotic gas was produced, when the instruments employed were impenetrable by air*. Dr Priestley had long before shown, that in similar experiments, when he employed earthenware retorts, containing moist clay, and exposed them... to a temperature above boiling heat; instead of vapour issuing from the beak of the retort, a quantity of air, which was nearly equal in weight to the quantity of water introduced, passed over. The conclusion which he drew from these experiments, was, that the water was converted into air; for he found that it possessed nearly the same properties as common air. But he proved afterwards by more accurate experiments, that water had made its way through the pores of the vessels, and that its place was supplied by the external air which was forced in by the pressure of the atmosphere. For it was clearly ascertained by the experiments of the Dutch chemists, that no gas was obtained, while perfectly sound glass or metallic tubes were employed.

Another theory has been proposed, of the composition of azotic gas, by Girtanner*. He supposes that azotic gas consists of hydrogen and oxygen gas, having a smaller proportion of oxygen gas than what enters into the composition of water†. But the experiments of other chemists, as those of Berthollet and Bouillon Lagrange, have afforded no such results (§).

5. There is no perceptible action between light and azotic gas. Combined with caloric, we have already seen it may be indefinitely expanded, but without undergoing any change in its properties.

Azotic gas, from its being found in such abundance in the air of the atmosphere, no doubt acts some important part in the economy of nature. It is given out, or seems to be given out, in great quantity, during the decomposition of animal and vegetable matters; but during these processes, it is the oxygen of the atmospheric air which is absorbed, and thus the residuary air is azotic gas. The base of azotic gas is unknown, and chemists are still unacquainted with its affinities.

Azotic gas combines with oxygen in different proportions, and forms compounds very different in their nature and properties. In one proportion it constitutes the air of the atmosphere; in another, what is called nitrous oxide, and in a third, nitrous gas. These we shall examine in their order in the following sections.

**Sect. I. Of Atmospheric Air.**

1. The air of the atmosphere is composed of azotic and oxygen gases. This is an invisible elastic fluid, which may be indefinitely compressed and dilated. The specific gravity of atmospheric air is 0.0012, or about 816 times lighter than water. This is to be understood when the temperature is between 50° and 65°, and when the barometer is at 30 inches. The pressure of the air of the atmosphere is nearly equal to 15 lb. on every square inch.

2. Till the discoveries of modern chemistry, atmospheric air was considered one of the four simple elementary substances, of which all bodies are composed. But the experiments and researches of Priestley and of Scheele fully demonstrated the existence of two separate substances, totally differing from each other in their natures and properties. Oxygen gas, one of the component parts of atmospheric air, was, according to Dr. Priestley, completely freed from phlogiston; and hence he calls it dephlogisticated air, which was in an eminent degree, fit for respiration and combustion; but azotic gas, the other component part, was supposed to be saturated with phlogiston, and therefore unfit, as it was found to be, for these purposes. To the latter, the azotic gas, Scheele gave the name of foul air.

3. According to the experiments of Lavoisier, the proportions of the two gases which exist in atmospheric air, are 73 parts of azotic gas, and 27 of oxygen gas. But according to later experiments the proportions are found to be 78 of azotic gas, and 22 of oxygen gas by bulk; or by weight, 74 of azotic and 26 of oxygen gas.

The proportions of these two gases in atmospheric air are uniform and constant. They have been found to be nearly the same in all parts of the world, and in all seasons of the year, where experiments have been made.

4. A question has arisen among philosophers concerning the constitution of the atmosphere, whether its component parts are to be considered merely as a mechanical mixture, or as a chemical combination. To the latter opinion the greater number of chemists are inclined, from the constancy of the proportions of the component parts of the atmosphere, these parts always being found in the same proportion at all heights, and never separating according to their specific gravities; and from its possessing distinct properties; and from its continuing the same, whatever processes are carried on in it, or whatever proportions of oxygen may be absorbed during these processes.

A contrary opinion has been adopted by Mr. Dalton, who has endeavoured to establish by some very acute mathematical reasoning. According to this ingenious hypothesis, the elastic fluids which exist in the atmosphere have no mutual action whatever. The particles of one fluid are only attracted and repelled by each other, but are not acted upon by the particles of another fluid. The particles of the different fluids, with regard to each other, are subjected to the laws of inelastic bodies*.

**Sect. II. Of Nitrous Oxide Gas.**

1. This gas is most readily obtained by decomposing nitrate of ammonia, a salt composed of nitric acid and obtaining ammonia, the properties of which will be afterwards particularly detailed. The crystals of this salt are put into a retort, and exposed to a temperature between 340° and 350°. It very soon melts after the heat is applied, and a great quantity of gas is emitted, at first in the form of white fumes, but afterwards transparent and colourless. This may be received in jars over water in the usual way. This is the nitrous oxide gas, the gaseous oxide of azote, or, as it has been called by some, from the pleasurable sensations it excites on being respired, the gas of paradise. The first part of the gas which comes over is not quite so pure as when it is given out slowly, and when it is transparent. When therefore it is respired, care should be taken to separate what comes off first, from the rest. This gas, as is obvious from the process, is obtained by the decomposition of the nitrate of ammonia; but the change which

(b) The component parts of water are oxygen and hydrogen, as we shall find afterwards. Azotic Gas, which takes place will be better understood, when we come to treat of the salt itself, being previously acquainted with its constituent parts.

2. This gas was called by Dr Priestley dephlogisticated nitrous gas; and it was discovered by him in the year 1776. Its component parts were ascertained by the associated Dutch chemists; but its nature and properties were more fully and precisely investigated by Mr Davy.

3. In its physical properties, this gas resembles common air. It is elastic, transparent, and colourless. The specific gravity, as it has been estimated by Mr Davy, is 0.9997. One hundred cubic inches of it weigh 50.20 grs. The component parts of nitrous oxide gas are 63% of azote, and 37% of oxygen gas.

Some combustibles burn in this gas nearly as well as in oxygen gas, but with this difference, that they must be in a state of ignition.

Pyrophorus, which spontaneously inflames so low as the temperature of 40° in atmospheric air, will not burn in nitrous oxide gas, till it is raised to a temperature above 212°. A burning taper introduced into pure nitrous oxide gas, burns at first with a brilliant white light, and sparkles as in oxygen gas; but as the combustion goes on, the flame gradually lengthens, and is surrounded with a pale blue light. Phosphorus burns in it with a brilliancy not much inferior to its combustion in oxygen gas.

4. It was at first supposed that this gas is unfit for respiration, but the experiments of Mr Davy have shown the contrary; and the singular effects which it produces on the animal frame have excited much interest. From these experiments, and from many others which have been since repeated, it appears that it may be respired for some minutes without injury. In some cases it produces no effect whatever; but, in general, the sensations it excites are similar to those of intoxication; but they are rarely followed by its unpleasant effects. Mr Davy describes his own feelings when he respired this gas, in the following words:

"Having previously closed my nostrils and exhausted my lungs, I breathed four quarts of nitrous oxide from and into a silk bag. The first feelings were giddiness, sense of fullness of the head, and indistinct sensation; but in less than half a minute, the respiration being continued, they diminished gradually, and were succeeded by a sensation analogous to gentle pressure on all the muscles, attended by a highly pleasurable thrilling, particularly in the chest and the extremities. The objects around me became dazzling, and my hearing more acute. Towards the last inspirations, the thrilling increased, the sense of muscular power became greater, and at last an irresistible propensity to action was indulged in; I recollect but indistinctly what followed; I know that my motions were various and violent.

These effects very soon ceased after respiration. In ten minutes I had recovered my natural state of mind. The thrilling in the extremities continued longer than the other sensations.

This experiment was made in the morning; no languor or exhaustion was consequent, my feelings throughout the day were as usual, and I passed the night in undisturbed repose."

But although it may be respired for a short time with impunity, not more than 3 or 4 minutes, yet animals that are confined in it soon become restless and uneasy, and at last expire. From this therefore it appears that it is unfit for the support of animal life, and perhaps could not at all be respired, if the lungs were previously exhausted of atmospheric air.

5. The taste of nitrous oxide gas, when in a state of taste and purity, is distinctly sweet to the tongue and palate; and, in fact, it has an agreeable odour. Mr Davy observes, that he often thought it produced a feeling somewhat analogous, as he expresses it, to taste, in its application to the lungs; for in one or two experiments he perceived a distinct sense of warmth in the chest.

6. Water absorbs nitrous oxide gas in considerable proportion. When the water is agitated, 0.54 parts by weight of its bulk, or 0.27 of its weight, combine with it. The water becomes sweetish, and the whole of the gas may be expelled from it unchanged, by boiling.

7. No change takes place upon this gas by the action of light, but when it is exposed to a high temperature, as when the electric spark is sent through it, or when it is made to pass through a red-hot porcelain tube, it is decomposed, and converted into common air and nitric acid.

Sect. III. Of Nitrous Gas.

1. If a quantity of pure copper filings be put into a Howden's retort, and diluted nitric acid be poured over them, a violent effervescence takes place, and a great quantity of gas is evolved. This is nitrous gas. It may be obtained also, by substituting for the copper other metals, as iron, silver, and mercury.

This gas is mentioned by Dr Hales, but it is to the labours of Dr Priestley that we are indebted for the knowledge of its nature and properties.

2. This gas is an elastic, colourless fluid, which has no sensible taste, and does not redden the tincture of turmeric (c).

According to Mr Kirwan, the specific gravity of nitrous gas is 0.99948, but by Mr Davy's estimation it is 0.999343. The weight of 100 cubic inches of it is 34.26 grs. and it is composed of 55.95 oxygen, and 44.05 azote. This gas is totally unfit for respiration. Animals that breathe it are instantly suffocated.

Some combustibles burn in this gas. Phosphorus, when introduced into it in a state of active inflammation, burns with almost as much vividness as in oxygen gas. Homberg's pyrophorus, a substance which takes fire when exposed to the air, when introduced into this gas, instantly becomes red, and burns very vividly. In this experiment, and in the former with the phosphorus, these substances combine with the oxygen of the nitrous gas, while heat and light are emitted and azotic gas is left behind.

3. Nitrous gas, when exposed to the action of heat, by being made to pass through a red-hot porcelain tube, undergoes

(c) This is a test for acid substances, which will be mentioned particularly afterwards. Chemistry.

It is absorbed by water. When the water is freed from air, it absorbs about \( \frac{1}{4} \) of its bulk of nitrous gas, at the common temperature, and when it is boiled or frozen, the gas separates unchanged. The water thus impregnated with nitrous gas, has no peculiar taste, nor does it alter the colour of vegetable blues.

4. When a quantity of atmospherical air is introduced into a jar containing nitrous gas, a red colour appears from the mixture of the two gases; they are diminished in bulk, and heat is evolved. The product is nitrous acid. If oxygen gas be employed in place of atmospheric air, the whole of the two gases will be converted into a liquid. The diminution of bulk is owing to the condensation of the elastic fluids, and the evolution of caloric must be ascribed to the change of state, from that of elastic fluid to that of liquid.

Azotic gas also enters into combination with oxygen in a different proportion from what has been stated above, forming nitrous and nitric acids; but these will come more properly to be treated of among the class of acids.

The following table exhibits at one view the different proportions of oxygen and azotic gases in the compounds formed by these two substances:

| 100 cubic inches | Weight in grains | In 100 grains Proportions of | |------------------|-----------------|----------------------------| | Atmospheric air | 31.10 | 73.00 | | Nitrous oxide | 50.20 | 63.30 | | Nitrous gas | 34.26 | 44.05 | | Nitric acid | 76.00 | 29.50 |

Chap. VI. Of Hydrogen Gas.

1. This gas has been long known under the name of the fire-damp of the miners. Its combustible property is described in the works of Boyle and Hales, of Boerhaave, and of Stahl; but it was not till the year 1766 that its properties were particularly ascertained, and the difference between it and atmospheric air pointed out by Mr Cavendish. Its properties and combinations were more fully investigated by Priestley and Scheele, Senebier and Volta, under the name of inflammable gas or air. It is now distinguished by the name of hydrogen gas, and its base by that of hydrogen.

Like the two former, oxygen and azote, it is never obtained in an uncombined state. Its properties can only be examined in a state of gas.

2. Hydrogen gas may be obtained in a state of tolerable purity by the following process. Take one part of clean iron filings, and introduce them into a tubulated retort, and add two parts of sulphuric acid previously diluted with four times its bulk of water. A violent effervescence immediately takes place, and great abundance of air bubbles make their escape. Put in the stopper of the retort, and place the beak of it under the shelf in the pneumatic trough, and let the gas which comes over be received in proper vessels. The gas which is thus obtained, is hydrogen gas, which is distinguished by the following properties.

3. In its physical properties it resembles common air. Hydrogen gas is invisible and elastic, and may be indefinitely compressed and expanded.

Its specific gravity has been variously estimated, owing, perhaps, to its different degrees of purity. According to Lavoisier, it is 0.000094, which is nearly 12 times lighter than atmospherical air; but, according to Mr Kirwan, it is 0.00010.

Hydrogen gas is unfit for supporting combustion. If a lighted candle be suddenly plunged in a vessel filled with hydrogen gas, it is immediately extinguished; or if an inverted jar filled with hydrogen gas be suddenly brought over a lighted candle, it is extinguished in the same way. The latter experiment is the most effectual, on account of the small specific gravity of the hydrogen gas, which is prevented from escaping by rising upwards when the jar is inverted.

It is also unfit for respiration.

When small animals are enclosed in a vessel filled with this gas, they are soon thrown into convulsions, and expire. Scheele, however, who first made the attempt, breathed it several times without much injury. Fontana made the same experiment, and he supposed that this was owing to the common air in the lungs before respiration of the hydrogen gas; for when he made a full expiration, before he began to breathe the hydrogen gas, he could only inspire it three times, and these three produced great languor and oppression about the breast. This is confirmed by Mr Davy of the royal institution, who, in some experiments on himself found, that, after having exhausted the lungs as much as possible, he could not respire this gas for half a minute. It produced uneasy feelings in the chest, momentary loss of muscular power, and sometimes a transient giddiness. From these experiments, therefore, it may be concluded, that hydrogen gas is totally incapable of supporting animal life.

4. But although hydrogen gas be unfit for the support of combustion, or for respiration, yet it is itself a highly combustible substance. If a jar be filled with hydrogen gas, and a burning taper be applied, the gas will take fire, and burn with a flame which is more or less coloured according to the purity of the gas. When the gas is in the purest state that can be obtained, it is of a white colour; but when it holds charcoal in solution, it is of a reddish colour.

5. Hydrogen gas, if other gases be entirely excluded, undergoes no change when it is kept in contact with water, nor is any part of it absorbed by the water; pressure. But when artificial pressure is employed, water is said to absorb a third part of its bulk of the gas. No perceptible change is observed in the taste of the water in dilute, thus impregnated with hydrogen gas; it is recommended by Mr Paul as beneficial in nervous disorders, vol. xv. p. 93, and in inflammatory fevers.

Hydrogen gas, on account of its being so much lighter than atmospherical air, has been employed for the purpose of filling air balloons. When perfectly pure, it is 12 or 13 times lighter than the same bulk of atmospherical air; but, in the usual way of obtaining it, the specific gravity of hydrogen gas is seven or eight times less than that of common air. See AEROSTATION.

6. If hydrogen gas and atmospherical air be mixed together, they remain unaltered; but if one part of oxy- gen gas, and two parts of hydrogen gas, be introduced into a phial, and a burning taper be applied to its mouth, the mixed gases will explode with a loud noise, and the bulk will be greatly diminished. The whole of the oxygen of the atmospheric air disappears, and the azotic gas only remains. If one part of oxygen gas and \( \frac{2}{3} \) parts of hydrogen gas be mixed together in a phial, and exploded in the same way, they both disappear. This may be proved by mixing the two gases in a jar over water or mercury, and exploding them by means of the electric spark. The gases disappear; a vacuum is consequently formed in the jar, and the water or the mercury, by the pressure of the air, is forced up. If the experiment has been made over mercury, and if the inside of the jar was previously free from moisture, drops of water will appear, which have been formed by the combination of the two gases. Water, therefore, is composed of oxygen and hydrogen gas. This is a case of true combustion. Oxygen combines with the combustible body; light and caloric are evolved, and the result of this action and combination is one of the products of combustion, namely water. The discovery of the composition of water, undoubtedly one of the most important in modern chemistry, will be the subject of the following section.

**Sect. I. Of Water.**

1. Water acts so important a part in many chemical actions and combinations, that its nature and properties should be early known. Before the discoveries of modern chemistry, it was considered as a simple substance, and one of the four elements which enter into the constitution of all bodies in nature.

The fortunate discovery of the composition of water, is undoubtedly one of the most important which has been made in chemical science. We have already mentioned, that the product of oxygen and hydrogen gases, when exploded together, is water (d): but in a subject of so much importance, it will be necessary to enter more into detail; and this we shall do, 1st, by stating the experiments on the basis of which the proofs of its composition rest; and 2dly, by giving a short historical view of the progress of the discovery.

2. Various experiments have been made to ascertain this fact; but those which were made by Lavoisier being on a larger scale, and performed with such precautions as to insure accuracy and precision, the following account of them will be the more satisfactory.

1. **Proof of the Composition of Water.**

**Exper. a.** Take a porcelain or glass tube from 8 to 12 lines diameter, and place it across the furnace EFCD, with a gentle inclination from E to F (e).

The higher extremity of the tube is then fitted to the glass retort A, containing a known quantity of distilled water. To the lower extremity F is fitted the plate worm SS, the lower end of which is fixed in the neck CXLII. of the bottle H, which bottle has the bent tube KK fixed to a second opening. This bent tube is intended to carry off any elastic fluids which may escape into the bottle H. A fire is then lighted in the furnace EFCD, sufficient to keep the tube EF red hot, but not to melt it. The water in the retort A is kept boiling by a fire in the furnace VVXX. The water is gradually changed into steam by the heat of the two furnaces. It passes through the tube EF into the worm SS, where it is condensed, and then drops into the bottle H. When the whole water is evaporated, and all the communicating vessels are emptied into the bottle H, it is found to contain exactly the same quantity which was put into the retort. This experiment therefore is a simple distillation.

**Exper. b.** Everything being disposed as in the last experiment, let 27 grains of pure charcoal, broken into small parts, and which has been exposed to a red heat in a clothe vessel, be introduced into the tube EF. The experiment is then performed in the same manner as the former. The water is evaporated, and a portion of it is again condensed in the worm SS, and then falls into the bottle H; but at the same time a considerable quantity of an elastic fluid escapes through the tube KK, which is received in vessels. When the water is entirely evaporated, and the tube examined, the 28 grains of charcoal have wholly disappeared.

When the water in the bottle H is examined, it is found to have lost 85.7 grains of its weight; and when the elastic fluid which passed off by the tube KK is weighed, it is found to weigh 113.7 grains, which is exactly the weight which the water has lost, added to the 28 grains of charcoal which had disappeared. The elastic fluid, on examination, is discovered to be of two kinds; namely, 144 cubic inches of carbonic acid gas weighing 100 grains, and 380 cubic inches of a very light gas weighing only 13.7 grains. Now 100 grains of carbonic acid gas consist of 72 grains of oxygen, combined with 28 grains of carbure. It is therefore evident, that the 28 grains of charcoal must have acquired 72 grains of oxygen from the water. It is also evident, that 85.7 grains of water are composed of 72 grains of oxygen, combined with 13.7 grains of a gas capable of being burned.

**Exper. c.** Everything being put in the same order as in the two former experiments, with this difference, that instead of the 28 grains of charcoal, 274 grains of soft iron, in thin plates rolled up spirally, are introduced into the tube EF. The tube is kept red hot while the water is evaporating from the retort.

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(d) Sir Isaac Newton having discovered in the course of his optical investigations, that combustible bodies possess the greatest refractive power in proportion to their density, and observing the great refracting power of water, conjectured with astonishing sagacity that it must contain a combustible substance. In the same way he was led to a similar conjecture with regard to the diamond; both which have been verified.

(e) The tube EF, if of glass, should be such as can bear a strong heat without melting. It should also be coated over with a lute composed of clay and powdered stone-ware; and to prevent it from bending during the experiment, it must be supported about the middle by an iron bar. After the water has been distilled, it is found to have lost 100 grains. The gas or elastic fluid weighs 15 grains, and the iron has gained 85 grains additional weight, which put together make up 100 grains, the weight which the water has lost. The iron has all the qualities which it would have received by being burned in oxygen gas. It is a true oxide (or calx) of iron. We have the same result as in the last experiment, and have therefore another proof for concluding, that 100 grains of water consist of 85 grains of oxygen, and 15 of the base of inflammable gas.

We have now exhibited two sufficient proofs, that water is composed of oxygen and hydrogen; but as the composition of water is so interesting and important a subject, M. Lavoisier was not satisfied with these proofs alone. He justly concluded, that if water be a compound of two substances, it ought to follow, that by reuniting these two substances, water would be produced. He accordingly proved the truth of this conclusion by the following experiment.

Exper. d. He took a large crystal balloon A, fig. 4, containing about 30 pints, and having a large mouth; round which was cemented the plate of copper BC, pierced with four holes, through which four tubes pass. The first tube H h is intended to exhaust the balloon of its air, by adapting it to an air pump. The second tube gg communicates with a reservoir of oxygen gas placed at MM. The third tube DD is connected with a reservoir of hydrogenous gas at NN. The fourth tube contains a metallic wire GL, having a knob at its lower extremity L, from which an electric spark is passed to D, in order to set fire to the hydrogen gas. The metallic wire is moveable in the tube, that the knob L may be either turned towards D, or away from it, as there is occasion. We must also add, that the three tubes H h, gg, DD are furnished with stopcocks.

It is necessary that the oxygen gas, before being put into the reservoir, should be completely purified from carbonic acid. This may be done by keeping it for a long time in contact with a solution of caustic potash. The hydrogen gas ought to be purified in the same manner. The quantity employed ought to be double the bulk of the oxygen gas. It is best procured from water by means of iron, as was described in Experiment Third.

Great care must also be taken to deprive the oxygen and hydrogen gas of every particle of water. For this purpose they are made to pass in their way to the balloon A, though salts which have a strong attraction for water; as the acetate of potash (a compound of vinegar and vegetable alkali), or the muriate or nitrate of lime (the muriatic or nitric acid combined with lime). These salts are disposed in the tubes MM and NN of one inch diameter, and are reduced only to a coarse powder, that they may not unite into lumps, and interrupt the passage of the gases.

Everything being thus prepared for the experiments, the balloon is exhausted of its air by the tube H h, and is filled with oxygen gas. The hydrogen gas is also pressed in through the tube DD by a weight of one or two inches of water. As soon as the hydrogen gas enters the balloon, it is set fire to by an electric spark. The combustion can be kept up as long as we please, by supplying the balloon with fresh quantities of these gases. As the combustion advances, a quantity of water is collected on the sides of the balloon, and trickles down in drops to the bottom of it. By knowing the weight of the gases consumed, and the weight of the water produced, we shall find that they are precisely equal. M. Lavoisier and M. Meunier found that it required 85 parts by weight of oxygen gas, and 15 parts of hydrogen gas, to produce 100 parts of water.

Thus we have complete proofs, both analytical and synthetical, that water is not a simple elementary substance, as it has been long supposed, but is compounded of two elements, oxygen and hydrogen.

But although the knowledge of the component parts of water was finally confirmed by Lavoisier and his friends, we shall find that science is indebted for its origin and progress, chiefly, if not entirely, to the English philosophers.

2. History of the Discovery of the Composition of Water.

1. So early as the year 1776, an experiment was made by Macquer, to ascertain what would be the product of the combustion of hydrogen gas. He accordingly set fire to a bottle full of it, and held a saucer over the flame, but no foot appeared upon it as he expected, for it remained quite clean; and was bedewed with drops which were found to be pure water. Various conjectures were now formed about the nature of the product of the combustion of oxygen and hydrogen gases. Some conjectured it would be the carbonic acid gas; by others it was conjectured it would be the sulphurous or sulphuric acid. The latter was the opinion of M. Lavoisier. Such were the experiments and opinions of the French chemists, previous to the year 1781.

2. About the beginning of that year, Mr Warltire, a lecturer in natural philosophy, had long entertained an opinion that the combustion of hydrogen gas with atmospheric air might determine the question, whether heat be a heavy body. Apprehensive of danger in making the experiment, he had for some time declined it; but was at last encouraged by Dr Priestley, and accordingly prepared an apparatus for the purpose. This was a copper vessel properly fitted, and filled with atmospheric air and hydrogen gas, which was exploded by making the electric spark pass through it. A loss of weight of two grs. was observed after the combustion. A similar experiment was repeated in close glass vessels, which, though clean and dry before the combustion, became immediately wet with moisture, and lined with a foamy matter. This foamy matter, Dr Priestley afterwards supposed, proceeded from the mercury which had been employed in filling the vessel.

3. During the same year, Mr Cavendish repeated the experiments of Mr Warltire and Dr Priestley. He performed them several times with atmospheric air and hydrogen gas, in a vessel which held 24,000 grs. of water, and he never could perceive a loss of weight more than ½ gr. and often none at all. In all these experiments, not the least foamy matter appeared in the inside of the glass. To examine the nature of the dew which appeared in the inside of the glass, he burnt 500,000 grain measures of hydrogen gas with about 2½ times that quantity of common air; and in this com- Hydrogen combustion he obtained 135 grs. of water, which had neither taste nor smell; and when it was evaporated, left no sensible sediment. It seemed to be pure water.

In another experiment, he exploded in a glass globe, 19,500 grain measures of oxygen gas, and 37,000 of hydrogen gas, by means of the electric spark. The result of the experiment was 30 grains of water, which contained a small quantity of nitric acid. The experiments of Mr Cavendish were made in the year 1781, and they are undoubtedly conclusive with regard to the composition of water.

It would appear, that Mr Watt entertained the same ideas on this subject. When he was informed by Dr Priestley of the result of these experiments, he observes; "Let us consider what obviously happens in the deflagration of hydrogen and oxygen gases. These two kinds of air unite with violence, they become red hot, and when cooling totally disappear. When the vessel is cooled, a quantity of water is found in it equal to the weight of the air employed. The water is then the only remaining product of the process; and water, light, and heat, are all the products, unless there be some other matter set free, which escapes our senses. Are we not then authorized to conclude, that water is composed of oxygen and hydrogen gases, deprived of part of their latent or elementary heat; that oxygen gas is composed of water, deprived of its hydrogen, and united to elementary heat and light; and that the latter are contained in it in a latent state, so as not to be sensible to the thermometer or to the eye. And if light be only a modification of heat, or a circumstance attending it, or a component part of the hydrogen gas, then oxygen gas is composed of water deprived of its hydrogen, and united to elementary heat."

Thus it appears that Mr Watt had a just view of the composition of water, and of the nature of the process by which its component parts pass to a liquid state from that of an elastic fluid.

Towards the end of the same year, M. Lavoisier had made some experiments, the result of which surprised him; for the product of the combustion of the oxygen and hydrogen gases, instead of being sulphuric or sulphurous acid, as he expected it, was pure water. This led him to procure an apparatus, with which the experiment might be performed on a large scale, and with more accuracy and precision. Accordingly the experiments which we have already detailed were performed on the 24th of June 1783, in presence of several academicians, and also of Sir Charles Blagden, who was at that time in Paris. A similar experiment was afterwards performed by M. Monge, with the same result; and it was repeated again by Lavoisier and Meunier, on a scale so large as to put the matter beyond a doubt. The conclusion, therefore, from the whole was (as has been stated in detailing the experiments themselves), that water is composed of oxygen and hydrogen; and this fact, we believe, since Dr Priestley's death, is universally admitted.

If farther proofs were necessary to establish the fact, we might refer the reader to an elaborate memoir on the combustion of hydrogen gas in close vessels by the celebrated chemists Fourcroy, Vauquelin, and Seguin, which was read at the academy of sciences in the year 1790.

Water exists in three different states; in the solid state or state of ice; in the liquid, and in the state of vapour or steam. Its principal properties have already been detailed, in treating of the effects of caloric. Water assumes the solid form when it is cooled down to the temperature of 32°. In this state it increases in bulk, by which it exerts a prodigious expansive force, which is owing to the new arrangement of its particles, which assume a crystalline form, the crystals crossing each other at angles of 60° or 120°. The specific gravity of ice is less than that of water.

When ice is exposed to a temperature above 32°, it absorbs caloric, which then becomes latent, and is converted into the liquid state, or that of water. At the temperature of 42°, water has reached its maximum of density. According to the experiments of Leveau Gineau, a French cubic foot of distilled water, taken at its maximum of density, is equal to 70 lb. 123 grs. French, = 298,452,9492 troy grains. An English cubic foot at the same temperature weighs 437,102,4946 grains troy. By Professor Robison's experiments it is ascertained, that a cubic foot of water at the temperature of 55° weighs 998.74 avoirdupois ounces, or 437.5 grains troy each, or about 1½ ounce less than 1000 avoirdupois ounces.

When water is exposed to the temperature of 212°, it boils, and if this temperature be continued, the whole is converted into an elastic invisible fluid, called vapour or steam. This, as has been already shown, is owing to the absorption of a quantity of caloric, which is necessary to retain it in the fluid form. In this state it is about 1800 times its bulk when in the state of water. This shews what an expansive force it must exert when it is confined, and hence its application in the steam engine, of which it is the moving power.

Sect. II. Of Ammonia.

Hydrogen also enters into combination with azote, and forms a compound of great importance. When hydrogen and azotic gases are mixed together, no change takes place, nor has any process been yet discovered by which these two gases can be directly combined; but when these are in their nascent state, as it is called, or in the moment of evolution from the bodies with which they were formerly in combination, they unite together and form ammonia, or the volatile alkali. It is demonstrated also by direct experiment, that this substance is composed of these two gases; but for the properties of it, we must refer to the chapter on alkalies, where they will be fully detailed.

Chap. VII. Of Carbone.

It may appear at first sight surprising, that the diamond, one of the hardest and most indestructible among combustible substances in nature, should be arranged among combustible bodies. This, however, was conjectured by Newton, when he considered its great refracting power, referring it to the general law, that combustible bodies have this power in greatest perfection. The sagacious conjecture The conjecture of this great philosopher has been fully verified. The first experiment to ascertain the combustibility of the diamond, was made in the year 1694, in the presence of Cosmo III., grand duke of Tuscany, by the Florentine academicians. In this experiment, the diamond, exposed to the heat of a burning-glass, first became dull and tarnished, lost its weight, and was at last entirely dissipated, without the smallest residue. Some years afterwards, a series of experiments was made before Francis I., emperor of Germany, in which diamonds were consumed in the heat of a furnace. In the year 1771, Macquer first observed the diamond swell up and burn with a very sensible flame. Rouelle the younger, Cadet, Mitouart, and Darcey, repeated the same experiments, all which tended to establish the volatility and combustibility of the diamond.

But it is to the celebrated Lavoisier that we are indebted for ascertaining the nature and product of this combustion.

2. But for the sake of comparison, we shall mention some of the general properties of the diamond. This precious stone is found in the warmer regions of the earth, and chiefly in the East Indies and the Brazils. It is found crystallized in regular octahedrons, which is its primitive form; that of the molecules is the regular tetrahedron. The most common form is the six-sided prism, terminating in a six-sided pyramid. What are called spheroidal diamonds, have 48 curvilinear, triangular faces, which form of crystal is owing, according to Haüy, to a regular decrement, which may be determined by calculation. The lapidaries are well acquainted with the direction of the laminae of the diamond, because in that direction it is found to be most easily polished. The hardest diamonds are found to have their fibres twisted, which by the lapidaries are called natural diamonds.

3. The diamond is the hardest body known. It can only be polished with the powder of itself, which is procured by rubbing one diamond against another. The specific gravity of the diamond is 3.5. One of its most remarkable properties is its brilliancy. When exposed to the light of the sun for some time, and afterwards carried into a dark place, it appears luminous, so that it has the property of absorbing light. It becomes very sensibly electric by friction, and is therefore a non-conductor of electricity.

4. As it was now ascertained, that the diamond exposed to a strong heat was susceptible of combustion, and might be entirely dissipated, Lavoisier directed his attention in the year 1772 to discover the product which was thus obtained; and he found by experiment, that the quantity of the diamond, exposed to the heat of a burning-glass in oxygen gas, consumed, was in exact proportion to the quantity of air which was absorbed. The air was converted into carbonic acid gas (f). The quantity of the carbonic acid obtained being found proportional to the quantity of diamond consumed, it was concluded that diamond was nothing else but pure carbure. This furnished a striking analogy between the diamond and charcoal, from the combustion of which a similar product is obtained. An experiment made by Guyton in the year 1785, and a similar one repeated in 1797 by Mr Tennant, proved that the diamond is combustible, and that it burns like charcoal when thrown into melted nitre. The conclusion from which was, that the diamond and charcoal are composed of the same substance.

5. We shall find, in investigating the properties of a simple charcoal in the following section, that the one is a simple, the other a compound substance, which will enable us to explain the remarkable difference between many of the properties of the diamond and charcoal. Charcoal burns in the heat of an ordinary fire, but the diamond requires for its combustion a temperature not less than 500°; nor is the difference between these two bodies in specific gravity, hardness, and colour, less profound.

Lavoisier had ascertained that 100 parts of carbonic acid contained

\[ \begin{align*} 28 & \text{ charcoal,} \\ 72 & \text{ oxygen.} \end{align*} \]

In the experiments made by Guyton on the diamond, it appeared that carbonic acid gas is composed of

\[ \begin{align*} 17.88 & \text{ diamond,} \\ 82.12 & \text{ oxygen.} \end{align*} \]

If then 100 parts of carbonic acid gas are composed of the same proportions of constituent parts, and these proportions are obtained both by the combustion of the diamond and charcoal, it must necessarily follow that the charcoal, which requires a smaller proportion of oxygen to make up the 100 parts of carbonic acid gas, must contain the difference of the quantity of oxygen between the quantity with which it combines, and the quantity necessary to saturate the diamond. Thus, diamond requires 81.12 of oxygen, and charcoal requires only 72, the difference between which is 10.12, which must have been previously combined with the charcoal before combustion. The 28 parts of charcoal, then, are composed of

\[ \begin{align*} 17.88 & \text{ diamond,} \\ 10.12 & \text{ oxygen.} \end{align*} \]

Hence it follows, that 100 parts of charcoal consist of

\[ \begin{align*} 63.86 & \text{ diamond,} \\ 36.14 & \text{ oxygen.} \end{align*} \]

From this account, therefore, of the nature and properties of the diamond, it must be considered as a simple substance, and that substance which has received the name of carbure in the new chemical nomenclature; very different in its properties from charcoal, which is a compound substance, and has received the name of

(f) Carbonic acid gas, as will appear afterwards, is composed of carbure and oxygen. oxide of carbone or diamond (c). But we shall consider the properties of the compound more particularly in the following section.

Sect. I. Of the Combinations of Carbone with Oxygen.

Carbone enters into combination with oxygen, 1. In the state of charcoal or oxide of carbone; 2. In the form of gas, which has been denominated the gaseous oxide of carbone, or carbonic oxide; and, 3. In another proportion, constituting carbonic acid, which also exists in the gaseous state. The nature and properties of the two first we are now to examine: the last will be treated of under the class of acids.

I. Of Charcoal.

1. Charcoal exists in great abundance in animal and vegetable matters, and it is obtained by the partial decomposition of these substances. It may be procured by burning wood in close vessels; and the matter that remains after this combustion, is a black, shining, brittle substance, which is well known under the name of charred wood, or charcoal. To obtain charcoal pure, it must be repeatedly washed with pure water, and be afterwards exposed for some time to a strong heat in close vessels. Thus prepared, if it be entirely deprived of moisture and excluded from air, it may be exposed to the strongest heat without any change.

2. Charcoal is a good conductor of electricity. When it is new made, it is found to have the property of removing the disagreeable odor with which animal matters beginning to putrefy, clothes and other substances, are tainted. On account of this property, perhaps, and also on account of its mechanical effects, it is greatly recommended as an excellent teeth powder. Charcoal seems to be quite indestructible. This is the best method of preserving wood from decay, which is exposed to the effects of air and moisture. Stakes charred on the outside, have remained in the ground for some thousand years, and are still in perfect preservation. This seems to have been a common practice among the ancients.

3. Charcoal has neither taste nor smell. It is insoluble in water, but it absorbs moisture in considerable proportion. When it is well dried, charcoal attracts the air very greedily. A piece of charcoal well dried, placed under a jar over mercury, absorbs the air, and the mercury ascends rapidly; but if a little water be introduced into the jar, the charcoal absorbs the moisture, gives out the air, and the mercury descends. In some experiments made with this view, it appeared that charcoal absorbed four times its bulk of air; and when the charcoal was plunged into water, a fifth part of this air was disengaged, which being examined, a quantity of oxygen had disappeared. In another experiment, the charcoal was introduced into a vessel filled with oxygen gas, when it absorbed eight times its bulk of the gas, and being plunged into water, gave out a fourth part. These experiments were made by Delametherie.

The experiments of Senebier seem to prove, that it was only the oxygen gas of the atmospheric air that was absorbed by charcoal; but it has been since demonstrated, that this only takes place when the charcoal is hot. The atmospheric air is absorbed unchanged when the charcoal is cold.

4. When the temperature of pure charcoal is raised to redness, and if it be then introduced into a jar of oxygen gas, it burns rapidly, giving out brilliant sparks, but with little flame. The charcoal disappears, and the oxygen gas is totally changed. By its combination with the charcoal during the combustion, it is converted into a peculiar gas, which has received the name of carbonic acid gas, the component parts of which were discovered by M. Lavoisier, to be

\[ \frac{28 \text{ charcoal}}{72 \text{ oxygen}} = \frac{1}{3} \]

The properties of this acid will be fully described in its place among the class of acids.

5. It is generally agreed among chemists, that charcoal consists of oxygen and carbone; but a controversy at present exists, whether hydrogen does not, in all cases, enter into its composition? Charcoal prepared in the common way, always contains a portion of hydrogen. It is therefore to be considered as a triple compound, consisting of carbone, oxygen, and hydrogen. But according to the experiments of Deformes and Clement, charcoal exposed for some time in a close vessel to a very strong heat, is entirely deprived of its hydrogen†. This, however, does not correspond with the experiments of Mr Cruickshank, in which the gases obtained from charcoal in all states of preparation were always found to contain hydrogen.

6. There is no direct action between carbone and azotic gas; but by the action of a third substance, Compounds of azote, hydrogen and carbone, which are combined also with a greater or lesser proportion of oxygen, frequently exist among vegetable and animal matters.

II. Of the Gaseous Oxide of Carbone.

1. A peculiar inflammable gas, which has been considered of the same nature with the carbonated hydrogen gas to be described in the next section, was announced by Dr Priestley, from the manner of its production and properties, as a confirmation of the truth of the phlogistic theory. His experiments were soon repeated by many other chemists, and particularly by Mr Cruickshank of Woolwich, who published a very satisfactory account of the nature, composition and properties of this gas. He gave it the name of the gaseous oxide of carbone. He considered it as consisting of carbone united with oxygen; the oxygen and carbone existing in it being nearly in the proportion of two

---

(c) In the present nomenclature of chemistry, the word oxide is used to denote the combination of oxygen with a base, the product of which combination exhibits no acid properties, as in the present case, the combination of oxygen with carbone or diamond. Dr Priestley obtained it from the gray oxide, or forge scales of iron and charcoal. Mr Cruickshank also obtained it by a similar process. He employed the oxides of zinc and copper; the black oxide of manganese and litharge. The gas which is obtained from these substances, is a mixture of carbonic acid and the gaseous oxide of carbone. Mr Cruickshank found, that the oxides which most readily part with their oxygen, afford the greatest proportion of carbonic acid; but the oxides which retain their oxygen more strongly, give the greatest proportion of the gaseous oxide of carbone. At the beginning of the process, carbonic acid comes over in greatest abundance; it then diminishes, and afterwards nothing but the gaseous oxide is extricated.

It is also obtained by exposing to a strong heat one part of pure charcoal and three parts of carbonate of lime, strontites, or barytes, in an iron retort. The carbonic acid which is in combination with the earths, is partly disengaged unchanged, and partly decomposed by the charcoal, and converted by the action of the charcoal into the gaseous oxide of carbone. The gas which is obtained in this process is composed of one part of carbonic acid and five parts of gaseous oxide*. The same gases are also obtained, by employing iron filings with the earthy carbonates, and the quantity is considerably increased when pure iron is used. Mr Cruickshank and the French chemists also obtained it, by making carbonic acid gas pass through red-hot charcoal, in an iron or porcelain tube. The carbonic acid is decomposed, and the gaseous oxide is formed.

The carbonic acid which is mixed with the gaseous oxide obtained in all these processes, may be separated by washing the gas with lime water, and the gaseous oxide remains in a state of purity.

2. This gas is invisible and elastic like common air. Its specific gravity is 0.001167; 100 cubic inches weigh 30 grains.

It is unfit for respiration. Small animals introduced into it are instantaneously suffocated; and in some persons who attempted to breathe it, it produced faintness and giddiness. Deformes and Clement think that it is probably owing to this gas disengaged from burning charcoal, that sudden death is induced in close apartments. It is not altered by passing it through a red-hot tube, nor does it undergo any change by being exposed to light; and it is neither inflamed nor diminished by passing the electric spark through it. This gas in contact with common air, when set fire to, burns with a blue flame. When it is made to traverse a red-hot tube full of air, it produces slight detonations. The residue of these combustions is carbonic acid and azote.

3. With oxygen gas, if in considerable proportion, the combustion is very rapid; a red flame is produced, and the whole of the gas is consumed. The residue in this combustion is carbonic acid †.

According to Mr Cruickshank, the gaseous oxide of carbone is a compound of carbone and oxygen. Thirty grams of it obtained from charcoal and metallic oxides, required 15 grams of oxygen to saturate it, and the quantity of carbonic acid produced was 35.5. Thirty grams obtained from iron filings and earthy carbonate, required 13.6 grams of oxygen, which gave 43.2 grams of carbonic acid.

But according to the experiments and conclusions of Berthollet, the gaseous oxides of carbone contain a certain portion of hydrogen in their composition. This quantity, he thinks, amounts to about \( \frac{1}{3} \). He distinguishes two species of inflammable gas, which contain carbone; the one consists entirely of hydrogen and carbone, which he proposes to denominate carbonated hydrogen gas, which will be treated of in the next section. The other species of inflammable gas is also formed of hydrogen and carbone, but contains a certain portion of oxygen. To this he proposes to give the name of oxycarbonated hydrogen gas. But the results of the experiments of Cruickshank and others do not correspond with the experiments and conclusions of Berthollet, in admitting any proportion of hydrogen as a component part of his oxycarbonated hydrogen gas, or of the gaseous oxide of carbone. But for an account of his observations and reasonings on this subject, see Memoires de l'Institut Nationale, tom. iv. p. 269, 319, and 325.

Sect. II. Of Carbonated Hydrogen Gas.

1. If a quantity of wet charcoal be introduced into a retort, and exposed to a red heat, a great quantity of procuring gas passes over, which may be collected in jars in the pneumatic apparatus, in the usual way. It may be also obtained by making the vapour of water pass through red-hot charcoal in a porcelain or iron tube placed across a furnace. The water is decomposed; the hydrogen, one of its component parts, combines with the carbone of the charcoal. The gas obtained by these processes has been called light inflammable air. A similar gas may be procured from ether, spirits of wine, or camphor, by making the vapour of these substances pass through red-hot porcelain tubes. This gas, from its greater specific gravity, has been called heavy inflammable air. The proportions of the substances which enter into the composition of this gas vary considerably, according to the process employed, or the materials from which it is obtained. It is the same gas which is given out in great abundance during hot weather, from stagnant waters.

2. This gas is like common air, invisible and elastic. Properties. When a candle is applied to it, it burns with a blue, lambent flame. If it be mixed with atmospheric air, the combustion is more rapid and brilliant, and still more so when it is mixed with oxygen gas, but without any detonation. The product of this combustion is carbonic acid and water. The oxygen combines partly with the carbone, and forms carbonic acid; and partly with the hydrogen, and forms water.

3. It is totally unfit for respiration. Animals introduced into it are instantly suffocated. It is also unfit for supporting combustion.

One of the most remarkable properties of this gas is, when it is mixed in a tube with common air or oxygen gas, about \( \frac{2}{3} \) its bulk of the latter, and fired by the electric spark, there is a considerable increase of volume.

The component parts of carbonated hydrogen gas, obtained from different substances, as they have been ascertained by Mr Cruickshank, are the following. When it is procured from ether, camphor, or stagnated water, it contains the greatest proportion of carbone. The specific gravity is 0.000804, and it is to common air nearly. Carbonic gas holds in solution 5 parts of carbone; 100 parts contain 52.35 carbone, 9.60 hydrogen, 38.05 water instead of vapour.

When it is obtained from ether, the specific gravity is 0.000787:

100 parts contain 45 carbone, 15 hydrogen, 40 water.

When it is obtained from spirit of wine, the specific gravity is 0.00063:

100 parts contain 44.1 carbone, 11.8 hydrogen, 44.1 water.

Mr Cruickshank has discovered a very easy method of distinguishing the gaseous oxide of carbone from the carbonated hydrogen gas. A mixture of the latter and oxymuriatic acid gas may be exploded by passing electric sparks through it. But a mixture of oxymuriatic acid gas and the gaseous oxide of carbone suffers no change by the action of electricity.

The following table, drawn up by Mr Cruickshank, exhibits the results of his experiments on these two gases.

| Gases, and the different Substances from which the Gases are obtained, &c. | Weight of 100 Cubic Inches, or Grains. | Proportion of Oxygen necessary to saturate 100 Measures of the Gas. | Products when combined with Oxygen. | |---|---|---|---| | | Grains. | Meaf. | Quan. of Grains. | Carbonic Acid. | Water produced. | Water held in Solution by the Gas. | Hence the Gases consist of | | | | | | In Vol. Meaf. | In Quan. Grains. | Grains. | Grains. | Oxyg. | Carbon. | Hydro. | Water. | | Pure carbonated hydrogen gas from camphor, &c. | 21 | 176 | 59.8 | 116 | 54.5 | 18 | 8 or 9 | none | 11 | 2+ | 8 or 9 | | from ether | 20 | 170 | 58 | 108 | 59.5 | 18 | 9 | none | 9 | 3 | 8 | | from alcohol | 16 | 118 | 40 | 75 | 36 | 13 | 7 | none | 7 | 1.9 | 7 | | coal | 14.5 | 66 | 22.4 | 40 | 19 | 9 | 9 | none | 4 | 1.3 | 9 | | Gaseous oxide from charcoal and metallic oxides | 30 | 44 | 15 | 76 | 35.5 | about | 8 | prob' nonc | about | nearly | uncertain | | from iron filings, and carbonate of lime, or barytes | 30 | 40 | 13.6 | 92 | 43.2 | none | none | 21+ | 8.6 | none | none |

**CHAP. VIII. OF PHOSPHORUS.**

This singular substance was accidentally discovered in 1677 by an alchemist of Hamburg, named Brandt, when he was engaged in searching for the philosopher's stone. Kunkel, another chemist, who had seen the new product, associated himself with one of his friends named Krafft, to purchase the secret of its preparation; but the latter deceiving his friend, made the purchase for himself, and refused to communicate it. Kunkel, who at this time knew nothing farther of its preparation, than that it was obtained by certain processes from urine, undertook the task, and succeeded. It is on this account that this substance long went under the name of Kunkel's phosphorus. Mr Boyle is also considered as one of the discoverers of phosphorus. He communicated the secret of the process for preparing it to the Royal Society of London in 1680. It is asserted, indeed, by Krafft, that he discovered the secret to Mr Boyle, having in the year 1678 carried a small piece of it to London, to show it to the royal family; but there is little probability, that a man of such integrity as Mr Boyle, would claim the discovery of the process as his own, and communicate it to the Royal Society, if this had not been the case.

Mr Boyle communicated the process to Godfrey Hankowitz, an apothecary of London, who for many years years supplied Europe with phosphorus; and hence it went under the name of English phosphorus. Many chemists now attempted to produce phosphorus, and different processes had been published for the purpose; but it would appear that they rarely succeeded.

In the year 1737, a stranger having sold to the French government a process for making phosphorus, the Academy of Sciences charged Dufay, Geoffroy, Duhamel, and Hellot, to superintend it. The latter published an account of the experiment, which succeeded. Rouelle the elder exhibited phosphorus which he had prepared, in the course which he opened at Paris some years after. In the year 1743, Margraaf made a great improvement in the process, but still it continued to be obtained with difficulty, and in very small quantity. It was not till 30 years after that considerable improvement was made in the process for procuring phosphorus.

In the year 1774, the Swedish chemists, Gahn and Scheele, made the important discovery, that phosphorus is contained in the bones of animals, and they improved the processes for procuring it.

2. The most convenient process for obtaining phosphorus seems to be that recommended by Fourcroy and Vauquelin*. Take a quantity of burnt bones, and reduce them to powder. Put 100 parts of this powder into a porcelain or stone-ware basin, and dilute it with four times its weight of water. Forty parts of sulphuric acid are then to be added in small portions, taking care to stir the mixture after the addition of every portion. A violent effervescence takes place, and a great quantity of air is disengaged. Let the mixture remain for 24 hours, stirring it occasionally, to expose every part of the powder to the action of the acid. The burnt bones consist of the phosphoric acid and lime; but the sulphuric acid has a greater affinity for the lime than the phosphoric acid. The action of the sulphuric acid uniting with the lime, and the separation of the phosphoric acid, occasion the effervescence. The sulphuric acid and the lime combine together, being insoluble, and fall to the bottom.

Pour the whole mixture on a cloth filter, so that the liquid part which is to be received in a porcelain vessel may pass through. A white powder, which is the insoluble phosphate of lime, remains on the filter. After this has been repeatedly washed with water, it may be thrown away, but the water is to be added to that part of the liquid which passed through the filter.

Take a solution of sugar of lead in water, and pour it gradually into the liquid in the porcelain basin. A white powder falls to the bottom, and the sugar of lead must be added so long as any precipitation takes place. The whole is again to be poured upon a filter, and the white powder which remains is to be well washed and dried. The dried powder is then to be mixed with one-sixth of its weight of charcoal powder. Put this mixture into an earthen-ware retort, and place it in a sand bath with the neck plunged into a vessel of water. Apply heat, and let it be gradually increased, till the retort becomes red hot. As the heat increases, air-bubbles rush in abundance through the neck of the retort, some of which are inflamed when they come in contact with the air at the surface of the water. A substance at last drops out similar to melted wax, which congeals under the water. This is phosphorus.

In this state the phosphorus is not quite pure. It is generally mixed with some charcoal powder, and a small portion of half burnt phosphorus, which give it a brown colour. To have it quite pure, melt it in warm water, and strain it several times through a piece of flax or leather under the surface of the water (H). To mould it into sticks, take a glass funnel with a long tube, which must be stopped with a cork. Fill it with water, and put the phosphorus into it. Immerse the funnel in boiling water, and when the phosphorus is melted, and flows into the tube of the funnel, then plunge it into cold water, and when the phosphorus has become solid, remove the cork, and push the phosphorus from the mould with a piece of wood. Thus prepared, it must be preserved in close vessels containing pure water.

3. When phosphorus is perfectly pure, it is semitransparent, and has the consistence of wax. It is so soft that it may be cut with a knife. Its specific gravity is from 1.770 to 2.033. It has an acid and disagreeable taste, and a peculiar smell somewhat resembling garlic. When a stick of phosphorus is broken, it exhibits some appearance of crystallization. The crystals are needle-shaped, or long octahedrons; but to obtain them in their most perfect state, the surface of the phosphorus, just when it becomes solid, should be pierced, that the internal liquid phosphorus may flow out, and leave a cavity for their formation.

4. When phosphorus is exposed to the light, it becomes of a reddish colour, which appears to be an incipient combustion. It is therefore necessary to preserve it in a dark place. At the temperature of 99° of heat, it becomes liquid; and if air be entirely excluded, it evaporates at 210°, and boils at 554°. At the temperature of 43° or 44°, it gives out a white smoke, and is luminous in the dark. This is a slow combustion of the phosphorus, which becomes more rapid as the temperature is raised. When phosphorus is heated to the temperature of 148°, it takes fire, burns with a bright flame, and gives out a great quantity of white smoke.

Phosphorus enters into combination with oxygen, azote, hydrogen, and carbure.

Sect. I. Of the Combinations of Phosphorus with Oxygen.

Phosphorus enters into combinations with oxygen in different proportions.

I. Oxide of Phosphorus.

When phosphorus is exposed to the light, or is kept in water that is not freed from air, it soon becomes of a white colour, having lost its transparency, and afterwards will be coloured.

Towards changes to a brown. This is the first combination of oxygen with it, and being in the smallest proportion, and giving no acid properties to the compound, it has been denominated an oxide of phosphorus. This shows that it is necessary to keep it excluded from air and light. But phosphorus thus changed on the surface may be freed from that part which is oxidated by a very simple process. Dissolve the phosphorus in warm water, the whole melts except the oxidated part, which remains at the surface, because it is not soluble at the same temperature.

II. Acids.

1. When phosphorus is burned in common air confined in a vessel, the combustion is pretty rapid, and continues till the whole of the oxygen be consumed. A great quantity of white fumes are produced, and when these fumes are mixed with water which absorbs them, it is found to have acid properties. This is the phosphorous acid, in which the oxygen is in smaller proportion than in the following, but greater than in the oxide.

2. But when a small bit of phosphorus is introduced into a jar filled with oxygen gas at the temperature of 60°, it dissolves slowly, but does not appear luminous till the temperature be raised to 80°, which shows that phosphorus requires a higher temperature to burn in oxygen gas than in common air. And if the phosphorus be introduced into the oxygen gas, which is perfectly pure at a lower temperature, it undergoes no change, gives out no smoke, and is not luminous in the dark. But when it is immersed in a state of ignition into oxygen gas, it exhibits the most brilliant combustion that can be conceived. The light which is emitted is almost as splendid as that of the sun, and is too powerful for the eye. During this combustion the oxygen gas disappears, it loses its gaseous form, and becomes solid in combination with the phosphorus. It is during this change from the fluid to the solid state that the caloric is emitted; and the light, according to Gren's theory of combustion, is given out by the phosphorus. The product is a concrete substance which adheres to the sides of the jar. This is the phosphoric acid, in which there is a greater proportion of oxygen in combination with the phosphorus. These acids will be treated of in the chapter on acids.

SECT. II. Of PHOSPHORATED AZOTIC GAS.

1. At first sight it seems difficult to explain the reason that phosphorus requires a higher temperature for its combustion in oxygen gas than in common air. But the cause of this singular phenomenon appears by examining the effects of azotic gas on phosphorus. The phosphorus, which is readily converted into vapour at a low temperature, combines with the azotic gas without combustion, and therefore without giving out any light. The azotic gas is thus saturated with the phosphorus, and its bulk is increased about 4/5. The combination is denominated phosphorated azotic gas.

2. When oxygen gas is introduced into a jar filled with this gas, it becomes luminous, because there is a combustion of the phosphorus which is held in solution by the azotic gas. The combustion is more rapid and brilliant when the phosphorated azotic gas is let up into the jar of oxygen gas.

SECT. III. Of PHOSPHORIZED and PHOSPHORATED HYDROGEN GAS.

1. When a piece of phosphorus is put into a jar filled with hydrogen gas, it does not appear luminous in daylight. But, after having remained for several hours, part of the phosphorus is dissolved. When this gas, to which Fourcroy and Vanquelin have given the name of phosphorized hydrogen gas, is introduced into a jar of oxygen gas, each bubble, as it passes up and comes in contact with the gas, produces a very brilliant blue flame, which fills the whole vessel. This effect does not take place in atmospheric air. This gas holds in solution only a small proportion of phosphorus; but it is owing to the combustion of this portion that the flame appears in the oxygen gas. This gas has a less fetid odour than that which is next to be described. It has, however, a slight smell of garlic.

2. Phosphorated hydrogen gas was discovered by Hilfry M. Gengembre in 1783, by boiling a solution of potash on phosphorus; and by Mr Kirwan in the following year. Its nature and properties have been more completely investigated by M. Raymond, in two papers in the Annales de Chimie for 1791 and 1800. It may be obtained by introducing a bit of phosphorus into a jar of hydrogen gas standing over mercury, and melting the phosphorus by means of a burning glass. The phosphorus is thus converted into the state of vapour, when the hydrogen gas dissolves a much greater proportion. But a more simple process has been recommended by Raymond.

Take two ounces of quicklime, flaked in the air, proceed about 60 grs. of phosphorus, and half an ounce of water; reduce the whole to a paste, and put it immediately into a small glass or stone-ware retort, the body of which may be filled with the materials. Immerse the beak of the retort under water in the pneumatic trough, and apply a moderate heat. As soon as the retort is heated, the gas begins to come over; and when the bubbles come to the surface of the water in contact with the air, they explode with flame and smoke. When the gas passes off slowly the bubbles are larger; and when they reach the surface they exhibit an elegant appearance, forming, after explosion, a beautiful coronet of white smoke, which rises with an undulatory motion to the ceiling, when the air is still. When this gas is brought into contact with oxygen gas, the combustion is more rapid and more brilliant.

The products of the combustion of this gas are phosphoric acid and water. The phosphorus which is held by combination with the hydrogen, combines with the oxygen, and forms phosphoric acid; while the hydrogen unites with another portion of oxygen and forms water.

This gas has a very fetid odour, which has some resemblance to the smell of putrid fish. When pure water is agitated in contact with this gas, it absorbs about one-fourth of its bulk at the temperature of 50°. The colour of the solution is not quite so deep as that of roll. roll sulphur. The smell is strong and disagreeable, and the taste extremely bitter. It does not appear luminous in the dark. But when it is exposed nearly to the temperature of boiling, the whole of the phosphorated hydrogen gas is driven off unchanged, and the water remains behind perfectly pure. When the solution is exposed to the air, the oxide of phosphorus is deposed, and the hydrogen gas escapes.

Sect. IV. Phosphuret of Carbone.

Phosphorus enters into combination with charcoal, and forms what Proult, who discovered it, denominates phosphuret of carbone. It is produced during the distillation of phosphorus, and remains behind on the leather, when it is strained through it to purify it from this substance. It is of a red colour, and does not melt like pure phosphorus. If it be distilled with a gentle heat, there is separated a small portion of phosphorus which it contains in excess. But the true compound of phosphuret of carbone is not decomposed without a very strong heat. When the vessels have cooled, there is found a light, flocculent powder, of a lively orange red, which M. Proult considers as the phosphuret of carbone. If it be exposed to a red heat in the retort in which it is formed, the whole of the phosphorus is driven off, and the charcoal remains behind. When this phosphuret is exposed to the open air on a heated metallic plate, it burns rapidly; but the charcoal which absorbs the phosphoric acid, as it is formed, escapes the combustion. It loses, in a short time, the property of burning, by being exposed to the air, and then it may be preserved without any risk of its catching fire spontaneously.

Chap. IX. Of Sulphur.

1. Sulphur is a simple undecomposed combustible substance, which is universally diffused in nature; but most commonly in a state of combination with mineral, vegetable, or animal matters. It is found in some mineral waters, but in greatest abundance in volcanic countries, where it is a valuable article of commerce.

2. Sulphur, as it is extracted from minerals and purified by art, is a hard brittle substance of a yellow colour, which can be easily reduced to powder. It is always opaque, has a lamellated fracture, and becomes electric by friction. The specific gravity, after it is melted, does not exceed 1.9907. It has no smell, and very little perceptible taste. When it is rubbed some time, it is volatilized, and diffuses a peculiar and slightly fetid odour, by which it is easily distinguished. It leaves on the skin which has been in contact with it, a very strong smell, which remains for some hours. It is insoluble in water.

3. Light has no sensible effect on sulphur. But if a roll of sulphur be held in the hand for a little, it begins to crackle, and at last it breaks to pieces. When a temperature equal to that of boiling water is applied to sulphur, it melts, becomes liquid and transparent, and changes to a brown red colour; but, on cooling, if the fusion is not too long continued, it resumes the yellow colour. If it be permitted to cool slowly, it crystallizes into prismatic needles. The crystals are better formed by pouring out part of the liquid sulphur as soon as the surface has become solid.

4. If the heat be continued it becomes thick and becomes viscous; and if it be then poured into cold water, it retains its softness, so that it is employed for taking impressions of seals and medals. In this state they are called sulphurs. When sulphur is exposed to heat in subliming vessels, it is volatilized or sublimed in the form of a very fine powder, known under the name of flowers of sulphur.

Sulphur enters into combination with oxygen, azote, hydrogen, carbone, and phosphorus.

The combination of sulphur with azotic gas has been with azotic little examined. Part of the sulphur is dissolved, when the gas is heated in a vessel filled with the gas. This sulphurated azotic gas, as it is called, has a fetid odour. When the temperature is diminished, part of the sulphur is deposed. It has been lately discovered in the mineral waters of Aix-la-Chapelle.—We shall consider the other combinations of sulphur in the following sections.

Sect. I. Sulphur combined with Oxygen.

1. When sulphur is kept some time in fusion in an open vessel, it assumes a red colour, and becomes viscous. After it is cooled, it retains its red colour, which is owing to the combination of oxygen in small proportion with the sulphur. In this state it has been denominated the oxide of sulphur. According to the experiments of Dr Thomson, the oxide of sulphur, formed by melting the substance in a deep vessel, is of a dark violet colour, fibrous fracture, and tough consistency; the specific gravity is 2.325. It contained 27% per cent. of oxygen. Another oxide, containing 6.2 per cent. of oxygen, was formed by passing a current of oxymuriatic acid gas through flowers of sulphur.

2. When sulphur is burnt in the open air, it emits a pale blue flame, with a great quantity of white common smoke. When these fumes are mixed with water, it is found to possess acid properties. This is a combination of sulphur with a greater proportion of oxygen than exists in the oxide, and is called sulphurous acid.

3. But when sulphur is burnt in oxygen gas, a very rapid combustion takes place with a reddish white gas flame, and it combines with a greater proportion of oxygen. When the fumes which are copiously emitted during this combustion are collected and mixed with water, it exhibits the properties of an acid, which is the sulphuric acid. Thus it appears, that sulphur combines with oxygen in four different proportions. In two of these, in which the proportions are unequal, the compounds are denominated oxides; but in the two others, in which the proportion of oxygen is increased, the compounds are acids, the properties of which will be afterwards investigated.

Sect. II. Sulphurated Hydrogen Gas.

1. This gas may be procured by various processes. It may be obtained by making hydrogen gas pass through procuring melted sulphur. In this way the hydrogen gas enters into combination with sulphur. The same gas may also be obtained by melting together in a crucible equal parts of iron filings and sulphur, by which means a black brittle mass is formed, which is to be reduced to powder, and introduced into a glass vessel (fig. 6.) with two mouths, the one of which has a stopper A and the other a bent tube B, accurately ground to fit the mouths C, D. When the mixture of iron filings and sulphur has been introduced into the phial, the bent tube is to be fitted into the mouth, with the other end under the surface of the water in the trough E. The apparatus being thus prepared, pour in muriatic acid through the other opening, and immediately close it with the ground stopper. The sulphurated hydrogen gas is copiously discharged, and fills the glass jar F, which is previously placed on the shelf to receive it. This gas was formerly known by the name of hepatic gas.

2. The odour is extremely fetid, resembling that from the washings of a gun, or from rotten eggs, which is owing to the extraction of the same gas. The specific gravity of this gas is 0.00135.

It is unfit for respiration, and a taper immersed in it is extinguished, so that it is also unfit for supporting combustion. When it is inflamed in contact with atmospheric air or oxygen gas, it burns with a reddish blue flame, and deposits a quantity of sulphur. Sulphur also is deposited by simple exposure to the air. From this it appears, therefore, that the affinity of hydrogen for oxygen is stronger than for sulphur. During the combustion, the hydrogen unites with the oxygen, and the sulphur is deposited. It is from this deposition that the sulphur found about mineral springs, the waters of which contain this gas, is derived.

3. According to the experiments of Thenard, 100 parts by weight of sulphurated hydrogen gas contain

\[ \begin{align*} 70.857 & \text{ sulphur,} \\ 29.143 & \text{ hydrogen.} \end{align*} \]

100,000*

4. Sulphurated hydrogen gas has the property of dissolving phosphorus. Fourcroy and Vauquelin introduced pieces of phosphorus into a jar filled with this gas over mercury. After the phosphorus had been exposed to the gas for twelve hours, the atmospheric air was admitted, and there instantly appeared a bluish, voluminous flame. The bubbles of the gas diffused in the air, presented by day light a white vapour, which seemed to adhere like viscid matter to the surface of the mercury; but in the dark, exhibited a very brilliant light. The mercury in the trough in which the experiment was made, continued for some minutes to give out sparks of light by agitation. The hands plunged into this gas, continued luminous for some minutes, and a sponge introduced into it retained the same property for some time in the air.

5. Sulphurated hydrogen gas is very readily absorbed by water, and in this state it possesses some of the properties of an acid. It changes vegetable blues to a red colour.

**Sect. III. Carburet of Sulphur.**

1. Sulphur and carbon combine together at a high temperature, and probably in different proportions; one of these combinations is liquid, at the ordinary temperature and pressure of the atmosphere. This is the carburet of sulphur. The following method of preparing it is given by Clement and Deformes, who have particularly investigated the action of sulphur and charcoal.

2. Put a quantity of charcoal in small pieces, or in powder previously dried, into a porcelain tube, which is to pass through a furnace that it may be exposed to a red heat. The gas from the charcoal is to be allowed to escape, before the other part of the apparatus is adjusted. To that extremity of the porcelain tube which contains the charcoal, fit a long glass tube, sufficiently wide to contain a number of small pieces of sulphur, which may be pushed successively into the porcelain tube with an iron rod passing through a cock which closes the end of the tube. To the other extremity there is to be fitted another glass tube, bent at the end, that it may be immersed in a vessel of water in the pneumatic trough. Heat is then to be applied till the porcelain tube and the charcoal become red-hot, when the pieces of sulphur are to be pushed slowly forwards into the tube, and when it acts on the charcoal a yellow liquid of an oily appearance passes through the tube. The heat being continued, it evaporates, and is condensed in the water of the vessel in which the tube terminates, traversing it in globules, which collect together at the bottom.

The success of this experiment is somewhat doubtful. When sulphur is exposed suddenly to a strong heat, in place of being sublimed, it appears in some measure fixed, and becomes soft by fusion. Sometimes it passes too rapidly through the charcoal to unite with it; the pieces of sulphur, therefore, should be slowly introduced, and the tube, in passing through the furnace, should be inclined from that extremity at which the sulphur is introduced.

3. When the carburet of sulphur is pure, it is transparent and colourless, but frequently has a greenish-yellow tinge. It has a disagreeable pungent odour. The taste is at first cooling, but afterwards becomes extremely pungent. It is heavier than water, does not mix with it; and therefore remains at the bottom of the vessel. The specific gravity of this liquor is various. In one trial it was found to be 1.3.

4. The carburet of sulphur evaporates at the ordinary temperature of the atmosphere, and increases its volume nearly as much as ether. When a quantity of this liquor in a vessel of water is placed under the receiver of an air pump, and the air exhausted, it rises through the water in bubbles, and assumes the gaseous form; and when the pressure of the air is restored, the gas is instantly condensed, and returns to the liquid state.

5. The carburet of sulphur burns with great facility, and during the combustion it emits a strong odour of bleached sulphurous acid, deposits a little sulphur, which afterwards burns, and there remains some black charcoal in its usual combustible state. The air which holds carburet of sulphur in solution, burns quietly; but when it is mixed with oxygen gas, and brought in contact with a burning body, it explodes with prodigious violence, and not without considerable danger.

6. This substance unites with phosphorus, which it very readily dissolves, but the solution is not more inflammable than the phosphorus itself. It combines also also with a small quantity of sulphur, but without any other change in its properties than becoming a little deeper coloured. It seems to have no action on charcoal.

**Sect. IV. Sulphuret of Phosphorus.**

1. Sulphur and phosphorus combine together in all proportions. If one part of phosphorus with eight times its weight of sulphur, be put into a matras, with 32 parts of distilled water; on the application of a gentle heat, the phosphorus melts and dissolves the sulphur. The new compound assumes a yellow colour, and remains fluid, till it is cooled down to the temperature of 77°, when it becomes solid. This substance is the sulphuret of phosphorus. In other cases, when the proportion of phosphorus exceeds that of the sulphur, it is called a phosphuret of sulphur.

2. The compounds of sulphur and phosphorus have been particularly investigated by Pelletier, and he has found that the compound is always more fusible than either of the uncombined constituents. The following table exhibits the results of his experiments:

| Phosphorus | remain fluid at 95° | |------------|-------------------| | 8 | | | 1 Sulphur | | | 4 Phosphorus | | | 1 Sulphur | 59 | | 1 Phosphorus | | | 3 Sulphur | 50 | | 1 Phosphorus | | | 1 Sulphur | 41 | | 1 Phosphorus | | | 2 Sulphur | 72 | | 1 Phosphorus | | | 3 Sulphur | 99 |

All these compounds, therefore, it must appear, are more fusible than the phosphorus itself, and much more so than the sulphur.

3. In making these combinations, great caution should be observed; for if the heat be applied suddenly, even when the substances are under water, a violent explosion sometimes takes place, from the sudden formation and extrication of the sulphurated and phosphorated hydrogen gases.

**Chap. X. Of Acids.**

1. We have seen, in describing the different substances which have been treated of in the five preceding chapters, that they all, excepting one, combine with oxygen in different proportions. Hydrogen combines with oxygen only in one proportion, and this compound is water. The first portion of oxygen which combines with the other four substances, namely azote, carbone, phosphorus, and sulphur, forms with them compounds which, possessing no acid properties, have received the name of oxides (1).

2. But when these substances combine with a greater proportion of oxygen, they exhibit very different properties; and possessed of these properties, they are ranked among the class of acids. The substances which possess the following properties are referred to this class:

a. They redden vegetable blue colours (K). Distinctive b. They possess a peculiar taste, which is well known characters, by the terms acid or sour. c. They combine with water in all proportions. d. They enter into chemical combination with alkalies, with earths, and metallic oxides, and form with them compounds which have been denominated salts.

3. The acids are a very important class of bodies, and not merely on account of their peculiar properties, of acids, and the singular and useful compounds which they form with other substances, but also as they are the instruments of analysis in the hands of the chemist for discovering the properties and combinations of the objects of his science. Without their aid he can scarcely move a single step in his investigations. It was therefore necessary to introduce the account of the acids in this place, that we might be early acquainted with the means of prosecuting our researches.

4. Acids which have the same base, combine with oxygen in different proportions. Thus, for instance, sulphur combines with oxygen in two proportions. The 100 parts of one compound contain 32 of oxygen, and the 100 parts of the other contain 38 parts. The characteristic properties of these compounds are totally different. It is therefore necessary that they should be distinguished by some appropriate name, and this accordingly has been attended to in the construction of the present chemical nomenclature. The name of the acid is derived from the base, and this name has a different termination according to the proportion of the oxygen combined with its base. With the smallest proportion the name terminates in the syllable os; with the greater proportion, it terminates in the syllable ic. Thus, in the case of the acid formed with sulphur, that compound in which there is the smaller proportion of oxygen is denominated the sulphurous acid; the other, which has the greater proportion of oxygen is the sulphuric acid. In the same way when phosphorus combines with oxygen in the smallest proportion which gives it acid properties, it is called the phosphorous acid; in the greater proportion, the phosphoric acid. And thus by the simple change of the termination, the name is descriptive of the peculiar state of the proportions in the compound.

---

(1) Perhaps the combination of oxygen and azote, as they exist in atmospheric air, should be excepted. It is to the combination of oxygen in greater proportion with azote than exists in atmospheric air, that the name of oxide is given. But philosophers are not agreed whether atmospheric air is to be considered as a chemical combination, or a mechanical mixture.

(K) Hence vegetable blue infusions, or paper stained with them, are employed as tests to discover acids. These are sometimes called re-agents. A great variety of substances are employed for this purpose, such as the infusion and tincture of litmus and of turnsole, the syrup of violets, the infusion of the flowers of mallow or red cabbage. Sect. I. Of Sulphuric Acid.

1. The name of sulphuric acid is given to the combination of sulphur and oxygen, with the greatest proportion of the latter. It was formerly called vitriolic acid, because it was obtained by distillation from vitriol, which is a compound of sulphuric acid and an oxide of iron. When it is strongly concentrated, it has a fluegill appearance; hence it was called oil of vitriol. It has also been denominated oleum sulphuris per campanam, because it was obtained by burning sulphur under a glass bell.

2. The ancients were unacquainted with this acid. Pliny speaks of vitriols, which were used for different purposes, in some of which it was probably decomposed. Sulphur was burnt in sacrifices, but in neither case was the product attended to. Basil Valentine is the first who mentions this acid, about the end of the 16th century. Agricola and Paracelsus have also spoken of it, but Dornaeus is the first who described it distinctly, in the year 1570.

3. If a quantity of flowers of sulphur be exposed to a degree of heat sufficient to inflame it, and if, when it is in a state of ignition, it be introduced into a jar filled with oxygen gas, it burns with great splendor, and emits a great quantity of white fumes. These fumes may be condensed, by pouring a small quantity of water into the jar, and when this is examined, it is found to possess acid properties. This is the sulphuric acid. It is procured, as appears by this experiment, by burning sulphur in oxygen gas.

4. The process for obtaining sulphuric acid in the large way is the following. A mixture of sulphur and nitre is burnt in leaden chambers. The use of the nitre is to supply a quantity of oxygen for the combustion of the sulphur. There is a little water in the bottom of the vessels, which serves to condense the vapors given out during the combustion. The acid which is obtained in this way is very weak, for it is diluted with the water in which it was condensed, which water may be separated by distillation. Even after this it is usually contaminated with a little lead from the vessels, some potash, and sometimes nitric and sulphurous acids. To obtain it perfectly pure, the sulphuric acid of commerce must be distilled. This process is conducted by putting a quantity of the acid into a retort, and exposing it to a degree of heat sufficient to make it boil. The neck of the retort is put into a receiver, in which the acid, as it comes over, is condensed.

5. The acid, thus purified, is a transparent colourless liquid, of an oily consistence. It has no smell, but a strong acid taste. It destroys all animal and vegetable substances. It reddens all vegetable blues. It always contains water. When this is driven off by a moderate heat, the acid is said to be concentrated. When as much concentrated as possible, the specific gravity is 2, or double that of water; but it can rarely be obtained of greater density than 1.84.

6. Sulphuric acid suffers no change from being exposed to the light. It boils at the temperature of 546°, or, according to Bergman, 540°. When this acid is deprived of its caloric, it is susceptible of congelation, and even of crystallization, in flat, six-sided prisms, terminating in a six-sided pyramid. It crystallizes most readily, when it is neither too much concentrated, nor diluted with water. Of the specific gravity of 1.65 it crystallizes at the temperature of a few degrees below the freezing point of water. Of the specific gravity of 1.84 it refills the greatest degree of cold. Chaptal observed it crystallize at the temperature of 48°, and Mr Keir found that it froze at 45° of the specific gravity of 1.78.

7. Sulphuric acid has a strong attraction for water. In some experiments that have been made, sulphuric water acid, when exposed to the atmosphere, attracted above strongly five times its weight of water. When four parts of concentrated sulphuric acid, and one part of ice at the temperature of 32°, are mixed together, the moment they come in contact the ice melts, and the temperature rises to 212°. A greater quantity of caloric is given out when the two bodies are mixed together in the liquid state. If four parts of the acid and one of water are suddenly mixed together, the temperature of the mixture rises to about 300°. This extraction of caloric, it is obvious, arises from the sudden condensation of the two liquids, the medium bulk of which is considerably less than the two taken together.

8. So great is the attraction of this acid for water, that the strongest that can be prepared can scarcely be determined supposed to be entirely free from it. It has therefore long greatly occupied the attention of chemical philosophers, to determine the proportions of real acid and water, in sulphuric acid of any given specific gravity. This subject has been investigated by Wenzel, Wiegleb, and Bergman, and more lately and successfully by Mr Kirwan. His method was the following. Eighty-five Mr Kirwan grains of potash, dissolved in water, were saturated with weak sulphuric acid of a known specific gravity. The solution being turbid, water was added till the specific gravity was 1.03 at temperature 60°. The whole weight was now equal to 3694 grams. Forty-five grs. of fulphate of potash dissolved in 1017 grs. of distilled water, had the same specific gravity at the temperature 60°. Hence the proportion of salt in each solution was equal. But in the last, the quantity of salt was $\frac{1}{22.6}$, then the quantity of salt in the former was $\frac{3694}{22.6} = 163.45$ grams. Of this quantity only 86 were alkali; the remainder, therefore, viz. 77.45 grams, were acid, or acid and water. The quantity of acid employed in the saturation amounted to 79 grs. standard; but the quantity of acid taken up was only 77.45 grs. therefore 1.55 were rejected, and consequently were mere water, therefore the acid taken up is stronger than standard; and since 79 parts standard lose 1.55 by combining with pure potash, 100 parts standard should lose 1.96; or 98.04 parts of acid of the strength of what is found in fulphate of potash, contains as much real acid as 100 parts standard. Hence 100 parts of this strong acid are nearly equivalent to 102 of standard. Therefore, 100 parts of potash take up nearly 92 of standard sulphuric acid, or 82 of the strongest, and afford 182 of fulphate of potash. Mr Kirwan thinks there is no reason to suppose that the sulphate of potash. potash contains any water of crystallization. One hundred grs. exposed to a red heat for half an hour fell into powder, and lost only a single grain.*

It having been suggested by Guyton-Morveau, Mr Kirwan observes, that the densities of mixtures of sulphuric acid and water being greater than what is found by calculation, should be ascribed to the condensation of the aqueous part, rather than to that of the acid; this led him to consider of a different method from what he had formerly employed in determining the quantity of real acid in sulphuric acid of different densities. Sulphuric acid of the specific gravity of 2,000 which is the strongest that can be produced by art, was taken as the standard of the strength of all other acids. He could not procure the acid of this strength at the temperature of 60°. But from many experiments made with acids of inferior density, as 1.8346, 1.8689, 1.8042, 1.7500, he concludes, that the condensation of equal weights of this standard acid and water amounts to \( \frac{1}{7} \)th of the whole. Then by applying Mr Pouget's formula (L) for investigating the increased densities of inferior proportions of acid and water, the successive increments of density will be found as in the following table.

Parts.

(L) The formula here alluded to was invented by M. Pouget in the investigation of the specific gravity of alcohol mixed with water in different proportions; and he has given a detailed account of his method in a letter addressed to Mr Kirwan, which is inserted in the Transactions of the Royal Irish Academy, vol. iii. p. 157.

Having purified alcohol by repeated distillations, the specific gravity at the temperature 65.75° was found to be 0.8199. This he took for his standard. And considering the specific gravity as the means of discovering the increase of density, or the diminution of volume, he thought the quantities in the mixture would be best determined, not by the difference of weight, but of volume. He therefore took ten mixtures, the first containing nine measures of alcohol and one of water, the second eight measures of alcohol and two of water, and so on to the last, which contained only one measure of alcohol and nine of water. But as the real measures are always uncertain, he weighed them to ascertain the specific gravity. Thus 10,000 grains of water and 8199 of alcohol formed a mixture of equal parts in bulk. Knowing the real specific gravities of mixtures of alcohol and water, taking a mean of a great number of observations made at the same temperature, and comparing them with the specific gravities found directly by calculation, he thus deduces the increase of density or the diminution of volume produced in the whole mass by the mutual penetration of the fluids. For calling A the real specific gravity, and B the specific gravity found by calculation, \( n \) the number of measures which compose the whole mass, \( n-x \) that to which it is reduced by mutual penetration, it is evident, since this increase of density does not diminish the weight of the whole mass, that

\[ nB = n-x \times A. \]

Then \( x = \frac{A-B}{A} \times n \), or making \( n = \frac{A-B}{A} \), which expresses the diminutions of bulk, or the quantity of fluid absorbed during the mixture.

The following table contains the result of Pouget's experiments, or the diminutions of volume which is supposed to be \( \frac{1}{7} \) of each of the mixtures, calculated according to the formula.

| Number of measures of Water | Alcohol | Diminution of the whole volume by experiment | By calculation | |-----------------------------|---------|--------------------------------------------|---------------| | 1 | 9 | 0.0109 | 0.0103 | | 2 | 8 | 0.0187 | 0.0184 | | 3 | 7 | 0.0242 | 0.0242 | | 4 | 6 | 0.0268 | 0.0276 | | 5 | 5 | 0.0288 | | | 6 | 4 | 0.0266 | 0.0276 | | 7 | 3 | 0.0207 | 0.0242 | | 8 | 2 | 0.0123 | 0.0184 | | 9 | 1 | 0.0044 | 0.0103 |

From this table it appears that the numbers which express the diminution of bulk follow a regular progression. The greatest correspond to the mixtures of equal parts, and they decrease towards each end of the progression. They must therefore be regulated by some general law. M. Pouget thinks that the alcohol may By adding, says Mr Kirwan, these increments to the specific gravities found by calculation, and taking arithmetical mediums for the intermediate quantities of standard, I made out the first 50 numbers of the following table; the remainder was formed by actual observation in the following manner, premising that the specific gravities were always taken between 59°3 and 60°, or at most 60°5 of Fahrenheit.

1st, I found by the preceding part of the table that 100 parts of sulphuric acid, whose specific gravity was 1.8472, contained 88.5 parts standard; consequently 400 grs. of this acid contain 354.

2dly, I then took five portions of this acid, each containing 400 grs. and added to them as much water as made them contain respectively 48.46.44.42.40. and 38. grains standard. To find the proportion of water that may be conceived as being dissolved in the water which has absorbed or retained part of it in its pores. The quantity absorbed ought to be in the ratio of that of the solvent and the body dissolved, and each measure of water will retain quantities of alcohol proportional to the number of measures of this fluid in the mixture. Thus, for example, in a mixture formed of nine measures of alcohol and one of water, this measure of water will absorb a quantity of alcohol = 9: and in another mixture of eight measures of alcohol with two of water, each measure of water will contain a quantity of alcohol = 8. Consequently the diminutions of bulk of each mixture are in a ratio compounded of the number of measures of alcohol and of water which form it; and in the table above, as \(1 \times 9, 2 \times 8, 3 \times 7, 4 \times 6, 5 \times 5\), &c. And in general taking for a constant quantity the diminution of bulk with equal measures, and calling it \(c\); calling the whole number of measures \(n\); the number of measures of alcohol in any mixture, \(x\), and the increase of density or diminution of volume \(z\), we shall have

\[ \frac{c}{n} : \frac{n}{2} : n - x \times z : \text{and } z = \frac{4c}{n^2} \times nx - nx^2 : \text{or making } n = 1, 4cx - 4cx^2. \]

The increase of density, calculated according to the formula, corresponds pretty nearly with experiments; for in all mixtures in which the alcohol is in greater quantity than water, but not in those cases in which the water is in greatest proportion, the real increase of density is much less than by calculation, and the differences become more considerable as the quantity of water is increased. M. Pouget thinks, that when the quantity of water is greater than that of alcohol, the law of absorption is disturbed; and he conjectures that it is owing to the attraction of the particles of the water among themselves, which consequently oppose their union with any other substance. But when the alcohol forms at least half of the whole mass, the diminutions of bulk are as the products of the numbers which express the proportions of alcohol and water forming the mixture: they may be represented by the formula

\[ z = \frac{4cnx - 4cx^2}{n^2}. \]

By this formula may be determined the strength of spirits of wine of commerce, or the number of parts of water and standard alcohol of which they are composed.

The number of measures of the whole mass or the bulk = 1 The number of measures of alcohol in any mixture = \(x\) The diminution of bulk of equal parts by experiment = \(c\) The diminution of bulk of a mixture containing \(x\) measures of alcohol by hypothesis = \(4cx - 4cx^2\) The specific gravity of water = \(a\) Specific gravity of alcohol = \(b\) Specific gravity of the unknown mixture = \(y\)

Since the increase of density does not change the weight of the mass, we shall have \(1 - x \times a + b \times x = 1 - 4cx + 4cx^2 \times y\).

By this equation may be found the value of \(x\) or the proportion of alcohol, having previously ascertained the specific gravity of the mixture, and to determine this specific gravity, or the value of \(y\) by knowing the proportions of alcohol. Hence,

\[ x = \frac{a - b}{8cy} + \sqrt{\frac{(a - b)^2}{(8cy)^2}} + \frac{(a - b)}{8cy} \]

\[ y = \frac{a - ax + bx}{1 - 4cx + 4cx^2} \]

And making \(a = 1, b = 0.8199, c = 0.0288\),

\[ x = \frac{0.1801}{0.2304y} + \sqrt{\frac{1 - y}{0.1152y}} + \frac{(0.1801)}{0.2304y} \]

\[ y = \frac{1 - 0.1801x}{1 - 0.1152x + 0.1152x} \] that should be added to each portion of acid, in order that it should contain the given proportion of standard, I used the following analogy: Let the quantity of water to be added to 400 parts of the acid that the mixture may contain 48 per cent. standard be \( x \).

Then \( 400 + x = 354 : 100 \cdot 48 \), then \( 19200 + 48x = 35400 \).

And \( 48x = 35400 - 19200 = 16200 \). And \( x = \frac{16200}{48} = 337.5 \).

"In this manner I found the quantities of water to be added to each of the other portions. The mixtures being made, they were set by for three days, stirring them with a glass rod (that remained in them) each day, and the 5th day they were tried; after which the half of each was taken out and as much water added to them, and then set by for three days, by which means the specific gravities corresponding to 24, 23, 22, 21, 20, and 19 per cent. standard were found, after which six more portions of 400 grs. each of the concentrated acid, whose specific gravity was 1.8393, were taken, the proper proportion of water added to each, and after three days left and repeated agitation, their densities in temperature 60° were examined as above, by which means the specific gravities corresponding to 36, 34, 32, 30, 28, and 26 per cent. standard were obtained, and half these portions mixed with half water exhibited, after three days left and agitation, the densities corresponding to 18, 17, 16, 15, 14, and 13 per cent. standard in the above temperature. The balance I used turned with \( \frac{1}{8} \) of a grain when charged with two ounces, and the solid employed was a small glass ball containing mercury which lost 27.88 grs. of its weight when weighed in water in temperature 56°, suspended commonly by a horse hair, but when dipped in strong nitrous and marine acids it is suspended by a fine gold wire, and then lost 27.78 grs. of its weight in water.

"I also examined and rectified, in some instances, many parts of the first 50 numbers of the table in the same manner, but in general I found them just."

**TABLE of the Quantity of the Standard Sulphuric Acid 2,000 in Sulphuric Acid of inferior Density.**

| Parts | Temp. 60° | Parts | Parts | |-------|-----------|-------|-------| | 2,000 | 100 | 1,7939 | 84 | | 1,9859 | 99 | 1,7849 | 83 | | 1,9719 | 98 | 1,7738 | 82 | | 1,9579 | 97 | 1,7629 | 81 | | 1,9439 | 96 | 1,7519 | 80 | | 1,9299 | 95 | 1,7416 | 79 | | 1,9168 | 94 | 1,7312 | 78 | | 1,9041 | 93 | 1,7208 | 77 | | 1,8914 | 92 | 1,7104 | 76 | | 1,8787 | 91 | 1,7000 | 75 | | 1,8660 | 90 | 1,6899 | 74 | | 1,8542 | 89 | 1,6808 | 73 | | 1,8424 | 88 | 1,6701 | 72 | | 1,8306 | 87 | 1,6602 | 71 | | 1,8188 | 86 | 1,6503 | 70 | | 1,8070 | 85 | 1,6407 | 69 |

"The last eleven numbers were only found by analogy, observing the series of decrements in the four preceding densities, and therefore are to be considered barely as approximations.

"To reduce vitriolic acids of given densities, at any degree of temperature between 49° and 70°, to that which they should have at temperature 60°, in order that their proportion of standard may be thereby investigated, I made the following experiments:

| Degrees of Temperature | Sp. Gr. of A. | Sp. Gr. of B. | Sp. Gr. of C. | |------------------------|---------------|---------------|---------------| | 70° | 1.8292 | 1.6969 | 1.3845 | | 65 | 1.8317 | 1.6983 | 1.3866 | | 60 | 1.8360 | 1.7005 | 1.3888 | | 55 | 1.8382 | 1.7037 | 1.3898 | | 50 | 1.8403 | 1.7062 | | | 49 | 1.8403 | | 1.3926 |

"Hence we see that vitriolic acid, whose density at any degree between 49° and 60° resembles or approaches the corresponding density in the column A, gains or loses 0.00126 of its specific gravity by every two degrees between 60° and 70° of Fahrenheit, and 0.00086 by every two degrees between 49° and 60°.

"Secondly, That any vitriolic acid, whose density at any degree between 50° and 70° resembles or approaches to the corresponding density in the column B, gains or loses 0.00158 for every two degrees between 60° and 70°; and 0.0017 by every two degrees between 50° and 60°. Whence it appears that the stronger acid is less altered by variation of temperature than the weaker, which formerly appeared to me an irregularity, but now seems to proceed from the increase of the accrued density, when larger proportions of water are mixed with the stronger acid.

"Thirdly, Sulphuric acid, whose density at any degree between 50° and 70° resembles the corresponding at the same degree in the column C, gains or loses 0.00086 for..." for every two degrees between 60° and 70° inclusively, and 0.00076 between 50° and 60°. Between 45° and 50° I could perceive no difference.

9. Attempts have been made to determine the proportion of oxygen and sulphur, which enter into the composition of sulphuric acid. According to the experiments of Lavoisier, in which he measured the quantity of oxygen absorbed, by a given weight of sulphur during combustion, the proportions are,

\[ \frac{71 \text{ sulphur}}{29 \text{ oxygen}} = \frac{100}{} \]

But other methods have been adopted, which promise more accurate results. These are, by decomposing other substances which contain oxygen, by means of sulphur. According to the experiments of Mr Chevieux, conducted in this way, the sulphuric acid consists of

\[ \frac{61.5 \text{ sulphur}}{38.5 \text{ oxygen}} = \frac{100}{} \]

10. Sulphuric acid does not combine with oxygen, nor has it any action with azotic gas.

11. It appears that hydrogen has a greater affinity for oxygen, than the sulphur has, and therefore the sulphuric acid is decomposed by means of hydrogen gas. In the cold there is no action between hydrogen gas and sulphuric acid; but if they are made to pass through a red-hot porcelain tube, the acid is decomposed; water is formed and sulphur is precipitated. When hydrogen gas is employed in a greater proportion than the half of the acid, the superabundant gas dissolves the sulphur, and is disengaged in the form of sulphurated hydrogen gas.

12. Charcoal has no action on sulphuric acid in the cold; but at the boiling temperature, it decomposes it, and converts it into sulphurous acid. If a piece of red-hot charcoal be immersed in a quantity of concentrated sulphuric acid, part of the acid is suddenly disengaged under the form of thick white fumes, accompanied with sulphurous acid gas. The sulphuric acid is decomposed; part of its oxygen is attracted by the charcoal, forming carbonic acid, and thus it is reduced to the lowest proportion of oxygen, in the state of sulphurous acid.

13. A similar effect is produced by phosphorus. Phosphorus, with the assistance of heat, partially decomposes the sulphuric acid, by abstracting part of its oxygen. Phosphoric acid is formed, and sulphurous acid driven off.

14. In the cold, sulphur has no action on sulphuric acid; but, when they are boiled together, the sulphur is partly dissolved in the acid, and converts it into sulphurous acid. The sulphur which has been added combines with the oxygen, which is necessary for the constitution of sulphuric acid, and thus the whole is converted into sulphurous acid.

15. Sulphuric acid combines with alkalies, the earths, and the metals, forming salts; which in the present language of chemistry, are denominated sulphates.

16. This acid is employed in great quantity in many arts and manufactures. It is employed also in medicine and pharmacy; the preparation of it, therefore, has long been an object of considerable importance.

17. The affinities of sulphuric acid are the following:

- Barytes, - Strontites, - Potash, - Soda, - Lime, - Magnesia, - Ammonia, - Glucina, - Yttria, - Alumina, - Zirconia, - Oxide of Zinc, - Iron, - Manganese, - Cobalt, - Nickel, - Lead, - Tin, - Copper, - Bismuth, - Antimony, - Arsenic, - Mercury, - Silver, - Gold, - Platina.

Sect. II. Of Sulphurous Acid.

1. According to the explanation of the nomenclature of the acids, the term sulphurous shows that this acid is in its diminished state of combination with oxygen. It was formerly called spirit of sulphur, and volatile sulphurous acid. Although the ancients must have been acquainted with some of its properties, as it is formed during the slow combustion of sulphur, yet Stahl is the first chemist who examined it with attention. He supposed that it was the sulphuric acid combined with his imaginary principle of phlogiston. Hence he called it phlogisticated sulphuric acid. It was not till the year 1774 that its nature and composition were discovered by the labours of Priestley and Lavoisier. Berthollet afterwards investigated the formation, decomposition, combinations, and uses of this acid. Fourcroy and Vauquelin also have examined many of its properties, especially the saline compounds which it forms, so that now its properties are well known.

2. The sulphurous acid exists in nature in great abundance, and particularly in the neighbourhood of volcanoes. It is disengaged from some lavas in a state of fusion, and from the soil which is impregnated with sulphur, when a sufficient degree of heat is applied. It was fatal to Pliny by the vapours of sulphurous acid that Pliny the naturalist was suffocated in the eruption of Mount Vesuvius, which destroyed Herculaneum, in the 79th year before the Christian era.

3. When sulphur is burnt in the open air, the fumes that are generated by this slow combustion, are sulphurous acid. It was in this way that this acid was formerly The method of procuring it, which is now followed, is to decompose the sulphuric acid by means of any substance which deprives it of part of its oxygen. If one part of mercury and two parts of concentrated sulphuric acid be exposed to heat in a glass retort, the mixture effervesces, and a gas is discharged, which may be collected in jars over mercury. In this process the mercury attracts part of the oxygen of the sulphuric acid, and leaves behind that portion which constitutes the sulphurous acid.

4. Sulphurous acid thus obtained is in the state of gas, and it is an elastic, invisible, and colourless fluid, like common air. It is rather more than double the weight of atmospheric air. Its specific gravity is 0.00246; 100 cubic inches weigh nearly 63 grains. It has a sharp pungent smell; it is unfit for respiration, and for supporting combustion. It reddens vegetable blues, and then destroys the greater number of them. It is on account of this property that the fumes of sulphur are employed to remove the stains of fruit from linen, and that the sulphurous acid is often used in bleaching.

5. Sulphurous acid gas refracts the light strongly, without undergoing any change. When it is strongly heated, as in a red-hot porcelain tube, it remains unaltered, according to the experiments of Fourcroy. But Dr Priestley and Berthollet found that it deposited sulphur after long exposure to heat. At the temperature of —31° it becomes liquid. This property, which distinguishes it from other gases, and which was discovered by Monge and Cloutet, Fourcroy thinks is owing to the water it holds in solution.

6. When sulphurous acid is in the form of gas, it does not readily combine with oxygen. In its fluid form it unites more freely, and is converted into sulphuric acid. In making a mixture of sulphurous acid gas and oxygen pass through a red-hot tube, they combine together, and are converted into sulphuric acid. There seems to be no action between sulphurous acid and azotic gas.

7. Hydrogen gas has no action on sulphurous acid gas in the cold; but when a mixture of these gases is made to pass through a red-hot tube, sulphurous acid is decomposed; the hydrogen combines with the oxygen and forms water, and sulphur is deposited. If the hydrogen gas be in greater proportion than the oxygen contained in the sulphurous acid, it dissolves part of the sulphur, and passes off in the form of sulphurated hydrogen gas.

8. Its action with charcoal is somewhat similar. In the cold there is no effect; but exposed together to a red heat, carbonic acid is formed, by the union of carbon and oxygen, and sulphur is deposited.

9. There is no action whatever between phosphorus and sulphurous acid gas; but phosphorated hydrogen gas is decomposed by this acid. When the two gases come in contact, a white thick vapour is produced; sulphur combined with phosphorus in the solid state is deposited, and water is formed.

10. Sulphur has no action on this acid; but sulphurated hydrogen gas, at the instant it comes in contact with sulphurous acid gas, is condensed; solid sulphur is deposited, and water is formed, with the extrication of caloric by the condensation of the two gases.

11. Water has a strong attraction for sulphurous acid gas. A bit of ice brought in contact with it, is immediately melted without any perceptible change of temperature. When water is saturated with this gas, it is known by the name of sulphurous acid, or liquid sulphurous acid. The specific gravity is 1.0240. At the temperature of 43° water combines with ¼ of its weight of sulphurous acid gas; but as the temperature increases, it absorbs it in smaller proportion. It freezes at a temperature a few degrees below 32°, and it passes into the solid state without parting with any of its acid. Liquid sulphurous acid has the smell, taste, and other properties of the gas, and particularly that of destroying vegetable colours. When exposed to the atmosphere, it gradually absorbs oxygen, and passes into the state of sulphuric acid. This change goes on more rapidly when it is diluted with water, and agitated in contact with the air.

12. Sulphuric acid separates the sulphurous acid within the gaseous form from its combinations, and even phuric acid from water. Concentrated sulphuric acid absorbs this gas, which imparts to it a yellowish brown colour, and renders it pungent and fuming. The two acids strongly attract each other, so that when they are exposed to the action of heat, the first vapour which rises crystallizes in long, white, needle-shaped prisms. This is a compound of the two acids. It smokes in the air; dissolves with effervescence in it, and when thrown into water produces a hissing noise, like a red-hot iron. It has the strong smell of sulphurous acid. This substance was formerly called glacial sulphuric acid.

13. Sulphurous acid is very much employed in the arts, and sometimes in medicine. In the state of gas it is used for the bleaching of silk and wool, by extracting the colouring matter. It removes also the stains arising from vegetable juices, and spots of iron from linen.

14. According to Fourcroy, 100 parts of this acid are composed of:

- 85 sulphur, - 15 oxygen.

But according to the analysis of Dr Thomson,

- 68 sulphur, - 32 oxygen.

15. The compound salts formed by this acid are denominated sulphites.

16. The following are the affinities of this acid:

- Barytes, - Lime, - Potash, - Soda, - Strontites, - Magnesia, - Ammonia, - Glucina, - Alumina, - Zirconia.

Sect. Sect. III. Of Nitric Acid.

1. This acid was formerly known by the name of aqua fortis, and spirit of nitre. Raymond Lully, who lived in the 13th century, seems to have been acquainted with it; and Basil Valentine, who lived in the 15th, describes the process for preparing it. He calls it water of nitre. But till the discoveries of modern chemistry, little was known of the nature, properties, and composition of this acid. It is to the experiments and researches of Cavendish and Priestley, of Lavoisier and Berthollet, that we are indebted for the knowledge we possess of this acid.

2. Nitric acid exists in great abundance in nature. It is formed by the union of its constituent parts which are evolved during the putrefactive process of animal and vegetable matters; but it is never found, except in combination with some base, from which it must be extracted by art. The component parts of nitric acid, are azote and oxygen. The name in this case is not derived from the base, which is azote, but from nitre, from which it is generally obtained. This acid cannot be formed merely by bringing into contact the gases which are its constituent parts; but if they are mixed together in certain proportions, and electric sparks sent through the mixture, the gases disappear, and are converted into a liquid. This is nitric acid. By a similar experiment Mr Cavendish discovered the composition of the acid.

3. This acid may be obtained by putting three parts of nitre or saltpetre with one of sulphuric acid into a glass retort, and distilling with a strong heat. The gas which comes over is condensed in a glass receiver, to which the retort is to be fitted. The gas which is condensed is nitric acid. Nitre is composed of nitric acid and potash; but potash has a stronger affinity for sulphuric acid than for nitric acid; it therefore combines with the sulphuric acid in the retort, and the nitric acid is disengaged, and passes over in the gaseous form.

4. The acid thus obtained is impure, and is contaminated with muriatic, and sometimes with sulphurous acid. It is purified by distillation with a gentle heat. At first too it is of a yellow colour, which is owing to the fumes of nitrous gas with which it is combined. These fumes are driven off by heat, after which the acid remains pure, and is transparent and colourless.

5. Thus prepared, it has a strong acid taste; a disagreeable pungent odour, and gives a yellow colour to the skin. The specific gravity of strong nitric acid is 1.583, or, according to Mr Kirwan, at temperature 60°, 1.554.

6. Nitric acid and one of its compounds, nitre, have long been the subject of the experiments and researches of chemical philosophers. In investigating the nature of nitre, Mayow found that it possessed a common property with atmospheric air; namely, the property of giving a red colour to the blood. And, from observing that air was deprived of this property by the process of combustion and respiration, he drew the singular conclusion, that nitre contained that part of the air which is necessary for respiration and combustion.

7. When nitric acid dissolves metallic substances, a great quantity of a peculiar gas makes its escape, and the metal acquires considerable weight during this process. According to the phlogistic theory, it was supposed that the metal was deprived of its phlogiston, and that this phlogiston had combined with the nitrous gas which had escaped. This was Dr Priestley's explanation. But it was differently explained by Lavoisier. He took 1104 grs. of mercury, and added to it 945 grs. of nitric acid. Nitrous gas was emitted during the solution, and when he exposed the mercury which had been converted into an oxide, to a red heat, oxygen gas was given out, and the mercury appeared in the metallic state. He therefore concluded, that the nitric acid in this case was decomposed, and that it consisted of oxygen which combined with the metal, and of nitrous gas which was driven off. The proportions, he supposed, were, 64 parts of nitrous gas by weight, and 36 of oxygen gas. He found, however, that the quantity of oxygen obtained in this process, was sometimes greater than what was necessary to saturate the nitrous gas; and he was at a loss to account for this quantity. His own experiments, as well as those of Dr Priestley's, proved, that azote is a component part of nitre.

Mr Cavendish, who discovered the composition of water, in his experiments and researches on that subject, found, that nitric acid was produced during the explosion of oxygen and hydrogen gases; and that he could increase this quantity by adding azotic gases to the mixture before combustion. From this he concluded, that the formation of the acid depended on the azotic gas. He proved this by passing electrical sparks through common air in a glass tube. The air diminished in bulk, and nitric acid was formed. Repeating a similar experiment with oxygen and azotic gases in certain proportions, he found that the whole could be converted into nitric acid*. Mr Cavendish repeated the same experiments, with a view to remove some objections which had been made to his conclusions. They were followed by the same result, so that the fact of the composition of nitric acid was fully established†.

To perform this experiment, take a glass tube of about one-sixth of an inch in diameter. Close one end with a cork, through which let a metallic conductor with a ball at each extremity be passed. Fill the tube with mercury; immerse the open end into the mercurial trough; introduce a mixture of .13 parts of azotic gas, and .87 of oxygen gas, occupying three inches of the tube, and a solution of potash filling one-half inch more. Let electrical explosions be sent through the tube till the air ceases to be diminished in bulk. If the experiment succeed, the potash will be found converted into nitre, which shows that the nitric acid, which is a component part of nitre, has been formed during the process.

8. Nitric acid, having a strong affinity for water, is always never found entirely deprived of this liquid. When exposed to the air, it attracts moisture from it, and heat is given out when it is mixed with water. Mr Kirwan has endeavoured to ascertain the relative strength of nitric acid of different densities, or specific gravities; and the method which he adopted is the following. He saturated 36 grs. of carbonate of soda quantity with with 147 grs. of nitric acid, of specific gravity 1.2754, which contained 45.7 per cent. of standard acid, of specific gravity 1.5543. The carbonic acid which escaped amounted to 14 grs.; and by adding 939 grs. of water, the specific gravity of the solution, at the temperature of 58.5°, was 1.0401. By a similar test with that employed in ascertaining the strength of sulphuric acid, namely, by comparing this solution with one of nitrate of soda of the same density, he found the quantity of salt amounted to 1.16 parts. There was an excess of acid of about 2 grs. The whole weight was 1439 grains. The quantity of salt, therefore, was

\[ \frac{1439}{16901} = 85.142 \text{ grs.} \]

The quantity of pure alkali was .50 — 14 = 36.05 grs. The quantity of standard acid was 66.7; the sum of both = 102.75. Of this quantity only 85.142 entered into combination with the salt, the remaining 17.608 were mere water, given out by the standard acid. If then 66.7 parts standard acid lose 17.608 parts water combining with the alkali, 100 parts should lose 26.38. And, as Mr Kirwan has made it probable, that nitrate of soda contains very little water in its composition; 100 parts of standard nitric acid is composed of 73.62 of pure acid, and 26.38 of water.

The following table drawn up by Mr Kirwan shews the quantity of pure acid in nitric acid of different specific gravities.

| 100 Parts. Sp. Gravity | Real Acid. | 100 Parts. Sp. Gravity | Real Acid. | |------------------------|-----------|------------------------|-----------| | 1.5543 | 73.54 | 1.4171 | 53.68 | | 1.5295 | 69.86 | 1.4120 | 52.94 | | 1.5183 | 69.12 | 1.4069 | 52.21 | | 1.5070 | 68.39 | 1.4018 | 51.47 | | 1.4957 | 67.65 | 1.3975 | 50.74 | | 1.4844 | 66.92 | 1.3925 | 50.00 | | 1.4731 | 66.18 | 1.3875 | 49.27 | | 1.4719 | 65.45 | 1.3825 | 48.53 | | 1.4707 | 64.71 | 1.3775 | 47.80 | | 1.4695 | 63.98 | 1.3721 | 47.06 | | 1.4683 | 63.24 | 1.3671 | 46.33 | | 1.4671 | 62.51 | 1.3621 | 45.59 | | 1.4660 | 61.77 | 1.3571 | 44.86 | | 1.4651 | 61.03 | 1.3521 | 44.12 | | 1.4582 | 60.30 | 1.3468 | 43.38 | | 1.4553 | 59.56 | 1.3417 | 42.65 | | 1.4524 | 58.83 | 1.3364 | 41.91 | | 1.4471 | 58.09 | 1.3315 | 41.18 | | 1.4422 | 57.36 | 1.3264 | 40.44 | | 1.4373 | 56.62 | 1.3212 | 39.71 | | 1.4324 | 55.89 | 1.3160 | 38.97 | | 1.4275 | 55.15 | 1.3108 | 38.34 | | 1.4222 | 54.12 | 1.3056 | 37.50 |

From experiments made by Mr Davy, he has deduced the real quantities of nitric acid in solutions of different specific gravities, and by his estimation the proportions will appear in the following table.

**Table of the quantities of True Nitric Acid in solutions of different Specific Gravities.**

| 100 Parts Nitric Acid, of specific gravity | True Acid (M.) | Water | |--------------------------------------------|---------------|-------| | 1,5040 | 91.55 | 8.45 | | 1,4475 | 80.39 | 19.61 | | 1,4285 | 71.65 | 28.35 | | 1,3906 | 62.96 | 37.04 | | 1,3551 | 56.88 | 43.12 | | 1,3186 | 52.03 | 47.97 | | 1,3042 | 49.04 | 50.96 | | 1,2831 | 46.03 | 53.97 | | 1,2090 | 45.07 | 54.73 |

5. When colourless nitric acid is exposed to the action of light, it undergoes a partial decomposition. Some light oxygen gas is separated, the acid assumes an orange yellow colour, and part of it passes into the state of nitrous acid.

10. It boils at the temperature of 248°, and is entirely distillated without alteration, if the heat be continued. When it is made to pass through a red-hot porcelain tube, it is decomposed, and converted into its constituent parts, oxygen and azotic gases.

When fourcrey nitric Cormetts. Chim. tom. ii. p. 81.

\[ X = \frac{238A}{239} \quad \text{and} \quad Y = \frac{A}{239}. \] nitric acid (N) is cooled down to the temperature of —55°; it begins to crystallize in a few minutes, assumes a deep-red colour, and congeals into a thick mass resembling butter, by agitating the vessel which contains

11. There is no action between nitric acid and oxygen or azotic gases; but, when concentrated nitric acid is exposed to the air, the vapour which it exhales combines with the moisture of the atmosphere, forms white fumes, and is condensed into a liquid.

12. Hydrogen gas has no action on nitric acid at the ordinary temperature of the atmosphere; but if they are made to pass through a red-hot porcelain tube, there is a violent combustion with detonation. Water is formed by the combination of the hydrogen with the oxygen of the acid; and azotic gas, its other constituent part, is evolved.

13. Nitric acid is also decomposed by charcoal at a high temperature. Carbonyl combines with the oxygen, and forms carbonic acid, while the azotic gas is let at liberty.

14. It is also decomposed in the same way by phosphorus and sulphur. When the acid is poured upon these combustibles at a high temperature, inflammation takes place, and they are converted into phosphoric and sulphuric acids.

15. When nitric and sulphuric acids are mixed together, heat is evolved. The sulphuric acid attracts the water which existed in the nitric acid, and this water being more condensed in combination with sulphuric acid, the caloric with which it was combined along with the nitric acid, is given out. Thus, the nitric acid becomes more concentrated by the addition of the sulphuric acid.

When nitric and sulphurous acids are mixed together, a very different action takes place. The nitric acid separates it from water and its other combinations; parts with its oxygen, and thus converts it into sulphuric acid, and passes itself into the state of nitrous gas.

16. According to Lavoisier, the proportions of the component parts of nitric acid are, one part azote and four parts oxygen. This was the result of his experiments on the decomposition of nitre by charcoal. According to Mr Cavendish, the proportions of the azote and oxygen combined by electricity are one part azote and 2.346 of oxygen. The result of Mr Davy's experiments shows that 100 parts of pure nitric acid are composed of

\[ \begin{align*} 29.5 & \text{ azote,} \\ 70.5 & \text{ oxygen.} \end{align*} \]

17. The combinations which are formed with the nitric acid, and the alkalies, earths, and oxides of metals, are denominated nitrates.

18. The order of the affinities of nitric acid is the following:

Barytes, Potash, Soda, Strontites, Lime, Magnesia, Ammonia, Glucina, Alumina, Zirconia, Oxide of Zinc Iron, Manganese, Cobalt, Nickel, Lead, Tin, Copper, Bismuth, Antimony, Arsenic, Mercury, Silver, Gold, Platinum.

19. This is one of the most important of the acids, considered as an instrument of analysis in the hands of the chemist. It is employed in many arts. It is also used in medicine, in diseases of the skin; and it has lately been exhibited as a cure in venereal affections. In this case, perhaps, it may be regarded as a useful auxiliary to the ordinary remedies.

**SECT. IV. Of NITROUS ACID.**

1. According to the present nomenclature, nitrous acid should bear the same relation to nitric acid that procured sulphurous acid bears to sulphuric; that is, the constituent parts of nitric acid should be in different proportion from those of nitrous acid; but this does not appear to be the case. What is usually denominated nitrous acid, may be formed by combining nitrous gas with nitric acid: Or if the lower stratum in a vessel of nitric acid be slowly decomposed by a metallic substance, the oxygen of the acid combines with the metal; nitrous gas is evolved, which combines with the superior strata of the nitric acid, and converts it into nitrous acid. It has then assumed a yellow colour, and its specific gravity is diminished.

The same effect takes place when nitric acid is exposed to light. It is deprived of part of its oxygen, and nitrous gas is evolved, which mixes with the acid, changes it to a yellow colour, and converts it into nitrous acid.

2. Thus it appears that nitrous acid is nitric acid combined with nitrous gas. The acid of commerce, or what is commonly called aqua fortis, is nitrous acid.

3. Nitric acid combines in different proportions with nitrous gas.

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(n) The acid employed in the experiment contained nitrous gas. nitrous gas, which gives rise to many varieties of nitrous acid; and, according to the quantity of nitrous gas absorbed, the acid exhibits very different colours. The following table, drawn up by Mr Davy, shews in one view the proportions of nitric acid and nitrous gas, in different coloured nitrous acids.

**TABLE containing Approximations to the quantities of Nitric Acid, Nitrous Gas, and Water in Nitrous Acids, of different colours and specific gravities.**

| Parts | Specific Grav. | Nitric Acid | Water | Nitrous Gas | |-------|---------------|-------------|-------|-------------| | Sol. nitric acid | 1,504 | 91.55 | 8.45 | - | | Yellow nitrous † | 1,502 | 92.5 | 8.3 | 1.2 | | Bright yellow | 1,500 | 88.94 | 8.10 | 2.96 | | Dark orange | 1,485 | 86.84 | 7.6 | 3.56 | | Light olive ‡ | 1,479 | 80.0 | 7.55 | 4.45 | | Dark olive ‡ | 1,478 | 85.4 | 7.5 | 7.1 | | Bright green ‡ | 1,476 | 82.8 | 7.44 | 7.76 | | Blue green * | 1,475 | 84.6 | 7.4 | 6.00 |

4. Light has no action on nitrous acid; but when heat is applied, the nitrous gas is driven off, and the nitric acid remains behind. In the state of vapour, nitrous acid remains unchanged by the action of heat.

5. Neither oxygen gas, azotic gas, nor atmospheric air, produce any change on nitrous acid.

6. On combustible bodies the action of nitrous acid is nearly similar to that of the nitric acid; but many substances are more rapidly inflamed by nitrous acid. This seems not only to depend on the state of the division or rarefaction of the nitrous gas combined with the nitric acid, but also on the nitrous gas itself being more easily decomposed, and giving up its oxygen, which is less strongly attracted by the azote, on account of the great proportion of caloric united with it in the gaseous state. It decomposes phosphated and sulphated hydrogen gas, and precipitates the phosphorus and the sulphur.

7. Sulphuric acid combines with the vapour of nitrous acid, which communicates the property of disposing the sulphuric acid to crystallise. Nitrous acid converts sulphurous into fulphuric acid, and, at the same time, parts with its nitrous gas.

8. Nitrous acid enters into combination with the alkalies and earths. The compounds are distinguished by the name of nitrates. These compounds are not made by direct combination, and therefore the affinities of this acid are little known.

**SECT. V. Of MURIATIC ACID.**

1. The component parts of this acid are unknown. No attempt which has hitherto been made to discover its constituent parts, has yet succeeded. But, as it resembles the other acids, the composition of which has been discovered, in many of its properties and combinations, it is usually arranged among this class of bodies. The name of muriatic acid is derived from the Latin word muria, which signifies sea-salt, or common salt, from which the acid is usually extracted. It was formerly denominated spirit of salt, acid of salt, and marine acid.

2. Muriatic acid may be obtained by putting 100 parts of dry common salt, and 35 parts of sulphuric acid into a retort or matras with a bent tube. The beak of the retort at the end of the tube must communicate with a receiver in which there is water, that the muriatic acid may be condensed as it passes into the receiver. In this way liquid muriatic acid may be obtained.

3. But if the gas which comes over is received in a jar inverted in the mercurial apparatus, its properties may be examined in the state of gas. When it first passes over, it is in the form of white smoke.

4. Muriatic acid gas possesses the physical properties of common air. It is an invisible elastic fluid. It has a strong acid taste, and a very pungent smell. The specific gravity, according to Kirwan, is 0.002315.

5. It is unfit for respiration, and equally so for supporting combustion.

6. This gas has a strong attraction for water. If a little water be introduced into a jar filled with this gas, standing over mercury, the whole of the gas will be absorbed, and the mercury will instantaneously rise to the top. Or if a jar filled with muriatic acid gas be inverted into a vessel of water, coloured with vegetable blue, the water suddenly rushes into the jar, which it completely fills, and the blue colour is changed to red, exhibiting the usual effects of acids on vegetable colours.

7. Light has no action whatever on this gas, nor does it undergo any change when it is made to pass through heat, a red-hot porcelain tube. In the state of gas, it has no action upon oxygen gas. When this gas comes in contact with atmospheric air, thick white fumes are produced, with the extrication of caloric. This is a combination of the gas with the water in the atmosphere, by which they are mutually condensed.

8. There is no action between muriatic acid gas and azote, hydrogen, charcoal, phosphorus, or sulphur.

9. The quantity of water which muriatic acid absorbs is very considerable. Ten grs. of water combine with ten grs. of the gas. The liquid acid thus formed occupies the space of 13.3 grs. and hence its proportion specific gravity is 1.500, and the specific gravity of the purest muriatic acid in its condensed state is 3.300 (0).

The specific gravity of the strongest muriatic acid that can easily be procured and preserved, is 1.196.

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* "The blue green acid is not homogenous in its composition: it is composed of the blue green spherules and the bright green acid. The blue green spherules are of greater specific gravity than the dark green acid, probably because they contain little or no water."

† "The composition of the acids thus marked, is given from calculations."

(o) "Let D = the density of a mixture; m the weight of the denser ingredient; d its density; l the weight of..." One hundred parts of this, Mr Kirwan calculates, will contain about 49 of acid, whose specific gravity is 1.500, which he calls the standard acid. By mixing this acid with different proportions of water, he obtained the results from which he constructed the following table.

**Table of the quantity of Real Acid in 100 parts of Muriatic Acid of different Specific Gravities, at the Temperature 60°.**

| 100 parts Sp. Gravity | Real Acid | 100 parts Sp. Gravity | Real Acid | |-----------------------|-----------|-----------------------|-----------| | 1.196 | 25.28 | 1.1282 | 16.51 | | 1.191 | 24.76 | 1.1244 | 15.99 | | 1.187 | 24.25 | 1.1206 | 15.48 | | 1.183 | 23.73 | 1.1168 | 14.96 | | 1.179 | 23.22 | 1.1120 | 14.44 | | 1.175 | 22.70 | 1.1078 | 13.93 | | 1.171 | 22.18 | 1.1036 | 13.41 | | 1.167 | 21.67 | 1.0984 | 12.90 | | 1.163 | 21.15 | 1.0942 | 12.38 | | 1.159 | 20.64 | 1.0901 | 11.86 | | 1.155 | 20.12 | 1.0868 | 11.35 | | 1.151 | 19.60 | 1.0826 | 10.83 | | 1.147 | 19.09 | 1.0784 | 10.32 | | 1.141 | 18.57 | 1.0742 | 9.80 | | 1.1396 | 18.06 | 1.0630 | 8.25 | | 1.1358 | 17.54 | 1.0345 | 5.16 | | 1.1320 | 17.02 | 1.0169 | 2.58 |

**Properties.**

10. Liquid muriatic acid, in its ordinary state, is of a pale yellow colour; but when it is pure, it is transparent and colourless.

11. Light has no action whatever on muriatic acid. When heat is applied, it readily assumes the gaseous form. Neither oxygen nor azotic gases are absorbed by muriatic acid, nor has this acid any action on hydrogen, charcoal, phosphorus, or sulphur.

12. Sulphuric acid separates the muriatic acid from its compounds, and even from its combination with water; but the muriatic acid drives off the sulphurous acid from this liquid.

13. One of the most remarkable characters of muriatic acid, is its combination with nitric acid. When these two acids are mixed together, they act upon each other, are strongly heated, and produce effervescence, with a change of colour to an orange red. A mixed acid is thus formed, which possesses properties which existed neither in the one acid nor the other when in a state of separation. It was formerly called aqua regia, from its property of dissolving gold, which was distinguished by the name of king of the metals. It is now denominated nitro-muriatic acid. This acid is not to be considered as a simple mixture of the two acids. A double attraction takes place in their mutual action; the muriatic acid attracts part of the oxygen of the nitric acid, and the nitric combines with the nitrous gas. The muriatic acid thus combined with a portion of oxygen, is disengaged with effervescence in yellow fumes: the undecomposed nitric acid leaves the nitrous gas which is formed, and when it is saturated with it, the action ceases. Hence arises the colour of the mixed acid. The peculiar effect of the nitro-muriatic acid on metallic substances, will be described in treating of the metals.

14. In analysing a mineral water, Mr Lambe concluded, from some appearances which presented themselves during his experiments, that the muriatic acid of muriate was formed or generated; for when iron was acted upon by fulphurated hydrogen gas, oxymuriate of iron was formed. He digested iron filings, previously purified, in a solution of fulphurated hydrogen gas, in distilled water. A bottle was filled with the solution, and corked. The iron was presently acted upon; air was extricated, probably hydrogen gas, which drove the cork out of the bottle. The liquor, gradually lost its odour, and at the end of some days it had a smell resembling that of stagnant rain water. As the bubble ceased to be produced, it recovered its transparency: A small quantity of this solution, evaporated to dryness, left behind a bitter, deliquescent salt. Sulphuric acid dropped on this salt, and paper moistened with ammonia, held over the glass, produced vapours, so that some volatile acid was separated. Eight ounces measures of the same liquor were evaporated, and a little sulphuric acid was dropped on the residue. A strong effervescence was excited, and acid fumes arose, which, from their smell, were readily known to be muriatic acid. Paper moistened with water rendered the vapours visible in the form of a gray smoke, which is the distinguishing characteristic of muriatic acid. The same appearances were exhibited with the same result, when manganese and mercury were dissolved in fulphurated hydrogen gas.

The same experiments have been repeated; but no traces of muriatic acid, in any of the compounds that were formed, could be found. In an experiment by Berthollet, indeed, iron filings washed with water which gave no marks of containing muriatic acid, when they were exposed some days to the air, and again washed, exhibited some traces of it; so that the acid itself, or its elements, must have come from the air or the iron.

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of an equal bulk of water; and \(m'\), \(d'\), and \(l\), the same elements of the rarer: Then \(D = \frac{m + m'}{l + l'}\). In the above case, \(m + m' = 20\), and \(l + l' = 13.3\). Then \(D = \frac{20}{13.3} = 1.5\). Now to find the specific gravity of the condensed muriatic acid gas, we have from the above equation \(l = \frac{m + m' - D}{D} = \frac{5}{1.5} = 3.3\); and \(d = \frac{m}{l} = \frac{10}{3.3} = 3.03\). Kirwan. *Iris Transact.,* vol. iv. p. 5. The bulk of muriatic acid gas is greatly diminished by the action of electricity, and hydrogen gas is given out; but this action is limited. Mr Henry has shown that it is not owing to the decomposition of the acid, as might at first sight be supposed, but to the decomposition of water which it holds in solution; so that the action continues as long as there is any moisture in the gas. The oxygen of the water combines with the acid, and forms oxymuriatic acid; while the hydrogen of the water is evolved.

Muriatic acid gas has been successfully employed in destroying noxious, putrid exhalations. It was applied in this way in the year 1773 by Morveau, in purifying the cathedral of Dijon from these exhalations, on account of which it had been altogether deserted. He put five pounds of common salt into a glass vessel, placed in the middle of the church, poured two pounds of sulphuric acid on the salt, placed the vessel on some live coals, and immediately shut the doors. It was allowed to remain 12 hours; after which the doors were opened; and a current of air being allowed to pass through it, it was found that the noxious vapors were entirely destroyed.

The compounds which are formed by muriatic acid, with alkalies, earths, and metallic oxides, are distinguished by the name of muriates.

The following is the order of the affinities of this acid:

- Barytes, - Potash, - Strontites, - Lime, - Ammonia, - Magnesia, - Glucina, - Alumina, - Metallic oxides.

Sect. VI. Of Oxymuriatic Acid.

Oxymuriatic acid was discovered by Scheele in the year 1774, and he gave it the name of dephlogisticated marine acid. On account of its singular properties, and the important uses to which it was soon applied, it has been much examined by chemical philosophers.

This acid is obtained by the following process: Take three parts of common salt, and one part of the black oxide of manganese reduced to powder. Introduce them into a tubulated retort; place the retort in a sand bath, and immerse its neck under the surface of the water in the pneumatic trough. Pour upon it two parts of sulphuric acid a little diluted with water. As effervescence takes place, and a yellow coloured gas is evolved, which may be received in jars, or preserved in large vessels with ground stoppers.

The nature of this process is sufficiently obvious. Common salt is composed of muriatic acid and soda; the affinity of sulphuric acid for soda is stronger than that of muriatic acid; it therefore combines with the soda, and the muriatic acid is disengaged in the state of gas. The black oxide of manganese is composed of oxygen and the metallic substance. The sulphuric acid combines with the manganese, and sets the oxygen at liberty in the state of gas. But there is also an affinity between the muriatic acid and oxygen, so that in the moment of evolution they unite, and pass off in the state of oxymuriatic acid gas.

This gas is of a yellowish green colour, has a strong penetrating odour, and excites violent coughing, when a mixture of it with atmospheric air is respired; but the pure gas is totally unfit for respiration. This gas supports combustion. It diminishes and reddens the flame of a taper; a great deal of smoke is evolved, and the taper consumes very rapidly.

Neither light nor heat have any action on the gas. When passed through red-hot porcelain tubes, it remains unchanged.

It has no action whatever on oxygen or azotic gases.

In the cold no effect is produced from a mixture of this gas with hydrogen gas; but when they are passed through a red-hot tube, there is a violent detonation.

In the cold there is no action between charcoal and this gas. When a mixture of equal bulks of this coal gas and carbonated hydrogen gas is set fire to, there is only a combustion of the hydrogen gas, with a deposition of charcoal. If two measures of oxymuriatic acid gas, and one measure of carbonated hydrogen gas are mixed together in a close phial, and allowed to remain for 24 hours, they decompose each other. Water, muriatic acid, carbonic acid, and gaseous oxide of carbon, are the products. When water is admitted, the whole will be nearly absorbed.

A bit of dried phosphorus introduced into this gas, is instantly inflamed, and converted into phosphoric acid. It also sets fire to phosphorated hydrogen gas, which has lost the property of spontaneous inflammation in the air.

Melted sulphur, plunged into this gas, is immediately inflamed, and converted into sulphuric acid. Sulphurated hydrogen gas is decomposed, but without inflammation, and sulphur is depoited.

There is no action between this gas and ful. Sulphurous acid; but, when sulphurous acid gas is mixed with it, a thick white vapour is formed, which is the sulphurous acid converted into sulphuric acid, by depriving the oxymuriatic acid gas of its oxygen. It has no effect on nitric acid; but nitrous gas brought into contact with it, is reddened, and converted into nitrous acid.

What is commonly known by the name of oxy-in the lime of muriatic acid, is water saturated with this gas. It has a pale green colour, and exhales the same odour as the gas. According to Berthollet, cubic inch of water absorbs 156 grs. French of the gas. The quantity absorbed by the water is in proportion to the temperature and the pressure. When vessels containing water, and receiving this gas, are surrounded with ice, while the water is saturated, the gas crystallizes at the surface, and even at the bottom of the liquid, in the form of six-sided plates, of a greenish white colour; but the slightest heat dissolves them, and they rise through the liquor in the form of gas.

Water saturated with this gas at the temperature of 45° has the specific gravity of 1.003.

This acid does not redden vegetable blues, like the other acids. It has the singular property of destroying vegetable colours, on account of which it has been been much employed in the art of bleaching. The effect which takes place in this process, is the combination of the colouring matter with the oxygen of the acid; for the acid which has been employed is deprived of its oxygen, and converted into muriatic acid. But for the full account of this process, see BLEACHING.

13. When this acid is exposed to the light, it is decomposed; it gives out its oxygen gas, becomes colourless, and passes into the state of muriatic acid. But, when heat is applied, the acid is disengaged in the state of gas, without any perceptible separation of its oxygen. Exposed to the air, the acid is gradually separated, exhaling, at the same time, its pungent, disagreeable odour.

14. The constituent parts of oxymuriatic acid, according to Berthollet, are

\[ \text{89 muriatic acid,} \] \[ \text{11 oxygen.} \]

But, according to the experiments of Mr Chenevix, it is composed of

\[ \text{84 muriatic acid,} \] \[ \text{16 oxygen.} \]

SECT. VII. Of HYPER-OXYMURIATIC ACID.

1. Oxygen combines in a different proportion with muriatic acid, and forms another acid, possessed of properties which are quite distinct from the properties of the last described. This acid has never been obtained in a separate state, but the peculiarity of its nature has been sufficiently demonstrated in its combinations with other substances. As it contains a greater proportion of oxygen than the oxymuriatic acid, it has been denominated hyper-oxymuriatic acid.

2. It may be procured in combination with potash by the following process. If a quantity of potash, with six times its weight of water, be put into one of the bottles of Woulfe's apparatus, and a stream of oxymuriatic acid gas be passed through it till the potash is saturated, crystals in the form of fine white scales fall to the bottom. These are crystals of hyper-oxymuriate of potash, composed of potash and of hyper-oxymuriatic acid. The liquid in which these salts have been formed being evaporated to dryness, yields another salt which is composed of muriatic acid and potash. This was the discovery of Berthollet; and the theory which he proposed to account for the products that appeared in this process was the following. He supposed that the oxymuriatic acid was decomposed; part of it being deprived of its oxygen, combined in the state of muriatic acid with part of the potash, forming the salt which was obtained by evaporation, namely, the muriate of potash; and part united with an additional portion of oxygen combined with another portion of the potash, and formed the salt which was deposited in the liquid. This theory has been confirmed by the experiments of Mr Chenevix. According to these experiments the hyper-oxymuriatic acid is composed of

\[ \text{65 oxygen,} \] \[ \text{35 muriatic acid.} \]

But its properties will be more fully detailed in considering its combination with potash, when we come to treat of that substance.

3. The order of the affinities of hyper-oxymuriatic acid, is the following, as they have been ascertained by Mr Chenevix:

- Potash, - Soda, - Barytes, - Strontites, - Lime, - Ammonia, - Magnesia, - Alumina,

SECT. VIII. Of FLUORIC ACID.

1. The component parts of this acid are unknown. History. It was discovered by Scheele in 1771, and by him and Priestley its peculiar properties, which have been confirmed by the experiments of other chemists, were first detected. Margraaff, three years before, had ascertained that the fluor spar, from which this acid is obtained, differed in its properties from other spars. When he distilled equal parts of sulphuric acid and fluor spar, he obtained a white sublimate, and found that the glass retort which he employed in the process was greatly corroded, and pierced with holes. Scheele afterwards proved by his experiments, that the fluor spar is composed of lime and the peculiar acid to which the name fluoric has been given.

2. To procure fluoric acid, put one ounce of fluor spar (fluorite of lime) reduced to powder into a retort, obtain tin or lead; pour over it three ounces of concentrated sulphuric acid, and adapt to the retort a tube and receiver of the same metal. When the acid comes in contact with the spar, a gas is driven off, which is the fluoric acid. Towards the end of the process, if a gentle heat be applied, a greater quantity of the acid may be obtained. If water has been previously introduced into the receiver, the gas is absorbed by it, and the acid may then be exhibited in the liquid state.

3. Fluoric acid appears under two forms, that of gas and that of liquid.

Fluoric acid gas has the common properties of air. It is invisible and elastic. Its specific gravity of this gas has not been accurately determined, but it is heavier than atmospheric air. Exposed to the air it combines instantly with the moisture of the atmosphere, and appears in the form of vapour or white fumes. Like muriatic acid, it has a penetrating pungent smell. It reddens vegetable blues, and corrodes the skin. It is totally unfit for respiration. Animals who breathe it are instantly destroyed. It is also unfit for the support of combustion. But before the flame of a candle introduced into this gas is extinguished, it assumes a greenish colour. The most remarkable property of this gas is that of corroding glass, in consequence of its strong affinity for the flux, one of the component parts. parts of glaas. This is the reason that it must be prepared in metallic vessels. And even with this precaution, it is seldom entirely free from this earth, which it probably derives from the fluor spar, from which it is obtained.

4. Light and caloric have no effect on it. Its properties undergo no alteration, even when it has passed through a red-hot porcelain tube.

In contact with oxygenous gas or atmospheric air, no changes take place on fluoric acid gas; nor has it any action on azote, hydrogen, carbone, phosphorus, or sulphur. The other acids, it has been observed, are decomposed by one or other of these combustibles; and in this way their constituent parts have been detected. We are not, however, to conclude from thence, that the fluoric acid is a simple substance. On the contrary, it would be more analogous to other facts, to draw the conclusion, that it is a compound, similar to the other acids, whose bases have been discovered, and that the base, whatever that may be, has so strong an attraction for oxygen as to be unsusceptible of decomposition by the action of any substances yet known.

5. When this gas comes in contact with water it is rapidly absorbed, and in considerable proportion. In this state it is called fluoric acid. The specific gravity of this acid is greater than that of water. By heat the gas is almost entirely expelled from the water; and when it is cooled down to the temperature 23° it freezes.

6. The compounds with the alkalies, earths, and metallic oxides, are called fluates.

7. The order of its affinities is the following:

- Lime, - Barytes, - Strontites, - Magnesia, - Potash, - Soda, - Ammonia, - Glucina, - Alumina, - Zirconia, - Silica.

**Sect. IX. Of Boracic Acid.**

1. The component parts of boracic acid are unknown. It was first discovered by Homberg in 1792, who gave it the name of narcotic or sedative salt. The substance called borax of the shops is a compound of this acid and soda.

2. The process for obtaining this acid is the following: Dissolve a quantity of this substance in hot water, and filter the solution. Gradually pour on it sulphuric acid, till the liquor acquires a slight degree of acidity. The sulphuric acid combines with the soda; and the boracic acid, as the solution cools, is precipitated in small, shining white scales. To purify the acid thus obtained, it is to be washed with cold water; which removes the more soluble salts with which it is mixed.

3. Boracic acid is in the form of filvery white hexagonal scales, which have a greasy feel, and some resemblance to spermaceti. It has a fourth taste, which afterwards gives the sensation of coolness. It has no smell. It changes vegetable blues to red. In the scale form, the specific gravity is 1.479; but when it is fused, it is 1.803.

4. When exposed to heat, it froths up, which is owing to the separation of the water of crystallization, and assumes the form of a viscid paste. In this state it is known by the name of calcined borax. When it is exposed to a red heat, it is converted into a hard, transparent glass, which, without attracting moisture from the air, becomes opaque when exposed to it, but it remains unchanged; for when it is re-dissolved in warm water, it refurnes its former properties, by cooling and crystallization.

5. Boracic acid has very little attraction for water; boiling water only dissolves about a 50th part of its weight, and cold water much less. When the solution in water is evaporated in close vessels, part of the acid rises in the state of vapour along with the water, and crystallizes in the receiver; but when the whole of the water is dissipated, the process stops; so that it is only by means of it that the acid is volatilized; otherwise it is perfectly fixed. The solution in water has little taste, but it reddens the tincture of turpentine.

6. Neither oxygen, azote, nor hydrogen gases, produce any effect upon it; and with charcoal, phosphorus, and sulphur, it also remains unchanged. When burnt with phosphorus, indeed, there is left behind an earthy, yellow matter.

7. At a red heat it drives off some of the acids from their combinations, even those acids which have the stronger affinity for the same substances in the cold. Boracic acid has some peculiar action with the sulphuric, the nitric, and oxymuriatic acids; for when it is heated with these acids, it deprives them of a portion of their oxygen; but the changes which take place by this action have not been distinctly ascertained.

8. Fabroni of Florence considers this acid as a modification of the muriatic, and he supposes that it may be entirely formed with this acid. The boracic acid, he further supposes, is probably produced by this modification of the muriatic acid in the water of the lakes of Tuscany; but the facts on which this opinion is founded, have not been published.

9. The boracic acid is employed in chemistry, not uses directly as an instrument of analysis, because its affinities and action have little energy compared with other acids, but to discover its peculiar combinations and compounds. It is also employed in the arts, as in foldering, to assist the fusion of metallic substances. It is of great importance to the mineralogist, in promoting the fusion of substances under the blow-pipe.

10. The compounds which boracic acid forms with the alkalies, earths, and metallic oxides, are distinguished by the name of borates.

11. The affinities of boracic acid are the following:

- Lime, - Barytes, - Strontites, - Magnesia, - Potash, - Soda, - Ammonia, - Glucina, - Alumina, - Zirconia, - Water, - Alcohol. Sect. X. Of Phosphoric Acid.

1. When phosphorus undergoes combustion in oxygen gas, a great quantity of white fumes are produced, which are deposited in white flakes. These are phosphoric acid; so that it is a compound of phosphorus and oxygen.

2. The phosphoric acid was first shown to be distinct from all other acids, in the year 1743, by Margraff. He found that it existed in the fats which were taken from human urine, and that phosphorus could only be obtained from this acid; as well as that it could be converted into phosphoric acid. This acid was found to exist in some vegetable substances, although it was formerly supposed to be peculiar to animal matters. It was discovered by Scheele and Gahn in bones, in the year 1772. Bergman, Proust, and Tenant detected it in several fossils; and Lavoisier proved, by a series of accurate and ingenious experiments, that it was composed of phosphorus and oxygen.

3. Phosphoric acid may be obtained, not only by the method just mentioned, but also by transmitting a current of oxygen gas through phosphorus melted under water. The acid, as it is formed, combines with the water, from which it may be obtained in a state of purity by evaporation. It may be procured also by dropping small bits of phosphorus into nitric acid moderately heated. An effervescence takes place, and nitrous gas is evolved. Phosphorus combines with the oxygen, and forms phosphoric acid. The precaution of adding but a little phosphorus at a time, and of applying a moderate heat to the acid, should be carefully observed. The liquid is then evaporated, and the phosphoric acid remains behind in the solid state. The water that may be combined with it is driven off, by exposing it to a red heat.

4. In this state phosphoric acid is a transparent, colourless, solid substance, resembling glass, known under the name of phosphoric glass.

The specific gravity of this acid varies, according to the different states in which it exists. In the liquid state it is 1.417; in the dry state it is 2.697; in the state of glass 2.8516. It changes the colour of vegetable blues to red; has no smell, but a very acid taste.

5. When it is exposed to the air, it attracts moisture, and is converted into a thick viscid fluid, like oil. It is very soluble in water. When in the form of dry flakes, it dissolves in a small quantity of this liquid, producing a hissing noise like that of a red-hot iron plunged into water, with the extrication of a great quantity of heat. In the state of glass it dissolves more slowly, but the concentrated liquid phosphoric acid unites with water with very little disengagement of caloric.

6. Phosphoric acid being fully saturated with oxygen, has no action whatever on oxygen gas; nor is there any action between hydrogen or azotic gases, or sulphur, with the phosphoric acid. Charcoal has no effect on phosphoric acid in the cold; but when they are exposed together to a red heat, the phosphoric acid is decomposed; the oxygen combines with the carbons of the charcoal, forming carbonic acid, and the phosphorus is set at liberty. This is the process already described in treating of phosphorus, which is generally employed for obtaining that substance.

7. Sulphuric acid has no action on phosphoric acid; but when the two acids are mixed together in the liquid state, the sulphuric acid, on account of its strong affinity for water, combines with the water in the phosphoric acid; and if heat be applied, the sulphuric acid is distillated, and the phosphoric acid remains behind in the state of a transparent viscid matter, or in that of glass. Sulphurous acid is separated from its combinations by the phosphoric acid. Nitric acid separates the phosphoric from its combinations. Muriatic acid has the same effect.

8. The component parts of this acid have been accurately ascertained by Lavoisier, and it consists of,

- 60 oxygen, - 40 phosphorus.

9. The accuracy of our information with regard to the component parts and properties of phosphoric acid, renders it of great importance in many chemical operations; and if it could be obtained with less difficulty and expense, its uses might be extended to medicine and the arts.

10. It combines with the alkalies, earths, and metallic oxides, and forms salts which are denominated phosphates.

11. The following is the order of its affinities.

- Barytes, - Strontites, - Lime, - Potash, - Soda, - Ammonia, - Magnesia, - Glucina, - Alumina, - Zirconia, - Metallic oxides, - Silica.

Sect. XI. Of Phosphorous Acid.

1. Phosphorous acid bears the same relation to phosphoric as sulphurous acid does to sulphuric. It is combined with oxygen in the smaller proportion. This was demonstrated by Lavoisier in 1777, when he pointed out the difference between the product from the slow or rapid combustion of phosphorus. It is obtained by the slow combustion of phosphorus at the common temperature of the air. If phosphorus, in small pieces, be exposed to the air in a glass funnel placed in a bottle, it attracts the oxygen and moisture from the atmosphere, and runs down into the bottle. This is the phosphorous acid. By this process, about three times the weight of the phosphorus is obtained.

2. It is then in the form of a white thick liquid, adhering to the sides of the vessel. It varies in consistence according to the state of the air. Its specific gravity gravity is not known. It has an acid, pungent taste, not different from phosphoric acid. It also reddens vegetable blue colours.

3. Phosphorous acid is not altered by light. When exposed to heat in a retort, part of the water combined with it is first driven off; and when it is concentrated, bubbles of air suddenly rise to the surface, and collect in the form of white smoke, and sometimes inflame, if there be any air in the apparatus. If the experiment be made in an open vessel, each bubble of air, when it comes to the surface, produces a vivid deflagration, and diffuses the odour of phosphorated hydrogen gas. This inflammable gas continues to be evolved for a long time, and when the action ceases, phosphoric acid only remains behind. It ought to be observed, that the phosphorated hydrogen gas is not disengaged till the phosphorous acid is concentrated and brought to a high temperature, which seems to prove that the phosphorus which is not saturated with oxygen, strongly adheres to it.

4. There is little attraction between oxygen and phosphorous acid, which seems to be owing to the great affinity between phosphorus and phosphoric acid. It absorbs, however, very slowly, a small quantity of oxygen; and even after long boiling, it is not completely converted into phosphoric acid.

5. Hydrogen gas has no action on phosphorous acid; but this acid is decomposed at a red heat, by means of charcoal, which separates from it a greater quantity of phosphorus than from phosphoric acid. There is no action between these bodies in the cold. Sulphur has no action on this acid at the ordinary temperature of the atmosphere, and they cannot be combined by means of heat, because the phosphorus is dissipated before it unites with the sulphur.

6. There is no action between phosphorous acid and sulphuric acid in the cold; but when they are heated together to the boiling temperature, the phosphorous acid deprives the sulphuric part of its oxygen, and is converted into phosphoric acid, while part of the sulphuric acid, thus decomposed, is disengaged in the state of sulphurous acid gas. Phosphorous acid produces a similar effect on nitric acid. The phosphorus is converted into phosphoric acid, and part of the nitric acid is converted into nitrous gas.

7. This acid is composed of the same constituent parts as the phosphoric, and is considered by some as the phosphoric acid holding in solution a small quantity of phosphorus.

8. Phosphorous acid forms compounds with alkalies, earths, and metallic oxides, which are known under the name of phosphites.

9. The order of its affinities is the following:

- Lime, - Barytes, - Strontites, - Potash, - Soda, - Ammonia, - Glucina, - Alumina, - Zirconia, - Metallic oxides.

1. When a piece of charcoal, in a state of ignition, is plunged into a jar of oxygen gas, it burns with great brilliancy; and after the combustion has ceased, the air in the vessel is totally changed. If a little water is introduced into the jar, and agitated, the air combines with it; and this water, when examined, exhibits acid properties. This is carbonic acid. It is formed by the combination of carbure and oxygen. This is one of the most important acids, both on account of its numerous combinations, and also on account of the discovery of it having occasioned a total revolution in chemical science.

2. It was regarded by the ancients, on account of the noxious effects which it produced, as a pestilent vapour, and they gave it the name of spiritus letharius. Paracelsus and Van Helmont considered it as a peculiar matter, to which they gave the name, spiritus sylvestris, or gas. Hales, although he considered it merely as contaminated air, distinguished it by the name of fixed air, because it entered into the composition of many bodies. Dr Black demonstrated, that it is a peculiar substance, different from the air; that lime, magnesia, and the alkalies, were deprived of their causticity, by being combined with this air, and therefore he gave it the name of fixed air. It was afterwards found by the experiments of Keir and Bergman, to be an acid, and hence Bergman gave it the name of aerial acid. The nature and properties of this acid were investigated by many chemical philosophers, and from them it received various names, as mephitic acid, calcareous or cretaceous acid, thus distinguished from its effects, or from the substances from which it was obtained. In the present chemical nomenclature it has the name of carbonic acid, from its base carbure.

3. For some time after the discovery of the difference between carbonic acid and common air, and its acid properties as an acid, it was considered by many as a simple elementary substance, and it was regarded as the acidifying principle. In the progress of investigation it was found to be a compound substance, and that oxygen was one of its constituent parts, and it was generally believed that phlogiston constituted the other. When hydrogen was substituted for phlogiston, it was supposed that oxygen and hydrogen constituted carbonic acid. The discovery of Mr Cavendish, proved that water, not carbonic acid, was the product of the combination of oxygen and hydrogen. But the experiments of Lavoisier have established the fact, and placed it beyond dispute. He demonstrated that the weight of the carbonic acid which was obtained, was exactly equal to the quantity of the oxygen and charcoal which had disappeared.

4. Carbonic acid may be obtained by taking a quantity of chalk or limestone, or marble, and reducing obtaining them to a coarse powder. Introduce it into a matrix, pour over it a quantity of diluted sulphuric or nitric acids; a violent effervescence takes place, carbonic acid gas is disengaged, which passes over, and may be received in vessels in the usual way. The chemical action that takes place in this change must be obvious. The affinity of the sulphuric acid for the lime is stronger. Chemistry.

5. Carbonic acid thus obtained in the state of gas, is an invisible, elastic fluid. Its specific gravity is 0.0018. One hundred cubic inches of it weigh 6.5 grs. It is nearly double the weight of common air. It has no smell; it is totally unfit for respiration, and equally so for supporting combustion. It reddens the tincture of turnsole, which has its blue colour restored on being exposed to the air, by the separation of the acid.

6. Water absorbs a considerable proportion of this acid, which is increased by agitation. At the temperature of 41° water absorbs its own bulk. When artificial pressure is employed, the quantity of gas absorbed may be greatly increased. It is in this way that what are called the aerated alkaline waters are prepared, some of which, it is said, contain no less than three times their bulk of the gas. Water impregnated with this gas, acquires an acidulous taste, and when poured from one vessel to another, has a sparkling appearance. When water impregnated with this acid is exposed to the air, it soon disappears. The air of the atmosphere attracts it from the water, having a stronger affinity for it than the water.

When water containing this gas is raised to the boiling temperature, the whole is driven off; and if water impregnated with it be exposed to the temperature of 32°, the whole of the gas separates during the freezing.

7. Carbonic acid undergoes no change by the action of light. It is not changed by the action of heat in close vessels, or by passing it through a red-hot tube.

8. There is no action between this gas and oxygen. Exposed to the air of the atmosphere, it is gradually dissipated. The air of the atmosphere generally contains from .01 to .02 parts of this gas.

9. There is no action between this acid and azote. Charcoal has no chemical action on carbonic acid; but when it is heated, it has the property of absorbing and condensing within its pores the carbonic acid; but the acid is separated by plunging the charcoal under water.

10. Phosphorus has no action on carbonic acid; but by the aid of compound affinity, phosphorus can decompose it.

11. Sulphur has still less action on carbonic acid than phosphorus. It is said, indeed, that a small quantity of sulphur is dissolved by this gas by means of heat, which gives it partly the fetid odour of sulphurated hydrogen gas.

12. Carbonic acid gas mixed with carbonated, phosphorated, and sulphurated hydrogen gases, diminishes the combustibility of these inflammable gases.

13. The carbonic acid combines with the alkalies, some of the earths, and metallic oxides, forming compounds known by the name of carbonates.

14. The following is the order of the affinities of this acid:

- Barytes, - Strontites, - Lime,

Potash, Soda, Magnesia, Ammonia, Glucina, Zirconia, Metallic oxides.

15. Carbonic acid exists in great abundance in nature. It is produced during the processes of combustion and respiration, and the fermentation of vegetable matters. Hence it is found in pits and caverns, where there is a stagnation of the air, and being specifically heavier than common air, it remains at the bottom. This is the reason why small quadrupeds, as dogs, are instantly suffocated, because they respire only this gas, when they enter places where it is accumulated. This has been long observed in the celebrated Grotto dell' Cani in Italy, where dogs are instantly suffocated; while men, whose heads are in the stratum of common air near the top of the cavern, receive no injury. Men have been suddenly killed by going down into large produced vats, in which the process of fermentation had been carried on. In consequence of the greater specific gravity of the carbonic acid gas, and the great quantity generated during the process, when the fermented liquor is drawn off, it sinks to the bottom of the vessel, and there remains till it is displaced by a denser fluid, or slowly attracted by the air. Similar accidents have happened to persons going down into pits or wells which have been long shut up, and where the air has been long stagnant. It is by respiring this gas that persons are suffocated who have been exposed to the fumes of burning charcoal in close places. During the combustion of the charcoal, the carbons combine with the oxygen of the atmosphere; carbonic acid is formed, which soon fills the apartment. In these cases, mode of recovery is said to be, to dash cold water on the head and body; a practice which is commonly observed in accidents of this kind, in northern countries, where charcoal is burnt in close apartments.

Sect. XIII. Of Arsenic Acid.

1. This acid, and the four following, having metallic substances for their base. Most metallic substances combine with oxygen in different proportions, and the compounds formed with these substances and oxygen, are denominated oxides, because they possess no acid properties; but some of the metals combine with oxygen in greater proportion, which gives them the characteristic properties of acid substances.

2. The metallic substance arsenic, combines with oxygen in two proportions; the first, which is usually called the white oxide of arsenic, has been denominated by Fourcroy, the arsenious acid. Macquer discovered some of the combinations of arsenic acid, previous to the year 1746; for he showed that a mixture of white oxide of arsenic and nitre, subjected to the action of a strong fire, yields a neutral salt, to which he gave the name of the neutral salt of arsenic. But it was by the investigation of Scheele in 1775 that its properties were fully known.

3. The process for obtaining it which was pointed out obtaining out by Scheele, is the following. Take three parts of the white oxide of arsenic, and dissolve it in seven parts of muriatic acid. Add five parts of nitric acid to the solution, and distill it to dryness. The arsenic acid remains behind. It may also be procured by dissolving the white oxide in liquid oxymuriatic acid, or by making a stream of oxymuriatic acid gas pass through a solution of the white oxide of arsenic. The chemical action which takes place in these processes, is the union of the arsenic with an additional portion of oxygen, which it derives from the nitric acid, the liquid oxymuriatic, or the oxymuriatic acid gas.

4. By whatever process it is obtained, the arsenic acid which is not crystallized has an acid, caustic, and metallic taste. It reddens the syrup of violets, and its specific gravity is 3.91. When it is exposed to a strong heat in a retort or crucible, it fuses, attacks the glass of the retort, or the earth of the crucible; it remains transparent and pure at a high temperature, gives out a little oxygen, and is partly converted into white oxide.

5. Exposed to the air, it attracts the moisture from it, and absorbs two thirds of its own weight of water from the atmosphere, which is sufficient to hold it in solution.

6. The arsenic acid is much more soluble in water than the white oxide. Three or four parts of water are sufficient to dissolve it. When it is evaporated, it fumes a thick consistency like honey.

7. Combustible substances decompose arsenic acid, by depriving it of part of its oxygen, and converting it into the white oxide. Hydrogen gas mixed with a solution of this acid, has the property of precipitating it. Charcoal, phosphorus, and sulphur produce a similar effect. Exposed in a retort to heat with charcoal; the charcoal is inflamed, and the arsenic acid is reduced to the metallic state. Sulphur heated with arsenic acid, is partly converted into sulphurous acid gas, and partly sublimed into the red sulphuret of arsenic. When heated with phosphorus, part of the phosphorus is converted into phosphoric acid, and the arsenic, reduced to the metallic state, unites with another part of the phosphorus, with which it forms a phosphuret of arsenic, which sublimes.

8. The arsenic acid is composed of the white oxide of arsenic and oxygen. The proportions of its constituent parts, according to the experiments of Proust, are:

\[ \begin{align*} \text{Arsenic} & : \text{Oxygen} = 65 : 35 \\ & = 1 : 0.53 \end{align*} \]

9. The compounds which arsenic acid forms with alkalies, earths, and some metallic oxides, are known by the name of arseniates.

10. The order of its affinities is the following:

- Lime, - Barytes, - Strontites, - Magnesia, - Potash, - Soda, - Ammonia, - Glucina, - Alumina, - Zirconia,

Sect. XIV. Of Tungstic Acid.

1. In the year 1781, Scheele and Bergman, in investigating the nature of a heavy stone (called tungsten by the Swedes), discovered that it is composed of lime combined with a peculiar acid. Their discovery was afterwards confirmed by several chemists, particularly by the experiments of D'Elhuyarts, who detected the same acid in the mineral wolfram.

2. This acid always exists in combination with lime Methods of and iron. It may be obtained by reducing the former obtaining to a fine powder, and treating it with nitric or muriatic acids, which unite with the lime, and then by alkalies, which dissolve the acid. The alkaline solution is to be precipitated by the nitric or muriatic acid; the precipitate is to be carefully washed and dried, which is the tungstic acid in the solid state.

3. Tungstic acid, thus prepared, is in the form of a white powder, which has an acid and metallic taste; changes the colour of vegetable blues into red; and has a specific gravity according to Bergman, equal to 3.600. Heated under the blow-pipe, this tungstic acid Action of becomes first yellow, then brown, and at last black; it heat affords no smoke, and gives no sign of fusion. When it is calcined for some time in a crucible, it is deprived of the property of dissolving in water.

4. Exposed to the air, it suffers no change. It is Of water-soluble in 20 parts of boiling water, but it is partially separated on cooling. This solution has an acid taste, and reddens the tincture of turpentine. Heated with charcoal, it is reduced, but with difficulty, to the metallic state. With sulphur and phosphorus it becomes of a grey colour, but without reduction.

5. The acids do not dissolve the tungstic acid in the form of white powder, but they change completely its properties. The sulphuric acid changes it to a blue, and the nitric and muriatic acids convert it into a fine yellow colour. In this state it has lost its taste and solubility, has become specifically heavier, and has acquired the property of forming salts with the same bases distinctly different from those formed with what was called the white acid. The Spanish chemists D'Elhuyarts, consider the latter as an acidulous triple salt, and yellow oxide as real tungstic acid.

6. Vaquelin and Hecdt, who instituted a set of experiments on these oxides, as they propose to denominate them, obtained the same results. They consider the tungstic acid of Scheele as a triple salt, which has retained a portion of the acid by which it was precipitated in its composition, and when the oxide of tungsten oxide is pure, it possesses none of the properties which are admitted and acknowledged as the characteristics of the acids, but that it has a strong tendency to form triple combinations, in which only it exhibits acid properties. The compounds which it forms with the alkalies, earths, and metallic oxides, are a species of neutral salts; but the chemical combination is not fully completed to hide the alkaline properties of the former. In forming these compounds, it is the only property in which it agrees with the acids. The compounds are denominated tungstates.

7. The order of its affinities is the following:

- Lime, - Barytes, - Strontites, Sect. XV. Of Molybdic Acid.

1. This acid was discovered by Scheele in the year 1778. It is a compound of the metallic substance molybdena and oxygen. Scheele supposed that it existed in the mineral from which he obtained it, and that this mineral was a compound of the acid, sulphur and iron. The experiments of later chemists have shown that the acid is formed in the process of preparing it, by the metal combining with oxygen.

2. There are various processes for the preparation of this acid.

a. Scheele found that by treating a little of the sulphuret of molybdena (sulphur combined with the metal) on a silver plate, the white fumes which exhaled from it, adhered to the plate in form of a small scale of a brilliant yellow with white colour, which was the true molybdic acid. But a very small quantity can only be obtained in this way.

b. Another process is by means of nitric acid. On one part of sulphuret of molybdena in powder, pour five parts of nitric acid, and distil it to dryness. The same process is repeated three or four times. The dry residuum is a white powder, which is the molybdic acid mixed with the sulphuric acid, which is also formed during the process with the nitric acid. The sulphuric acid may be washed off with hot water, and the molybdic acid remains behind in a state of purity.

c. It may be also prepared by projecting into a red-hot crucible three parts of nitrate of potash, and one part of sulphuret of molybdena, reduced to fine powder and well mixed together. A red mass remains after the detonation, composed of the oxide of iron, of the sulphate of potash, and the molybdate of potash. By throwing the mass into water, the two salts are dissolved, and the oxide of iron is precipitated. Evaporate the solution to obtain the sulphate of potash, and drop into the liquid which refuses to crystallize, and which should be diluted with water, sulphuric acid, till there is no farther precipitation. The precipitate is molybdic acid, but not in a state of perfect purity; for it is combined with a certain portion of potash.

3. Molybdic acid, prepared in this manner, and sufficiently purified, is a white powder of a sharp metallic taste. According to Bergman, the specific gravity is 3.4.

4. When heated in a large glass retort, it yields a little sulphurous acid. But when it is exposed to a strong heat in a close vessel, it fuses, attaches itself to the sides of the vessel, and crystallizes on cooling in rays going out from a centre. But if at the moment the acid is in fusion the vessel be uncovered, it rises into a white smoke by contact with air, and this vapour attaches itself to cold bodies in form of brilliant scales of a golden-yellow colour.

It is readily soluble in warm water. One part of the acid requires about 500 grs. The solution is of a yellow colour, has little smell, and reddens litmus paper.

5. Molybdic acid is decomposed by charcoal, with the assistance of heat; it is also decomposed by fulvous sulphur, with the extrication of sulphurous acid, and the formation of sulphuret of molybdena.

6. The concentrated sulphuric acid dissolves a considerable quantity of molybdic acid, with the aid of heat. The solution on cooling becomes of a violet blue colour, which disappears when it is heated. The muriatic acid dissolves a considerable proportion by boiling. When this solution is distilled to dryness, one part of the acid is sublimed, of a blue and white colour. The nitric acid has no effect whatever.

7. Molybdic acid combines readily with the alkaline and earthy bases, which have the name of molybdates.

8. This acid has not been applied to any use.

Sect. XVI. Of Chromic Acid.

1. This acid was discovered by Vanquelin in the year 1797. It has only been found in small quantity, in combination with lead or iron.

2. Chromic acid may be obtained by boiling the red lead ore of Siberia in a solution of carbonate of potash, and precipitating it by means of another acid, which has a stronger attraction for the potash. A red or yellow orange powder falls to the bottom, which is chromic acid.

3. It has an acrid and peculiar metallic taste, more perceptible than any other metallic acid.

4. When exposed to the action of light and caloric, in open vessels, it assumes a green colour; but in close vessels, it gives out pure oxygen gas, and losing its acid properties it returns to the state of green oxide. This is the only metallic acid, which by the action of caloric, easily parts with its oxygen.

5. Strongly heated with charcoal, chromic acid becomes black, and is easily reduced to the metallic state without fusion. It is probable also, that it may be decomposed with equal facility by hydrogen, phosphorus, and sulphur.

6. Chromic acid is soluble in water, and crystallizes by cooling and evaporation, in prisms of a ruby red colour.

7. The muriatic acid by distillation with a moderate heat with the chromic acid, passes to the state of oxy-acid muriatic acid, and the mixture acquires the property of dissolving gold. In this respect it resembles the nitric acid, and it is the only metallic acid which is distinguished by this property.

8. The chromic acid combines readily with the alkalies, and has the peculiar property of giving an orange colour to the crystals; from this it derived its name. The compounds are called chromates.

9. The chromic acid, from its peculiar colour, and the beautiful colours which it communicates to other bodies, promises to be useful in painting on porcelain and glass, or even in dyeing.

Sect. XVII. Of Columbic Acid.

1. The last of the metallic acids is the columbic, which was discovered by Mr Hatchet in 1801. In the the ore from which it was extracted, it is combined with oxide of iron, from which it was separated, by exposing it to a strong red heat, with five times its weight of carbonate of potash. The alkali combined with part of the acid, and from this it was separated by water. By repeatedly fusing the residuum with potash, he separated the whole of the acid from the iron, which latter combined with muriatic acid that was added to it. By treating the alkaline solution with nitric acid, a precipitate of a white, flaky, insoluble substance was obtained. This is the columbic acid.

2. It is of a pure white colour, but not very heavy, and has scarcely any perceptible taste; it is not soluble in boiling water. When some of the powder is placed upon litmus paper, moistened with distilled water, the paper in a few minutes becomes red. When exposed to the blow-pipe, it is not fusible, but only becomes of a less brilliant white.

3. It is dissolved in boiling sulphuric acid, and forms a transparent colourless solution, which is only permanent while the acid is in a concentrated state; for if it be diluted with water, it assumes a milky appearance; a white precipitate is deposited, which, as it dries on the filter, changes when completely dry to a brownish gray. It is then insoluble in water, has no taste, is semitransparent, and breaks with a glossy, vitreous fracture. This compound appears to be formed of the sulphuric and columbic acids. Nitric acid has no effect on the columbic acid.

Sect. XVIII. Of Acetic Acid.

1. Acetic acid, or vinegar, was one of the earliest known. This indeed was to be expected, from the manner and the abundance in which it is produced, as it is the first change to which wine and similar liquids are subject. The fourness which exists in these liquids, is owing to the production of this acid. It has different names, according to the state in which it is found. When it is first prepared, it is known under the name of vinegar; when purified by distillation, it is called distilled vinegar; and when it is strongly concentrated, it is called radical vinegar, or acetic acid.

2. The process by which vinegar is obtained is the fermenting process of many vegetable matters, what is usually denominated the acetous fermentation, or the second stage of the fermentative process of vegetable matter. The circumstances in which this fermentation takes place are, a temperature between 75° and 80°, the addition of some fermenting substance, and exposure to the air.

The process which is recommended by Boerhaave, is generally followed. Two large hogheads are prepared, by fixing about a foot from the bottom, a grating of rods, on which vine branches are to be placed. The wine to be fermented is poured into the vessels; the one is to be filled to the top, and the other only one half. They are both left exposed to the air. Fermentation begins in the vessel which is half full; when it is completely begun, fill it up from the other vessel, which interrupts the fermentation in the full hoghead, and it commences in that which is half full. When this has continued for a little time, it is filled up from the other vessel, in which the fermentation again commences, and is interrupted in the other.

Thus, the process is carried on by alternately emptying and filling the vessels till vinegar is formed, which generally requires a period of from 12 to 15 days.

3. Vinegar is generally of a yellowish colour, an acid taste, and agreeable smell. It reddens vegetable blues, and when it is exposed to heat, it is entirely dissipated. The specific gravity varies from 1.005 to 1.0251. It varies considerably in colour, specific gravity, and other properties, according to the substances from which it has been obtained. Vinegar in this state is extremely apt to be decomposed. Scheele has pointed out a very simple process, by which it may be preserved for a long time. Put the vinegar into bottles, and place them over the fire in a vessel filled with water. Let the water boil for a moment, and then take out the bottles, after which it may be kept for several years.

4. To separate the impurities with which vinegar is contaminated, it is distilled with a moderate heat; distillation, the temperature must not exceed that of boiling water, and the process should be carried on only till about 1/4 of the quantity have passed over. This is distilled vinegar, or the acetic acid of the chemists. It is then perfectly transparent and colourless, has an agreeable odour, and a strong acid taste. The vinegar in this state, when exposed to a sufficient degree of cold, is partly frozen. As the ice which is formed consists almost entirely of water, when it is separated the fluid which remains is the vinegar highly concentrated.

5. To prepare what has been denominated radical vinegar, a fall, of which this acid forms a component part, must be decomposed. The acetate of copper, or verdigris, is generally employed for this purpose. It is reduced to powder, and distilled in a retort with a strong heat. The liquid which first comes over is insipid and colourless, and must be kept separate from the remaining part of the product, which is the acetic acid in a highly concentrated state. It has generally a green colour, being contaminated with a little copper, but it may be purified by distillation with a moderate heat, by which it is rendered colourless.

6. The acid in this state was at first considered by Acetous chemists as different from the acetic acid in its properties, affinities, and in the compounds it forms with acids and other bodies. This was the opinion of the celebrated poet to be chemical philosopher Berthollet, and this opinion was adopted by almost all chemists. It was supposed that it was the acetic acid in combination with another portion of oxygen, and hence it was denominated, according to the present nomenclature, acetic acid.

7. The nature and properties of these two supposed acids were at last investigated fully by Adet and Darthe, who proved that there was no difference in the proportion of oxygen in the acetic and acetic acids. This conclusion was controverted by Chaptal and Dabat, who endeavoured to support the opinion of Berthollet, that the two acids are distinguished from each other by different properties and different combinations with other bodies. It is now generally admitted, that what have been called the acetic and acetic acids, are essentially the same, their apparent differences depending on the quantity of water, mucilage and other substances with which the acetic acid is combined.

8. This acid when pure, is transparent and colourless. Acids. In the state of acetic acid, it has an agreeable, aromatic odour. In the state of acetic acid, or when it is highly concentrated, it acquires a sharp, penetrating odour, different from that of the vinegar, and in this state it is extremely acid. Applied to the skin it reddens and destroys it. It is highly volatile; and when exposed to the open air, it is soon dissipated. When heated in contact with the air, it inflames.

9. This acid may be obtained in crystals, by forming distilled vinegar into a paste with charcoal, and subjecting the mixture to a temperature which does not exceed 212°. By this heat the watery part is distillated, and the acid remains behind; but when a stronger heat is applied, the acid itself is driven off. By repeating the process the acid may be obtained crystallized.

10. Acetic acid undergoes no perceptible change by the action of oxygen, hydrogen, or azotic gases; and it is not altered by charcoal, phosphorus, or sulphur.

11. Acetic acid is decomposed by the sulphuric acid. It absorbs carbonic acid, and dissolves boracic acid. It is also decomposed by nitric acid, and is converted into carbonic acid and water. Dr Higgins analyzed the acetic acid by decomposing it in combination with an alkali. He distilled in a glass retort 7680 grs. of acetate of potash, that is, potash combined with acetic acid, and he obtained the following products:

- Potash: 3862.9940 - Carbonic acid gas: 1473.5640 - Carbonated hydrogen gas: 1047.6018 - Charcoal: 0078.0000 - Oil: 0180.0000 - Water: 0340.0000 - Deficiency: 0726.9402

Dr Higgins was at a loss to account for this deficiency, till by repeated experiments he found that it is always owing to the water and oil, and chiefly to the water which is carried off by the elastic fluids. He states the quantity of water carried off in vapour at 700 grs. and the quantity of oil carried off in the same way at 26.9402, which together make up the whole deficiency †. The potash remained behind unaltered; the acetic acid, therefore, has been decomposed, and has yielded the products which were obtained by distillation. But the constituent principles of these products are oxygen, hydrogen, and carbone; and from the proportions of oxygen and carbone which enter into the composition of carbonic acid, the proportions of carbone and hydrogen in carbonated hydrogen gas, and of oxygen and hydrogen in the composition of water, 100 parts of acetic acid are composed of about:

- 50 oxygen, - 36 carbone, - 14 hydrogen.

100

Compounds. 12. The compounds which acetic acid forms with alkalies, earths, and metallic oxides, are denominated acetates.

Affinities. 13. The order of its affinities is the following:

- Barytes, - Potash, - Soda, - Strontites, - Lime, - Ammonia, - Magnesia, - Metallic oxides, - Glucina, - Alumina, - Zirconia.

Sect. XIX. Of Oxalic Acid.

1. This acid exists ready formed in the oxalis acetosella or wood-forrel, and some other species belonging to the same genus of plants. From this it derives the name of oxalic acid. It was originally denominated the saccharine acid, or the acid of sugar, because it was obtained from that substance. Its properties were first particularly investigated by Bergman and Scheele, and the method of preparing it is given by the former.

2. An ounce of white sugar in powder is put into a retort, with three ounces of strong nitric acid. During obtaining the solution, a great quantity of fumes of the nitrous acid escapes. Apply heat till the liquor boils, and nitrous gas is then driven off. When the liquor in the retort acquires a reddish brown colour, add three ounces more of nitric acid; continue the boiling till the fumes cease, and the colour of the liquor vanishes. Pour out the liquor into a wide shallow vessel; and, when it cools, crystals will be formed in slender four-sided prisms, which may be collected and dried on blotting paper. The crystals thus obtained may be again dissolved in distilled water, and evaporated to obtain new crystals. Oxalic acid may be obtained by a similar process from other vegetables, and from some animal substances, as gum arabic, alcohol and honey.

3. Prepared in this way, oxalic acid is in the concrete state, crystallized in four-sided prisms, terminating in two-sided summits. They are white and transparent, and have a considerable lustre. They have a strong sharp taste, and change vegetable blues into a red colour, and produce the same effect on all vegetables except the indigo.

The acid properties of this substance are so strong, that one part of concrete oxalic acid gives to 3600 parts of water, the property of reddening paper stained with turpentine.

4. When oxalic acid is exposed to heat, it is volatilized partly in a liquid, and also in a solid and crystalline form. It is not decomposed, but at a high temperature; but, when it is exposed to a moderate heat, it dries, is covered with a white crust, and is soon reduced to powder. It loses \( \frac{1}{3} \) of its weight when put upon burning charcoal; it exhales a pungent, irritating smoke, and there remains behind a white alkaline residue.

5. This acid is deliquescent in the air, when it is loaded with moisture. Cold water dissolves about \( \frac{1}{3} \) of its weight of the acid; boiling water dissolves a quantity equal to its own weight.

6. Oxalic acid is decomposed by the sulphuric acid with the assistance of heat, and charcoal is deposited; at the boiling temperature it is decomposed by the nitric acid, and converted into water and carbonic acid. According to Fourcroy, the component parts of oxalic acid, as they have been ascertained by him and Vauquelin, are

77 oxygen, 13 carbone, 10 hydrogen.

100 *

7. Oxalic acid combines with the alkalies, earths, and metallic oxides, and the salts thus formed are distinguished by the name of oxalates.

8. The affinities of this acid are in the following order:

Lime, Barytes, Strontites, Magnesia, Potash, Soda, Ammonia, Alumina.

Sect. XX. Of Tartaric Acid.

1. This acid was procured by Scheele in a separate state, in the year 1772, the proceeds for which he communicated to M. Retzius, who published the account of it in the Swedish Memoirs for that year. It was the first discovery in the bright career of that distinguished chemist.

2. The proceeds which he followed was by boiling a quantity of the substance called tartar, or cream of tartar, in water, and adding powdered chalk till effervescence ceases, and the liquid no longer reddens vegetable blues. It is then allowed to cool; the liquor is filtered; and a white insoluble powder remains on the filter, which is carefully removed and well washed. This is put into a matras, and a quantity of sulphuric acid, equal in weight to the chalk employed, diluted with water, is poured upon it. The mixture is allowed to digest for 12 hours on a sand bath, stirring it occasionally with a glass rod. The sulphuric acid combines with the lime, and forms a sulphate of lime, which falls to the bottom. The liquid contains the tartaric acid dissolved in it. This is decanted off, and a little acetate of lead is dropped into it, as a test to detect the sulphuric acid, should any remain. With it it forms an insoluble precipitate; and if this be the case, it must be digested again with more tartaric of lime, to carry off what remains of the sulphuric acid. It is then evaporated, and about \( \frac{1}{7} \) of the weight of tartar employed is obtained, of concrete tartaric acid. To purify this, the crystals may be dissolved in distilled water, and again evaporated and crystallized. It seems probable, Fourcroy observes, that this acid exists in a state of purity in some vegetables. Vauquelin has found a 64th part in the pulp of the tamarind.

3. Tartaric (or tartarous) acid, thus obtained, is in the form of very fine needle-shaped crystals; but they have been differently described by different chemists. According to Bergman, they are in the form of small plates attached by one extremity, and diverging at the other. They have been found by others grouped together in the shape of needles, pyramids, regular fixed prisms, and square and small rhomboidal plates. The specific gravity is 1.5962.

4. This acid has a very sharp, pungent taste; diluted with water, it resembles the taste of lemon juice; and it reddens strongly blue vegetable colours.

5. When it is exposed to heat on burning coals, it melts, blackens, emits fumes, froths up, and exhales a heat, sharp, pungent vapour. It then burns with a blue flame, and leaves behind a spongy mass of charcoal, in which some traces of lime have been detected. Four ounces of the concrete crystallized acid, carefully distilled, gave the following products:

| Cub. In. | Properties | |----------|------------| | 431 carbonic acid gas, | | | 120 carbonated hydrogen gas, | |

6. In the decomposition of tartaric acid by heat, action of one of the most remarkable products which particularly characterizes it, is an acid liquid of a reddish colour, which amounts to one-fourth part of the weight of the former. This was formerly known by the name of pyrotartaric acid. It has a slightly acid taste, produces a disagreeable sensation on the tongue, is strongly empyreumatic, and reddens the tincture of turpentine. But it has been found by the experiments of Fourcroy and Vauquelin, to be the acetic acid impregnated with an oil \( \frac{1}{Q} \).

7. Tartaric acid is very soluble in water. The specific gravity of a solution formed by Bergman, was found to be 1.230. This solution in water is not liable to spontaneous decomposition, unless it is diluted. While it is concentrated, it loses nothing of its acid nature or its other properties.

8. Bergman supposed that tartarous acid could not be changed by the strongest mineral acids, and more into oxalic, especially by the nitric; but Hermstedt has succeeded in converting it into oxalic acid by several successive distillations, with six times its weight of nitric acid. Three hundred and sixty parts of tartaric acid yielded 562 parts of oxalic acid, which shows that it had combined with a great additional proportion of oxygen \( \frac{1}{J} \).

9. According to the analysis of Fourcroy and Vauquelin, 100 parts of this acid are composed of

| Oxygen | Carbone | Hydrogen | |--------|---------|----------| | 70.5 | 19.0 | 10.5 |

100.0

(Q) The pyromucous and the pyrolignous acids are to be regarded in the same light. The peculiar properties which were supposed to distinguish them from other acids, were found by the same philosophers to be owing to a similar impregnation. The affinities of this acid are in the following order.

Lime, Barytes, Strontites, Magnesia, Potash, Soda, Ammonia, Alumina.

Sect. XXI. Of Citric Acid.

1. The sour or acid taste of the juice of lemons and oranges is well known. This is citric acid; but it is mixed with water and mucilage; and various processes have been proposed to obtain it in a state of purity.

2. The first which succeeded was proposed by M. Georgius, an account of which was published in the Swedish Memoirs for the year 1774. His process was the following. It consisted in filling bottles with lemon juice, shutting them up close, and placing them for some time in a cellar to separate the mucilage. He afterwards exposed it to a temperature of about 24°; the watery part froze, and carried with it a portion of mucilage. This was removed, and the liquid part which remained was again frozen, till the solid part had a perceptible acid taste. The juice thus reduced to one-eighth part of its original bulk, is eight times stronger, and requires the same quantity of potash for saturation. In this state of concentration it was preserved.

3. But in this state it is not pure. We are indebted to Scheele for the discovery of the process by which it is obtained in a state of purity, and for ascertaining the characters by which it is distinguished from tartaric acid, with which it was formerly confounded. Lemon juice which has been filtered, is saturated with powdered chalk. While the chalk is added, an effervescence takes place, which is owing to the combination of the citric acid with the lime, and the separation of the carbonic acid from it in the state of gas. When the effervescence ceases, a white powder falls to the bottom. This is the lime combined with the citric acid. Wash this powder with warm water till it passes off colourless, then put the salt which has been washed into a matrix with a little water. Take such a quantity of concentrated sulphuric acid, diluted with six or seven parts of water, as may be necessary to saturate the lime which has been employed; boil it for a few minutes, then let it cool, and filter the liquor. The sulphate of lime, formed by the decomposition of the calcareous citrate, remains upon the filter. The filtered liquor contains the pure citric acid, which is to be evaporated to the consistence of a syrup, and to be set by in a cool place to crystallize. The citric acid is thus obtained in small crystals.

Scheele thinks that it is necessary to add a small excess of sulphuric acid, to take up the whole of the lime from the citric acid. But Dizè is of opinion that this excess of sulphuric acid is only necessary, to destroy the remaining portion of mucilage which adheres to the citric acid, and thus to separate from it every extraneous substance.

But it has been observed, that when an excess of sulphuric acid is employed, it may act upon the citric acid itself, decompose it, and produce the black matter which was supposed to be owing to the mucilage which adhered to it. And it appears, from an investigation by Proult on the preparation of this acid, that when too much sulphuric acid is employed, it decomposes the citric acid, and prevents it from crystallizing. To prevent this, a small quantity of chalk is added. He found that four ounces of chalk were necessary for the saturation of 94 ounces of lemon juice, and that the product which he obtained amounted to 7½ ounces of citrate of lime; and to decompose this, he added 20 ounces of diluted sulphuric acid.

4. When citric acid is pure, it crystallizes in rhombohedral prisms, whose sides are inclined to each other at angles of 60° and 120°, terminating at each end in four trapezoidal faces which include the solid angles. By slow cooling of large quantities of the solution of the pure acid, evaporated to the consistence of syrup, Dizè obtained very fine crystals.

5. Citric acid has a very strong acid taste, and even seems to be caustic; but when it is diluted with water, the taste is cooling and agreeable. It has a very slight odour of lemons, and it reddens blue vegetable colours.

6. When exposed to heat, it melts rapidly in its own water of crystallization. When the solid acid is heated, put upon burning coals, it quickly fuses, froths up, exhales a sharp, penetrating vapour, and is reduced to the state of charcoal. Distilled in a retort, it is partly defanged without decomposition, seems to be converted partly into vinegar, and then yields carbonic acid gas, carbonated hydrogen gas, and there remains in the retort a mass of light charcoal.

7. Exposed to the air, it effloresces in a dry, warm atmosphere; but when the air is moist, it absorbs water, and loses its crystalline form. It is very soluble in water. Seventy-five parts of water dissolve 100 of the acid.

8. Sulphuric acid, when concentrated, converts it acids into acetic acid. It is also decomposed by the nitric acid, which converts it partly into oxalic acid, but the greater proportion into acetic acid.

9. From the experiments which have been made with this acid, by decomposing it by means of other acids, and the products which it affords, and its conversion into acids whose component parts are known, it seems to be pretty certain that oxygen, hydrogen, and carbons enter into the composition of citric acid.

10. This acid enters into combination with alkalies, compound earths, and metallic oxides, and forms salts which are denominated citrates.

11. The affinities of citric acid are the following:

Lime, Barytes, Strontites, Magnesia, Potash, Soda, Ammonia, Alumina, Zirconia. Sect. XXII. Malic Acid.

1. Malic acid is found in considerable proportion in the juices of a great number of fruits. In them it exists ready formed, and particularly in the juice of apples, from which it has derived its name. In some fruits it exists in small quantity, mixed with a great proportion of citric acid, as in two species of vaccinium, oxycoccus and vitis idea, prunus padus, and folium dulcamara. These acids are found in nearly equal proportions in some other fruits, as in the gooseberry, cherry, and strawberry; but it exists in greatest abundance, and in the greatest purity, in the juice of apples.

2. It is prepared by the following process, which was discovered by Scheele. Bruise a quantity of four apples, express the juice, and filter it through a linen cloth. Saturate this juice with potash, add to the solution acetate of lead (sugar of lead) dissolved in water, and continue the addition till there is no more precipitation. The acetic acid combines with the potash, and remains in the liquid, while the malic acid unites with the lead, and being insoluble, falls to the bottom. Wash the precipitate with water, and pour upon it diluted sulphuric acid. The sulphuric acid combines with the lead, and forms an insoluble salt, which falls to the bottom. The malic acid remains uncombined in the liquid. Care should be taken to add a sufficient quantity of the sulphuric acid to separate the whole of the malic acid from the lead, which may be known by the pure acid taste unmixed with the sweet taste of the salt of lead.

3. When this acid is mixed with citric acid, as is the case in the juices of many fruits, Scheele contrived the following process to separate them. The juice is first evaporated to the consistence of honey; alcohol is poured upon it, by which the two acids are dissolved, and a great quantity of mucilage is separated; the alcohol is then evaporated; the residue after evaporation is diluted with two parts of water, and saturated with chalk, which combines with both the acids. The citrate of lime, which is the least soluble, is separated by evaporation; the malate of lime, or the combination with the malic acid, may be also separated, by adding another portion of alcohol, which does not dissolve the salt, but a saccharine matter which had combined with the malate of lime. The malic acid may then be separated as before, with the solution of the sugar of lead.

4. Vauquelin has extracted a very pure and nearly colourless malic acid from the juice of house-leek, (femperariae teetorum, Lin.) It exists in this juice combined with lime. He extracted it by evaporating the juice, pouring alcohol upon the residue to separate a small quantity of sugar which it contained, and by adding to the remaining matter an equal weight of concentrated sulphuric acid, previously diluted with seven or eight times the quantity of water. But as some traces of sulphate of lime are always found in the malic acid prepared in this way, he prefers the following method.

Add to the juice, a solution of sugar of lead; a precipitate is formed, which is to be decomposed by means of diluted sulphuric acid.

5. Malic acid thus obtained, is a reddish brown liquid, of a pungent acid taste, leaving afterwards the fenulation of sweetnels. It reddens blue vegetable colours. It never assumes a crystalline form, but becomes thick and viscid like syrup; and when exposed to dry air, it dries in thin strata like a brilliant varnish, for which purpose it might be employed on polished surfaces.

6. Malic acid is very readily decomposed by heat. Action of It becomes of a dark colour, swells up, exhales a thick heat, acid vapour in the open air, and leaves behind a bulky mass of coal. When distilled in a retort, it yields an acid water, a great deal of carbonic acid gas, a little carbonated hydrogen gas, and a light spongy coal.

7. It is spontaneously decomposed in the vessels in which it is kept; undergoes a kind of vinous fermentation, and deposits a mucous, flaky substance. This decomposition is owing to the intimate reaction of its constituent parts.

8. All the strong acids decompose it. Concentrated by nitric sulphuric acid chars it; and it is converted into oxalic acid. Scheele discovered, that mucous matters treated with nitric acid, passed to the state of malic acid, or were converted into this acid, and into oxalic acid.

9. The proportions of the constituent parts of this acid have not been ascertained; but from its decomposition, and the products which are thus obtained, it is evident that it is composed of oxygen, hydrogen, and carbon, of which the latter is supposed to be in great proportion.

10. The affinities of this acid are not determined, and also the compounds which it forms with alkalies, earths, and metallic oxides, are denominated malates.

11. It is very soluble in water.

Sect. XXIII. Of Gallic Acid.

1. This acid exists most abundantly in a well-known substance, nut galls, and hence it has obtained the name of gallic acid. It is also found in the bark and wood of many other plants. It was first examined by the academicians of Dijon in 1772, and its acid properties clearly ascertained; but it is to Scheele that we are indebted for the discovery of the process by which it may be obtained pure and crystallized. The account of this process was published in 1782, which is the following.

2. To one part of nut galls, reduced to a coarse powder, add five parts of pure water. Let the infusion macerate for fifteen days at the temperature of between 70° and 80°; filter it, and put the liquid into a large glass or earthen vessel, expose it to the air, and allow it to evaporate slowly. A thick glutinous pellicle forms on the top; a great quantity of mucous flakes are precipitated, and the solution has no longer an astringent, but a perceptibly acid taste. At the end of two or three months, Scheele had observed on the sides of the vessels in which the solution was contained, a brown crust covered with shining crystals of a yellowish gray colour. He found also a great quantity of these crystals under the thick pellicle which covered the liquid. He then decanted it, and added alcohol to the precipitate, the pellicle and the crystal line. line crust, and applied heat. The alcohol dissolved the crystallized acid, without touching the mucilage. The solution was now evaporated, and the gallic acid was obtained pure, in small shining crystals, of a yellowish gray colour.

3. Deyeux has pointed out another method by which with proper precautions, gallic acid may be more readily obtained. He introduces into a large glass retort, a quantity of nut galls reduced to powder, and applies heat slowly and cautiously, by which he obtains a large quantity of laminated, brilliant, silvery crystals, sufficiently large, and which have all the properties of gallic acid. But in following this process, it is necessary to observe, that the heat must be very moderate, and not continued till an oil is disengaged, which instantly dissolves all the crystals sublimed before its appearance.

4. Mr Davy prepares it by boiling together for some time carbonate of barytes, and a solution of gall nuts. This affords a bluish green liquor. When diluted sulphuric acid is dropped into it, it becomes turbid; sulphate of barytes is deposited, and after filtration, if the saturation of the earth be complete, a colourless solution of gallic acid, apparently pure, is obtained.

5. Gallic acid is crystallized in transparent octahedrons, or brilliant plates; it has a sharp, pungent, and austere taste, but less strong and astringent than that of the gall nut.

6. This acid is not sensibly affected by exposure to the air. It requires 24 parts of cold water, and about two-thirds of its weight of boiling water, to dissolve it, from which it can only be crystallized by a very slow evaporation.

7. With a moderate heat, it rises into vapour, which on cooling is condensed and crystallized. In the state of vapour, it has a sharp, aromatic odour, resembling that of the benzoic acid. Every time that it is sublimed, even with a moderate heat, it is partially decomposed; water is formed, an acid liquid, carbonic acid gas, carbonated hydrogen gas, and some drops of a brown coloured oil; and there remains behind, a great quantity of coaly matter.

8. Concentrated sulphuric acid decomposes and chars the gallic acid. Nitric acid converts it into the malic and oxalic acids. Oxymuriatic acid produces peculiar changes on the gallic acid, but these have not been distinctly ascertained.

9. Although we have not yet treated of metallic substances, it may be necessary to anticipate a little, and mention the effects of gallic acid on metallic oxides. This indeed is its chief characteristic. On this account, it is much employed by chemists, to discover metallic substances, which are held in solution along with other bodies. Its effects on the metallic oxides are extremely various, and with different metals it affords different coloured precipitates. The more readily the metallic oxides give up their oxygen, the greater is the change produced by the gallic acid. On lime metallic solutions it has no effect; such are, solutions of platina, of zinc, of tin, of cobalt, and of manganese. The precipitates of the different metals produced by means of gallic acid, exhibit the following colours.

| Gold | Brown | | Silver | Brown | | Mercury | Orange-yellow | | Copper | Brown | | Bismuth | Citron-yellow | | Iron | Black | | Lead | White | | Nickel | Gray | | Antimony | White | | Tellurium | Yellow | | Uranium | Chocolate | | Titanium | Reddish-brown | | Chromium | Brown | | Columbium | Orange |

10. The component parts of gallic acid are the same as those of the other vegetable acids, but having a greater proportion of carbon; but these proportions have not been ascertained.

11. The compounds which the gallic acid forms with alkalies, earths, and metallic oxides, are denominated gallates.

12. The affinities of this acid have not been ascertained.

**Sect. XXIV. Of Benzoic Acid.**

1. Benzoic acid is obtained from several plants, and particularly from the *phytaxis benzoe*, a tree which grows in Sumatra; from the balsam of Peru and Tolu; from vanilla, and liquid amber. It also exists in the urine of children, and sometimes in that of adults, but constantly in the urine of quadrupeds which live on grass and hay, especially in that of the horse and cow. It is suspected also that it exists in many of the grapes, and that it is derived from them by means of the aliment to the urine of the animals in which it is found. Fourcroy and Vauquelin suspect that it exists in the sweet-scented grapes, (*anthoxanthum odoratum*, Lin.) which gives the fine flavour to hay.

The first mention of benzoic acid is made by Blaise de Vigenere, who wrote about the commencement of the 17th century (R). He says, that he obtained by distilling benzoin, an acid salt which crystallized in needles, of a penetrating odour. It was then called flowers of benzoin, but at present benzoic acid.

2. To obtain this acid by the most common process, put into an earthen pot a quantity of benzoin powdered. Cover the vessel with a cone of paper, and apply a very gentle heat. The benzoic acid is sublimed, and attaches itself to the sides of the cone, which may be renewed every two hours. Continue the process till the acid sublimed begins to be coloured by the oil which is disengaged. By a process proposed by Geoffroy, the benzoin reduced to powder is digested in warm water, and this being filtered, yields on cooling needle-shaped crystals of benzoic acid; but the quantity obtained in this way is very small, which led Scheele to adopt the following process. He took

(R) *Traité du feu et du sel*, which was printed at Paris in 1608. took 1 part of quicklime, to which were added 3 parts of water, and afterwards about 30 parts more, which is then to be gradually mixed with 4 parts of powdered benzoic acid. Heat the whole on a moderate fire for half an hour, continually agitating the mixture; then remove it from the fire, and let it remain at rest for several hours. Decant the clear supernatant liquor, and add 8 parts more water to the residuum. Boil it for half an hour, and mix it with the former. Reduce the liquor by evaporation to two parts; add drop by drop, to a slight excess, muriatic acid, which causes the benzoic acid to precipitate, by separating it from the lime. Wash the precipitate well on a filter; and to obtain it in crystals, dissolve it in 5 or 6 times its own weight of boiling water, which on cooling, yields crystals in the form of long compressed prisms.

3. Pure benzoic acid is either in the form of a light powder, perceptibly crystallized, or in the form of very small needles, of which it is extremely difficult to determine the shape. It is white and brilliant, and has some degree of ductility and elasticity. It has an acrid, pungent, acidulous, and very bitter taste. In the cold the odour is slight, but is aromatic, and this is sufficient to characterize it. It reddens the tincture of turpentine, but has no effect on the syrup of violets. The specific gravity of benzoic acid is 0.667.

4. Exposed to a moderate heat, it melts, forms a soft brown and spongy body, which cools into a solid crust, exhibiting on the surface some appearance of crystallization. With a stronger heat it is sublimed, and exhales a white acid vapour, which affects the eyes. It burns when brought into contact with flame, and the whole is consumed without any residuum. When it is distilled in close vessels, great part sublimes unchanged, but part is decomposed and yields a viscid liquid, a considerable quantity of oil, and a much greater quantity of carbonated hydrogen gas than any other body of this nature. A very small portion of oily matter remains in the retort.

5. It is not sensibly changed by exposure to the air. It is scarcely soluble in cold water. Four hundred parts of boiling water dissolve 20 parts of the acid, 19 of which are separated on cooling.

6. Concentrated sulphuric acid readily dissolves this acid, and one part of the sulphuric acid passes into the state of sulphurous acid. Benzoic acid may be separated from this solution without having undergone any change, by adding water. The nitric acid dissolves it in the same way, and it is also separated by means of water. Guyton found, by distilling nitric acid on the concrete benzoic acid, that nitrous gas was disengaged, only towards the end of the process, and that the acid itself then sublimed without alteration.

7. As this acid yields by distillation oil and carbonated hydrogen gas, it is obvious that it must be composed of carbons and hydrogen, and probably also oxygen, although this latter has not been discovered in any experiments that have been made on this substance.

8. Benzoic acid unites very readily with alkalies, earths, and metallic oxides, and the compounds which are thus formed are denominated benzoates.

9. The order of the affinities of benzoic acid is the following:

- White oxide of arsenic, - Potash, - Soda, - Ammonia, - Barytes, - Lime, - Magnesia, - Alumina.

**Sect. XXXV. Of Succinic Acid.**

1. Succinic acid, formerly called volatile salt of amber, was long regarded as an alkaline salt. It was not till towards the end of the 17th century, that its acid properties were discovered. As amber, the substance from which the acid is obtained, is found in considerable quantity under strata of substances which contain pyrites, it was thought that this acid was formed by sulphuric acid. This was the opinion of Hoffman and Neuman. Amber is found on the seacoast of different countries, especially in the Prussian territory on the shores of the Baltic. The name of the acid is derived from *succinum*, the Latin name for this substance.

2. Succinic acid may be obtained by the following process. Introduce a quantity of amber in powder into a retort, and let it be covered with dry sand. Adapt a receiver, and distill with a moderate heat in a sand bath. There passes over first a liquid which is of a reddish colour, and afterwards a volatile acid salt, which crystallizes in small, white, or yellowish needles in the neck of the retort; and if the distillation be continued, a white light oil succeeds, which becomes brown, thick, and viscid. The acid which is obtained in this way is contaminated with the oil; and therefore to separate this oil, it may be dissolved in hot water, and passed through a filter on which has been placed a little cotton moistened with oil of amber, which retains the oil, and prevents it from passing through along with the acid. The acid may then be evaporated and crystallized. Guyton has observed, that the acid may be rendered quite pure, by distilling off it a sufficient quantity of nitric acid, but with this precaution, that the heat employed is not strong enough to sublime the succinic acid.

3. The acid thus obtained is in the form of white, shining, transparent crystals, which are foliated, triangular, and prismatic. The taste is acid, but not corrosive. It reddens the tincture of turpentine, but has no effect on the infusion of violets.

4. With the heat of a sand bath, the crystals of succinic acid first melt, and are then sublimed and condensed in the upper part of the vessel. There is, however, a partial decomposition, for there is a coaly matter left behind in the vessel.

5. At the temperature of 212°, two parts of water dissolve one of this acid, which crystallizes on cooling. When the water is cold at the temperature of 50°, it requires 96 parts of water to dissolve one of the acid.

6. This acid like other vegetable acids, is composed of oxygen, hydrogen, and carbon; for when it is distilled in a retort with a strong heat, carbonic acid gas, and carbonated hydrogen gas are evolved, and char- coal remains behind in the retort. The proportions of the component parts have not been ascertained.

729 Compounds. 7. This acid enters into combination with alkalies, earths, and metallic oxides, and forms with them compounds which are denominated succinates.

730 Affinities. 8. The affinities of this acid are in the following order:

- Barytes, - Lime, - Potash, - Soda, - Ammonia, - Magnesia, - Alumina, - Metallic oxides.

Sect. XXVI. Of SAGLACTIC ACID.

1. To this acid Fourcroy has given the name of Mucous acid, because it is obtained from gum arabic and other mucilaginous substances; and it was formerly called acid of sugar of milk. This latter name it received from Scheele, who discovered it in the year 1780, while he was employed in making experiments on the sugar of milk, in order to obtain from it oxalic acid, which he procured from sugar.

2. This acid may be obtained by the following process. To 1 part of gum arabic, or other mucilaginous substance, add 2 parts of nitric acid in a retort, and apply a gentle heat. There is at first disengaged a little nitrous gas and carbonic acid gas, after which let the mixture cool. There is then precipitated a white powder which is slightly acid. This powder is the saglactic acid.

3. Thus obtained, saglactic acid is in the form of a white powder, a little gritty, and with a weak acid taste.

4. It is readily decomposed by heat, and yields an acid liquor which crystallizes by rest in the shape of needles, a small quantity of an acrid caustic oil, of a blood red colour, carbonic acid gas, and carbonated hydrogen gas; and there is left behind a considerable quantity of coaly matter. It is partly sublimed in needles or brown plates, with an odour similar to that of benzoic acid.

5. Saglactic acid in the state of powder is not very soluble in water. Cold water does not take up more than 200 or 300 parts of its weight; boiling water does not take up above one half more. On cooling, the acid is deposited in brilliant scales, which become white in the air. The solution has an acid taste. It reddens the tincture of turpentine. Its specific gravity at the temperature of 59° is 1.0015.

6. This acid enters into combination with earths, alkalies, and metallic oxides; and the salts which it forms are known by the name of saglactates.

7. The order of its affinities, according to Bergman, is the following:

- Lime, - Barytes, - Magnesia, - Potash, - Soda, - Ammonia, - Alumina, - Metallic oxides.

Sect. XXVII. Of CAMPHORIC ACID.

1. This acid is obtained, as the name imports, from camphor, a concrete substance procured from a species of laurel (Laurus camphora, Lin.) which is a native of the East Indies.

2. Camphoric acid was first obtained by Koegarten, by distilling nitric acid 8 times successively off camphor. This experiment was repeated by Bouillon Lagrange with the same result. He introduced into a glass retort, 1 part of camphor, and he poured over it 4 parts of nitric acid. A receiver was adapted to the retort, and the joinings were well fitted. The retort was placed on a sand-bath, and a gradual heat was applied. A great deal of nitrous gas and carbonic acid gas was disengaged. One part of the camphor is sublimed, and another part settles on the oxygen of the nitric acid. The same process must be repeated till the whole of the camphor is acidified, which is known by its crystallizing when the liquor cools which remains in the retort. These crystals are camphoric acid. To purify it, it must be dissolved in distilled warm water, and the liquor is then to be filtered and evaporated to nearly half its volume, or till a thin pellicle is formed on it. When it cools, crystals of pure camphoric acid will be obtained.

3. Camphoric acid has a slightly acid, bitter taste. It reddens the tincture of turpentine. The crystals resemble, when, in a mass, those of the muriate of ammonia. Exposed to the air the mass effloresces.

4. Cold water dissolves this acid with great difficulty. An ounce of water at the temperature of between water 50° and 60°, cannot dissolve more than 6 grs. while water at the boiling temperature will hold in solution eight times that quantity.

5. When this acid is put upon burning coals, it exhales a dense, aromatic vapour; with a less degree of heat, it melts, and is sublimed. When put into a heated porcelain tube, and if a stream of oxygen gas be passed through it, the acid remains unchanged, but it is sublimed from the sides of the tube. When distilled alone, it first melts and then sublimes. This sublimation produces some change in its properties. It no longer reddens the tincture of turpentine, and acquires a strong aromatic odour, and a less pungent taste; becomes insoluble in water, and in the sulphuric and muriatic acids. The nitric acid heated, makes it yellow, and diffuses it.

6. Camphoric acid enters into combination with the compound alkalies, earths, and metallic oxides, and the compounds thus formed are denominated camphorates.

7. The affinities of this acid are the following:

- Lime, - Potash, - Soda, - Barytes, - Ammonia, - Alumina, - Magnesia.

Sect. XXVIII. Of SUBERIC ACID.

1. This acid is obtained from cork, a well-known substance, which is the bark of a tree (the quercus fischeri, Lin.). Lin. or cork-tree.) From the Latin name of this substance, *saber*, the name of the acid is derived, and hence it is called *saberic acid*. The acid which is obtained from cork, by treating it with nitric acid, was supposed to be the oxalic acid, on account of possessing some common properties, and particularly that of forming with lime an insoluble salt. But the experiments of Bouillon Lagrange have shown, that this is a peculiar acid.

2. This acid is obtained by the following process. Take a quantity of clean cork, grated down. Introduce it into a retort, and pour on it five times its weight of nitric acid; the acid ought not to be too concentrated. It is then to be distilled with a moderate heat. The cork swells up and becomes yellow, and there is discharged a quantity of red vapours; and as the distillation goes on, the cork is dissolved, and swims on the surface like foam. If this scum is not formed, the cork has not been acted upon by the acid. In this case when the distillation begins to stop, return into the retort the acid which had passed over into the receiver, and distil as long as any red vapours appear, and then immediately remove the retort from the sand bath, and pour out the contents while yet hot into a glass or porcelain vessel; put it upon a sand bath and apply a gentle heat, stirring it constantly with a glass rod. The matter gradually thickens, and as soon as white vapours are discharged, which excite a tickling in the throat, it is to be removed from the sand bath, and constantly stirred till the mass is nearly cold. In this way a substance is obtained of the consistence of honey, of an orange-yellow colour, of a sharp penetrating odour while it is warm, but which gives out a peculiar aromatic smell when it is cold.

To procure the acid which is contained in this substance, put it into a matrafs, and pour upon it double its weight of distilled water. Apply heat till the mass becomes liquid, and separate by filtration that part which is insoluble in water. The liquor which is obtained is of a clear amber colour, and of a peculiar odour. The filtered liquor on cooling becomes muddy, is covered with a thin pellicle, and deposits a powdery sediment. The precipitate is to be separated from the liquid by filtration, and it is to be dried with a gentle heat. This precipitate is the saberic acid. The remaining liquor is then to be evaporated to dryness with a moderate heat, to obtain the whole of the acid which it holds in solution.

The acid which is prepared by this process is a little coloured, and may be purified, either by saturating the saberic acid with potash, and precipitating with an acid, or by boiling it with charcoal powder.

3. Saberic acid is in the solid form, but it is not crystallized. When it is obtained by precipitation, it is in the state of a powder, and by evaporation it is in the form of thin irregular pellicles.

4. It has a slightly bitter and acid taste. Dissolved in a small quantity of boiling water, it tickles the throat, and excites coughing. It reddens vegetable blues.

5. Exposed to the light, it becomes brown after a certain time; but this effect is more speedily produced when it is exposed to the sun's rays. Heated in a matrafs, the saberic acid is sublimed, and the glass remains marked with zones of different colours. If the sublimation be stopped in time, the acid is obtained on the sides of the vessel, in small points formed of concentric circles. When exposed to the heat of the blowpipe on a spoon of platinum, it first melts, then falls down into powder, and at last is totally dissipated by sublimation.

6. It undergoes no change from the action of oxygen or acids. The action of the acids on saberic acid is very weak. The solution is not complete, especially when it is impure.

7. Water at the temperature of 60° or 70° dissolves of water, the concrete acid only in the proportion of 10 grs. to the ounce. When the acid is very pure, the water will not dissolve more than 4 grs. Boiling water dissolves half its weight; but as the liquor cools, it becomes muddy, and the acid is deposited.

8. This acid combines with the alkalies, earths, and compounds metallic oxides, and forms with them compounds which are known by the name of *saberate*.

9. The order of its affinities is the following:

- Barytes, - Potash, - Soda, - Lime, - Ammonia, - Magnesia, - Alumina, - Metallic oxides.

**Sect. XXIX. Of Mellitic Acid.**

1. The acid is procured from a mineral substance which was discovered about the year 1790. Werner gave it the name of honigstein, (honeystone) from its colour. By other mineralogists it has been denominated mellite, from the Latin name of honey, and hence the acid which it affords has been called *mellitic acid*. The mineral from which this acid is obtained seems to be of vegetable origin. It is found in small crystals among the layers of wood coal at Arten in Thuringia. In the first analysis to which this mineral was subjected no new acid was detected. But in the year 1799 the acute and accurate Klaproth examined its nature and component parts, and found that it is a compound of a peculiar acid and alumina. His experiments have been since repeated by Vauquelin, and the result of his analysis has been fully confirmed.

2. It is procured from mellite by the following process. The mineral is to be reduced to powder, and obtaining boiled with about 72 times its weight of water. The alumina is precipitated in the form of flakes, and the acid combines with the water. By filtration and evaporation, crystals are deposited, which are the crystals of mellitic acid.

3. This acid crystallizes in the form of fine needles, or in small short prisms with shining faces. They are considerably hard. It has a slightly acid taste, accompanied with some degree of bitterness.

4. This acid has very little solubility in water, but action of it has not been ascertained to what degree; or what water proportion of water it requires for its solution.

5. A small quantity of this acid exposed to the flame of the blowpipe, at first gave out sparks like nitre; and then melted up, and left a matter which penetrated... penetrated the charcoal. Heated in a crucible of platinum, it swells up at first, is then charred, without the production of any oily vapour, and leaves behind a light coaly alkaline matter.

6. When the nitric acid is added to this acid, it produces no other change than giving it a yellowish colour. It has not yet converted it into any of the vegetable acids, to which it is nearly allied in its properties and constituent parts.

7. According to Klaproth's analysis the mineral from which the acid is obtained consists of

- 46 mellitic acid, - 16 alumina, - 38 water.

When it was distilled in a retort the acid was completely decomposed; and the products obtained by Klaproth in this way from 100 grains of mellite were the following:

- 54 cubic inches of carbonic acid gas, - 13 hydrogen gas, - 38 grs. of acidulous water, - 1 aromatic oil, - 9 charcoal, - 16 alumina.

The constituent parts of mellitic acid are obviously carbone, hydrogen, and oxygen. But the proportions have not been ascertained.

8. Mellitic acid enters into combination with the earths, alkalis, and metallic oxides, and forms compounds with them which are called mellates.

**Sect. XXX. Of Lactic Acid.**

1. In investigating the changes which spontaneously take place in milk, the celebrated Scheele discovered that it contains a peculiar acid. To this has been given the name of lactic acid. The formation of this acid depends on the change of the sugar of milk or of the saccharine mucous matter; for after the acid is once well formed, when the feros part of the milk being very four reddens vegetable blues, no more is obtained by evaporation and crystallization.

2. Scheele did not succeed in separating the acid from the feros part of the milk by distillation. He therefore contrived the following process. He evaporated a quantity of four whey to ¼th of its bulk, and then filtered it to separate the whole of the coagulated cheesy matter. He then added lime-water to precipitate the phosphate of lime, and diluted the liquid with three times its weight of pure water. He then precipitated the excess of lime by means of the oxalic acid, adding no more of the latter than what is necessary. He evaporated the solution to the consistency of honey, poured on a quantity of alcohol which separates the portion of sugar of milk and of other extraneous matter, and dissolves the lactic acid; and distilled the clear filtered liquor till the whole of the alcohol employed be driven off: what remains in the retort is the lactic acid.

3. This acid is never crystallized; but always appears in the form of a viscid mucilaginous substance. It has a strong sharp taste, which is far from being agreeable. It reddens the tincture of turpentine, and gives a reddish violet tinge to the syrup of violets.

4. When it is distilled in a retort it yields an empyreumatic acid which is very strong and analogous to the tartaric, very little oil, carbonic acid gas, and carbonated hydrogen gas, and a small quantity of coaly matter which adheres to the glass. This shows what are the constituent parts of this acid, but the proportions of these have not been determined.

5. The compounds with alkalis, earths, and metallic oxides which are formed with the lactic acid, are denominated lactates.

6. The affinities of this acid are in the following Affinity order.

- Barytes, - Potash, - Soda, - Strontites, - Lime, - Ammonia, - Magnesia, - Metallic oxides, - Glucina, - Alumina, - Zirconia.

**Sect. XXXI. Of Lactic Acid.**

1. The substance from which this acid is obtained, history is collected in the neighbourhood of Madras. It was first described by Dr Anderson, who says that nests of insects resembling small cowry shells were brought to him from the woods by the natives, who eat them with avidity. These supposed nests he shortly afterwards discovered to be the coverings of the females of an undescribed species of coccus; and having noticed in the abbé Grosier's account of China, that the Chinese called a kind of wax, much esteemed by them, under the name of pêla from a coccus deposited for the purpose of breeding on certain shrubs, and managed exactly in the same manner as the Mexicans manage the cochineal insects, he followed the same process with his new insects, and found means to propagate them with great facility on trees and shrubs in the neighbourhood.

This substance, which he called white lac, was found on examination to have a considerable resemblance to the beeswax. Dr Anderson supposes, that the animal which secretes it provides itself, by some means or other, with a small quantity of honey, resembling that produced by our bees. The sweetness of it tempted the children who were employed to collect it, to eat so much of it as very much to diminish his crop. A small quantity of this matter was sent to Europe in 1789. It was examined by Dr Pearson, who published an account of his analysis in the Philosophical Transactions for 1794, from which we have extracted the information which we now lay before our readers.

A piece of white lac, which weighs from three to fifteen grains, is supposed to be produced by each insect. These pieces are about the size of a pea, of a gray colour, opaque and roundish, but with a flat side, by which they adhere to the bark. In its dry state, white lac is soft and tough, and has a salutary and bitterish taste. A watery liquid, which has a slight salt taste, oozes out on pressing a piece of this substance. White lac has no smell, unless it be pressed or rubbed, when it becomes soft, and then it emits a peculiar odour. When it is gathered from the tree, the pieces of lac are lighter than bees-wax; but after being melted and purified, it sinks in water. It melts in alcohol and in water at the temperature of $145^\circ$, and very readily in boiling water.

2. Dr Pearson exposed 2000 grains of white lac to such a degree of heat as was sufficient to melt them. They became soft and fluid, and there oozed out 550 grains of a reddish watery liquid, which emitted the smell of newly baked bread. The liquid was filtered and purified from extraneous matter. This liquid is laccic acid.

3. It has a slightly saltish taste, with some degree of bitterness. It smells when heated like newly baked hot bread. It reddens the tincture of turpentine. Its specific gravity, at the temperature of $60^\circ$, is $1.025$. When this liquid remains for some time at rest, it becomes turbid, and deposits a sediment. When it is evaporated, it becomes more turbid; and allowed to remain at rest, it affords small needle-like crystals in mucilaginous matter.

4. Two hundred and fifty grains of this liquid were exposed to heat in a small retort. As the liquor grew warm, mucilage-like clouds appeared, but when it grew hot, they disappeared. At the temperature of $200^\circ$ it distilled over very fast. On distillation to dryness, a small quantity of extractive matter remained. The distilled liquid was transparent and yellowish, and while hot, had the smell of newly baked bread. Paper stained with turpentine, which had been put into the receiver, was not reddened. One hundred grains of yellowish transparent liquid being evaporated till it became turbid, afforded in the course of a night, acicular crystals which had a bitterish taste. Under a lens they appeared in a group, somewhat resembling the umbel of parsley. One hundred grains of yellowish transparent liquid being evaporated in a low temperature to dryness, a blackish matter remained behind, which did not entirely disappear when exposed to pretty strong heat; but on heating oxalic acid to a less degree, it evaporated and left no trace behind.

From these properties, and from its peculiar action with alkaline, earthy, and metallic salts, Dr Pearson concludes, that this acid is different from any of the acids already known.

5. The experiments which have been made on white lac, and on the acid obtained from it, show that it is closely allied to the vegetable acids. Its component parts, therefore, probably are, carbons, hydrogen, and oxygen; but experiments are still wanting fully to ascertain its nature and properties*.

**Sect. XXXII. Of Prussian Acid.**

1. This is one of the most important acids, both to the chemist, and to the manufacturer. It has been alleged that the ancients were acquainted with Prussian blue, which they employed in painting; but Landriani has shown, in his dissertation on this substance, from the evidence of Theophrastus and Pliny, and from the analysis of an Egyptian mummy, that the ancients employed ultramarine blue and the smalt or azure of cobalt; and that Prussian blue, which is readily acted on by the substances to which it must have been exposed in these countries, could not resist their influence for so many ages, and retain the beautiful colours which are admired in the paintings of Herculaneum.

2. Stahl relates, in his 300 experiments, that the discovery of Prussian blue was owing to an accident. About the beginning of the 18th century, Dietzsch, a chemist of Berlin, wishing to precipitate a decoction of cochineal with an alkali, borrowed from Dippel some potash, on which he had distilled several times his animal oil; but as there was some sulphate of iron in the decoction of cochineal, the liquor instantly exhibited a beautiful blue in place of a red precipitate. Reflecting on the circumstances which had taken place, he found that it was easy to produce at pleasure the same substance, which afterwards became an object of commerce. It obtained the name of Prussian blue, from the place where it was discovered.

3. This discovery was announced in the Memoirs of the Academy of Berlin, for the year 1710; but the process by which it was obtained was kept secret, that those who were in possession of it might derive the whole advantage from the manufacture. It was published for the first time by Woodward in the Philosophical Transactions for the year 1724, who declared, that it had been sent to him from Germany, by one of his friends. This is all that is known of the manner by which this process was made public. It is not certain whether it came originally from the first inventors, or whether it be owing to the researches of some chemist.

4. The method which is described by Woodward succeeds very well. It is by preparing an extemporaneous alkali, by dissolving four ounces of nitre, and an equal quantity of tartar; then to add four ounces of bullock's blood, well dried, and to calcine the whole with a moderate heat, till the blood be reduced to a coal, or emit no smoke capable of blackening any white body that is exposed to it. Towards the end of the process the fire is to be increased, till the crucible which contains the materials shall be moderately red. Throw the red-hot matter into water, and boil it for half an hour; and having poured off the first water, add another quantity, and boil it again. Repeat this operation till the last water comes off insipid, then add all the quantities of water together, and evaporate to the quantity of two pints. To this liquid the Germans have given the name of blood ley. By others it has been denominated phlogisticated alkaline ley.

5. A solution of 2 ounces of sulphate of iron, and 8 ounces of alum, in two pints of boiling water, is to be mixed with the former solution while both are hot. A great effervescence takes place; the liquor becomes muddy, assumes a greenish colour, inclining more or less to blue; and a precipitate is formed of the same colour. Separate this precipitate, and to heighten the colour, pour upon it carefully muriatic acid till it no longer increases the intensity of the blue colour; then wash it with water, and dry it slowly.

6. Such was the process by which Prussian blue was obtained, before the theory was discovered, to account for the different changes and effects which it presented. The same year in which Woodward published an account of the process, Brown instituted a set of experiments, to discover the nature of this substance, and the circumstances which attended its formation. He found that flesh, as well as bullock's blood, possessed a similar property. He thought that Prussian blue was the bituminous part of iron, developed by the alkaline ley, and fixed in the aluminous earth. Geoffroy adopted the same explanation. He found that, in the animal kingdom, oils, wool, hartshorn, sponge, had the same effect as blood with the alkali, in precipitating iron of a blue colour; and that some vegetable charcoal treated with the alkali, in some measure communicated to it a similar property. Neuman discovered that the animal empyreumatic oils might be employed for the same purpose. The abbé Menon was of opinion, that the colour of iron is blue; but that this colour, usually disguised by some false matter, reappears, when it is separated by the phlogisticated alkaline ley, and thus Prussian blue was only iron precipitated in its natural state. The aluminous earth, he saw, served only to diminish the intensity of the colour, and to give it a more agreeable shade.

7. It is to the celebrated Macquer that we are indebted for the first correct views in developing the theory of this process. He observed, 1. That pure alkalies precipitated iron from its solutions of a yellow colour. 2. That this precipitate is soluble in acids. 3. That the blue fecula obtained from the blue phlogisticated ley after the addition of muriatic acid, was not acted on by acids. He therefore concluded that the first green precipitate was not a homogeneous substance, but a mixture of two precipitates, the one yellow and the other blue; and that it was sufficient to remove the first by any acid, to give to the second its full intensity of colour. Hence he supposed, that the acid of the alum employed in this process was useful in saturating, in a great measure, the pure alkaline portion of the ley, and diminishing proportionally the yellow precipitate of iron. Having found that it was impossible to saturate the alkali with a colouring matter by means of calcination; and, having discovered that the pure alkali deprived iron (which was converted into Prussian blue) of its characteristic properties; and finally, having ascertained that the alkali which was employed in the process became exactly similar to that which was calcined with combustible matters, to prepare it for the precipitation of iron of a blue colour, and that its alkaline properties disappeared as it was more or less saturated with the colouring matter, he attempted to saturate it fully. He therefore saturated an alkali so completely with the colouring matter, that it underwent no change by boiling, and exhibited none of its alkaline properties by chemical tests. By this discovery we are now in possession of this valuable substance which had been hitherto known under the name of the saturated ley of the colouring matter of Prussian blue.

In the course of his experiments Macquer found, that the saturated ley could not be decomposed by sulphuric acid, or by the solution of alum; but, on the contrary, that every metallic substance dissolved in an acid, separated the phlogistic matter from all the fixed and volatile alkalies. Hence he concluded, that in the process of the formation of Prussian blue, it is necessary that the affinity of the iron should combine with that of the acid with the alkali, to form a sum of affinities capable of effecting the separation. This luminous explanation of so striking a process, has not a little contributed to establish the theory of compound affinities.

8. After the publication of Macquer's dissertation, and almost all chemists were occupied in researches into the nature of Prussian blue, either to discover the nature of its principles, or to improve the process for preparing the colouring matter; but they were chiefly occupied in examining those bodies which were capable of phlogisticating the alkali, as it was called; and this property was found to exist in a great number of substances. Till the year 1775, no change or modification was proposed on the theory of Macquer.

9. About this time the celebrated Bergman, in his dissertation on elective attractions, threw new light on this subject of investigation, by considering the colouring matter of Prussian blue as a distinct acid, and possessed of peculiar attractions. According to Sage, the alkali which precipitated Prussian blue was nothing but an alkali saturated with phosphoric acid; but Lavoisier justly remarked, that, according to this theory, the salt formed of phosphoric acid and an alkali ought to precipitate a solution of sulphate of iron of a blue colour, which was not the case.

Many chemists examined the nature of this substance by means of heat; and among others Delius and Scopoli, Deyeux and Parmentier, Bergman and Erxleben, subjected it to distillation, the product of which was a quantity of ammonia. By others an oil was obtained in this process, and sometimes a peculiar acid, which had the properties of sulphuric acid. The difference of these results probably arose from the different states of purity of the Prussian blue which was employed in the experiment.

Fontana discovered that the sulphuric acid distilled by Fonta on Prussian blue passed to the state of sulphurous acid, and that the colouring matter produced detonation with nitre. Landriani found that it yielded by distillation, besides ammonia, a small portion of liquid perceptibly acid, and some oil, and a great quantity of elastic fluids, which consisted of azotic and hydrogen gases, the latter burning with a blue flame, and detonating strongly with oxygen gas.

10. But the most important step in the progress of the discovery of the nature and properties of this singular substance, was made by Scheele, an account of which he published in two dissertations in the Stockholm transactions for 1782 and 1783. He began by examining the blood-ley, and he found by exposing it to some time to the air, that it lost the property of precipitating iron of a blue colour, and the precipitate which it then yields is soluble in acids. To discover what change had taken place on the air, he put some of the ley freshly prepared into a large glass globe close shut up, and he found some time after, that neither the air nor the ley had undergone any change. He concluded, therefore, that the colouring matter was not pure phlogiston. He suspected that carbonic acid might have some effect in changing the nature of the carbonic alkali when exposed to the open air. He filled a glass globe with carbonic acid gas, and having introduced a quantity of Prussian alkali, he kept it close shut up. up for 24 hours, after which, on examining the alkali, it gave a precipitate which was soluble in acids; the change, then, must have been occasioned by the carbonic acid gas. He repeated this experiment by adding to the colouring matter a small quantity of sulphate of iron. This matter was not changed by the action of the carbonic acid gas. The same result was observed when he boiled the colouring matter in an oxide of iron precipitated by an alkali. It suffered no change in the carbonic acid gas, but precipitated the iron as before. The iron then has the property of fixing the colouring principle, of defending it against the action of carbonic acid gas; and hence it happens that the neutral colouring salt formed with an alkali boiled on Prussian blue, does not so easily lose its properties. But if the colouring ley be digested on an oxide of iron, as that which is obtained from the sulphate of iron boiled in nitric acid, and afterwards precipitated by an alkali, no effect is produced. By this digestion the action of the gas is not prevented, and if the sulphate of iron be added, even with an excess of acid there is no longer a production of Prussian blue.

To discover what happened to the colouring principle, when it was charged with carbonic acid gas, Scheele introduced into a globe filled with this gas, some of the Prussian alkali, and suspended in it a bit of paper, previously dipped in a solution of sulphate of iron, and on which he had let fall two drops of alkaline liquor to precipitate the iron. The paper was removed at the end of two hours, and, with the addition of a little muriatic acid, was covered with a fine blue colour. The same experiments repeated with alkali saturated with excess of sulphuric acid, gave the same result; that is to say, the paper charged with oxide of iron and suspended as above, became of a blue colour on adding muriatic acid. Hence it follows, that the colouring principle is disengaged by acids, without decomposition, for it still has the property of being fixed with oxide of iron with which it comes in contact. Thus he found that the colouring matter might be separated from the substances with which it was generally in combination, and without undergoing decomposition.

11. To obtain it, therefore, in a separate state, he contrived the following process. He put into a glass vessel two parts of Prussian blue reduced to powder, one part of red oxide of mercury, and five parts of water. He boiled the mixture for some minutes, continually stirring it. It then assumes a yellowish green colour. He put the whole on a filter, and poured upon the residue two parts more of boiling water, to wash it completely. This liquid is a solution of mercury combined with the colouring matter, which has the metallic taste, and is neither precipitated by acids nor alkalis. Pour this liquid into a glass vessel upon one half part of clean iron filings, and a smaller quantity of concentrated sulphuric acid. Shake the mixture well for some minutes, when it becomes black by the reduction of the mercury. The liquid then loses its metallic taste, and gives out the odour which is peculiar to the colouring matter. Having allowed it to remain at rest for some time, it is poured off, put into a retort to which a receiver is adapted, and distilled with a gentle heat. One-fourth part of the liquid only should be allowed to pass over, for the colouring matter is much more volatile than water, and consequently rises first. The liquid in the receiver is commonly mixed with a little sulphuric acid, from which it may be separated by distilling again off a little powdered chalk, which takes up the sulphuric acid. The liquid Prussian acid then passes over in a state of purity; and this liquid is obtained.

12. In this process the oxide of mercury which was Nature of mixed with the colouring matter, takes it from the Prussian iron with which it is combined in the state of Prussian blue, and is then a crystallizable prussiate of mercury. The iron which is added in the metallic state, reduces the oxide of mercury, and at the moment it combines with the sulphuric acid, which has also been added, the heat applied sublimes the prussic acid which has been disengaged from the mercury, which is now reduced to the metallic state. The prussic acid thus obtained, partly in the liquid, and partly in the gaseous state, combined with alkalis, produces the same effects as the blood icy, and the colourless Prussian blue.

13. Having obtained the prussic acid in a separate Compounds state, it was his next object to discover its composition. Parts. He had observed in the process for procuring it, that the air in the receiver was inflammable; and in decomposing the prussiates, he obtained ammonia and carbonic acid, and found that some metals were reduced by distillation with the metallic prussiates. He concluded from this, that prussic acid was composed of ammonia and oil, and he endeavoured to prove this by the test of experiment; but he soon found that he could not succeed in forming the colouring compound, by combining ammonia and the different oils heated together. Seeing that water was an obstacle to the formation of the prussic acid, he conducted his experiments in a different way, by combining the ammonia with the dry combustible principle, which he supposed existed in oils, and with the carbonic acid, equally in the dry state. He saw that charcoal alone, strongly heated with fixed alkalies, gave them the property of colouring iron blue. Having heated these two substances in crucibles, he added to the one muriate of ammonia, at the moment when the first mixture had acquired a white heat, and he continued the heat till no more vapour was disengaged. This process furnished him with a pure Prussian alkali, whilst the combination of the alkali and the charcoal, without the addition of the muriate of ammonia, afforded none.

14. Such was the state of our knowledge with regard to the colouring matter of Prussian blue, when Berthollet, at the end of 1787, communicated to the Academy of Sciences, the result of his investigations into the nature and properties of this substance. He repeated the experiments of Scheele, improved and extended his views, and confirmed his conclusions. The result of his researches on this substance was closely connected with the light which he had thrown on the nature and composition of ammonia some years before. He proved that the alkaline prussiate is a triple salt, which is composed of prussic acid, the alkali and iron; that when it is evaporated and re-dissolved, it affords crystals in the form of octahedrons; and mixed with sulphuric acid, and exposed to the sun, there is precipitated Prussian blue, which does not happen in After these preliminary experiments, he proceeded to the examination of prussic acid, by the action of oxymuriatic acid. This acid, in proportion as it is dissolved in the prussic acid, is deprived of its oxygen, and is converted into the state of muriatic acid. The prussic acid becomes more odorous and volatile, and less susceptible of combination with the alkalies, precipitating iron from its solutions, of a green colour. This green precipitate recovers its blue colour when exposed to the light, by contact with sulphuric acid, by iron. It is the oxy-prussic acid.

When the oxymuriatic acid is still continued to be added in the state of gas, and is exposed to the light, the new acid separates from the water, and is precipitated to the bottom in the form of an aromatic oil, which is converted by heat to an insoluble vapour, which is no longer capable of combining with iron. Thus superoxigenated, this acid can no longer return to its original state. It is totally different in its properties.

When the oxyprussiate of iron, which is prepared by treating Prussian blue with the oxymuriatic acid, and which is distinguished by its green colour, is deprived of its acid, by being brought into contact with a caustic fixed alkali, it is instantly decomposed, and is converted into carbonate of ammonia.

Scheele and Bergman were of opinion, that prussic acid contained ammonia ready formed. Berthollet, however, concludes from his experiments, that it only contains the elements, namely, the azote and hydrogen, both in combination with carbone; and prussic acid thus he considers prussic acid to be a triple compound of hydrogen, carbone, and azote, but he has not been able to ascertain the proportions. He thinks, however, that the hydrogen and azote come near to the proportions which exist in ammonia.*

In some experiments by M. Clouet, on the colouring matter of Prussian blue, he attempted to combine the elements of ammonia with charcoal, with the view of producing prussic acid; but in whatever proportion he employed them, no colouring matter was obtained. He therefore concluded, that it was necessary to combine directly the ammonia with the charcoal, for the production of this substance. He took 25 parts of quicklime in powder, and mixed them with one part of sal ammoniac dried, and also in the state of powder. He put the mixture into a porcelain retort, which he placed upon a sand-bath. To the beak of the retort was adapted a porcelain tube filled with dry powdered charcoal. The porcelain tube passed across a furnace, in which it might be strongly heated. It was then made red hot, and heat being afterwards applied to the retort, the ammonia was disengaged in the state of gas, which passed through the red hot porcelain tube containing the charcoal. The product was received in proper vessels, and when examined, was found to be the colouring matter of Prussian blue†.

Prussic acid thus obtained, is a colourless, transparent liquid, having a strong odour of peach flowers, or of bitter almonds. This odour impregnates for some time the saliva of those who expire it. The taste is at first sweetish, but soon becomes acid and hot. It is apt to excite coughing, and has a strong tendency to assume the gaseous form, and is therefore soon dissipated from the vessels which contain it. It has no effect on vegetable blues.

It is decomposed at a high temperature; and when exposed to light, is converted into carbonic acid, heat and ammonia, and carbonated hydrogen gas. It combines light with difficulty with alkalies and earths, and without destroying their alkaline properties.

The carbonic acid drives it off from these combinations. It deprives oxymuriatic acid gas of its acid oxygen, and by this addition changes its properties &c. It has no action on the metals; but it combines with their oxides, changing the colour, and forming salts which are in general insoluble.

This acid has the greatest tendency to form triple salts with the alkaline and metallic bases. These complex combinations are more permanent and fixed than the simple alkaline prussiates. They are not decomposed by carbonic acid, light, air, or the other acids.

The affinities of prussic acid are the following:

- Barytes - Strontites - Potash - Soda - Lime - Magnesia - Ammonia

Sect. XXXIII. Of Sebacic Acid.

1. The penetrating fumes which are exhaled from melted tallow, and which affect the eyes, the nostrils, and even the lungs, had been long ago observed, and Olaus Borrichius has thrown out some hints, warning against the danger of being exposed to these fumes. But little attention was paid to their nature and properties. Grutzmacher was the first who demonstrated the existence of this acid, in a dissertation de ollum medulla, printed at Leipzig in the year 1748. Rhodes published a small work in 1753 at Gottingen, in which he makes particular mention of this acid. The following year appeared a dissertation by M. Segner, on the acid of animal fat, which contained a number of well-conducted experiments. Crell endeavoured to improve the process for the separation and purification of this acid, and to ascertain the properties of its combinations. These were published in the Philosophical Transactions for the years 1780 and 1782.

But it appears, as Thenard, who made experiments on this acid, observes, that the acid obtained by those who first treated the subject, was either the acetic acid, or some acid different from the sebacic, the properties of which are quite distinct from those which had been formerly described.

2. The process by which this chemist obtained the sebacic acid is the following. He distilled a quantity of hogs lard, and washed the product several times with hot water. He then dropped it into acetate of lead; there was formed a flaky precipitate, which was collected and dried, put into a retort with sulphuric acid, and heated. The liquor in the receiver had no acid character; but there appeared in the retort a melted matter analogous to fat. This is carefully separated; and after being washed, is boiled with water. By the action of heat the whole is dissolved by the water, and when it cools, crystals in the shape of needles are deposited. These are fumaric acid. To be certain that these were not produced by means of the sulphuric acid, he washed the fat which had been distilled with water, which was filtered and evaporated, and needles were formed, exhibiting exactly the same properties. Or, after having washed with water the distilled fat, he saturated the filtered liquor with potash, evaporated it, and dropped into it a solution of lead. There was instantly formed a salt composed of the fumaric acid and lead. This is to be decomposed as before with sulphuric acid. This acid has the following properties.

1. It has no smell, a slight acid taste, and reddens strongly the tincture of turpentine. When heated, it melts like tallow.

2. It is much more soluble in warm than in cold water. Boiling water saturated with this acid forms a solid mass on cooling. It crystallizes in small needles, but with certain precautions may be obtained in the form of long, large, and very brilliant plates.

Sect. XXXIV. Of Uric Acid.

1. This acid was discovered by Scheele in the year 1776. It was at first called lithic acid. It constitutes one of the component parts of urinary calculi, and is also found in human urine. There is one species of calculus which is almost entirely composed of this substance. It is that species which resembles wood in appearance and colour.

2. This acid, as its properties have been described by Scheele, is thus characterized. It is insipid, inodorous, almost insoluble in cold water, and soluble only in about 360 parts of boiling water. It separates from this when it cools, into small yellowish crystals. The solution in water reddens the tincture of turpentine.

3. There is scarcely any action between uric acid and sulphuric and muriatic acids. It is soluble in the concentrated nitric acid, to which it communicates a red colour. It would appear that in this change of colour the nature of the acid is also changed, for part of it is converted into exalic acid. Oxymuriatic acid very readily acts upon uric acid, either by suspending a calculus in the liquid acid, or, which is easier, by passing a stream of oxymuriatic acid gas through water, at the bottom of which is placed the uric acid in powder. Its colour becomes pale, the surface swells up, it softens, and is at last converted into a jelly. This part disappears, and is soon dissolved, giving a milky colour to the liquid. There is extracted by slow evaporation small bubbles of carbonic acid gas. The liquid by evaporation gives muriate of ammonia, acidulous oxalate of ammonia, both crystallized; muriatic acid, and malic acid. Thus the oxymuriatic acid decomposes the uric acid, and converts it into ammonia, carbonic, oxalic, and malic acids.

4. When uric acid is distilled, there is a little of it sublimed without decomposition. It yields also a very small quantity of oil and water, crystallized carbonate of ammonia, carbonic acid gas; and there remains behind a very black coal without any alkali, and without any lime.

5. All these facts show that uric acid is a compound of a very peculiar kind, formed of azote, of carbone of hydrogen and oxygen, and susceptible of a great number of different changes by chemical agents.

Sect. XXXV. Of Rosacic Acid.

1. During certain diseases, the urine, when it cools, deposits a peculiar substance, which has been denominated from its colour, which resembles bricks, lateritious sediment. During fevers, this appearance of the urine takes place; and in gouty persons, at the termination of the paroxysm, it is very abundant. And when this suddenly disappears, and the urine at the same time continues to deposit this substance, a relapse may be dreaded. It appears in the form of red flakes, and adheres strongly to the sides of the vessel. If the urine be heated, this sediment is again dissolved.

2. This substance was formerly considered by chemists as uric acid. If into fresh urine a little nitric acid is dropped, it becomes muddy, and a precipitate is formed. The nitric acid, and the substance to which the name of roscacic acid has been given, combine together, and are deposited. The uric acid being much less soluble than the roscacic acid, it is very easy to separate them. All that is necessary is to pour boiling water on the sediments, and to wash them on the same filter, in which case the uric acid remains behind.

Proust, who made experiments on this substance, considers it as another characteristic of roscacic acid, that it produces with a solution of gold, a cloudy precipitate of a violet colour.

Sect. XXXVI. Of Amniotic Acid.

1. A peculiar acid has been detected in the liquor of the amnios of the cow. This was discovered by Buvia and Vauquelin. This acid is concrete, white, and brilliant, has a very slight acid taste, and reddens the tincture of turpentine. It is little soluble in cold water, but dissolves more readily in boiling water, from whence it is deposited, by cooling, in long needle-shaped crystals. When this acid is exposed to heat, it swells up, and exhales an odour of ammonia sensibly mixed with prussic acid. It leaves behind a voluminous coal.

2. It seems at first to have some analogy with the acetic and uric acids, but this is not really the case. The acetic acid does not furnish ammonia by distillation; the uric acid yields ammonia and prussic acid by heat, but it is not equally soluble in warm water, and does not crystallize, in long, white, brilliant needles, nor is it soluble in boiling alcohol, as the amniotic acid is.

Chap. XI. Of Inflammable Substances.

The class of bodies which we are to examine in this chapter, under the title of inflammable substances, are alcohol, ether, and oils. These substances are closely allied to many of the bodies which were treated of in the last chapter. Their constituent parts are the same with many of the vegetable acids, arranged, however, in different proportions, and totally different in their properties and effects. The elements of these inflammable substances are carbons and hydrogen chiefly, but... but in some there is a triple compound of carbons, of hydrogen and oxygen; the latter does not exist in that quantity as to exhibit acid properties, or these properties are concealed by the proportions of the other constituent parts. It was therefore thought necessary to treat of these substances in this place, that we might be early acquainted with their properties, some of which are of great importance in chemical researches, particularly their effects on many saline bodies. They may be regarded, therefore, as valuable instruments of chemical analysis. We shall consider the inflammable substances in the four following sections, namely; 1. Alcohol, 2. Ether, 3. Fixed oils, and 4. Volatile oils.

Sect I. Of Alcohol.

1. When vegetable matters have been subjected to the vinous fermentation, the fluid is totally changed. It is converted into a substance called wine or beer, according to the nature of the materials from which it has been prepared. When this product, the wine or beer, is subjected to another process, a very different product is obtained. By distillation a fluid is obtained of very different properties from the beer or wine from which it is extracted. This liquid, when it is perfectly pure, is known in chemistry by the name of alcohol, or spirit of wine, because it is produced from wine. It is sometimes denominated also ardent spirit, from its effects. Ardent spirit, as it is first obtained by distillation, is to be considered as a mixture of alcohol and water, because the alcohol in the process of distillation is condensed by water. In this state, ardent spirit is different in flavour, in colour and in strength, according to the nature of the materials from which it is obtained, and hence in common language it is distinguished by different names. When it is obtained from the fermented juice of the grape, it is known by the name of brandy; from that of the sugar-cane, by that of rum; and from that of farinaceous substances by that of whisky. All these substances, therefore, are to be considered as composed of alcohol, or pure spirit of wine, water, and a peculiar oil, to which the flavour is owing.

Ardent spirit, it is supposed, was known in the dark ages. It does not appear, from any of the writings of the Greeks or Romans, that they were acquainted with such a liquor. The preparation of it from wine, and even the discovery of alcohol, or pure spirit itself, is ascribed to Arnold de Villa Nova, who lived in the 13th century.

2. Ardent spirit thus obtained, it has been observed, is a mixture of alcohol or pure spirit, water and oil, with some colouring matter. To purify it from these substances, it is again distilled; and to have it perfectly pure, this process must be repeated several times. When ardent spirit is distilled for the first time, after it is extracted from the fermented liquors, it is distinguished by the name of rectified spirits. The process which is recommended by some is the following. Distil it in a water bath, till one fourth of the quantity has passed over; then distil it again for several times, taking only the first half of the product. Mix all these products together, and distil them with a very gentle heat; the first half of the liquor which passes over, is the purest alcohol that can be obtained; the remainder may be reserved for ordinary purposes.

Even in this state, the alcohol, thus obtained, contains a certain proportion of water, to separate which, Boerhaave has given a very good process, by means of an alkali. Take a quantity of carbonate of potash which has been exposed to a red heat, to separate the moisture; reduce it to powder, and put it into the spirit. This salt, on account of its strong attraction for water, combines with the water of the alcohol; and this solution of the alkali having the greater specific gravity, falls to the bottom. The alcohol which remains at the top may be easily separated. To purify this alcohol, from a small quantity of potash which it holds in solution, it may be redistilled in a water bath. It ought to be observed, however, that the distillation should not be carried on till the whole of the alcohol is driven off, because towards the end of the process, it carries part of the potash along with it.

3. Alcohol, thus prepared and purified, is a light, transparent, and colourless liquor, of a sharp, penetrating, agreeable smell, and of a warm, stimulating, acrid taste. It has the property, in a much greater degree than wine, of producing intoxication. The specific gravity of alcohol when perfectly pure, is 0.800, but the strongest spirit which is afforded by mere distillation, according to Mr Nicholson, is 0.820 at the temperature of 71°. The alcohol or rectified spirit of commerce, has rarely a specific gravity below 0.837.

4. When alcohol is exposed to the air at a temperature between 50° and 60°, it evaporates, and when it is pure, without leaving any residuum. By this rapid evaporation it produces great cold, which is very sensibly felt by dipping the fingers in alcohol, and exposing them to the air. It boils at the temperature of 176°, and is then converted into an elastic fluid. In heat, the vacuum of an air-pump it boils at 56°. It has never yet been frozen by the greatest degree of cold to which it has been exposed. It remains fluid when the thermometer stands at —69°. When it is passed through a red-hot porcelain tube, it is decomposed, and converted into carbonic acid gas, carbonated hydrogen gas, and water.

5. With the aid of heat, alcohol dissolves a small quantity of phosphorus. When this solution, which has a fetid odour, is precipitated, by dropping a little of it into water, it becomes luminous in the dark. These arise jets of flame from the surface of the water; and there is formed an oxide of phosphorus in the state of white powder. Alcohol seems also capable of dissolving phosphorated hydrogen gas.

6. There is no action between alcohol and sulphur, neither at the ordinary temperature, nor even when they are boiled together; but when the two bodies are brought in contact with each other in the state of vapour, they combine readily, and there is formed a fetid sulphurated alcohol, which deposits a small quantity of white sulphur, and becomes muddy in cooling. The sulphur is precipitated by water, and gives about 3/5 part. Alcohol combines still more readily with sulphurated hydrogen gas, which communicates to the alcohol a little colour, and in this combination is decomposed with more facility by oxygen gas, and all other oxygenated bodies, than when it is in the state state of gas. Alcohol combines with sulphurated hydrogen gas, which is contained in mineral waters, and deprives them of this gas by distillation.

7. The strong acids have a very powerful effect on alcohol. It is decomposed by the sulphuric, the nitric, the oxymuriatic, and the acetic acids; and the product of this decomposition varies according to the nature of the acid, its strength, and the proportions in which it is employed. Some of the acids are soluble in alcohol. With the aid of heat, it dissolves the boracic acid, which communicates to it the property of burning with a green flame. It also holds in solution carbonic acid gas in greater proportion than its own bulk. It precipitates from water, on the contrary, the phosphoric acid, almost in the concrete state, and also the metallic acids which are soluble in this liquid.

8. Alcohol combines with water in all proportions. The affinity between the two fluids is so strong that water is capable of separating from alcohol many bodies with which it is combined, while the alcohol decomposes many saline solutions, and precipitates the salt. When water and alcohol are combined together, there is an increase of temperature, which shows that there is a condensation of the two liquids. Accordingly it is found, that the density or specific gravity of the mixture is greater than the mean of the uncombined liquids. The density varies according to the different proportions of the alcohol and water which are employed. In consequence of this variation, it becomes an object of considerable importance to be able to ascertain the strength of spirits; that is, the proportions of alcohol and water of different degrees of density or specific gravity. This object is important, both in a political and commercial view. For the purposes of commerce, various instruments have been contrived, and tables constructed, for the convenience of those who are concerned in the purchase and sale of spirituous liquors. For the purposes of revenue, a most elaborate and minute set of experiments was instituted by Sir Charles Blagden, who was expressly employed by the British government to ascertain the relative value or strength of ardent spirit at different temperatures and different specific gravities. An account of these experiments was published in the Philosophical Transactions for the year 1792. Tables which show the result of the experiments, were published by Mr Gilpin in 1793; but as they are not immediately connected with the elements of chemistry, we refer our readers to the original papers, and to the article SPIRITUOUS LIQUORS, in this work.

9. Alcohol dissolves the fixed alkalies in the pure state, and forms with them an acrid solution of a redish colour. The solution of potash in alcohol was formerly denominated the acrid tincture of tartar. It is in this way that the fixed alkalies are obtained in their purest state. Alcohol, therefore, becomes a valuable instrument of analysis for separating the fixed alkalies from a great number of extraneous substances. Ammonia also combines with alcohol by the assistance of heat. The ammonia with a higher temperature is driven off, and carries with it part of the alcohol. Many of the saline bodies may be dissolved in alcohol, and on this account also it is valuable to the chemist in his researches. Tables have been constructed, showing the quantity of different salts which may be dissolved at different temperatures. The following tables were drawn up from the experiments of M. Guyton.

I. Table of Salts which are readily Dissolved.

| Temperature | Grains | |-------------|--------| | 54.5° | 240 | | 54.5° | 240 | | 54.5° | 240 | | 54.5° | 240 | | 54.5° | 240 | | 113° | 240 | | 180.5° | 694 | | 180.5° | 1313 | | 180.5° | 240 | | 180.5° | 240 |

II. Table of Salts that are little Soluble.

| Grains | |--------| | 240 | | 214 | | 212 | | 112 | | 100 | | 23 | | 18 | | 17 | | 9 | | 7 | | 5 | | 3 | | 4 | | 1 |

III. Salts that are Insoluble.

Borax, Tartar, Alum, Sulphate of ammonia; iron, copper, zinc, fafa, potash, lime, silver, mercury, Tartrate of soda, Nitrate of lead, mercury, Muriate of lead, Carbonate of potash, fafa. The following table, drawn up by Mr Kirwan, shews the quantity of salts that are soluble in 100 parts of alcohol of different densities. The temperature in which the solutions were made was from 50° to 80°.

| Salts | Alcohol of | |------------------------|------------| | | 0.900 | 0.872 | 0.848 | 0.834 | 0.817 | | Sulphate of soda | 0 | 0 | 0 | 0 | 0 | | Sulphate of magnesia | 1 | 1 | 0 | 0 | 0 | | Nitrate of potash | 2.76 | 1 | 0 | 0 | 0 | | Nitrate of soda | 10.5 | 6 | 0.38 | 0 | 0 | | Muriate of potash | 4.62 | 1.66 | 0 | 0.38 | 0 | | Muriate of soda | 5.8 | 3.67 | 0 | 0.5 | 0 | | Muriate of ammonia | 6.5 | 4.75 | 0 | 1.5 | 0 | | Muriate of magnesia | 21.25 | 0 | 23.75 | 36.25 | 50 | | Muriate of barytes | 1 | 0.29 | 0.185 | 0.09 | | | Do. crystallized | 1.56 | 0.43 | 0.32 | 0.06 | | | Acetate of lime | 2.4 | 0 | 4.12 | 4.75 | 4.88 |

A great variety of different opinions have been proposed with regard to the composition of alcohol. It had been observed, in burning this combustible substance, in close vessels, that water was formed. Some philosophers had even observed that the quantity of water obtained by the combustion of alcohol, was greater than the whole weight of the alcohol which was consumed. From observing this circumstance, it was supposed to consist of water, combined with an acid, an oil, or phlogiston, according to the views and theories of different philosophers.

It is to the experiments of Lavoisier that we are indebted for ascertaining the real constituent parts of this substance. He burnt in a proper apparatus, with a known quantity of oxygen gas, 76.7083 grs. troy of alcohol, and, after the combustion, carbonic acid gas and water were found to be the only products; and by estimating the oxygen gas consumed, the quantity of carbonic acid and of water which were formed, it appeared that the quantity of alcohol consumed was composed of

\[ \frac{22.840}{6.030} \text{ carbons}, \] \[ \frac{47.830}{76.700} \text{ water}. \]

But it has been since proved, by the experiments of Fourcroy and Vauquelin, that oxygen is a component part of alcohol; for when they mixed together equal parts of alcohol and concentrated sulphuric acid, and while ether is formed from it, there was also at the same time a production of water; the alcohol in this case was decomposed, but the sulphuric acid suffered no change. The oxygen, therefore, which combined with the hydrogen in the formation of water, must have come from the alcohol.

Sect. II. Of Ether.

By the action of different acids with alcohol, the latter is decomposed, and different products are obtained, according to the proportions of the acid employed, and the heat which is applied. When the acid and the alkali are in a certain proportion, and are exposed to a moderate temperature, the product is a peculiar substance, which has received the name of ether. Ether has been obtained by the action of different acids on alcohol, and hence it has received different names, as sulphuric ether, nitric ether, muriatic ether. The first, namely, sulphuric ether, which seems to have been longest known, and is most easily obtained, has excited the greatest attention among chemists. We shall therefore consider it first.

I. Of Sulphuric Ether.

1. It appears from different passages in the writings of the earlier chemists, that the knowledge of sulphuric ether was among their secrets. It was then called oleum vitrioli dulce. The method of preparing it is described in a book published at Nuremberg about the year 1540. But the nature of this substance was not much attended to till the year 1730, when a certain quantity was presented to the Royal Society by Dr Frobenius, with a paper which was published in their Transactions for that year, containing an account of a number of experiments which were made upon it. It was long known under the name of naphtha among the German chemists.

2. The following is the process by which sulphuric ether may be obtained. Equal parts of concentrated sulphuric acid and alcohol are put into a retort, to which a receiver is to be adapted and fitted. Or perhaps it is better to add the acid by small portions at a time, that the action may not be too violent, and the heat produced too great. The receiver should be immersed in cold water, or surrounded with ice, or it may be kept cool by the application of wet cloths, over which a small stream of water is directed. Heat is then applied, and the first product which comes over is a fragrant spirit of wine; but as soon as the mixture begins to boil, the ether comes over, condensed by the cold, and runs in streams down the sides of the receiver. When the quantity obtained amounts to about one half of the alcohol employed, the process should be stopped, and the receiver unluted and removed; but if it be continued, white fumes begin to come off, which are known to be the fumes of sulphurous acid. After this there rises a light yellowish coloured oil, which has been called the sweet oil of wine. The heat should now be moderated after the ether has passed over, because the matter contained in the retort becomes black, thick, and swells considerably. When the whole of the sweet oil has come over, there is still an evolution of sulphurous acid, which becomes thicker and thicker, till at last there is nothing but a dark coloured sulphuric acid.

3. The ether which is obtained by this process is impure. It is generally contaminated with sulphurous acid. To purify it, it has been usual to mix a quantity of potash with the fluid, and to distil it over again. The acid in this case combines with the potash, and the ether being separated, passes over into the receiver. Dizé, however, considering this process as tedious and uncertain, has proposed other substances in the room of potash, and he has tried several metallic oxides, such as the red oxide of lead, the yellow oxide of iron, the red oxide of mercury, and the black oxide of manganese. But after a variety of experiments, he is of opinion, that the black oxide of manganese is the most convenient for the purification of ether. It is mixed with ether, allowed to remain some time, and is to be frequently agitated. The oxygen of the manganese combines with the sulphurous acid, and converts it into sulphuric acid, which is a more fixed body than the

*Ann. de fulphurous acid.*

To separate the liquid from the sulphurous acid, Proust recommends the following method, which he says is employed in the large way, as by far the most preferable. Introduce into a bottle which is filled with impure ether, some water, and a portion of flaked lime. Agitate the bottle strongly, and do not open it to examine its odour, till after it has remained for some minutes in cold water, and when the vapour within the bottle has ceased to exert its elastic force against the cork; if the sulphurous smell is not entirely removed, the process is to be repeated till it is completely destroyed. This method, which was employed by Woulfe, Proust prefers on account of its economy, particularly as it affords at the same time a fulphite of lime, which is formed by the combination of the sulphurous acid with the lime. When the liquids have separated, the ether which swims on the top, may be drawn off by means of a syphon, and it may be introduced into a retort to be rectified by distillation.

4. The ether which is thus obtained, is a transparent colourless fluid, of a very fragrant smell, and a hot pungent taste. The specific gravity is only 0.7581, p. 257, so that it is considerably lighter than alcohol. It is extremely volatile, so that when it is agitated, or poured from one vessel to another, it is instantly dilutated. It produces to a great degree of cold, that water may be frozen by means of it. It rises in the state of gas which burns with great rapidity, and the air which holds ether in solution may be passed through water without being deprived of its combustibility or fragrance.

5. It boils in the open air at the temperature of 98° Action of and in the vacuum of an air-pump at —20°, so that it would constantly remain in the state of gas if the pressure of the air were removed.

When ether is kindled in the open air, it burns very readily. The electric spark also inflames it. It burns with a copious white flame, and leaves behind it a black trace on the surface of bodies exposed to the flame. Lavoisier has observed that there is always formed an acid during the combustion of this liquid; and Scheele says that the residuum of ether burnt over a little water, contains sulphuric acid. When the ether is exposed to a cold of —46°, it freezes and crystallizes. It is decomposed when the vapour is passed through a red-hot porcelain tube, and the product is carbonated hydrogen gas.

6. Dr. Priestley discovered that ether agitated with any kind of gas, greatly increased its volume, and in the volume of gases mofe doubled it. Mr. Cruickshank made a similar experiment, by agitating some oxygen gas with a little ether. The bulk was exactly doubled. In this state the gas did not explode, but when one part of this mixture was added to three parts of oxygen, an ignited body or the electric spark produced a dreadful explosion. The products were water, with 2½d carbonic acid gas. Hence it would appear, Mr. Cruickshank observes, that one part of this vapour requires about seven of oxygen to saturate it; and according to this experiment, the proportion of carbon to hydrogen in the vapour of ether or ether itself, should be as five p. 205, to one +.

7. Phosphorus is dissolved in small quantity in ether, and produces a transparent solution; but when alcohol phosphorus, is added to the solution, it becomes milky.

8. Sulphuric acid has a peculiar action on ether, by converting it into a kind of oil, which is called the sweet oil of wine. This is one of the products in the preparation of sulphuric ether. When a small quantity of ether is introduced into a bottle filled with oxymuriatic acid gas, it explodes, and inflames; or if paper moistened with ether be introduced, the same effect follows. Carbonic acid gas is produced, and charcoal is deposited on the sides of the bottle.

9. Various theories have been proposed, to account for the production of ether. From the manner of its production by means of sulphuric acid, it was natural to suppose that this acid formed one of its component parts. This accordingly became a general opinion, till it was found that the sulphuric acid suffered no change in the process, but merely assisted or disposed the alcohol to that change which it undergoes when it is converted into ether. According to Macquer, the alcohol has not been changed, but merely deprived of the whole of its water. Scheele supposed, that ether was alcohol deprived of its phlogiston; and when the new theories were introduced, ether was considered as a combination of alcohol and oxygen.

10. The experiments and researches of Fourcroy and Vauquelin have thrown new light on this subject, and have led to different views of the nature and composition of ether. According to these experiments, ether contains a smaller proportion of carbon, but a greater proportion of hydrogen and oxygen. From their experiments, and from those of others, it appears that the changes induced by the action of sulphuric acid on alcohol, depend on the quantity and strength of the acid, and the temperature.

A. Equal parts of concentrated sulphuric acid and alcohol mixed together raise the temperature to 189°. Bubbles of gas are emitted; the liquid becomes turbid, and at the end of some hours assumes a deep red colour.

B. A mixture of two parts sulphuric acid, and one part alcohol, produces a temperature of 200°. The mixture becomes instantly of a deep red colour, passes to black a few days after, and diffuses an odour which is perceptibly that of ether.

C. When equal parts of sulphuric acid and alcohol are exposed to the action of heat, in a proper apparatus, such as is employed for the preparation of ether, the following phenomena are observed.

a. When the temperature is raised to 207°, the liquid boils; there is produced a fluid which is condensed by cold, into a light, colourless and fragrant liquor, which from its properties has received the name of ether. If the process be properly conducted, no permanent gas is evolved, till about \( \frac{1}{2} \) of the alcohol is converted into ether.

b. If, as soon as the sulphurous acid appears, the receiver be changed, there is no longer any production of ether; but the sweet oil of wine, water, and acetic acid are formed, without a single particle of carbonic acid. When the sulphuric acid makes about \( \frac{3}{4} \) of the mass which remains in the retort, there is evolved an inflammable gas, which has the odour of ether, and which burns with a white oily flame. This is the gas which the Dutch chemists have called carbonated hydrogen gas, or olefiant gas, because when it is mixed with oxymuriatic acid it forms oil. At this period, the temperature of the matter contained in the retort is elevated to 230° or 234°.

c. When the sweet oil of wine ceases to flow, if the receiver be again changed, there is only sulphurous acid emitted, water which was previously formed, carbonic acid gas; and there remains only in the retort, a mass which consists chiefly of sulphuric acid thickened with charcoal.

From these phenomena, which were uniform and constant, the following conclusions were drawn.

a. A small quantity of ether is formed spontaneously without the aid of heat, by the combination of two parts of sulphuric acid and one part of alcohol.

b. As soon as the ether is formed, and there is at the same time a production of water, the sulphuric acid undergoes no change in its intimate nature, while the first of these compositions takes place.

c. When the sulphurous acid appears, there is no longer any production of ether; but then there pass over the sweet oil of wine, water, and acetic acid.

d. The sweet oil of wine having ceased to pass over, nothing is obtained but sulphurous acid, carbonic acid, and at last sulphur, if the distillation be continued.

The operation of ether, then, may be divided into three periods; the first, in which a small quantity of ether and water is formed, without the assistance of heat; the second period, in which the greatest quantity of ether which can be obtained without the evolution of sulphurous acid at a temperature of 207°; and the third, in which the sweet oil of wine, olefiant gas, acetic acid, sulphurous and carbonic acid are produced, while the temperature of the mixture is raised to 230° and 234°. In all these three periods there is only one common circumstance, and this is, the continual formation of water from the beginning to the end of the operation.

On these observations, Fourcroy and Vauquelin have established their theory of the formation of ether. In the case in which ether is formed by the simple mixture of alcohol and sulphuric acid, without the aid of heat, the formation which appears by heat as well as by the black precipitate, the charcoal which is separated without the production of sulphurous acid, proves that the sulphuric acid acts in a different manner on alcohol from what was supposed. This acid is not decomposed by charcoal at that temperature. There is no action between these two bodies in the cold, nor is there any action between this acid and alcohol; for in that case, sulphurous acid would be formed, of which not the smallest trace can be perceived at the beginning of the operation. Recourse then must be had to a different action, namely the strong affinity which exists between sulphuric acid and water. It is this which determines the union of the constituent principles of water existing in the alcohol, and with which this acid comes in contact; but this action must be very limited. There is soon established a balance of affinities, and no farther change takes place.

If then it be proved that ether is formed by the mixture of certain quantities of sulphuric acid and alcohol, it must obviously follow, that a mass of alcohol may be completely converted into ether, water, and acetic acid, by increasing the quantity of sulphuric acid; and it is equally obvious, that this acid would undergo no change but that of being diluted with water.

It is not necessary to suppose, according to this theory, that ether is alcohol deprived of a certain portion of oxygen and hydrogen, for there is separated at the same time a quantity of charcoal proportionally greater than that of the hydrogen; and it may be conceived, that the oxygen which is combined in this case with the hydrogen, to form water, would not only saturate this hydrogen in the alcohol, but that it would saturate at the same time the carbons which has been precipitated. Thus, then, in place of considering ether as alcohol with a smaller proportion of hydrogen and oxygen, if we take into account the carbons which is precipitated, and the small quantity of hydrogen contained in the water that is formed, it must be considered as alcohol with a greater proportion of hydrogen and oxygen. Such seems to be the nature of the spontaneous action between sulphuric acid and alcohol without the aid of heat.

But when the mixture is subjected to heat, the production of ether is more complicated, and the products more numerous.

It ought to be observed, that the mixture of sulphuric acid and alcohol in equal proportions, boils only at the temperature of 207°, whilst alcohol alone boils at 176°; whence we must conclude, that the alcohol is retained by the affinity of the sulphuric acid, which fixes it. Now, if we compare what happens in this case to the change produced on all other vegetable matter exposed to the action of heat, in which the principles are volatilized, according to the order of their affinity for caloric, carrying with them a small quantity of the more fixed elements, in proportion as the sulphuric acid attracts the alcohol and the water, of which it favours the formation, the ether which is evolved attracts caloric, and is sublimed; and when the greatest part of the alcohol has been changed into ether, the mixture becomes denser, the heat more considerable, and the affinity of the sulphuric acid for the undecomposed alcohol being increased, the acid is decomposed, so that on one hand its oxygen combines with the hydrogen of the alcohol, and forms water, which rises gradually into vapour, whilst, on the other, the ether retaining a greater quantity of carburet, with which it rises in vapours at this temperature, affords the sweet oil of wine, which ought to be considered as an ether with a greater proportion of carburet. This seems to be proved by its greater specific gravity, less volatility, and its citron colour.

II. From this theory, the ingenious authors of it have deduced the following practical conclusions.

a. The formation of ether is not owing, as was supposed, to the immediate action of the principles of the sulphuric acid on those of alcohol, but to the reaction of the principles of the latter on each other, and particularly of its oxygen and hydrogen, occasioned by the sulphuric acid.

b. A portion of alcohol may be converted into ether without the aid of heat, by increasing sufficiently the proportion of sulphuric acid.

c. With regard to the change which takes place on alcohol in the production of ether, the process may be divided into two periods. In the one, ether and water are only produced; in the other, sweet oil of wine, water, and sulphuric acid.

d. During the formation of ether, the sulphuric acid is not decomposed, and there is no production of the sweet oil of wine. When the latter makes its appearance, there is given out no more, or at least very little, ether; and at the same time the sulphuric acid is decomposed by hydrogen solely, whence sulphurous acid is formed.

e. The formation of the sweet oil of wine may be avoided, by keeping the temperature of the mixture between 200° and 205°. This is managed by introducing a few drops of water into the retort.

f. And lastly, alcohol differs from ether, in containing more carburet, less hydrogen and oxygen, and the sweet oil of wine is to ether very near what alcohol is to the latter*.

II. Of Nitric Ether.

1. Nitric acid, or rather nitrous acid, acts with much greater violence on alcohol than sulphuric acid. In this case the action must be moderated, either by diluting the two liquids, or by cooling the mixture. The first easy process which was proposed for the preparation of nitric ether, was given by Navier, a physician of Chalons.

2. The process of Navier is the following. He put into a strong bottle 12 parts of pure alcohol, and plunged it into cold water, or rather surrounded it with ice. To this he added, in different portions, eight parts of concentrated nitric acid, agitating the mixture, after every addition. The bottle is then stopped with a cork, which is secured with leather, and the mixture is set in a convenient place, to avoid the danger of accidents on the bursting of the bottle, which sometimes happens. At the end of some hours, bubbles rise from the bottom of the vessel, and drops are collected on the surface of the liquid, which gradually form a stratum of ether. This action continues for the space of six days. When it ceases, the cork is to be pierced with a needle, to permit the escape of a quantity of nitrous gas, which, without this precaution, would rush out rapidly on uncorking the bottle, and would carry along with it the ether, which would be lost. When the gas is dissipated, the cork is to be drawn out, and the whole liquid in the bottle is to be poured into a funnel. The ether floats on the top, and the remaining liquor being heavier, is allowed to pass off, and the ether is retained.

3. This process was improved by Beaumé. He found that the greatest produce of ether was from two parts of acid to three of alcohol. He directed both ingredients to be used in the coldest state, by keeping each in melting ice, and the bottle in which the mixture is made, to be kept equally cold. In this proportion of ingredients, the danger of explosion is avoided, and the low temperature greatly moderates the violent action. The mixture in the bottle is always to be well agitated before any new addition of acid is made, and by this means the accumulation in any particular spot is prevented. The ether begins to form, as in the former process, in the course of a few hours, and if the bottle is allowed to remain undisturbed for eight or ten days, a quantity of ether equal to one half the weight of the alcohol is obtained, after which no more is produced.

4. Dr Black's process is described by himself in the following words. "Into a strong phial, having a ground stopper, I first pour four ounces of strong hale nitric acid. I then add three ounces of water, pouring it in so gently, that it floats on the surface of the acid. I then pour in after the same manner five ounces of alcohol. I put in the stopper slightly, and I set the phial in a tub of water and ice. The acid mixes slowly with the water, and in a diluted state comes in contact with the alcohol on which it immediately acts, and ether is produced slowly and quietly. The liquor gets a dim appearance, because imperceptible bubbles are formed, which get to the top, and having collected... ed to a certain degree, they lift the stopper, and escape (s). After eight or ten days I find upwards of three ounces of nitric ether, though I am certain by the smell, that much escapes with the vapour. This is, however, a certain, easy, and safe process, though it is slow and imperfect.*

5. Many other processes have been proposed for the preparation of nitric ether. Laplanche, a Parisian apothecary, has employed nitre, which he introduced into a tubulated stone-ware retort, and first pouring the concentrated sulphuric acid, and then the alcohol upon it, there is an immediate production of ether; but by this process it is suspected that the nitric ether may be mixed with sulphuric ether. He has therefore proposed another process, which is more complicated.

6. The process which has been proposed by Chaptal, is, according to Prout, the best that can be adopted. This process, with some additions and alterations, which he has found it necessary to make from his own experience, is the following. The proportions which he employs are, 32 ounces of alcohol, and 24 of nitric acid. These are introduced into a large retort, which is to be fitted to a globular glass vessel, furnished with a tube of safety. A tube passes from this globe to a second, which is also furnished with a tube of safety. One or two ounces of water should be introduced into the second globe to shut up its tube of safety. Three bottles of Woulfe's apparatus, containing from 64 to 80 ounces of liquid, are then to be connected with the second globe. These bottles are half filled with alcohol. The alcohol and the acid are poured into the retort, and are mixed by agitation. The retort is fitted to the glass globe, and heat is applied, with this precaution, that it must be removed as soon as there is any effervescence. The process now goes on, and requires no farther attention than occasionally cooling the globes and the bottles with cloths moistened with snow-water. The greatest part of the ether which is formed, condenses in the first bottle, and gives the alcohol a yellow colour. It then passes to the second, in which the colour is lighter, and at last to the third, where there is little perceptible change. To separate the ether of the first bottle, the mixture is to be saturated with an alkali, and distilled.

7. But by whatever process nitric ether is obtained, it requires to be purified, to separate the acid and alcohol, which are generally mixed with it. This is done by distilling it from potash, which reduces its quantity, for the distillation must not be continued longer than when two-thirds or one-half of the first ether has come over. To purify this still more, it is directed to be mixed with one-fifth of nitrous acid, and distilled again, taking two-thirds of the product set apart, and rectify it from an alkali. The remainder which comes over is a less pure ether, which has been known under the name of Hoffman's mineral anodyne liquor. What remains in the retort has been called dulcified spirit of nitre.

8. Nitric ether, thus obtained, is a yellowish coloured liquid, equally volatile as sulphuric ether. Its odour, though stronger and less sweet, is analogous to the sulphuric ether. The taste is hot and more disagreeable. It is often of a deeper yellow colour, and always contains a small excess of acid and nitrous gas. The stopper is frequently driven out of the bottle in which it is kept, for there is a constant evolution of a considerable quantity of gas.

9. When it is set fire to, it gives out a more brilliant flame, and a denser smoke, than sulphuric ether; and it deposits a greater quantity of charcoal. When it is long kept in a close vessel, there is formed some water, holding a small quantity of oxalic acid in solution, which falls to the bottom of the vessel.

10. Nitric ether is not only analogous to sulphuric ether in its properties, but also in the nature of the process by which it is obtained, and in the other products which accompany this process. But in the production of nitric ether, there is no deposition of charcoal, and the acid itself is decomposed. This appears from the great quantity of nitrous gas which is evolved during the process; and the reason assigned for the disappearance of the charcoal is, that the oxygen of the acid combines with it, and forms carbonic acid, which escapes in the form of gas. The products which are generally obtained in the processes for the preparation of nitric ether are nitrous gas, ether, oil, acetic acid, oxalic acid, and carbonic acid gas.

If equal parts of nitric acid and alcohol are mixed together, a violent effervescence immediately takes place, which is owing to the evolution of a great quantity of gas, which being a compound of ether and nitrous gas, has been denominated etherified nitrous gas. The same gas is obtained by employing a diluted acid; but then the mixture requires the affluence of heat. This gas may be collected in vessels over water. It has a disagreeable ethereal odour, quite different from the odour of nitric ether, and exactly similar to that kind of ether which is furnished by the oily, carbonated hydrogen gas, treated with oxymuriatic acid gas. If a candle be applied to this gas, it burns slowly with a yellow flame. This gas is soluble in water, and is wholly absorbed; but the absorption is slow. The water acquires the odour of the gas. Alcohol also dissolves it completely, and more rapidly. Oxygen gas mixed with this gas, provided it be pure, produces no change; but when the mixture is set fire to, there is a violent detonation. When this gas was exposed to sulphuric, nitric, and muriatic acids, the ether was absorbed by the acids, and the nitrous gas remained behind. The sulphuric acid in the state of gas, combined with an equal bulk of the inflammable gas, also decomposed it; but this effect did not take place till after several days.*

If the alcohol and nitric acid be mixed together in the proportion of one of the former to three of the latter, and a gentle heat be applied, there is a copious evolution of gas, which is composed of the etherified nitrous gas and nitrous gas. If towards the end of the process, when a small part of the liquid remains in the retort,

(s) Dr Black, we believe, contrived a spring for the stopper which kept down the cork till it was pushed up by the elastic vapours; and when they had escaped, it returned to its place by the force of the spring. retort, it be allowed to cool, crystals are formed; and these crystals are found to be oxalic acid. They were formerly called crystals of Hierne, from the name of a Swedish chemist, who first discovered them.

If one part of nitric acid be added to its own weight of alcohol, and one part of sulphuric acid be added soon after, the mixture is suddenly inflamed, and burns with great violence. In this case, when the products are collected, they are found to be ether and oil.

From this statement of facts, therefore, it appears, that the production of nitric and sulphuric ethers is nearly the same; that the differences which take place, are owing to the different nature of the acids; the violent action which follows in the formation of nitric ether, depending on the nitric acid itself being decomposed, and by the operation of new affinities, new actions having taken place.

III. Of Muriatic Ether.

1. Muriatic acid has no sensible action on alcohol, either by simple mixture, or by distilling them together, as in the former case. Beaumé obtained a small quantity of muriatic ether, by combining together muriatic acid and alcohol in the state of vapour. But other means were thought of for this purpose, and particularly the oxymuriate of antimony, and the oxide of zinc dissolved in muriatic acid, and to distil this salt, concentrated by evaporation, in cleft vessels with alcohol. By this process muriatic ether has been obtained. But the most successful method of procuring this ether, was proposed by Courtanvaux. His process is the following.

2. One part of alcohol is mixed with three parts of oxymuriate of tin, or the fuming liquor of Libavius, in a glass retort. A strong heat is produced, with the production of a white suffocating vapour, which disappears when the mixture is agitated. There is then emitted an agreeable odour, and the liquor assumes a lemon colour. The retort is then to be placed on a sand bath; two receivers are to be attached, one of which is to be immersed in cold water. There passes over at first some pure alcohol, and soon after the ether, which is known by its fragrant odour, and the streams which run down the sides of the retort. When the odour changes, and becomes sharp and suffocating, the receiver must be changed; and if the distillation be continued, a clear acid liquor is procured, on the surface of which are observed some drops of sweet oil, which is succeeded by a yellow matter of the consistence of butter, which is a true muriate of tin, and at last a brown heavy liquid, which exhales very copious white vapours; and there remains in the retort a gray matter in the state of powder.

3. To purify this ether, it is put into a retort over carbonate of potash. A brisk effervescence takes place, and a very copious precipitate is produced. This is owing to the oxide of tin which the acid had carried off during the distillation. A little water is to be added, and distilled with a gentle heat. About the one-half of the product of the ether is thus obtained. All the fluids which come over after the muriatic ether, are loaded with oxide of tin; they attract moisture from the air, and combine with the water without any precipitation.

4. Another method has been proposed for the preparation of muriatic ether by Laplanche. He pours into a tubulated retort sulphuric acid and alcohol on common salt which has been strongly dried. The muriatic acid gas, disengaged by the sulphuric acid, prepared meeting the vapours of the alcohol in the retort, combines with them. In this way an ether is obtained, which may be purified in the usual way. But in this process, Fourcroy thinks, that the production of ether is owing to a small portion of oxymuriatic acid which is formed during the process.

5. Pelletier has succeeded in obtaining muriatic and manganese ether, by distilling in a large tubulated retort, a mixture of oxide of manganese, common salt, concentrated sulphuric acid, and alcohol. The quantity of ether obtained by this process, is equal to one half the weight of the alcohol employed.

6. Another process has been proposed by Berthollet, by distilling with a gentle heat, alcohol which muriatic acid has been saturated with oxymuriatic acid gas, and by acid gas, distilling the oxide of manganese, a mixture of alcohol, and strongly concentrated muriatic acid.

7. Muriatic ether, thus obtained, is transparent and very volatile. It has nearly the same odour as sulphuric ether. It burns like it, and gives out a similar smoke; but it differs in two of its properties; the one is, that it exhales, while burning, an odour as pungent and acrid as sulphurous acid; and the other is, that the taste is astringent like that of alum. This difference in odour and taste is owing, it is supposed, to some extraneous substances with which it is contaminated; for in the whole process of its formation it appears to be exactly the same; a constant product of the decomposition of alcohol, by whatever re-agent this is effected.

IV. Acetic Ether.

1. An ether has also been obtained by distilling a mixture of acetic acid and alcohol. This was the first process which was employed in the production of this ether. It was discovered by the count de Lauraguais in 1759. It has been improved by Pelletier, who distilled equal quantities of acetic acid, obtained from acetate of copper, and alcohol. It was then poured back into the retort, and distilled a second time. When this process is finished, it is distilled a third time, and the product of the third distillation is a mixture of acetic acid and ether. To separate the acid from the ether, it is saturated with potash, and distilled with a gentle heat. The acetic ether passes over in a state of purity.

2. Another process has been proposed to obtain the famous ether. Take 16 parts of acetate of lead, five parts of concentrated sulphuric acid, and nine parts of alcohol. Let it be distilled till ten parts come over. Let this liquid be agitated with one third of its bulk of lime water; the ether separates and swims on the top. The quantity generally amounts to about six parts.

3. This ether is similar to the other ethers in its properties, excepting that it has a slight odour of acetic acid.

4. Ether has also been formed by several other acids, and it appears, that these acids possess one common property in their action on alcohol, for all the ethers. Inflammable substances produced by the different acids are nearly the same, and indeed it is supposed would be exactly the same, were it not that they are contaminated with extraneous matters derived from the acids, the alcohol, or other substances, which are employed in their formation.

**Sect. III. Of Fixed Oils.**

1. Oils, which are copious productions of nature, have been long known; and their extensive utility in domestic economy and the arts, has always rendered them objects of great importance. The general characters of oils are combustibility, insolubility in water, and fluidity. From the peculiar properties of different oils, they are naturally divided into two kinds; fixed or fat oils, and volatile or essential oils. The fixed or fat oils require a high temperature to raise them to the state of vapour, a temperature above that of boiling water; but the volatile or essential oils are volatilized at the temperature of boiling water, and even at a lower one. Both the volatile and fixed oils are obtained from plants, and sometimes from the same plant, but always from different parts of it. While the seeds yield fixed oil, the volatile oil is extracted from the bark or wood.

2. One of the most distinguishing characteristics of the fixed oils is, that they exist only in one part of the vegetable. They are only found in the seeds. No trace of fixed oil can be detected in the roots, the stem, leaves or flowers of those plants, whose seeds afford it in great abundance. The olive may seem an exception to this. The oil which it yields is extracted, not from the seed, but from its covering. Among plants too, fixed oils are only found existing in those whose seeds have a peculiar structure. The seeds of plants have sometimes one lobe, in which case they are called monocotyledonous plants; and sometimes they have two, when they are denominated dicotyledonous. The formation of fixed oil in plants is exclusively limited to the latter class. There is no instance of fixed oils being found in the seeds of plants which have only one lobe*. Those seeds which yield the fixed oils, contain also a considerable portion of mucilage, so that when such seeds are bruised and mixed with water, they form what is called an emulsion, which is a white fluid containing a quantity of the oil of the seed mixed with the mucilage. One of the most common emulsions, that of almonds, is an instance of this.

Fixed oils are extracted from the seeds of a great number of plants. Those which yield it in greatest abundance are, the olive, thence called olive oil; the seeds of linseed, and the kernels of almonds, called linseed, or almond oil. Fixed oils are also obtained from animals, such as train oil, as it is called, which is extracted from the fat or blubber of the whale. Fixed oil is obtained also in great abundance from the liver of animals, and is found to exist in the eggs of fowls.

3. These different kinds of fixed oils, although they possess many common properties, yet in others they are very different. Many of the vegetable oils have no smell, and scarcely any perceptible taste. The animal oils, on the contrary, are generally extremely nauseous and offensive. These differences are supposed to be owing to the mixture of extraneous bodies, or to certain chemical changes which arise from the action of these bodies upon each other, or on the oil itself.

4. As the fixed oils exist ready formed in the seeds of plants, they are generally obtained by expression, and hence they have been called expressed oils. This is done by reducing the seeds to a kind of pulp, or paste, which is enclosed in bags, and subjected by means of machinery, when it is obtained in the large way, to strong pressure, so that the oil flows out, and is easily collected. The oil which is obtained by this process, which has been called cold drawn oil, because it is procured without the application of heat, and merely by pressure, is the purest; but the quantity which feeds in general yield is comparatively small, and some feeds which contain a considerable portion of oil, scarcely afford any when treated in this way. It therefore becomes necessary for extracting the oil from seeds of the latter description, and to have it in greater abundance from all seeds, to employ heat, to facilitate the separation of the oil from the mucilage or other matters with which it is combined. For this purpose heat is applied, either to the apparatus which is employed in pressing out the oil, or the bruised seeds are exposed to the vapour of water, and sometimes they are boiled in the water itself, by which means those substances which are soluble in water, are separated, and thus the oily part which adhered to these substances, is disengaged.

5. The oils which are obtained in this way are very impure. They are mixed with mucilage, and other parts of the substances from which they have been extracted. Many of these matters separate from the oils when they are left at rest. They are sometimes mechanically purified by filtration through coarse cloths, by which means the groarser parts are separated. Different oils too, it is said, undergo different kinds of purification by different manufacturers, but these processes are kept secret. After they have remained at rest for some time, they are filtered and agitated with water, by which the parts that are soluble in this fluid are separated from the oil. Sometimes they are gently heated, for a shorter or longer time, according to the nature of the substances with which the oil is contaminated. Acids diluted with water are employed to separate the mucilage; lime and the alkalies are also used to combine with an acid which holds this mucilage in solution, and thus to favour its precipitation. Alum, chalk, clay, and ashes, are also employed in the purification of oils.

6. Fixed oils are generally liquid, but of a thick, viscous consistence. They are mild or insipid to the taste; sometimes, however, they have a peculiar taste, which is analogous to that of the plant from which they have been extracted. When pure, they have no smell, but are sometimes impregnated with the odour of the seed which produces them. The fixed oils are rarely quite colourless, but are generally green or yellowish. If they are green when fresh prepared, this colour changes to a yellow, and in time to an orange or red. Fixed oils in general are lighter than water. The specific gravity varies from 0.9153, which is that of olive oil, to 0.9403, that of linseed oil. The boiling point of the fixed oils is not under the temperature of of 60°. When exposed to cold, they congeal, and even crystallize. There is, however, a considerable variety in this respect, among fixed oils: some become solid at the temperature of a few degrees above the freezing point of water; while others, on the contrary, require a degree of cold =5°; and some remain fluid when exposed to the greatest cold. Those oils, it has been observed, which most readily become solid, such as olive oil, are least subject to change, while those which congeal with difficulty have a greater tendency to spoil and become rancid.

7. When fixed oil is exposed to heat, it does not evaporate, till it is raised to the temperature of boiling, or 620°; but when it is thus raised in vapour its properties are changed. It is decomposed by the separation of some of its principles. The part that is volatilized has a greater proportion of hydrogen; charcoal is deposited, and water and fatty acid are formed, while carbonated hydrogen gas is disengaged. By this distillation an oil was produced, denominated by the older chemists, philosophical oil.

When oil is exposed to the open air, and a burning body is brought in contact with it, it readily takes fire, and burns rapidly, with a yellowish white flame. It is on this conversion of oil into vapour, and the inflammation of this vapour, that the application of oil in lamps and candles depends. The oil is gradually, and in small quantities, brought into contact with the burning part of the wick; it is converted into vapour, which is immediately inflamed, and continues to burn till new portions are supplied to undergo the same change, and thus keep up a constant and uniform light and heat.

8. According to the analysis of olive oil by Lavoisier, it is composed of hydrogen and carbure. In the experiment which he instituted to ascertain its component parts, he burnt

| Oil | 15.79 grs. troy | | Oxygen gas | 50.86 |

The products of this combustion were water and carbonic acid. The weight of the water could not be ascertained with much precision, but the quantity of carbonic acid which was formed, amounted to 44.50 grs. This quantity subtracted from the whole weight of the substances consumed, namely the oil and oxygen gas, left 22.15 grs. for the weight of the water. The proportion of oxygen in this quantity of water is 18.82 grs. which leaves 3.33 grs. of hydrogen, the other component part. The proportion of oxygen in 44.50 grs. carbonic acid gas is 32.04 grs. which leaves 12.46 of carbure. The oxygen of the water and of the carbonic acid, namely 18.82 grs. of the one, with 32.04 grs. of the other, make up the whole quantity of oxygen, namely 50.86 grs. that was consumed. From this analysis, therefore, 15.79 of olive oil are composed of

| Carbure | 12.46 | | Hydrogen | 3.33 |

The component parts, therefore, of 100 grains of olive oil are

| Carbure | 78.92 | | Hydrogen | 21.08 |

9. The fixed oils are insoluble in water. When it is necessary to combine them with this liquid, it is by means of mucilaginous substances, in which case the mixture is known under the name of emulsion, or with alkaline substances, when it is distinguished by the name of soap.

10. When fixed oils are exposed to the air, they undergo peculiar changes; and these changes are different, according to the nature of the oil.

11. Some of these oils become thick, opaque, white, granulated, and are analogous in appearance to tallow. Oils subject to this change are called fat oils, such, for instance, is olive oil, almond oil, and rape seed oil. This change is more or less rapid in different circumstances. If a thin layer of oil be spread on the surface of water, and exposed to the air, it takes place in a few days, and this effect is owing to the absorption of oxygen, which combines with the oil. It was supposed by Berthollet, that it depended on the action of light; but his experiments were repeated by Senebier, who found that olive oil when kept in the dark, became rancid, while the same kind of oil exposed to the light, but excluded from the air, remained unchanged.*

12. But other oils, when they are exposed to the air, dry altogether, yet have the property of retaining their transparency. Oils which have this peculiar property are called drying oils. The oil of poppies, hemp, linseed oil, are possessed of this property. The nature of the change which takes place in these drying oils, is supposed to depend on the absorption of oxygen; and this oxygen combining with the hydrogen of the oil forms water. This opinion is supported by the practice which is followed to increase the drying property of linseed oil. It is usually boiled with litharge, before it is employed by painters. The litharge in this case is partly reduced to the metallic state, by being deprived of its oxygen, which is supposed to combine with the oil.

13. But many of the fixed oils, when exposed to the air for a sufficient length of time, undergo a farther change, and acquire very different properties. They are then said to become rancid. During this change, they assume a brown colour, have the property of changing vegetable blues to red, and acquire a peculiar smell and taste. In this change, the fatty acid is formed, which depends on a new combination of the hydrogen and carbure of the oil in certain proportions with the oxygen absorbed from the atmosphere. To this acid, therefore, the rancidity of oils seems to be owing. Part of the hydrogen of the oil too, it would appear, combines with the oxygen and forms water.

14. Carbure in the state of charcoal, has no action upon oils; but they are purified and rendered colourless by being passed through charcoal powder.

15. Phosphorus combines with oils, with the assistance of phosphorescence of heat. A small portion of the phosphorus is diffused, solved, which communicates a luminous property to the oils, so that when they are spread upon any surface, they shine in the dark. When the oil is completely saturated with the phosphorus with the assistance of heat, and is allowed to cool, part of the phosphorus is deposited, and crystallized in transparent octahedrons. When this phosphorated oil is distilled, phosphorated hydrogen gas is disengaged.

16. Sulphur easily combines with fixed oil, with the assistance of heat. The solution, which was formerly called ruby of sulphur, is of a reddish colour. When it cools, the sulphur crystallizes, by which process Pelletier obtained sulphur in the form of octahedrons. When the cooling is too rapid, the sulphur is precipitated at a yellow colour, in the shape of needles. If this sulphurated oil, which has a peculiarly fetid odour, be distilled, it affords a great quantity of sulphurated hydrogen gas.

17. The acids have a powerful effect on the fixed oils. The sulphuric acid, when concentrated, decomposes them. They become brown, thick, and at last of a black colour. Water is formed, charcoal is precipitated, and even an acid is formed. Nitric acid in the cold, thickens fixed oils by communicating part of its oxygen. In the state of nitrous acid it produces a more violent action. There is a considerable effervescence, with the evolution of a great quantity of nitrous gas. If a mixture of nitrous acid and concentrated sulphuric acid be thrown upon fixed oils, they instantly inflame, and leave behind a spongy mass of charcoal. Muriatic acid has little effect on fixed oils, but the oxymuriatic acid thickens and bleaches them, in the same way as tallow or wax.

18. The various purposes to which fixed oils are applied, are too well known to require particular enumeration. They are employed in domestic economy, either as articles of food, and for this purpose are used alone, or in combination with other substances; or they are employed for giving light, by being burnt in lamps. They are used in medicine, either on account of the properties which peculiar oils possess, or on account of the properties they communicate to other substances with which they are combined. In this state the use of oils is well known in the form of unguents, plasters, and liniments. In the arts, fixed oils are of the most extensive utility. They are employed in the fabrication of soaps, for mixing colours in painting, for some kinds of varnish, and for defending substances from the action of air and moisture.

19. The order of the affinities of fixed oils is the following:

- Lime, - Barytes, - Fixed alkalies, - Magnesia, - Ammonia, - Oxide of mercury, - Other metallic oxides, - Alumina.

Sect. IV. Of Volatile Oils.

1. Volatile oils are distinguished from the fixed oils by their volatility, fragrance, and acrid taste. They are also known under the name of aromatic oils, from their odour; or essential oils, or simply essences, from being supposed to constitute the essence or the exhalation of the vegetable matters which furnish them.

2. Volatile oils are not limited to particular parts of plants, but are found to exist in every part of the plant, excepting in the seed, which furnishes the fixed oils. A great number of roots which are generally distinguished by an aromatic odour, and have more or less of an acrid taste, afford volatile oils. They are furnished also by many woods, such as those of the pine and fir tribe, and by many of those which are natives of warm climates. The leaves of a great number of plants belonging to the didynamia class also afford volatile oil, as well as many of the umbelliferous plants. It is obtained also from many flowers of vegetables, and also from the covering of many fruits, as the skin of oranges and lemons. It is also obtained from a great number of seeds; but it is never found in the cotyledons or lobes themselves, but only in the external covering. The quantity of volatile oil which is obtained from vegetables, varies according to the age, the soil in which they grow, and the state of the plant. Some plants, while green, furnish it in greatest abundance; while others yield most when they are dry.

3. There are two processes by which volatile oil may be obtained. When it exists in plants in great abundance, and in vehicles in a fluid state, it may be separated by mechanical means. Thus, by simple expression, the volatile oils are extracted from many plants, as, for instance, from the fruit of the orange and the lemon. From the outer rind of these fruits, when they are fresh, the volatile oil is obtained in the liquid form; but in general, the volatile oils of plants are neither so abundant, nor do they exist in that state of fluidity, by which they can be procured by so simple a process. In most cases they are subjected to the process of distillation; and for this purpose they are macerated for some hours in water. They are then introduced into a still along with the water; a moderate heat is applied and continued till the fluid boils, when a great quantity of vapour of water, mixed with the volatile oil, passes over, and is received in proper vessels. The oil collects on the surface of the water, from which it may be easily separated. The water itself is of a milky colour, on account of a small quantity of oil suspended in it; and even after the water becomes transparent by the particles of the oil separating from it, and rising to the top, it is still loaded with the peculiar odour of the plant. This was supposed to be a separate principle of vegetables, to which Boerhaave gave the name of spiritus rectus, and which is still known by the name of aroma. This fragrance of the water is owing to the solution of a certain portion of oil in it. In the distillation of the volatile oils, different practices are followed, according to the nature of the plant, and the proportion of the oil existing in it. The roots, wood, bark, fruits, dried plants, after being cut in pieces, rasped down or bruised, are macerated for some hours, or for some days, according to the solidity or particular state of the vegetable matter. Fresh plants are distilled with the smallest quantity of water, have no need of previous maceration, and do not require so high a temperature.

4. The volatile oils are particularly distinguished by their fragrance, which varies in the oils extracted from different different plants. The consistence of the volatile oils also varies considerably. Sometimes they are as fluid as water, which is the case with those oils obtained by expression. Some are thick and viscid, as those generally are which are extracted from woods, roots, barks, and fruits of the warmer regions. Some congeal, or assume a granulated solid consistence at different temperatures. Of these last, some are always found to be in the concrete state. Several of the volatile oils are susceptible of crystallization, depositing in the remaining portion of the oil which continues liquid, transparent polyhedrons, more or less of a yellow colour, which are found to be pure oil. This last change, Vauquelin thinks, is owing to an incipient oxidation; for it never takes place, unless oils have been kept for some time.

5. There is great variety of colour among volatile oils. Some indeed are nearly colourless, as the oil of turpentine; but in general they are of different shades of colour. Some are yellow, as the oil of lavender; some are of a reddish yellow or brown, as the oil of cinnamon or of rhodium; some are blue, as the oil of chamomile; and some are green, as that of parsley. But the most prevailing colour among volatile oils is yellow or reddish.

6. Volatile oils have almost always an acid, hot, and even burning taste. It is observed that the most acid vegetable matters do not yield an oil possessed of this quality. The specific gravity of volatile oils is generally less than that of water. Some volatile oils, however, as those of saffron and canella, have a greater specific gravity. The specific gravity of oils varies from 0.8997 to 0.9910, in those which are lighter than water; but those which are heavier are from 0.0363 to 1.4240.

7. When volatile oils are exposed to the light, the colour becomes considerably deeper; they become thicker, and increase in specific gravity. In speaking of a similar change which takes place in the fixed oils, this change was ascribed to the absorption of oxygen; but, according to the experiments and observations of M. Tingry, it is effected merely by the action of light; for in his experiments oxygen gas was entirely excluded.

8. When volatile oils are exposed to heat, they evaporate very readily. They are much more combustible than the fixed oils; and in burning give out a great quantity of smoke, a very bright white flame, and a good deal of heat. They require a greater proportion of oxygen than the fixed oils, and yield a greater quantity of water. This arises from a greater proportion of hydrogen, and a smaller quantity of carbons, which they contain.

9. When volatile oils are exposed to the open air, they undergo another change. They assume a deeper colour, and become viscid, exhaling at the same time a very strong odour. The air around is deprived of its oxygen; it combines with the hydrogen of the oil, and forms water, which is observed in drops on the surface. Many of the volatile oils when thus exposed pass into the resinous state, and are almost entirely deprived of their odour. This depends on the loss of part of their hydrogen, and consequently the increase of the proportion of carbons.

10. The volatile oils are in some degree soluble in water. When they are agitated with this liquid, they combine with it, and communicate a very strong odour, and a slightly acid taste.

11. Phosphorus and sulphur are soluble in volatile oils. With phosphorus the solution is luminous in the dark, is extremely fetid, and gives out, by the force of heat, phosphorated hydrogen gas. The combination with sulphur is known under the name of balam of sulphur. This gives out sulphurated hydrogen gas on the application of heat.

12. The concentrated sulphuric acid produces a brown colour, increases the viscosity of the volatile oils, and disengages part of their hydrogen with effervescence and heat. Part of the oil is decomposed; charcoal is deposited, and it contains an acid. Nitrous acid, when brought into contact with the volatile oils, produces instantaneous deflagration; converts them into water in a great measure, and carbonic acid; and there remains behind a voluminous mass of charcoal. Muriatic acid has scarcely any action; but oxymuriatic acid renders them colourless, concrete in part, or viscid, and brings them more nearly to the state of resins.

13. Some of these oils are employed in medicine. They are used also for the solution of those substances which are to be employed as varnishes; and many of them are used in perfumery.

14. As many of the volatile oils are produced but in small quantity, they are consequently highly priced. There is therefore some temptation to adulterate them with fixed oils, with cheaper volatile oils, or with other substances, to increase the quantity. It is therefore of some importance, to be able to detect such frauds. When a volatile oil is adulterated with a fixed oil, there is a very easy test to discover it. Let a single drop of the oil that is suspected fall on clean paper, and expose it to a gentle heat. If the oil is pure, the whole will be evaporated, and no trace remain on the paper; but if it has been mixed with a fixed oil, a greasy spot remains behind. Volatile oils are frequently adulterated with oil of turpentine; but this can only be detected by its peculiar odour, which continues for a longer time than most of the other volatile oils. When they are adulterated with alcohol; it is easily detected by mixing a little of the oil with water, which immediately produces a milky appearance, by the abstraction of the alcohol from the oil, and its combination with the water.

15. There is another class of oils known under the name of empyreumatic oils, which have different properties from those which have been described. These oils are acid and stimulating, with a strong fetid and disagreeable odour. It would appear, that these properties are owing to a partial decomposition of other oils. These oils are produced, as the name imports, by the action of fire. They are obtained when oils are forced to rise in vapour, and pass over in common distillation, with a greater degree of heat than that of boiling water, or by the application of a strong heat to substances from which no oil was previously extracted. These empyreumatic oils agree in some of their properties with the volatile oils. They combine in small proportion with water, and they are soluble in alcohol; and probably any difference that exists between them, is owing to a partial decomposition; for when they are distilled, distilled, the oil is restored to a state of purity, and the carbonaceous matter which had been separated, remains behind.

**CHAP. XII. OF ALKALIES.**

The word alkali is derived from the Arabian name of a plant, which affords the substance now distinguished by that term. The name of the plant is kali, to which the Arabic particle al was added, expressive of the valuable qualities of the plant. When other substances were discovered, possessed of similar properties, the meaning of the term was extended, and applied to such matters as had several common properties. Three substances are generally ranked under the head of alkalies. These are potash, soda, and ammonia. They are characterized by the following properties.

1. They have a peculiar taste, which is disagreeably caustic, even when they are diluted with water. 2. They change vegetable blue colours to a green. 3. They have a strong attraction for water, and combine with it in all proportions. 4. They have a strong affinity for acids. 5. They melt in a moderate heat, but with a stronger heat they are volatilized.

The alkalies have been divided into two kinds, namely, the fixed and volatile. The two first, potash and soda, are denominated fixed alkalies, because they require a great degree of heat to distillate or volatilize them. Ammonia has been called the volatile alkali, because a very moderate degree of heat is sufficient to volatilize it.

Fourcroy has clasped two of the earths, namely, barites and strontites, under the head of alkalies. In some of their properties, these earths, no doubt, are analogous to the alkalies; but in other properties they are more closely allied to the earths. There seems, therefore, to be no inconvenience or ambiguity in clasping them, as usual, among earthly substances.

It may perhaps be considered as one of the general characters of the alkalies which we have now enumerated, that they have no action on oxygen, azotic, or hydrogen gases; nor is there any action between the alkalies and carbons.

**SECT. I. Of POTASH and its Combinations.**

1. This substance has been long known in commerce, under many different names, derived from the substances from which it is extracted, or from the processes by which it is prepared. The name of a/b or afh has been given to this substance, because it is procured from the burnt ashes of vegetables; and it has received the epithet of pot-ashes, because it is prepared in iron pots. It got the name of vegetable alkali, because it was supposed that it only existed in vegetables. Being prepared from nitre and tartar, it was called the alkali of nitre or tartar, and the salt of tartar, a name which it still retains in the shops. It has been proposed also to distinguish it by the name of kali, the name of the plant from which it was originally procured.

2. Potash is generally prepared by burning wood or other vegetable matters, and thus reducing them to ashes. The ashes are then to be washed repeatedly with water, till the liquid comes off perfectly tasteless. If the liquid thus obtained be purified by filtration, and evaporated to dryness, a salt is obtained, which is the potash. In this state it is contaminated with much extraneous matter; but if it be exposed to a red heat, many of the foreign substances with which it is mixed, are dissipated; it becomes whiter, and from its colour is then sold under the name of pearl-afh. This salt is prepared in great abundance in those countries where wood abounds, as in North America and the north of Europe; and hence it is known in commerce under the name of Russian or American pearl-afh.

3. Potash, in this state, is considered as sufficiently pure for the ordinary purposes of life to which it is applied; but it is still mixed with much foreign matter, which renders it unfit for the purposes of the chemist. It has therefore always been considered as an object of great importance, to obtain it in a state of purity.

But even when it is seemingly pure, by being deprived of all extraneous substances, it is found to possess very different properties, after being subjected to certain processes. In one state it is comparatively mild and inactive; in another, extremely acid and corrosive. Various opinions were entertained of the cause of this remarkable difference, which it is unnecessary to enumerate. The true cause was discovered and demonstrated by Dr Black in the year 1756. This ingenious philosopher, by a few simple and satisfactory experiments, clearly proved, that the different effects of the alkalies, lime, and magnesia, are owing to their combination with a peculiar substance, to which he gave the name of fixed air, because it is fixed in these bodies. This fixed air, it has been already observed, is now known by the name of carbonic acid. When the alkalies are in combination with carbonic acid, they are in the mild state; but, when they are deprived of this acid, their effects being more powerful and corrosive, they are said to be in the caustic state.

When sulphuric acid is poured upon a quantity of potash in its ordinary state, a violent effervescence takes place. This, Dr Black proved, is owing to the escape of the carbonic acid in the state of gas; for when the alkali is in its pure or caustic state, no effervescence whatever takes place. He also proved, that the alkalies and lime in their mild state, that is, when combined with carbonic acid, are heavier than in the caustic state, and that this difference of weight is exactly equal to the quantity of carbonic acid which escapes. Since, then, these substances exhibit such different properties in these two states, it is necessary to procure them in a state of purity, to examine their properties and effects. This is not without difficulty, on account of the strong affinity which exists between the alkalies and carbonic acid; for although they are perfectly pure, as soon as they are exposed to the air, they begin to attract the carbonic acid and return to their former mild state.

4. As this, therefore, is an object of importance, various processes have been proposed, to procure them as pure as possible. Some of these processes we shall now detail.

a. The following process for the purification of pot-afh is recommended by Berthollet. It is to be mixed with with double its weight of quicklime, with eight or ten times the weight of the whole mixture, of pure or rain water. Boil it for two or three hours in an iron vessel; then let it remain in a clofe vessel for 48 hours, taking care to agitate it occasionally. Let it afterwards be filtered, and boiled in a silver vessel with a strong heat, till it assume the consistence of honey. Pour a quantity of alcohol upon it, equal in weight to \( \frac{1}{2} \) of the alkali which has been employed; then put it on the fire, and let it boil for some minutes. Pour it afterwards into a bottle, and allow it to cool. The matter in the bottle separates into three different strata: at the bottom are deposited solid bodies; in the middle there is an aqueous solution, or carbonate of potash; and on the top a liquor of a reddish brown colour, mixed with alcohol. Let this be carefully decanted off by means of a syphon. This is a solution of pure potash in alcohol. Put it into a basin of silver, or of tinned copper; evaporate it rapidly, till a dry, black and charry crust forms on the surface, and the liquor below, which has an oily appearance, becomes solid by cooling. Let the crust be removed, and pour the solution into porcelain vessels. When it cools, it becomes solid. It is then to be broken in pieces, and put into clofe vessels. This is the potash in a state of purity, not only freed from foreign matters, but also deprived of the carbonic acid.

Lime has a stronger affinity for carbonic acid than the potash. When, therefore, the lime deprived of its carbonic acid, as it is in the state of quicklime, is brought into contact in sufficient quantity with the potash, it deprives it of the carbonic acid. It is with this view that the lime is employed in this process. The alcohol has the property of dissolving potash, but has no action on the other substances with which it is combined. This is the reason why the alcohol, holding in solution the pure potash by its less specific gravity, forms the upper stratum in the bottle. By the evaporation, the last step of the process, the alcohol and water are driven off, and the pure potash remains behind in the solid state.

A more economical process has been proposed by Professor Lowitz of Pittsburgh. He boils together the potash and quicklime, as in the former process; filters the liquor, and evaporates, till a thick pellicle is formed on the surface. It is then set by to cool, till crystals are formed in it, which are crystals of extraneous salts, and are to be removed. He then continues the evaporation, and removes the pellicle as it forms on the surface during the process. When the fluid ceases to boil and no more pellicle is formed, he removes it from the fire, and keeps constantly stirring it while it cools. He then dissolves it in double the quantity of cold water, filters the solution, and evaporates in a glass retort, till regular crystals begin to be deposited. If the mass should consolidate ever so little by cooling, a small quantity of water is to be added, and it must be heated again, to render it fluid. When a sufficient quantity of regular crystals has been formed, he decants the liquid, which has a brown colour, and re-dissolves the salt after it is suffered to drain, in the same quantity of water. The decanted potash, &c. liquor is preserved in a well-closed bottle for several days, till it subsides and become clear. He then decants it, evaporates, and crystallizes a second time, and repeats this process as long as the crystals afford, with the least possible quantity of water, solutions that are perfectly limpid. These solutions are to be preserved in well-closed bottles, to defend them from the access of air.

The method of preparing pure potash by the indefatigable and accurate Klaproth, is somewhat different from this. We shall detail it in his own words.

"As many persons think that the preparation of a perfectly pure caustic ley is subject to more difficulties than it really is, I will here briefly state my method of preparing it. I boil equal parts of purified salt of tartar, (carbonate of potash, or vegetable alkali prepared from tartar) and Carrara marble, burnt to lime, with a sufficient quantity of water, in a polished iron kettle; I strain the ley through clean linen, and though yet turbid, reduce it by boiling, till it contain about one half of its weight of caustic alkali; after which I pass it once more through a linen cloth, and set it by in a glass bottle. After some days, when the ley has become clear of itself, by standing, I carefully pour it off from the sediment into another bottle. To convince myself of its purity, I saturate part of it with muriatic or nitric acid, evaporate it to dryness, and re-dissolve it in water. If it be pure, no turbidness will take place in the solution. The quantity of caustic alkali which this ley contains, I ascertain by evaporating a certain weighed portion of the ley to dryness, in an evaporating dish of a known weight. I also take care, in the preparation of this caustic ley, that the alkali be not entirely deprived of carbonic acid; because, in that case, I can with greater certainty depend on the total absence of dissolved calcareous earth. By employing burnt marble, or, in its stead, burnt oyster-shells, I avoid the usual contamination of the caustic ley by aluminous earth; because lime, prepared from the common species of lime-stone, is seldom entirely free from argill."

Potash, thus obtained, is a white solid substance, which is susceptible of crystallization, in long, compressed, quadrangular prisms, terminating in sharp-pointed pyramids. These crystals, which are only obtained from very concentrated solutions, are soft and deliquescent. The taste is extremely acrid; and it is so corrosive, that it destroys the texture of the skin, the moment it touches it. It is from this property that it has derived the name of caustic; and in surgical language it has obtained the name of potential cautery, because it is employed for the purpose of opening abscesses, or for destroying excrescences. According to Haffner, the specific gravity of potash is 1.7085. It converts vegetable blues into a green colour.

Light has no action on potash. When it is heated in clofe vessels, it becomes soft and liquid, and is afterwards converted into a white, opaque, and granulated mass, when it cools. If the heat be increased

(t) By deliquescence is meant the melting of substances in the water which they attract from the air. Such salts are said to be deliquescent. Potash, &c., to redness, it swells up, and rises in vapour. If the vessel be opened, there arises a white smoke, which is extremely acrid, and condenses on cold bodies with which it comes in contact. But though it is thus sublimed, it undergoes no other change than assuming a slight green colour.

7. There is no action between potash and oxygen or azotic gases, nor is there any direct action between potash and carbons. Phosphorus and sulphur enter into combination with potash, and form peculiar compounds, the nature of which we shall consider, after having detailed the general properties of potash.

8. Potash has a very strong affinity for water. Water at the ordinary temperature dissolves double its weight of potash. The solution, when the potash is pure, is colourless and transparent, and is nearly of the consistence of oil.

9. Potash combines readily with the acids, and forms compounds with them, having different properties, according to the nature of the acid which is employed. Its affinities for the acids are in the following order:

- Sulphuric, - Nitric, - Muriatic, - Phosphoric, - Phosphorous, - Fluoric, - Oxalic, - Tartaric, - Arsenic, - Succinic, - Citric, - Lactic, - Benzoic, - Sulphurous, - Acetic, - Sulfuric, - Boracic, - Carbonic, - Prussic.

10. Potash is employed for a great variety of purposes; it enters into combination with many substances, and forms with them valuable and important compounds. It is employed in medicine as a useful and powerful remedy; in many arts and manufactures, as in bleaching, dyeing, and glass-making.

11. Potash is to be considered as a simple substance. No attempts yet made have succeeded in decomposing it. But although not the slightest proof has been adduced of its formation or decomposition, it is considered by some as a compound substance. This opinion is founded on the analogy of its properties with ammonia; the composition of which has been fully demonstrated. According to some, it is composed of lime and azote; and, according to others, of hydrogen and lime; but all these are mere conjectures, which have probably had their origin in that eagerness of the human mind, which leads it to fancy what it wishes to be true.

12. But we shall now consider more particularly the action of the different substances which have been already treated of, on potash, and the different combinations which it forms with them.

I. Action of Phosphorus on Potash.

1. There is no direct combination between potash and phosphorus; but although these two bodies have had but little tendency to unite, they have a very powerful effect upon each other when they are heated together with water. It was in this way that Gengembre first obtained the singular gas, which has been already described, when treating of phosphorus, under the name of phosphorated hydrogen gas.

2. If one part of phosphorus and ten parts of concentrated solution of pure potash be introduced into a small retort, and exposed to heat till it boils, phosphorated hydrogen gas will pass over, which may be received in jars over water; or if the beak of the retort be kept under the surface of water, the bubbles of the gas, as they rise to the surface, explode, and form the beautiful coronet of white smoke, formerly mentioned. In making this experiment, the retort should not be larger than to hold the solution, or, it should be filled with hydrogen or azotic gases, in which the phosphorated hydrogen gas will not inflame and explode, with the risk of breaking the vessel; for the inflammation can only take place when it comes in contact with the oxygen of the atmosphere.

3. In this process, the water which holds the potash in solution, is decomposed. The oxygen combines with the part of the phosphorus, and forms phosphoric acid, while another part of the phosphorus unites with the hydrogen, and passes over in the form of phosphorated hydrogen gas. Thus, without any perceptible action between the phosphorus and the potash, the decomposition of the water is aided by means of the potash, in consequence of its attraction for the phosphorus, combined with the oxygen in the state of phosphoric acid. For it is found, that a quantity of phosphorus of potash is formed, corresponding to that of the phosphorated hydrogen gas which is obtained. The decomposition is also assisted by the affinity of the phosphorus for the oxygen and hydrogen of the water. The whole of the phosphorated hydrogen gas which is formed, being disengaged, shows that no combination takes place between it and the potash.

II. Action of Sulphur on Potash.

1. Sulphur and potash very readily combine together. If one part of potash and three of sulphur be triturated together in a glass or porcelain mortar, the mixture becomes hot, the sulphur loses its yellow colour, and acquires a greenish tinge. There is disengaged a fetid smell of garlic; the mixture attracts moisture from the air, becomes soft, and is almost entirely soluble in water.

If two parts of potash and one of sulphur be well mixed together, and heated in a crucible, the mixture of potash fuses; and by this process is obtained sulphuret of potash in the dry state. This was formerly called hepatic sulphuris, or liver of sulphur, from its resemblance to the liver of animals. The same substance may be obtained by treating sulphur with the potash of commerce, with this precaution, not to apply too strong a heat, to occasion a sublimation of the sulphur, and the too rapid evolution of the carbonic acid from the potash. When the fusion is completed, it is poured out. 2. The solid sulphuret of potash, thus prepared, is of a shining brown colour like that of the liver of animals, from which it derived its former name. Exposed to the air it becomes green, then palles to gray, and even to white. It is dense, smooth and has a vitreous fracture. It has no other smell than that of heated or sublimed sulphur; it is acrid, caustic, and bitter to the taste, and leaves a brown spot on the skin. With a strong heat, in a porcelain retort, the sulphur is sublimed, and the potash remains in a state of purity at the bottom of the vessel. The sulphuret of potash converts vegetable blue colours to green, and afterwards destroys them.

3. But the sulphuret of potash possesses these properties, only while it is recently prepared, and very pure. When exposed to the air, it is readily decomposed, and more so, as the air is loaded with moisture. It absorbs water with avidity, acquires a green colour, and exhales the fetid odour of sulphured hydrogen gas. This change is owing to the decomposition of the water which has been absorbed. Part of the sulphur combines with the hydrogen, and forms sulphured hydrogen gas, which combines with the sulphuret, and forms hydrogenated sulphuret of potash.

4. This may also be formed by passing the sulphured hydrogen gas into a solution of potash. The gas is absorbed and condensed, till the potash is fully saturated. To this substance Berthollet, who particularly investigated the nature of these compounds, gave the name of hydro-sulphuret of potash.

This compound crystallizes, and is more permanent than the sulphuret. The crystals are transparent and colourless, while those of the sulphuret are brown and opaque. The crystals are large and in the form of four-sided prisms, terminating in four-sided pyramids. It is decomposed by heat, and by the action of the acids. Sulphured hydrogen gas is disengaged, but there is no deposition of sulphur. The oxymuriatic acid decomposes the sulphured hydrogen, and then sulphur is precipitated. The pure hydro-sulphuret has no smell, when it has no addition of sulphur beyond the saturation of the hydrogen. The alkali seems to have a stronger affinity for the sulphured hydrogen than for the sulphur, so that when it is saturated with the first, that is, in the state of hydro-sulphuret of potash, which is in the form of crystals, and without smell or inodorous, it combines with no more sulphur; but when sulphured hydrogen gas is made to pass into a solution of the sulphuret of potash, already hydrogenated by its solution in water to a certain degree of saturation, the sulphured hydrogen acts in the manner of acids, precipitates the sulphur like them, renders the liquid colourless, and leaves behind nothing but the hydro-sulphuret of potash.

5. Sulphur combines with the latter compound, and forms a new compound, which may be obtained by pouring a liquid hydro-sulphuret upon sulphur. The sulphur is dissolved without the affluence of heat; the liquid assumes a darker colour, and then it is converted into the hydrogenated sulphuret. Hydrogenated sulphuret of potash is prepared by boiling together a mixture of pure potash and sulphur in water. This solution is of a deep greenish yellow colour, has a very acid bitter taste, and a powerful action on many substances. It readily absorbs oxygen when exposed to the air. When it is kept in close vessels, sulphur is deposited; the liquid becomes transparent, and the smell is dissipated. Thus, there are three different compounds of sulphur with potash; namely, sulphuret of potash, hydro-sulphuret of potash, and hydrogenated sulphuret, which are all distinguished by peculiar properties.

III. Compounds of Potash with Acids, or Neutral Salts.

1. Sulphate of Potash (u).

1. This salt, which was one of the most early known, is a compound of sulphuric acid and potash. It has been distinguished by a great variety of names, as sal de dubibus, sal polycheirus, or salt of many virtues, arcanum duplicatum, and more lately vitriolated tartar, till in the new nomenclature it received the name of sulphate of potash.

2. It is prepared by different processes, either by preparing directly combining the sulphuric acid with the potash, and evaporating and crystallizing it; or by decomposing other salts which have potash for their base, by means of the sulphuric acid, which having a stronger affinity for the potash, combines with it and forms the new compound.

3. The sulphate of potash crystallizes in hexagonal prisms, terminated by six-sided pyramids; but this form is susceptible of several varieties. It has a disagreeable bitter taste; it is not very hard, and may be easily reduced to powder. The specific gravity is 2.4073. At the temperature of 62°, it is soluble in 16 times its weight of water; boiling water dissolves about one-fifth part; on cooling it crystallizes in a confused mass; and it is only by slow spontaneous evaporation that regular crystals can be obtained.

4. It suffers no change by the action of the air. When placed upon burning coals, it decrepitates, and loses its water of crystallization. At a greater heat it melts, and is converted into a kind of enamel as it cools.

5. When this salt is exposed to a red heat, along with hydrogen gas or carbons, it is decomposed, and converted into a hydrogenated or carbonated sulphuret of potash.

6. The sulphuric acid, with the affluence of heat, combines with the salt, and forms another with excess of acid. It undergoes a partial decomposition by the action of oxygen.

(u) The compounds of acids with any base are known by this name in the present chemical nomenclature; and when the acid has its greatest proportion of oxygen, as in this case the sulphuric acid, the name of the compound terminates in the syllable ate, as sulphate of potash, nitrate of potash; but when the acid has its smaller proportion of oxygen, the name of the compound terminates in ite, as fulphite of potash, nitrite of potash. Potash, &c. section of nitric acid. The nitric acid combines with nearly \( \frac{1}{2} \) of potash, which is owing to the action of double affinity. The nitric acid combines with one part of the potash, while the sulphuric acid unites with the sulphate of potash, and forms a salt with excess of acid. A similar decomposition takes place by means of the muriatic acid.

7. The component parts of sulphate of potash are, according to

| Bergman | Kirwan | |---------|--------| | Acid | 40 | 45.2 | | Potash | 52 | 54.8 | | Water | 8 | 00.0 |

Acidulous sulphate of potash, or super-sulphate of potash.—1. This salt was formerly called vitriolated tartar with excess of acid. It is prepared by heating together, in a retort, three parts of the sulphate of potash, with one part of its weight of concentrated sulphuric acid.

2. It crystallizes in long flexible, thinning crystals, and sometimes it exhibits the form of fixed prisms. It has a sharp, acrid, and hot taste. It reddens vegetable blues. Exposed to the air it becomes a little more opaque, but without any other change. It is more soluble in water than the sulphate of potash, requiring only 2 parts of water at 60°, and dissolves in less than its own weight of boiling water. It melts very readily, and has the appearance of a thick oil. When it cools, it becomes a white, opaque mass, exhibiting on its surface thinning silky crystals. When exposed to a great heat, the excess of acid is driven off, and it is converted into the sulphate of potash.

3. It is readily decomposed by the action of hydrogen and of red-hot charcoal, which deprive it of a great portion of the sulphur; and by sulphur itself, which carries off the excess of sulphuric acid in the form of sulphurous acid.

4. The first of these salts, the sulphate of potash, is employed in medicine as a purgative; the last has been applied to no use whatever.

2. Sulphite of Potash.

1. This salt was long known under the name of the preparation, sulphurous salt of Stahl. It is a compound of the sulphurous acid and potash. Its nature and properties have been particularly investigated by Berthollet, Fourcroy, and Vauquelin. It may be formed by passing a current of sulphurous acid gas into a solution of carbonate of potash in three times its weight of distilled water, till the effervescence ceases. The liquor becomes transparent and hot, and, as it cools, the sulphite of potash is deposited in crystals.

2. This salt is in the form of long, small needles, diverging from a centre, or in rhomboidal plates, or in dodecahedrons formed by two tetrahedral pyramids, united and truncated very near the base. The crystals are white and transparent, but sometimes of a slight yellow colour. The taste is acid and sulphureous. The specific gravity is 1.586. The sulphite of potash, exposed to the air, very readily effloresces (u); becomes white and opaque, and is converted into sulphate of potash. This is owing to the sulphurous acid abstracting oxygen from the air, and becoming sulphuric acid. It is very soluble in water, at the temperature of the atmosphere, and much more so in boiling water. When this solution is exposed to the air, it is soon covered with a thick pellicle, which falls to the bottom, and is afterwards replaced by another. This is sulphate of potash, which is formed in contact with the air. The oxymuriatic acid gas combined with this solution, forms almost immediately thinning crystals of the sulphate of potash.

3. Charcoal heated with this salt in a retort, yields char-sulphurated hydrogen gas, and carbonic acid; and there remains in the retort, a hydrogenated sulphuret of potash.

3. Nitrate of Potash.

1. This salt is composed of nitric acid and potash, and is well known under the names of saltpetre and nitre. It has also been denominated salt of nitre, nitre of potash, or nitrated potash. It is one of the most important of the salts, not only on account of the attention which it has excited, in tracing its formation, and studying its nature and composition, but also on account of its numerous and valuable applications in domestic economy and in the arts.

2. The nitrate of potash exists ready formed in many plants, as in tobacco, borage, bugloss, pellitory. It has many been observed crystallized in needles in their dried plants stalks. According to some, it has been absorbed by the vegetable from the soil in which it grows, while others suppose that it is formed within the plant, from the elementary principles.

Nitre exists in great abundance on the surface of the earth in different parts of the world, especially in the warmer regions, as in India, Egypt, and South America. But the production of nitre is not limited to these countries. It is produced artificially in Germany and France, by means of what are called nitre beds. These are formed by collecting together the refuse of animal and vegetable matters, in which the putrefactive process is going on. They are mixed with earthy substances, but chiefly with calcareous earth, such as the rubbish from buildings, or collections of the soil in which lime abounds. All that is necessary to favour the formation of the nitre, is to moisten occasionally with water the mixture of the animal, vegetable, and earthy matters; to expose it to a moderate temperature, and to defend it from rains, which would carry off the salt as it is formed. This artificial production of nitre was greatly improved and extended by the French during the late war, when they were precluded.

(u) A salt is said to effloresce, when deprived of its water of crystallization in the ordinary temperature of the atmosphere. A powdery crust is first formed on the surface; and as the process goes on, the whole falls down into powder. The term efflorescence is opposed to deliquescence, by which the deliquescent substance attracts moisture from the air.

is now produced, it is said, in great abundance in France.

The nature of the process, and the change which takes place in this artificial production of nitre, will be understood by considering its component parts. The constituent parts of the nitric acid are azote and oxygen. The oxygen is furnished by the air; and unless there is a supply of air, no change takes place. A great quantity of azotic gas is given out by animal matters during the putrefactive process. But although these substances, when brought into contact with each other, do not combine to form nitric acid, it has been found by experiment, that azote, in its nascent state, or in the moment of evolution, enters into union with oxygen, and forms nitric acid, while the nitric acid thus formed combines with the potash which is furnished by the soil, or the vegetable matters.

3. After the nitre is formed, it is mixed with water, which is evaporated, and a salt is obtained of a brown colour, which is called crude nitre. This is a mixture of several salts, and from these the pure nitre is separated by other processes. When it is sufficiently purified, it is obtained in crystals of six-sided prisms, terminating in six-sided pyramids. The primitive form of its crystals is a rectangular octahedron, in which two faces of a pyramid are inclined to the other pyramid at an angle of 120°, and the two others at an angle of 111°. The form of the integrant molecule is the tetrahedron; but there are considerable varieties in the crystals of this salt, according as it is slowly or more rapidly evaporated.

4. This salt is distinguished by a cool, sharp, and bitterish taste. It is very brittle. When nitre in large crystals is reduced to powder, it is found to be a little humid; but that which is in the form of a white, opaque, irregular mass, yields a dry powder, on which account it is generally preferred for many purposes, particularly in the manufacture of gunpowder. The specific gravity of nitre is 1.9369. It is not altered by exposure to the air. At the temperature of 60° it dissolves in seven times its weight of water, and during the solution, a great degree of cold is produced. Boiling water dissolves twice its weight of this salt.

5. When the nitrate of potash is exposed to heat, it fuses before it becomes red, and is converted into a liquid of an oily consistence. It loses but very little of its water of crystallization, and if it be allowed to cool, it congeals into an opaque mass with a vitreous fracture, which is known by the name of mineral crystal. While it is melted, it undergoes no change; but when the temperature necessary for simple fusion is increased, it gives out oxygen gas to the amount of about \( \frac{1}{3} \) of its weight. Towards the end of the process, azotic gas is evolved, and the potash remains behind pure, so that the salt has been completely decomposed. But to effect this decomposition, a very strong heat is necessary. When only part of the gas is extracted, the nitrate of potash is converted into the nitrite.

6. When nitre is mixed with charcoal in the proportion of three parts of the former to one of the latter, a violent inflammation takes place, either by exposing the mixture to a red heat, or by bringing it into contact with a burning body. Or the mixture may be projected into a red-hot crucible, when a deflagration or detonation takes place, and when the re-potash, &c., is examined, it is found to be partly united with carbonic acid, or the carbonate of potash. This was formerly called nitre fixed by charcoal, or an extemporaneous alkali of nitre. The deflagration in this case is owing to the combustible matter, the charcoal, coming in contact with the oxygen which is evolved by the nitre, exposed to a high temperature. In another process, this experiment was performed in close vessels, to collect the elastic fluids which are disengaged; and besides the carbonic acid gas which is formed by the union of the carbure and oxygen, and the azotic gas disengaged by the decomposition of the nitre, a small quantity of water was found in the vessels. To this product the alchemists gave the name of elysium, and ascribed to it very wonderful properties in the preparation of the philosopher's stone.

7. A violent deflagration also takes place when phosphorus and nitre are treated in the same way. But this experiment should be performed with very small quantities, and with great caution. A mixture of nitre and phosphorus struck smartly with a hammer, produces a very violent detonation.

8. When sulphur is combined with three times its weight of nitre, it burns with great rapidity. This preparation was formerly made by detonating the two substances in a red-hot crucible. The product is sulphate of potash, known by the name of sal polyphosphat of Glauber. The sulphur combines with the oxygen of the nitric acid, and forms sulphuric acid, which enters into combination with the potash.

9. But one of the most important combinations of gunpowder is with charcoal and sulphur, in the formation of gunpowder. This substance was first known in Europe in the 14th century. It is said that it was known to the Chinese much earlier. The proportions of the materials which enter into the composition of gunpowder are,

| Nitre | 76 | |-------|----| | Charcoal | 15 | | Sulphur | 9 |

The materials are first reduced to a fine powder separately. They are then carefully mixed together, and formed into a paste with a little water. When the paste has dried a little, it is forced through a sieve, by which means it is reduced to grains of such a size as may be wanted. The powder is then dried in the air, or in the sun; and, after being dried, it is put into barrels which turn round by means of machinery, and thus by the friction of the grains of powder against the sides of the barrel and against each other, it is polished. This is called glazing the powder.

10. The theory of the combustion, and terrible effects of gunpowder is thus explained. The fulphur and the charcoal burn with great rapidity by the addition of the nitre with which they are intimately mixed. During the combustion carbonic acid gas, azotic gas, sulphurous acid gas, and according to some, sulphurated hydrogen gas, are formed. Water and ammonia also are said to be produced. But according to Mr Cruickshank, the quantity of water formed is not perceptible. The substances which remain after the deflagration are, carbonate of potash, sulphate and sulphuret. Potash, &c; sulphuret of potash, and some charcoal. It is obvious, that the irresistible effects of gunpowder are owing to the sudden evolution and expansive force of the elastic fluids which are formed and disengaged.

11. Another combination of nitre produces effects still more terrible. When three parts of nitre, two parts of potash, and one of sulphur, are previously well dried and mixed together by trituration, they form a compound which is known by the name of fulminating powder. A few grains of this mixture exposed to heat in an iron ladle first melt, assuming a darker colour; and when the whole is in fusion, there is a violent explosion. The heat should be applied slowly and gradually, till it is completely fluid, and then by bringing it nearer the heat, the full effect of the explosion is obtained. This combustion and explosion are also owing to the instantaneous evolution of elastic fluids. The potash unites with the sulphur, and forms a sulphuret, which, with the assistance of the nitre, is converted into sulphurated hydrogen. At a certain temperature the sulphurated hydrogen gas is disengaged, along with the oxygen gas of the nitre, and suddenly taking fire, strikes the air by the explosion which accompanies the evolution of the gases. When the mixture is made with equal parts of nitre and solid sulphuret of potash, the detonation is more rapid, but the explosion is less violent. With three parts of nitre, one of sulphur, and one of sawdust, well mixed together, what is called powder of fusion is formed. If a little of this powder is put into a walnut shell, with a thin plate of copper rolled up, and the mixture set fire to, it detonates rapidly, and reduces the metal to a sulphuret, without any injury to the shell.

12. A mixture of equal parts of nitre and tartar detonated in a crucible, gives a product which is much employed in metallurgy. This compound, called white flux, is a mixture of pure potash with the carbonate. When one part of nitre and two of tartar are treated in the same manner, the product obtained is a mixture of potash and charcoal. From its black colour, it is known under the name of black flux. This also is employed for a similar purpose.

13. Nitrate of potash, according to Bergman, is composed of

\[ \begin{align*} \text{acid} & : \quad 31 \\ \text{potash} & : \quad 61 \\ \text{water} & : \quad 8 \end{align*} \]

According to Kirwan, it is composed of

\[ \begin{align*} \text{acid} & : \quad 44 \\ \text{potash} & : \quad 51.8 \\ \text{water} & : \quad 4.2 \end{align*} \]

14. Nitre is not only employed for the purposes already mentioned, but it is used in medicine as a cooling remedy in feverish disorders, and as a diuretic in urinary affections. It is employed also in many arts, as in dyeing, and in domestic economy, for the preservation of animal matters, which are to be used as food. To these substances it imparts a red colour. From nitre, nitric acid is obtained, by decomposing it by means of sulphuric acid. Nitre is also employed to burn along with sulphur in the formation of sulphuric acid.

4. Nitrite of Potash.

This salt cannot be formed by direct combination of the nitrous acid with potash; but if a quantity of nitre be exposed for some time in a crucible or retort, to a strong heat, it becomes deliquescent and acid. It changes the blue colours of vegetables into green, attracts moisture from the air, detonates feebly with combustible substances, and gives red thick vapours by the action of sulphuric, nitric, muriatic, phosphoric, and fluoric acids. This is the nitrite of potash, which is decomposed by these acids, and gives out the red fumes of nitrous acid. Little more is known of the nature of this salt, with regard to its form, solubility, affinities, or proportion of its constituent parts.

5. Muriate of Potash.

1. This salt was formerly known by the name fæbri-name: fæge salt of Sylvius. It was afterwards called diglative salt, regenerated sea salt, and by Bergman salified vegetable alkali.

2. It is prepared by the direct combination of muriatic acid and potash. The solution is evaporated till a pellicle appears, when it is set by crystallization.

3. The crystals are in the form of regular cubes, or proper rectangular parallelopipeds. It has a disagreeable bitter taste, and by this is easily distinguished from muriate of soda or common salt. The specific gravity of this salt is 1.856. When the air is moist, it deliquesces; but when the air is dry, it parts with its moisture. Three parts of cold water are sufficient for its solution. Boiling water dissolves a little more, but regular crystals cannot be obtained by cooling. The solution must be left to flow spontaneous evaporation.

4. When the muriate of potash is exposed to heat, it decrepitates, loses its crystalline form, and falls into powder by the separation of .08 parts of its weight of water. When it acquires a red heat, it melts; if the temperature be elevated, it is sublimed in the form of white vapour, unchanged. After complete fusion, if it is allowed to cool suddenly, it becomes solid, and divides on the surface, into many small plates of a square form.

5. This salt is decomposed by means of the sulphuric and nitric acids. The first disengages the muriatic acid with effervescence in the gaseous form. By the action of the nitric acid the muriatic acid is converted into the oxymuriatic by combining with the oxygen of the nitric acid. With one part of nitric acid and two parts of muriate of potash, a compound of the two acids is formed, which was formerly employed in the solution of gold. This is a nitro-muriatic acid, or aqua regia.

6. This salt is no longer employed in medicine. It is recommended to be used for the decomposition of nitrate of lime in the mother waters of nitre, to obtain the nitrate of potash, and also for procuring the crystallization of alum.

6. Hyper-oxymuriate of Potash.

1. This singular salt was the first known of all the combinations with the acid in this state. Fourcroy and Hilf mentions

Dr Higgins prepared this salt, which he calls nitre, by passing the oxymuriatic acid gas into a solution of potash; but he seems to have paid no farther attention to it, except observing, that it detonated on red-hot coals (x). It was first formed, and its nature and properties were first investigated, by Berthollet. And since its discovery, it has been particularly examined by Lavoisier, Dolfuz, Vannons, Fourcroy, and Vauquelin, on the continent, and in England by Hoyle and Chenevix. The method of preparing this salt has been already described (at No 556, p. 520.) in treating of hyperoxymuriatic acid. After the salt has been removed from the solution in which it crystallizes, it may be purified by dissolving it in boiling water. The solution may be filtered, and allowed to cool, when the crystals are depolished.

2. The crystals of this salt are most commonly in the form of square plates or of parallelepipeds, of a shining silvery white colour. The primitive form of the crystals is an obtuse, rhomboidal prism; they are very transparent and brittle; the taste is cool, pungent, and disagreeable, very different from that of nitrate of potash. When it is rubbed smartly, it phosphoresces, and gives out a great quantity of sparks or luminous traces.

3. It becomes yellow after long exposure to the air, but is otherwise not changed. It is soluble in about 20 parts of water at the ordinary temperature of the atmosphere; but boiling water dissolves about one-third of its weight, so that the whole is nearly crystallized by cooling.

4. When this salt is exposed to heat, although it contains a considerable proportion of water of crystallization, it fuses quietly; and when the heat is increased, it gives out a quantity of oxygen gas nearly equal to one-third of its weight. This is the purest oxygen gas that can be obtained.

5. But the most extraordinary effects of this salt are those produced by its action on combustible substances.

a. If a small quantity of charcoal reduced to powder and this salt be rubbed together in a mortar, there is a slight explosion, and the charcoal is inflamed.

b. Three parts of the salt with one of sulphur, rubbed together in a mortar, produce a violent detonation. Or, if the same mixture is struck with a hammer on an anvil, there is an explosion like the report of a pistol (y).

c. The same effect is produced by employing phosphorus, and treating it in the same way with this salt. One or 1½ grains of the salt should first be reduced to powder, and brought together to one place in the bottom of the mortar, and then introducing the phosphorus, and rubbing it strongly on the salt, a violent explosion will instantly take place. A similar detonation may be produced with the same substances, by percussion.

d. Three parts of the salt, one-half part of sulphur, and one-half charcoal, give more rapid and stronger detonations, with the evolution of a very bright flame. Detonations are also produced, by treating this salt with sugar, gums, oils, and some metallic substances.

6. When concentrated sulphuric acid is poured upon this salt, there is a considerable detonation; it is thrown about to a great distance, sometimes with a red flame; and there is exhaled a brown vapour, accompanied with a strong odour of oxymuriatic acid. Even when a lighted taper is brought into contact with the gas which is disengaged, it explodes more violently than when the acid first came in contact with the salt. In some cases, the explosion was so sudden and so violent, that it broke the vessels in which the mixture was made. This happened to Mr Hoyle of Manchester, and afterwards to Mr Chenevix; so that experiments with sulphuric acid and this salt, should be conducted with small quantities, and with great caution. If concentrated sulphuric acid be poured on any of the mixtures of this salt with sulphur, charcoal, the metals, or with sugar, there is an instantaneous inflammation, the most brilliant that can be conceived. There is no detonation, but the combustion is extremely rapid, and the odour of oxymuriatic acid is perceptible. Concentrated nitric acid poured upon this salt, causes it to crackle and effervesce, but without explosion, and without flame; oxymuriatic acid gas is disengaged. With the muriatic acid this salt produces effervescence, with the evolution of a considerable quantity of gas, similar in colour and smell to oxymuriatic acid gas; but in some of its properties considerably different. This gas is more rapidly absorbed by water. If a small jar or bottle be filled with this gas, and a slip of paper moistened with ether be introduced into it, and the mouth of the jar be slightly covered to prevent the contact of air, an explosion takes place, with a deposition of charcoal. A similar experiment may be made, by moistening a feather with oil of turpentine, and introducing it into the jar filled with this gas. It instantly takes fire with a red flame, and a great quantity of black smoke.

7. According to the analysis of this salt, as given by Fourcroy, it consists of:

| Component | Quantity | |-----------------|----------| | Muriate of potash | 67 | | Oxygen | 33 | | **Total** | **100** |

But according to the experiments of Mr Chenevix, its constituent parts are,

| Component | Quantity | |-----------|----------| | Acid | 4 B |

(x) "The acid elastic fluid (says Dr Higgins), which issues when two pounds of manganese are mixed and distilled with two or three of ordinary spirit of sea salt (muriatic acid), may all, except a small portion of phlogistic air, be condensed in a solution of fixed vegetable alkali; and the solution, thus impregnated, yields a considerable quantity of nitre, which crystallizes in the ordinary form, and detonates on red-hot coals. The solution at the same time yields regenerated sea-salt (muriate of potash)." Higgins, Exper. p. 181.

(y) In experiments with this salt, the quantity employed should never exceed one or two grains, at least by those who have not been previously acquainted with its terrible effects. 8. This salt has been employed in bleaching; but other substances, particularly lime, have been substituted for the potash; so that at present it is more rarely used. It was proposed by M. Berthollet, when he first observed its effects, to employ it as a substitute for nitre in the manufacture of gunpowder; and when it was tried in the way of experiment, it seemed to be more powerful than the usual component parts of powder; but when it was attempted to be made in the large way, at Effione, in the year 1788, a dreadful accident, which happened by the spontaneous explosion of the mixture, in the death of M. le Tors, and Mademoiselle Chevraud, prevented its effects from being fairly proved. The danger which attends the trituration of the proper materials with this salt, has precluded any future attempt.

7. Fluate of Potash.

This salt has only been examined by Scheele and Bergman. It is the combination of fluoric acid with potash. When the acid is saturated, there is formed a gelatinous mass, which does not crystallize, and which has a slightly acid saline taste. When it is evaporated to dryness, and exposed to the air, it attracts moisture. If it be strongly heated in a crucible, it fuses without effervescence. It then becomes caustic, is very soluble in water, and is decomposed by the sulphuric and nitric acids.

8. Borate of Potash.

This is a compound of the boracic acid and potash; but very little is known of its nature and properties. It is prepared by decomposing nitre by means of the boracic acid with the assistance of heat. The heat drives off the nitric acid, and there remains behind a white, half-fused porous mass, which is soluble in water, and yields by evaporation and cooling, small crystals. The same salt may be formed by direct combination of the boracic acid and potash. This salt seems to be analogous in many of its properties to borax.

9. Phosphite of Potash.

This combination of phosphoric acid with potash was announced and described by Lavoisier in the year 1774. Its properties have been more carefully investigated by Vauquelin; but from the investigation of other chemists it appears, that there are two salts formed from the same acid and base; the one in which they are neutralized, and the other in which there is an excess of acid.

a. Superphosphate of Potash, is formed by the direct combination of phosphoric acid and potash. This salt does not crystallize, but exists in a gelatinous form, and has a fetidish saline taste. Its specific gravity, when dry, is 2.8516. It is very soluble in water; it attracts the moisture from the air, and becomes thick and viscid.

b. Phosphate of Potash.—This salt may be formed by exposing pure potash and the former variety to a strong heat. The alkali combines with the excess of acid, and neutralizes the whole. By the action of heat, a white-colored substance is obtained, which is heat-resistant. It is scarcely soluble in cold water, but soluble in hot water; and as the solution cools, there is deposited a thinning gritty powder. This salt is very fusible. Before the blow-pipe it melts into a transparent bead, which becomes opaque on cooling.

2. This salt is soluble in nitric, muriatic, and phosphoric acids, and forms with them thick glutinous solutions. It has not yet been applied to any use.

10. Phosphite of Potash.

This salt is prepared by dissolving carbonate of potash in phosphoric acid. The solution is evaporated, and it deposits crystals of the phosphate of potash. It has a sharp saline taste. It is crystallized in four-sided rectangular prisms with dihedral summits. It is very soluble in water, requiring only three parts of it for solution. It is not altered by exposure to the air.

11. Carbonate of Potash.

1. This salt, which is a compound of carbonic acid and potash, has been known under a great variety of names, in some measure descriptive of its properties, before its composition was discovered by Dr Black.

2. This salt is obtained from vegetable matters by burning, and washing out the salt and evaporating it; but the potash obtained in this way is not fully saturated with carbonic acid. After it has been purified from foreign ingredients, the saturated carbonate of potash may be prepared by exposing a pure solution of potash to carbonic acid gas, as it is disengaged from fermenting liquors. The carbonate of potash, as it is formed, crystallizes in the solution. The crystals may be taken out and dried upon unlined paper, and put up in well-closed bottles. Or it may be prepared by passing a current of carbonic acid gas, disengaged from the carbonate of lime by an acid, into a solution of potash, in tall narrow bottles. The carbonate crystallizes at the surface of the liquid. It may also be obtained by the process of Berthollet, which is to distill with an unfatuated solution of potash, solid carbonate of ammonia, from which the potash carries off the carbonic acid, while the ammonia is disengaged in the state of gas.

3. The carbonate of potash crystallizes in quadrangular prisms, terminated by quadrangular pyramids. It has a sweet alkaline taste, and changes vegetable blues to a green colour. The carbonate of potash requires very near four times its weight of water to dissolve it. At the boiling temperature it dissolves five-sixths of its weight. It does not crystallize by cooling, but only by slow evaporation. Pelletier has observed, that carbonate of potash dissolved in boiling water, gives out bubbles of carbonic acid gas, which shows that this salt loses a portion of its acid at this temperature. Its specific gravity is 2.012. When it is exposed to the air, it soon effloresces. When it is deliquescent,

4. When it is exposed to a flight degree of heat, it loses its water of crystallization. Part of its carbonic acid also separates from it, but the whole cannot be driven off by this process. The last portions adhere with a very strong affinity.

5. When the carbonate of potash is heated with sulphur at a high temperature, the acid escapes in the state of gas; and there is formed a sulphuret, at the moment of the effervescence produced by the extraction of the acid.

6. All the acids hitherto discovered, have the property of separating the carbonic acid from potash, and of forming with its base particular salts. This salt loses more than a third of its weight, by being deprived of its carbonic acid. The component parts of carbonate of potash are, according to,

| Bergman, Pelletier, Kirwan. | |-----------------------------| | Carbonic acid, 20 43 43 | | Potash, 48 40 41 | | Water, 32 17 16 | | **100** | **100** | **100** |

7. Potash of commerce is never saturated with carbonic acid. It is in this state that the carbonate of potash is generally employed. It has a stronger alkaline taste, and is more acid and corrosive. It soon liquefies when exposed to the air. It does not combine with a greater proportion of carbonic acid, merely by exposure to the atmosphere. For the purposes of the manufacturer it is of great importance to be able to ascertain, by a simple test, the quantity of pure potash in the different kinds which are brought to market. Mr Kirwan has proposed to discover the proportion of the salt, by determining the quantity of the earth of alum which is precipitated by the potash. A different method has been proposed by Vauquelin with the same view. His method is to saturate a given weight of the salt with nitric acid of known density. He has also made a number of experiments to discover the quantity of foreign ingredients in different kinds of potash. The following table shows the kinds of matter and the proportions in six species of potash*.

| Potash of Russia, | Sulphate of Potash. | Muriate of Potash. | Insoluble Refuse. | Carbonic Acid and Water. | Total. | |------------------|---------------------|--------------------|-------------------|--------------------------|-------| | 772 | 65 | 5 | 56 | 254 | 1152 | | Potash of America, | 857 | 154 | 20 | 2 | 119 | 1152 | | American pearl-ash, | 754 | 80 | 4 | 6 | 308 | 1152 | | Potash of Treves, | 720 | 165 | 44 | 24 | 199 | 1152 | | Potash of Dantzig, | 603 | 152 | 14 | 79 | 304 | 1152 | | Potash of Voges. | 444 | 148 | 510 | 34 | 304 | 1140 |

12. Arseniate of Potash.

1. The compound of arsenic acid and potash forms a salt which does not crystallize. When evaporated to dryness, this salt deliquesces in the air, gives a green colour to syrup of violets without changing the tincture of turpentine.

2. When strongly heated it fuses into a white glass; and by the contact of silica and alumina in the crucible it passes to the acidulous state, having been deprived of part of the potash. Exposed to a red heat, in close vessels with charcoal, the arsenic is sublimed. It is decomposed by the sulphuric acid. It decomposes salts which have bases of lime and magnesia; forming in the solution arseniates of lime and magnesia*.

Superarseniate of Potash.—If the arsenic acid be added to the arseniate of potash till it no longer change the colour of violets, but reddens that of turpentine, it yields regular transparent crystals in quadrangular prisms, terminated by tetrahedral pyramids. This salt is the arsenical neutral salt of Macquer. He obtained it by decomposing the nitrate of potash, by means of the white oxide of arsenic, employing equal parts of each. It is different from the former, because it crystallizes, reddens vegetable blues, and does not decompose salts with a base of lime or magnesia.

13. Tungstate of Potash.

1. This compound of tungstic acid and potash, is prepared by dissolving the oxide of the metal in a solution of pure potash, or its carbonate. The alkali is not fully neutralized. The salt precipitates from the solution by evaporation, in the state of a white powder.

2. It is distinguished by a caustic metallic taste, deliquesces in the air, and is soluble in water. This solution in water is decomposed by all the acids which produce a white precipitate. This precipitate is a triple salt, differing according to the nature of the acid which is employed†.

14. Molybdate of Potash.

1. The compound of molybdic acid and potash is prepared by detonating three parts of nitre and one of sulphuret. Potash, &c., sulphuret of molybdena in a crucible; or by combining directly the molybdic acid with potash. The salt affords small irregular crystals, from its saturated solution in boiling water. According to Klaproth, the crystals are in the form of small rhomboidal plates, of a thin appearance, and heaped together.

2. The taste is metallic. When exposed to the blow-pipe on charcoal, they fuse rapidly, without swelling up, and are converted into small globules, which are absorbed by the charcoal. In a silver spoon they are melted by the blow-pipe into small gray particles, which shrink on cooling, and deposit, during the process, a whitish powder. This salt is completely soluble in distilled water with the assistance of heat. It has an excess of acid, and is therefore an acidulous molybdate of potash, or supermolybdate of potash. It is decomposed by the nitric acid, which unites with the alkali, and precipitates the molybdic acid in the form of small crystals.

15. Chromate of Potash.

Nothing farther is known of the nature of this salt, than that it is easily formed by the combination of the chromic acid with potash, and that the crystals are of an orange colour, which sufficiently distinguishes them from the crystals of all other salts.

16. Columbite of Potash.

Columbic acid, digested for an hour with a solution of potash, affords this salt by evaporation and cooling, in the form of white glittering scales, resembling the concrete boracic acid. It is not changed by exposure to the air, has a disagreeable acid taste, and is not very soluble in cold water; but after it is dissolved, the solution is perfect and permanent. It is decomposed by nitric acid, and precipitates in the form of white powder.

17. Acetate of Potash.

1. This salt, which is a compound of acetic acid and potash, has been long known under a variety of names, which were derived from the substances from which it was obtained; or, from its properties and effects. It was called regenerated tartar, secret foliated earth of tartar, essential salt of wine, digestive salt of Sylvius, diuretic salt. It may be formed by saturating carbonate of potash with distilled vinegar, and by evaporating the solution slowly to dryness. When the heat is too great, the acid is decomposed, and the salt assumes a brown colour.

2. This salt has a pungent, and somewhat alkaline taste. Exposed to the air, it becomes moist. It is very soluble in water, and if the solution be diluted, it is spontaneously decomposed in close vessels. Thick, mucous flakes are deposited.

3. When it is heated, it melts and froths up, and is then decomposed and charred. When distilled in a retort, it yields an acid liquid, an empyreumatic oil, and a great deal of carbonic acid gas, and carbonated hydrogen gas. In this process the acid is completely decomposed; what remains in the retort is potash mixed with charcoal. According to Proust, this acid liquid contains ammonia and the prussic acid, and the carbonate and prussiate of potash are found in the retort.

4. This salt is decomposed by the strong acids. If filled with sulphuric acid, it yields an acetic acid which is very acid. The component parts of the acetate of potash are, according to Dr Higgins,

\[ \begin{align*} 38.5 \text{ Acid and water}, \\ 61.5 \text{ Potash}. \end{align*} \]

18. Oxalate of Potash.

The compound of oxalic acid and potash may be formed by direct combination of the acid and the alkali. The oxalic acid combines in two proportions with potash, either in a small quantity, or in sufficient quantity to saturate the potash. When the acid is in excess, it is called the acidulous oxalate, or superoxalate of potash.

1. The oxalate of potash is formed by completely saturating the oxalic acid with potash; and by adding an excess of the alkali, crystals are obtained.

2. Without this excess of acid, the salt does not crystallize, but assumes a gelatinous form.

3. When this salt crystallizes, it is in the form of fixed prisms, with two-sided summits. It is decomposed by heat, and also by the strong acids, which deprive it of a portion of the potash, and convert it into the acidulous oxalate. With an addition of oxalic acid the acidulous oxalate is also formed.

Superoxalate of Potash.—This salt exists ready made in the rumex acetosa, and the oxalis acetosella plants; hence it has been distinguished by the name of salt of sorrel, because it is extracted from this plant.

2. This salt may be formed by gradually combining potash with a saturated solution of oxalic acid. When a sufficient quantity of the alkali has been added, the salt is precipitated in crystals. Scheele discovered that the salt which is extracted from these plants, is in this state of combination. He proved the existence of the acid, and he showed that the natural salt might be imitated by this process.

3. The crystals of this salt are in the form of small opaque parallelepipeds. The taste is acid, pungent and bitter. It is not very soluble in cold water, but soluble in about ten times its weight of boiling water. Exposed to the air, it undergoes no change. It is decomposed by heat.

19. Tartrate of Potash.

1. This is a compound of tartaric acid and potash. It has been long known under the name of soluble tartrate, and vegetable salt. It is formed by adding tartar or cream of tartar to a hot solution of carbonate of potash. The additions of the tartar are to be continued as long as there is any effervescence. The solution is then boiled for half an hour, filtered and evaporated, till a pellicle appears on the surface, and when it is allowed to cool slowly, it deposits crystals.

2. The crystals of this salt are in the form of long rectangular prisms, terminated by two-sided summits. This salt has a bitter taste. The specific gravity is 2.5567. Exposed to the air it is deliquescent. Four parts of cold water dissolve one of the salt; hot water dissolves a greater quantity. When heated, it swells up and blackens. By distillation it yields an acid liquid, some oil, and a great quantity of gas. It leaves behind behind a considerable portion of alkali, mixed with charcoal. It is decomposed by the stronger acids, which deprive it of a portion of its potash, and reduce it to the acidulous tartrate, which is precipitated in the solution. By the addition of tartaric acid to the solution of this salt, it is also converted into the acidulous tartrate.

**Supertartarate of Potash.**—1. This is a compound of tartaric acid with potash, but with an excess of acid. The substance which is well known under the name of tartar, and which is found encrusted on the bottom and sides of vessels in which wine has been kept, is the supertartarate or the acidulous tartrate of potash; but in this state it is very impure. It is purified by solution in boiling water, and by filtration while it is hot. When it cools, there is a copious deposition of the pure salt in crystals. These are the crystals or cream of tartar.

2. It had been long known to chemists, that potash could be obtained from tartar, by exposing it to a strong heat, which produced a controversy whether the alkali existed ready formed in the tartar, or whether it was not, in some way or other produced by the action of heat during the process. This point was not fully settled till Scheele discovered the method of extracting the acid, the other component part of tartar.

3. The crystals of tartar are in the form of small irregular crystals, but chiefly of six-sided prisms. This salt has an unpleasant acid taste, is very brittle, and its specific gravity is 1.953. It requires for its solution 30 parts of boiling water, and 60 of cold water. It undergoes no change when exposed to the air, but in the solution in water the salt is decomposed, depositing a mucous matter, and leaving behind an impure carbonate of the alkali.

4. Exposed to heat, it melts, swells up, blackens, and the acid is totally decomposed. When it is distilled, an oily matter, and an acid liquid, which is an impure acetic acid, with a great quantity of carbonic acid, are obtained. This acid was formerly called pyrotartarous acid (z).

5. The component parts of tartar, according to Bergman are,

| Acid | 77 | |------|----| | Potash | 23 |

Or of the saturated salt,

| Tartrate of potash | 56 | |-------------------|----| | Acid | 44 |

By the analysis of Thenard, it is composed of

| Acid | 57 | |------|----| | Potash | 33 | | Water | 7 |

97 *

(z) The pyrotartarous acid, the pyromucous, and the pyrolignous acids, were discovered by Fourcroy and Vauquelin to be nothing else than the acetic acid impregnated with extraneous substances, particularly with what is called an empyreumatic oil. See Annales de Chimie, xxxv. p. 161.

20. Citrate of Potash.

This compound of citric acid with potash may be formed by combining together 36 parts of the acid with 6x parts of the carbonate of the alkali. This salt is very soluble in water, but little disposed to crystallize. It is very deliquescent. According to the analysis of Vauquelin, it consists of

| Acid | 55.55 | |------|-------| | Potash | 44.45 |

100.00

21. Malate of Potash.

This salt, which is a compound of malic acid and potash, is deliquescent, and very soluble in water, but its properties are little known.

22. Gallate of Potash.

The compound of gallic acid and potash has little solubility in water, but its other properties are unknown.

23. Benzoate of Potash.

This salt, composed of benzoic acid and potash, crystallizes on cooling, into small needles. A drop of the solution spread on the side of the vessel, as it evaporates, exhibits an arborealcent crystallization. It has a sharp saline taste, is deliquescent in the air, and very soluble in water.

24. Succinate of Potash.

This compound of succinic acid and potash, forms crystals in three-sided prisms; the taste is bitter and saline; it deliquesces in the air, and is very soluble in water.

25. Saccolate of Potash.

This is the compound of saccharic acid and potash. It forms small crystals, which are soluble in eight times their weight of boiling water.

26. Camphorate of Potash.

1. This salt, which is a combination of camphoric preparatory acid and potash, may be formed by saturating a solution of carbonate of potash with camphoric acid. When the effervescence has ceased, the solution is to be evaporated with a gentle heat, when it affords crystals by cooling.

2. The camphorate of potash is in the form of regular hexagonal crystals, which are white and transparent; the taste is bitterish and slightly aromatic. Exposed to the air, when it is moist, the salt loses its transparency; but if the air is dry, there is no change. It is soluble in four parts of boiling water; but in water at the temperature of 60°, it requires 100 parts.

3. Exposed to heat before the blow-pipe, it burns with heat. Potash, &c. with a blue flame, and the potash remains behind pure.

When the heat is stronger, it froths up, the acid is sublimed, and it gives out a thick smoke, which is slightly aromatic.

4. It is decomposed by the mineral acids. If the solution be much diluted with water, the decomposition is not perceptible; but if brought to the confluence of a thick syrup, the camphoric acid crystallizes in cooling. A new salt also is partially crystallized. By solution in cold water the acid may be separated.

5. The camphorate of potash is soluble in alcohol, and it burns with a deep blue flame.

6. It is decomposed by, 1. Nitrate of barytes and of silver; 2. By all the salts whose base is lime; 3. Sulfate of iron; 4. Muriate of tin and of lead.

27. Suberate of Potash.

1. This salt, which is a compound of fumaric acid with potash, is formed by saturating the acid with the crystallized carbonate of the alkali.

2. It crystallizes in four-sided prisms, which have unequal sides. The taste is bitter and saline. It reddens vegetable blues, and is very soluble in water.

3. Exposed to heat, it swells up and melts; the acid is distillated, and the potash remains behind. It is decomposed by the mineral acids, which combining with the potash, precipitate the fumaric acid. It is decomposed also by barytes, by all the metallic salts, by sulfate and phosphate of alumina, by the nitrates and muriates of lime and of alumina.

28. Mellate of Potash.

The mellitic acid combines with potash, and forms this salt, which is fully saturated with the acid, and in this state it crystallizes in long prisms; but with an additional portion of acid, an acidulous mellate, or supermellate, is formed. This salt, as Vauquelin observes, also crystallizes; but the properties of these salts have not been much examined.

29. Lactate of Potash.

This salt is only known as being deliquescent, and soluble in alcohol.

30. Prussiate of Potash.

The compound of prussic acid and potash, is formed by dissolving the alkali in the acid. The salt is very soluble in water, produces a green colour on vegetable blues, and with the application of a moderate heat, it is decomposed.

31. Sebate of Potash.

This salt has been little examined. According to the experiments of Thenard, it has little taste, is not affected by exposure to the air, and is decomposed by the sulphuric, nitric, and muriatic acids: the solution, if it be concentrated, becoming solid on the addition of the acid from the crystallization of the sebacic acid.

32. Urate of Potash.

This compound of the uric acid with potash, is formed by triturating the acid with the alkali. The mixture assumes the form of a saponaceous paste, which is very soluble in water, when there is an excess of the alkali, but less so when the acid is saturated. This soda salt has little taste; when neutralized is not very soluble in water, and seems little disposed to crystallize. It is decomposed by the muriatic acid.

IV. Compounds of Potash with Inflammable Substances.

1. Potash is very soluble in alcohol. The solution affumes a red colour, and becomes acid. It is by a solution of potash in alcohol, that the former is obtained in a state of purity; for the alcohol dissolves the potash, while other substances are deposited. By the application of heat to this solution, there is a partial decomposition of the alcohol.

2. Ether has no perceptible action on potash.

3. Potash readily enters into combination with the fixed oils, but particularly with that class of them denominated fat oils; and forms with them very important compounds, namely, soaps. The compound with potash and the fat oils is a soft soap.

4. Potash also enters into combination with the volatile oils, but in very small proportion, which likewise forms a species of soap.

Sect. II. Of Soda and its Combinations.

1. Soda, the other fixed alkali, has been distinguished by a great number of different names. It was called fayal or mineral alkali, because it was supposed that it only existed in the mineral kingdom. It is the substance which is mentioned in Scripture as a detergent, under the name of nitre.

2. This alkali exists in great abundance in different parts of the earth, and particularly on the surface of the soil in Egypt, where it is distinguished by the name of natron. It is also found on the walls of caves and places under ground, and old edifices.

But the soda of commerce is generally obtained from different species of plants which grow on the sea-shore; and as it is prepared from them, it has received different names in different countries. The saltpeter soda yields this alkali in greatest abundance. This plant is called barilla in the Spanish language, and from this the soda which is prepared on the shores of that country, has been called barilla ashes. For the purposes of commerce also, soda is prepared in great quantities from the ashes of another tribe of marine plants, namely the algae, and particularly from the fucus, all of which yield it in greater or less proportion. As it is prepared from these plants, it is known in France by the name of warec, and in Britain by the name of kelp. Soda exits in great abundance in the waters of the ocean. There it is in combination with the muriatic acid, forming the well-known compound of common salt.

3. In many of their properties soda and potash approach very near to each other. They were accordingly considered as the same alkali, till, towards the middle of the 18th century, by the experiments of Duhamel, Pott, and Margraff, they were distinctly characterized, and the properties of each fully ascertained.

4. The soda of commerce is in very different degrees of purity, according to the care and attention with which it is prepared, and the purposes for which it is intended. To have it perfectly pure, it must be subjected jected to a similar process with those which have been already detailed for the purification of potash; and by means of these processes it may be procured in a solid and crystalline form.

5. When soda is in a state of purity, it is usually in the form of solid plates, of a grayish white colour, and the taste exactly similar to that of potash. It is also extremely caustic and corrosive. By slow evaporation from a solution in alcohol, it assumes the form of prismatic crystals; but these, when exposed to the air, very soon effloresce, and fall to powder. Soda changes the blue colour of vegetables to green. Its specific gravity is 1.336. When it is exposed to heat, it softens, and readily melts. It liquefies by the action of heat like an oily matter, and when it becomes red-hot, boils, and is reduced to vapour, which is the soda unchanged, extremely acid, and corroding the skin when it comes in contact with it.

6. When exposed to the air, it first becomes moist and soft, by absorbing water and carbonic acid; but when the air becomes dry, it effloresces and falls into a powder; and in this respect is sufficiently distinguished from potash. Soda has a very great affinity for water. When the dry alkali is moistened with water, it is absorbed, and becomes solid, with the extrication of caloric. When more water is added, it dissolves, and also gives out heat, and a peculiar odour, which is no doubt owing to a portion of the alkali raised in the state of vapour along with the water.

7. Soda, as well as potash, is to be considered as a simple substance; for no attempt which has yet been made to decompose it has succeeded. Supported by certain analogies, Fourcroy is of opinion that soda is a compound of magnesia and azote; and he thinks this conjecture derives some degree of probability from the constancy with which magnesia accompanies soda in the waters, and different compounds, of which this alkali makes a part; especially in animal matters and marine productions. Vauquelin, he observes, has detected magnesia in considerable abundance in the ashes of the saltpeter soda; and the same earth is always obtained in great quantity during the process for the extraction and purification of soda.

8. The affinities of soda are the same with those of potash.

9. Soda is employed for many similar purposes as potash. On account of some of its qualities, it is preferred to potash, in many manufactures, because it is less acid and corrosive, and is therefore less apt to destroy the texture of animal and vegetable matters to which it is applied.

I. Action of Phosphorus on Soda.

Soda scarcely enters into combination with phosphorus. There is no phosphuret formed either by the dry or humid way; but when phosphorus is boiled with a pure solution of soda, phosphorated hydrogen gas is evolved in the same way as when it is treated with potash.

II. Action of Sulphur on Soda.

Soda readily combines with sulphur by simple trituration, by fusion, and by the humid way. In the two first cases, there is formed a sulphuret of soda, which may be decomposed by heat, and by the acids, and soda, &c., which decomposes water in the same way as the sulphuret of potash. By the humid way there is formed a hydrogenated sulphuret of soda, which has an extremely fetid odour, and emits, by the action of the acids which decompose it, sulphurated hydrogen gas.

Hydrofulphuret of Soda.

This may be prepared in the same way as the hydrofulphuret of potash. It forms a crystallized salt in the shape of four-sided prisms, terminated by quadrangular pyramids. The crystals are colourless, odorless, and very soluble in water. When this salt is exposed to the air, it deliquesces, and becomes of a green colour. It is decomposed by the action of acids. Soda, it would appear, has less affinity for sulphur and sulphurated hydrogen, than potash.

III. Compounds of Soda with the Acids.

1. Sulphate of Soda.

1. This salt, which is a compound of sulphuric acid and soda is well known under the name of Glauber's salt, from the name of Glauber, a German chemist, who discovered it, in examining the residuum of the decomposition of common salt by means of sulphuric acid. It has also been called the admirable salt of Glauber, vitriolated mineral alkali, and vitriol of soda.

2. This may be obtained by the direct combination of sulphuric acid and soda. But it is more commonly prepared by the decomposition of muriate of soda or sea salt, by means of sulphuric acid. The solution is then to be filtered, purified and crystallized in the usual way.

3. It crystallizes by slow evaporation, in transparent, fix-sided prisms, terminated by two-sided summits; but the crystals are seldom regular, and the sides of the Maneche prisms are furrowed. The taste is cool, bitter, and nauseous. The specific gravity is 1.4457.

4. When it is exposed to the air, especially when the air is dry, it effloresces, which is owing to the escape of air. The water of crystallization. It loses about 0.3 of its weight. It is very soluble in cold water, and it requires only 4ths of its weight of boiling water.

5. When it is exposed to heat, it melts on account of the great quantity of water of crystallization which it contains; and this is called the aqueous fusion. Afterwards it dries when the water is evaporated. It loses about 38 of its weight. To melt it afterwards, it must be exposed to a red heat long continued, which is called the igneous fusion. After it is cooled, it is found to have suffered no change. When water is added, it returns to its former state.

6. It is decomposed by means of charcoal, which at a red heat converts it into sulphuret of soda, by depriving the acid of its oxygen. The component parts Composition of this salt, according to Bergman, are

| Acid | 27 | |------|----| | Soda | 15 | | Water| 38 |

But But according to Mr Kirwan, it is composed of

| Crystalized | Dried at 70° | |------------|-------------| | Acid | 23.52 | | Soda | 18.48 | | Water | 58 |

100.00

It is decomposed by barytes and by potash, but less powerfully. Lime and fritonites are also capable of producing a partial decomposition in the humid way, and in contact with the air.

7. This salt is a good deal employed in medicine, as a purgative; in chemistry, for the purpose of decomposing other substances; and in the arts, for the extraction of soda.

2. Sulphite of Soda.

1. This salt, which is a compound of sulphurous acid and soda, was first taken notice of by Berthollet. It is prepared by passing sulphurous acid gas into a saturated solution of carbonate of soda. The sulphite of soda is precipitated at first, in a confused mass of very small crystals, which are re-dissolved in warm water, and crystallize again on cooling.

2. The crystals of sulphite of soda are in four-sided prisms, two broad, and two narrow, terminated by two-sided summits. They are perfectly transparent. The taste is cool and sulphureous. The specific gravity is 2.9566.

3. Exposed to the air, it effloresces, and the powder formed on the surface is converted into a sulphate. It is extremely soluble in water. Boiling water takes up more than its own weight. It crystallizes again on cooling, but sometimes the solution is formed into a single mass when it is exposed to the air; and if quickly cooled with agitation, it affords nothing but needle-formed crystals. This solution exposed to the air is converted into the sulphate.

4. This salt readily undergoes the aqueous fusion; if the heat be increased, a portion of sulphur is driven off, and it is converted into a sulphate.

5. It is decomposed by means of the acids, which disengage the sulphurous acid in the state of gas. The oxymuriatic acid gas brought into contact with a solution of this salt in water, instantly converts it into sulphate. It is decomposed by barytes, lime and potash; by the sulphates of lime, of ammonia, and of magnesia.

6. The component parts of this salt have been found by analysis to be,

| Sulphurous acid | 31 | |-----------------|----| | Soda | 18 | | Water | 51 |

100

It has not been applied to any use.

3. Nitrate of Soda.

1. This compound of nitric acid and soda was formerly known by the name of cubic nitre, and rhomboidal nitre. It is prepared by the direct combination of the acid with the alkali; or by decomposing the muriate or carbonate of soda by nitric acid.

2. It crystallizes in the form of rhomboids and prisms. The taste is cooling, but more bitter than that of the soda, nitrate of potash.

3. The specific gravity is 2.0064. Exposed to the air, it attracts moisture in a slight degree. It is soluble in three parts of cold water, and in less than its own weight of boiling water.

4. When it is thrown on red-hot coals, it decrepitates slightly; it is not so fusible as nitre, but it is also decomposed, and gives out oxygen gas mixed with azotic gas.

5. In its decomposition it is similar to the nitrate of potash. It detonates, however, less powerfully with combustible bodies, and burns them with less facility.

6. The proportions of its constituent parts are, according to Bergman,

| Acid | 43 | |------|----| | Soda | 32 | | Water| 25 |

100

According to Mr Kirwan,

| Acid | 53.21 | |------|-------| | Soda | 40.58 | | Water| 6.21 |

After being ignited.

| Acid | 57.55 | |------|-------| | Soda | 42.34 | | Water| 00.00 |

100.00

Chemists are not acquainted with the properties of this salt, although it is known to be formed after the partial decomposition of nitrate of soda by means of heat.

5. Muriate of Soda.

1. The muriate of soda, which is a compound of muriatic acid and soda, of all the other salts, from its great abundance in nature, and its valuable uses, was the earliest known under the name of salt. It has been distinguished by the names of common salt, kitchen salt, names sea-salt, and sometimes sal gem, rock salt.

2. This salt, which is found in such abundance in nature, is never formed by art. In some parts of the world it exists in the bowels of the earth in large masses, from whence it is dug out, and simply reduced to powder, to be applied to use. But to obtain it from the waters of the ocean, in which it exists in different proportion, according to the temperature, the climate, and other circumstances, it must be extracted by evaporation, which is effected by different processes, according to the strength of the solution, and the art of the manufacturer. In some parts of the world, all that is done is to collect the salt as it forms on the shores of the sea, or on the rocks, by the evaporation of the water; but, in general, some art is necessary, even when the salt is obtained by spontaneous evaporation. On the coasts of France, Spain, Portugal, and the shores of the Mediterranean, the sea water is admitted into ponds during the flowing of the tide, and its return is prevented by sluices which are shut. It is then evaporated by the heat of the sun; and, as this evaporation is gradual and slow, the salt crystallizes in large cubes, and it is known in commerce by the name of bay. bay salt, from the circumstance of its having been formed in creeks and bays of the sea.

3. But as this process can only be followed in those climates where there is a sufficient degree of temperature to promote the evaporation speedily; artificial heat is generally employed in the manufacture of salt. Sometimes the water is received in large ponds or flat vessels, where it is allowed to evaporate for some time in the open air. It is afterwards boiled in flat iron pans; and, during the boiling, the impurities which rise to the surface are removed. When the water is sufficiently concentrated by the evaporation, a pellicle forms on the surface, which is the crystallization of the salt. This falls to the bottom, and another pellicle forms, till the whole of the salt is crystallized. The purity of the salt and the size of the crystals depend on the slow evaporation; and hence it is, that the purest salt, as it is manufactured in Britain, is that which is called Sunday salt. This is obtained from the last quantity of water which is boiled on the Saturday night; and as it has time to cool slowly, the evaporation is more gradual, and the crystals are purer and larger.

4. But in this state the muriate of soda is far from being pure. A very ingenious method has been proposed for the purification of sea salt by Lord Dundonald. The salts with which common salt is impregnated, are more soluble in water than the salt itself, and they dissolve in much greater proportion in hot than in cold water. But common salt is nearly equally soluble in both. On this principle, therefore, the process proceeds: A quantity of salt to be purified is put into a conical vessel or basket, which is slightly stopped at the apex, so that the water may pass through. A saturated solution of common salt is then prepared. This solution of salt is poured boiling hot over the salt in the basket. It can dissolve none of the common salt in the basket, because it is already saturated; but, as it passes through, it dissolves the other salts, and carries them along with it. It was found by experiment, that a saturated solution of 1 lb. of common salt poured upon 10 lbs., removes about 5/8ths of all the foreign salts with which it is impregnated.

5. But, even after this process, the salt is not perfectly pure for the purposes of chemistry. For this purpose it may be dissolved in four parts of cold water. Filter the solution, to separate any substances with which it is mixed. Pour into it some drops of a solution of soda, till no farther precipitate is observed. The fluid is then to be evaporated, and the salt, as it forms on the surface in small cubical crystals, may be extracted; or it may be obtained in larger crystals by slow evaporation.

It may also be purified, by dropping into a solution of common salt, a solution of muriate of barytes, and then of carbonate of soda, as long as any precipitate is formed. The liquid may then be filtered and evaporated, till the solution crystallizes.

6. The muriate of soda crystallizes in perfect cubes; but from these there are several deviations in the form of its crystals. Sometimes the angles of the cubes are truncated; sometimes they are in the form of octahedrons; which is the case when common salt is dissolved in human urine, and allowed to evaporate spontaneously. But the primitive form of the crystal, as well as of the integrant particle, according to Hauy, is

the cube. The taste is sweetish and agreeable, and Soda, &c. is that which is properly called salt, with which all similar tastes are compared. The specific gravity is 2.120.

7. It undergoes no change by exposure to the air. Action of Common salt attracts moisture from the atmosphere; but this is owing to an impregnation of other salts which are deliquescent. These salts are muriate of magnesia, sulphate of magnesia, and sulphate of lime. It is from these that it is to be purified by the processes, which have been described above. It is soluble in little more than 2½ times its weight of water; and it is almost equally soluble in hot and cold water.

8. When it is exposed to a strong heat, it decrepitates and gives out its water of crystallization. It melts in a red heat, and rises in the air in the state of white vapour; but it is unchanged; for if this vapour be collected by condensing it in the cold, it is found to possess all the properties of common salt.

9. The muriate of soda is decomposed readily by Decomposition. fulphuric acid, as well as by several other acids which it have a stronger attraction for its base than the muriatic acid; or by the aid of double affinity, when an acid is in combination with a base, which at the same time acts on the muriatic acid. It is by means of the fulphuric acid that the chemist procures muriatic acid from the muriate of soda. Sometimes the salt is decomposed by the same acid to obtain the soda. The fulphuric acid combines with the soda, and forms sulphate of soda, while the muriatic acid is disengaged, and that it may not be lost, it is conveyed into a leaden chamber, which contains a solution of ammonia, where it forms sal ammoniac. The sulphate of soda is exposed to strong heat in a furnace, to drain off any portion of fulphuric acid that it may contain. It is then mixed with its own weight of chalk, and half its weight of charcoal in powder. The mixture is strongly heated in a reverberatory furnace, and occasionally stirred to permit the escape of gas and fulphur, which fly off. When the mass cools, it becomes solid and black. The charcoal, in decomposing the fulphuric acid of the sulphate of soda, sets the sulphur free, which combines with the lime of the carbonate of lime, and is partly sublimed; while a part of the carbonic acid combines with the soda; so that the product is a mixture of carbonate of soda, of lime and charcoal, analogous to the soda of commerce. In this way 58% of crude soda may be extracted. Other acids, as well as the fulphuric, such as the acetic, the phosphoric, and boracic, have been proposed to be employed with the same view; or indeed, any acid which has a stronger affinity for the soda than the muriatic acid, and is not decomposed with much difficulty.

10. But these processes are not sufficiently economical to answer the purposes of the manufacturer: Other processes have, therefore, been proposed and tried with the same view; but scarcely any has succeeded. This salt is very readily decomposed by barytes or potash, which combines with the muriatic acid, and sets the soda free; but the expense of preparing these substances far exceeds the price of the soda in the market, so that they cannot be employed to advantage.

It has been proposed to decompose sea salt by means of lime, for obtaining the soda. Soda is separated from the acid by mixing the common salt with lime, in the form of paste, and by exposing it to moisture. In a short time the soda appears on the surface in the state of efflorescence. Scheele, it is observed by Berthollet, was the first who noticed the decomposition of the muriate of soda by means of lime. He explains this decomposition by showing, that lime acts on salts with fixed alkaline bases. It decomposes a small part of the muriate of soda, with which it is in contact, and the soda, eliminated by this means, combines with the carbonic acid of the atmosphere. The carbonate of soda effloresces, so that it opposes all resistance to the action of the lime, and the decomposition of the muriate of soda continues until it is impeded by the quantity of muriate of lime formed. It is in this way that the same philosopher accounts for the formation of soda in the soil of Egypt. The circumstances necessary for this are, 1st, A sand containing a great quantity of carbonate of lime; 2nd, moisture; and 3rd, muriate of soda; and these circumstances are found to exist in those places where there is an abundant production of sea salt.

A manufactory for the purpose of extracting soda from sea salt, by means of lime, was established in France by Guyton.

Common salt is decomposed for the purpose of obtaining the soda, by means of litharge. In a mixture of four parts of litharge, and one of sea salt, with a little water, in the course of a few hours, a decomposition of the salt is effected. The muriatic acid of the salt combines with the lead, and is precipitated; while the soda remains in the solution, from which it may be separated by filtration and evaporation.

It has been found too, that sea salt may be decomposed by other metallic substances. Scheele observed, that iron produced this effect. By dipping a plate of iron in a solution of salt, and exposing it in a moist place, it was incrusted with soda. From other experiments it appears, that this decomposition may be effected by means of copper and zinc.

Muriate of soda, according to Bergman, is composed of:

| Acid | 52 | |------|----| | Soda | 42 | | Water| 6 |

According to Kirwan, when dried in the temperature of 80°, it is composed of:

| Acid | 38.88 | |------|-------| | Soda | 53.00 | | Water| 8.12 |

Common salt may be regarded almost as a necessary of life. It is the most useful of all substances for the preservation of animal matters which are intended for food. It is probable that it is highly useful, not merely as a seasoning for food, of which it is one of the most agreeable, but also to promote its digestion. It is also employed in many arts, as in metallurgy, in dyeing, and in the enamelling of stoneware.

6. Hyperoxymuriate of Soda.

This salt is prepared in the same manner as the combination of this acid with potash. It is, however, difficult to obtain it pure, as it has nearly the same degree of solubility in water as the muriate of soda. It is soluble in three parts of cold and less of warm water. It is also soluble in alcohol, and it seems to communicate a greater degree of solubility to the muriate of soda.

The crystals of this salt are in the form of cubes, or rhomboids. It produces the sensation of cold in the mouth, and its taste is easily distinguished from muriate of soda. It is decomposed by heat, by combustible bodies, and by acids, in the same manner as the hyperoxymuriate of potash.

This salt is composed of:

| Hyperoxymuriatic acid | 66.2 | |-----------------------|-----| | Soda | 29.6 | | Water | 4.2 |

7. Fluate of Soda.

This salt, which is a compound of fluoric acid and soda, is formed by saturating the acid with the alkali. If the solution be evaporated till a pellicle appears, crystals of fluate of soda are obtained.

These crystals are in the form of small cubes, have a bitter and astringent taste, are not deliquescent, and not very soluble in water. They decrepitate on hot charcoal, and melt before the blow-pipe into a transparent globule.

The concentrated acids disengage the fluoric acid with effervescence. This salt is also decomposed by limewater, barytes, and magnesia.

8. Borate of Soda.

This salt, a compound of the boracic acid and soda, is formed by saturating the acid with the alkali; but nothing is known of its nature and properties. The specific gravity is 1.1351. But the combination of soda with this acid, which is a natural production, has been particularly examined.

Sub-borate of Soda, or Borax.

This substance has been long known. Indeed it is supposed, that the ancients were acquainted with it, and that they employed it for several purposes, under the name of chrysocolla which is mentioned by Pliny. It received this name from them, it is supposed, from knowing its property of soldering gold and the other metals. The name borax is derived from some of the oriental languages. Although borax was the subject of research among the alchemists and earlier chemists, yet nothing was known of its nature and composition, till the beginning of the 18th century. It was then decomposed by Homberg, by exposing it to heat with sulphate of iron. The acid was separated by sublimation, and long after known by the name of the sedative salt of Homberg. In 1732 its real composition was discovered by Geoffroy. He obtained the acid crystallized in the humid way. In 1748 Baren decomposed posed borax by means of the vegetable acids, and he completed the knowledge of its composition, by forming it with the acid and the alkali. Bergman afterwards showed that borax is a salt with excess of soda; and to be neutralized, it requires one half of its weight of boric acid.

2. Borax is a natural production of the earth in many parts of the world. It is formed at the bottom of some lakes in Persia, the Mogul territory, in Thibet, in China and Japan. It has been also found in some lakes in Tuscany. In the East Indies it is known under the name of tincal, and in commerce under that of crude borax. In this state the borax is in the form of small, semitransparent, greenish crystals, intermixed with a greasy matter, of a dirty grey colour, and of a sweetish alkaline taste.

3. The purification of borax was originally in the hands of the Venetians; but it has since been practised, and now almost exclusively, by the Dutch. Their process is not exactly known. Valmont-Bomare, who visited one of these places in Holland, says, that 80 parts of purified borax are obtained from 100 of the crude materials; and to extract the salt completely, from eight to twelve solutions and crystallizations are necessary; that all the vessels employed in the purification of this salt, are either of lead, or covered with lead; but he adds, that one part of the process was concealed from him, and he suspects that lime-water may have been employed in this part of the process.

4. Borax, after being thus purified, is in the form of compressed six-sided prisms with three-sided summits. The taste is sweetish, and perceptibly alkaline. It changes the vegetable blues to a green colour. The specific gravity is 1.742. It effloresces slightly in the air, and is soluble in water. Twelve parts of water of the temperature of 65° dissolve one of borax. Six parts are only necessary at the boiling temperature.

5. When borax is exposed to heat, it readily melts. As the water of crystallization flies off, it swells up and acquires a greater bulk, and assumes the form of a porous mass. By this process it loses more than one-third of its weight, and in this state it is called calcined borax. When it is exposed to a red heat, it is converted into a transparent glass, which is soluble in water.

6. Borax is decomposed by all the acids which have a stronger affinity for the soda. It is by means of the sulphuric and the nitric acids, that boric acid is obtained from borax.

7. The component parts of borax, according to Kirwan, are:

| Component | Parts | |-----------------|-------| | Boracic acid | 36 | | Soda | 17 | | Water | 47 | | | 100 |

It is supposed that only five parts of the soda are saturated with the acid, and that the other twelve parts form the excess of alkali which is contained in the salt.

8. Borax is much employed in the arts, as a flux for metals, and to promote the soldering of the more precious metals. It is also employed by the mineralogist as a flux for treating minerals by the blow-pipe. Calcined borax is employed in medicine as an absorbent.

9. Phosphate of Soda.

This compound of phosphoric acid and soda, was first discovered by the combinations of phosphoric acid. Margraff was the first who extracted it from human urine, then in combination with ammonia, forming a triple salt, which was known by the name of fusible or microcosmic salt. Haupt afterwards obtained it separate, and distinguished it by the name of sal mirabile perlatum, or wonderful perlat salt, on account of its pearl-like colour. At last the younger Rouelle discovered that soda was one of its constituent parts. By some it was supposed, that the acid was different from the phosphoric, because no phosphorus could be obtained from it. To this acid Bergman gave the name of perlat acid; but by the analysis of Klaproth, it was proved that this salt consists of phosphoric acid and soda, with an excess of acid.

2. This salt is prepared by saturating the liquid acid preparation phosphate, which is obtained from burnt bones by the means of the sulphuric acid, with carbonate of soda, which must be added in excess. The carbonate and a little phosphate of lime are precipitated in the solution, which must be filtered and evaporated till a thin pellicle appears on the surface. The phosphate of soda is crystallized by cooling. Or it may be obtained by the direct combination of phosphoric acid and soda, which must also be added in excess.

3. The phosphate of soda crystallizes in lengthened rhomboids whose angles are often truncated, and sometimes it affords rhomboidal prisms, and several other varieties. The excess of soda is necessary, to make it assume a regular form, and thus it changes vegetable blues to a green. The specific gravity is 1.33. It has a sweetish, saline taste, similar to that of common salt.

4. It effloresces in the air, and is very soluble in water. Four parts of water at the temperature of 60°, water, and one half its weight of boiling water, are sufficient to dissolve it.

5. The phosphate of soda, exposed to heat, undergoes the watery fusion. In a red heat it melts, and is converted, on cooling, into a milky white glass. By the action of the blow-pipe on charcoal, it melts into a globule which is transparent while it is hot, but becomes opaque on cooling, and assumes the polyhedral form when it becomes solid.

6. The sulphuric, nitric, and muriatic acids decompose it partially, and convert it into the acidulous phosphate of soda.

7. Since the properties of this salt were discovered, it has become an object of considerable importance, on account of the various uses to which it has been applied. It was introduced into medicine by Dr Pearson, and is found to be a mild laxative, particularly agreeable on account of its taste, as it may be taken in broth, as a substitute for common salt. It is employed by mineralogists as a test for the fusion of mineral substances by the blow-pipe, and in soldering, as a cheap substitute for borax.

10. Phosphite of Soda.

This compound of phosphorous acid and soda, may be formed by the direct union of the acid and alkali. alkali in solution; and by evaporation crystals may be obtained.

2. This salt crystallizes sometimes in four-sided prisms with unequal faces; sometimes in long rhomboids, or in the form of feathers. The taste is cool and sweetish. It effloresces in the air, and is soluble in two parts of cold water, and little more soluble in warm water; so that it crystallizes by evaporation rather than in cooling.

3. It melts readily under the blow-pipe, gives out fine phosphoric light, and is converted into a glass which continues transparent while it is hot, but becomes opaque when it cools.

4. The component parts of this salt are,

| Component | Percentage | |--------------------|------------| | Phosphorous acid | 16.3 | | Soda | 23.7 | | Water | 60.0 |

100.0

5. This salt is easily decomposed by lime, barytes, and magnesia. It decomposes the sulphates, nitrates, and muriates of lime, of barytes, strontites, and magnesia. It has not yet been applied to any use.

11. Carbonate of Soda.

1. This salt, which is a compound of carbonic acid and soda, was long applied to various uses, before its nature and composition were known; nor was it perfectly understood till the discovery of Dr Black, which showed the two states in which the alkali exists; in the caustic or pure state, and in the mild state, when it is combined with fixed air, or carbonic acid. The different names under which it is known, have been already mentioned in treating of soda. It is found in great abundance in Egypt, where it effloresces on the soil, and is distinguished by the name of natron. In a similar state of efflorescence, the carbonate of soda is found in subterranean places, and on the walls of buildings; but it is chiefly extracted, as has been already observed, from sea-plants, especially from those which belong to the genus of fuci.

2. Carbonate of soda may be obtained by dissolving a quantity of the soda of commerce with three or four times its weight of pure cold water, and then by filtering the liquor, and evaporating till a slight pellicle is formed. This pellicle, which consists of small cubes of common salt, is to be removed. The heat is to be continued as long as any pellicle is formed, after which the liquid is let by to cool, and the carbonate of soda crystallizes.

3. The form of the crystals of carbonate of soda are irregular or rhomboidal octahedrons, formed by two quadrangular pyramids, truncated near the base, which exhibits dodecahedral solids, with two acute and two obtuse angles. The taste is slightly acrid; it converts vegetable blues to a green colour, and its specific gravity is 1.3591.

4. The carbonate of soda effloresces very rapidly in the air. It is soluble in two parts of cold, and little more than its weight of boiling water. It crystallizes on cooling; but to obtain regular crystals, the evaporation must be slow and spontaneous.

5. When exposed to heat, it undergoes the watery fusion, and if the heat be continued, it passes into the igneous fusion. It is somewhat more fusible than the soda carbonate of potash, which renders it preferable in the manufacture of glaas.

6. In its decomposition by other substances, it is exactly similar to the carbonate of potash.

7. The component parts of carbonate of soda are according to Kirwan.

| Component | Bergman | In crystals | Dry | |---------------|---------|-------------|-----| | Carbonic acid | 16 | 14.42 | 40.05 | | Soda | 20 | 21.58 | 59.86 | | Water | 64 | 64.00 | 00.00 |

100.0 100.00 99.91

12. Arseniate of Soda.

1. This is the compound of the arsenic acid with soda; and when the acid is saturated with the alkali, the salt crystallizes.

2. According to Scheele the form of the crystals of this salt is like those of the acidulous arseniate of potash. Pelletier observes that the arseniate of soda crystallizes in six-sided prisms, terminated by planes perpendicular to their axis. In other respects it is similar to the arseniate of potash, being decomposed by charcoal, by the acids and the earths. With an excess of acid, it does not crystallize, but becomes deliquescent.

13. Tungstate of Soda.

1. This salt, which is the compound of tungstic acid and soda, may be formed by dissolving the oxidation of tungsten in a solution of pure soda, or carbonate of soda. By evaporating the solution, crystals of tungstate of soda are obtained.

2. The crystals of this salt are in the form of elongated, six-sided plates. The taste is acrid and metallic. It is soluble in four times its weight of cold water; and boiling water dissolves one half of its weight. It restores the colour of turnsole which has been reddened by an acid.

3. This salt is decomposed by the sulphuric, nitric, and muriatic, acetic, and oxalic acids. They form a white acid triple salt, which is also produced by lime water. The phosphoric acid produces no change, and if the sulphuric acid be afterwards added, it no longer causes a precipitate. The tungstate of soda is not decomposed by the sulphate of potash or of magnesia. The muriates of lime and barytes occasion a white precipitate. The solution of tin, and all other metallic solutions, also decomposes it.

14. Molybdate of Soda.

15. Chromate of Soda.

The chromic acid combines with soda, and forms a salt, the crystals of which are of an orange colour, but its other properties are unknown.

16. Columbate of Soda.

Columbic acid enters into combination with soda, but little is known of its properties.

17. Acetate of Soda.

1. The combination of the acetic acid with soda was formerly known. 23. Benzoate of Soda.

The compound of benzoic acid with soda, forms a salt which readily crystallizes. It is deliquescent in the air, and very soluble in water. The taste is sharp and saline. This salt exists ready formed in the urine of graminivorous animals.

24. Succinate of Soda.

The combination of succinic acid with soda, forms beautiful transparent crystals by spontaneous evaporation. The crystals are in the form of four-sided prisms with two-sided summits. The taste of the salt is bitter. It is not deliquescent in the air, and it requires about three times its weight of water to dissolve it. It is decomposed when it is exposed to heat in close vessels.

25. Saccolate of Soda.

All that is known of this salt is, that it crystallizes in small crystals, and is soluble in five times its weight of boiling water.

26. Camphorate of Soda.

1. This compound of camphoric acid with soda is formed by saturating a solution of carbonate of soda in water with the acid; and by evaporation with a gentle heat, the crystals are obtained, when the solution cools.

2. The crystals of camphorate of soda are irregular. They are white and transparent. The taste is bitter. Exposed to the air, this salt effloresces. It is soluble in eight parts of boiling water.

3. Exposed to heat, it melts and swells, and the acid is distipated in thick vapours of an aromatic odour. With the blow-pipe it burns with a blue flame, and is decomposed. The acid is sublimed, and the alkali remains behind. It is decomposed by potash, and by the strong acids *.

27. Suberate of Soda.

The compound of suberic acid with soda, forms a salt which does not crystallize. It has a slightly bitter taste, and reddens the tincture of turpentine. It deliquesces in the air, and is very soluble in water. Exposed to heat, it swells and melts; the acid is sublimed, and the alkali remains behind. The mineral acids decompose it, and it is also decomposed by the calcareous, aluminous and magnesian salts †.

28. Mellate of Soda.

The compound of mellitic acid with soda, when it is saturated, forms crystals in cubes or three-sided tables. Sometimes they are formed in groups, and sometimes they are infloated.

29. Lactate of Soda.

All that is known of this salt is, that it does not crystallize, but is soluble in alcohol.

30. Prussiate of Soda.

This salt, which is a compound of prussic acid and soda, is very soluble in water, converts vegetable blues to green, and when it is exposed to a very moderate heat, it is partially decomposed.

31. Sebate. 31. Sebate of Soda.

Nothing farther is known of the compound of sebacid acid with soda, than that it is soluble in water.

IV. Compounds of Soda with Inflammable Substances.

1. Soda enters into combination with alcohol, and forms a reddish coloured acrid solution; but when heat is applied to this solution, it appears that the alcohol is partially decomposed.

2. There is no action between ether and soda.

3. Soda readily combines with the fixed oils, and especially that class of them called fat oils, and forms with them compounds called soaps.

4. Soda combines in very small quantity with the volatile oils, and the compounds thus formed have some of the properties of soap.

Sect. III. Of Ammonia and its Combinations.

1. This substance has been long known under the names of volatile alkali, volatile spirit of sal ammoniac, caustic volatile alkali, hartshorn, spirit of hartshorn and of urine, because it was obtained from these substances. It has received the name ammonia, from sal ammoniac, a salt which was extracted from the urine and dung of camels, collected near the temple of Jupiter Ammon in Africa. This salt was first known to the ancients. It is first mentioned by Basil Valentine, who lived in the 15th century, as being prepared from certain substances, with an account of some of its properties. But the difference between the pure salt and its compound with the carbonic acid was not known till the discovery of Dr Black. It was supposed to be in the state of greatest purity in the solid and crystalline form; and in its pure, caustic, and liquid state, it was supposed to be changed, and contaminated with the lime or the different matters which had been employed in extracting it from sal ammoniac. It was afterwards examined by Dr Priestley in the state of gas, and he decomposed it by electricity, but without discovering its constituent parts. This was at last effected by the researches and experiments of Scheele and Bergman, and finally confirmed by those of Berthollet.

2. Ammonia may be obtained by the following process. Three parts of quicklime, and one part of sal ammoniac reduced to powder, are to be put into a retort, and the neck of the retort immersed under mercury in the mercurial apparatus. A jar filled with mercury is inverted above it. Heat is applied to the retort, and a gas comes over in great abundance. This gas is ammonia, or ammoniacal gas. Sal-ammoniac consists of the muriatic acid and ammonia. The affinity of lime for muriatic acid is stronger than that of ammonia, and therefore the ammonia is disengaged in the state of gas, while the lime combines with the acid. The gas must be received over mercury, because it is readily absorbed by water.

3. Ammonia in the state of gas resembles common air. It is transparent and colourless, and may be indefinitely compressed and dilated. The smell is extremely pungent and acrid, particularly irritating the eyes and nostrils. It has an acrid and caustic taste, but is much less corrosive than the other alkalies. It changes vegetable blues to a green colour. It's lighter than common air. Its specific gravity is 0.90732; so that it is nearly one half lighter. According to Mr Kirwan, a cubic inch of this gas weighs only .27 of a grain.

It is totally unfit for respiration. No animal can breathe it without instant death. It is also unfit for the support of combustion; but although it extinguishes burning bodies, the flame of a candle let down into this gas, is considerably enlarged in volume by the addition of another flame, which is of a pale yellow colour.

4. This gas is unaltered by the action of light. When it is exposed to a strong heat, as when it is passed through a red-hot porcelain tube, it is decomposed and converted into azotic and hydrogen gases. It is also decomposed by the electric spark. When it is exposed to the temperature of -42°, it is condensed, and assumes a liquid form; but it returns to the gaseous state by an elevation of temperature.

5. There is no action between oxygen gas and this gas in the cold; but if the two gases mix together are made to pass through a red-hot porcelain tube, the ammonia is decomposed; a detonation takes place; the hydrogen combines with the oxygen and forms water. The azote passes off in the state of gas.

6. There is no action between this gas and azotic gas, nor is there any action between common air and ammoniacal gas in the cold; but if the mixture be made to pass through a red-hot porcelain tube, water is formed, and the gas which escapes is a combination of the azotic gas of the atmosphere, and of that which entered into the composition of ammonia. But if the same experiment be made with a greater proportion of oxygen gas, the product is nitric acid, which is formed by the combination of part of the oxygen and the azote.

7. It has been already mentioned, that the constituent parts of ammonia were discovered by Scheele and Bergman, and Priestley and Berthollet. According to the experiments of the latter, ammonia is composed of 121 parts of azote, and 29 of hydrogen. This result was obtained by decomposing the ammonia by means of electricity. One hundred parts of ammonia, therefore, are composed of

| Azote | Hydrogen | |-------|----------| | 80 | 20 |

8. Ammoniacal gas combines very rapidly with water. If a bit of ice be brought into contact with this gas, it absorbs and condenses it, and instantly becomes liquid. There is at the same time a production of cold; but water in the liquid state, as it absorbs this gas, becomes warm, because the gas is deprived of that quantity of caloric which is necessary to retain it in the gaseous form. The water, as it absorbs the gas, becomes specifically lighter. When water is saturated with this gas, it is known under the name of liquid ammonia. The specific gravity of a saturated solution is 0.9054. When this solution is exposed to the temperature of 130° the ammonia is driven off, and assumes the gaseous form; and when it is slowly and gradually cooled to the temperature of from -35° to -42°,

Ammonia, —42°, it crystallizes; but when the temperature is rapidly diminished to —58° it assumes the form of jelly. At that temperature it has no smell.

By Mr Davy's experiments, a saturated solution of ammonia contains, in 100 parts,

| Water | 74.63 | |-------|-------| | Ammonia | 25.37 |

100.00

He has also ascertained the different proportions of water and ammonia which are contained in 100 parts of liquid ammonia of different specific gravities.

These are exhibited in the following table.

**TABLE of the quantities of Ammonia, such as exists in the aeriform state, saturated with water at 53°, in Aqueous ammoniacal Solutions of different specific gravities.**

| Specific grav. | Ammoniac. | Water. | |----------------|-----------|--------| | 9054 | 25.37 | 74.63 | | 9166 | 22.07 | 77.93 | | 9255 | 19.54 | 80.46 | | 9326 | 17.52 | 82.48 | | 9385 | 15.88 | 84.12 | | 9435 | 14.53 | 85.47 | | 9476 | 13.46 | 86.54 | | 9513 | 12.40 | 87.60 | | 9545 | 11.56 | 88.44 | | 9573 | 10.82 | 89.18 | | 9597 | 10.17 | 89.83 | | 9619 | 9.60 | 90.40 | | 9684 | 9.50 | 90.50 | | 9639 | 9.99 | 90.91 | | 9713 | 7.17 | 92.83 |

9. The order of affinities of ammonia is the same as the fixed alkalies.

I. Action of Phosphorus on Ammonia.

1. There is no action between ammonia and phosphorus in the cold; but when the two gases are passed through a red-hot porcelain tube, the ammonia is decomposed, and its constituent parts enter into combination with the phosphorus. There is formed phosphorated hydrogen gas, and phosphorated azotic gas. In this case, there is a double action of the phosphorus, one part combining with the hydrogen, and another with the azote.

2. Ammonia is also decomposed by red-hot charcoal, when it passes over in the state of gas at this temperature. Part of the carbon of the charcoal combines with the ammonia, and forms prussic acid.

II. Action of Sulphur on Ammonia.

1. Ammonia combines with sulphur in the state of vapour. This combination constitutes a sulphuret of ammonia, which has the property of decomposing water, and is then converted into a hydrogenated sulphuret of ammonia. This may be prepared by distilling in a retort, a mixture of muriate of ammonia, lime, and sulphur. By this process a liquid of a deep orange colour, which exhales extremely fetid vapours, on account of the excess of ammonia which it contains, is produced. This was known under the name of the fuming liquor of Boyle. This sulphuret is decomposed by heat, by the acids and sulphurated hydrogen gas.

2. When ammonia absorbs sulphurated hydrogen gas, either by agitating the gas in a vessel with liquid ammonia, or by passing a current of the gas through it, there is an evolution of caloric and the formation of vapour, and the liquid is converted into an orange colour. This is the hydrofulphuret of ammonia. It has no longer the fetid odour of the hydrogenated sulphuret, and it may be crystallized. It is decomposed by the action of heat, by the acids, and by the metallic oxides.

III. Compounds of Ammonia with the Acids.

1. Sulphate of Ammonia.

1. The compound of sulphuric acid with ammonia was formerly called secret sal ammoniae of Glauber, because it was discovered by that chemist. It was also called vitriolated ammonia, and vitriolated volatile alkali. It was discovered by Glauber in examining the residuum of the decomposition of ammonia by means of sulphuric acid.

2. This salt may be formed by saturating the acid with the alkali, and afterwards crystallizing it.

3. The crystals of sulphate of ammonia are six-sided prisms with unequal sides, terminated by six-sided pyramids. The sulphate of ammonia undergoes little change in the air. It slowly attracts moisture in a humid atmosphere. It is soluble in two parts of cold water, and in a similar quantity of boiling water.

4. When exposed to heat, it melts; and if the heat be continued, it loses a part of its base, and is converted into the acidulous sulphate of ammonia. This differs from the sulphate by its sharp taste, and its property of reddening vegetable blues, greater solubility, and a different action on several compounds.

5. This salt is not decomposed like the other sulphates, on account of its greater volatility. The component parts of this salt, according to Mr Kirwan, are:

| Acid | 54.66 | |------|-------| | Ammonia | 14.24 | | Water | 31.10 |

100.00

2. Sulphite of Ammonia.

1. The compound of sulphurous acid with ammonia is prepared by passing a stream of sulphurous acid gas into a vessel with liquid ammonia. The gaseous acid is readily absorbed, much heat is produced, and the sulphite of ammonia crystallizes on the cooling of the saturated solution.

2. This salt is in the form of six-sided prisms terminating in six-sided pyramids, or in that of four-sided rhomboidal prisms, with three-sided summits. The taste is at first cool and pungent, and afterwards sulphurous. It is deliquescent in the air, from which it absorbs oxygen, and is converted into the sulphate. It is soluble in its own weight of cold water. The solution produces... Ammonia produces a great degree of cold. Boiling water dissolves still more. Water saturated with sulphite of ammonia, and agitated in the open air, presents this salt in a few hours converted into the sulphate, without any crust on the surface, or muddiness in the liquid, because it is very soluble in water.

3. It decrepitates slightly on red-hot coals; when it is gradually heated in a close vessel, it gives out at first water and ammonia, and then sublimes totally in the state of acidulous sulphite.

4. The constituent parts of this salt are,

| Sulphurous acid | 60 | | Ammonia | 29 | | Water | 11 |

100

3. Nitrate of Ammonia.

1. This compound of nitric acid and ammonia was formerly called nitrous sal ammoniac, inflammable nitre. This salt has been particularly examined by Berthollet, and more lately by Mr Davy.

2. Nitrate of ammonia is prepared by directly combining the acid and the alkali, and it may be obtained in crystals by careful evaporation and slow cooling.

3. This salt crystallizes in six-sided prisms, terminating in long six-sided pyramids; but the appearance of the crystals varies with the temperature in which the evaporation goes on. Sometimes they are in long silky threads, soft and elastic; the taste is very acrid, bitter, and penetrating; and the specific gravity is 1.5785.

4. When the nitrate of ammonia is exposed to the air, it attracts moisture, and deliquesces. It is soluble in two parts of cold water. Boiling water dissolves double of its own weight.

5. Nitrate of ammonia very readily undergoes the watery fusion. If the heat be continued, it is entirely deprived of its water of crystallization; and when the temperature is increased, it explodes spontaneously, giving out at the same time a brilliant white flame, with considerable noise; it is then entirely distillated into vapour. This detonation instantaneously takes place, when the nitrate of ammonia is thrown on a red-hot iron. It was from this property that the salt derives its name of inflammable nitre. The nature of this rapid combustion will be understood by considering the component parts of the salt. The hydrogen of the ammonia enters into combination with the oxygen of the acid; water is formed, and azotic gas is disengaged from each of the component parts of the salt. In the different states of crystallization, this salt requires different temperatures for its fusion and decomposition. The following are the conclusions from Mr Davy's experiments.

"a. Compact or dry nitrate of ammonia undergoes little or no change at temperatures below 265°.

b. At temperatures between 275° and 300°, it slowly sublimes without decomposition, or without becoming fluid.

c. At 320° it becomes fluid, decomposes, and still slowly sublimes; it neither affuming, nor continuing in, the fluid state, without decomposition.

d. At temperatures between 340° and 480°, it decomposes rapidly.

e. The prismatic and fibrous nitrates of ammonia become fluid at temperatures below 300°, and undergo ebullition at temperatures between 360° and 400°, without decomposition.

f. They are capable of being heated to 430° without decomposition or sublimation, till a certain quantity of their water is evaporated.

g. At temperatures above 450°, they undergo decomposition without previously losing their water of crystallization."

6. The component parts of nitrate of ammonia are, according to Kirwan, Fourcroy,

| Acid | 57 | 46 | | Ammonia | 23 | 40 | | Water | 20 | 14 |

Mr Davy has ascertained the proportions of the component parts of this salt in its three different states.

| Acid | Fibrous | Prismatic | Compact | |------|---------|-----------|--------| | | 72.5 | 69.5 | 74.5 | | Ammonia | 19.3 | 18.4 | 19.8 | | Water | 8.2 | 12.1 | 5.7 |

100.0 100.0 100.0

7. This salt has been applied to no use, but for the purposes of chemical experiment, and especially for the preparation of the nitrous oxide or gaseous oxide of azote, which has been already described in treating of the compounds of azote.

4. Nitrate of Ammonia.

If this salt be formed by depriving the nitrate of ammonia of part of its acid, it must be extremely difficult, Fourcroy observes, to obtain it in this way, before the salt is totally decomposed.

5. Muriate of Ammonia.

The compound of muriatic acid and ammonia has been known, from time immemorial, by the name of sal ammoniac. It derives this name from Ammonia, a country of Libya, which name is descriptive of the sandy soil of that region (A). Hence too is the origin of the epithet Ammon given to Jupiter, to whom a temple was erected in that country. This salt was originally collected in great quantities near this temple, where it was formed in the sand from the excrementitious matters of different animals, particularly camels. It was well known to the Greeks and Romans, and was employed by them in several arts. Before the nature

(A) From the Greek word ἀμμός, which signifies sand. The muriate of ammonia is fusible and volatile. Of heat. When it is thrown on red-hot coals, it is entirely diffused in white vapour. Exposed to a high temperature, it is decomposed.

6. This salt is readily decomposed by the sulphuric acid, which disengages the muriatic acid with violent effervescence. It is also decomposed by the nitric acid, which oxygenates the muriatic acid. In this way a nitro-muriatic acid is prepared, which is employed for the solution of gold. Barytes, potash, soda, and lime, decompose the muriate of ammonia, and disengage the ammonia in the state of gas, merely by trituration; but if heat be applied, the decomposition is more rapid and complete.

7. According to the analysis of Mr Kirwan, the composition of the muriate of ammonia are:

| Acid | 42.75 | | Ammonia | 25.00 | | Water | 32.25 |

100.00

8. No salt is more generally employed than muriate of ammonia. In chemistry it is used for the extraction of ammonia, and the carbonate of ammonia; for the production of cold, and as an instrument of analysis. It is also employed in medicine; in the art of dyeing, for the preparation of colours; in metallurgy, for the indication and separation of some metallic substances, and in the arts, for covering the surface of copper and other vessels, to prevent oxidation in the process of tinning; and for the same purpose in soldering.

6. Hyperoxymuriate of Ammonia.

The compound of hyperoxymuriatic acid and ammonia is formed by pouring carbonated ammonia into a solution of any of the earthy hyperoxymuriates. A double decomposition takes place, and a hyperoxymuriate of ammonia is formed. This salt is very soluble in water and in alcohol. It is decomposed at a low temperature, and gives out a quantity of gas together with a smell of hyperoxymuriatic acid. Such a smell, Mr Chenevix observes, is doubtless owing to the great quantity of oxygen contained in the acid, which is more than what is necessary to combine with the hydrogen contained in the alkali. Some part, therefore, is disengaged without decomposition. Mr Chenevix who formed this salt, could not succeed in ascertaining the proportion of its constituent parts.

7. Fluate of Ammonia.

This compound of fluoric acid and ammonia is prepared by saturating the acid with the alkali. By proper evaporation it crystallizes in small needles or prisms, which have a pungent taste analogous to that of phosphate of ammonia.

2. When it is heated, this salt gives out ammonia, and is sublimed in the state of an acidulous fluate. This salt decomposes the nitrate and muriate of lime, and the sulphate of magnesia. 8. Borate of Ammonia.

The compound of boric acid and ammonia is little known. It is formed by the direct union of the acid with the alkali. It has so little permanency, that the solution being evaporated, the whole of the ammonia is volatilized, while the boric acid crystallizes. The base of every other salt decomposes it.

9. Phosphate of Ammonia.

1. This salt, the compound of phosphoric acid and ammonia, was long confounded with the phosphate of soda, as it exists with it in urine, under the names of fusible salt, native salt of urine, microcosmic salt. It was first accurately distinguished by Schloesser, De Chauvines, and Rouelle, about the year 1775; soon after by Lavoisier, and more lately by Vauquelin.

2. At first it was extracted from the salt of urine; and many processes were adopted to obtain it pure, and separate from the muriate and phosphate of soda, with which it is always accompanied. It is now prepared artificially by directly combining phosphoric acid with ammonia; and by slow evaporation of the solution to a certain consistence crystals are obtained on cooling.

3. The phosphate of ammonia crystallizes in regular four-sided prisms, terminated by four equal-sided pyramids, and sometimes in the form of small needles closely interwoven with each other. It has a cooling, saline, pungent taste, and changes the syrup of violets to a green colour. Its specific gravity is 1.804.

4. In moist air, it is slightly deliquescent, but otherwise it is unchanged. It is soluble in four parts of cold water, and still more so in boiling water.

5. Explored to heat, it undergoes the watery fusion, swells up, and melts into a transparent glass, which is acid, part of the base being driven off. Hence it derived the name of fusible salt.

6. It is readily decomposed by charcoal by the sulphuric, nitric, and muriatic acids, and by the two fixed alkalies.

7. The phosphate of ammonia is employed as a flux in assaying mineral substances with the blow-pipe. It is greatly used also in the fabrication of coloured glasses and artificial precious stones.

10. Phosphite of Ammonia.

1. This is a compound of phosphorous acid and ammonia. It is prepared by the direct combination of the acid with ammonia or the carbonate of ammonia, and by slow evaporation it may be obtained in crystals.

2. It sometimes crystallizes in long transparent needles, and sometimes in four-sided prisms, terminated by four-sided pyramids. It has a strong pungent taste.

3. This salt is slightly deliquescent in the air, is soluble in twice its weight of cold water, and being more soluble in boiling water, it crystallizes on cooling.

4. When it is heated on charcoal with the blow-pipe, it boils up, and loses its water of crystallization. When this has escaped, it is surrounded with a fine phosphoric light; and as the salt begins to vitrify, there are evolved bubbles of gas, which burn as they come in contact with the air, with a vivid flame, and form with the atmosphere a ring of white vapour of phosphoric acid. What remains is phosphoric acid in Ammonium, the vitreous state. The same effect may be produced by heating six or seven grains of the salt in a small glass globe to which a tube is adapted, and immersed under jars over mercury. The salt melts, swells, and gives out bubbles of phosphorated hydrogen gas, which spontaneously inflame as they come in contact with the air, and exhibit the white coronet of vapour which is the characteristic property of the combustion of this gas. During this decomposition, the base of the salt, the ammonia, is also volatilized, and pure phosphoric acid remains behind. This salt is decomposed by charcoal, the acids, and by potash and soda.

5. The constituent parts of this salt are the following:

| Component | Quantity | |-----------------|----------| | Phosphorous acid | 26 | | Ammonia | 51 | | Water | 23 | | Total | 100 |

6. It has not hitherto been applied to any use.

II. Carbonate of Ammonia.

1. The compound of carbonic acid with ammonia has been distinguished by different names, as concrete volatile alkali, aerated volatile alkali, and cretaceous salt ammoniac. Its peculiar nature and properties were not clearly understood, till, by the discovery of Dr Black, it was demonstrated to be a compound salt. This salt is obtained by a great many different processes. Formerly it was procured by distilling animal matters, and particularly horns, as the horns of the hart, whence it derived the name of volatile salt of hartshorn.

2. Carbonate of ammonia may be prepared by directly combining carbonic acid and ammonia in the state of gas over mercury; or it may be obtained by mixing together two parts of chalk, and one part of muriate of ammonia, well dried and reduced to powder, and exposing them to heat in a porcelain retort. The gas, as it comes over, is collected in a receiver, which is to be cooled with cloths moistened with water. This is the carbonate of ammonia, which is sublimed and attaches itself to the sides of the receiver. In this process there is a double decomposition. The carbonic acid of the lime combines with the ammonia, and forms carbonate of ammonia, which is driven off by heat; and the muriatic acid of the muriate of ammonia combines with the lime, and forms muriate of lime, which remains in the retort.

3. The carbonate of ammonia is crystallized; but the crystals are so irregular, that their form has not been accurately ascertained. Bergman describes them as octahedrons, whose four angles are truncated; while, according to Rome de Lisle, they are compressed four-sided prisms, terminated by a two-sided summit. The taste of this salt is slightly acid, and the smell is perceptibly that of ammonia, though more feeble. It converts vegetable blues to green. Its specific gravity is 0.966.

4. When this salt is pure, it is not sensibly changed by exposure to the air. It is very soluble in water, and, during its solution, produces cold. Two parts of cold water dissolve more than one of the salt. Water, at the temperature of about 120°, dissolves more than its own weight, &c. When it is rapidly cooled, the salt crystallizes in the most regular form which it assumes. Boiling water cannot be employed for its solution, because at this temperature the salt is driven off in the state of vapour. When this salt is thrown upon hot iron, it melts, boils, and is converted into vapour.

5. It is decomposed by all the acids with effervescence; and the effervescence with this salt is more violent than with the carbonate of the two fixed alkali, because the proportion of carbonic acid is greater.

6. The constituent parts of this salt, according to Bergman, are,

| Carbonic acid | 45 | | Ammonia | 43 | | Water | 12 |

But Mr Davy has found, that the proportion of acid and water in this salt depends on the temperature at which it is formed. It is greater when the temperature is low, and diminishes as the temperature is increased.

7. This salt is employed in medicine, and also in the manufacture of muriate of ammonia, for which purpose it is produced by distillation from animal matters. The use of it, when it is mixed with volatile oils, as a perfume, or as a stimulant in smelling bottles, is well known.

12. Arseniate of Ammonia.

1. This salt, the compound of arsenic acid and ammonia, is formed by combining the acid with the alkali. When the solution is evaporated, it affords crystals of arseniate of ammonia.

2. It crystallizes in the form of rhombohedral prisms; or, with an excess of acid, in the form of needles. The crystals of the first convert the syrup of violets into green, and those of the second are deliquescent in the air.

3. When this salt is gently heated, the ammonia is disengaged, and the arsenic acid remains behind; but when the heat is violent and sudden, part of the alkali and of the acid are decomposed, water is formed, azotic gas is disengaged, and the arsenic is sublimed in the metallic state.

13. Arsenite of Ammonia.

This is a compound of the white oxide of arsenic, or arsenious acid, with ammonia; but nothing is known of its properties.

14. Tungstate of Ammonia.

1. This compound of tungstic acid and ammonia is formed by dissolving the oxide of tungsten in the solution of ammonia or carbonate of ammonia; and by evaporating the solution, the salt is obtained in the form of crystals.

2. It crystallizes in small scales, which have some resemblance to boracic acid; or in small needles, which are four-sided. This salt has a metallic taste. It is not deliquescent in the air, but is soluble in water. When it is exposed to heat, it is decomposed.

3. The component parts of this salt are,

- Tungstic acid 18 - Ammonia and water 22

15. Molybdate of Ammonia.

16. Chromate of Ammonia.

17. Acetate of Ammonia.

1. This compound of acetic acid and ammonia has been long known by the name of spiritus minderii. In this state it is combined with an excess of acid. It may be obtained, but with some difficulty, on account of its volatility, by slow evaporation. It then crystallizes in the form of needles. Crystals are also obtained by very slow sublimation of this salt.

2. The crystals of acetate of ammonia are long, slender, flat, and pointed, of a pearly white colour. The taste is cooling, with a mixture of sweet. Exposed to air, it is deliquescent, and is very soluble in water. When it is heated to the temperature of 170°, it melts; and when the temperature is raised to 250°, it is sublimed. By distillation of the salt in solution, with a strong heat, it is partly decomposed. The ammonia is first driven off, then the acid, and, towards the end of the process, part of the neutral salt.

18. Oxalate of Ammonia.

1. The compound of oxalic acid and ammonia may be prepared by directly combining the acid with the alkali. By evaporating the solution, the salt crystallizes.

2. When the acid is saturated with the alkali, the crystals are in the form of four-sided prisms, terminated by two-sided summits; one of which is larger, and includes three sides of the prism. These salts are soluble in water.

3. When this salt is exposed to heat, carbonates of ammonia are driven off, and nothing remains behind but heat.

4. This is one of the most useful salts to be employed as a reagent in detecting lime in liquid solutions, and for ascertaining the nature and proportions of calcareous salts.

19. Tartrate of Ammonia.

The compound of tartaric acid and ammonia forms a salt which very readily crystallizes. This salt has a cooling bitter taste, is very soluble in water, and easily decomposed by heat. It is subject also to spontaneous decomposition. By the action of the stronger acids, part of the base is separated, and it is converted into an acidulous tartrate of ammonia.

20. Citrate of Ammonia.

1. This salt, which is a compound of citric acid and ammonia, is formed by the direct combination of the Ammonia, acid and alkali, and it crystallizes when the solution is evaporated to the consistence of a thick syrup.

2. The crystals are in the form of an elongated prism. They are very soluble in water, and have a saline cooling taste. This salt is decomposed by heat, the ammonia being driven off.

3. It is composed of:

| Acid | 62 | |--------|----| | Ammonia| 38 |

100

21. Malate of Ammonia.

This salt, which is a compound of malic acid and ammonia, is very soluble and deliquescent salt. Its other properties are unknown.

22. Benzoate of Ammonia.

The compound of benzoic acid and ammonia forms a very soluble salt, which readily crystallizes, and the crystals arrange themselves in an arborecent or plumose form. This salt is volatile, and is decomposed by all other acids *.

23. Succinate of Ammonia.

The compound of succinic acid and ammonia forms a salt, which affords needle-shaped crystals that are deliquescent, and are sublimed by heat, without being decomposed.

24. Saccolate of Ammonia.

Nothing farther is known of this salt, than that it has an acid taste, and is readily decomposed by heat.

25. Camphorate of Ammonia.

1. This salt, which is a compound of camphoric acid and ammonia, is prepared by adding the acid to a solution of carbonate of ammonia, and hot water, till effervescence ceases. The evaporation must be conducted with a very gentle heat, on account of the volatility of the ammonia.

2. It is difficult to obtain this salt crystallized. When the solution is too much evaporated, it affords a crystalline mass, in which appear small needles; but if it be evaporated to dryness there remains a solid opaque mass, which has a slightly bitter and pungent taste.

3. This salt is slightly deliquescent in the air; it is not very soluble in cold water, but may be dissolved in three parts of boiling water. In these salts, it would appear that the acid resists the action of the water; for when there is an excess of base, they become more soluble.

4. Exposed to heat on red-hot coals, it swells and melts, and then rises in vapour. With the blow-pipe, it gives a blue and red flame, and is entirely dissipated.

5. This salt is decomposed by the sulphuric, nitric, and muriatic acids, and if the solution be sufficiently concentrated, the camphoric acid is deposited. It is also decomposed by potash and soda, and more rapidly with the assistance of heat. This salt is completely soluble in alcohol †.

26. Suberate of Ammonia.

This compound of suberic acid with ammonia affords crystals in the form of parallelepipeds. It has a slight faintish taste, leaving an impression of bitterness. It reddens vegetable blues, and is deliquescent in the air. It is very soluble in water. When it is thrown on burning coals, it swells up, and is deprived of its water of crystallization. It is entirely dissipated by the action of the blow-pipe. It is decomposed by the sulphuric, nitric, muriatic, and oxalic acids, by the fixed alkalies, and the alumino and magnesian salts ‡.

27. Mellate of Ammonia.

This salt, which is a compound of mellitic acid and ammonia, is formed by saturating the acid with the alkali. By evaporation it affords transparent, six-sided crystals. This salt when exposed to the air, becomes opaque, and of a filvery white colour.

28. Lactate of Ammonia.

This compound of lactic acid and ammonia forms a salt which crystallizes. It is deliquescent in the air, and is decomposed by heat, great part of the ammonia being driven off.

29. Prussiate of Ammonia.

The compound of prussic acid and ammonia affords a salt which has the odour of ammonia. When this salt is exposed to heat, it is entirely dissipated.

30. Sebate of Ammonia.

31. Urate of Ammonia.

The compound of uric acid and ammonia, forms a salt which is not very soluble in water, and in many of its properties resembles the acid itself.

IV. Compounds of Ammonia with Inflammable Substances.

1. Ammonia enters into combination with alcohol, with the assistance of a moderate heat; but the ammonia is separated when the mixture is exposed to a temperature below the boiling point of alcohol.

2. Ammonia readily mixes with ether; but the nature of the compound, or whether it be a chemical combination, is not known.

3. Ammonia forms a compound with the fixed oils, which is well known under the name of soap or limon.

4. With the volatile oils it forms compounds, which have somewhat similar properties.

CHAP. XIII. OF EARTHS.

1. The word earth is taken in different significations. Sometimes it signifies the globe, and sometimes it is used to denote the soil on the surface of the globe. In chemistry it is employed to signify certain elementary substances, of which a great proportion of the solid parts of the globe is composed; and these substances are found to possess many peculiar, and some common properties.

2. The general properties of the earths are the following.

a. They have neither taste nor smell.

b. They b. They are incombustible. c. They are nearly insoluble in water. d. They have a specific gravity which is under 5.

The number of the earths which are at present known, is nine, and we shall treat of them in the following order.

1. Lime, 2. Barytes, 3. Strontites, 4. Magnesia, 5. Alumina, 6. Silica, 7. Yttria, 8. Glucina, 9. Zirconia.

Sect. I. Of Lime.

1. Lime has been known from the remotest antiquity. The great abundance in which it is found in nature, and the important uses to which it may be applied, led men to employ it for many purposes from the earliest ages of the world. It was well known to the ancients as mortar, and as a manure, and they were not unacquainted with some of its medicinal virtues. But it was long before the nature and properties of lime were fully known; and particularly those changes which quicklime undergoes when it is exposed to the air, or limestone to the action of heat. It was not till Dr Black made his brilliant discoveries, that the nature of these changes was fully developed, and the fanciful theories which had been proposed to account for them were entirely rejected.

2. Lime is seldom found perfectly pure in nature; but it is universally diffused, and exists in some places in the greatest abundance, in combination with other substances, and particularly with carbonic acid. To obtain it pure, a quantity of chalk, or marble, or limestone, is exposed to a strong heat, by which means the carbonic acid with which it is in combination is driven off. When the limestone, or marble, or chalk, which has been employed, is sufficiently burnt or calcined, and removed from the fire, and water poured upon it, it swells up, and at last falls down into a powder. This powder is called quicklime. In this process of slaking lime, as it is called, a great quantity of water is quickly absorbed, and the water being fixed in the lime in the solid state, gives out that caloric which is necessary to retain it in the state of liquidity, so that a great quantity of heat is evolved. Part of the water, also, rises in vapour, in consequence of the great heat, before it is consolidated with the lime. The heat produced is so great, that water may be boiled, and combustible bodies may be inflamed. Accidents have happened to carriages and vessels loaded with lime, to which water had been admitted. So much heat was produced, that they have been set fire to, and burnt. Light is also emitted when lime is slaked. This, it is said, is seen when the process is conducted in a dark place, and the quantity of lime is considerable.

3. The purity of lime, thus obtained, is in proportion to the purity of the substance which was calcined. The lime which is obtained by burning pure white marble, or what is called calcareous spar, is tolerably pure. But there are other processes by which those substances with which it may happen to be mixed may be separated. If a quantity of chalk be washed in pure water, dissolved in distilled acetic acid, and afterwards precipitated by carbonate of ammonia, the precipitate being washed and calcined, pure lime is the product. The lime which is obtained from oyster-shells, may be rendered pure by the following process. First wash the shells in different quantities of water, and boil them, to separate any mucilaginous substance. Introduce them into a furnace, and calcine them to whiteness. After the first calcination, put them into a porcelain retort, and expose it to a red heat. By this process pure lime is obtained. To preserve it in this state of purity, it must be kept in close vessels.

4. Pure lime is of a white colour, has a hot, sharp, caustic taste, and destroys the texture of animal substances, to which it is for some time applied. It converts the syrup of violets and other vegetable blues to a green colour. The specific gravity of lime is 2.3.

5. After the lime has been thus prepared and flaked, if more water be added to dilute it, and reduce it to the consistence of thick cream, this is what was formerly called milk or cream of lime. But if a greater quantity of water be added, and the solution be filtered, a transparent liquid is thus obtained, which is known by the name of lime water. Four hundred and fifty parts of water are required, it is said, to dissolve one of lime. This water is clear and limpid, has a sharp, acrid taste, and renders the syrup of violets green. When this water is evaporated, and the whole driven off, the lime remains pure. If the solution of lime-water be exposed to the air, the surface is soon covered with a pellicle, which gradually acquires solidity and thickness. The pellicle is owing to the attraction of the lime for the carbonic acid of the atmosphere, forming a carbonate of lime, which being insoluble in water, is precipitated.

6. Lime, according to Trommelfeld, crystallizes. This was first discovered by Scheele. The method by which Mr Trommelfeld obtained the crystals of lime is the following. Boil any quantity at pleasure of muriate of lime, with one-fourth or less of caustic lime, and evaporate the solution till a drop of it let fall on a cold stone assume the consistence of syrup. It is then to be filtered, and put into a close vessel, that the solution may cool as slowly as possible. Crystals of lime are thus obtained, which must be washed in alcohol, to separate any part of the muriate of lime which may adhere. For the complete success of this experiment, some pounds of the muriate of lime must be employed.

7. Lime undergoes no change by the action of light, and it remains unaltered when it is exposed to the greatest heat.

8. Lime is one of the most important of the earthy bodies. It is applied to a great many valuable purposes, and fortunately it can be obtained in the greatest abundance. It is employed in medicine, both as an internal remedy, and an external application. As a manure, it is of the most extensive utility; nor is it of less importance, as it is employed for a cement in building. When quicklime is mixed with sand and water, and reduced to the form of a thick paste, it is in the state... It is an object of the utmost importance that the mortar which is employed as a cement in building, should be durable. To obtain this object, a good deal of attention has been paid by different philosophers in ascertaining the proportions which seem to answer best, or the additions which may be made to the usual materials in the formation of good and durable mortar. The proportions which have been proposed by Dr Higgins are,

- Coarse sand, 4 parts, - Fine sand, 3 - Quicklime, 1

The lime should be recently flaked, and the quantity of water should be just sufficient to bring it to a proper consistency.

Dr Higgins found that burnt bones, if they did not exceed one-fourth of the lime, added to the mortar, improved its tenacity, and prevented it from cracking in drying.

It has been proposed to add a certain proportion of unflaked lime to the mortar, with the view of giving it greater solidity. Mortar acquires its hardness from the lime absorbing carbonic acid, and returning to the state of lime-stone, and also from the combination of part of the water with the lime. According to Guyton's experiments, the following proportions compose a good, durable mortar,

- Fine sand, 3 parts; - Cement of well-baked bricks, 3 - Slaked lime, 2 - Unflaked, 2

It is sometimes necessary to use mortar as a cement under water, but common mortar is unfit for this purpose. It has been found by experiment, that manganese added to mortar, gives it the property of consolidating under water. To prepare a mortar for this purpose, Guyton recommends the following process. Mix together 90 parts of limestone, five parts of black oxide of manganese, and 4 parts of blue clay in the state of powder. Let the mixture be calcined, to drive off the carbonic acid; then add 60 parts of sand, and mix it together with a sufficient quantity of water, to bring it to the consistency of mortar.

9. The order of the affinities of lime is the following:

- Oxalic acid, - Sulphuric, - Tartaric, - Succinic, - Phosphoric, - Sulfuric, - Nitric, - Muriatic, - Suberic, - Fluoric, - Arsenic, - Lactic, - Citric, - Benzoic, - Sulphurous, - Acetic, - Boracic, - Carbonic, - Prussic.

I. Phosphuret of Lime.

1. Lime combines with phosphorus, and forms a compound which is called phosphuret of lime. To prepare this compound, introduce into the bottom of a glass tube, closed at one end, one part of phosphorus, and afterwards place a little above it four or five times its weight of quicklime in powder. Expose to a heat that part of the tube which contains the lime, so that it may become red hot. In this state raise the tube and draw it along the coals, till that part of it containing the phosphorus be also exposed to the heat. The phosphorus is raised in the state of vapour through the lime, and combines with it, so that the whole mass forms a compound of a brown colour. This is the phosphuret of lime.

2. It has a deep brown colour, no smell, and when exposed to the air it falls to pieces. It is insoluble in water, but it decomposes that liquid at the moment it comes in contact with it. An effervescence takes place, and phosphorated hydrogen gas is emitted, which is spontaneously inflamed when it comes to the surface of the water. It is owing to this gas that phosphuret of lime, when it is moistened, gives out the fetid smell of garlic; and as this gas is formed by the decomposition of the water, part of it combines with the phosphuret of lime and forms a hydrogenated phosphuret, so that the phosphuret when it is taken from the water and dried, gives out flame, when concentrated muriatic acid, which disengages the phosphorated hydrogen gas, is poured upon it.

II. Sulphuret of Lime.

1. This compound of sulphur and lime may be prepared by exposing to heat in a crucible, sulphur and lime reduced to powder. They fuse slightly, or rather combine into an acrid, reddish mass, which is the sulphuret of lime, formerly called calcareous liver of sulphur.

2. When it attracts moisture from the air, or if a little water be thrown upon it, it changes colour, and passes to a greenish yellow, emitting at the same time a most extremely fetid odour, and forming sulphurated hydrogen gas, becomes a hydrogenated sulphuret.

3. When sulphur and lime are combined together by means of water, the result is not a simple sulphuret, but always a hydrogenated sulphuret, on account of the water which is decomposed. This may be prepared, either by throwing water on quicklime, covered with sulphur in powder; the heat which is emitted by the flaking of the lime effecting the combination; or it may be prepared by heating in a matra, sulphur and lime in powder with ten times their weight of water, or by heating lime water on sulphur. By the two first processes, a liquid is obtained of a red, orange, or yellow colour, of an extremely fetid odour, and a pungent, acrid taste. This hydrogenated sulphuret of lime exposed to the air, is deprived of its colour, gradually decomposed, and the sulphur combining with the oxygen of the air, is first converted into sulphurous, and afterwards into sulphuric acid. It is decomposed by

Anhydrous Sulphate of Lime.

This is a variety of the sulphate of lime found native in different places, which, as the name imports, contains no water of crystallization. It is found crystallized. The primitive form of the crystal is a rectangular prism, having two of its bases broader than the other two. The specific gravity is 2.950. It has a pearly lustre, considerable hardness, phosphoresces when it is heated, is transparent, and insoluble in water. The component parts are, according to the analysis of Mr Chenevix,

| Acid | 44.88 | |------|-------| | Lime | 55.12 |

100.00

2. Sulphite of Lime.

1. This salt may be prepared by passing a current of sulphurous acid gas into a bottle of distilled water, in which is suspended pure carbonate of lime in powder. A brisk effervescence takes place; the sulphite, as it forms, falls to the bottom in the state of powder; and if the gas be continued to be added after the effervescence has ceased, the sulphite of lime in the state of powder is completely redissolved; the liquid becomes warm; and as it cools, it affords crystals.

2. This salt is either in the state of white powder, or in the form of fixed prisms, terminated by long, fixed pyramids. At first it has no taste, but when it is kept in the mouth for some time, it becomes fulphurous. It effloresces slowly when exposed to the air, and is converted into sulphate of lime on the surface. It is less soluble in water than the sulphate of lime, requiring 800 parts of water to dissolve it.

3. When it is exposed to heat, it is deprived of some water, becomes white, and is reduced to powder. A strong heat separates some sulphur, and it is then converted into sulphate of lime.

4. The component parts of this salt are,

| Sulphurous acid | 48 | | Lime | 47 | | Water | 5 |

100

3. Nitrate of Lime.

1. This salt, which is the compound of nitric acid and lime, has been long known under the names of calcareous nitre, mother water of nitre, Baldwin's phosphorus. It always accompanies nitre, and, as one of its names imports, remains in the solution from which nitre has been obtained.

2. This salt may be prepared by dissolving carbonate of lime in nitric acid, evaporating to the constance of syrup, and allowing the solution to cool slowly. It is thus obtained in the state of crystals.

3. The crystals of nitrate of lime are in the form of fixed prisms, terminated by long pyramids. Sometimes they are in the form of long striated needles, grouped together, of a silvery whiteness. The taste is acrid, hot, and bitter. The specific gravity is 1.6207.

4. This is one of the most deliquescent salts. Exposed to the air for a few hours, it is totally melted.

III. Compounds of Lime with Acids.

1. Sulphate of Lime.

The compound of sulphuric acid and lime has been known under a great variety of names, as selenite, gypsum, plaster of Paris, alabaster, vitriol of lime. The sulphate of lime is found in great abundance in nature; and it is found sufficiently pure, so that artificial preparation is not required.

When sulphate of lime is pure, it is frequently found crystallized. The primitive form of its crystals is a quadrangular prism, whose bases are rhomboidal, and the angles 113° and 67°. The integrant particle has the same form. The specific gravity is from 2.1679 to 2.3144. It is not changed by exposure to the air. It is little soluble in water. Five hundred parts of cold water, and 450 of boiling water, are required to dissolve it. When it is exposed to heat, it loses its water of crystallization, decrepitates, becomes very friable, and falls down into a very white opaque powder. When this powder is reduced to a paste with water, it absorbs it very rapidly, and becomes in a very short time solid. From this peculiar property, it is employed for forming casts, under the name of plaster of Paris. When it is strongly heated for a long time, it becomes phosphorescent, and then melts; and before the blow-pipe it gives an opaque, vitreous globule.

This salt becomes more soluble by the action of sulphuric acid, without being converted into an acidulous sulphate of lime. The nitric and muriatic acids increase its solubility without decomposing it. It is partly decomposed by the phosphoric acid in the cold.

The component parts of sulphate of lime, according to Bergman, are,

| Acid | 46 | | Lime | 32 | | Water | 22 |

100

After being dried in different temperatures, according to Mr Kirwan, the component parts are,

| Acid | 50.39 | 56.84 | 56 | | Lime | 35.23 | 38.81 | 41 | | Water | 14.38 | 5.35 | 00 |

100.00 100.00 100 It is sometimes employed in chemistry on account of this property of attracting moisture, to deprive gases of the vapour of water with which they may be combined. For this purpose, the gases are made to pass through tubes which contain dried nitrate of lime. It is owing to a mixture of this salt, that nitre is sometimes deliquescent in the air. The nitrate of lime is extremely soluble in water. One part of cold water dissolves four of this salt. Boiling water dissolves still more.

5. When heated, this salt is very fusible. It melts like oil, and after it becomes dry, it often acquires, during calcination, the property of becoming luminous in the dark. Hence the origin of one of its names. More strongly heated, it is decomposed; gives out red vapours of nitrous gas, oxygen and azotic gases, and there remains behind pure lime.

6. This salt is decomposed by the sulphuric acid, partially by the phosphoric, and by potash and soda. By double affinity it is decomposed by the sulphates of potash, of soda, and ammonia. Sulphate of lime, which is an insoluble salt, is always precipitated.

7. By the analysis of Bergman, the constituent parts of nitrate of lime are the following:

| Acid | Lime | Water | |------|------|-------| | 43 | 32 | 25 |

100

By the analysis of Mr Kirwan, when it is well dried in the air,

| Acid | Lime | Water | |------|------|-------| | 57.44| 32.00| 10.56 |

100.00

This salt has not been applied to any use. It is recommended by Fourcroy as a substitute for nitre in the extraction of nitric acid.

4. Nitrite of Lime.

When the nitrite of lime is exposed to heat, till it give out some bubbles of oxygen gas, there remains behind a calcareous nitrite, which converts vegetable blues to green, and gives out a great quantity of red vapour by the action of acids. It seems to be in the state of nitrite of lime, that this compound possesses the phosphorescent property.

5. Muriate of Lime.

1. The compound of muriatic acid and lime has been known by the names of calcareous marine salt, fixed sal ammoniac, and Homberg's phosphorus. This salt is frequently found in solution in some mineral waters.

2. It is prepared by saturating muriatic acid with carbonate of lime, and evaporating the solution to the consistence of syrup. It crystallizes on cooling.

3. The muriate of lime crystallizes in six-sided prisms, terminated by six-sided pyramids. The taste is acid, bitter, and disagreeable. It is extremely deliquescent in the air. Cold water dissolves nearly double its weight. Its specific gravity is 1.76.

4. Exposed to heat, it becomes soft, melts, and lime swells up, and then is deprived of its water of crystallization. At a very high temperature it is also deprived of part of its acid. In this state, with an excess of heat, of lime, it acquires the property of shining in the dark, from which it has been called the phosphorus of Homberg.

5. This salt is decomposed by the sulphuric acid, of acid by the nitric acid, which converts it into the oxymuriatic, and partly by the phosphoric and fluoric acids.

6. According to the analysis of Bergman, the constituent parts of this salt are,

| Muriatic acid | Lime | Water | |---------------|------|-------| | 31 | 44 | 25 |

100

But according to Mr Kirwan, when it is dried in a red heat, it is composed of

| Acid | Lime | Water | |------|------|-------| | 42 | 50 | 8 |

100

7. This salt is only employed for chemical experiments, and particularly for the production of artificial cold, by mixing it with snow or pounded ice. Of all the salts employed for this purpose, it seems to have the greatest effect, in consequence of the rapid transition from the solid to the liquid state. To prepare the salt for this purpose, it is most convenient to evaporate it to the consistence of a pretty thick syrup; and then by stirring it constantly as it cools, it is obtained in a dry granulated state, which should be reduced to powder in the cold, and put up in bottles secured with ground stoppers.

6. Hyperoxymuriate of Lime.

This salt, which is the compound of hyperoxymuriatic acid and lime, is prepared by putting a quantity of pure white marble, reduced to powder, into one of the bottles of Woulfe's apparatus, half filled with water, and by passing a current of oxymuriatic acid gas into the liquid, till the effervescence ceases, and the powder has nearly disappeared. It acquires a pungent fleshy taste, with a reddish colour. It exhales the odour of oxymuriatic acid, and not of the hyperoxymuriatic acid. When ammonia is added to this solution, it is decomposed, and there remains ordinary muriate of lime, from which circumstance it seems doubtful whether there is at all formed a hyperoxymuriate of lime. According to Mr Chenevix, this salt is extremely deliquescent, melts at a low heat, in its water of crystallization, and is very soluble in alcohol. The component parts of this salt are,

| Acid | Lime | Water | |------|------|-------| | 55.2 | 28.3 | 16.5 |

100.0* This salt has been successfully employed in the processes of bleaching.

7. Fluate of Lime.

1. The compound of fluoric acid and lime has been long known under the names of fluor spar, cubic spar, and phosphoric spar, from the figure of its crystals, or from some of its properties. This salt exists in great abundance in nature, and in a state of considerable purity.

2. It may be artificially prepared, by combining fluoric acid with lime in solution in water. The salt is deposited in the form of powder in the bottom of the vessel; and when it is taken out, it is to be well washed and dried.

3. When the fluate of lime is found native, it is generally crystallized in the form of cubes, the angles of which, and sometimes the edges, are truncated. The primitive form of the crystal is the regular octahedron. The form of its integral particle is the regular tetrahedron. It has frequently a considerable degree of transparency, and exhibits a great variety of colours. The specific gravity is 3.15. It has no taste, is not altered by exposure to the air, and it is insoluble in water.

4. When it is exposed to heat, it decrepitates and becomes luminous in the dark; but when it has once given out this light, it cannot be restored, either by exposing it to the sun's rays, or by calcination with charcoal or any other combustible substance. From this circumstance it appears, that this phosphorescent property is owing to some volatile principle which has been a constituent part of the salt. The artificial fluate of lime also possesses the same property, and even, according to Scheele, in a higher degree. When it is strongly heated, it melts into a transparent glass.

5. This salt is decomposed by the sulphuric, nitric, and muriatic acids, by the carbonates of potash and soda, and by most of the phosphates. It is by decomposing it by means of the sulphuric acid, that the fluoric acid is obtained.

6. The fluate of lime is much employed in small pieces of sculpture, and for ornamental purposes in the formation of cups, vases, and pyramids. It is employed also as a flux for mineral substances.

8. Borate of Lime.

This salt, which is a compound of boracic acid and lime, is prepared by pouring a solution of boracic acid into lime water, or by decomposing the soluble alkaline borates by means of lime water. A precipitate is thus formed, of a salt nearly insoluble, which is insipid, and in the form of a white powder. Little is known of the properties of this salt.

9. Phosphate of Lime.

1. The compound of phosphoric acid and lime, known under the name of calcareous phosphoric salt, is one of the most interesting discoveries of modern chemistry. This was made by Scheele and Gahn in 1774, when they proved that it formed the basis of bones. To obtain this salt in a state of purity, a quantity of bones is calcined to whiteness, reduced to powder, and well washed with water to separate the carbonate of soda and other soluble salts which are generally combined with it. The phosphate of lime is thus procured in the form of an insipid white powder. In this state it is generally mixed with a little carbonate of lime, which may be separated by diluted acetic acid, and afterwards washing it with water.

2. By this process the phosphate of lime is procured Properties, in a state of purity from the solid matter of bones. It has no taste, and does not change the colour of vegetable blues. When it is prepared artificially, it is in the form of white powder, but as it exists in nature, it is found regularly crystallized. This is known to mineralogists under the name of apatite, of which there are several varieties. The primitive form of its crystal is the regular six-sided prism; the primitive form of the integrant molecule is a three-sided prism, whose bases are equilateral triangles. It remains unaltered by exposure to the air, and it is soluble in water.

3. When this salt is exposed to heat, it scarcely undergoes any change; but when it is exposed to the strong heat of a glasshouse furnace, it is converted into a transparent porcelain.

4. The phosphate of lime is decomposed by the fulphuric, nitric, muriatic, and other acids; but this decomposition is only partial. Part of the lime only is abstracted, and the salt is converted into an acidulous phosphate of lime.

5. The component parts of phosphate of lime, according to Fourcroy and Vauquelin, are,

| Acid | 41 | |------|----| | Lime | 59 |

6. The phosphate of lime is of great importance in Uses, chemistry, for the purpose of extracting phosphoric acid, to be decomposed to obtain phosphorus. It is also employed for making cupels, for polishing metals and precious stones, and for removing spots of grease from linen, paper, and silk. It is used in medicine as a remedy for rickets, to correct the supposed effects of acids in softening the bones.

Superphosphate of Lime.

1. This salt, with an excess of acid, was discovered History, by Fourcroy and Vauquelin in 1795. Scheele had remarked, that the phosphate of lime was dissolved by an acid in human urine; but he had not ascertained that this combination between the phosphoric acid and the phosphate of lime constituted a permanent salt.

2. It may be obtained artificially by the partial de-Preparation composition of the phosphate of lime by means of any tion, acid, or by dissolving this salt in phosphoric acid. This last process, Foureroy observes, is the most certain; and when the phosphoric acid has dissolved as much as it can take up of the phosphate of lime, the salt is in the state of acidulous phosphate, or superphosphate.

3. This salt crystallizes in small silky threads, or in Properties, brilliant plates of a pearly lustre, which are attached to each other, and seem to have the consistence of honey or glue. It has a strong acid taste. Exposed to the air, it is slightly deliquescent. It is soluble in water, and the solution produces cold. It is more soluble in boiling water, and crystallizes by cooling.

4. When this salt is exposed to heat, it first melts, Action of and then swells up and dries. If the temperature be heat increased, it undergoes the igneous fusion, and is con- Lime, &c., verted into a transparent glass. The phosphoric acid in this salt is more readily decomposed by charcoal than in the neutral phosphate of lime. It is not decomposed by any of the acids, excepting the oxalic. The proportions of its constituent parts are the following.

| Acid | Lime | |------|------| | 54 | 46 |

100 *.

10. Phosphite of Lime.

1. This salt, composed of phosphorous acid and lime, is formed by the direct combination of the acid with the earth, and when they are saturated, it falls to the bottom in the form of white powder. This powder is re-dissolved with an excess of acid, and in this state of acidulous phosphite of lime, crystallizes by evaporating the solution.

2. When thus obtained, it is in the form of a white powder, if it is just neutralized; but with an excess of acid, it forms small prisms or needles. This salt has no taste; it is not changed by exposure to the air; and it is insoluble in water.

3. When it is exposed to heat, it gives out a phosphoric light, yields a small quantity of phosphorus, and is converted into a phosphate. By the action of the blow-pipe it melts into a transparent globule.

4. The neutral phosphite of lime is soluble in acids, without being decomposed. The proportions of its constituent parts are,

| Phosphorous acid | Lime | Water | |------------------|------|-------| | 34 | 51 | 15 |

100

11. Carbonate of Lime.

1. This salt exists in great abundance in nature, and it is known by great variety of names, as limestone, marble, chalk. It may be prepared artificially, by directly combining carbonic acid with lime; but in this process the proportions of the acid and earth must be accurately adjusted; for, if there is too little acid, the first precipitate which is formed is re-dissolved in the water, and seems to form carbonate with excess of lime. If there be too much acid, the carbonate first precipitated is also re-dissolved, and disappears in this excess of carbonic acid.

2. The carbonate of lime is perfectly tasteless. The specific gravity is 2.7. It is frequently found crystallized, and exhibits a great variety of forms. When it is transparent and in the rhomboidal form, it has the property of double refraction. The primitive form of its crystals is an obtuse rhomboid, whose angles are about 101° and 78°. The integrant molecule has the same form.

3. When it is exposed to the air it undergoes no change. It is insoluble in water.

4. Exposed to a strong heat, it decrepitates, and is deprived of its water of crystallization. It becomes white, opaque, and friable. If the heat be increased and continued, the whole of the carbonic acid is driven off in the state of gas.

5. The carbonate of lime is readily decomposed by all the acids with effervescence, owing to the disengagement of the carbonic acid in the state of gas.

6. The component parts of carbonate of lime, as they have been ascertained by the analysis of Bergman and Kirwan, are the following.

| Bergman. Kirwan. | |-------------------| | Acid | Lime | Water | | 34 | 55 | 11 |

100 100

12. Arseniate of Lime.

This salt, which is a compound of arsenic acid and lime, is prepared by dropping the acid into lime water. A precipitate is formed, which is soluble, either with an excess of the base, or the acid. Or it may be formed by dissolving carbonate of lime in arsenic acid. The acidulous arseniate of lime, when it is evaporated, affords small crystals. When this salt is heated, it melts, but is not decomposed.

13. Tungstate of Lime.

The compound formed by tungstic acid and lime, is found native. It is from the mineral called tungsten, that the metallic substance is obtained which bears this name. When the solution of tungstic acid is added to lime water, a precipitate of tungstate of lime is formed, similar to the native compound tungsten. This mineral is found crystallized. The primitive form of the crystal is the octahedron, which is composed of two four-sided pyramids, applied base to base. It is of a yellowish colour, with some degree of transparency and considerable hardness. It is insoluble in water, and is scarcely altered by the action of heat. The specific gravity is about six. The component parts of this salt are,

| Tungstic acid | Lime | |---------------|------| | 70 | 39 |

100

14. Molybdate of Lime.

15. Acetate of Lime.

1. The compound of acetic acid and lime is formed by dissolving the carbonate of lime in the acid, till it is saturated. By evaporating the solution till a pellicle forms on the surface, it crystallizes on cooling.

2. The crystals of acetate of lime are in the form of small prisms, with a shining silky lustre. The taste is bitter and sour. It is not changed by exposure to the air, but is soluble in water. The specific gravity is 1.005.

3. When it is exposed to heat, it is decomposed, partly by the separation of the acid, and partly by its decomposition. The component parts of this salt, according to Dr. Higgins, are,

| Acetic acid and water | Lime | |-----------------------|------| | 64.3 | 35.7 |

100 100 16. Oxalate of Lime.

The oxalic acid saturated with lime, forms an insoluble salt, which may be formed by dropping oxalic acid into any of the acid solutions of lime. The oxalate of lime, thus formed, is a white powder, which converts the syrup of violets to a green. This salt cannot be decomposed by any other acid, the affinity of oxalic acid for lime is so strong. It is on this account that oxalic acid is employed as a test for lime, whether it is in a state of combination, or uncombined. This salt may be decomposed by exposing it to heat. The acid itself is driven off, and undergoes decomposition.

The component parts of this salt, according to Bergman, are,

| Acid | 48 | |------|----| | Lime | 46 | | Water| 6 |

17. Tartrate of Lime.

The compound of tartaric acid and lime may be formed, by dissolving lime in the acid; or by adding a solution of lime in water to a solution of tartar in boiling water, till it ceases to effervescence, and to redden vegetable blues. The salt precipitates in the form of a white powder, which is insoluble, excepting with an excess of acid. This salt is decomposed by the sulphuric, nitric, and muriatic acids.

18. Citrate of Lime.

This salt, which is a compound of citric acid and lime, may be formed by the direct combination of the acid and the earth. Small crystals are formed, which are precipitated, and are scarcely fusible in water, excepting with an excess of acid, and from this solution it may be obtained crystallized. The component parts of this salt are,

| Citric acid | 62.66 | | Lime | 37.34 |

19. Malate of Lime.

1. The compound of malic acid and lime may be formed by combining the acid with the earth, and neutralizing them. Small irregular crystals are thus obtained, which are scarcely soluble in boiling water, but become very soluble with an excess of acid. In this state it is the supermalate of lime. This salt is found ready formed in some vegetables, as in horseradish and similar succulent plants.

2. This acidulous malate of lime has an acid taste. When it is evaporated, it forms a solid, shining substance, analogous to varnish. It is decomposed by the sulphuric and oxalic acids, and also by the alkalis. Lime water added to a solution of this salt, combines with excess of acid, and precipitates the malate of lime.

20. Gallate of Lime.

The gallic acid combined with lime, forms a yellowish coloured, insoluble salt, which, with an excess of base, becomes soluble.

21. Benzoate of Lime.

The compound of benzoic acid and lime, forms a salt which is very soluble in water. This salt crystallizes in an arboreal form on the sides of the vessel which contains the solution. It is decomposed by the sulphuric, nitric, and muriatic acids. It exists in great abundance in the urine of granivorous quadrupeds.

22. Succinate of Lime.

The compound of succinic acid and lime forms salts which are not very soluble in water, and are not altered by exposure to the air.

23. Saccolate of Lime.

Saccharic acid and lime form an insoluble salt.

24. Camphorate of Lime.

1. This salt, which is a compound of camphoric acid and lime, is formed by adding lime water to crystallized camphoric acid. The solution is then to be boiled, filtered, and evaporated to three-fourths of its quantity. As it cools, the salt is deposited.

2. The camphorate of lime has no regular shape, unless the evaporation has been properly managed, when it is found in the form of plates lying on each other. It is of a white colour, and has a slightly bitter taste.

3. It effloresces in the air, and falls down into powder. It is scarcely soluble in cold, and requires water and about 200 parts of boiling water for its solution. When it is exposed to heat, if it be moderate, it melts and swells, but if thrown on red-hot coals, or heated in close vessels, the acid is decomposed and sublimed, and the lime remains pure.

4. It is decomposed by the sulphuric, nitric, and muriatic acids. With the sulphuric acid there is formed an insoluble precipitate. The nitric and muriatic acids precipitate the camphoric acid. This salt is also decomposed by the carbonate of potash, and the phosphate of soda.

5. The component parts of this salt are,

| Camphoric acid | 50 | | Lime | 43 | | Water | 7 |

100*

25. Suberate of Lime.

This salt, which is a compound of suberic acid and lime, does not crystallize, is perfectly white, has a slight saline taste, and does not redden the tincture of turpentine. It is scarcely soluble in cold water. Boiling water dissolves it more abundantly, but as it cools, a part of it is precipitated. When it is placed upon burning coals, it swells up, the acid is decomposed, heat, and the lime remains in the state of powder. This salt is decomposed by the sulphuric, nitric, and muriatic acids, by potash and soda, and their carbonates, and by the phosphate and borate of soda.

26. Mellate of Lime.

The mellitic acid dropped into lime-water, forms a precipitate which is re-dissolved by adding nitric acid. Or when the mellitic acid is mixed with a solution of sulphate of lime, a precipitate is formed of small, gritty crystals, which do not affect the transparency of the water.

27. Lactate of Lime.

The compound of lactic acid and lime forms a deliquescent salt, which is soluble in alcohol.

28. Prussiate of Lime.

The compound of prussic acid and lime is formed by dissolving the lime in the acid. The solution is then to be filtered, and the lime which has not combined with the acid is to be separated by adding carbonic acid in water, in the proportion necessary to precipitate the lime from the same bulk of lime-water. The solution, after a second filtration, must be preserved in close vessels. By distillation the prussic acid is driven off, and the pure lime remains behind. This salt is decomposed by all the other acids, and also by the alkalies.

29. Sebate of Lime.

When sebatic acid is dropped into lime-water, the transparency of the water is not disturbed, so that the compound of this acid with lime is soluble in water.

IV. Compounds of Lime with Inflammable Substances.

Lime does not enter into combination with alcohol or ether; but it forms compounds with the fixed oils, which are known by the name of soaps. Lime combines also in small quantity with the volatile oils, forming a similar compound.

Sect. II. Of BARYTES and its Combinations.

1. For the knowledge of this earth we are indebted to modern chemistry. It was discovered by Scheele in 1774; and its properties were investigated by him, and in the following year by Gahn, who analyzed a mineral which had been distinguished by the name of ponderous spar, on account of its weight, and found that it was composed of sulphuric acid and the new earth. It received the name of terra ponderosa from Bergman, who also examined its properties, and confirmed the experiments of Scheele and Gahn. Mr Kirwan gave it the name of barytes, from the Greek word βαρύς, which signifies heavy. Its properties were further investigated by Dr Hope, in 1793*, and by Pelletier, Fourcroy, and Vauquelin, in 1797†.

2. This earth may be obtained in a state of purity by the following process: A quantity of sulphate of barytes, a mineral found in considerable abundance in nature, is first reduced to a fine powder. Mix it with 1/3 of its weight of charcoal powder, and expose the mixture in a crucible to a strong heat, for several hours. The sulphuric acid, by this process, is decomposed, by being deprived of its oxygen, which combines with the carbure of the charcoal, and forms carbonic acid, which is driven off. The sulphur remains in combination with the earth, forming a sulphuret of barytes. This sulphuret is to be dissolved in water, and nitric acid poured into the solution. The nitric acid combines with the barytes, and forms nitrate of barytes, while the sulphur is precipitated. The solution is to be filtered, and slowly evaporated till it crystallizes. The crystals thus formed are then put into a crucible, and exposed to a strong heat. The nitric acid is decomposed, and driven off, and the earth remains behind in a state of purity.

Dr Hope has recommended another process, which is more economical. By this process the sulphate of barytes is decomposed as in the former. The sulphuret which is obtained, is thrown into water, that all soluble matters may be dissolved. To the solution, after filtration, a solution of carbonate of soda is to be added. A precipitate takes place in the form of a white powder. This powder is to be washed with water, made up into balls with charcoal, and exposed to a strong heat in a crucible. The balls are afterwards to be thrown into boiling water, when part of the barytes is found dissolved, and, as the water cools, it crystallizes.

3. Barytes, as it is obtained by decomposing the proper nitrate in the first process, is in the form of small, gray, porous masses, which are easily reduced to powder. It has a hot, burning taste; and when introduced into the stomach, is a deadly poison. Its specific gravity is 4.00. It destroys the texture of all animal substances. It converts vegetable blues to a green colour. In many of its properties it is perfectly analogous to the fixed alkalies.

4. When it is exposed to the air, especially if the atmosphere be loaded with moisture, it swells up in a few minutes, becomes hot, and at last falls into a white powder. It is then deprived of part of its acrimony, and is increased in weight 0.22. This is owing to the absorption of water from the atmosphere. If a small quantity of water be thrown upon barytes, it boils up, is strongly heated, is enlarged in volume, and gives out a great quantity of heat. After being flaked in this manner, it is diluted with water, the earth crystallizes, and assumes the appearance of needle-formed crystals, which, at the end of some time, if exposed to the air, spontaneously fall to powder. With a greater quantity of water the barytes is completely dissolved. Cold water takes up about 1/5 of its weight. This solution changes the syrup of violets to green, and at last destroys the colour. When this liquid is exposed to the air, a thick pellicle is formed on the surface, which is owing to the absorption of carbonic acid from the atmosphere. Boiling water dissolves 1/5 of its weight of pure barytes. The solution affords crystals as it cools. They are in the form of long, four-sided prisms, transparent and white, which effloresce in the air; but the form of the crystals varies according to the rapidity of the evaporation and crystallization.

5. Light has no action on barytes. Heated on charcoal with the blow-pipe, it melts into an opaque, gray globule, which soon penetrates the charcoal. Exposed to heat in a crucible, it melts, and attaches itself to the sides of the vessel, to which it adheres strongly, forming a kind of greenish covering. Left strongly heated, it hardens, and internally assumes a bluish green shade. There is no action between barytes and oxygen, azote, hydrogen, or carbure.

I. Phosphuret I. Phosphuret of Barytes.

1. Barytes enters into combination with phosphorus, forming the compound called phosphuret of barytes. This is prepared by introducing a mixture of barytes and phosphorus into a glass tube closed at one end, and exposing the mixture to the heat of burning coals. The two substances rapidly combine together.

2. The phosphuret of barytes, thus obtained, is of a dark or shining brown colour, having a metallic appearance, very fusible, and exhaling, when it is moistened, a strong fetid odour; in the dark it is luminous. When it is thrown into water, it is decomposed, giving out phosphorated hydrogen gas, and is gradually converted, by the action of the air and the water, into phosphate of barytes.

II. Sulphuret of Barytes.

1. A similar combination also takes place between barytes and sulphur. The combination may be formed by introducing barytes and sulphur well mixed together, into a crucible, and exposing them to a red heat. At that temperature the mixture melts, and the compound which is formed is the sulphuret of barytes.

2. This substance is very soluble in water, which it instantly decomposes; and, when it is saturated with the sulphurated hydrogen which is formed, it is converted into a hydrogenated sulphuret of barytes, which deposits by cooling, crystals of different forms, sometimes in that of small needles, sometimes in that of large six-sided prisms, sometimes in the form of octahedrons, and often in that of small, brilliant, hexagonal plates, which are crystals of sulphurated hydrogen and barytes, denominated by Berthollet, hydrofulphuret of barytes. When the sulphuret of barytes is dissolved in water, it instantly exhales the fetid odour of sulphurated hydrogen gas. The liquid which has deposited crystals of hydrofulphuret of barytes, retains a hydrogenated sulphuret in solution. When it is exposed to the air, this solution becomes an orange yellow. Crystals of hydrofulphuret of barytes, with spots or yellowish plates, are often observed in the midst of the white masses.

3. The sulphuret of barytes is most remarkable for the great rapidity with which it decomposes water, and the great quantity of the sulphurated hydrogen with which it combines, forming the hydrofulphuret of barytes; which latter is slowly, and with difficulty, decomposed by the air, and the great proportion of sulphurated hydrogen gas which is disengaged by the action of acids, without any precipitation of sulphur.

4. Thus, there are three different combinations of sulphur with barytes. In the first, the sulphur is directly combined with the barytes, as when they are exposed to heat in the state of dryness, which is the simple sulphuret of barytes. In the other, the sulphur combined with the hydrogen, is in the state of hydrofulphuret of barytes. This compound is prepared by passing sulphurated hydrogen gas into water holding barytes in solution, which, as it combines with the gas, becomes more soluble, and is condensed and absorbed by the water. The distinctive character between the latter combination and that of the sulphuret of barytes is, that the first, by the action of acids, only gives out sulphurated hydrogen gas, without any deposition of sulphur; and the second, exposed to heat, is deprived of its sulphur, which is sublimed, without affording sulphurated hydrogen gas. Between these two states, there is an intermediate combination, in which the sulphuret of barytes holds in solution more or less sulphurated hydrogen; so that, by the action of acids, it affords sulphurated hydrogen gas, with a deposition of sulphur at the same time. To this intermediate compound, Berthollet has given the name of hydrogenated sulphuret of barytes.

III. Compounds of Barytes with the Acids.

Barytes enters into combination with the acids, and forms with them compounds, which are distinguished by the name of salts. The order of the affinities of barytes for the acids, according to Bergman, is the following:

- Sulphuric acid, - Oxalic, - Succinic, - Fluoric, - Phosphoric, - Sulfuric, - Nitric, - Muriatic, - Suberic, - Citric, - Tartaric, - Arsenic, - Lactic, - Benzoic, - Acetic, - Boracic, - Sulphurous, - Carbonic, - Prussic.

1. Sulphate of Barytes.

1. This salt, which is a compound of sulphuric acid and barytes, was formerly distinguished by the name of heavy spar, phosphoric spar, or Bolognian stone. It exists in great abundance in nature, particularly accompanying metallic veins; from which circumstance, probably, and from its great weight, it was supposed to contain a metallic substance. It is rarely formed artificially, as that found in nature is sufficiently pure.

2. The sulphate of barytes is the heaviest of all the salts, the specific gravity being 4.4. It has neither taste nor smell. Sometimes it is found crystallized, and sometimes compact. There is a considerable variety among the forms of its crystals. The primitive form of sulphate of barytes is a rhomboid, with right angles at the bases, whose angles are 101° and 78°. The integrant molecule is the same.

3. This salt remains unchanged in the air, and it is infusible in water. When it is suddenly heated, it decomposes. By the action of a strong heat, it melts with difficulty; and before the blow-pipe it fuses, and is converted into a white opaque globule. It is decomposed at a red heat by hydrogen and charcoal, and is converted into a sulphuret which is phosphoric. This was formerly called, from an accident, Bolognian phosphorus. phosphorus. A piece of the sulphate of barytes was found in the neighbourhood of Bologna, by a hoe-maker of that city, who suspecting that it contained silver, put it into the fire to separate the metal. He found no metal, but he observed that by heating it acquired the property of shining in the dark, and thence it obtained the name of Bolognian stone or phosphorus.

This salt is decomposed by the carbonates of potash and soda, either by exposing them to a strong heat in a crucible, or by boiling them together in solution.

According to the different analyses which have been made to ascertain the constituents of this salt, it appears that there is a considerable difference between the natural and artificial sulphate of barytes, as in the following table.

| Acid | Native | Artificial | |------|--------|------------| | | 13 | 33 | | Barytes | 84 | 64 | | Water | 3 | 3 | | | 100 | 100* |

By another analysis, when the artificial sulphate was heated to redness, the component parts were found according to

| Acid | Thenard † | Cheney ‡ | |------|-----------|----------| | | 25.18 | 24 | | Barytes | 74.82 | 76 | | | 100.00 | 100 |

2. Sulphate of Barytes.

1. This compound of sulphurous acid and barytes, is formed by passing sulphurous acid gas into water, in which is mixed, or suspended, carbonate of barytes in the state of fine powder; or by the direct combination of sulphurous acid and barytes, either solid or in solution. In whatever way it is prepared, the salt is deposited in the form of powder, or crystallized.

2. The crystals of sulphate of barytes are sometimes in the form of small, brilliant, and opaque needles, or very hard transparent crystals in the form of tetrahedrons, with truncated angles. It has little taste. The specific gravity is 1.6938. It is scarcely altered when exposed to the air, and is insoluble in water. When it is exposed to heat, sulphur is driven off, and there remains a sulphate of barytes. It is decomposed by the sulphuric and muriatic acids, with the disengagement of sulphurous acid.

3. This salt has been applied to no use, excepting for the chemical purpose of ascertaining the purity of sulphurous acid. It is employed in this way by Fourcroy. If there be any mixture of sulphurous acid with the sulphuric, it may be detected by this salt; for as there is a stronger affinity between sulphuric acid and barytes than between sulphurous acid and the same earth, the sulphuric acid, if any be present, combines with the barytes, and forms with it an insoluble salt, which is precipitated.

4. The following are the proportions of the constituent parts of this salt.

Sulphurous acid 39 Barytes 59 Water 2

100*

3. Nitrate of Barytes.

1. This compound of nitric acid and barytes is prepared by saturating the acid with native carbonate of barytes; or, by the decomposition of sulphuret of barytes, by nitric acid. By filtration and evaporation this salt crystallizes.

2. The crystals of nitrate of barytes are in the form of regular octahedrons, or in small brilliant plates. The specific gravity is 2.9149. It has a hot, acrid, and astringent taste, and is little changed by being exposed to the air. It is soluble in 12 parts of cold, and in about three or four parts of boiling water. When placed upon burning coals, it decrepitates, boils up, and becomes dry, and gives out sparks round the points where it comes in contact with the burning coal. When it is heated in a retort, it gives out a little water, oxygen gas, and azotic gas; and there remains behind, the barytes in the form of a solid, gray, porous mass.

The constituent parts of this salt, according to Fourcroy, Vauquelin, and Kirwan, are the following:

| Nitric acid | 38 | 32 | | Barytes | 50 | 57 | | Water | 12 | 11 |

100 100

This salt is only employed for detecting sulphuric acid in nitric acid, and to be decomposed for the purpose of obtaining pure barytes.

4. Nitrite of Barytes.

Nothing farther is known of this salt, than that it is formed when the nitrate of barytes is decomposed in a retort by means of heat. If the operation be stopped at the time that a third part of the oxygen gas has been disengaged, the nitrite of barytes remains.

5. Muriate of Barytes.

1. This salt, which is a compound of muriatic acid and barytes, was first investigated by Scheele and Bergman, and little more has been since added by the experiments and researches of other chemists.

2. It is prepared by the direct combination of muriatic acid with the carbonate of barytes; or, by decomposing the sulphuret of barytes by the muriatic acid, filtering the solution, and evaporating till a pellicle appear on the surface. If it be allowed to cool slowly, crystals of muriate of barytes are formed. But the sulphate of barytes, which is employed, sometimes contains iron; so that a muriate of this metal is formed along with the muriate of barytes. To separate the iron, the mixture is to be calcined, by which the acid is driven off, and the iron remains behind in the state of oxide, which is insoluble in water.

3. The primitive form of the crystals of this salt is... a four-sided prism with square bases. The form of the integrant particle is the same. It crystallizes in tables, or in eight-sided pyramids. The taste is acid, attrin- gent, and metallic. The specific gravity is 2.8257.

4. It undergoes no change by exposure to the air. It is soluble in five or six parts of cold water, but boiling water dissolves more; and, on cooling, the salt crystallizes.

5. When exposed to heat, it decrepitates, loses its water of crystallization, dries, falls down to powder, and at last melts; but no heat that can be applied decomposes it.

6. This salt is decomposed by the sulphuric and nitric acids, and a precipitation of nitrate or of sulphate of barytes is formed.

7. The constituent parts of this salt, according to Mr Kirwan, are,

| Acid | Barytes | Water | |------|---------|-------| | 20 | 64 | 16 | | 23.8 | 76.2 | 00.0 |

When dried.

100 100.0

8. This is one of the most delicate tests for detecting sulphuric acid in any solution. Water, which holds 0.0002 parts of sulphuric acid, exhibits a visible precipitate by a single drop of the solution of muriate of barytes. Nay, there is a slight cloud in a few minutes produced by the addition of a solution of this salt to water which holds 0.00009 parts of sulphuric acid in solution. The muriate of barytes has been proposed and recommended as a cure for scrofula; and it is said, in some cases in which it has been used, with good effect; but it ought to be administered with the utmost caution. The carbonate of barytes is one of the most active poisons, and probably all the salts of this earth are possessed of similar properties. The active dose should not exceed five or six drops of the solution at first.

6. Hyperoxymuriate of Barytes.

1. The compound of hyperoxymuriatic acid and barytes was formed by Mr Chevenix. The process which he followed was, to cause a current of oxymuriatic acid gas to pass through a solution of a large quantity of barytic earth in warm water. This salt he found soluble in four parts of cold, and less of warm water; but as it crystallizes like the muriate of this earth, and has the same degree of solubility, he could not separate the hyperoxymuriate from the muriate, which was formed at the same time. He therefore thought of obtaining it by double affinity, as in the following process.

2. When phosphate of silver is boiled with muriate of barytes, a double decomposition takes place; muriate of silver and phosphate of barytes are formed, both of which being insoluble, are precipitated. But the phosphate of silver does not decompose the hyperoxymuriate of barytes. When therefore the muriate and hyperoxymuriate of barytes are boiled with phosphate of silver, the muriate of barytes only is decomposed. The muriate of silver and the phosphate of barytes are precipitated, and the hyperoxymuriate of barytes remains in solution. When this salt is decomposed by the stronger acids, it is accompanied with a flash of light, which Mr Chevenix conjectures, is owing to the relative proportionate affinities, and consequently the greater rapidity of the disengagement.

The proportions of this salt are,

| Hyperoxymuriatic acid | Barytes | Water | |-----------------------|---------|-------| | 47.0 | 42.2 | 10.8 |

100.0 *

* Phil. Trans. 1802.

7. Fluate of Barytes.

This compound of fluoric acid and barytes may be formed, by pouring fluoric acid into a solution of nitrate or muriate of barytes. A precipitate is formed, which is the fluate of barytes. This salt is decomposed with effervescence by the sulphuric acid, and it is precipitated by lime water. Of the proportions of its constituent parts and other properties nothing is known.

8. Borate of Barytes.

The compound of boracic acid and barytes is formed by pouring a solution of boracic acid into a solution of barytes. An insoluble white powder is precipitated, which, according to Bergman, may be decomposed, even by the weak vegetable acids.

9. Phosphate of Barytes.

1. The compound of phosphoric acid and barytes, prepared has been only examined by Vauquelin. It is prepared, either by the direct combination of phosphoric acid with barytes, or the carbonate of barytes; or by precipitating a solution of nitrate or muriate of barytes, by means of an alkaline phosphate. The phosphate of barytes is precipitated in the form of powder.

2. This salt is in the form of white powder, without any appearance of crystallization. It is not altered by exposure to the air, and is insoluble in water. The specific gravity is 1.2867.

3. This salt at a high temperature is fusible. It is converted into a vitreous matter or gray enamel. Before the blow-pipe, on charcoal, it gives out a yellow phosphoric light. The vitreous globules become opaque on cooling. It is decomposed by the sulphuric acid. The phosphoric and phosphorous acids, when added in excess, have the property of re-dissolving the salts which they form with barytes.

10. Phosphite of Barytes.

1. This compound of phosphorous acid and barytes, is prepared by the direct combination of the acid with the earth; or by precipitating the soluble phosphites by a solution of barytes. By the last process the salt is obtained in the greatest purity.

2. The phosphite of barytes is in the form of a white powder, which is infusible, not altered by exposure to the air, not very soluble in water, and without an excess of acid, by which means it is converted into the acidulous phosphite.

3. The phosphite of barytes melts under the blow-pipe into a globule, which is soon surrounded with a heat, most brilliant light. The vitreous globule becomes, on cooling, white and opaque.

4. This salt is decomposed by most of the acids; by Of acids. lime and lime water. The other alkaline and earthy bases combine with the excess of phosphorous acid, when it is in the state of acidulous phosphate, and there remains behind a neutral phophite.

5. The component parts of this salt are,

| Phosphorous acid | 41.7 | |------------------|------| | Barytes | 51.3 | | Water | 7.0 |

100.0

11. Carbonate of Barytes.

1. This compound of carbonic acid and barytes has been known by the names of aerated heavy spar, aerated barofenite, and witherite from the name of Dr Withering, who first discovered that it is a natural product. Its nature and properties were first investigated by Scheele and Bergman, about the year 1776, and since that time by Kirwan, Hope, Klaproth, Pelletier, Fourcroy, and Vauquelin.

2. The carbonate of barytes is found native in flinty, lamellated, felspar-transparent masses. The primitive form of its crystals is the six-sided prism. The specific gravity is 4.331.

3. The carbonate of barytes may be prepared artificially, by exposing a solution of pure barytes to the air; or, by passing carbonic acid gas into the solution. It may be prepared also in the dry way, by mixing together sulphate of barytes and carbonate of potash or soda, and exposing the mixture to strong heat; or, by decomposing, by means of carbonate of potash, soda, or ammonia, the nitrate or muriate of barytes in solution in water. By whatever process the carbonate of barytes is obtained, it is in the form of a white transparent powder. When thus prepared, the specific gravity is 3.763.

4. It undergoes no change by exposure to the air. Cold water dissolves \( \frac{1}{2} \); boiling water \( \frac{1}{3} \) part.

5. The carbonate of barytes undergoes little change when it is exposed even to the strongest heat. The artificial carbonate loses about 0.28 of its weight by calcination, while the native carbonate becomes white and opaque, and is converted into a bluish green colour, without any perceptible loss of weight; but if it be heated in a black lead crucible, or if it be formed into a paste, with 100 parts of the salt to 10 of charcoal, the carbonic acid is separated.

6. The component parts of the carbonate of barytes are the following:

### Native Carbonate

| Acid | Withering | Fourcroy | |------|-----------|----------| | Barytes | 80 | 90 |

100 100

### Artificial Carbonate

| Acid | Bergman | Pelletier | |------|---------|----------| | Barytes | 65 | 62 | | Water | 28 | 16 |

100 100

When both the natural and artificial are exposed to a red heat, the component parts, as ascertained by Mr Kirwan, are,

| Acid | 22 | |------|----| | Barytes | 78 |

100

7. This salt has been found native only in small quantity, otherwise it is supposed, that it might be of great use for the preparation of baryte salts, which promise great service in several arts and manufactures. It has been proposed to employ it in medicine; but in experiments on animals, it has been found to act as a most deadly poison. Great caution, therefore, should be observed in employing it as an internal remedy.

12. Arseniate of Barytes.

The compound of arsenic acid and barytes is formed by dissolving the earth in the acid. It is an insoluble, uncrystallized salt; but with an excess of acid it becomes soluble, and is decomposed by sulphuric acid. It melts when exposed to a strong heat, but is not decomposed.

13. Tungstate of Barytes.

With the tungstic acid, barytes forms an insoluble salt.

14. Molybdate of Barytes.

Barytes with the molybdic acid forms a salt which has very little solubility.

15. Chromate of Barytes.

It is little known, but said to be insoluble in water.

16. Columbate of Barytes.

17. Acetate of Barytes.

1. This salt, which is a compound of acetic acid and barytes, may be prepared by directly combining the acid with the earth; or, by decomposing sulphuret of barytes by means of acetic acid. By evaporating the solution, it may be obtained crystallized.

2. The crystals of the acetate of barytes are in the form of fine transparent prisms. The specific gravity is 1.828. This salt has an acid bitter taste, effloresces in the air, is very soluble in water, is decomposed by the carbonates of the alkalis, but not by the alkalis themselves, or the pure earths.

3. This salt may be employed to detect the presence and quantity of sulphuric acid in solutions, particularly in vinegar, which may be adulterated with the addition of this acid.

18. Oxalate of Barytes.

1. The compound of oxalic acid and barytes is formed by adding the acid to a solution of barytes in water. A white powder precipitates, which is oxalate of barytes; it is insoluble in water. With an excess of oxalic acid, this precipitate is dissolved, and small angular crystals are formed.

2. If these crystals are dissolved in boiling water, they become opaque, and fall down in the form of an insoluble

19. Tartrate of Barytes.

The compound of tartaric acid and barytes forms a salt in the state of white powder, which has little solubility, excepting with an excess of acid. It is decomposed by the sulphuric, nitric, muriatic, and oxalic acids.

20. Citrate of Barytes.

1. The compound of citric acid and barytes forms a salt, by adding the earth to a solution of the acid. A flocculent precipitate at first appears, which is dissolved by agitation. The precipitate afterwards becomes permanent when the acid is saturated.

2. This salt, which is at first deposited in the form of powder, shoots out afterwards into a kind of vegetation, of a filvery whiteness, with great brilliancy and beauty. It is soluble in a great proportion of water. This salt is composed of

| Acid | 50 | |------|----| | Barytes | 50 |

21. Malate of Barytes.

The compound of malic acid and barytes is formed by adding the acid to a solution of the earth in water. A crystallized, soluble salt is precipitated.

22. Gallate of Barytes.

The compound of gallic acid and barytes is formed by the direct combination of the acid with the earth. A salt is thus formed, which is not very soluble, but with an excess of the base.

23. Benzoate of Barytes.

Benzoic acid combines with barytes, and forms a salt which is soluble in water, crystallizes, undergoes no change by exposure to the air, and is decomposed by heat and the stronger acids.

24. Succinate of Barytes.

Barytes forms, with succinic acid, a salt which has little solubility.

25. Saccolate of Barytes.

This salt is insoluble in water.

26. Camphorate of Barytes.

1. The compound of camphoric acid and barytes is formed by adding the crystallized acid to the solution of the earth, and then boiling the mixture. It is afterwards to be filtered and evaporated to dryness. What remains is camphorate of barytes.

2. This salt does not crystallize; but when it is slowly evaporated, small plates are deposited, which seem transparent in the liquid, but become opaque when exposed to the air. It has scarcely any taste; but an impression remains on the tongue, which is slightly acid and bitter.

3. This salt undergoes no change by exposure to the air. It is only soluble in 600 parts of water at the boiling temperature.

4. When exposed to the action of the blow-pipe, the acid is volatilized, and the earth is converted into Action of a vitreous substance. The camphoric acid, as it burns, heat first exhibits a blue, then a red, and at last a white flame.

5. This salt is decomposed by the sulphuric, nitric, and muriatic acids, and by the oxalic, tartaric, and citric.

27. Suberate of Barytes.

This salt does not crystallize, and is only soluble in water with an excess of acid; when exposed to heat, it fizzes up and melts, and is decomposed by the sulphuric, nitric, muriatic, and oxalic acids.

28. Mellate of Barytes.

By adding mellitic acid to a solution of acetate of barytes, there is formed a flaky precipitate, which is re-dissolved with the addition of more acid. When the acid is poured into a solution of muriate of barytes no precipitate is formed; but a short time afterwards a group of transparent needle-formed crystals is deposited.

29. Lactate of Barytes.

Barytes forms with lactic acid, a deliquescent salt.

30. Prussiate of Barytes.

Prussic acid and barytes form a salt which is very little soluble in water, and is decomposed, not only by the sulphuric acid, but even by carbonic.

31. Sebate of Barytes.

Sebacic acid, added to a solution of barytes in water, forms no precipitate; from which it is inferred that the sebate of barytes is insoluble in water.

SECT. III. Of STRONTITES and its Combinations.

1. This earth was not discovered till about the year History. 1791 or 1792. Dr Crawford, indeed, previous to this period, in making some experiments on what he supposed was a carbonate of barytes, and observing a striking difference between this mineral, and the carbonate of barytes which he had been accustomed to employ, conjectured that it might contain a new earth; and he sent a specimen to Mr Kirwan for the purpose of analyzing it. This conjecture was fully verified by the experiments of Dr Hope†, Mr Kirwan, and M. Edin. Klaproth, who were all engaged in the same analysis nearly about the same time. Strontites is found native in combination with carbonic and sulphuric acids. With the former it is found in considerable quantity in the lead mines of Strontian in Argyleshire, from which it has derived its name strontites, or strontian as it is called by others. The nature and properties of this earth have been still farther investigated by Pelletier, Fourcroy, and Vaquelin.

2. This earth may be obtained in a state of purity, either by exposing the carbonate of strontites, mixed with charcoal powder, to a strong heat, by which the carbonic acid is driven off; or, by dissolving the native Strontites, salt in nitric acid, and decomposing the nitrate of &c. Strontites thus formed, by heat. Strontites obtained by either of these processes, is in small porous fragments of a greenish white colour. It has an acrid, hot, alkaline taste, and converts vegetable blues to green. The specific gravity is 1.647.

3. Light has no perceptible action upon this earth. When it is exposed to heat, it may be kept a long time, even in a red heat, without undergoing any change, or even the appearance of fusion. By the action of the blow-pipe it is not melted, but is surrounded with a very brilliant white flame.

4. When a little water is thrown on strontites, it exhibits the same appearance as barytes. It is flaked, gives out heat, and then falls to powder. If a greater quantity of water be added, it is dissolved. According to Klaproth it requires 200 parts of water at the ordinary temperature of the atmosphere for its solution. Boiling water dissolves it in greater quantity, and when the solution cools, it affords transparent crystals. These crystals are in the form of rhombooidal plates, or in that of flattened silky needles, or compressed prisms. The specific gravity is 1.46. These crystals effloresce in the air, and have an acrid hot taste. The solution of this earth in water is acrid and alkaline, and converts vegetable blues to green. It is soon covered with a pellicle, by absorbing carbonic acid from the atmosphere.

5. Strontites has the property of communicating a purple colour to flame.

6. The order of the affinities of strontites is the following.

- Sulphuric acid, - Phosphoric, - Oxalic, - Tartaric, - Fluoric, - Nitric, - Muriatic, - Succinic, - Acetic, - Arsenic, - Boracic, - Carbonic,

I. Phosphuret of Strontites.

The phosphuret of strontites is prepared in the same way as the phosphuret of barytes.

II. Sulphuret of Strontites.

The sulphuret of strontites is formed by exposing sulphur and the earth in a crucible, to heat. This sulphuret is soluble in water, by means of sulphurated hydrogen, which is disengaged by the decomposition of the water. The strontites thus combined with sulphurated hydrogen, forms a hydro-sulphuret of strontites; and if this solution be evaporated, the hydro-sulphuret of strontites may be obtained in crystals, and the hydrogenated sulphuret remains, as in similar compounds, in solution. When the hydrogenated sulphuret is decomposed by means of an acid, the sulphurated hydrogen gas which is disengaged, burns with a beautiful purple flame, on account of holding in solution a small quantity of the earth, which communicates this property.

III. Compounds of Strontites with the Acids.

1. Sulphate of Strontites.

1. The compound of sulphuric acid with strontites, may be formed by adding sulphuric acid to a solution of strontites in water, and it is obtained in the state of a white powder. It is found native in different places, crystallized in fine needle-formed prisms. It has no taste, and is scarcely soluble in water. It suffers no change in the air. By the action of the blow-pipe it gives out a yellowish purple light. It is not decomposed by any of the acids; but it is decomposed by the carbonate of potash and soda, by the barytic salts, by the sulphates of potash and of soda, the phosphates of potash, soda, and ammonia, and by the borate of ammonia.

2. The component parts of this salt, according to Vauquelin, are,

| Acid | 46 | |------|----| | Strontites | 54 |

But according to Klaproth, Kirwan, and others,

| Acid | 42 | |------|----| | Strontites | 58 |

2. Sulphite of Strontites.

This salt is yet unknown.

3. Nitrate of Strontites.

1. The compound of nitric acid and strontites, is formed by precipitating, by means of nitric acid, the sulphuret of strontites, obtained from the decomposed sulphate, or by dissolving the carbonate of strontites in the acid. By evaporation it may be obtained in crystals.

2. The crystals of nitrate of strontites are in the form of octahedrons. The taste of this salt is cool and pungent. It is not altered by exposure to the air. The specific gravity is 3.0061. It is soluble in 15 parts of cold water, and much more soluble in boiling water, in which it crystallizes on cooling. Exposed to sudden heat it decrepitates. When it is subjected to heat in a crucible, it fizzes up, gives out oxygen and nitrous gas, and there remains behind pure earth. This salt has the property of communicating a purple flame to combustible substances with which it is mixed; as when a little of the salt in powder is thrown on the wick of a candle.

3. The component parts of this salt are, according to Vauquelin.

| Acid | 48.4 | |------|------| | Strontites | 47.6 | | Water | 4.0 |

4. Nitrite of Strontites.

The properties of this salt have not been examined. 5. Muriate of Strontites.

1. The compound of muriatic acid and strontites is prepared by dissolving carbonate of strontites in the acid. By evaporating the solution, the salt is obtained crystallized.

2. This salt crystallizes in long, slender, hexagonal prisms. The taste is cooling and pungent. The specific gravity is 1.4402. It is not altered by exposure to the air. It is very soluble in water. Three parts of the salt are dissolved in two parts of cold water. These crystals, which are soluble in alcohol, communicate a purple colour, which is the distinguishing characteristic of this salt. When heated, it melts, and parts with its water of crystallization, without being decomposed; and there remains behind a semitransparent enamel. This salt is decomposed by a very strong heat. It is decomposed also by the sulphuric, nitric, and phosphoric acids; and by potash, soda, and barytes.

3. The constituent parts of this salt are, according to

| Vauquelin. | Kirwan. | |-----------|---------| | Acid, | | | 23.6 | 18 | | Strontites,| | | 36.4 | 40 | | Water, | | | 40.0 | 42 |

6. Hyperoxymuriate of Strontites.

1. This combination of hypoxymuriatic acid and strontites was prepared by Mr Chenevix, by a similar process to that which he employed in the formation of barytes with the same acid; and in many of its properties it is analogous.

2. The crystals of this salt are in the form of needles. They melt in the mouth, and give the sensation of cold. It is composed of

| Acid, | Strontites, | Water, | |------|-------------|--------| | 46 | 26 | 28 |

7. Fluate of Strontites.

The properties of this salt have not yet been investigated.

8. Borate of Strontites.

This compound of boracic acid and strontites, is in the form of a white powder, and requires 130 parts of water for its solution. It converts the syrup of violets to a green colour, from which it is inferred, that it contains an excess of the earth.

9. Phosphate of Strontites.

1. The compound of phosphoric acid and strontites, is formed by dissolving the carbonate of the earth in acid; or, by mixing together the solutions of muriate of strontites, with those of the alkaline phosphates.

2. It is thus obtained in the form of white powder, which is perfectly tasteless. It is not altered by exposure to the air. It is insoluble in water, without an excess of acid. It melts under the blow-pipe into a white enamel, and gives out a purple, phosphorescent light.

3. The constituent parts of this salt are,

| Acid, | Strontites, | |------|-------------| | 41.24| 58.76 |

10. Phosphite of Strontites.

The name of this salt is unknown.

11. Carbonate of Strontites.

1. This salt is found native; and, as we have already mentioned, was pointed out by Dr Crawford as different from the carbonate of barytes, with which it had been formerly confounded.

2. It may be prepared artificially, by saturating a solution of strontites in water with carbonic acid; or, by precipitating soluble salts with a base of this earth, by means of alkaline carbonates. The carbonate of barytes crystallizes in needles, or in fixed prisms. It has no taste. The specific gravity is 3.6750. It is not changed by exposure to the air, and it is nearly insoluble in water. When it is strongly heated in a crucible, to produce fusion, it is deprived of part of its carbonic acid. When heated under the blow-pipe, it melts into an opaque, vitreous globule, and gives out a purple flame.

3. The component parts of this salt, according to different chemists, are

| Hope. | Klapproth and Kirwan. | Pelletier. | |-------|-----------------------|-----------| | Acid, | 30.2 | 30 | | Strontites, | 61.2 | 69.5 | | Water, | 8.6 | 0.5 |

12. Arseniate of Strontites.

When arsenic acid is dropped into a solution of strontites in water, a copious precipitate is formed, which is re-dissolved when there is an excess of acid. When the arseniate of strontites is neutralized, it is only in a slight degree soluble in water.

13. Tungstate of Strontites.

14. Molybdate of Strontites.

15. Chromate of Strontites.

16. Columbate of Strontites.

17. Acetate of Strontites.

1. This compound of acetic acid and strontites is formed by dissolving the carbonate in the acid. By evaporation the salt may be obtained crystallized.

2. The crystals remain unaltered by exposure to the air. They change vegetable blues to green, and are equally soluble in hot and cold water.

18. Oxalate of Strontites.

The compound of oxalic acid and strontites is formed by the direct combination of the acid with the earth in solution. A precipitate appears in the form of a white powder, which is nearly insoluble in water. It is decomposed by heat. The component parts of this salt are,

| Acid | 40.5 | |------|------| | Strontites | 59.5 |

19. Tartrate of Strontites.

1. This salt is formed by dissolving the earth in the acid. The crystals are in the form of small triangular tables; they are not altered by the air, are impervious to the taste, and soluble in 320 parts of boiling water.

2. The constituent parts of this salt are,

| Acid and water | 47.12 | |----------------|-------| | Strontites | 52.88 |

20. Citrate of Strontites.

1. This combination of citric acid with strontites may be formed by mixing together a solution of nitrate of strontites and citrate of ammonia. A double decomposition takes place, but no precipitate is formed. By slow evaporation, crystals of citrate of strontites may be obtained.

2. This salt is soluble in water.

21. Malate of Strontites.

This salt is scarcely known.

22. Gallate of Strontites.

Little known also.

23. Benzoate of Strontites.

Unknown.

24. Succinate of Strontites.

Succinic acid combines with strontites, and forms crystals, which may be obtained by slow evaporation.

25. Camphorate of Strontites. 26. Suberate of Strontites. 27. Mellate of Strontites. 28. Laclate of Strontites. 29. Prussiate of Strontites. 30. Sebate of Strontites.

Sect. IV. Of MAGNESIA and its Combinations.

1. Magnesia was first known about the beginning of the 18th century, when it was sold by a Roman canon, under the name of magnesia alba, or white magnesia, and the powder of the count of Palma, as a cure for diseases; and like many new remedies, it was considered as universal. In the year 1707, Valentini discovered that this boasted panacea was the produce of the calcined lea which remains after the preparation of nitre. He gave it the pompous name of the laxative powder of many virtues. In the year 1709, Slevogt described the method of obtaining it by precipitation, from the mother lea of nitre. Lancefi and Hoffman examined some of its properties in 1717 and 1722; and although the latter discovered that it formed different combinations with acids from those of lime, it was generally confounded with this latter substance.

But the nature of magnesia was not fully known, till Dr Black, in 1755, entered upon his celebrated investigations of the different properties of this substance, lime and the alkalies, in the mild and caustic state. Margraaf published the result of his experiments and researches on it in 1759, in which he gave many distinctive characters of this earth, and of its combinations; and, at last, by the observations of Bergman, published in 1775, and those of Butini of Geneva in 1779, the nature and properties of magnesia were fully demonstrated.

2. Magnesia, although it exists in great abundance in combination with other substances, has never been found perfectly pure in nature. The process by which it may be obtained in greatest purity, is the following. A quantity of Epsom salt, which is a compound of sulphuric acid and magnesia, is to be dissolved in water, and then precipitated by potash. The precipitate which is formed is to be well washed and dried, both with cold and hot water, to separate any saline matters with which it may be mixed. The nature of this process is obvious. The potash has a stronger affinity for sulphuric acid than magnesia. It therefore combines with the acid, and the magnesia is precipitated.

3. Magnesia, when it is obtained pure, is in the form of a fine white powder, or in white friable cakes resembling starch. It has no smell, and no sensible taste; but becomes dry, and leaves on the tongue a slight sensation of bitterness. Its specific gravity, according to Kirwan, is 2.330. It gives a slight tinge of green to syrup of violets, or other delicate vegetable blues.

4. Magnesia is not acted upon by light. It is not melted when exposed to the greatest heat. By strong heat, calcination it becomes finer, whiter, and more friable. When it is exposed to heat in the form of paste with water, it contracts its dimensions, and acquires a phosphorescent property; for when it is strongly rubbed on a hot iron plate, it becomes luminous in the dark. It is not altered by the action of the blow-pipe on charcoal, but gives out a flame of a slight yellow colour.

5. There is no action between magnesia and oxygen or azote. When exposed to the air, it attracts a little moisture from the atmosphere, but this goes on very slowly.

Butini exposed a quantity of magnesia for the space of two years in a porcelain cup slightly covered with paper, and he found that it had acquired only 1/3 part of its weight in addition, during that time.

6. There is no action between magnesia and hydrogen or carbure, and very little between it and phosphorus.

7. Magnesia is very little soluble in water. According to Mr Kirwan, it requires near 8000 times its weight of cold water to dissolve it. Butini found, that water boiled with this substance, and left in contact with it for three months, had scarcely acquired 1/1000 part of its weight; but water combines with magnesia in the solid state. One hundred parts of magnesia, according to Bergman, thrown into water, and taken out and dried, acquired 18 parts of additional weight.

8. Magnesia enters into combination with the acids, and... Magnesia, and forms with them peculiar salts. The order of its affinities is the following, according to Bergman.

Oxalic acid, Phosphoric, Sulphuric, Fluoric, Arsenic, Saccharic, Succinic, Nitric, Muriatic, Tartaric, Citric, Lactic, Benzoic, Acetic, Boracic, Sulphurous, Carbonic, Prussic.

Magnesia does not enter into combination with the fixed alkalies; but in combination with some of the earths, it becomes fusible by means of a strong heat. With lime in certain proportions, it forms a greenish yellow glass.

Magnesia is much employed in medicine as a gentle laxative, and as an absorbent to destroy the acidity in the stomach. It is used in pharmacy to suspend or aid the solution of resinous and gummy substances, such as camphor and opium, in water, which are otherwise little soluble.

I. Of Sulphuret of Magnesia.

1. Magnesia enters into combination with sulphur, either in the dry or humid way. Two parts of magnesia and one of sulphur, put into a crucible, and exposed to heat, form an orange yellow mass, which is not very soluble in water, but emits the odour of sulphurated hydrogen gas, when it comes in contact with that liquid, and which is very readily decomposed by means of heat. The heat that is applied to obtain this sulphuret must be very moderate, otherwise the sulphur is driven off.

2. The sulphuret of magnesia is formed with more difficulty in the humid way. When two parts of magnesia and one of sulphur in powder, with 20 parts of water, are exposed to heat on a sand bath, the liquid becomes of a pale yellow colour, which is slightly fetid, but has nothing of the strong odour of the other sulphurets. There is formed very little of the sulphuret of magnesia; for the greatest part of the sulphur and magnesian earth remains uncombined. There is very little sulphurated hydrogen produced, the water scarcely exhaling the odour of this gas.

3. The solid sulphuret of magnesia decomposes rapidly when exposed to the air. It seems to absorb very little sulphurated hydrogen gas; so that the properties of the hydro-sulphuret of magnesia are yet unknown*.

II. Compounds of Magnesia with Acids.

1. Sulphate of Magnesia.

The compound of sulphuric acid and magnesia was formerly known under the name of Epsom and Seidlitz salts, because it exists in the water of these springs, and sal catharticus amarus, bitter purging salt, on account of its properties. It was long confounded with sulphate of soda, till its properties were investigated by Black, Macquer, and Bergman, and its nature and composition fully ascertained.

This salt exists abundantly in nature. It is found in many mineral springs, and it forms a considerable proportion of the saline ingredients of sea water. The bittern or mother water of common salt, that is, the water which remains after the crystallization, consists chiefly of sulphate of magnesia. It is therefore rarely prepared by art, by the direct combination of its constituent parts. It is easily purified by dissolving the salt in water, and by evaporation and crystallization.

The sulphate of magnesia, thus prepared, is crystallized in four-sided prisms, terminated by four-sided pyramids. There is, however, some deviation from this form. The primitive form of the crystal is a quadrangular prism with square bases. The integrant molecule is a triangular prism, whose bases are right-angled isosceles triangles. It has a cool, bitter taste. The specific gravity is 1.66.

Exposed to the air, it effloresces. It is soluble in its own weight of cold water: boiling water dissolves more than two-thirds of its weight. Exposed to heat, it undergoes the watery fusion, and being deprived of its water of crystallization, it does not melt, nor is it decomposed by the strongest heat. By the action of the blow-pipe it melts with difficulty into an opaque, vitreous globule.

The sulphate of magnesia is decomposed by the fixed alkalies, but with ammonia it forms a triple salt.

The component parts of this salt are, according to Kirwan:

| Compound | Bergman | In crystals | Dry. | |-------------------|---------|-------------|------| | Sulphuric acid | 33 | 29.35 | 63.32| | Magnesia | 19 | 17.00 | 36.68| | Water | 48 | 53.65 | 00.00| | Total | 100 | 100.00 | 100.00*|

* Nirbol. Journ. iii. p. 215.

The sulphate of magnesia is employed in medicine as a purgative. From this salt, too, the earth of magnesia is usually extracted.

2. Sulphate of Ammonia and Magnesia.

1. This is a triple combination of sulphuric acid with ammonia and magnesia. It is prepared by the partial decomposition of the sulphate of magnesia by means of ammonia. By evaporating the solution, the triple salt is obtained in crystals.

2. This salt crystallizes in octahedrons. It has a bitter acid taste, does not effloresce in the air, is less soluble in water than either of the salts of which it is composed, but it is more soluble in hot than in cold water, and it crystallizes on cooling. By heat it undergoes the watery fusion. It then dries and is decomposed.

The component parts of this salt are,

| Compound | Sulphate of magnesia | Sulphate of ammonia | |-------------------|----------------------|--------------------| | | 64 | 32 | | Total | 100 | |

† Fournoy. Connaiss. Chim. iii. 49. 3. Sulphite of Magnesia.

1. The compound of sulphurous acid and magnesia is formed by passing sulphurous acid gas into two parts of water, with one of carbonate of magnesia. A violent effervescence takes place, with the evolution of heat. The sulphite of magnesia is formed, and precipitated to the bottom in the state of powder; but with an excess of acid it is re-dissolved, and crystallizes.

2. The crystals of sulphite of magnesia are in the form of depressed transparent tetrahedrons. It has a mild earthy taste, which soon becomes sensibly sulphurous; it has no smell. Its specific gravity is 1.3802.

3. It effloresces in the air, and is slowly converted into sulphate of magnesia. It is soluble in 20 parts of cold water. Boiling water dissolves a greater proportion, and from this it crystallizes on cooling. Exposed to heat, this salt becomes viscid, and by calcination it loses 0.45 of its weight. If the heat be increased, it is decomposed; the acid is driven off, and the pure earth remains behind.

The component parts of this salt are,

| Substance | Quantity | |-----------------|----------| | Sulphurous acid | 39 | | Magnesia | 16 | | Water | 45 | | **Total** | **100** |

4. Sulphite of Ammonia and Magnesia.

1. This triple salt is formed by decomposing the sulphite of ammonia by magnesia, or the sulphite of magnesia by ammonia, in solution in the cold; or, by mixing together the solutions of the two salts.

2. This salt is in transparent crystals, the form of which has not been determined. When it is exposed to the air, it is converted into sulphate of ammonia and magnesia. It is less soluble in water than either of the two sulphites of which it is formed. By the action of heat, sulphurous acid is given out, acidulous sulphite of ammonia is sublimed, and there remains behind pure magnesia.

† Ibid. p. 89, magnesia †.

5. Nitrate of Magnesia.

1. This compound of nitric acid and magnesia was formerly called nitre with base of magnesia, and magnesian saltpetre. It is formed by the direct combination of the acid with the earth. By evaporation it is crystallized.

2. This salt crystallizes in four-sided rhombohedral prisms, whose summits are oblique or truncated. Sometimes it is in the form of small needles combined in groups. The taste is penetrating and bitter. The specific gravity is 1.736.

3. It is deliquescent in the air, and is soluble in its own weight of cold water. It is more soluble in boiling water, in which it crystallizes on cooling; but, it can only be obtained in regular crystals by slow evaporation from its solution in cold water.

4. By the action of heat it undergoes the watery fusion; the water is driven off, and it becomes dry. It is decomposed in a strong heat, gives out a little oxygen gas, then nitrous gas, and at last the nitric acid. The pure earth remains behind.

The component parts of this salt are, according to Bergman:

| Substance | Quantity | |-----------|----------| | Acid | 43 | | Magnesia | 27 | | Water | 30 | | **Total** | **100** |

Kirwan:

| Substance | Quantity | |-----------|----------| | Acid | 46 | | Magnesia | 22 | | Water | 32 | | **Total** | **100** |

6. Nitrate of Ammonia and Magnesia.

1. This triple salt is formed, either by the direct combination of the solutions of nitrate of ammonia, and nitrate of magnesia, by which the salt is obtained pure and crystallized; or, by partially decomposing the nitrate of ammonia by magnesia, or the nitrate of magnesia by ammonia.

2. The crystals of this salt are in the form of fine prisms. It has a bitter, acrid, and ammoniacal taste. It is less deliquescent in the air than either of the constituent salts, and less soluble in water. It requires 11 parts of cold water to dissolve it, but less of boiling water. It crystallizes on cooling.

When it is rapidly heated, it inflames spontaneously. Action. When slowly heated in close vessels, it gives out oxygen gas, azotic gas, a greater proportion of water than it contains, nitrous gas, and nitric acid, without the smallest trace of ammonia; which shows that it is decomposed, that the hydrogen combines with the oxygen of the acid, and forms water.

The component parts of this salt are,

| Substance | Quantity | |-----------|----------| | Nitrate of magnesia | 78 | | Ammonia | 22 | | **Total** | **100** |

7. Nitrite of Magnesia.

Nothing is known of the properties of this salt.

8. Muriate of Magnesia.

1. This compound of muriatic acid and magnesia was formerly called marine salt of magnesia, and was confounded with the muriate of lime, with which it is frequently accompanied. The difference between these two salts was first pointed out by Dr Black, and Bergman afterwards examined the nature and properties of muriate of magnesia. The salt is obtained by dissolving magnesia in muriatic acid till they are saturated, and then evaporating the solution. Small irregular crystals are obtained. This salt exists in the waters of the ocean, and in mineral waters, along with the muriates of soda and lime.

2. It is extremely difficult to obtain the muriate of magnesia in any regular form. It is either in the state of powder, or very small regular needles, or in a kind of jelly. It has a disagreeable bitter taste. The specific gravity is 1.601.

3. It is very deliquescent in the air. Cold water readily dissolves its own weight, and it is still more soluble in boiling water.

4. It is completely decomposed by heat; the acid is driven off, and the pure earth remains behind.

Bergman:

| Substance | Quantity | |-----------|----------| | Acid | 34 | | Magnesia | 41 | | Water | 25 | | **Total** | **100** |

Kirwan:

| Substance | Quantity | |-----------|----------| | Acid | 34.59 | | Magnesia | 31.07 | | Water | 34.38 | | **Total** | **100.04** |

9. Muriate of Magnesia. 9. Muriate of Ammonia and Magnesia.

This triple salt is formed by mixing the solutions of muriate of magnesia and muriate of ammonia; and by evaporating the solution the salt crystallizes in the form of small polyhedrons. It has a bitter, ammoniacal taste. It is little altered by exposure to the air, and is soluble in five parts of cold water. It is decomposed by heat. The muriate of ammonia is sublimed, and the muriate of magnesia is deprived of its acid.

The component parts of this salt are,

| Component | Parts | |-----------------|-------| | Muriate of magnesia | 73 | | ammonia | 27 | | | 100 |

10. Hyperoxymuriate of Magnesia.

This is similar in its chemical and physical properties to the hyperoxymuriate of lime, and it is prepared in the same way. It is precipitated by lime and ammonia.

The component parts are,

| Component | Parts | |-----------|-------| | Acid | 60 | | Magnesia | 25.7 | | Water | 14.3 | | | 100.0 |

11. Fluate of Magnesia.

1. This salt is formed by combining together fluoric acid and magnesia. According to Scheele, it precipitates in the form of a gelatinous mass; but Bergman observes that great part of the salt is deposited as the saturation approaches. By evaporating the solution, crystals in the form of six-sided prisms, terminated by a low pyramid composed of three rhomboidal sides, are obtained.

2. This salt is not decomposed by the strongest heat, or by any acid.

12. Fluate of Ammonia and Magnesia.

This triple salt is formed by mixing the solutions of the fluate of ammonia and magnesia. A precipitation is formed, which is the triple salt in crystals. The properties of this salt are unknown.

13. Borate of Magnesia.

1. This salt is formed by the direct combination of boracic acid with magnesia. The earth is slowly dissolved, and when the solution is evaporated, crystals are obtained.

2. The crystals of this salt are very small and irregular. It melts when exposed to heat, without being decomposed; but it may be decomposed, it is said, by alcohol.

14. Borate of Magnesia and Lime.

1. This salt, which has been lately discovered native, is called by mineralogists cubic quartz. It was analyzed by Wetzlumb in 1783. It is an infusible salt, and is regularly crystallized in polyhedrons of 22 faces. The specific gravity is 2.566.

2. It is not altered by exposure to the air, nor is it soluble even in boiling water. Exposed to a strong red heat, the crystals lose their lustre; and with a white heat they decrepitate, and at last melt into a yellow coloured glass.

3. The component parts of this salt are,

| Component | Parts | |-----------|-------| | Acid | 73.5 | | Magnesia | 14.6 | | Lime | 11.9 | | | 100.0 |

15. Phosphate of Magnesia.

1. This salt may be obtained by the direct combination of phosphoric acid and carbonate of magnesia; for it may be prepared by mixing together phosphate of soda and sulphate of magnesia in solution. In a few hours, large, transparent crystals are formed in the solution.

2. This salt crystallizes in six-sided prisms with unequal sides, but it is frequently in the form of powder. It has a cooling, sweetish taste. The specific gravity is 1.5489.

3. It effloresces in the air, is not very soluble in action of cold water, and requires about 50 parts of boiling water water for its solution, and part of it crystallizes on cooling.

When it is heated, it is easily deprived of its water of heat, crystallization, and if the heat be moderate, it melts and falls down into a white powder. With a stronger heat, it is melted into glass.

16. Phosphate of Ammonia and Magnesia.

1. This triple salt was discovered by Fourcroy in a found naevus calculous concretion, found in the colon of a horse. The results of his experiments on this substance have been confirmed by Berthollet and Vauquelin.

2. It may be prepared artificially, by mixing together a solution of phosphate of magnesia with a solution of phosphate of ammonia.

3. The crystals are in the prismatic form, but cannot be accurately ascertained. This salt has no taste. In the concrete form, it is found in the cavities of animal bodies, and sometimes it is crystallized, but most frequently lamellated and semitransparent.

4. It is not changed by the action of the air, and is action of scarcely soluble in water. When it is heated moderately, it falls to powder. With a strong heat it is deprived of the ammonia, and under the blow-pipe it melts into a transparent globule. It is decomposed by the sulphuric, nitric, and muriatic acids.

The component parts of this salt found in the intestine of the horse are,

| Component | Parts | |-----------------|-------| | Phosphate of ammonia | 33.3 | | magnesia | 33.3 | | water | 33.3 | | | 100.0 |

17. Phosphite of Magnesia.

1. This salt may be prepared by directly combining phosphorous acid with magnesia. Or it may be obtained in a purer state, and crystallized, by mixing together solutions of phosphites of soda or of potash, and sulphate of magnesia, by which means it is obtained in brilliant milky flakes. 2. This salt, which has no sensible taste, sometimes crystallizes in the form of tetrahedrons. It effloresces in the air, and is soluble in 400 parts of cold water. When exposed to heat, it suddenly swells up, and melts into a glaas. Under the blow-pipe it gives out a phosphoric light, and becomes opaque on cooling.

The component parts of this salt are,

| Acid | 44 | |------|----| | Magnesia | 20 | | Water | 36 |

18. Phosphite of Ammonia and Magnesia.

This salt is formed by the partial decomposition of phosphite of ammonia by means of magnesia, or by mixing together the solutions of the two phosphites. If the solutions be sufficiently concentrated, the triple phosphite is readily deposited. It forms crystals, and has little solubility in water. Its other properties are unknown.

19. Carbonate of Magnesia.

1. This salt, which was first distinguished by Dr Black, has been called mild magnesia, aerated magnesia. It is formed by mixing together sulphate of magnesia and carbonate of potash in solution. Or it may be obtained by dissolving pure magnesia in water saturated with carbonic acid. The salt, as the solution is evaporated, crystallizes.

2. The magnesia of commerce, which is in the state of powder, or light friable cakes, is not fully saturated with the acid. But when it is crystallized by the above processes, it is in the form of transparent six-sided prisms, terminated by a hexagonal plane. This salt has little taste. The specific gravity is 0.2941.

3. When it is crystallized, it soon loses its transparency in the air. It is soluble in 48 parts of cold water. Exposed to heat in a crucible, it slightly decrepitates, is deprived of its water and acid, and falls down into a powder. It is decomposed by all the acids. The component parts of this salt are, according to

| Bergman. | Butini. | Fourcroy. | |----------|---------|-----------| | Acid | 50 | 36 | 50 | | Magnesia | 45 | 43 | 25 | | Water | 25 | 21 | 25 |

The magnesia of commerce is composed of

| Fourcroy. | Kirwan. | |-----------|---------| | Carbonic acid | 48 | 34 | | Magnesia | 40 | 45 | | Water | 12 | 21 |

20. Carbonate of Ammonia and Magnesia.

This triple salt is prepared by decomposing carbonate of ammonia by means of magnesia; or by precipitating a solution of carbonate of magnesia by means of pure ammonia. This salt, however, has not been particularly examined.

21. Arseniate of Magnesia.

When arsenic acid is saturated with magnesia, a thick matter forms towards the point of saturation, which is soluble in excess of acid; but when it is evaporated, it does not crystallize. It assumes the form of a jelly. It is decomposed by the alkaline arseniates.

22. Tungstate of Magnesia.

This acid, in combination with magnesia, forms a salt which appears in the form of brilliant scales. It is not altered by exposure to the air, and it is soluble in water. It is decomposed by acids, and a white powder is precipitated.

23. Molybdate of Magnesia.

24. Chromate of Magnesia.

25. Columbate of Magnesia.

26. Acetate of Magnesia.

This salt is formed by the direct combination of magnesia with acetic acid. It does not crystallize, but a viscid mass remains when the solution is evaporated. It has a sweetish taste, leaving afterwards an impression of bitterness. The specific gravity is 1.378. It deliquesces in the air, is very soluble in water, and is decomposed by heat.

27. Oxalate of Magnesia.

This salt is formed by combining oxalic acid with magnesia, and evaporating the solution. A salt is obtained in the form of white powder, which is scarcely soluble in water. It is decomposed by heat. The component parts of this salt are,

| Acid and water | 65 | | Magnesia | 35 |

28. Tartrate of Magnesia.

This compound of tartaric acid and magnesia forms a salt which is insoluble in water, without an excess of acid. When this is the case, it crystallizes by evaporation. The crystals are in the form of hexangular truncated prisms. It is first melted, and then decomposed by heat.

29. Citrate of Magnesia.

This salt is obtained by dissolving carbonate of magnesia in citric acid. From the thick solution of this salt, there is no crystallization; but after some days, by a slight agitation, it assumes the form of a white opaque mass, which remains soft, as it separates from the edges of the vessel. The component parts of this salt are,

| Acid | 66.66 | |------|-------| | Magnesia | 33.34 |

30. Malate of Magnesia.

This is a deliquescent salt, and very soluble in water.

31. Gallate 31. Gallate of Magnesia.

Magnesia boiled with an infusion of nut galls, affords a clear liquid, which afflues a green colour. By evaporation to dryness the green colour vanishes, and the acid is decomposed.

32. Benzoate of Magnesia.

The combination of benzoic acid with magnesia affords plumose crystals which are easily soluble in water. This salt has a bitter taste.

33. Succinate of Magnesia.

This salt which is formed by the combination of succinic acid and magnesia, does not crystallize. It is a white glutinous mass which is deliquescent in the air.

34. Saccolate of Magnesia.

This salt is insoluble in water.

35. Camphorate of Magnesia.

1. This salt is formed by mixing carbonate of magnesia with water, and adding crystallized camphoric acid. A slight effervescence takes place. The temperature should be increased, to drive off the carbonic acid. The solution is filtered while it is hot, and evaporated to dryness. The mass is dissolved in distilled water, filtered and evaporated by a gentle heat, till a pellicle appears on the surface. By cooling there are deposited small plates, which are heaped upon each other.

2. This salt, which does not crystallize, is white and opaque, and has a bitter taste. In the air it is slightly efflorescent. It is not very soluble in water. Boiling water dissolves a little, but it is precipitated in cooling. When it is thrown on red-hot coals, the acid is volatilized, and pure magnesia remains behind. By the action of the blow-pipe it gives out a bluish flame. It is decomposed by sulphuric, nitric, and muriatic acids *.

36. Suberate of Magnesia.

The compound of suberic acid and magnesia is in the form of powder. It has a bitter taste, is deliquescent in the air, and soluble in water. It reddens the tincture of turpentine. Exposed to heat, it swells up and melts. By the action of the blow-pipe, the salt is decomposed, the acid is driven off, and pure magnesia remains behind. The sulphuric, nitric, and muriatic acids, decompose it. It is also decomposed by the alkalies, barytes, and lime †.

37. Mellate of Magnesia.

Unknown.

38. Lactate of Magnesia.

A salt in small deliquescent crystals.

39. Prussiate of Magnesia.

This salt may be prepared by directly combining prussic acid with pure magnesia; but the magnesia is precipitated when the solution is exposed to the air. It is also decomposed by the alkalies and lime.

Sect. V. Of Alumina and its Combinations.

1. Alumina, which is now employed to signify one of History's simple earths, is derived from the word alum, of which this earth forms a constituent part, and from which it is obtained in greatest purity. It was formerly denominated argil and argillaceous earth; but these names, being expressive of mixtures of different earths, have been properly rejected. Pott and Margraaf were the first who distinguished this earth from the calcareous earth or lime, and proved that this latter earth could not be obtained from it by calcination. In the year 1739, Hellot showed, that the basis of alum, separated from this salt by an alkali, was pure argil, or alumina. In 1758 and 1762 Macquer examined this earth, and detailed its characteristic properties. These were afterwards further elucidated and confirmed by the experiments and researches of Bergman and Scheele, so that the nature and characters of this earth were completely developed, and it was universally admitted as distinct from all others hitherto known.

2. Although alumina exists in great abundance in nature, yet it is rarely found uncombined, or in a state of perfect purity. It may be obtained pure by the following process.

Dissolve a quantity of common alum in water, and add to the solution, a solution of potash or carbonate of potash, or what is supposed to be still better, liquid ammonia. An abundant white precipitate is immediately formed. Continue the addition of the alkali as long as any precipitate appears. When the whole of the precipitate has collected at the bottom of the vessel, pour off the fluid part, and wash the precipitate repeatedly with large quantities of water, to free it from all saline matters which it may have retained. Dry the precipitate in a moderate heat, and the substance thus obtained is alumina in a state of tolerable purity. If this precipitate retain any portion of sulphuric acid, it may be separated by adding muriatic acid in small quantities at a time, till the whole is dissolved. Evaporate the solution till a drop of it, when suffered to cool on a plate of glass, yields minute crystals. Then set by the solution till it cools, and crystals will be deposited. Let these crystals be removed by pouring off the fluid, and continue the evaporation till no more crystals are formed. In this way the alum which the earth retained, may be separated. The liquid which remains is to be mixed with ammonia as long as any precipitate appears. This precipitate, well washed and dried, is pure alumina.

3. The alumina obtained by this process, is either in the form of friable fragments, or of very fine white powder, soft to the touch, and insipid to the taste. It has a peculiar odour, which is distinguished by the name of earthy smell, and is only perceptible when it is breathed upon, or moistened (o). It adheres to the tongue in consequence

(o) This smell, however, as it has been justly observed by Saussure, is owing to the oxide of iron, with which the alumina, in its ordinary state of purification, is contaminated; for when it is perfectly pure, and no traces Alumina, consequence of its rapidly absorbing moisture. The specific gravity is 2.

4. Sauflure has observed, that alumina exhibits two different appearances, according to the quantity of water which has been employed in the solution of the aluminous salt. If the quantity of water does not exceed what is necessary for the solution of the salt, we obtain a light friable white earth, which is very spongy, and adheres to the tongue. This he calls spongy alumina. But when the salt is dissolved in a large quantity of water, we obtain, after drying the precipitate in the same temperature, a yellowish brittle transparent mass, which splits into small fragments, when held in the hand, like solid sulphur. It has a smooth conchoidal fracture, no earthy appearance, does not adhere to the tongue, and does not swell up when put into water. It occupies 10 or 12 times less volume than in the spongy state, and has some resemblance to gum arabic, or a dried jelly. This he distinguishes by the name gelatinous alumina.

5. Alumina undergoes no change by being exposed to light. When it is exposed to heat, it is diminished in bulk, in consequence of being deprived of the water with which it is combined. Accordingly, Sauflure has observed, that the spongy alumina, exposed to the same temperature, loses a greater quantity of moisture than the gelatinous alumina. The former, when exposed to a red heat, loses 0.58 part of its weight; but the latter only 0.43 part. When they are both exposed to a very strong heat, the spongy alumina is deprived of no more water that what it gives out with a red heat, while the gelatinous parts with only 0.4825. On this property of the contraction of bulk of alumina when exposed to heat, depends the principle of the thermometer, or pyrometer, of Wedgwood, of which we shall immediately give a short description.

When alumina is exposed to a very strong heat suddenly applied, as by means of the blow-pipe, with a stream of oxygen gas, it is susceptible of a kind of fusion; and, when it is cooled, it appears under the form of an enamel, of a greenish colour, and so hard as to cut glass.

6. Alumina is not soluble in water, but it absorbs and retains that fluid in considerable quantity. With a greater quantity of water it is diffused in it, and may be formed into a paste, in which state it is moulded with great facility into any form.

7. There is no action between alumina and oxygen, azote, hydrogen, or phosphorus; and very little between it and sulphur, except when they are in a state of minute division, or in combination with some other substances. Carbone combines with alumina, of which there are many natural compounds, among the class of bituminous fossils; but even in these compounds, the carbone and alumina are mixed with other earths, and with the oxide of iron.

8. Alumina enters into combination with almost all the acids, and forms salts which are more or less soluble, and susceptible of crystallization. Some are insoluble in water, and others require an excess of acid.

9. The order of its affinity for the acids, is the following:

- Sulphuric acid, - Nitric, - Muriatic, - Oxalic, - Arsenic, - Fluoric, - Tartaric, - Succinic, - Slaclastic, - Citric, - Phosphoric, - Lactic, - Benzoic, - Acetic, - Boracic, - Sulphurous, - Carbonic, - Prussic.

10. Alumina combines with the fixed alkalies. When they are heated together, an opaque mass, which has little coherence, is formed. Fixed alkali dissolved in water, with the affluence of heat, has the property of dissolving alumina; but from this solution it may be precipitated by means of an acid, and then it is obtained in great purity. Liquid ammonia also holds a small quantity of alumina in solution, if it has been recently precipitated.

11. Alumina enters into combination with many of the earths, and particularly with lime and silica. These compounds form the chief basis of all kinds of pottery and porcelain. Alumina combines with lime, and enters into fusion with it by means of heat. A compound is also formed with alumina and barytes, or strontites, by exposing them together in a crucible to a strong heat; or, by boiling them together in water. Magnesia and alumina alone, do not enter into combination by means of the strongest heat; but a porcelain is obtained from a mixture of lime, magnesia, and alumina. But in the proportions that are employed, it is necessary that the alumina be greatest. The following table shews the results of experiments on these earths in different proportions:

| Alumina | Lime | Magnesia | |---------|------|----------| | 3 | 2 | | | | | 1 |

A porcelain.

| Alumina | Lime | Magnesia | |---------|------|----------| | 3 | | 2 |

A porcelain.

| Alumina | Lime | Magnesia | |---------|------|----------| | 3 | | 1 |

Porous porcelain.

| Alumina | Lime | Magnesia | |---------|------|----------| | 3 | | 2 |

Porous porcelain.

Alumina,

traces of oxide of iron can be detected, it has no perceptible smell. To alumina which was perfectly inodorous, he communicated this smell, by triturating it with oxide of iron. Journal de Physique, lii. p. 287. This is one of the most important of the earths, on account of the variety of purposes to which it is applied. It forms the bases of all kinds of earthenware, from the coarsest brick to the finest china. It is also chiefly employed in the pots or crucibles which are exposed to very strong heat, as in glass manufacture and cast iron. It is employed also in dyeing and calico-printing, and in the cleansing or scouring of woollen stuffs. It has been applied to a valuable use by the late Mr Wedgwood, in the construction of an instrument capable of ascertaining high degrees of temperature, to which the common thermometer cannot reach.

This instrument is constructed on the principle of the contraction of pure clay, when it is exposed to heat. Mr Wedgwood took a very pure clay, and formed it into small short cylinders, which were made exactly of the same size. They are then baked in a low red heat, to expel the whole of the air and moisture which adhere to the clay. The cylinders are thus prepared for the measurement of strong heats. For this purpose, one of the cylinders is introduced between two rulers, to which a scale is attached, and its bulk is exactly measured. It is then introduced into the furnace whose heat is to be tried, and the temperature is to be estimated according to the diminution of bulk which the cylinder has sustained. The quantity of contraction is measured by means of two metallic rulers, which are fixed upon a plate. These rulers are 24 inches in length, and are divided into 240 parts. The distance between the rulers at the upper extremity of the scale is 0.5 of an inch, and at the lower extremity 0.3 of an inch. The size of the clay cylinder, before it is introduced into the furnace, nearly fits the upper part of the scale; or at least the degree at which it stands, before it is introduced into the furnace, is marked. After being heated, the clay cylinder is again applied to the scale, and the diminution of bulk is measured by the distance at which it stands between the rulers from the top of the scale, or from the degree at which it stood before it was exposed to the heat.

Mr Wedgwood connected the scale of his pyrometer with Fahrenheit's thermometer. The first degree of his scale which marks a red heat, corresponds to the 947° Fahrenheit; but to make this instrument better understood, we may state a few of the corresponding degrees of the two instruments.

| Wedgwood, Fahrenheit | |----------------------| | Red heat | 0 = 947 | | Fine silver melts | 28 4717 | | Fine gold melts | 32 5237 | | Welding heat of iron | 95 13427 | | Cast iron melts | 135 17977 | | Greatest heat in an air furnace eight inches square | 163 21877 | | Extremity of the scale, or highest temperature observed | 240 32277 |

This instrument has been of considerable importance in some arts and manufactures, and it is undoubtedly fitted to give some information concerning those intense heats which can be measured by no other instrument which has yet been contrived. But as the same kind of clay cannot always be obtained, and as it is probable that the contractions of the cylinders are not proportional to the temperatures, their estimation by this instrument can only be considered as an approximation to certainty.

I. Compounds of Alumina with Acids.

1. Sulphate of Alumina.

This is a compound of sulphuric acid and alumina. It may be formed by the direct combination of the acid with the earth. But in the preparation of this salt, the earth and the acid must be in a state of purity, and must be saturated with each other. The solution is then evaporated to dryness; the salt is again dissolved in distilled water, and evaporated slowly till it crystallizes.

The crystals of this salt are in the form of thin plates, soft and pliant, with a brilliant pearly lustre, and of an alluring taste. It is not altered by exposure to the air; it is very soluble in water, but it does not crystallize readily. When it is heated, it is infusible; but by long calcination, it dries and falls down heat, &c., to powder. At a high temperature it is decomposed, and the acid is driven off.

The sulphuric acid readily combines with this salt, and forms with it an acidulous sulphate of alumina. This salt has a more acid taste than the former; it crystallizes with more difficulty, and the crystals have more brilliancy. It reddens vegetable blues, and frequently assumes the form of a thick gelatinous mass.

All the alkaline and earthy bases, except silica and zirconia, decompose either of these two salts. The saturated sulphate of alumina, according to Bergman, is composed of

| Sulphuric acid | 50 | | Alumina | 50 | |---------------|----| | | 100 |

2. Acidulous Sulphate of Alumina and Potash, or Alum.

The alum of commerce, now of such extensive utility in many of the arts and manufactures, was imported into Europe from Asia, previous to the 15th century, during which it was begun to be manufactured in Italy. Alum works were erected in Spain and Germany in the 16th century; and towards the end of it, a manufactory of this salt was established in Yorkshire in England. But the true nature of alum has been only of late understood. It is to the experiments and researches of Vauquelin, that we are indebted for the knowledge of its component parts.

Alum is generally obtained by exposing to the preparation for some time, aluminous schistus, or what are called aluminous ores, which are natural productions sometimes found in the neighbourhood of volcanoes, and sometimes, as in Britain, dug out of coal mines which abound with pyrites or sulphuret of iron. When these substances, which are also mixed with a consider- Alumina, able proportion of clay, are exposed to air and moisture, the sulphur combines with the oxygen of the air, or with that of the water, by decomposing it, and is thus converted into sulphuric acid. This combines with the alumina, and thus there is formed a sulphate of alumina. The salt, thus formed, is dissolved in water, and must be purified by repeated boilings and crystallizations. This alumino-schifus is generally mixed with a considerable proportion of sulphate of iron. From this it is to be separated during the process, and the potash or ammonia which is necessary to constitute the triple salt, must be added. Even before the component parts of alum were discovered, the addition of potash or ammonia was found to be necessary to complete the process. This was well known to the manufacturers, who supposed that it was necessary to take up a quantity of acid, which being in excess prevented the granulation, as it was called, or the crystallization of the alum.

3. Alum crystallizes in regular octahedrons; but this form is subject to considerable variety, according to the difference of proportion which is found to take place among its component parts. The primitive form of the crystal is the regular octahedron, and the integrant molecule the regular tetrahedron. It has a very astringent, styptic, and somewhat sweetish taste. It usually reddens vegetable blues. The specific gravity is 1.7109.

4. It is little changed by exposure to the air. By long contact there is a slight efflorescence on the surface. Alum is soluble in 16 or 20 parts of cold water. Boiling water dissolves a greater proportion. When exposed to heat, it melts in its water of crystallization. It then swells up, enlarges in volume, and there remains behind a light, porous, dry mass, which has a sharp acid taste, and reddens more strongly vegetable blues. In this state it is called burnt or calcined alum. When it is exposed to a stronger heat, the acid is driven off.

5. According to the experiments of Vauquelin, there are three kinds or varieties of alum, which, although they possess nearly the same properties, have different constituent parts, or different proportions of the same constituents. The first is sulphate of alumina and potash with an excess of acid; which indeed is necessary to constitute alum. The second consists of alumina and ammonia, also with an excess of acid. The third variety, which is most frequently found among the alum of commerce, is a mixture of both. It contains both potash and ammonia. When an additional quantity of potash is added, the alum crystallizes, not in its usual form, but in the form of cubes, and hence it has been denominated cubic alum. If a still greater quantity of potash be added, the crystallization is nearly interrupted; and it then appears in the form of flakes.

The component parts of alum, are according to Vauquelin. Kirwan.

| Component | Vauquelin | Kirwan | |-----------------|-----------|--------| | Sulphate of alumina | 49 | Acid | 17.66 | | Potash | 7 | Bafe | 12.00 | | Water | 44 | Water | 70.34 |

6. The three varieties of alum are nearly decomposed in the same way, by combustible substances. If alum be exposed to a moderate heat with charcoal, it is converted into the flake of neutral salt, because the charcoal acts on the excess of acid, before it can effect the decomposition of the salt; but when it is strongly heated, there is formed with the sulphate of alumina and potash, a black substance, which spontaneously takes fire in the air. This substance has been distinguished by the name of pyrophorus; and it is called Homberg's pyrophorus, because it was discovered by that chemist.

Pyrophorus is prepared by mixing together three parts of alum, and one of flour or sugar, in an iron ladle, and exposing the mixture to heat till it ceases to swell, and becomes black. It is then to be reduced to powder, put into a glass phial, and again exposed to heat, till a blue flame proceeds from the mouth of the phial. After it burns for a minute, it is allowed to cool, and must be kept in a well-closed bottle.

7. The pyrophorus thus formed, contains a hydrogenated sulphate of potash and alumina, mixed with charcoal in a state of minute division. It kindles more readily in humid than in dry air. The oxygen gas of the atmospheric air is absorbed. Part is converted into carbonic acid, and part combines with the sulphur, and forms sulphuric acid; so that when the pyrophorus is burnt, it no longer contains the hydrogenated sulphate as before, but sulphate of alumina and potash; not in the state of alum, because it has been deprived of the excess of acid, which gives alum its peculiar character.

8. Pyrophorus gives out a very fetid odour, when it is thrown into water, and leaves behind a sulphuret of potash, and of hydrogenated alumina. It is inflamed by nitrous gas, and by oxymuriatic acid.

9. The uses of alum are very numerous. It is employed in medicine as an astringent and styptic. It is also employed in the arts of bleaching, of tanning, dyeing, calico-printing, and others. It is sometimes used in preserving animal matters from putrefaction, and it might be employed for the purpose of securing wood from catching fire.

Sulphate of alumina and potash.—1. If a solution of crystallized alum be boiled with a solution of pure alumina, the saturated sulphate of alumina and potash is formed. The excess of acid, it is obvious, in this process, enters into combination with the alumina. The alum, as the earth is added, is gradually precipitated in the solution, in the form of a white powder.

2. This salt, saturated with alumina, never assumes any regular form. It has no taste, is not changed by exposure to the air, is not soluble in water, and when it is exposed to heat, it is not altered, except at a very high temperature. This salt is less easily decomposed than any of the other varieties of sulphate of alumina. By the action of some of the acids it is converted into alum, which is owing to the acid combining with the additional portion of alumina, that saturated the excess of acid existing in the alum. This salt has been applied to no use.

3. Sulphite of Alumina.

1. The compound of sulphurous acid and alumina.

1. This salt was formerly known under the names of nitre of argil, and nitrous alum. It is formed by the direct combination of the nitric acid with alumina. It has been found impossible to neutralize the acid; and it cannot be obtained crystallized, excepting in the form of thin plates, and often only in a gelatinous mass.

2. This salt has an austere and acid taste. The specific gravity is 1.645. It is deliquescent in the air, and extremely soluble in water. When it is heated, the acid is driven off, and the pure earth remains behind. It is readily decomposed by the sulphuric acid, which disengages the nitric acid; and by the muriatic acid, which is converted into the oxymuriatic acid.

3. Nitrite of Alumina.

This salt is unknown.

4. Nitrate of Alumina.

This salt is prepared by passing sulphurous acid gas into water in which pure alumina is mixed or suspended.

5. Muriate of Alumina.

This salt, which is a compound of muriatic acid and alumina, is formed by the direct combination of the acid with the earth; but is never neutralized. The acid is always in excess.

6. Fluate of Alumina.

The combination of fluoric acid and alumina affords a salt which cannot be crystallized, but which is in the form of a jelly. It has always an excess of acid, and an astringent taste. It is decomposed by all the earthy and alkaline bases. With the latter it forms triple salts.

7. Borate of Alumina.

It is extremely difficult to form a compound of alumina and boracic acid by direct combination. This salt may be formed by mixing together a solution of borate of soda, with a solution of sulphate of alumina. Its properties have not been examined.

8. Phosphate of Alumina.

This salt is little known. By saturating phosphoric acid with alumina, a white powdery mass is obtained, which has little taste, except there be an excess of acid, and then it seems to form an acidulous salt. It melts under the blowpipe into a transparent globule, without decomposition. It is decomposed by the alkalies, some of the earths, and the acids.

9. Phosphite of Alumina.

This salt is formed by the direct combination of phosphorous acid with alumina. The solution is to be evaporated to a proper consistence.

10. Carbonate of Alumina.

Little is known of the combination of carbonic acid and alumina. Bergman had observed, when alum was pounded little precipitated by an alkaline carbonate, that very little or no effervescence took place; he therefore concluded, that the carbonic acid, not being driven off, must have combined with the alumina which was precipitated. And besides he found, that the liquid contained a portion of carbonate of alumina, which is deposited some hours or some days afterwards by the evaporation of the carbonic acid, which held it in solution.

Common clay, which is a mixture of alumina and silica, contains a certain portion of carbonic acid, which is disengaged by the application of strong heat. He obtained from one species of clay, several times its volume of this acid, mixed with a small portion of hydrogen gas. It is owing to the same combination of carbonic acid, that clays treated with acids, effervesce, without containing any carbonate of lime.

According to Sauflure, alumina is dissolved in water, the acid is which is saturated with carbonic acid; but when the combined solution is exposed to the air, it is decomposed.

11. Arseniate of Alumina.

This salt is formed by dissolving alumina in arsenic acid, and evaporating the solution to dryness. A thick mass is thus obtained, which is insoluble in water. It is decomposed by the sulphuric, nitric, and muriatic acids, as well as by the earthy and alkaline bases.

12. Tungstate of Alumina.

This salt has not been examined.

13. Molybdate. 15. Molybdate of Alumina.

16. Chromate of Alumina. Unknown.

17. Columbite of Alumina.

18. Acetate of Alumina.

The acetic acid enters into combination with alumina, and forms with it small, needle-shaped crystals, which are soft, deliquescent, and have an astringent taste. The specific gravity of this salt is 1.245. Its other properties are unknown.

19. Oxalate of Alumina.

Oxalic acid very readily combines with alumina. When the solution is evaporated, a yellowish, soft, transparent mass is obtained, but it does not crystallize. This salt has an astringent taste, is deliquescent, and reddens the tincture of turpentine. When it is heated, it swells up, is deprived of its acid, and the alumina remains behind, slightly coloured. It is decomposed by the stronger acids.

The component parts of this salt are,

| Acid and water | 56 | | Alumina | 44 |

20. Tartrate of Alumina.

Alumina enters into combination with tartaric acid, and forms an uncrystallized, gelatinous mass, which has an astringent taste, is not deliquescent in the air but is soluble in water.

21. Citrate of Alumina.

The properties of this salt have not been examined.

22. Malate of Alumina.

When malic acid is added to a solution containing alumina, a precipitate is formed, which is scarcely soluble in water.

23. Gallate of Alumina.

If pure alumina be added to a solution of nut-galls, an insoluble compound is formed with the tannin and extract. The liquid remained clear and white, and it afforded by evaporation, small crystals, which are galate of alumina with excess of acid.

24. Benzoate of Alumina.

The compound of benzoic acid and alumina affords a salt, which crystallizes in an arboreal form. It has a bitter taste, is deliquescent in the air, soluble in water, is decomposed by the action of heat, and even by most of the vegetable acids.

25. Succinate of Alumina.

The compound of succinic acid and alumina affords salts which crystallize in the form of prisms, and are easily decomposed by heat.

26. Saccolate of Alumina.

This compound of fæcalastic acid and alumina forms a salt which is insoluble in water.

27. Camphorate of Alumina.

1. The compound of camphoric acid and alumina is formed by precipitating alumina by means of ammonia, washing the precipitate, and diluting it with distilled water. Crystals of camphoric acid are then to be added. The mixture is to be heated, filtered, and evaporated.

2. A white powder is then obtained, which has a property bitter, acid, and astringent taste. It reddens vegetable blues. This salt is scarcely altered by exposure to the air. Water dissolves about $\frac{1}{10}$ part of its weight. Boiling water dissolves it more readily; but on cooling, a precipitate is formed. When it is exposed to heat, it swells up, and the acid is volatilized. By the action of the blow-pipe, a blue flame is produced, the salt is decomposed, and the pure alumina remains behind. This salt is decomposed by the mineral acids, and even by some of the vegetable acids. It is also decomposed by the nitrates of lime and barites.

28. Suberate of Alumina.

The compound of fumaric acid and alumina may be formed by evaporating the solution with a very moderate heat, in a large open vessel. This salt does not crystallize; but the dried matter which is obtained, is transparent, of a yellowish colour, and has a flaky, bitterish taste. When too much heat is employed, the salt melts and blackens. It reddens the tincture of turpentine, and is slightly deliquescent in the air. Exposed to the action of the blow-pipe, the acid is volatilized and decomposed, and the alumina remains behind. It is decomposed by the mineral acids, the earths, and the alkalis.

29. Mellate of Alumina.

The properties of this salt are unknown.

30. Lactate of Alumina.

This is a deliquescent salt.

Sect. VI. Of Silica and its Combinations.

1. Silica has been distinguished by the names of fibrous earth, or quartzy earth, because it is obtained from flint, or flint, and from the stone called quartz. This earth exists in great abundance in nature, and it constitutes the bases of some of the hardest stones of which the nucleus of the globe consists; and, on account of its great abundance, it has been regarded as the primitive or elementary earth, the base of all the other earths. Silica forms one of the constituent parts of most stony bodies; but it exists in greatest abundance in agates, jasper, flints, quartz, and rock crystal; in the latter it is nearly in a state of purity.

2. But to obtain it perfectly pure, a quantity of quartz or rock crystal may be exposed to a red heat. When it is taken from the fire, and while it is yet hot, it is suddenly immersed in cold water. It is then to be reduced to powder; and, if transparent rock crystal has been employed, it is then in a state of tolerable purity. To have it perfectly pure, mix one part of the pounded stone, with three parts of potash, and expose them in a crucible to heat which is sufficient for the fusion of the mixture. The mass thus obtained is soluble in water. Add a sufficient quantity of water for its solution, and drop in muriatic acid, as long as there there is any precipitate. Let this be repeatedly washed with water, and dried. The substance thus obtained is pure silica.

3. It is in the form of a very fine white powder, which has neither taste nor smell. The particles are rough and harsh to the feel, as when they are rubbed between the fingers, or touched with the tongue. The specific gravity is 2.66.

4. Light has no action on silica; and it is one of the peculiar characters of this earth, that it resists, unchanged, the greatest degree of heat.

5. There is no action between silica and oxygen, azote or hydrogen, nor is it changed by exposure to the air. It is not acted upon by carbons, phosphorus, or sulphur. It is insoluble in water; but in a state of minute division, it absorbs a considerable portion, and forms with this liquid, a transparent jelly. When it is exposed to the air, the whole of the moisture is evaporated.

6. Silica is frequently found in nature in the crystallized form, and then it is distinguished by the name of rock crystal. It is most commonly in hexagonal prisms, terminated by hexagonal pyramids. Crystals of silica have also been formed artificially. In a solution of silica in fluoric acid which had remained at rest for two years, Bergman found crystals, some of which were cubes, and some had truncated angles, at the bottom of the vessel. Crystals of silica have also been formed, by diluting largely with water, the combination of silica and potash, and allowing it to remain for a long time. Professor Seigling of Erfurt obtained crystals from a solution which had been kept eight years in a glass vessel. A crust was formed on the top, composed of carbonate of potash and crystallized silica. The crystals of the latter were in the form of tetrahedral pyramids, perfectly transparent, and so hard as to strike fire with steel.

7. Silica is only acted on by a very few of the acids. These are, the phosphoric and boracic, which combine with it by fusion, and the fluoric, which dissolves silica either in the gaseous or liquid state. When silica is held in solution in water by means of an alkali, it is also dissolved by the muriatic acid.

8. The alkalies have a very powerful action on this earth. In the preparation of the pure earth, it was combined with potash by means of fusion. This compound is different in its nature and properties, according to the proportions of the silica and the alkali. Two or three parts of potash with one of silica, form a compound which is deliquescent in the air, and soluble in water. This was formerly distinguished by the name liquor silicum, or liquor of flint. It is now called silicated alkali. When this solution is long exposed to the air, the earth is deposited in a flaky gelatinous form. It is decomposed by acids, which combine with the alkali, and the pure earth falls to the bottom in the state of fine powder. When the solution is largely diluted with water, and if a greater quantity of the acid be added than is sufficient to saturate the alkali, the silica remains in solution. This is particularly the case when muriatic acid is employed. When the silica is in greater proportion than the potash, a compound is formed which is possessed of very different properties. The substance thus obtained is glass.

9. This earth also enters into combination with some of the earths. If to a solution of the liquor of silica, &c., flints, lime water be added, a precipitate is formed, which is found to be a compound of silica and lime. Silica also combines with lime by means of heat, and in certain proportions a glass is formed.

The following table, drawn up by Mr Kirwan, exhibits the effects of heat on these earths in different proportions:

| Proportions | Wedgew. | Effect | |-------------|---------|--------| | 50 Lime | 150° | Melted into a mass between porcelain and enamel, of a white colour, semitransparent at the edges, and which gave feeble sparks with steel. | | 80 Silica | 150° | Not melted, but formed a brittle mass. | | 80 Lime | 150° | Formed a yellowish-white loose powder. |

10. Silica enters into combination with barytes. The following table will show the effect of different proportions of these earths, as they were ascertained by Mr Kirwan:

| Proportions | Wedgew. | Effect | |-------------|---------|--------| | 80 Silica | 150° | Formed a white brittle mass. | | 75 Silica | 150° | A brittle hard mass, semitransparent at the edges. | | 66 Silica | 150° | Melted into a hard, somewhat porous, porcelain mass. | | 50 Silica | 148° | A hard mass not melted. | | 80 Barytes | 148° | The edges melted into a pale greenish mass, between a porcelain and an enamel. | | 75 Barytes | 150° | Melted into a somewhat porous porcelain mass. | | 66 Barytes | 150° | Melted into a yellowish, and partly greenish white, porous porcelain. |

11. Silica also enters into combination with stonites. Three parts of stonites and one of silica, strongly heated in a silver crucible for an hour, afforded a gray, fumous, vitreous mass, which has no taste, and is insoluble in water.

12. Siliceous earth enters with difficulty into combination with magnesia; but if equal parts of silica and magnesia be exposed to very strong heat, they melt into a white enamel. 13. But the most important compounds of all the earths are those of silica and alumina. These earths may be combined together, as appears from the experiments of Guyton, in the humid way. He mixed together equal parts of alumina dissolved by means of potash, and of silica held in solution by the same alkali. When the solutions came into contact, a brown zone was immediately formed, which spread by agitation through the whole mass, and communicated to it a yellowish colour. The mixture was no farther changed during the space of an hour, although it was occasionally stirred by a glass rod; but at the end of that time the whole mass assumed the appearance of a thick, opaque, white jelly*. When the silica and alumina are mixed together, and formed into a paste with water, and exposed to heat, they strongly cohere, and assume a considerable degree of hardness. This compound forms the bases of all kinds of pottery and porcelain.

I. Compounds of Silica with Acids.

1. Muriate of Silica.

When muriatic acid is poured upon a solution of silicated potash, part of the silica remains in the solution combined with the acid. To this compound Fourcroy has given the name of muriate of silica. This solution, which is perfectly transparent, is always acid. When it is concentrated by slow evaporation, it assumes the form of a transparent jelly. But if the solution be boiled, it is decomposed, and the silica is precipitated in the form of small crystalline particles, so that it is totally separated from the water and the acid†.

2. Fluate of Silica.

Fluoric acid combines with silica, either in the gaseous or liquid state. When it is disengaged from lime in the state of gas, by means of an acid, if the process be performed in glass vessels, they are corroded. The fluoric acid in the state of gas combines with the silica, and retains it, even when it is condensed by water. This earth may be precipitated from the liquid solution by means of an alkali. When fluoric acid gas is condensed by water, part of the silica with which it was combined, is precipitated; but this portion is at last dissolved by new additions of the acid, so that the salt is in the state of an acidulous fluate. If this solution be evaporated, a quantity of silica, corresponding to the portion of acid disengaged, is deposited, and the liquid which remains, contains a portion in proportion to that of the acid which is left in the solution‡.

3. Fluate of Potash and Silica.

This triple salt is formed, when a solution of fluate of potash is exposed to heat in glass vessels; or, when the fluoric acid which has been prepared in glass vessels is combined with potash. But the nature of this triple salt has not been examined.

4. Fluate of Soda and Silica.

This triple salt is formed in the same way as the former.

5. Borate of Silica.

Boracic acid and silica combine together by means of a strong heat, and form a transparent glass. To this Fourcroy has given the name of borate of silica. This compound has no taste, is not altered by the air, nor is it soluble in water.

6. Phosphate of Silica.

This compound of phosphoric acid and silica is formed by means of fusion; and the compound is a hard, dense, transparent glass. When it is exposed to strong heat, it combines with the alkalies, and forms a triple salt. It is not decomposed by any of the acids. This substance is employed in the fabrication of artificial gems.

Sect. VII. Of Yttria and its Combinations.

1. This earth was discovered by Gadolin in 1794; history and the account of his analysis of the mineral from which it is obtained, was published in the memoirs of the Swedish academy, and in Crell's Annals for the year 1796. In 1797 Ekeberg analyzed the same mineral, and confirmed the results of Gadolin. To the new earth found in this mineral, Ekeberg gave the name of yttria, derived from Yterby, a place in Sweden where the stone is found. The same mineral was afterwards analyzed by Vauquelin and Klaproth, about the year 1830. The mineral from which this earth is obtained, has received the name of gadolinite, is of a black colour, has a vitreous fracture, and its specific gravity is 4.0497. It is magnetic. When it is heated with borax, it melts, and communicates to the salt a yellowish colour inclining to violet. The component parts of this mineral are,

| Component | Specific Gravity | |-----------------|------------------| | Yttria | .47 | | Silica | .25 | | Oxide of iron | .18 | | Alumina | .04 |

2. Yttria is obtained from this mineral, by reducing it to powder, and adding a mixture of nitric and muriatic acids, till the whole is decomposed. The solution is then to be filtered, and evaporated to dryness. If then it be diluted with water, the silica will remain behind. The liquid which passes through the filter is also to be evaporated to dryness, and what remains is to be exposed to a red heat in a close vessel. It is afterwards dissolved in water, and filtered. The liquid which passes through the filter is transparent and colourless. By adding a solution of ammonia, a precipitate is formed, which being collected, is pure yttria.

3. This earth is in the state of a white powder. It possesses neither taste nor smell. It is not fusible. It is not soluble in water, or in any of the caustic fixed alkalies; but it readily dissolves in carbonate of ammonia. The specific gravity of this earth is 4.842.

4. This earth undergoes no change by the action of light. It is not acted on by oxygen, azote, or hydrogen, nor does it combine with sulphur. It forms compounds... I. Compounds of Yttria with the Acids.

1. Sulphate of Yttria.

Sulphuric acid combines readily with yttria, and during the combination there is an evolution of caloric; and as the union goes on, the salt which is formed crystallizes in small brilliant grains.

2. The crystals are sometimes irregular, but often have the form of six-sided prisms, terminated by four-sided summits, and are of an amethyst red colour. This salt has a sweetish astringent taste, something like the salt of lead. The specific gravity is 2.791. It undergoes no change by exposure to the air. It is soluble in about 50 parts of cold water, but less so where there is not an excess of acid. This salt is partially decomposed when exposed to a red heat.

2. Sulphite of Yttria.

Unknown.

3. Nitrate of Yttria.

Nitric acid combines with yttria by dissolving the earth in the acid. This salt crystallizes with difficulty. When it is evaporated by heat, if too much be applied, in place of becoming solid as other salts, it becomes soft, and assumes the appearance of a thick, transparent honey. When it cools, it becomes hard and brittle. It deliquesces in the air. When sulphuric acid is poured into a solution of nitrate of yttria, a precipitate is formed which crystallizes. These are crystals of sulphate of yttria *.

4. Muriate of Yttria.

This salt, which is a compound of muriatic acid and yttria, resembles the nitrate in many of its properties. It dries with difficulty, is fusible with a moderate heat, and is deliquescent in the air. This salt is decomposed by ammonia.

5. Fluate of Yttria.

6. Borate of Yttria.

7. Phosphate of Yttria.

Phosphoric acid does not precipitate yttria from its combination with the other acids; but the phosphate of soda decomposes the salts of yttria, and forms a phosphate of yttria, which is precipitated in white, gelatinous flakes †.

8. Phosphite of Yttria.

Unknown.

9. Carbonate of Yttria.

This compound of carbonic acid and yttria was formed by Klaproth, by precipitating the earth by means of an alkaline carbonate, from its solution in acids. The carbonate of yttria is in the form of an insipid white powder. It is insoluble in water.

The component parts of this salt are,

Vol. V. Part II.

10. Arseniate of Yttria.

This salt is formed by boiling the earth in the acid. A white powder is precipitated, which is arseniate of yttria.

11. Tungstate of Yttria.

12. Molybdate of Yttria.

13. Chromate of Yttria.

14. Columbate of Yttria.

15. Acetate of Yttria.

This salt is formed by the direct combination of the earth with the acid. By evaporating the solution, a salt is obtained in crystals. These crystals, which are of a red colour, are in the form of six-sided plates obliquely truncated. This salt undergoes no change by exposure to the air.

16. Oxalate of Yttria.

This salt is formed by adding oxalic acid to the solution of yttria in acids. A precipitate is formed in the state of a white powder, which is insoluble in water. It may be obtained also by employing the oxalate of ammonia.

17. Tartrate of Yttria.

This compound is formed by precipitating yttria from its solution in acids by means of tartrate of potash. This salt is soluble in water.

18. Citrate of Yttria.

19. Malate of Yttria.

20. Gallate of Yttria.

21. Benzoate of Yttria.

22. Succinate of Yttria.

If the succinate of soda be added to a concentrated solution of muriate or acetate of yttria, a precipitate is formed, which is the succinate of yttria in the state of cubic crystals.

23. Saccolate of Yttria.

24. Camphorate of Yttria.

25. Suberate of Yttria.

26. Mellate of Yttria.

27. Laclate of Yttria.

28. Prussiate of Yttria.

The prussiate of potash crystallized and re-dissolved in water, causes a precipitate in the solution of yttria in acids. This is in the form of a white, gritty matter *.

Sect. VIII. Of Glucina and its Combinations.

1. This earth was discovered by Vauquelin in the year 1789. He was requested by Haüy to analyze the beryl, to ascertain whether its constituent parts were... Ytria, &c., were the same with those of the emerald, which the latter had conjectured, in observing a perfect correspondence in structure, hardness, and specific gravity.

In the course of this analysis, Vauquelin discovered the new earth, to which, from its properties, he gave the name of glucina, from the Greek word γλυκός, which signifies sweet. The same experiments were repeated by Klaproth and Bindeheim, and the results obtained by Vauquelin were confirmed.

2. This earth is obtained by the following process. One hundred parts of the beryl or emerald, reduced to a fine powder, are fused with 300 parts of caustic potash. The fused mass is then diluted with distilled water, and dissolved in muriatic acid. The solution is to be evaporated to dryness, taking care to stir it towards the end of the evaporation. Dilute the residue with a large quantity of water, and filter it. The filtrate is thus separated by means of the first process. The filtered solution, which contains the muriates of alumina and glucina, is precipitated by carbonate of potash. The precipitate is to be well washed, and dissolved in sulphuric acid. Add to this solution, a quantity of sulphate of potash, and evaporate to obtain crystallized alum. When by a new addition of sulphate of potash, and by a new evaporation, the solution yields no more alum, add to it a solution of carbonate of ammonia in excess, and agitate it well. The glucina, after being deposed, is dissolved by means of the excess of this salt, and the small quantity of alumina which may remain is precipitated without being dissolved. After some hours, when the aluminoous precipitate is not diminished in volume by a new addition of carbonate of ammonia and agitation, the solution is to be filtered, and boiled in a glass matra, and as the carbonate evaporates, there is precipitated a white, gritty powder, which is carbonate of glucina. The carbonic acid may be driven off, by exposing the powder in a crucible to a red heat.

3. Glucina prepared by this process, is in the form of a soft powder, or light white fragments, which are insipid to the taste, and adhere to the tongue. The specific gravity is 2.967+. It is altogether infusible in the fire, and it neither contracts nor becomes harder, like alumina. It has no effect on vegetable colours.

4. There is no action between glucina and oxygen, azotic, or hydrogen gases. It is not changed by exposure to the air, nor is it acted on by carbons, phosphorus, or sulphur. It combines with sulphurated hydrogen. When sulphurated hydrogen gas is made to pass into water in which this earth is suspended, it combines with it, and forms a hydrofulphuret, whose properties are similar to those of the other hydrofulphurets.

5. Glucina is insoluble in water; but it forms with this liquid in small quantity, a paste which is slightly ductile, but has less tenacity than that of alumina.

6. Glucina combines readily with all the acids, and forms with most of them soluble salts, which are distinguished by a sweet and slightly astringent taste. Its affinities are in the following order:

- Sulphuric acid, - Nitric, - Muriatic, - Phosphoric,

Fluoric, Boracic, Carbonic.

7. This earth is soluble in solutions of the fixed alkalies. It is also soluble in carbonate of ammonia, but it is insoluble in pure ammonia.

8. The characteristic properties of this earth are, according to Vauquelin, the following:

a. It forms with acids sweetish and slightly astringent salts. b. It is soluble in sulphuric acid when a little in excess. c. It decomposes aluminous salts, by separating the earth when it is boiled in their solutions. d. The salts of glucina are completely precipitated by ammonia. e. It is soluble in the liquid carbonate of ammonia. f. The affinity of this earth for the acids is between that of magnesia and alumina.

I. Compounds of Glucina with Acids.

1. Sulphate of Glucina.

This salt, which was first discovered by Vauquelin, is prepared by the direct combination of fulphuric acid with the earth, either in the pure state, or in that of carbonate. The solution is to be evaporated to the consistence of syrup, and crystals are obtained on cooling.

2. This salt crystallizes with difficulty in the form of small needles; but their form has not been accurately ascertained. It has a sweet, and somewhat astringent taste. It is not perceptibly altered by exposure to the air, and is very soluble in water.

3. When it is exposed to heat, it melts, swells up, and then dries. With a red heat it is entirely decomposed, the acid is driven off in the state of vapour, and the pure earth remains behind.

4. This salt is not decomposed by any of the acids, of acids, but it is decomposed by the alkaline, and most of the earthy bases. The infusion of nut-galls added to a solution of this salt produces a yellowish white precipitate, which is characteristic of the salt.

2. Sulphite of Glucina.

This salt is yet unknown.

3. Nitrate of Glucina.

The compound of nitric acid and glucina is formed by the direct combination of the acid and earth in a state of purity. The solution is evaporated by a moderate heat to dryness, and then the salt is obtained in the state of powder.

2. The nitrate of glucina does not crystallize. It is either in the form of powder, or in that of a soft ductile mass. The taste is sweetish and astringent.

3. It is extremely deliquescent in the air, and is very soluble in water. It readily melts when exposed to heat, and if the heat be increased it is decomposed; the acid is driven off in the gaseous form, and the earth remains behind. It is only decomposed by sulphuric acid.

4. Nitrite of Glucina.

Unknown.

5. Muriate 5. Muriate of Glucina.

This salt, according to Vauquelin, by whom only it has been described, comes very near the nitrate of glucina in its properties. It seems to crystallize with more facility, but the crystals are so small that the form cannot be determined. It does not deliquesce in the air. When it is dissolved in alcohol, and diluted with water, it affords a very agreeable sweet liquor.

It is decomposed by heat, by the sulphuric acid, the nitric, and by the phosphoric by the assistance of heat.

6. Fluate of Glucina. Unknown.

7. Borate of Glucina. Unknown.

8. Phosphate of Glucina.

1. Vauquelin procured this salt by adding the phosphate of soda to the solution of the nitrate, the sulphate, or muriate of glucina. A copious mucilaginous matter is instantly precipitated. Or it may be obtained by heating together the muriate of glucina and phosphoric acid in the state of glaas.

2. This salt does not crystallize, but is in the form of mucilage or of white powder. It has no perceptible taste. It is not altered by exposure to the air, and it is insoluble in water without an excess of acid. It is not decomposed by strong heat. It melts under the blow-pipe into a transparent vitreous globule. It is decomposed by the sulphuric, nitric, and muriatic acids.

9. Phosphite of Glucina. Unknown.

10. Carbonate of Glucina.

1. The compound of carbonic acid and glucina, which was discovered by Vauquelin, and only examined by him, is prepared by exposing the earth to the air, from which it attracts the acid, or by precipitating some of the soluble salts of glucina by means of an alkaline carbonate. The precipitate is to be washed with water, and dried in the air.

2. This carbonate is in the state of a white powder, soft and greasy to the touch. It has not the sweet taste of the other salts of glucina. It is not changed by exposure to the air, and is insoluble in water. When exposed to heat, the acid is driven off, and the pure earth remains behind. It is decomposed by all the acids with a brisk effervescence.

II. Carbonate of Ammonia and Glucina.

This triple salt is formed by adding the earth of glucina to a solution of carbonate of ammonia. It is soluble in the same quantity of water which holds the carbonate of ammonia in solution. Its other properties are unknown.

12. Arseniate of Glucina. Unknown.

13. Tungstate of Glucina. Unknown.

14. Molybdate of Glucina. Unknown.

15. Chromate of Glucina. Unknown.

16. Columbate of Glucina. Unknown.

17. Acetate of Glucina.

Glucina readily dissolves in acetic acid. This salt does not crystallize; but by evaporation it is reduced to a gummy substance, which becomes slowly dry and brittle. For a long time it retains a kind of ductility. The taste is sweet and strongly astringent.

18. Oxalate of Glucina. Unknown.

19. Tartrate of Glucina. Unknown.

20. Citrate of Glucina. Unknown.

21. Malate of Glucina. Unknown.

22. Gallate of Glucina. Unknown.

23. Benzoate of Glucina. Unknown.

24. Succinate of Glucina.

This salt according to Ekeberg, is formed by precipitating the earth from its solutions, by means of the succinates. It is therefore nearly insoluble.

25. Saccolate of Glucina. Unknown.

26. Camphorate of Glucina. Unknown.

27. Suberate of Glucina. Unknown.

28. Mellite of Glucina. Unknown.

29. Lactate of Glucina. Unknown.

30. Prufiate of Glucina. Unknown.

31. Sebate of Glucina. Unknown.

Sect. IX. Of Zirconia and its Combinations.

1. The name of this earth is derived from a stone called zircon or jargon, which is found in the island of Ceylon. It was from this stone that Klaproth extracted the earth, some time before the year 1793. He soon after found the same earth in the oriental hyacinth. By this discovery, Guyton was led to analyze the hyacinths of France; and in those which were collected in the river of Expilly, he detected the same earth. The experiments of Klaproth and Guyton were repeated by Vauquelin, and their results were confirmed, so that the nature and properties of this earth have been fully developed.

2. Zirconia is extracted from this mineral, in which preparation it has been found, by the following process. A tincture of the mineral is to be reduced to fine powder, and fused with five or six times its weight of pure potash, in a silver crucible. The fused mass is then dissolved in water, by which means the alkali is separated. The residue is then dissolved in muriatic acid, which is to be heated, to separate the silica; and when no farther precipitate appears by means of heat, add a caustic fixed alkali. Another precipitate is formed, which is to be well washed and dried. This is pure zirconia.

3. Zirconia, thus prepared, is in the state of fine Properties. white powder, which is nearly soft to the touch, and without taste or smell. When it retains water, it assumes the form of a jelly, and is semitransparent. The specific gravity is 4.3.

4. Light has no action on this earth. When it is exposed to the heat of the blow-pipe, it remains infusible, but gives out a yellowish, phosphoric light. Heated in a charcoal crucible, and surrounded with powdered charcoal, it undergoes a kind of fusion, but without becoming transparent, or assuming a vitreous form. It becomes extremely hard, strikes fire with steel, and scratches glass.

5. There is no action between zirconia and oxygen or azotic gases, nor is it changed by exposure to the air. Zirconia, air. It is not acted on by hydrogen, carbons, phosphorus, or sulphur.

6. This earth is insoluble in water; but it mixes with a considerable portion of this fluid, and forms with it a transparent jelly. If in this state it be slowly dried, it retains the water, and assumes a yellowish colour, and something of the transparency of gum arabic*. When it is dried in a very high temperature, it loses more than one-third of its weight. After having been exposed to a red heat, it becomes of a gray colour, harsh to the feel, and less soluble in acids.

7. Zirconia combines with the acids, and forms with them peculiar salts. Many of these are insoluble in water, and are distinguished by an astringent taste.

The order of the affinities of this earth, is the following:

- Vegetable acids, - Sulphuric, - Muriatic, - Nitric.

8. Zirconia does not combine with the alkalies by fusion, and is insoluble in liquid alkalies. It may be dissolved, however, by the alkaline carbonates.

I. Compounds of Zirconia with Acids.

1. Sulphate of Zirconia.

1. This salt is formed by the direct combination of the earth with sulphuric acid. The solution is to be evaporated to dryness. The salt thus obtained is in the form of a white powder, which is very friable. Sometimes it is in the form of crystals like small needles. It has no taste, is not changed by exposure to the air, and is insoluble in water.

2. This salt is readily decomposed by heat, the acid is driven off, and the earth remains behind. When it is boiled in water, the earth is precipitated, and the acid remains in the liquid. At a high temperature it is decomposed by charcoal, and converted into a sulphuret which is soluble in water, and the solution furnishes by evaporation crystals of hydro-sulphuret of zirconia†.

2. Sulphite of Zirconia.

Unknown.

3. Nitrate of Zirconia.

1. This salt is formed by the direct combination of zirconia with concentrated nitric acid; and by evaporation it is obtained in the form of a yellow, transparent, viscid mass, which dries with difficulty.

2. This salt has a pungent and astringent taste, and leaves on the tongue a thick matter, which proceeds from a decomposition of the salt by means of the saliva.

3. When nitrate of zirconia, after being evaporated, is put into distilled water, a very small quantity only is dissolved. The greatest part remains under the form of gelatinous and transparent flakes. This salt is very readily decomposed by heat.

4. It is also decomposed by sulphuric acid, which forms in the solution a white precipitate, soluble in excess of acid; by carbonate of ammonia, which produces a precipitate, soluble in an excess of this salt; and by an infusion of nut galls in alcohol, which affords a white precipitate, soluble in an excess of this infusion. But if the zirconia contains iron, the colour of the precipitate is bluish gray, of which a part remain in the solution, communicating to the liquor a pure blue colour. When this liquid is mixed with carbonate of ammonia, it affords a purple matter, by the refracted rays, but of a violet colour by reflected light. Crystallized gallic acid also precipitates the nitrate of zirconia, of a bluish gray colour. Most of the other vegetable acids also decompose this salt, and form combinations with the earth which are insoluble in water*.

4. Nitrite of Zirconia.

Unknown.

5. Muriate of Zirconia.

1. Of all the acids, the muriatic combines most readily with zirconia, when the latter is in the state of carbonatate. This salt was first formed by Klaproth, and its properties were afterwards more particularly investigated by Vauquelin.

2. The muriate of zirconia has no colour, but possesses a very astringent taste, is very soluble in water, and also in alcohol. By slow evaporation, it affords small, transparent, needle-formed crystals, whose figure has not been determined. When muriate of zirconia contains any portion of silica, the crystals are cubical, have little consistence, and resemble a jelly. These crystals, exposed to the air, gradually lose their transparency, and are diminished in volume. There are formed, in the middle of the mats, white silky crystals in the shape of needles, which arise from the cubes.

3. Muriate of zirconia is decomposed by heat, which drives off the acid. It is even decomposed in the mouth by means of the saliva.

4. a. It is also decomposed by sulphuric acid, which forms a precipitate with the earth in heavy white flakes, while another part is retained in solution by the muriatic acid. But by the influence of heat, the latter is diffused, and the remaining part of the phosphate of zirconia is deposited. If the evaporation be stopped before it is brought to a state of dryness, it assumes the appearance of a jelly by cooling. The sulphate of zirconia is then soluble in muriatic acid.

b. This salt is also decomposed by the phosphoric, citric, tartaric, oxalic, and lactacetic acids, which forming with its base insoluble compounds, precipitate in the form of white flakes.

c. The gallic acid precipitates the muriate of zirconia in the form of white matter, if the salt has been pure, but of a grayish green if it contain iron. In the latter case, the precipitate becomes, when dry, of a shining black colour, which has the same appearance as china ink. The liquid, in which are formed the gallates of zirconia and iron, preserves a green colour; and although new portions of gallic acid are added, no farther precipitation is produced. But the carbonate of ammonia throws down a copious flaky matter, which has a purple colour, and nearly resembles that of lees of wine. Thus, it appears, that the gallic acid has a greater affinity for zirconia than the muriatic, and that the gallates of zirconia and iron are soluble in muriatic acid.

d. The d. The carbonate of potash, when fully saturated, decomposes the muriate of zirconia; and although this solution is attended with effervescence, the precipitate washed and dried in the air, retains a large proportion of carbonic acid; for when this earth is afterwards dissolved in acids, it produces a brisk effervescence. The carbonate of ammonia at first forms a precipitate in the solution of muriate of zirconia. This precipitate is in great part re-dissolved by new additions of the ammoniacal salt, and there is produced a triple salt, which may be decomposed by heat.

e. A solution of sulphurated hydrogen gas in water, mixed with a solution of muriate of zirconia containing iron, becomes turbid, and produces a reddish colour; but there is no real precipitate. Hydroxysulphuret of ammonia instantly precipitates this earth of a fine green colour, which appears black when it is dry. When this precipitate is placed on burning coals, it emits the odour of sulphurated hydrogen gas, and becomes of a purple blue colour when reduced to powder.

f. Pure alumina decomposes the muriate of zirconia, with the aid of heat. The alumina is dissolved, the liquid becomes milky, and assumes the form of a jelly as it cools. It has been remarked, when the muriate of zirconia contains iron, it remains in solution with the alumina, and the zirconia, which has been precipitated in this way, contains no perceptible portion of this metal.

g. The prussiate of mercury produces in the solution of muriate of zirconia, a copious white precipitate, which is soluble in muriatic acid.

h. A plate of zinc introduced into a solution of muriate of zirconia, produces a slight effervescence. The liquid becomes milky, and assumes the appearance of a white semitransparent jelly in a few days*.

6. Fluate of Zirconia. 7. Borate of Zirconia. 8. Phosphate of Zirconia. 9. Phosphite of Zirconia. 10. Carbonate of Zirconia.

When an alkaline carbonate in solution is added to a solution of muriate of zirconia, the earth is precipitated without effervescence; and when this precipitate is exposed to heat in close vessels, it gives out carbonic acid gas. It also enters into combination with the alkaline carbonates, and forms with them triple salts. This, Vauchelin observes, is one of the remarkable characters of this salt.

The component parts of carbonate of zirconia, according to the same chemist, are,

| Acid and water | 44.5 | |---------------|------| | Zirconia | 55.5 |

11. Arseniate of Zirconia. 12. Tungstate of Zirconia. 13. Molybdate of Zirconia. 14. Chromate of Zirconia. 15. Columbate of Zirconia.

16. Acetate of Zirconia.

Acetic acid combines with zirconia, and forms with it a salt which does not crystallize. When the solution is evaporated to dryness, the acetate of zirconia remains in the state of powder. This salt has an attri-

17. Oxalate of Zirconia. 18. Tartrate of Zirconia. 19. Citrate of Zirconia. 20. Malate of Zirconia.

21. Gallate of Zirconia.

Gallic acid added to a solution of muriate of zirconia, it has been already mentioned, produces a precipitate of a white matter, which is the gallate of zirconia. The properties of this compound have not been examined.

22. Benzoate of Zirconia. 23. Succinate of Zirconia. 24. Saccolate of Zirconia. 25. Camphorate of Zirconia. 26. Suberate of Zirconia. 27. Mellate of Zirconia. 28. Lactate of Zirconia. 29. Prussiate of Zirconia. 30. Sebate of Zirconia.

CHAP. I. OF METALS.

1. The metals, on account of their importance and utility, have always greatly occupied the attention of mankind. Indeed such is their importance, that man could not take a single step in the improvement even of the simplest of the arts of life, without the assistance of some of the metals. In this view, the origin and improvement of many arts, and the knowledge of metallic substances, may be, in some measure, considered as coeval. The metals, therefore, became very early, and were probably the first objects of chemical investigation. In the extraordinary pursuits of the alchemists, they were the subjects of their eager researches, in the discovery of the means of converting the more abundant and baser metals, as they were called, into those which were more valued, on account of their durability and fecundity. They failed of their purpose; but their labours were not in vain. The facts which they discovered in the progress of their investigations, were of no small importance to science.

2. The metals are distinguished from other substances by a number of characteristic properties. These are, brilliancy, colour, opacity, density, hardness, elasticity, ductility, malleability, tenacity, fusibility, power of conducting caloric and electricity.

3. Lustre or brilliancy is one of the most striking characteristics of metallic substances, and hence it has been denominated metallic lustre. This is owing to the reflection of a great proportion of the rays of light by metallic surfaces. On account of this property, metals are employed in the construction of mirrors. Other substances, indeed, exhibit the appearance of this brilliancy, which is the case with the mineral called mica; but in this substance, as well as every other which is not metallic, it is merely superficial, and it entirely disappears when the surface is is broken, or scratched with a sharp-pointed instrument. But the metal, treated in the same way, becomes more brilliant. The following is the order in which the metals possess this lustre:

Platina, Steel, Silver, Mercury, Gold, Copper, Tin, Zinc, Antimony, Bismuth, Lead, Arsenic, Cobalt; and the other brittle metals.

4. Colour is one of the constant properties of metallic substances, while it is only accidental and variable in other minerals. And as the metals are the most opaque, and the densest bodies in nature, colour in them is very intense, or rather confounded with their brilliancy. The prevailing colour of metals is white; some however are yellow, and others reddish. Those of a white colour were formerly distinguished by the name of lunar metals, because silver, which was called luna, being placed at the head of these metals, has a white colour. Gold, which was distinguished by the name of sol, having a yellow colour, gave the name of solar metals to such as resembled it. The colour of metals is permanent, while they remain unaltered; but it is often totally lost when they enter into new combinations.

5. It is generally admitted, that all metallic substances are perfectly opaque. Newton indeed observed, that gold-leaf when reduced to \(\frac{1}{2}\) of an inch thick, appeared of a green colour, from which he concluded that it transmits the green rays; and he supposed that other metals might also transmit light, if they were sufficiently thin. But no metal has yet been found so malleable as to be reduced to that state of thinness to permit light to pass through it. Silver-leaf, so thin as to be only \(\frac{1}{10000}\) part of an inch, is quite opaque.

6. The metals are particularly distinguished from other substances by their density. Metallic substances have a greater specific gravity than any other bodies in nature; that is, the quantity of matter contained in a given bulk, is greater in the metals than in other substances. Even the lightest of the metals possess a greater density than the heaviest bodies known of any other kind of matter. The particles of which they are composed must therefore be in closer contact than in any other body. To this greater density is owing their superior lustre.

7. The metals differ from each other greatly in degrees of hardness. In general, metallic substances are not so hard as many other natural bodies. The degree of hardness does not depend on the density, for the hardest metals are by no means the heaviest. This property, therefore, must be owing to the nature of the particles of which the metal is composed, or to some peculiar disposition or arrangement of these particles. It is found that some of the metals can be hardened by art, merely by hammering, or by sudden cooling after being heated. The hardness of metals, too, is greatly increased by being combined with each other, or with other substances; as, for instance, when copper and tin are combined together, or iron and carbon in the formation of steel, the utility of which latter, as it is applied for cutting instruments, depends on its hardness. Metallic substances, in comparing their different degrees of hardness, have been divided into eight classes, which are arranged in the following order:

1st, Iron and manganese. 2nd, Platina and nickel. 3rd, Copper and bismuth. 4th, Silver. 5th, Gold, zinc, and tungsten. 6th, Tin and cobalt. 7th, Lead and antimony. 8th, Arsenic.

Mercury being always fluid at the ordinary temperature of the atmosphere, cannot be compared with regard to this property; and the degree of hardness which some of the other metals possess has not been ascertained.

8. The elasticity of metals seems to follow the same Elasticity order in which they possess the property of hardness. The elasticity of some metals can be increased in the same way as their hardness, either by mechanical means, as by hammering, or by new combinations.

9. One of the most important physical properties of Ductility the metals, is ductility. By this is meant that peculiar property which some metals possess, of being drawn out into wire, without destroying or diminishing the cohesive power of their particles. Some metals possess this property in a great degree, while others are entirely deprived of it; and some metals are extremely ductile, while they possess in a very small degree another property, namely malleability. Iron is one of the most ductile metals, but is much less malleable than many others.

10. Malleability is also one of the most valuable Malleability properties of metallic substances. By this property they can be reduced to any form or shape which may be wanted, for those purposes to which they are to be applied. This property of malleability is supposed to depend on the form of the particles, or on the mode of their aggregation. Those metals which possess this property of malleability or laminability, seem to be composed of small plates, while the ductile metals seem to have their particles arranged in a fibrous form. When metallic substances are hammered, they become harder, denser, and more elastic, which is owing to their particles being brought into closer contact.

11. Tenacity is expressive of the power of cohesion between the particles of metallic substances. Different metals possess this property in very different degrees. The method which has been adopted to estimate the different degrees of tenacity, is by suspending wires of the same diameter of the different metals by one extremity, and attaching weights to the other, till the wires are broken. Iron, which has the greatest tenacity of all the metals, when formed into wire, \(\frac{1}{10}\) of an inch in diameter, will support a weight of 500 lb. without breaking, while a wire of lead of the same diameter, ter, can only support about 29 lbs. The following is the order of the ductile metals, according to the degree of their tenacity.

Iron, Copper, Platina, Silver, Gold, Tin, Lead.

12. Another property of the metals is fusibility. When they are exposed to a sufficient degree of heat, they melt, and are reduced to the state of liquidity. One of the metals, namely mercury, is always in the fluid state, at the ordinary temperature of the atmosphere. The different metals which are generally in the solid state, require very different temperatures for their fusion. Thus lead and tin require comparatively a lower temperature to be melted; while gold and platina can only be brought to the state of fusion, by the greatest degree of heat that can be applied.

13. Metallic substances are the best conductors of caloric, but the comparative degrees of this property have not been ascertained. They are also found to be the best conductors of electricity.

14. The metals possess some properties in common with other substances, as taste and smell, by which some of them are peculiarly distinguished; and in being susceptible of crystallization, which is the case with some, or of being volatilized, as happens to others.

15. But metallic substances are not only of vast importance in the arts of civilized life, on account of the properties which we have now detailed, which belong to them in the metallic state; but many of them are not less valuable in those changes which they undergo by new combinations, and the new properties they acquire, in consequence of these changes. One of the first and most ordinary changes to which metallic substances are subject, is their combination with oxygen. This is called in chemical language oxidation. When a metal, as, for instance, a piece of iron, is exposed to the air, when it is moist, it soon undergoes a remarkable change. It loses its metallic lustre, and the surface is covered with a brownish powder, well known by the name of rust. This change is owing to the combination of oxygen with the metal, and the rust of the metal in this state is known in chemistry by the name of oxide. The process by which this compound of oxygen and a metallic substance is formed, is called oxidation, and the product is denominated an oxide.

16. But this process of oxidation is effected more rapidly when metals are exposed to the action of heat; and indeed many metals require a very high temperature to produce the combination, while it cannot be accomplished in others by the greatest degree of heat that can be produced. This process was formerly called calcination, or calcining the metal; and the product, now denominated an oxide, was distinguished by the name of calx or cales, from its being reduced to the state of powder, in the same way as limestone, by burning.

17. Metals differ very much from each other in the circumstances in which this oxidation takes place, in the temperature which is necessary, the facility of the combination, the proportions of oxygen which combine in different parts of the oxide. Some metals are oxidated in the lowest temperature, as, for instance, iron and manganese; while others require the greatest degree of heat that can be applied. Such are silver, gold, and platina.

18. The facility with which oxidation takes place in some metals is so great, such as iron, tin, lead, copper, and manganese, that they must be completely defended from the action of oxygen; but in gold and platina, no perceptible change is observed, for whatever length of time they are exposed to the atmosphere.

19. This oxidation and the quantity of oxygen absorbed is proportional to the temperature. There are, however, many metals which combine with a determinate proportion of oxygen at certain temperatures, and from this may be estimated the quantity of oxidation from the degree of heat which has been applied. The rapidity of the oxidation is almost always increased by the elevation of temperature. In this way actual combustion or inflammation is produced. Thus filings of metals thrown upon a body in the state of ignition, give out brilliant sparks; and steel, struck upon a flint, burns with a vivid flame in the air, in consequence of the great heat which is communicated to it by percussion.

20. Metallic substances combine with very different proportions of oxygen; and this quantity varies according to the manner in which the process has been conducted, or the temperature to which the metal has been exposed.

21. In these different states and conditions of oxidation, different phenomena are exhibited. Sometimes the metal becomes red-hot and is inflamed; sometimes the oxidation takes place without fusion, or does not combine with oxygen till after it has been melted; sometimes it is covered with a brittle crust, or with a sublimate in the form of powder. At other times a pellicle, exhibiting different colours, forms on the surface; but, in all cases, the metal is tarnished, loses its brilliancy and its colour, and assumes another, which announces the change that has taken place.

22. Another difference which takes place among different metals, is the different degrees of force with which the affinities, oxygen adheres to the metal. The knowledge of this, and the different degrees of affinity between oxygen and metallic substances, is of great importance in many operations and chemical results.

23. During the fixation of oxygen in metallic substances, it is absorbed by some in its solid state, and given out during oxidation, it gives out a great deal of caloric. In others it is combined, without giving out the same quantity. This proportion of caloric given out corresponds to the facility with which oxides part with their oxygen, or are reduced to the metallic state. Those which have combined with oxygen with the greater proportion of caloric, are most easily reduced; but those, on the contrary, in which the oxygen has been deprived of its caloric, are reduced to the metallic state by a great addition of caloric. caloric, and the greatest number of oxides require the addition of substances whose affinity for oxygen is greater than that of the metal.

24. Metallic oxides are extremely different in different metals, and even in the same metal, according to the proportion of oxygen. They are, however, possessed of some common properties. They are all in the form of powder or earthy substance, or so brittle as to be easily reduced to this state. They exhibit every shade of colour from pure white to brown and deep red, and they are heavier than the metals from which they have been obtained. Some oxides are revived, as it is called, or are reduced to the metallic state, merely by being in contact with light or caloric. Some require the addition of a combustible substance and a high temperature; while others have so strong an affinity for oxygen, that they cannot be deprived of it by the strongest heat, but become fusible in the fire, and afford a glairy matter more or less coloured, and even serve as a flux to the earths. Some oxides are volatile, but the greatest number are fixed. Some have an acrid and caustic taste, are more or less soluble in water, and even possess an acid quality; others are insoluble and insipid.

25. Observing this remarkable change produced on metallic substances by the action of air or of heat, philosophers began early to account for it. According to Beccher and Stahl, the founders of chemical science, metals are composed of earths and phlogiston, and the process which takes place during the calcination of a metal, is merely depriving it of its phlogiston. This doctrine, which had undergone various modifications, from the difficulties which it presented in accounting for the phenomena of the calcination of metals, was finally overthrown by the celebrated experiments of Lavoisier. In one of these experiments he introduced eight ounces of tin into a glass retort, and having hermetically sealed it, after previous heating to expel some of the air, it was accurately weighed, and exposed to heat. The tin melted; and a pellicle appeared on its surface, which was soon converted into a gray powder. The heat was continued for three hours, but no farther change appeared upon the metal. When the retort was cooled, it was found to have the same weight as before the operation. The point of the retort was then broken off, and a quantity of air rushed in. This was equal to 10 grs. which was the additional weight acquired by the retort. The whole of the metallic substance in the retort was 10 grains heavier than when it was introduced, so that he concluded, that the 10 grains of air which had disappeared, had combined with the metal, and caused its increase of weight. The inference which he drew from this was, that the calcination of metals is not owing to their being deprived of any substance, but to their combination with air, and with the oxygen of the air; for it was found by future experiments, that the calcination or oxidation of metals could not be effected without oxygen; and when it took place in a given quantity of common air, it was only the oxygen which was absorbed.

26. But as a still farther proof, that the calcination of metals is owing to the absorption of oxygen, they are reduced by those substances which have a greater affinity for oxygen. If charcoal in powder be mixed with a metallic calx or oxide, the oxygen combines with the carbone of the charcoal, forming carbonic acid, and the oxide is restored to the metallic state. If this process be performed in close vessels, the quantity of oxygen in the carbonic acid, corresponds to the quantity which was absorbed by the metal during calcination.

27. From these observations, therefore, it appears that metallic substances combine with oxygen; and it has been observed, that not only different metals combine with it in different proportions, but the same metal forms compounds of one, two, and sometimes three different portions. No combination takes place between azote or hydrogen and metallic substances; but some of them enter into combination with carbone, phosphorus, and sulphur, forming carburets, phosphurets, and sulphurets. The metals also combine with the acids, and form salts, some of which are of the utmost importance, not only in chemistry, but also in the arts of life. They also enter into combination with each other, forming a class of bodies which are distinguished by the name of alloys.

28. Metallic substances were formerly divided into noble or perfect, and imperfect metals. The noble or perfect metals were platinum, gold, silver, mercury; and the property on which this character was founded, was that of their being susceptible of being reduced by being exposed to heat. The other metals then known, were called imperfect metals, because, to reduce them to the metallic state, the addition of some combustible substance was found to be necessary. They were also divided into metals and semimetals. Among the first were included those metals, which were malleable and ductile; the semimetals comprehended those which possessed neither of these properties, and were therefore considered as less perfect. These distinctions, however, are now neglected, because they afford no well-founded or just marks of discrimination.

29. In the arrangement of the metals which we propose to follow, that of Fourcroy is adopted. He has divided them into five different classes, according to their ductility, and the proportions of oxygen with which they combine, or the facility with which that combination takes place. In the first class he includes those metals which are brittle, and in some of their combinations with oxygen have acid properties. These are,

- Arsenic, - Tungsten, - Molybdenum, - Chromium, - Columbium.

The second class comprehends those which are brittle, and simply susceptible of oxidation. These are the following:

- Titanium, - Uranium, - Cobalt, - Nickel, - Manganese, - Bismuth, - Antimony, - Tellurium. The third class comprehends those metals which have some degree of ductility, which are only two in number, viz.

Mercury, Zinc.

The fourth class, which consists of three metals, includes such as are ductile, and easily oxidized. These are,

Lead, Iron, Copper.

The fifth class is composed of three metals, which are characterized by being very ductile, but oxidized with great difficulty. These are,

Silver, Gold, Platinum.

30. To these preliminary observations we have only to add, that metallic substances are found, either on the surface or in the interior of the globe, and either uncombined, or forming compounds with different substances. Some metals, as gold and platinum, are generally found in small grains, mixed with the soil. These, as well as the matters with which they are accompanied, have proceeded from the decomposition of the more solid parts of the globe. But metallic substances, which are met with in greater abundance, exist in the interior of the globe, in veins which traverse the other strata of the earth in different directions. The metals most commonly found in veins are, lead, copper, silver, zinc, mercury, and antimony. Some exist in detached masses.

31. Metals, as they exist in the earth, are either in a state of purity, or the metallic state, when they are called native or virgin metals; or combined with each other, when they are said to be alloyed. They are found also combined with other substances, very frequently with sulphur; when they are said to be mineralized; or, they are combined with oxygen, when they come under the denomination of oxides; or they are combined with acids in the state of salts.

Sect. I. Of Arsenic and its Combinations.

1. It would appear that the ancients were acquainted with arsenic in its state of combination with sulphur, which is a reddish-coloured mineral, and was employed by them in painting; and although Theophratus arranged it among metallic stones, probably on account of its weight, it was not known to possess a metallic substance till the middle of the 17th century. Paracelsus, indeed, who lived at an earlier period, is said to have known it in the metallic state; but the process of obtaining it from orpiment and arsenic, was only first described by Schroeder in 1649. Lemery also published a process for extracting this metal in 1675. It was afterwards fully demonstrated by Brandt in 1733, and by Macquer in 1746, that arsenic possessed peculiar properties, and is totally distinct from all other metals. These facts were farther confirmed by Monnet in 1773, and by Bergman in 1777.

2. Arsenic is frequently found native, and is then in dark-coloured masses, which have little brilliancy, and exhibit no metallic lustre, except at the fracture. It is frequently found combined with other metals. In this state it is combined with iron, and is known by the name of arsénical pyrites, or mispickel. One of the most frequent combinations of arsenic is with sulphur, of which there are two principal varieties; the one is of a yellow colour, well known under the name of orpiment, and the other red, called realgar. It is also sometimes found in the state of white oxide, or arsenious acid; but this is a rare occurrence.

3. In whatever state arsenic is found, it can easily be detected, by throwing a little of it on burning coals. The white fume which arises, and the garlic smell which is exhaled, are sufficiently characteristic of this metal. To obtain the metal from its oxide, it may be mixed with three times its weight of black flux. This mixture is put into a crucible, to which another crucible inverted is adapted. They are then to be melted together, to exclude the air. Apply heat to the lower crucible till it becomes red, defending the upper one as much as possible from the heat, by means of a plate of iron or copper, through which the lower crucible passes. When the apparatus has cooled, a crust of metallic arsenic is found in the upper crucible, in the form of crystals. This being detached and weighed, shows the quantity of pure metal in the mineral which has been tried.

In the humid way, Bergman recommends to treat native arsenic by dissolving it in four parts of nitric acid, concentrating the solution by evaporation, and precipitating the muriate of arsenic which is formed, by means of water. If there is any silver, it is first precipitated in the form of an insoluble muriate, and iron is sometimes found in the solution precipitated by water.

The sulphures of arsenic are to be treated by muriatic acid, adding a small quantity of nitric acid, to separate the sulphur. The oxide of arsenic may then be precipitated by water. The pure metal may be obtained by immersing a plate of zinc in the solution, having previously added a quantity of alcohol.

4. Arsenic is in the form of small plates of a blackish Properties, gray, brilliant, and metallic colour, with considerable lustre where there is a fresh fracture. The specific gravity is 8.31. It is extremely brittle, and is therefore easily reduced to powder. It has neither smell nor perceptible taste when it is cold; but when it is heated, and in the state of vapour, it is remarkable for a strong fetid odour of garlic. It sublimes before it melts, so that its fusing point is not known. It is the most volatile of all the metals. When slowly sublimed, it crystallizes in the form of regular tetrahedrons, and sometimes in that of octahedrons. The tetrahedron is the form of its integrant molecule.

5. When arsenic recently prepared is exposed to the action of air, it is soon tarnished, loses its lustre, becomes at first air-yellowish, and then passes to a black colour. It loses at the same time its hardness, and becomes extremely friable. When it is heated in contact with air, or if it be thrown in the state of powder on burning coals, it burns with a blue flame, and exhaling the strong odour of garlic, is sublimed in the form of a white, acrid, soluble mass, which has been called the white oxide of arsenic, or white arsenic. By this latter name it is well known in the shops. To this oxide of arsenic, nic, because it possesses some acid properties, Fourcroy has given the name of arsenious acid. This acid bears the same relation to arsenic acid as the phosphorous and sulphurous acids do to phosphoric and sulphuric acids.

6. This oxide or acid is extremely volatile. When it is heated in clofe vefvils, it is sublimed in transparent, regular tetrahedrons. It is extremely acrid and caustic, corroding and destroying the organs of animals, so that it is the most violent poison known. The specific gravity is between 4 and 5. It reddens vegetable blues, and, when exposed to the air, it is covered with a slight efflorescence.

7. The arsenious acid is decomposed by hydrogen, carbons, phosphorus, and sulphur. At a red heat, the hydrogen and carbons combine with the oxygen, and reduce it to the metallic state. Phosphorus and sulphur are partly converted into phosphoric and sulphuric acids, and partly combine with the arsenic, forming a phosphuret or sulphuret of arsenic.

8. This acid is very soluble in water. It requires about 15 parts of boiling water for its solution, from which it may be obtained crystallized on cooling, or by slow evaporation. The crystals are in the form of regular tetrahedrons. The solution in water is extremely acrid, reddens vegetable blues, combines with earthy bases, decomposes the alkaline sulphurets, and affords with them a yellow precipitate in which the arsenic returns to the metallic state. The component parts of arsenious acid are,

| Arsenic | Oxygen | |---------|--------| | 75.2 | 24.8 |

9. Arsenic combines with a greater proportion of oxygen; and in this compound it still exhibits acid properties, and is known by the name of arsenic acid. The method of preparing this acid, and its properties, have already been described, in the chapter on acids; and the compounds it forms with the alkalies and earths, have been particularly detailed in the chapters which treat of these substances.

10. Arsenic does not decompose water. It may be kept for any length of time under water, without undergoing any change. There is no action between arsenic and carbons or azote. Arsenic, however, is soluble in hydrogen gas, to which it communicates a fetid odour and a poisonous property.

11. Arsenic enters into combination with phosphorus. When equal parts of phosphorus and arsenic are distilled together with a moderate heat, there is sublimed a dark-coloured brilliant substance, which burns on red-hot coals, with a mixed odour of arsenic and phosphorus. This is the phosphuret of arsenic, which must be preserved under water. This compound may be formed under water at a boiling temperature in a retorts. As the phosphorus melts, it combines with the arsenic. The properties of this phosphuret of arsenic have not been examined.

12. Arsenic combines readily with sulphur, either by fusion or by sublimation. The result of this combination is a yellow or red mass. This compound of sulphur and arsenic, which is a sulphuret of arsenic, is found native. The red is known by the name of realgar, and the yellow by that of orpiment.

13. Arsenic enters into combination with the acids, and forms with them peculiar salts. It also combines with the metals, forming alloys. The following is the order of the affinities of arsenic and of its oxide, as they have been arranged by Bergman.

| Arsenic | Oxide of Arsenic | |---------|------------------| | Nickel | Lime | | Cobalt | Muriatic acid | | Copper | Oxalic | | Iron | Sulphuric | | Silver | Nitric | | Tin | Tartaric | | Gold | Phosphoric | | Platina | Fluoric | | Zinc | Saccharic | | Antimony| Succinic | | Sulphur | Citric | | Phosphorus | Lactic | | | Arsenic | | | Acetic | | | Prussic |

14. Arsenic, in the metallic state, is scarcely applied to any use, except for chemical purposes. It is sometimes alloyed with the metals, by which means they acquire new properties. In the state of white oxide, it is much employed in the arts. It has even been exhibited as an internal remedy in the diseases of cancer and intermittent fevers; but in all cases this terrible poison ought to be administered with the greatest caution. To counteract the effects of arsenic, when it has been accidentally taken into the stomach, one of the best antidotes is water impregnated with sulphurated hydrogen gas, or some of the alkaline sulphurets dissolved in water.

I. Salts of Arsenic.

1. Sulphate of Arsenic.

Concentrated sulphuric acid has no action on arsenic in the cold; but when they are boiled together, an effervescence takes place, sulphurous acid gas is disengaged, the arsenic is oxidated, and falls to the bottom in the state of white powder. According to Fourcroy, this powder retains but a small portion of sulphuric acid, the whole of which is nearly carried off by washing with water; nor are crystals obtained from the solution. By evaporation the white oxide of arsenic is precipitated, and sulphuric acid remains pure in the solution. There is no action between sulphurous acid and arsenic.

2. Nitrate of Arsenic.

Concentrated nitric acid produces a violent action with arsenic. Nitrous gas is disengaged, and towards the end of the process, azotic gas. The arsenic is converted at first into the white oxide, which, with a new addition of acid, passes to the state of arsenic acid; and when a great quantity of nitric acid is employed, with the aid of heat, the metal is instantly converted into arsenic acid. There remains no oxide in the solution, and there is no nitrate of arsenic formed. But, according to Bergman, when the nitric acid is diluted, it dissolves the oxide, and affords a crystallized salt like the white oxide.

3. Muriate 3. Muriate of Arsenic.

1. Muriatic acid has no action on arsenic in the cold; but when they are boiled together, the solution takes place, and there is disengaged a fetid gas, which seems to be arseniated hydrogen gas. From this it appears, that muriatic acid enables the arsenic to decompose water. A little nitric acid added, promotes the solution; and this solution, heated and concentrated at first in close vessels, is entirely sublimed in the form of a thick liquid, which was formerly called butter of arsenic. This salt is decomposed by water alone, which precipitates the metal. The muriate of arsenic, therefore, can scarcely be considered as a permanent salt.

2. When arsenic in the state of powder is thrown into oxy-muriatic acid gas, it instantly catches fire, burns with a very brilliant white flame, and is converted into white oxide. If arsenic be added to liquid oxy-muriatic acid, it is converted into arsenic acid, while the acid returns to the state of muriatic acid.

4. Fluate of Arsenic.

Fluoric acid combines with the white oxide of arsenic, and affords small grains, which have a crystalline form; but their properties are unknown.

5. Borate of Arsenic.

Boracic acid also combines with the white oxide of arsenic, and affords a salt which is in the state of white powder, or in the form of small needles. Their properties are also unknown.

6. Acetate of Arsenic.

Acetic acid enters into combination with the white oxide of arsenic, and forms crystals, which are only known to be difficultly soluble in water.

7. Oxalate of Arsenic.

Oxalic acid, combined with arsenic, affords crystals in the form of prisms. Similar crystals are obtained by the combination of arsenic with the tartaric acid.

8. Benzoate of Arsenic.

Benzoic acid combines with the white oxide of arsenic, and by evaporating the solution, plumose crystals are obtained. This salt has an acid and acid taste, is soluble in water, sublimes with a moderate heat, but with a stronger heat is decomposed, and is not precipitated from its solutions by alkalies.

Sect. II. Of Tungsten and its Combinations.

1. The name of tungsten is derived from a white, transparent mineral, which contains this metal in the state of acid united to lime. This mineral was analyzed by Scheele in 1781, and he found that one of its component parts is lime, and the other an earthy-like substance, to which he gave the name of tungstic acid. His discovery was confirmed about the same time by Bergman, who conjectured that the basis of the acid might be a metallic substance. This conjecture was verified by the experiments of Medeiros D'Elhuyart, two Spanish chemists, who discovered the Molybdena, same metal in the mineral called wolfram, and ascertained some of its metallic properties. It has since been farther examined by Vauquelin and Hecht, and by Allen and Aikin in London.

2. This metallic substance has been only found in the state of acid in combination with lime, iron, manganese and lead. When it is combined with lime, it is the tungsten of the Swedes, and in combination with iron it is called wolfram.

3. To obtain this metal from the acid, it is mixed with charcoal in a crucible, and exposed to a very strong heat. By this process the metal was obtained in the form of a small button at the bottom of the crucible, in the first experiments which were made upon it by the German chemists. This crumbled to pieces between the fingers; and when it was examined with a magnifying glass, it was found to consist of a number of metallic globules, none of which were larger than a pin head.

4. The colour of the metal is a steel gray. The specific gravity is 17.6, or, according to others 17.22. It is one of the hardest of the metals. It is also one of the most infusible, requiring a temperature of 170° Wedgwood. It crystallizes on cooling.

5. When it is heated in the open air, it is readily converted into a yellow oxide, which afterwards, by a heat stronger heat, becomes of a black colour, and then by combining with a greater proportion of oxygen, it assumes the character of an acid, namely the tungstic acid, whose properties and combinations with alkalies and earths, have been already described.

6. There is no action between tungsten and azote, of phosphorus or carbone. Tungsten combines with phosphorus, forming a phosphuret, the properties of which are unknown. It also combines with sulphur, forming a sulphuret of a bluish black colour, and which may be crystallized. There is no action between this metal and sulphuric, nitric, or muriatic acids. It is only acted on by nitro-muriatic acid at a boiling temperature, and nitrous gas is disengaged. Nothing therefore is known of the combinations of tungsten with the other acids.

7. This metal combines with the other metals, and forms alloys with them.

8. It is too little known, and has been produced in too small quantity, to be able to ascertain any thing of its uses or application.

Sect. III. Of Molybdena and its Combinations.

1. The mineral called molybdena, from which this metal is extracted, was analyzed by Scheele in 1778. He found that it contained sulphur, and a substance which he discovered to be possessed of acid properties. Previous to this time, this mineral had been confounded with plumbago or black lead, which it resembles in appearance. The acid which Scheele obtained from this substance, Bergman conjectured was a metallic oxide. These experiments were repeated by Pelletier; and he proved that molybdena was a peculiar metal combined with sulphur, and that in all the different processes the sulphur was separated, and the metal oxidated. The metal has since been called molybdena, Molybdena, and the mineral from which it is obtained sulphuret of molybdena.

2. Molybdena has never been found existing in any other but in the state of sulphuret, or in that of oxide. The sulphuret of molybdena, it has been observed, was long confounded with plumbago, or the carburet of iron. It has, however, a less greasy feel, more brilliant, and inclining more to a blue colour. It stains the fingers less than carburet of iron, and leaves a bluish trace on paper. It is difficult to reduce it to powder, on account of the elasticity of the plates or scales of which it is composed. The sulphuret of molybdena, too, becomes electric by friction. When the sulphuret of molybdena is treated with the blow-pipe, it exhales sulphur, which is detected by its odour, and a white vapour which is condensed on cold bodies in the form of plates or crystallized needles, of a yellowish colour, but which become blue by the contact of the interior flame. Molybdena has only been obtained in black, friable, agglutinated masses, which have some metallic brilliancy; and when broken, exhibit small round grains, of a greyish brilliant appearance. The specific gravity is about 7, and it is extremely infusible; but since the experiments of Dr Hielm, which were made in 1781, this metal has been procured in such small quantity, that its characteristic metallic properties have not been ascertained.

3. When molybdena is exposed to a high temperature in contact with air, it is converted into a white oxide, which sublimes and crystallizes in the form of brilliant needles. This oxide has acid properties. When it is heated with combustible bodies, it assumes a bluish colour, with little brilliancy, as it approaches to the metallic state. According to Mr Hatchet, who made a set of experiments on the compound of this acid with lead, the molybdate of lead, molybdena, when it is not in the metallic state, appears to suffer four degrees of oxidation. The first is the black oxide, which contains the smallest proportion of oxygen. This oxide is obtained by exposing to heat in a crucible, a mixture of molybdic acid and charcoal in powder. A black mass remains, which is the oxide. The second is the blue oxide, which may be obtained by the same process, but it must not be continued too long. The third is the green oxide, which seems to be intermediate between an oxide and acid. Mr Hatchet proposes to call it molybdous acid. The fourth degree of oxidation is the molybdic acid itself, which has at first a white colour; but when it is fused and sublimed, is converted into a yellow colour. The properties of this acid and some of its combinations have been already described.

4. Molybdena combines with phosphorus; but the properties of this phosphuret are not known. It also combines readily with sulphur, and returns to the state of sulphuret of molybdena, in which it has only been found native.

5. Molybdena enters into combination with the acids, forming with them peculiar salts.

6. The alkalies have the property of dissolving molybdena, and of promoting its oxidation. With the affluence of heat the alkalies form with the sulphuret of molybdena, an alkaline sulphuret which holds the metal in solution.

7. Molybdena enters into combination with the metals, and forms alloys with them.

I. Salts of Molybdena.

1. Sulphite of Molybdena.

Sulphuric acid, with the affluence of heat, dissolves molybdic acid, and affords a colourless solution; but when it is cold it becomes of a deep blue. But neither this nor any other of the salts of molybdena seem disposed to crystallize.

2. Nitrate of Molybdena.

Nitric acid converts the oxides of molybdena into molybdic acid, by giving up its oxygen.

3. Muriate of Molybdena.

Muriatic acid, when boiled with the oxide of molybdena, affords a solution of a deep blue colour, and there is formed a blue precipitate.

4. Fluate of Molybdena.

Fluoric acid forms a compound with the oxides of molybdena. The solution is of a greenish yellow colour when it is hot; but when it is evaporated to dryness, it becomes of a greenish blue.

5. Phosphate of Molybdena.

The oxide of molybdena is dissolved by phosphoric acid with the affluence of heat, and a solution of a blue colour is obtained.

6. Acetate of Molybdena.

7. Oxalate of Molybdena.

8. Tartrate of Molybdena.

9. Benzoate of Molybdena.

All these salts in solution are of a blue colour, and when evaporated to dryness, afford a blue powder. They are formed by digesting the several acids with the oxides of molybdena.

Sect. IV. Of Chromium and its Combinations.

1. This metal was discovered by Vauquelin in 1797, in a mineral called the red lead ore of Siberia. This ore had been formerly analyzed by several chemists, and even by Vauquelin himself; but their results of the nature of its composition only agreed, that lead was one of its constituent parts. Vauquelin by his last analysis found that it contained lead, combined with the new acid, of which the basis is a metal,

2. The process which he followed was the following: He boiled one part of the red lead-ore of Siberia with two parts of carbonate of potash, in 200 parts of water. The potash combined with the new acid, while the carbonic acid united to the lead. The carbonate of lead precipitated to the bottom in the form of a white powder, and the new salt remained in solution. By adding nitric acid, the new salt was decomposed, the acid combining with the potash. This mineral is completely dissolved in muriatic acid. The solution assumes a deep green colour, and by evaporation affords muriate of lead. The fine green colour is owing to the oxide of the new metal having been deprived of part of its oxygen. oxygen by the muriatic acid, and being thus converted from an orange red to a green.

3. The acid which is obtained by the first process, and the oxide by the second, being strongly heated with charcoal in a crucible, afforded a metal different from any other formerly known. To this metal the name of chromium was given, from the Greek word χρώμα, on account of the remarkable property which it possesses of communicating colour to all its saline combinations.

4. The metal which was obtained, is of a grayish white colour, very hard and brittle, and extremely difficult of fusion; but the small quantity which has been hitherto obtained, precludes chemists from ascertaining its properties.

5. This substance has been found in four different minerals, existing in two states; in the state of green oxide, combined with the oxide of lead, and in the same state in the emerald; and in the state of acid, combined with the oxide of lead in the red lead-ore of Siberia, and also in the spinel ruby. It has also been discovered in the state of chromic acid, combined with iron, forming a chromate of iron. It has also been discovered in France.

6. Chromium, therefore, combines with oxygen in two different proportions; the green oxide, and the yellow, or the chromic acid. It is this acid which exists in the red lead-ore. When it is separated from the lead, it is in the form of powder, of an orange yellow colour, and is soluble in water. Its other properties have been already examined. The green oxide is prepared by exposing the latter to heat in close vessels. The chromic acid is partially decomposed; part of the oxygen is driven off, and the green oxide remains behind. Another oxide also, it is said, which is intermediate between chromic acid and the green oxide, has been obtained.

7. Little is known of the action of acids on this metal; but in the few experiments which have been made, it appears, that it undergoes no change by means of sulphuric and muriatic acids. Nitric acid distilled upon it several times successively, changes it into green oxide, and at last into chromic acid. The same effect is produced more rapidly by means of the nitromuriatic acid.

**Sect. V. Of Columbium and its Combination.**

1. This metal was discovered by Mr Hatchet, in the year 1822, in a mineral which he found in the British Museum. This mineral had been sent along with specimens of iron ores from Massachusetts in America, to Sir Hans Sloane, in whose catalogue it is described as a "very heavy black stone, with golden streaks." These streaks, Mr Hatchet observes, proved to be yellow mica. This mineral is externally of a dark-brownish gray colour; internally the same, inclining to iron gray. The longitudinal fracture is imperfectly lamellated; the cross fracture shows a fine grain. The lustre is vitreous, in some parts inclining to the metallic. It is moderately hard, but very brittle. The colour of the powder is dark chocolate brown. The particles are not attracted by the magnet. The specific gravity is 5.918.

2. In the analysis of this mineral, Mr Hatchet discovered, that it consists of one part of oxide of iron, and three parts of a white-coloured substance, which exhibited the properties of an acid. This acid, under the name of columbic acid, with its combinations with the alkalies and earths, has been already described. Having found that it possessed properties different from all other acids, and also, that its base is metallic, he gave to the metal the name of columbium. In the attempts which Mr Hatchet made to reduce it to the metallic state, even when it was exposed to a very strong heat with charcoal, the oxide was only found in the state of powder, of a black colour. From these experiments it appeared, that this metal combines with oxygen in different proportions, and these oxides are distinguished by different colours.

3. When the white oxide of this metal was added to phosphoric acid in solution, and evaporated to dryness, the whole was put into a crucible, lined with charcoal, and exposed to a strong heat for half an hour. The inclosed matter had assumed a dark brown, spongy appearance, which had some resemblance to the phosphuret of titanium.

4. No sulphuret was obtained when it was mixed and distilled with sulphur.

5. Columbium combines with some of the acids, and forms salts, although few of these have been examined.

**I. Salts of Columbium.**

1. Sulphate of Columbium.

Boiling sulphuric acid forms a transparent colourless solution with columbic acid. When water is added to this solution, it becomes turbid, assuming a milky appearance; and a white precipitate is gradually deposited, which cracks as it becomes dry upon the filter, and, from white, it changes to a lavender blue colour; and, when completely dry, to a brownish gray. It is then insoluble in water, is semitransparent, and breaks with a vitreous fracture. This precipitate obtained from the sulphuric solution, by the addition of water, is a sulphate of columbium.

2. Nitrate of Columbium.

The oxide of columbium seems to be perfectly insoluble, and remains unchanged in colour, when digested in boiling concentrated nitric acid.

3. Muriate of Columbium.

Columbic acid, when recently separated from potash, is soluble in boiling muriatic acid. This solution may be considerably diluted with water, without any change being produced. When evaporated to dryness, it left a pale-yellow substance, insoluble in water, and which is dissolved with great difficulty, when it is again digested with muriatic acid.

4. Phosphate of Columbium.

A few drops of phosphoric acid being added to a part of the solution of columbium in concentrated sulphuric acid, at the end of about 12 hours converted the whole into a white, opaque, stiff jelly, which was insoluble in water. When a small quantity of phosphoric acid was Titanium, was added to the muriatic solution of columbium, in &c., a few hours a white flocculent precipitate was formed *(A)*.

**Sect. VI. Of Titanium and its Combinations.**

1. This metal was discovered in 1793 by Klaproth. He obtained it from a mineral called red schorl. In this mineral he found the oxide of a metal different from any other then known. Previous to this time, indeed, the same oxide had been discovered by Mr Gregor, in a black sand which is found in Menachan in Cornwall. To this, from the place, he gave the name of menachine, but he had not succeeded in reducing it to the metallic state. Klaproth afterwards analyzed the menachinite of Mr Gregor, and found that it was precisely the same as the oxide of the metal which he discovered in red schorl. To this metal he gave the name of titanium. The experiments of Klaproth were afterwards repeated by Vauquelin and Hecht in 1796. His results were confirmed, and they also succeeded in reducing a small quantity of the oxide to the metallic state.

2. This metal has been found only in the state of oxide. Red schorl consists entirely of this oxide. It has been found in different countries, as in Spain, France, and Hungary. This oxide is disseminated in the fine specimens of rock crystal, which are brought from Madagascar, crystallized in long brilliant needles, the form of the primitive crystal being a six-sided prism, with two-sided summits; that of the molecule is a triangular prism, with right-angled faces. It is of a red colour of different shades. It is brittle, but the fragments are so hard as to scratch glass. The specific gravity is from 4.180 to 4.246. The other mineral, to which Klaproth has given the name of titanite, is composed of oxide of titanium, silica, and lime, nearly in equal proportions. Its specific gravity is 3.510.

3. Titanium was obtained by Vauquelin, by reducing the native red oxide. He mixed together 100 parts of this oxide with 50 of calcined borax, and 50 of charcoal, formed into a paste with oil; and exposed the whole to the heat of a forge raised to 1660° Wedgwood. By this process he obtained a dark-coloured, agglutinated mass, having a brilliant appearance on the surface.

4. Titanium obtained in this way is of a reddish yellow colour, shining and brilliant on the surface, and equally brilliant in some of its internal cavities. Its other properties, as it has been only procured in very small quantity, have not been determined.

5. Titanium seems to be one of the most infusible metals known. When the red oxide is exposed to heat, heat in a crucible, it loses its lustre. By the action of the blow-pipe it is deprived of its transparency, and becomes of a grayish white colour. On charcoal it becomes still more opaque, and of a slate gray. The artificial carbonate of titanium, exposed to heat in a crucible, loses $\frac{1}{10}$ of its weight, becomes yellow, and, as it cools, recovers its white colour.

6. Titanium enters into combination with phosphorus, and forms with it a phosphuret. This was prepared by Mr Chenevix, by exposing a mixture of phosphate of titanium, charcoal, and a little borax, in a crucible, to a very strong heat. The phosphuret which he obtained was in the form of a metallic button, of a pale white colour, brittle and granular, and infusible by the action of the blow-pipe. Titanium has not been combined with sulphur.

7. This metal enters into combination with acids, and forms salts with them. The affinities of the oxides of titanium, as they have been ascertained by Lampadius, are in the following order:

- Gallic acid, - Phosphoric acid, - Arsenic acid, - Oxalic acid, - Sulphuric acid, - Muriatic acid, - Nitric acid, - Acetic acid.

8. In the experiments which were made by Vauquelin and Hecht, to combine titanium with other metals, they did not succeed with silver, copper, lead, or arsenic; but they formed an infusible alloy with iron, of a gray colour, intermixed with yellow-coloured, shining particles.

I. Salts

*(A)* Another metal has been more lately announced by Ekeberg, which, in some of its properties, seems to resemble columbium. He obtained this metal from two minerals; to one of which he gave the name of tantalite, which is of a blackish gray colour, with some metallic lustre, and some appearance of crystallization. This mineral is very hard; the specific gravity is 7.953. When reduced to powder, it is of a brownish gray colour, and is not attracted by the magnet. To the other mineral he gave the name of ytrotantalite. It was found in small insulated masses, in veins of feldspar, and black mica. The fracture of this mineral is granular, of a gray metallic appearance, and may be scratched, although with difficulty, with a knife. It is not attracted by the magnet. The specific gravity is 5.13. From these minerals this chemist extracted a substance, which he concluded to be a peculiar metal in the state of oxide, having the appearance of a white powder. The following are the properties which he ascertained.

1. It is not soluble in any of the acids. 2. The alkalies attract and dissolve a considerable quantity of this substance, which may afterwards be precipitated by means of the acids. 3. The whole oxide of this metal undergoes no change of colour by the action of heat. 4. Its specific gravity when it has been exposed to a red heat is 6.5. 5. It fuses with phosphate of soda, and borax, without communicating to them any colour. 6. The oxide of this metal, heated with charcoal powder, is reduced to the metallic state, exhibits a brilliant fracture, of a dark gray colour. 7. It is again converted into a white powder by the action of the acids. The other properties of this substance have not been detailed*. To this metal Ekeberg has given the name of tantalum.

*Ann. de Chim. xiii. p. 276. 1. Salts of Titanium.

1. Sulphate of Titanium.

According to the experiments of Klaproth, sulphuric acid has no action on the native red oxide of titanium from Hungary; but this acid is found to dissolve the carbonate of titanium with effervescence; and when this solution is evaporated, the red oxide is converted into a white, opaque, gelatinous mass. This was the result of Klaproth's experiment. In those of Vauquelin and Hecht, sulphuric acid being boiled with carbonate of titanium, assumed a milky appearance, and there were formed white, light flakes, which were dissolved by a stronger heat; the fluid became transparent, but did not afford crystals.

2. Nitrate of Titanium.

Nitric acid has scarcely any perceptible action on titanium, but it combines with the carbonate, and forms a transparent solution, which affords an oily appearance in the air, and affords transparent crystals in the form of elongated rhombs, having the opposite angles truncated, so as to represent hexagonal tables. But according to Vauquelin and Hecht, when they heated a mixture of nitric acid with carbonate of titanium, nitrous gas was disengaged, and the liquid remained milky. Sugar added to the mixture causes a precipitate of the oxide, of a whiter colour than the carbonate; and if the nitric acid be employed diluted, the oxide of titanium is dissolved, but the solution becomes turbid by means of heat, and thus the addition of caloric opposes the combination of this oxide with nitric acid, by oxidizing it in a higher degree than what is soluble in this acid.

3. Muriate of Titanium.

The carbonate of titanium is soluble in muriatic acid; and according to Klaproth, the solution affords a yellowish, transparent jelly, which contains numerous transparent, cubic crystals. Vauquelin and Hecht found, that the carbonate of titanium is dissolved with effervescence in concentrated muriatic acid; and the solution affords a deep yellow colour, when it is made without the affluence of heat. When it was heated, it was reduced to a flaky mass, which was neither re-dissolved by water, nor by new additions of the acid. A similar solution which was not heated remained transparent; but when this solution was exposed to a temperature of about 170°, it was converted into a yellow, transparent jelly, of an acid and very astringent taste, which, by cooling, deposited a great number of small crystals which effloresced in the air. When this solution was boiled, oxymuriatic acid gas was disengaged, the oxide was precipitated, and is no longer soluble in muriatic acid, till it is boiled for a long time with nitric acid; from which it appears, that the oxide of titanium must have a great proportion of oxygen, to combine with muriatic acid, and in this state it can only combine with it in the cold, because when it is exposed to heat, the acid carries off a portion of its oxygen, which renders it insoluble. The oxide of titanium, separated from muriatic acid by the action of the blow-pipe, assumes a beautiful orange-yellow colour.

4. Carbonate of Titanium.

One part of the red oxide of titanium, and five parts of carbonate of potash, exposed to a red heat in a crucible, were soon fused, and formed a solid mass of a whitish gray colour, with small needle-form crystals on the surface. When this was reduced to powder, and washed with warm water, there was deposited a light white powder, which was found to be carbonate of titanium. The arsenic and phosphoric acids cause a white precipitate of the oxide of titanium from its solution in acids. A similar precipitate is produced by oxalic and tartaric acids; but it is instantly re-dissolved, and the solution recovers its transparency.

The oxide of titanium is precipitated from its solution in acids; 1. By carbonate of potash, in the form of a white flaky matter, and by ammonia in the same compound. 2. Prussiate of potash causes a copious precipitate of a mixed colour of green and brown. 3. Infusion of nut-galls produces a very voluminous precipitate, of a reddish brown colour; and if the solution be not too much diluted with water, it coagulates like blood. A rod of tin introduced into a small bottle, with a solution of this oxide in muriatic acid, caused in a few minutes a pale rose colour, in that part of the solution near the rod. This colour soon changed to a beautiful ruby. A rod of zinc first produced a violet colour, and afterwards that of indigo. 4. Sulphuret of ammonia combined with this solution, produced a pale green colour, and a precipitate of a bluish green.

Sect. VII. Of Uranium and its Combinations.

1. This metal was discovered by Klaproth in the discovery year 1789. It was then announced as a metal more difficult to be reduced than manganese, externally of a gray colour, and internally of a clear brown, of considerable lustre, and middling hardness; that it might be scratched and filed, and that its oxide gives a deep orange colour to porcelain.

2. It has been obtained from three different mines—Natural minerals. The first is in the state of sulphuret, of a black-flaky, iridescent colour, and of a shining fracture, and sometimes lamellated. This has been called pitch blende. The specific gravity is from 6.37 to 7.50. In this state it is sometimes combined with iron and sulphurated lead. The uranium is in the metallic state. The second ore, from which this metal is obtained, is the native oxide of uranium. It is always in the state of yellow powder, on the surface of the sulphuret. The specific gravity is 3.24. When it is of a pure yellow colour, it is then a pure oxide. The third ore of the metal is the native carbonate of uranium. Of this there are two distinct varieties, the one of a pale green, and sometimes of a silvery white colour. This contains but a small quantity of the oxide of copper, and is very rare. The other is of a shining deep green, which is the green mica or glimmer of mineralogists. Klaproth supposed that it contained an oxide of uranium, mixed with the oxide of copper; but it has been since discovered to have carbonic acid in its composition. It is crystallized in small square plates, and sometimes, though rarely, in complete octahedrons. 3. The process by which Klaproth reduced this metal, is the following. He mixed the yellow oxide of uranium, precipitated from its solutions by an alkali, with linseed oil, in the form of a paste, and this being exposed to a strong heat, there remained a black powder, which had lost rather more than one-fourth of its weight. It was then exposed to the heat of a porcelain furnace, in a close crucible, and the oxide was afterwards found in a coherent mass, but friable under the fingers, and reduced to a black shining powder. It decomposed nitric acid with effervescence. This black powder covered with calcined borax, was for the second time exposed to a still stronger heat, by which a metallic mass was obtained, consisting of very small globules adhering together.

4. The colour of uranium is of a dark gray, and internally of a pale brown. It has little brilliancy, on account of the spongy mass, in which state it was obtained. It may be scratched with a knife, and is extremely fusible. The specific gravity is 6.440.

5. When uranium is exposed to a red heat in the open air, or when it is acted on by the blow-pipe, it undergoes no change. The yellow oxide of uranium does not melt. It acquires a brownish gray colour when it is long heated in the air, but it has not been ascertained whether it gains or loses oxygen.

6. The oxide of uranium is reduced by means of charcoal, when it is exposed to heat. Little is known of the combination of uranium with phosphorus; but when the oxide was treated with blood, and a strong heat applied, an acrid bitter mass was obtained, which was supposed to owe its fusibility to the phosphorus which it contained.

7. Uranium has not been artificially combined with sulphur, but it is not improbable that such a combination might take place, since it is found native in this state. Of the alloys of uranium with other metals nothing is yet known.

I. Salts of Uranium.

1. Sulphate of Uranium.

The yellow oxide of uranium is readily dissolved in diluted sulphuric acid; and the solution affords, by evaporation, a salt of a yellow colour, in the form of small prisms. This sulphate of uranium is different from all other metallic salts yet known, in colour, form, and other properties.

2. Nitrate of Uranium.

Nitric acid dissolves with equal facility the oxide of uranium. The solution being slowly evaporated, yields large crystals in regular hexagonal tables, of a yellowish green colour. The crystals of nitrate of uranium are the most beautiful of all the metallic salts.

3. Muriate of Uranium.

Muriatic acid also dissolves the oxide of uranium, and furnishes small yellow crystals, which are deliquescent in the air.

4. Fluate of Uranium.

Fluoric acid combines with the oxide of uranium, and forms with it a crystallized salt, which is not altered by exposure to the air.

5. Phosphate of Uranium.

Phosphoric acid enters into combination with the oxide of uranium, and forms with it yellowish white flakes, which are very little soluble in water.

6. Arseniate of Uranium.

Arsenic acid may be combined with uranium, by decomposing the nitrate by means of an alkali. A precipitate is obtained of a yellowish powder, which is the arseniate of uranium.

7. Molybdate of Uranium.

In the same way molybdate of uranium may be obtained by adding a solution of molybdate of potash to the nitrate of uranium. It is obtained in the form of powder.

8. Acetate of Uranium.

The oxide of uranium is soluble in concentrated acetic acid, with the assistance of heat; and beautiful yellow crystals are obtained, in the form of long, slender, transparent, four-sided prisms, terminated by four-sided pyramids.

The solutions of the oxide of uranium in acids are precipitated by the alkaline sulphurates, of a brownish yellow, and their surface is covered at the same time with a gray metallic pellicle. The fixed alkalies precipitate from their solutions an oxide of uranium, of an orange yellow colour; and ammonia occasions a precipitate of a bright yellow; and the alkaline carbonates throw down a carbonate of uranium of a whitish yellow, which is redissolved in an excess of alkali. The infusion of nut-galls thrown into one of these solutions, the excess of whose acid has been taken up by an alkali, produces a chocolate brown precipitate. Zinc, iron, and tin, introduced into these solutions, produce no change of colour, either in the cold or by heat.

Sect. VIII. Of Cobalt and its Combinations.

1. The mineral called cobalt, or cobolt, (B) seems to have

(b) The following curious information from Beckmann, with regard to the discovery of this mineral will, we doubt not, prove interesting to the reader. "About the end of the 15th century, cobalt appears to have been dug up in great quantity in the mines on the borders of Saxony and Bohemia, discovered not long before that period. As it was not known at first to what use it could be applied, it was thrown aside as a useless mineral. The miners had an aversion to it, not only because it gave them much fruitless labour, but because it often proved prejudicial to their health by the arsenical particles with which it was combined; and it appears even that the mineralogical name cobalt then first took its rise. At any rate, I have never met with it before the beginning of the sixteenth century; and Matthias and Agricola seem to have first used it in their writings. Fréch derives it from..." have been first employed to give a blue colour to glass after the middle of the 16th century; but it was not till about the year 1732, that cobalt was distinguished as a peculiar metal by Brandt, a Swedish chemist, who extracted it from its ore, and examined some of its properties. In 1761 Lehman gave a particular account of the nature and properties of this substance; but his researches were chiefly limited to the mineral in the state of ore. Bergman afterwards examined this metal, and pointed out the difference between it and nickel, manganese, and iron. The nature of it has been more lately investigated by Taffaert and Thenard, and some other French chemists.

2. Cobalt has never been found in nature in a state of purity. It is either alloyed with arsenic, both metals being in the metallic state, or it is combined with sulphur and arsenic, or in the state of oxide, or forming a salt with arsenic acid. 1. In the first state, when it is alloyed with arsenic, it is of a gray or whitish appearance, with some degree of brilliancy. The specific gravity is 7.72. It is sometimes crystallized in cubes, or octahedrons. When small fragments of this mineral are exposed to the action of the blow-pipe, or even to the flame of a candle, they give out a garlic smell.

2. The combination of sulphur and arsenic with cobalt is denominated gray cobalt ore. The specific gravity is from 6.33 to 6.45. The structure is lamellated, and when it is heated, it emits no garlic smell. It crystallizes in octahedrons, dodecahedrons, and some other forms resembling the sulphuret of iron, with which it is frequently combined. 3. The third species of cobalt ore, is the oxide. It is found in black, friable masses, or in the state of a black efflorescence, which foils the fingers. This is a pure oxide of cobalt. 4. The fourth species is the arseniate of cobalt, which has been distinguished by the names of flowers of cobalt, cobalt bloom. It is of a peach-blossom colour, sometimes in the state of efflorescence, sometimes in the form of small needles of a deep colour, which remains even after they are reduced to powder, and sometimes in four-sided prisms terminated by two-sided summits. When it is placed on hot coals, it gives out a strong garlic smell, loses its colour, and becomes black.

3. To procure the pure metal from the ores of cobalt, the oxide in the state of black powder, after being roasted, is mixed with three times its own weight of black flux and a little common salt, put into a crucible lined with charcoal, and exposed to a forge heat. When the fusion is completed, the crucible is to be slightly agitated, to collect together the metallic globules into one mass. Sometimes two metallic buttons are found under the vitreous scoriae. The cobalt occupies the upper part, and the bismuth being heavier, is lowest. In this state the cobalt is almost always combined with a small portion of arsenic, nickel, or iron. But if the crystallized gray oxide of cobalt has been employed, the metal is obtained very pure, by the above process; and when the ore is rich, it yields from 60 to 80 per cent.

By a different process, cobalt may be obtained in the metallic state, which consists in treating the ore with nitric acid, which oxidizes and dissolves both the cobalt and the iron. These oxides are precipitated by carbonate of soda, and well washed with water. They may be separated by means of nitric acid, which dissolves the oxide of cobalt, without touching that of the iron.

4. Cobalt is of a gray colour, inclining to red, and of properties a very fine granulated texture. It is very brittle, so of cobalt, that it is easily reduced to a fine powder, which is of a gray colour, and with little brilliancy. The specific gravity, according to Bergman, is 7.702; according to others, it is from 7.811 to 8.5384.

5. Cobalt is one of the most fusible metals, requiring a temperature equal to 130° Wedgwood. It becomes red before it melts. When it is slowly cooled, and by pouring out a part of the fluid when it becomes solid at the edges, the cavity is found lined with prismatic crystals. The same crystallization may be effected by inclining the crucible at the moment the surface becomes solid.

6. When cobalt is exposed to a red heat in an open vessel, it first loses its colour and its brilliancy, becomes of a deep gray colour, and then passes to a black, or an intense blue. With a still more violent heat, this last oxide melts into a bluish black glass. It appears, from the experiments of Thenard, that cobalt combines with different proportions of oxygen, forming different oxides. When a solution of cobalt in acids is precipitated by an alkali, the precipitate which is formed is first of a lilac colour; and with an excess of base it becomes successively blue and olive, and at last by drying it becomes entirely black. These different changes depend on the different proportions of oxygen with which it combines.

He precipitated a solution of cobalt by pure potash. The oxide collected on a filter, was blue, and when exposed to the air it became of an olive colour; and when washed with oxymuriatic acid, it changed from green to brown, and from this shade to the deepest black. The black oxide dissolved with effervescence in muriatic acid; oxymuriatic acid gas was emitted in great abundance,

from the Bohemian word kov, which signifies metal; but the conjecture that it was formed from cobalus, which was the name of a spirit that, according to the superstitious notion of the times, haunted mines, destroyed the labours of the miners, and often gave them a great deal of unnecessary trouble, is probable; and there is reason to think that the latter is borrowed from the Greek. The miners, perhaps, gave this name to the mineral out of joke, because it thwarted them as much as the supposed spirit, by exciting false hopes, and rendering their labour often fruitless. It was once customary, therefore, to introduce into the church service a prayer that God would preserve miners and their works from kobolts and spirits."

"Matheius, in his tenth sermon, p. 501, where he speaks of the cadmia folilia, says: 'Ye miners call it kobolt; the Germans call the black devil and the old devil's whores and hags old and black kobel, which by their witchcraft do injury to people and to their cattle.'—Whether the devil, therefore, and his hags gave this name to cobalt, or cobalt gave its name to witches, it is a poisonous and noxious metal." Cobalt, abundance, and when the muriatic acid was concentrated, the solution was of a green colour, which in the space of 24 hours became purple. When the acid was diluted, it became instantly red. The oxide is soluble in sulphuric and nitric acids, and the solution is of a red colour, accompanied with the evolution of bubbles, which seem to be oxygen gas.

The brown and coloured oxides produce with sulphuric, nitric, and muriatic acids, similar effects with the black oxide. With muriatic acid they both give out oxy-muriatic acid, and form a solution of a green colour, which in time passes to a purple; or, if the acid be diluted with water, it becomes instantly red. The olive-coloured oxide is prepared by pouring potash into a solution of cobalt. There is formed a blue precipitate, which exposed to the air becomes green. If this oxide be treated with diluted muriatic acid, oxy-muriatic acid is obtained with a slight degree of heat, and the solution becomes more and more red, as this acid is disengaged; so that the blue oxide combines with the oxygen of the air.

The blue oxide of cobalt, Thenard thinks, is most conveniently obtained by calcining the black oxide for half an hour in a cherry-red heat. It assumes a blue colour, by being deprived of part of its oxygen. This oxide dissolves in acids, without the disengagement of any gas. Its solution in concentrated muriatic acid is green, but if the acid be diluted with water, it is red. Thenard concludes from his experiments, that there are four different oxides of cobalt; the blue, the olive, the brown, and the black; although he supposes that the brown may be a mixture of the olive and black oxides*.

7. There is no action between azote, hydrogen, or carbone, and cobalt.

8. Phosphorus enters into combination with cobalt, by projecting bits of phosphorus on small pieces of cobalt, red hot, in a crucible. The metal is instantly fused, and it absorbs about $\frac{1}{3}$ of its weight of phosphorus. A crust is formed at the same time on the surface, of a violet-red colour. This phosphuret of cobalt has a metallic lustre, is of a whiter colour than the metal itself, and is more brittle. It loses its brilliancy in the air; and by the action of the blow-pipe, phosphorus is disengaged from the metallic globule, and inflames on the surface. There remains behind a vitreous globule of a deep blue colour.

9. Sulphur combines with difficulty with cobalt, but the compound may be formed by the aid of the alkalies. This metal is soluble in the alkaline sulphurets, and the result is a sulphuret of cobalt, of a yellowish white colour, which is only decomposed by means of the acids.

10. Cobalt enters into combination with the acids, and forms salts. It forms alloys also with most of the metals. The order of the affinities of cobalt and its oxides, according to Bergman, is the following:

| Cobalt | Oxide of Cobalt | |--------|----------------| | Tin | Fluoric | | Antimony | Saccharic | | Zinc | Succinic | | Phosphorus | Lactic | | Sulphur | Acetic | | Arfenic | Boracic | | Copper | Pruflic | | Gold | Carbonic | | Platina| |

I. Salts of Cobalt.

1. Sulphate of Cobalt.

1. Concentrated and boiling sulphuric acid is decomposed by cobalt, with the evolution of sulphurous acid. A thick, grayish mass, inclining to red, is formed. Water dissolves the sulphate of cobalt, and affords a grayish-coloured liquid.

2. The sulphate of cobalt crystallizes in small needles, or four-sided rhomboidal prisms, terminated by two-faced summits. It is of a reddish colour, and is soluble in 24 parts of water. It is decomposed by heat, and there remains behind the black oxide of cobalt. By the action of the blow-pipe it swells up with effervescence. The alkalies also decompose it, by precipitating a reddish yellow oxide. One hundred parts of cobalt furnish 140 parts of this precipitate by pure alkalies; but when the precipitation is effected by means of the alkaline carbonates, 160 parts are obtained.

2. Nitrate of Cobalt.

1. Nitric acid combines with cobalt, with the assistance of a moderate heat. Nitrous gas is disengaged, the metal is oxidated, and is dissolved in the acid. The solution is of a flesh-red colour, but when it is concentrated, of a brown colour. By evaporation it affords small reddish-coloured prismatic crystals, which are deliquescent in the air, and which being placed on red-hot burning coals, fizzle up, and are decomposed, leaving behind a deep red oxide.

2. It is by the precipitation of this salt, that the oxide of cobalt is obtained for the purpose of enamels, and for giving a colour to porcelain. When the oxide is precipitated by means of an alkali, it is re-dissolved when the alkali is added in excess.

3. Nitrate of Ammonia and Cobalt.

This triple salt was formed by Thenard by adding to a solution of cobalt in nitric acid, ammonia in excess. No precipitate is obtained. This solution being filtered and evaporated to dryness, and the residue being dissolved in water, and again evaporated, yielded, on cooling, regular cubic crystals of a red colour, and of a pungent taste. They were not changed by exposure to atmospheric air. Being calcined in a crucible, they burned like nitrate of ammonia, with a vivid, yellowish white flame. The residue was a black substance, which had all the properties of cobalt. The solution of this salt in water is not precipitated by any of the alkalies or earths. It is still more readily decomposed by fulphurated hydrogen, or the hydro-sulphurets. When it is boiled with potash, ammonia is disengaged; the oxide of cobalt is precipitated, and a nitrate of potash is formed.

4. Muriate of Cobalt.

1. Muriatic acid has no effect on cobalt in the cold; but a small quantity is dissolved with the assistance of heat. But the black oxide of cobalt is readily dissolved in muriatic acid. The solution is accompanied with effervescence, and the disengagement of oxyuric acid gas. When this solution is concentrated by evaporation, it becomes of a fine green colour, which changes to red when it is diluted with water. By farther evaporation it is crystallized, and affords small deliquescent crystals of muriate of cobalt in the form of needles.

2. When these crystals are dissolved in water, and so diluted that the solution is nearly colourless, characters marked with it on paper disappear entirely; but when heated, assume a fine green colour. This solution was one of the first known sympathetic inks. In making experiments with this solution, the characters are written on paper, or, that the experiment may be more amusing, a landscape is drawn with a pencil, representing the verdure of summer on a winter scene. Those parts of the picture in which the sympathetic ink has been used, are invisible in the cold; but when it is moderately heated, they become of a fine green colour, changing from the winter to the summer scene. When it is removed to the cold, the colour again disappears, and if too much heat be not applied, the same change may be frequently repeated. When too much heated, the blue colour is converted to a brown, which becomes permanent.

3. Various theories have been proposed to account for this remarkable change. According to some, it is owing to the moisture of the atmosphere being absorbed that the colour disappears; and when this is driven off by heat, it is restored. But to this opinion it has been objected, that the same effect is produced, when paper, on which characters have been written with this solution, is entirely excluded from the atmosphere, by being introduced into close vessels. According to others, the sympathetic effect of this solution depends on the iron which is combined with the cobalt. Some suppose that the concentration of the solution, which takes place by the action of heat, is the cause of the appearance of the colour; and its dilution, by absorbing moisture from the atmosphere, the cause of its disappearance; while others are of opinion that it is partially deprived of its oxygen by being heated, and absorbs it again in the cold, when the colour vanishes.

This sympathetic ink may be easily prepared, by dissolving the zaffre of commerce in nitro-muriatic acid.

5. Fluorite of Cobalt.

Fluoric acid dissolves the oxide of cobalt, and forms with it a yellow-coloured gelatinous solution; or, by careful evaporation, it affords crystals, which are fluoite of cobalt.

6. Borate of Cobalt.

Boracic acid has no action on cobalt; but it combines with the oxide, by mixing a solution of nitrate of cobalt with a solution of borax.

7. Phosphate of Cobalt.

Phosphoric acid dissolves the oxide of cobalt, and forms with it a reddish-coloured turbid solution, which affords a precipitate when the acid is saturated.

8. Carbonate of Cobalt.

This salt is formed by precipitating cobalt from its solutions in acids, by means of alkaline carbonates. One hundred parts of cobalt, which afford only 140 of precipitate by means of the pure alkalies, yield 160 parts, when the precipitate is effected by carbonate of soda.

9. Arseniate of Cobalt.

This salt is formed by combining the nitrate of cobalt with the arseniate of potash or of soda. It is sometimes found native, and it exhibits the deepest and most beautiful red of all the salts of cobalt.

10. Tungstate of Cobalt. 11. Molybdate of Cobalt. 12. Chromate of Cobalt. 13. Columbate of Cobalt. 14. Acetate of Cobalt.

This salt is readily formed, by dissolving the oxide of cobalt in acetic acid. It does not yield crystals by evaporating, but is deliquescent in the air. It assumes a blue colour when it is heated, but is red in the cold, so that it forms a sympathetic ink.

15. Oxalate of Cobalt.

This salt may be formed by precipitating the oxide of cobalt from its solution in acids, by means of oxalic acid. This precipitate, when it is dried, is in the form of a red powder, which is insoluble in water, but may be dissolved in excess of oxalic acid, and crystalized.

16. Tartrate of Cobalt.

The oxide of cobalt is soluble in tartaric acid, and forms a red-coloured solution, which affords crystals by evaporation.

II. Action of Alkalies, Earths, and Salts.

1. The alkalies have no action whatever on cobalt; but when the oxides are suspended in water, they separate them from other matters.

2. Some of the earths, but particularly silica, enter into combination with the oxide of cobalt and the fixed alkalies, and form a beautiful blue-coloured glass. The quantity of oxide must be small, otherwise the glass will appear nearly black and opaque, on account of the intensity of the colour.

3. Some of the neutral salts exposed to a high temperature along with cobalt burn with a perceptible flame. It is by this means that the oxide is prepared for the purpose of enamels and colouring porcelain.

The hyperoxymuriate of potash, with one-third of its weight of cobalt in powder, detonates by percussion. Cobalt is scarcely at all employed in the metallic state. Zaffre is used for coarse enamels and pottery ware. The purer oxides of cobalt are chosen for the purpose of colouring porcelain. Azure is a vitreous blue in the state of fine powder, which is prepared for similar purposes. Zaffre is fused along with silica and an alkali, and thus forms a deep blue glass, which is known by the name of smalt. This is reduced to a powder, and mixed with a great quantity of water. The first portion which precipitates is called coarse azure. Four different quantities are separated in this way. The last, which is the finest, is called azure of four fires.

**Sect. IX. Of Nickel and its Combinations.**

1. The first mention which is made of this metal is by Hierne, a Swedish chemist, in a work entitled *The art of discovering metals*, published in 1694. He particularly describes the mineral from which nickel is extracted, and which was first called kupfernickel, or false copper, because it was taken for an ore of copper, and none could be obtained from it. This was the opinion of Henckel and Cramer, who supposed it to be copper combined with arsenic or cobalt. This mineral was generally arranged among copper ores, till it was examined and analyzed by the celebrated Swedish mineralogist Cronstedt, in 1751, and 1754. In these experiments, the account of which was published in the memoirs of the Swedish Academy, he proved that this mineral contains a new metal, different from all those which had been hitherto known, to which he gave the name of nickel. This opinion was generally adopted, and objected to only by Monet and Sage of France, who affirmed that this new metal was merely an alloy of cobalt, arsenic, iron, and copper. To remove these differences of opinion with regard to this substance, Bergman undertook an elaborate analysis of the ores of nickel, and an accurate examination of its peculiar properties in the metallic state. His experiments were detailed in a dissertation which was published in 1755. The object of his researches was, to ascertain if nickel was a peculiar metal; and, from the result of his experiments it appeared, that it did not contain the smallest trace of copper, but that it is generally alloyed with cobalt, arsenic, and iron, from which indeed it can scarcely be completely separated; but that it possessed peculiar and distinct properties from the other metals; and these properties became more striking and characteristic in proportion to its purity.

2. Nickel is found in the state of sulphuret, when it is called kupfernickel. It is of a reddish yellow colour, with little brilliancy, somewhat similar to tarnished copper, with which, from its appearance, it is frequently confounded. This mineral soon loses its brilliancy in the air, becomes of a brownish colour, and is covered at last with greenish spots. It is found forming veins in the earth, and is usually combined with arsenic, cobalt, and iron. Nickel has been found alloyed with iron, when it is of a laminated texture, and composed of rhomboidal plates. The fresh fracture is of a pale yellow, which becomes black by exposure to the air. Nickel is also found native in the state of oxide, when it is of a bright green colour. In this state it is generally on the surface of sulphuret of nickel. Native nickel has also been found, according to Bergman, or at least with a very small proportion of sulphur, but combined with iron, cobalt, and arsenic. He says, too, that it exists in combination with sulphuric acid.

3. To obtain nickel from its ores in the state of fulphuret, they are first roasted, by which means the fulphur and arsenic are driven off. In this process the talc mineral loses one-third or one-half of its weight; and in proportion to the quantity of pure metal, which exists in the ore, it assumes a richer green. The roasted ore is then mixed with two parts of black flux, put into a crucible covered with muriate of soda, and exposed to a forge heat, to bring it to fusion. When the apparatus has cooled, there is found under the brown, black, or blue scoriae, a metallic button, which amounts to one-tenth, and sometimes to one-half, of the mineral employed.

4. Nickel, in the purest state in which it can be obtained, is of a yellowish white, or of a reddish white colour, with more or less lustre, and of a granulated texture. The specific gravity is 9 according to Bergman, but according to Guyton it is only 7.807. Bergman speaks of it as possessing some degree of ductility; but this, it is supposed, is owing to its alloy with iron, which latter constitutes $\frac{1}{4}$ of its weight. It is also magnetic, and this property has also been supposed to depend on the same alloy. Nickel is a very infusible metal, requiring a temperature equal to $150^\circ$ Wedgwood. Its power of conducting caloric has not been ascertained, nor has its taste or its smell been recognized. It has never been obtained in crystals.

5. When nickel is exposed to heat in an open vessel, it combines with oxygen, and affumes a brown colour; but this requires a very high temperature. After long exposure to the air, when it is moist, and in the cold, it becomes covered with an efflorescence of a bright green colour, of a peculiar and distinct shade. It is this oxide, efflorescence which is found on the surface of the native sulphurets of nickel, the shade of which is so remarkable, and so different from that of copper, that they can be easily distinguished. This oxide is composed of

| Nickel | 77 | |--------|----| | Oxygen | 23 |

6. There is no action between nickel and azote, hydrogen, or carbone; nor is it at all acted upon by water.

7. Nickel combines with phosphorus, and forms with phosphuret, it a phosphuret. This is prepared by decomposing phosphoric acid in the state of glas, which is done by mixing phosphoric glas, charcoal and nickel, and fusing them together. Or it may be prepared, by projecting bits of phosphorus on the metal, while it is red-hot, in a crucible. It acquires an addition of one-fifth part to its weight; but it parts with a small portion of phosphorus as it cools. The phosphuret of nickel is of a more brilliant and purer white than the metal itself. The texture resembles a collection of small needles heaped together. When it is heated under the blowpipe, Nickel, pipe, the phosphorus burns on its surface, and the metal is oxidated. The component parts of this phosphuret, according to Pelletier, are,

| Nickel | 83.3 | |--------|------| | Phosphorus | 16.6 |

100.0 *

8. Nickel combines readily with sulphur, and forms with it a sulphuret, which is somewhat different in its properties from the native sulphuret. It is hard, of a yellowish colour, and in small brilliant facets. When it is strongly heated in the open air, it gives out luminous sparks.

9. Nickel enters into combination with several of the metals, and forms with them alloys; the properties of which are but little known. With cobalt and arsenic it forms native alloys. The alloy with the latter is of a reddish colour, has no magnetic property, is considerably hard, and its specific gravity is less than the mean specific gravity of the two metals.

10. Nickel enters into combination with the acids, and forms with them salts, which are distinguished by peculiar properties.

11. The order of the affinities of nickel and its oxide, as they have been ascertained by Bergman, is the following:

| Nickel | Oxide of Nickel | |--------|----------------| | Iron | Oxalic acid | | Cobalt | Muriatic | | Arsenic| Sulphuric | | Copper | Tartaric | | Gold | Nitric | | Tin | Phosphoric | | Antimony| Fluoric | | Platina| Saccharic | | Bismuth| Succinic | | Lead | Citric | | Silver | Lactic | | Zinc | Acetic | | Sulphur| Arsenic | | Phosphorus | Boracic | | | Prussic | | | Carbonic |

I. Salts of Nickel.

1. Sulphate of Nickel.

Concentrated sulphuric acid, with the assistance of heat, is decomposed by nickel. Sulphurous acid gas is discharged, and there remains behind a gray mass soluble in water, to which it communicates a beautiful green colour. By evaporating this solution, crystals of a pale emerald green are obtained, which are sulphate of nickel. The oxide of nickel is also readily dissolved by sulphuric acid, from which also crystals are obtained. It crystallizes in the form of square prisms, or in decahedrons, which are composed of two four-sided pyramids, truncated at the summits.

2. Nitrate of Nickel.

Nitric acid oxidates and dissolves nickel with the assistance of heat. The oxide is dissolved by this acid, without effervescence. The solution has a blackish green colour, which affords rhomboidal, deliquescent crystals, that are decomposed by heat, and leave, after being strongly calcined, and giving out oxygen gas, a black oxide. When the nitrate of nickel is exposed to a warm dry air, it is deprived of its water of crystallization, and even of its acid, so that there remains behind only an oxide of the metal.

3. Nitrate of Ammonia and Nickel.

This triple salt is formed, by adding ammonia in excess to the solution of nitrate of nickel. This salt is of a green colour. It is obtained in crystals by evaporation. The solution does not become turbid by the addition of alkalies, but the metal is precipitated by hydrofulphurates.

4. Muriate of Nickel.

Muriatic acid dissolves nickel and its oxide slowly, except with the assistance of heat. The solution is of a green colour, and affords irregular crystals. The muriate of nickel is decomposed by heat, and by exposure to the air.

5. Fluate of Nickel.

Fluoric acid dissolves the oxide of nickel with difficulty, and affords crystals of a bright green colour.

6. Borate of Nickel.

The compound of boracic acid and nickel can only be formed by double affinity, by adding the borate of soda, for instance, to a solution of nickel in acids.

7. Phosphate of Nickel.

Phosphoric acid has not a very strong affinity for the oxide of nickel. The solution which is formed is scarcely of a green colour, and does not afford crystals.

8. Carbonate of Nickel.

Liquid carbonic acid, exposed to the contact of nickel, did not appear, to Bergman, to combine with the metal. But when nickel is precipitated from its solutions by means of alkaline carbonates, the precipitate acquires a greater weight than when the pure alkali is employed; from which it is concluded, that part of the carbonic acid has combined with the oxide.

9. Arseniate of Nickel.

Arsenic acid forms with the oxide of nickel a green saline mass, which is obtained by precipitating the oxide of nickel from its solution in acids, by means of an alkaline arseniate. The arseniate of nickel is in the form of powder, which is scarcely soluble in water.

10. Tungstate of Nickel. 11. Molybdate of Nickel. 12. Chromate of Nickel. 13. Columbite of Nickel.

14. Acetate of Nickel.

Acetic acid dissolves the oxide of nickel, and forms a salt in rhomboidal crystals, which are of a deep green colour.

* Ann. de Chim. xlii. 217. 15. Oxalate of Nickel.

With the assistance of heat, oxalic acid acts upon nickel, and a pale green powder precipitates. This salt is scarcely soluble in water. It may be formed also, by precipitating nickel from its solutions in sulphuric, nitric, and muriatic acids, by means of oxalic acid.

16. Tartrate of Nickel.

This salt, and the combinations of the oxide of nickel with the other acids, are unknown.

II. Action of Alkalis.

The fixed alkalis dissolve the oxide of nickel, but in small quantity. They assume a yellow colour; but this oxide is very soluble in ammonia; the solution of which is of a deep-blue colour, and of a peculiar shade. When it is evaporated, it precipitates in the form of a blackish brown powder, which passes from blue to green. Most of the metals separate the nickel from this solution.

III. Action of the Earths.

1. Many of the earths, as silica and alumina, have no action on nickel; but others, as barytes and strontites, convert the oxide in solution into an orange red. If it contain arsenic or cobalt, the glass, which is coloured with nickel, becomes of a blue or violet colour.

2. The nitrates and the hyperoxymuriates very readily decompose the salts of nickel, and reduce it to the state of oxide. With the boracic and phosphoric salts it assumes a pale red colour. The nitrate of potash detonates feebly with nickel, but has the property of detecting the smallest trace of cobalt, which could not have been discovered by any other reagent.

So far as is known, this metal has not been applied to much use. There is, however, little doubt, that it might be employed for enamels, and for colouring glasses, porcelain and pottery. Fourcroy observes, that it is probably employed in some of the secret processes of these manufactures, as it is brought in considerable quantities from Saxony to Paris.

Sect. X. Of Manganese and its Combinations.

1. A substance was long employed in the manufacture of glasses, which, on account of its property of deriving glasses of its colour, was known under the name of glassmaker's soap; from its appearance it was called black magnesia, or manganese. But although it was long employed in manufactures, nothing was known of its intimate nature or constituent parts. It was generally considered as an ore of iron, because it was found sometimes combined with the oxide of this metal. By others it was arranged among the ores of zinc, supposing that it was some combination of this metal. To Bergman and Scheele we are indebted for the first accurate knowledge of its nature. Bergman, in a dissertation which he published in 1774, announces it as a peculiar metal, on account of its weight, its property of colouring glasses, and of affording a white precipitate with the alkaline prussiates. Scheele, in the same year, presented to the academy of Stockholm, a memoir, containing his researches concerning the nature and peculiar properties of this mineral. From these experiments he concludes that this mineral is the oxide of a peculiar metal, totally distinct from all others. Gahn, the pupil of Bergman, was the first who obtained the metal in its pure state, from the native oxide of manganese. His experiments have been repeated by others, and the results of Scheele and of Bergman fully confirmed.

2. Manganese is most generally found in the state of ores. Of this there are three principal varieties, the white, the red, and the black. 1. The first, or the white ore of manganese, contains the smallest proportion of iron and of oxygen. Sometimes it is crystallized. This ore soon tarnishes in the air by absorbing oxygen. 2. The red ore of manganese contains more iron than the former. It is either friable, or hard as it is found in carbonate of lime, on flints, or accompanying ores of iron; or in lamellated masses, radiated or crystallized in pyramids, rhomboids, or in short brittle needles. 3. The black or the brown ore is frequently crystallized like the red. It is also found in solid masses having a metallic or dull carthy appearance, mixed with quartz and other stony bodies. The specific gravity is 4.0. Manganese has been found native by Lapeyrere in some iron mines in France. It was in the form of small, flattened metallic buttons, of a lamellated texture. But it has been supposed that the manganese in this state is alloyed with iron.

3. Manganese is procured in the metallic state by separation of the following process. The native oxide of manganese is reduced to a fine powder, and formed into a paste with water. Part of it is then made into a ball, and introduced into a crucible lined with charcoal. A thick stratum of charcoal is placed at the bottom of the crucible, and the ball of manganese is to be surrounded and covered with the same substance, and the crucible, which is inverted and fitted to the other, is to be filled with it. The whole is then to be exposed to a very strong heat, not less than 160° Wedgwood, for more than an hour. When the apparatus cools, the metal is found in the bottom of the crucible, or in the midst of the scoriae, in the form of globules, which amount to nearly one-third of the manganese employed. But if the heat has been too low, it will be found in grains.

4. Manganese is of a grayish white colour, with considerable brilliancy, and of a granular texture. The specific gravity is 6.850. It has neither taste nor smell. In hardness it is equal to iron. It is one of the most brittle of the metals, and at the same time one of the most fusible, requiring a temperature of 160° Wedgwood to melt it. When in the state of powder it is often attracted by the magnet, on account of the iron, from which it can only be separated with great difficulty.

5. When this metal is exposed to the air, it is soon tarnished. It becomes gray, brown, and black, and at last falls down into powder, which is found to have acquired considerable addition to its weight. But when it is heated in the open air, it passes more rapidly through the different changes of colour, in proportion as it combines with oxygen, to the absorption of which these changes are owing. It appears, therefore, that manganese, like some of the other metals, combines with different portions of oxygen, forming different The black oxide, which is manganese, combined with oxygen in the greatest proportion, is found native in great abundance. The red oxide is supposed to contain the oxygen in the next proportion. This also exists native, and it may be found by distilling the black oxide made into a paste with concentrated sulphuric acid in a retort to dryness. It is deprived of a great quantity of oxygen, which is given out in the state of gas. The residue is then to be mixed with water, which is to be filtered. This solution, which is sulphate of manganese, is of a red colour. By adding an alkali, a precipitate is formed, which is the red oxide of manganese. The white oxide is also prepared by depriving the black oxide of part of its oxygen. This is effected by pouring nitric acid on the black oxide of manganese, with the addition of sugar, which absorbs the oxygen and converts it into the white oxide. The latter is then dissolved in the acid, from which it may be precipitated by potash. The precipitate is in the form of a white powder. The proportion of manganese and oxygen in the white and brown oxides of manganese, according to Bergman, and in the black, according to Fourcroy, are,

| White Oxide | Brown Oxide | Black Oxide | |-------------|------------|-------------| | Manganese | 80 | 74 | 60 | | Oxygen | 20 | 26 | 40 |

When these oxides are exposed to the air, they absorb oxygen, and are again converted into the black oxide with the greater proportion of oxygen.

6. It is from the black oxide of manganese that chemists generally procure oxygen gas. The most economical process is that which has been already described in the chapter on oxygen. This is by exposing it to a red heat in an iron bottle. The manganese is reduced to the state of red oxide by being deprived of the difference of the quantity of oxygen between the black and the brown oxides. The same manganese may be employed after it has been for some time exposed to the air, and occasionally moistened with water. This process, however, goes on much more slowly than is generally supposed. We have kept several quantities of manganese, which had furnished abundance of oxygen, and had ceased to give out more in a red heat, exposed to the air for many months, and frequently moistened with water, but when it was again heated to redness, it did not yield above \( \frac{1}{15} \) part of the original quantity from the native manganese.

7. Manganese does not enter into combination with azote, hydrogen, or carbone. It is by means of charcoal that the oxide of manganese is reduced, by being deprived of its oxygen; and what has been supposed to be a compound of manganese and carbone, is a carburet of iron, or carbone combined with the iron, with which manganese is almost always alloyed.

8. Phosphorus combines very readily with manganese. Pelletier formed the phosphuret of manganese by fusing a mixture of equal parts of manganese in the metallic state, and phosphoric glass, with about \( \frac{1}{5} \) part of charcoal in powder; or by fusing equal parts of the two former without the charcoal; or by projecting small bits of phosphorus on manganese heated to redness in a crucible. The phosphuret obtained by any of these processes, is of a white colour, of a granulated texture and brittle, and much disposed to crystallize. It undergoes no change by exposure to the air. It was covered with an opaque, vitreous matter of a yellowish colour. It is more fusible than the manganese itself. When it is exposed to the action of the blow-pipe, the phosphorus burns, and the metal is oxidated.

9. Bergman failed in forming a compound with sulphur and manganese by direct combination. But he succeeded in combining sulphur with oxide of manganese. Three parts of sulphur, and eight parts of the oxide, exposed to heat in a glass retort, formed a greenish yellow mass, which effervesced with acids, and emitted sulphurated hydrogen gas. Scheele has observed, that a part of the sulphur is converted into sulphurous acid during the process.

10. Manganese enters into combination with the Affinities, acids, and forms salts with them. The order of the affinities of the oxides of manganese for the acids, according to Bergman, is the following:

**Oxide of Manganese**

- Oxalic acid, - Citric, - Phosphoric, - Fluoric, - Muriatic, - Sulphuric, - Nitric, - Saccharic, - Succinic, - Tartaric, - Lactic, - Acetic, - Prussic, - Carbonic.

I. Salts of Manganese.

1. Sulphate of Manganese.

1. Concentrated sulphuric acid acts on manganese even in the cold; but the action is more powerful if the acid be diluted with two or three parts of water. Hydrogen gas is given out, and there remains behind in the liquid, a black, spongy mass, which is the carburet of iron. The solution is colourless, and it affords by evaporation, transparent, colourless crystals. Sulphuric acid does not combine with the black oxide of manganese, till it is deprived of part of its oxygen, and reduced to the state of red or white oxide; but the acid combines with either of the two latter oxides, forming salts possessed of distinct properties. There are therefore, two sulphates of manganese, which may be distinguished, from the colour of the base or oxide, by the names of white and red sulphates.

2. **White sulphate of manganese.**—This is the compound with the sulphuric acid and the white oxide of manganese, white oxide. This oxide combines with the acid without effervescence, and forms a colourless solution, which yields by evaporation, transparent rhomboidal crystals, which have a very bitter taste. This salt is decomposed by heat; the acid is driven off, and oxygen gas is given out. It is decomposed also by the pure alkalies, and a precipitate... Manganese tate is formed, of the white oxide of manganese, which soon becomes brown by exposure to the air, in consequence of the absorption of its oxygen. The alkaline carbonates precipitate a carbonate of manganese, which does not absorb the oxygen from the air, and does not become black like the former. It is the white sulphate of manganese, which is obtained by dissolving the metal in diluted sulphuric acid. In this process the manganese combines with the oxygen of the water, which is decomposed, and is converted into the white oxide, which unites with the sulphuric acid, to form the sulphate. The hydrogen of the water is driven off in the state of gas, so that the salt formed in this way occasions an effervescence. This salt may also be formed by dissolving the black oxide in sulphuric acid, but in this case it is necessary, as Scheele discovered, to add some vegetable matter, as sugar, honey, or gum, to absorb the superabundant quantity of oxygen, which prevents the solution of the manganese in the acid. When, therefore, the black oxide is reduced to the state of white oxide, by depriving it of part of its oxygen, it combines with the acid, and forms white sulphate of manganese, as in the former processes.

3. Red Sulphate of Manganese.—If the black oxide of manganese be distilled to dryness with sulphuric acid, diluted with half its weight of water, and if the residue be washed with water, a reddish or violet-coloured solution, which is the red sulphate of manganese, is obtained. By evaporation it affords thin crystalline masses, which have no regular form. These are also of a reddish colour. The alkalies occasion a red precipitate, which becomes black by exposure to the air. This sulphate may be also formed by the direct combination of the red oxide with the acid.

Bergman has observed, that the red oxide of manganese is intermediate between the black and the white; that it is more soluble in sulphuric acid than the former, and less soluble than the latter; that the red forms a red-coloured sulphate, while the white affords a colourless sulphate.

4. Sulphurous acid acts feebly or scarcely at all on manganese; but it dissolves the black oxide readily, and without effervescence. There is not formed, however, a sulphite of manganese; for the sulphurous acid deprives the black oxide of a portion of its oxygen, and thus converts it into a white oxide, while the acid itself is converted into sulphuric acid. The white oxide is then dissolved in the sulphuric acid, and forms the white sulphate of manganese.

2. Nitrate of Manganese.

1 Nitric acid dissolves manganese with effervescence, and with the evolution of nitrous gas. There remains behind a black, spongy mass, which is carburet of iron, and insoluble. The solution thus formed, is of a dark colour, on account of the iron which it contains; for it does not appear that the red oxide of manganese combines with nitric acid. The white oxide of manganese dissolves very readily in nitric acid, and without effervescence, or the emission of nitrous gas. This solution, if the oxide be pure, is colourless. It does not afford crystals, even by slow evaporation. The black oxide of manganese cannot be dissolved in nitric acid, but by long digestion; but by adding some vegetable matters, as honey, sugar, oils, &c., or even some of the metals, to deprive the oxide of part of its oxygen, the combination is effected. Carbonic acid gas, which is formed by the union of the carbones of the vegetable matters with the oxygen of the manganese, is given out during the process.

2. Nitrous acid dissolves the oxide of manganese much more readily than the nitric acid. No effervescence takes place, because the oxygen of the manganese combines with the nitrous acid, and forms nitric acid, which latter combines with the oxide of manganese, reduced to the state of white oxide; and thus there is formed, not a nitrite, but a nitrate of manganese.

3. Muriate of Manganese.

1. Manganese is dissolved with effervescence, and with white oxide, the evolution of hydrogen gas, in liquid muriatic acid. The white oxide combines with the acid, without effervescence, and without the separation of any gas, because it is sufficiently oxidated, to be dissolved in this acid. The black oxide is dissolved with equal facility in muriatic acid as in the other acids. In this case an effervescence takes place, with the disengagement of oxymuriatic acid gas. The nature of this action is obvious. Part of the muriatic acid combines with part of the oxygen of the manganese, and forms oxymuriatic acid, which is disengaged in the state of gas. The black oxide is deprived of part of its oxygen, and converted into the white oxide, which latter dissolves in the remaining part of the muriatic acid, and forms a muriate of manganese. This salt, being a compound of the white oxide of manganese and muriatic acid, may be called the white muriate of manganese. If any combustible matter be added, the solution of the black oxide of manganese in this acid goes on, without the production of oxymuriatic acid.

2. Oxymuriatic acid readily parts with its oxygen to manganese, which is thus converted into the white oxide. It combines also with the oxides of manganese, and forms solutions of a brown, red, or violet-colour, which afford crystals of the same colour. There is, therefore, a red muriate of manganese.

It is from the black oxide of manganese, that oxymuriatic acid is obtained, either by adding to the oxide muriatic acid, part of which combines with the oxygen of the manganese, and is converted into oxymuriatic acid; or, by adding sulphuric acid to a mixture of the black oxide of manganese and muriate of soda. The sulphuric acid decomposes the latter, and the muriatic acid being disengaged, combines with part of the oxygen of the manganese, and forms oxymuriatic acid.

4. Fluate of Manganese.

Fluoric acid has little action on manganese or its oxides; but a fluate of manganese may be formed by double affinity, by adding an alkaline fluate to the nitrate or muriate of manganese. The fluate of manganese thus formed, is not very soluble in water. Its other properties are unknown.

5. Borate of Manganese.

This salt may be formed in the same way as the former. Manganese, former. It is equally soluble in water, and its other properties are also unknown.

6. Phosphate of Manganese.

A phosphate of manganese may be formed in the same way as the two former salts. It is not very soluble in water, and its other properties have not been examined.

7. Carbonate of Manganese.

Liquid carbonic acid dissolves a small portion of manganese, as well as of its black oxide. When this solution is exposed to the air, the oxide is gradually precipitated, and appears on the surface in the form of a white pellicle. Bergman has remarked, that during the combination of manganese with carbonic acid, there is evolved an odour somewhat analogous to that of burnt fat.

8. Arseniate of Manganese.

Arsenic acid combines with the white oxide of manganese, and forms an arseniate. The arsenious acid, or white oxide of arsenic, deprives the black oxide of manganese of part of its oxygen, and passes to the state of arsenic acid, and then combines with the manganese, now reduced to the state of white oxide. When the arsenic acid is nearly saturated with the oxide, the solution becomes thick, and small crystals make their appearance. This salt, when heated, does not melt, nor is the arsenic sublimed, without the addition of charcoal.

9. Tungstate of Manganese.

10. Molybdate of Manganese.

11. Chromate of Manganese.

12. Columbate of Manganese.

13. Acetate of Manganese.

Acetic acid dissolves part of the black oxide of manganese, but acts very feebly on the metal itself. This acid may be employed to separate manganese from iron; for when it is added to a solution containing both these metals, the acid combines with the manganese, for which it has a stronger affinity, and leaves the oxide of iron. Several successive solutions and evaporations are necessary to separate the whole of the iron, which is known when the solution becomes colourless, and when it affords a white precipitate with prussiate of potash. The solution of acetate of manganese does not crystallize, and when evaporated to dryness, it soon deliquesces*.

14. Oxalate of Manganese.

Oxalic acid forms a salt with the oxide of manganese, which, when the solution is saturated, precipitates in the form of white powder. It may be formed also by adding oxalic acid to the sulphate, nitrate, and muriate of manganese in solution.

15. Tartrate of Manganese.

This salt may be formed by double affinity, by adding tartrate of potash to the solution of manganese in sulphuric or nitric acids. The black oxide of manganese is dissolved in tartaric acid, and gives a black coloured solution. When it is heated, an effervescence takes place; the acid is partially decomposed, carbonic acid gas is evolved, and the solution at last becomes colourless.

16. Citrate of Manganese.

Citric acid, in its combination with the black oxide of manganese, exhibits the same phenomena as the former.

17. Benzoate of Manganese.

Benzoic acid readily combines with the white oxide of manganese. By evaporation, crystals in the form of small scales are obtained, which are little altered by exposure to the air, and are soluble in water.

II. Action of Alkalis on Manganese.

The pure alkalis favour the oxidation of manganese, and the decomposition of water, because they likewise combine readily with this oxide. In the dry way, the fixed alkalis fuse with manganese, and form a mass of a deep green colour, which is soluble in water, and communicates to it the same colour. If this solution be kept in a close vessel, there is precipitated an oxide of manganese, of a yellowish colour, and the green liquid changes to a blue. Water precipitates the alkaline solution, and converts it, first to a violet and then to a red colour. As the particles of the oxide collect together, the liquid becomes white. The addition of a few drops of acid, on exposure to the air, produces the same precipitation and the same shades of colour, by oxidating the manganese. The white oxide of arsenic, or arsenious acid, added to this alkaline solution, deprives it of the whole of its colour, and renders it white, by combining with the oxygen. By adding charcoal to the oxide of manganese which has been fused with an alkali, an effervescence takes place, with the evolution of carbonic acid, and the colour of the solution changes to a greyish white. This carbonic acid is here formed by the union of the carbones of the charcoal with the oxygen of the manganese, and this latter passes to the state of white oxide. On account of these remarkable changes of colour, and the chameleon-like shades which this liquid, treated in various ways, assumes, this compound has received the name of mineral chameleon.

2. Scheele had observed the change which ammonia undergoes by the action of oxide of manganese, in the distillation of this oxide with the muriate of ammonia. He suspected that the ammonia was partially decomposed, and to this decomposition he attributes the formation of a gas, which he obtained by this process, and which he found to be different from carbonic acid. Berthollet has shown, that in this process, the hydrogen, leaving the ammonia which is decomposed, combines with the oxygen of the oxide of manganese, and forms water; and the azote, the other component part of ammonia, is set at liberty.

A very interesting experiment was contrived by Dr Milner, which illustrates the reciprocal action, and experiment, decompositions of the oxide of manganese and ammonia. He filled a tube with oxide of manganese, exposed it to a red heat, and made a stream of ammoniacal gas pass through it. The gas was decomposed, and its azote combining with the oxygen of the oxide, formed nitrous gas. Some of the alkaline salts have peculiar effects on the oxides of manganese and their compounds. The sulphates have the property of destroying the colour of glaiss, which has been communicated by manganese; but for this effect a high temperature is necessary. The nitrates readily burn this metal, and oxidate it strongly. Melted nitre gives a violet or red colour to glaiss, which has been rendered colourless, by referring to it the oxygen of which it has been deprived by the fusion of the glaiss. With the nitrate of potash and the black oxide of manganese, heated in a crucible to redness, a compound is formed, similar to that which is the result of the direct combination of the oxide with the alkali.

The alkaline phosphates and borates fused by means of the blow-pipe, with the oxide of manganese, produce various colours, according to the degree of oxidation, and the intensity of the heat.

A white precipitate is formed, by adding hydrofulphuret of potash to the salts of manganese, and a yellowish-white precipitate is obtained, by means of the triple prussiate of potash.

III. Action of the Earths on Manganese.

There is no action between manganese and any of the earths; but its oxide combines with them, and forms vitreous matters, which are of different colours, according to the degree of oxidation of the manganese, and its mixture with iron. In general, these colours are green, brown, black, or yellowish green.

Manganese and its oxides are of great importance, both in chemistry and in the arts. This must be obvious, from the minute detail of its properties and combinations, which has now been given.

Sect. XI. Of Bismuth and its Combinations.

1. Bismuth, it would appear, was known to the ancients, to the alchemists, and some of the earliest mineralogists; but it was considered merely as a variety of some other metal, and generally of tin and lead. Hence it was distinguished by the name of green tin, gray lead, and white antimony. It was not till the year 1753, when its properties were particularly examined by Pott and Geoffroy the younger, that it was ascertained to be a peculiar metal. Darcey and Rouelle afterwards instituted a set of experiments on this metal, and discovered more of its properties. Monnet and Beaume investigated its principal combinations at still greater length; and Bergman examined with more accuracy, some of its compounds and precipitates.

2. Bismuth is found native in the state of sulphuret, and in that of oxide. Native bismuth is easily distinguished by its colour, brittleness, and fusibility. The sulphuret of bismuth is of a bluish gray, sometimes with a yellowish shade, and is in irregular masses, or crystallized in the form of small prisms. It has a brilliant, lamellated fracture. The native oxide of bismuth accompanies the metal, or is found on the surface of the sulphuret. It is of a greenish yellow colour.

3. Bismuth is easily extracted from its ores. The mineral, after being reduced to powder, and well washed, is mixed with about \( \frac{1}{4} \) of its weight of black flux, is put into a crucible lined with charcoal, and well covered. It is then exposed to a moderate heat, which must be quickly applied, to prevent the metal from being sublimed. By this process a metallic button is obtained.

In the humid way, the ore of bismuth being reduced to powder, is dissolved in nitric acid, and precipitated from this solution by water. If the native bismuth be combined with any other metals, they remain in the solution. The sulphuret of bismuth is also dissolved in the same acid by boiling. The sulphur is separated, as the metal, being oxidated, combines with the acid. The native oxide is treated in the same way, and is precipitated by water.

4. Bismuth is of a white colour, inclining to yellow, exhibiting a texture composed of large brilliant plates. Its specific gravity is 9.822. It has scarcely either taste or smell. By a violent stroke of the hammer it is broken, and divides into small fragments of a lamellated structure; the figure of its particles is the regular octahedron. It has considerable hardness; and by hammering, its density may be increased. It has very little elasticity, and no ductility. Bismuth is very fusible. When it is exposed to the temperature of 490°, according to Guyton, it melts; and, if after fusion, it be allowed to cool slowly, it crystallizes in parallelepipeds which cross each other at right angles. This metal crystallizes more easily and more regularly than any other yet known. If the heat be long continued after the fusion, and sufficiently strong; and if the process be conducted in close vessels, it sublimes, and attaches itself to the upper part of the apparatus, where it crystallizes in brilliant plates.

5. Bismuth is but slightly affected by exposure to the air in the cold. It loses its brilliancy, and is covered with a fine powder of a yellowish gray colour; but, when it is heated in contact with air, the surface is soon covered with an iridescent pellicle, which, by agitation and continuing the heat, is converted into a greenish gray or brown-coloured oxide. It acquires about \( \frac{1}{10} \) of addition to its weight. By continuing the heat, and occasionally stirring the fused metal, it becomes of an orange-yellow colour, and acquires a farther addition to its weight. If the metal in fusion be exposed to a red heat, it takes fire with a slight explosion, burns with a bluish flame, and is sublimed in the form of a yellowish vapour, which, being condensed and collected, is known under the name of flowers of bismuth. It appears then, that bismuth combines with oxygen in two proportions. The first, or the brown and smaller proportion, is that of the brown oxide; and yellow, the second is the yellow oxide or flowers of bismuth.

6. There is no action between bismuth and azote, hydrogen, or carbone. It combines but in very small proportion with phosphorus, forming a phosphuret. When phosphorus is dropped into bismuth in fusion, it seems to unite with it, according to Pelletier, in the proportion of four parts in the hundred. But the properties of the bismuth are very little changed.

7. Sulphur unites readily with bismuth. When equal parts of bismuth and sulphur are heated together in a crucible, the fusion of the metal is greatly retarded. It requires a higher temperature than when the metal is alone. This sulphuret of bismuth is of a shining dark gray colour, and crystallizes by proper cooling into needle-form prisms, shaded with splendid blue and deep- deep-red colours: The crystals are obtained by piercing the surface when it becomes solid after fusion, and pouring out the liquid parts; a cavity is thus left in which they are formed.

Sulphurated hydrogen gas occasions a dark colour on the surface of bismuth, and converts the oxides into a deep black colour, which is the commencement of reduction.

8. Bismuth combines with many of the metals, and forms alloys; but its combinations with the metals, already described, are little or scarcely at all known. Bismuth also combines with the acids, and forms salts.

9. The affinities of bismuth and its oxides are arranged by Bergman in the following order:

| BISMUTH | OXIDE OF BISMUTH | |---------|------------------| | Lead | Oxalic acid | | Silver | Arsenic | | Gold | Tartaric | | Mercury | Phosphoric | | Antimony| Sulphuric | | Tin | Muriatic | | Copper | Nitric | | Platina | Fluoric | | Nickel | Saccharic | | Iron | Succinic | | Sulphur | Citric | | | Lactic | | | Acetic | | | Prussic | | | Carbonic |

I. Salts of Bismuth.

The solutions of bismuth in the acids, and also the crystallized salts which are obtained from them, resemble each other, but differ from almost all other metallic solutions, as well as from all other salts; and particularly in one circumstance, which is, that water in sufficient quantity decomposes them, and precipitates an oxide of bismuth of a white colour. This shows that bismuth is strongly oxidized by the action of the acids, to which it adheres with no great affinity, and that it forms with them compounds which are not very permanent. It seems at the same time remarkable, that this metal should be more oxidized in this way, than by the usual process of oxidation, by means of heat, and by the action of water; and that it should have a white colour, while in the usual way, it is of a yellowish gray.

1. Sulphate of Bismuth.

Concentrated sulphuric acid has no action on bismuth in the cold; but this metal decomposes the acid at a boiling temperature. Sulphurous acid gas is disengaged, and the bismuth is oxidized, and converted into a white powder. If the heat be strong, sulphur is sublimed. When the remaining mass is washed with water, it carries off the remaining acid and a small quantity of the oxide of bismuth. The solution by proper evaporation, affords small soft needle-formed crystals, which are sulphate of bismuth. This sulphate is decomposed by water, which separates a white oxide.

2. Sulphite of Bismuth.

Sulphurous acid has no action on bismuth; but it unites with its oxide, and forms a white sulphite which is insoluble in water, and even in its own acid; of a sulphurous taste; fusible by the blow-pipe into a reddish yellow mass, which is reduced on charcoal into metallic globules; decomposed with effervescence by means of sulphuric acid; giving out by distillation sulphurous acid, and leaving behind a pure white oxide.

3. Nitrate of Bismuth.

1. Nitric acid exhibits a very violent action with violent bismuth. When the acid is a little concentrated, and action, the bismuth in the state of powder, there is a violent effervescence, with the evolution of nitrous gas. There is at the same time great heat produced. The bismuth is converted into white oxide at the expense of the acid, and when the action ceases, if no more acid be added than what is necessary to its oxidation, remains dry.

2. The nitric solution, thus prepared, is colourless, and affords crystals by evaporation. It crystallizes in tetrahedral prisms, compressed into obtuse three-sided summits. It has sometimes been obtained in flattened rhomboidal parallelepipeds, similar to those of Iceland crystal. When this salt is thrown on red-hot coals, it melts, boils, and froths up; exhales nitrous vapour, and leaves behind a greenish yellow oxide. It dries in the air, and becomes moist when the air is humid. When it is brought into contact with water, it becomes turbid, is decomposed, and a white oxide is precipitated. This decomposition is effected with the nitric acid, which is poured gradually into a large quantity of water. The oxide which is thus obtained, was formerly called magisterium of bismuth. It is known in the shops by the name of pearl white. It becomes of a deep gray, brown, or even black colour, when it is exposed to the action of sulphurated hydrogen gas.

4. Muriate of Bismuth.

Muriatic acid has but a feeble action on bismuth. Preparation is necessary to assist its action, that the acid be concentrated, and long digested with the metal, or distilled off it in the state of powder. During the process, a fetid odour is emitted, which is owing to the decomposition of water, its oxygen combining with the metals, and the hydrogen being set at liberty. By evaporating this solution, small needles of muriate of bismuth are obtained; but only in very small quantity; for the greatest part of the oxide of bismuth is separated by water. The muriate is sublimed by heat into a thick, solid, fusible matter, which was formerly called butter of bismuth. It is deliquescent, and may be decomposed by water, which separates a very fine white oxide.

Oxymuriatic acid readily dissolves bismuth, and forms with the oxide which is previously produced, a salt similar to the preceding.

5. Fluate of Bismuth.

6. Borate of Bismuth.

These two salts may be formed by adding a fluate or borate of an alkali to a solution of nitrate of bismuth. A white precipitate is formed of the fluate or borate. Bismuth, borate of bismuth; but little is known of their properties.

7. Phosphate of Bismuth.

This salt is formed by combining the acid with the oxide of the metal, when precipitated by an alkali. The phosphate of bismuth is in the state of an insoluble white powder.

8. Carbonate of Bismuth.

This salt may be formed by precipitating the oxide of bismuth from its solution in acids, by means of an alkaline carbonate.

9. Arseniate of Bismuth.

Arsenic acid acts upon bismuth with the assistance of heat. A white powder appears on the surface of the metal, and the oxide is precipitated from the solution, by adding water. The arseniate of bismuth may be formed by adding arsenic acid to a solution of the nitrate of bismuth. The arseniate of bismuth falls to the bottom in the form of precipitate.

10. Tungstate of Bismuth.

Unknown.

11. Molybdate of Bismuth.

Muriate of bismuth is precipitated, if there be no excess of acid, by molybdic acid. The molybdate of bismuth, thus formed, is of a white colour.

12. Chromate of Bismuth.

13. Columbate of Bismuth.

14. Acetate of Bismuth.

This salt may be formed, by adding a solution of acetate of potash to a solution of nitrate of bismuth. A precipitate of acetate of bismuth is formed. The addition of acetic acid to the nitrate of bismuth, Guyton observes, prevented the latter from being precipitated by means of water.

15. Oxalate of Bismuth.

Oxalic acid combines with the oxide of bismuth, and forms with it a salt in the state of white powder, which is scarcely soluble in water. Oxalic acid added to nitrate of bismuth, occasions a precipitate in the form of small transparent crystals, which are oxalate of bismuth.

16. Tartrate of Bismuth.

Tartaric acid added to the solution of bismuth in any of the mineral acids, precipitates the oxide in the form of a white powder, which is the tartrate of bismuth, and is insoluble in water.

17. Benzoate of Bismuth.

Benzoic acid combines readily with the oxide of bismuth. The solution, by evaporation, affords crystals in the form of needles. They undergo no change by exposure to the air, are soluble in water, and decomposed by sulphuric and muriatic acids. This salt is also decomposed by heat, which drives off its acid.

18. Succinate of Bismuth.

Succinic acid combines with the oxide of bismuth, at a boiling heat. By evaporating the solution, crystals of succinate of bismuth are obtained, in the form of plates, and of a yellow colour.

II. Action of Alkalies, Earths, and Salts, on Bismuth.

1. Scarcely anything is known of the action of the alkalies, alkalies on bismuth. Ammonia, it is said, communicates to it a yellow colour, and the oxide of bismuth is soluble in ammonia in the liquid state.

2. The oxide of bismuth combines by fusion, with silica, to which it communicates a greenish yellow colour.

3. Bismuth is not changed by the action of the sulphites or sulphites. It is oxidized by the nitrates. When it is strongly heated, and thrown into a red-hot crucible with nitrate of potash, it detonates feebly, and without much inflammation. It is reduced to the state of oxide, of which one part combines with the potash. Bismuth has no action on muriate of ammonia, but its oxide very readily decomposes this salt. In the cold, it engages a little ammonia, by simple trituration; but when exposed to heat, it is totally decomposed, and there remains a muriate of bismuth.

4. Bismuth is applied to a great many uses. It forms some important alloys with the softer metals, to give them hardness and tenacity. The oxides of bismuth are of still more extensive utility. It is employed in this form by the manufacturers of porcelain, for the preparation of yellow enamels, and it is mixed with other oxides, to give variety of shade to their colours. It is sometimes employed in the fabrication of coloured glasses, to communicate a greenish yellow. The white oxide, which is most commonly employed for these different purposes, is also employed as a paint for the skin, under the name of pearl white; but it is extremely improper for this purpose, for besides the injury which it does to the skin, it becomes black, when it is exposed to the action of sulphurated hydrogen gas. It is sometimes used also, to give a black colour to the hair.

Sect. XII. Of Antimony and its Combinations.

1. It does not appear that the ancients were acquainted with antimony as a distinct metal, although it is supposed that it was employed by them in alloys of other metals. It is said, that they were acquainted with the oxide of antimony, and that it was employed as an external remedy in inflammation of the eyes. As a peculiar metal it was not certainly known till the time of Basil Valentine, who lived about the end of the 15th century. In his work, entitled Cursus Triumphalis Antimonii, he has detailed all that was then known of this metallic substance, and he has particularly described the process by which it is extracted from its ore.

No substance has been more the subject of investigation than antimony, and on no subject, perhaps, has there been so much written. The alchemists regarded antimony as peculiarly appropriate to the object Antimony, jeft of their researches. Their labours on this subject were almost incredible; and indeed this is scarcely to be wondered at, since it appears that they were inspired with the hope of making, by its means, the fortunate discovery of the universal medicine. It was therefore tortured and tried in every possible way, to obtain the object of their researches; and on this account it is almost impossible to reckon up the number of medicinal preparations which were proposed and employed with this metal and its ores. It is owing to these views and researches, concerning antimony, that its nature and properties are now so fully known.

2. About the end of the 17th century, Lemery published a treatise, which was the first correct and rational account of antimony. In this he arranged and detailed the discoveries of his predecessors, and added some of his own, with a number of curious experiments and accurate processes for many of the preparations of antimony and its sulphuret. Mender afterwards published a very complete history of all the facts that were then known concerning antimony; and it has been since examined by more modern chemists; among whom Bergman, Scheele, Berthollet, Proust, and Thénard, are the principal writers on this subject.

3. Antimony exists in nature in four different states: In the state of native antimony, that of sulphuret, hydrophilphuret of the oxide of antimony, and muriate. Native antimony is easily distinguished by its colour and brilliancy. It has been found in Sweden and in France. The most common ore of antimony is the sulphuret, which is of a grayish colour, and stains the fingers. It is sometimes crystallized in square prisms, which are slightly rhomboidal, and terminated by four-sided pyramids. The hydrophilphuret oxide of antimony is in shining filaments, of a deep red colour, disposed in rays going from a common centre, adhering to the surface or cavities of the sulphuret. The muriate of antimony, which is a rare production, is of a brilliant, pearly-white colour, in the form of small divergent needles, somewhat resembling radiated zeolite.

4. To obtain the pure metal from the sulphuret of antimony, the ore is first roasted, to separate the greatest part of the sulphur. It is then mixed with its own weight of black flux, formed into a paste with oil, and exposed to a strong heat in a crucible, at the bottom of which the metal is found reduced. By a shorter process, eight parts of sulphuret of antimony, six of tartar, and three of nitre, reduced to powder, and well mixed, are projected in small quantities into a red-hot crucible. At each projection there is a strong detonation; the tartar forms, by means of the nitre, a black flux, and the sulphuret being burnt, the metal is fused, but not oxidated, on account of the charcoal of the tartar with which it is surrounded, and the liquid alkali which covers it. The whole is then fused in a conical iron pot; and, when it is cool, the metallic antimony is found at the bottom, marked on its surface with needle-shaped crystals, arranged in the form of a star.

5. Antimony, in a state of purity, is of a brilliant white colour, having a good deal of resemblance to that of silver or of tin. It has a lamellated texture, composed of plates which cross each other in all directions. It exhibits sometimes perceptible traces of crystallization. The form of the crystals, which was discovered with difficulty by Hauy, on account of its complicated structure, is the octahedron, composed of a great number of regular tetrahedrons. Antimony has a very perceptible taste and smell, and particularly if it is rubbed for some time on the hands. The specific gravity is 6.702. It is very brittle, so that it can be reduced to powder, which is of a grayish white colour.

6. Antimony undergoes no change by being exposed to the air, nor is there any perceptible action between antimony and water in the cold; but when water comes in contact with antimony red-hot, it is instantaneously decomposed, and accompanied with a violent detonation, and a very brilliant white flame. Accidents of this kind have happened, attended with considerable danger.

7. When antimony is heated to the temperature of 80°, it melts. If the heat be continued after its fusion, it is sublimed, and if the process be performed in clothe vessels, it is condensed in shining crystallized plates. If it be allowed to cool slowly, and part of it be poured off when the surface becomes solid, the cavity is lined with pyramidal crystals, composed of small octahedrons.

8. When antimony is kept in fusion in the open air, it rises in the form of white vapour, which is precipitated on the surface of the metal, or upper part of the crucible, and crystallizes in long prisms, or in small, white, brilliant needles. This is an oxide of antimony, which was formerly called argentine flowers, or snow of regulus of antimony. By this process it is found, that the antimony has acquired an addition of weight of about 50 per cent. This oxide may be obtained, by exposing the antimony in a crucible to a white heat, and then by suddenly agitating it in contact with air, it takes fire with a kind of explosion, and burns with a white light.

Thenard, in his researches concerning antimony, distinguishes five different degrees of oxidation of this metal. But in a memoir on the same metal by Proust, he considers that the oxides of antimony may be reduced to two. According to the experiments of this chemist, 100 parts of antimony treated with nitric acid in a retort, uniformly afford 130 of a yellow oxide in the state of powder. It is reduced to 126 by washing with water before drying it, because the nitric acid dissolves a small proportion. This oxide is not reduced by being exposed to a red heat, but it is sublimed, and condensed in clothe vessels, in groups of crystals. It is insoluble in water. It is the same oxide which was formerly distinguished by the name of argentine flowers. The component parts of this oxide, according to Proust, are,

| Antimony | 77 | | Oxygen | 23 |

The oxide with a smaller proportion of oxygen, is formed by dissolving antimony in muriatic acid; and by adding water to the solution, a white powder is precipitated, which being washed, is separated from any acid that may adhere to it. To purify it still more, it is to be boiled with carbonate of potash, and afterwards washed, and dried on a filter. This oxide is of a yellowish white colour, and has little brilliancy; it melts. Antimony melts at a moderate red heat, and when it is allowed to cool, it crystallizes on the surface. The crystals are of a yellowish white colour, which are thrown together in heaps, in a radiated form. This oxide was formerly known by the name of powder of algaroth. Its component parts are,

\[ \begin{align*} \text{Antimony} & \quad 81.5 \\ \text{Oxygen} & \quad 18.5 \\ \end{align*} \]

There is no action between antimony and azote, hydrogen, or carbone.

9. Antimony enters into combination with phosphorus, and forms with it a phosphuret. Equal parts of phosphoric glass and antimony are fused together in a crucible, or with the addition of \( \frac{1}{4} \) of charcoal, or by projecting pieces of phosphorus on the metal in fusion in a crucible; and thus a phosphuret of antimony is obtained. The phosphuret has a metallic lustre, is brittle, and has a lamellated fracture. When it is placed on burning charcoal, it melts, gives out a small green flame, and is converted into the white oxide of antimony, which is sublimed.

10. Antimony combines very readily with sulphur, and forms with it an artificial sulphuret, which is exactly similar to the native sulphuret. It is formed by mixing the antimony and the sulphur together, and fusing them in a crucible. This sulphuret is of a brilliant gray colour, is more fusible than the metal itself, and by slow cooling, may be obtained in crystals. The component parts of the sulphuret, according to Proust, are,

\[ \begin{align*} \text{Antimony} & \quad 75.1 \\ \text{Oxygen} & \quad 24.9 \\ \end{align*} \]

The yellow oxide of antimony combines with different proportions of sulphur, and forms compounds of different colours, and which were formerly distinguished by different names. With eight parts of the oxide and one part of the sulphuret, a red-coloured, semitransparent mass is obtained, which was formerly called glass of antimony. When two parts of sulphuret are added to eight parts of the oxide, a yellowish mass is formed, which was known by the name of crocus metallorum. Six parts of oxide and one of sulphur, form a dark red, opaque mass, with a vitreous fracture, which is the true liver of sulphur. In these combinations, the sulphur deprives the oxide of part of the antimony, and combines with it, forming a sulphuret. This sulphuret then combines with the oxide.

13. Antimony enters into combination with the acids, and forms salts. It also forms alloys with many of the metals. The affinities of antimony and its oxides are, according to Bergman, in the following order:

| Antimony | Oxide of Antimony | |----------|------------------| | Iron | Muriatic acid | | Copper | Oxalic | | Tin | Sulphuric | | Lead | Nitric | | Nickel | Tartaric |

Sulphuric acid has no action on antimony in the cold. At a boiling temperature the acid is decomposed; fulphurous acid gas is emitted with effervescence, and if distilled in a retort to dryness, sulphur is sublimed. There remains a white oxide of antimony. If this mass be washed with water, the acid which adheres to it is carried off, with a small portion of the oxide; and what remains is the white oxide, which is insoluble. By adding a large quantity of water to the solution, the oxide which it had carried off is precipitated; but this solution being evaporated yields no crystals. It is decomposed by the earths and the alkalies, which precipitate a white oxide. Sulphuric acid, therefore, oxidizes antimony, but does not seem to have the property of forming a salt.

2. Sulphite of Antimony.

Sulphurous acid, with the assistance of heat, is decomposed by antimony. The metal is oxidized, and there is formed a sulphite of antimony. This salt may be also obtained by adding sulphurous acid to the solution of antimony in muriatic acid. A white precipitate appears, which is insoluble, of an acrid, bitter taste, and is decomposed by heat. When it is distilled in clothe vessels, it yields a little fulphurous acid, then fulphuric acid, and the residuum is a reddish brown mass, which is soluble in fixed alkali, and may be precipitated by means of muriatic acid, into a hydrofulphuret of antimony.

3. Nitrate of Antimony.

Nitric acid is rapidly decomposed by antimony, even in the cold. There is evolved a great quantity of nitrous gas, and sometimes the rapidity of the oxidation is such, that it is accompanied with actual combustion. The water also is partially decomposed. The antimony is converted into a white oxide. The hydrogen of the water combines with the azote of the acid, and forms ammonia, which combines with part of the nitric acid, and the compound is nitrate of ammonia. The small quantity of oxide of antimony which is dissolved in nitric acid, is precipitated by water, so that it adheres very slightly to the acid.

4. Muriate of Antimony.

Muriatic acid acts on antimony very feebly. By digesting the metal with the acid for a long time, it dissolves a small quantity, and the solution becomes of a yellowish colour. The white oxide is more soluble in this Antimony, this acid, and forms with it a colourless solution. The first solution yields crystals by evaporation, in the form of small needles, which are deliquescent, and sublimed by heat, and are precipitated and decomposed by water. The solution formed with the oxide is fixed in the fire, and crystallizes in brilliant plates. It is also decomposed by water. Muriatic acid dissolves more readily the sulphuret of antimony, for it does not require the aid of heat. There is discharged a strong odour of sulphurated hydrogen gas. When the mixture is heated, the whole of the metal is dissolved.

Nitromuriatic acid dissolves antimony more readily than any of the acids which have been mentioned. This solution is colourless. The muriate of antimony which remains after the evaporation, by being distilled, comes over of a thicker consistence, in proportion as it is concentrated. The muriate of antimony was formerly called butter of antimony. It is of a grayish white colour, and sometimes crystallizes in four-sided prisms. It is deliquescent in the air, and extremely caustic and corrosive. When it is diluted with water, a white powder is precipitated, which is the powder of algaroth.

5. Fluate of Antimony.

6. Borate of Antimony.

Fluoric and boracic acids have no action on antimony, but combine with its oxide, or precipitate it from its solution in acids, in the form of white powder, forming a fluate or borate of antimony.

7. Phosphate of Antimony.

Phosphoric acid combines with the oxide of antimony. The solution, by evaporation, yields a blackish green mass.

8. Phosphate of Lime and Antimony.

This triple salt is formed by calcining together equal parts of sulphuret of antimony and the ashes of bones; or, according to the process recommended by Mr Chenevix, by dissolving white oxide of antimony and phosphite of lime in equal parts in muriatic acid; and then by adding this solution to a sufficient quantity of distilled water, which contains pure ammonia. A precipitate is formed in the state of white powder. This powder is nearly insoluble in water. It has been long known as a diaphoretic and emetic, under the name of James's Powder. According to the analysis of Dr Pearson, it is composed of

| Substance | Quantity | |--------------------|----------| | Phosphate of lime | 43 | | Oxide of antimony | 57 | | **Total** | 100 |

9. Carbonate of Antimony.

Unknown.

10. Arseniate of Antimony.

By digesting together arsenic acid and antimony, a white powder is obtained, which is arseniate of antimony. Muriatic acid dissolves this powder, but it may be separated by adding water. This salt may be formed also, by adding an alkaline arseniate to the solution of antimony in muriatic, tartaric, or acetic acids.

II. Molybdate of Antimony.

Muriate of antimony is precipitated by molybdic acid; and if the acid be not in excess, the precipitate is white.

12. Acetate of Antimony.

Acetic acid dissolves a small portion of the oxide of antimony, and according to some, yields small crystals. The acetate of antimony has been employed as an emetic.

13. Oxalate of Antimony.

Oxalic acid combines with the oxide of antimony, and the solution affords crystals in the form of small grains, which are scarcely soluble in water.

14. Tartrate of Antimony.

Tartaric acid also combines with a small portion of the oxide of antimony, and affords a salt which assumes the form of a jelly.

15. Tartrate of Potash and Antimony.

This triple salt was formerly prepared by boiling together the preparation of what was called crocus metallorum, and tartar, in water. But if the white oxide Tartar be mixed with its own weight of tartar, and the mixture boiled in 10 or 12 parts of water, till the tartar be saturated, and the solution filtered and evaporated, crystals are obtained, which are crystals of the tartrate of potash and antimony, which have been long and better known by the name of tartar emetic. This salt is of a white colour, and it crystallizes in regular tetrahedrons. It effloresces by exposure to the air, and is soluble in 80 parts of cold, and in half that quantity of water at the boiling temperature. When it is exposed to heat, it is decomposed. It is also decomposed by the alkalis and their carbonates.

According to the analysis of Thenard, this salt is composed of

| Substance | Quantity | |-----------|----------| | Antimony | 38 | | Acid | 34 | | Potash | 16 | | Water | 8 | | **Total** | 96 |

This salt has been greatly employed as a diaphoretic and emetic, from which property it has derived its name. An account of the mode of preparing a similar powder, which, it is said, was invented by an earl of Warwick, and became famous in Italy as a powerful and effectual medicine, was published in Italy, in the year 1620. The preparation of tartar emetic itself was first published in 1631.

16. Benzoate of Antimony.

Benzoic acid combines with the oxide of antimony, and, by evaporating the solution, crystals are obtained. This salt is not altered by exposure to the air, but it is readily decomposed by heat.

II. Action of Alkalies, &c. on Antimony.

1. All the alkalies have a peculiar action on the alkalies, sulphuret of antimony. Sulphuret of antimony and potash. Antimony, potash form a preparation which is known by the name &c. of kermes mineral, a name which it derives from the red animal called kermes. This is prepared in the dry way, by mixing together one part of sulphuret of antimony and two of potash, and in proportion to the quantity of sulphuret, add a sixteenth part of sulphur. Fuse the mixture in a crucible, and pour it into an iron mortar. When it is cool reduce it to powder, and boil it in water; filter the liquid, and as it cools, a reddish brown powder is deposited. Wash the precipitate, first with cold, and then with boiling water, till it comes off impudic. It may be prepared in the humid way, by boiling 10 or 12 parts of pure liquid alkali with two of sulphuret of antimony, for half an hour, and then filtering the liquid; the kermes is deposited as it cools.

The compound which is first formed, is a hydrofulphuret of potash and antimony. When boiling water is added in sufficient quantity, the whole is dissolved, but the solution becomes turbid in cooling, and divides into two parts; the one, which is deposited in the form of a reddish brown powder, is the kermes mineral, and the other, which remains in solution, containing a smaller proportion of sulphur and oxide of antimony than the former, has been distinguished by the name of golden sulphur. The cause of the separation is, that the alkali, if it is not in great quantity, cannot hold the fulphurated oxide of antimony in solution while it is cold. What remains in solution after the spontaneous precipitation, contains a greater proportion of sulphur, and less of the oxide of antimony. When an acid is added to this solution, another precipitate is formed, which is of an orange yellow colour, from the greater proportion of sulphur, and on this account has been called golden sulphur. Kermes mineral, or the hydrofulphuret of antimony, according to Thenard, contains the following proportions.

| Brown oxide of antimony | 72.760 | |-------------------------|--------| | Sulphurated hydrogen | 20.298 | | Sulphur | 4.156 | | Water and loss | 2.786 | | **Total** | **100.000** |

From the analysis of the same chemist, the golden sulphur, or sulphur auratum, is also a hydrofulphuret, having a greater proportion of sulphur, and a smaller proportion of the oxide. The component parts are the following.

| Brown oxide of antimony | 68.300 | |-------------------------|--------| | Sulphurated hydrogen | 17.877 | | Sulphur | 12.000 | | **Total** | **98.177** |

2. The oxide of antimony has the property of combining with some of the earths during their vitrification, and communicating to them different shades of colour, more or less yellow and orange.

3. Most of the salts have a peculiar action on antimony or its sulphuret. By fusing in a crucible two parts of sulphuret of potash and one of antimony, the metal disappears, and a vitreous mass of a yellow colour is formed, which has a caustic property. Dif. Tellurium, dissolved in hot water, it affords, on cooling, a hydrofulphuret of antimony. The antimony has carried off the oxygen of the acid, and combined in the state of oxide, with the sulphuret of potash, which is formed by the sulphur of the acid uniting with the potash during the process.

The nitrates have a powerful action on antimony and its sulphuret. A mixture of two or three parts of nitrate of potash and one of antimony in fine powder, well rubbed together in a mortar, produces a lively detonation, by throwing it on burning coals, or projecting it into a red-hot crucible, or heating it to redness in a clothe vessel. This detonation is accompanied with a bright white flame; and the antimony is strongly oxidized by the oxygen of the nitre, which is decomposed, and reduced to its alkaline base. The residuum of this detonation is a white scoriified mass, which being washed with water, leaves a portion of the oxide of antimony united to a small quantity of potash, and affords beside another compound, with more of the alkali. The white matter which is first deposited, has been called washed diaphoretic antimony. The water which remains holds in solution a portion of metallic oxide, united to the potash of the nitre. The oxide in this case performs the part of an acid. This compound has been found susceptible of crystallization. It is decomposed by acids, and the precipitate from it, which is an oxide of antimony, has been distinguished by the names of cerule of antimony, magister of diaphoretic antimony, and pearly matter of Kerkringius.

When equal parts of nitre and sulphuret of antimony are treated in the same way, a vitrified mass is obtained, similar to what has been already described, by the name of liver of antimony.

III. Alloys.

Antimony enters into combination with the metals, and forms alloys with them, some of which are of considerable importance. But the alloys of antimony, with the metals already described, are either little known, or have been applied to no use. The alloys of cobalt and nickel, with antimony, have not been examined. With manganese antimony forms but an imperfect alloy, and the compound of antimony and bismuth is very brittle.

Besides the various preparations of antimony used in medicine, which are now comparatively but few in number, it is much employed in many arts. In the metallic state it is of the greatest importance as an alloy with other metals which will be afterwards mentioned. In the state of oxide, it is much used in the fabrication of coloured glazes, and of enamels for pottery and porcelain; particularly in forming different shades of brown, orange, and yellow colours. The oxide is mixed with different other metallic oxides, to produce various shades of colour.

Sect. XIII. Of Tellurium and its Combinations.

1. In the year 1782, Muller of Richenstein, in examining a gold ore, distinguished by the names of aurum paradoxum and aurum problematicum, conjectured that it Tellurium, it contained a peculiar metal. Bergman, to whom this mineralogist had sent a specimen of the mineral, could not, from the small quantity which he had received, ascertain whether it was really a new metal, or merely antimony, with which it possesses some common properties. He inclined, however, to the former opinion. This mineral was analyzed by Klaproth in the end of the year 1797, the account of which was published in 1798. By this analysis the conjecture of Muller was verified, and to the new metal Klaproth gave the name of tellurium.

2. This metal has been found in four different minerals. First, in that in which Klaproth first detected it, which is called white gold ore, a mineral found in the mountains of Fatzbay in Transylvania. In this mineral the tellurium is combined with iron and gold. The second is what is called graphic gold ore, which is composed of tellurium, gold, and silver. The third is known by the name of yellow gold ore of Nagyag. This mineral contains, besides tellurium, gold, silver, and a little sulphur. The fourth is a variety of the last, and is denominated gray gold ore. Besides the metals in the former, it contains a little copper. To obtain the metal from the ore, a quantity of it is lightly heated with six parts of muriatic acid, and having added three parts of nitric acid, it is then boiled. A considerable effervescence takes place, and the whole is dissolved. The solution being diluted with distilled water, is mixed with a solution of caustic potash, to dissolve the precipitate; and there remains only a brown, flaky matter, formed of the oxides of gold and iron. The alkaline solution of the oxide of tellurium is mixed with muriatic acid, to saturate the potash, and there is deposited a copious, very heavy, white powder. By forming this powder into a paste with oil, and heating it to redness in a small glass retort, the metal is obtained, partly fused and crystallized at the bottom of the retort, and partly sublimed at the upper part.

4. Tellurium is of a white colour, somewhat resembling lead, and has a considerable lustre. It is very brittle, and may be easily reduced to powder. It has a lamellated texture, similar to antimony. By slow cooling it assumes a crystalline form, especially on the surface. Its specific gravity is 6.115. It is one of the most fusible of the metals, and when heated in clothe vessels, it boils readily, and is sublimed in the form of brilliant globules, which adhere to the upper part of the vessels.

5. When tellurium is heated by the action of the blow-pipe on charcoal, it burns, after being melted, with a lively flame, of a blue colour, and green at the edges. It is entirely volatilized in the form of a greyish white smoke, diffusing a fetid odour, which Klaproth compares to that of radishes.

The oxide of tellurium is very fusible. By heating it in a retort, a yellow, straw-coloured mass is obtained, which assumes a radiated texture on cooling. When the oxide is heated on charcoal, and surrounded with it, it is so rapidly reduced, that it is accompanied with a kind of explosion.

6. Tellurium enters into combination with sulphur, and forms with it a sulphuret. This sulphuret is of a greyish colour, of a radiated structure, and is easily crystallized.

VOL. V. Part II.

I. Salts of Tellurium.

1. Sulphate of Tellurium.

One part of tellurium mixed in the cold, in a clothe vessel, with 100 parts of concentrated sulphuric acid, communicates to it a beautiful crimson colour. By adding water drop by drop to this solution, the colour vanishes, and the metal is deposited in the form of black flakes. When the solution is heated, the colour also disappears, and the oxide of tellurium is gradually precipitated in the state of white powder; but, when diluted sulphuric acid is employed, with the addition of a small quantity of nitric acid, a larger portion of tellurium is dissolved. The solution is transparent and colourless, and is not decomposed by adding water.

2. Nitrate of Tellurium.

Nitric acid readily dissolves tellurium, and forms a transparent, colourless solution, which being concentrated, spontaneously affords small, light, white, needle-shaped crystals, disposed in a dendritical form.

3. Muriate of Tellurium.

Nitromuriatic acid very readily dissolves tellurium, which is precipitated by adding a considerable quantity of water in the form of oxide. This is a white powder, which is soluble in muriatic acid.

The infusion of nut-galls added to solutions of tellurium in acids, occasions a flaky precipitate, which is of a yellow colour.

II. Action of Alkalies and Earths.

1. All the pure alkalies precipitate the solutions of tellurium in acids, in the form of white oxide. With an excess of alkali the precipitate is re-dissolved. With the alkaline carbonates a precipitate is obtained, which is much less soluble in excess of alkali.

2. The alkaline sulphurates added to solutions of tellurium in acids, produce a brown or black precipitate, as the metal is more or less oxidated. This precipitate sometimes resembles the hydrophilousphurates of antimony. The hydrophilousphuret of tellurium thus formed, exposed to heat on burning coals, burns with a small blue flame, and is volatilized in white smoke. No precipitate is formed by the prussiate of potash.

3. The action of the oxide of tellurium with the earths is not known; but from its great fusibility, it has been supposed that it is susceptible of forming a vitreous matter with the earths, and communicating to them a straw colour.

III. Action of Metals.

The alloys of tellurium are unknown.

Tellurium is separated from its solutions in acids, by precipitating zinc and iron, in the form of small, black flakes, which ted by zinc may be reduced to the metallic state on burning charcoal, and iron, or even by simple friction. Antimony causes a similar precipitation in a solution of nitrate and sulphate of tellurium. Tin produces a similar effect.

Tellurium has hitherto been found in such small quantities, that it has not yet been applied to any use. Were it found in abundance, it has been supposed, from its easy fusibility, that it might be of considerable importance in some of the arts. Sect. XIII. Of Mercury and its Combinations.

1. Mercury appears to have been known from the earliest ages. By comparing its properties with silver, and being in the fluid state, it has been called quicksilver. Mercury was long the subject of the researches of the alchemists, with the view of discovering the method of transmuting it into gold or silver. It was supposed to approach so near to these metals, particularly to the latter, in its nature, that all that was wanted for this transmutation, was to fix it, or bring it to the solid state. In consequence of the numerous experiments to which it was subjected, and the great variety of forms it assumed, they regarded it as the principle of all other bodies, and one of the elements of nature. It was supposed to exist in all metals, and also to form one of the component parts of many bodies. Hence, according to this theory, there were two kinds of mercury; the one the principle of a great number of bodies, and the other common mercury, or the metal known by that name. Hence, according to Beccher, it was called the mercurial principle, or the mercurial earth. But however extravagant the researches of the alchemists may now be considered to have been, it is to their labours that chemistry is indebted for the knowledge of many important properties and combinations of this metal.

2. Mercury is found in four different states. In the metallic state, alloyed with other metals, combined with sulphur, and with muriatic acid. 1. Native or virgin mercury is found in the cavities or clefts of rocks, in strata of clay, or of chalk, in the form of liquid globules, which are easily distinguished by their brilliancy. 2. It is found more frequently alloyed with other metals, or, as it is called when mercury is combined with a metal, amalgamated, and most frequently with silver. 3. A frequent ore of mercury is the red sulphuret, which is known by the name of cinnabar. The sulphuret of mercury is of various colours, from vermilion red to brown. Sometimes it effloresces on the surface of the ore, when it is called flowers of cinnabar, or native vermilion. 4. The fourth ore of this metal is the muriate. This salt is white and brilliant, and of a lamellated structure.

3. Native mercury is frequently alloyed with other metals; it is therefore of importance to be able to ascertain the proportions. For this purpose it is to be dissolved in nitric acid. If it contain gold, this metal remains in a state of powder at the bottom of the vessel. If alloyed with bismuth, it may be precipitated with water, which does not separate the oxide of mercury. Silver is detected by precipitating the solution by means of muriate of soda. The muriate of silver and the muriate of mercury fall down together; but the latter being more soluble in water than the former, may be easily separated.

The sulphuret of mercury may be decomposed by boiling it with eight times its weight, of a mixture of three parts of nitric, and one of muriatic acid; the metallic part is dissolved, and the sulphur remains in the state of powder.

To discover its purity. It may be known whether mercury has been adulterated with other metals, by its dull and less brilliant lustre, and by its foiling the hands, or white bodies on which it is rubbed, and by its dividing with more difficulty into round globules, which appear flat and uneven, adhere to the vessels in which they are agitated, and when poured along a smooth surface, by their dragging a tail. Mercury is also impure, when the globules do not readily run together, and when it is agitated with water, separating from it a black powder.

To procure mercury in a state of purity, or to re-purify it, as it is called, two parts of cinnabar and one of filings of iron are well triturated together, and distilled in an iron retort, introducing the beak of the retort into a receiver, with water. The iron has a greater affinity for the oxygen and the sulphur of the mercury than the latter. The mercury, therefore, rises in vapour, and is condensed by the water. There remains in the retort a sulphuret of iron, in which the metal is a little oxidised. The mercury thus obtained, being dried and passed through a skin, is very pure and brilliant.

4. Mercury is of a white colour, is one of the most brilliant of the metals, and when its surface is clean and not tarnished, makes a good mirror. Next to gold, platinum, and tungsten, it is the heaviest of the metals; its specific gravity is 13.568. It has no perceptible taste or smell.

5. At the ordinary temperature of the atmosphere mercury is always in the liquid state; but when it is exposed to a degree of cold equal to −39° it becomes solid. This was first discovered in the year 1759 by the academicians of Peterburgh. Similar experiments have since been frequently repeated. In 1772, Pallas succeeded in the congelation of mercury at Kranjnojark, by a natural cold equal to −55.5° Fahrenheit. Mercury was also congealed by a natural cold in 1775 at Hudson's bay. The freezing of mercury is now a common experiment by means of artificial cold, and the method of producing this has been already described, in treating of freezing mixtures. In some experiments which have been made on the congelation of mercury, it was remarked, that a slight shock was communicated to the person who held the tube containing the metal, by its sudden contraction at the moment it became solid. Mercury crystallizes in very small octahedrons. It appears to be malleable, for by striking it with a hammer in the solid state, it was flattened and extended.

6. At the temperature of 660° mercury boils, and is then converted into vapour. This vapour, like common air, is invisible and elastic. When mercury is exposed to the air, the surface becomes tarnished, and is covered with a black powder. This change is owing to the absorption of the oxygen of the air, and the conversion of the mercury into an oxide. This process is greatly promoted by applying heat to the mercury, or by shaking it, so that it may be brought in contact with the air. To this black powder, which is the first degree of the oxidation of the metal, the name of ethiops per se was formerly given, because it is obtained without the assistance of any other substance. According to Four-Blackcroy, this oxide contains

| Mercury | 96 | |---------|----| | Oxygen | 4 |

By By a strong heat the oxygen is driven off, and the mercury is reduced to the metallic state; but when the oxide is exposed to a more moderate degree of heat, it combines with more oxygen, and is converted into the red oxide, so called from its colour. This oxide may also be obtained, by exposing a quantity of mercury for some length of time in a vessel provided with a long narrow neck, by which means the vapours of the mercury are prevented from escaping, while the air is admitted. By this process the mercury is also converted into the red oxide; and, obtained in this way, it was formerly called precipitate per se, or red precipitate. This oxide may also be obtained by dissolving mercury in nitric acid, evaporating to dryness, and exposing the mass to a very strong heat, to drive off the acid. What remains being reduced to powder, is the red oxide of mercury, or red precipitate. This oxide, according to Fourcroy, contains one-tenth of its weight of oxygen. It is of an acrid disagreeable taste, and has so powerful an effect upon animal matters, that it may be considered as a poison. It corrodes the skin with which it comes in contact. When this oxide is exposed to heat, it is decomposed; part of its oxygen is given out, and it is converted into the black oxide. Even by exposure to the light of the sun, this change is effected, as it passes through different shades of colour.

7. Mercury does not enter into combination with azote, hydrogen, or carbone; but if hydrogen gas be kept in contact with the red oxide, it is gradually converted into the black oxide. If hydrogen gas be made to pass through a tube heated to redness, containing red oxide of mercury, a detonation takes place. The oxygen and hydrogen combine together to form water, while the mercury is reduced to the metallic state. This oxide may be also reduced by means of charcoal, with the assistance of heat. The oxygen of the oxide combines with carbone, and forms carbonic acid, and the mercury is revived.

8. Phosphorus combines with mercury with difficulty. Pelletier took equal parts of phosphorus and red oxide of mercury, and introduced them into a matrix, to which he added a little water, to cover the mixture. It was exposed to the heat of a sand bath, and agitated from time to time. The oxide soon became black, and united to the phosphorus. The water retained phosphoric acid; so that it appears to be a compound of phosphorus and the black oxide of mercury. The phosphuret of mercury, thus formed, becomes soft in boiling water, and acquires some consistence in the cold. When it is heated, it is decomposed. The phosphorus and the mercury are separately emitted. Exposed to a dry air, it diffuses white vapours, which have the odour of phosphorus.

9. Mercury combines readily with sulphur, either by simple trituration in the cold, or by the action of heat. One part of mercury and two of sulphur, triturated together in a mortar, the mercury soon disappearing, form a black powder, which was formerly distinguished by the name of ethiops mineral. Fourcroy is of opinion, that in this process the mercury is oxidated, and the sulphur is combined with the black oxide; in support of which, he states that the sulphur cannot be separated from the mercury, but by some chemical action. Berthollet supposes that this substance contains sulphurated hydrogen; and hence it is concluded that ethiops mineral is a hydrogenous fulphuret of mercury, composed of mercury, sulphur, and sulphurated hydrogen.

When this compound is heated in an open vessel, the sulphur, which is in a state of minute division, takes fire, and is soon reduced to sulphurous acid gas. The mercury is at the same time more strongly oxidated; is converted to a deep violet-coloured powder; and if in this state it be heated in a matrix, it is sublimed in the form of a deep red cake, of a brilliant, crystalline appearance. This substance was formerly called artificial cinnabar, or, in the present language of chemistry, red sulphurated oxide of mercury. Various processes have been given for the preparation of this substance. Seven parts of mercury squeezed through leather to purify it, are to be fused with one part of sulphur in an earthen vessel, agitating the mixture till it is completely reduced to the black sulphurated oxide. Introduce this into a matrix, placed in a crucible furnished with sand, and expose it gradually to the heat of a furnace, which is to be increased till the matter is sublimed, and collected, at the top of the vessel. It is then removed, and when the vessel is broken, a red mass is obtained, with a degree of beauty and brilliancy in proportion to the temperature which has been employed, and the small quantity of sulphur which it retains. Fourcroy considers this as a compound of sulphur and the red oxide of mercury; but according to Proust, it is a sulphuret of mercury; that is, a compound of sulphur and metallic mercury. Its component parts are,

| Mercury | 85 | |---------|----| | Sulphur | 15 |

This sulphuret is of a fine scarlet colour. It is not altered by exposure to the air, and is insoluble in water. The specific gravity is 10. When a sufficient degree of heat is applied to it, it takes fire, and burns with a blue flame. When reduced to powder, vermilion, it is then called vermilion, which is well known as a paint.

10. The order of the affinities of mercury is the following:

| MERCURY | OXIDE OF MERCURY | |---------|------------------| | Gold | Muriatic acid | | Silver | Oxalic | | Tin | Succinic | | Lead | Arfénic | | Bismuth | Phosphoric | | Platina | Sulphuric | | Zinc | Sulfuric | | Copper | Tartaric | | Antimony| Citric | | Arfénic | Sulphurous | | Iron | Nitric | | | Fluoric | | | Acetic | | | Boracic | | | Prussic | | | Carbonic |

4 M 2 L Salts I. Salts of Mercury.

1. Sulphate of Mercury.

1. Sulphuric acid forms salts with the different oxides of mercury, and with different proportions of these oxides, so that there is a considerable variety of the sulphates of mercury. This seems to depend on the nature of the action between sulphuric acid and mercury, according to the temperature in which the combination is made, and the quantity of acid employed.

2. Sulphuric acid has no effect on mercury in the cold; but if two parts of mercury and three of sulphuric acid be introduced into a retort, and exposed to heat, an effervescence takes place, with the evolution of sulphurous acid gas. If the process be stopped, when the mercury is converted into a white mass, and there yet remains part of the liquid, it is found to be acid and corrosive, and it reddens vegetable blues. This is the sulphate of mercury with excess of acid. This acidulous sulphate of mercury contains very different proportions of sulphuric acid, according to the original quantity employed. If this sulphate be washed with a smaller quantity of water than is necessary for its complete solution, and if this be repeated till the water no longer changes vegetable blues, there remains a white salt without acidity, and which is much less acid and corrosive than the saline mass from which it is obtained. This may be considered as a neutral sulphate of mercury.

3. It is of a white colour, crystallizes in plates, and in fine, needle-shaped prisms. The taste is not acid. It is soluble in 500 parts of cold water, and in one half that quantity of boiling water. When crystallized, it is composed of

| Mercury | 75 | | Oxygen | 8 | | Sulphuric acid | 12 | | Water | 5 |

It is soluble both in cold and hot water, without being decomposed. The pure alkalies and lime water, occasion a precipitate of a grayish-black powder. When sulphuric acid is added, it is then reduced to the state of acidulous sulphate, and its solubility increases in proportion to the additional quantity of acid. A twelfth part of acid renders it soluble in 157 parts of cold water, and in 33 of boiling water. But if \( \frac{1}{4} \) of this quantity of cold water be added, it combines with the whole excess of acid, and forming a liquid of greater density than when it is diluted with 157 parts of water necessary for its complete solution, it dissolves much more of the sulphate of mercury, and brings the salt to a state of greater acidity. It then requires 500 parts of water for its solution.

4. But if the same proportions of sulphuric acid and mercury, namely, three parts of acid, and two of mercury, be exposed for a longer time to the action of heat, a greater proportion of sulphuric acid is decomposed, and the mercury combines with a greater proportion of oxygen. The salt thus obtained, possesses different properties from the former. It crystallizes in small prisms, and when it is neutralized, it is of a dirty-white colour; but if it be obtained in the dry state, it is pure white, and in this state it is combined with an excess of acid. It is then deliquescent in the air; but, in the neutral state, it undergoes no change. When hot water is added to this salt, it is converted into a yellow powder, which has been long distinguished by the name of turpeth mineral.

5. It was formerly supposed that turpeth mineral, which is obtained by the addition of warm water to this salt, was a simple oxide of mercury, without any portion of sulphuric acid. Fourcroy mentions, that Rouelle first conjectured, that it was combined with a certain portion of the acid, and that his experiments have verified and confirmed this conjecture: for in treating turpeth mineral, after being well washed with muriatic acid, this solution precipitates by means of muriate of barytes, a sulphate of barytes from this base. Fourcroy denominates this salt sulphate of mercury with excess of acid, or yellow sulphate of mercury. It is soluble in 600 parts of boiling water; but another sulphate of mercury remains in the solution. This contains an excess of acid, and is therefore more soluble in water.

6. From a series of experiments which Fourcroy made on this subject, he concludes, that there are three distinct sulphates of mercury. 1. The first is the neutral sulphate of mercury, which crystallizes, is soluble in 500 parts of cold water, and forms a copious precipitate with the alkalies, which is not decomposed by nitric acid, but forms a mild muriate of mercury with the addition of muriatic acid. 2. The acidulous sulphate of mercury, which is more soluble than the former, is precipitated of an orange colour by means of the alkalies. The excess of acid is removed, and also a portion of the salt, with \( \frac{1}{4} \) of the water necessary for its complete solution. The neutral sulphate of mercury remains behind, and is not decomposed by means of nitric acid. 3. The third sulphate of mercury contains an excess of base, or of the oxide of mercury. It is of a yellow colour, soluble in 200 parts of water, and is precipitated of a gray colour by the alkalies. It is decomposed by nitric acid; and muriatic acid converts it into a hyperoxymuriate of mercury.

2. Sulphate of Ammonia and Mercury.

This triple salt is formed by adding ammonia to a preparation of neutral sulphate of mercury. A copious gray precipitate is thrown down, which, being exposed to the light of the sun, is partly reduced to the metallic state, and partly to that of a gray powder. This last is the sulphate of ammonia and mercury. It is soluble in ammonia; and by evaporation, brilliant polygonal crystals are formed. Or, if a large quantity of water be added to the solution, it becomes white and milky, and there is precipitated the same salt, but without any regular form. This salt has a pungent, astringent taste. When it is heated, it gives out ammonia, azotic gas, a small quantity of metallic mercury, and a little sulphite of ammonia. There remains in the retort yellow sulphate of mercury. According to the analysis of Fourcroy, this triple salt is composed of... 3. Nitrate of Mercury.

1. Nitric acid is rapidly decomposed by mercury. It is accompanied with effervescence, and the evolution of nitrous gas. The mercury combines with part of the oxygen of the acid; it is thus oxidated, and is then dissolved in the remaining portion of the acid. This solution of mercury in nitric acid, when it is made in the cold, is colourless, very heavy, and so extremely caustic, that it has been employed as an elixir, under the name of mercurial water. It produces an indelible brownish black spot on all animal and vegetable substances. By spontaneous evaporation it affords regular transparent crystals, composed of two four-sided pyramids, truncated near their bases, and on the four angles which result from the union of the pyramids. But different crystals are formed, according to the nature of the solution, and the evaporation, whether it has been more slowly or more rapidly conducted. When this solution of mercury in nitric acid is made in the cold, the compound formed is a nitrate of mercury without excess of the oxide or base; but if mercury be added to this solution, and the action be aided by heat, a new portion of the oxide is dissolved. It is then a nitrate of mercury with excess of base. Fourcroy distinguishes three nitrates of mercury. 1. Nitrate of mercury neutralized. From this regular crystals are obtained, and it is not precipitated by water. 2. The acidulous nitrate of mercury, or with excess of acid. This is obtained by dissolving the first in water containing nitric acid, or by adding this acid to the other nitrates. 3. The nitrate of mercury with excess of oxide. This exists in the solution precipitated by water, or by exposing the other nitrates to the action of heat. In this way is produced what was formerly called nitrous turpeth.

2. These different nitrates of mercury possess many common properties, but are sufficiently distinguished by others, and particularly by their decomposition. When the nitrate of mercury is placed upon burning coals, it detonates feebly, although with a vivid white flame, when it has been sufficiently dried; but when it is moist it melts, blackens, extinguishes that part of the coal which it touches, and throws out small red sparks, with a slight decrepitation about the dried edges of the mass. The nitrate of mercury with excess of oxide possesses a still more feeble detonating property. The nitrate of mercury with excess of acid boils up, melts very rapidly, swells greatly, and exhales red vapours, with very little detonation. If the nitrate of mercury, neutralized, be heated in a crucible without any combustible matter, it melts, exhales nitrous gas, becomes of a deep yellow colour, then passes to an orange, and at last is converted into a deep red. In this state it was formerly called red precipitate. It is the red oxide of mercury, which is obtained by the decomposition of the nitrate.

3. The pure nitrate of mercury exposed to the air in the state of crystals, is soon changed. It gradually absorbs oxygen from the atmosphere, and passes from a white to a yellow colour. This is the nitrous turpeth. It is a yellow oxide of mercury combined with a small portion of nitric acid, or a nitrate of mercury with excess of base. The yellow colour becomes deeper with the addition of boiling water. The nitrous turpeth, it has been observed, contains a greater quantity of oxygen than that which is prepared by sulphuric acid, and from this circumstance it is more readily converted into red oxide by the action of heat.

4. The nitrate of mercury is decomposed by all the Decomposition alkalies, but with different phenomena, according to the state of the combination, and particularly the degree of oxidation of the base. Bergman has distinguished the two solutions of mercury, that which is not precipitated by water, from that which is precipitated by the different products which are obtained by means of alkalies. The nitrate of mercury affords with potash, a yellowish white oxide; with carbonate of potash, a white oxide; and with ammonia, an oxide of a dark gray colour. Sulphuric acid and the sulphates occasion a precipitate in form of a white powder. Muriatic acid and the muriates give a thick mass resembling curd. But the solution which is precipitated by water, and which is more acid, and less disposed to crystallize, affords precipitates by means of the fixed alkalies, of a deeper yellow or brown colour. By means of ammonia, a white precipitate is formed; by means of the sulphuric acid and the sulphates, a yellow precipitate, and by the muriatic acid, a more copious, curdled matter. Fourcroy has observed in the decomposition of nitrate of mercury with excess of acid, that a precipitate in the state of black powder is formed, with a great addition of the alkali; but if it be added in small quantity, the precipitate is white or gray. A copious precipitate is obtained, from the clear supernatant solution, by diluting it with water. The same white precipitate is obtained, by mixing together nitrate of mercury and nitrite of ammonia. By evaporating the liquid, which is rendered turbid by the addition of water, fixed prismatic crystals are deposited, as the ammonia is volatilized. The white precipitate is a brittle salt, which has very little solubility, having an excess of oxide, of mercury, and ammonia. The component parts of this salt, according to Fourcroy are:

| Acid and water | 15.80 | | Oxide of mercury | 68.20 | | Ammonia | 16.00 |

100.00

5. From a solution of mercury in nitric acid, Mr Howard prepared a fulminating powder possessed of fulminating peculiar properties; the process which he found to ing powder, after being, is the following:

"One hundred grains, or a greater proportional quantity, of quicksilver (not exceeding 500 grains) are to be taken, dissolved, with heat, in a measured ounce and a half of nitric acid. This solution being poured cold upon two measured ounces of alcohol, previously introduced into any convenient glass vessel, a moderate heat is to be applied until an effervescence is excited. A white fume..." Mercury fume then begins to undulate on the surface of the liquor; and the powder will be gradually precipitated upon the cessation of action and re-action. The precipitate is to be immediately collected on a filter, well washed with distilled water, and carefully dried in a heat not much exceeding that of a water bath. The immediate edulcoration of the powder is material, because it is liable to the re-action of the nitric acid; and, whilst any of that acid adheres to it, it is very subject to the influence of light. Let it also be cautiously remembered, that the mercurial solution is to be poured upon the alcohol.

"I have recommended quicksilver to be used in preference to an oxide, because it seems to answer equally, and is less expensive; otherwise, not only the pure red oxide, but the red nitrous oxide and turpeth may be substituted; neither does it seem essential to attend to the precise specific gravity of the acid or the alcohol. The rectified spirit of wine and the nitrous acid of commerce never failed, with me, to produce a fulminating mercury. It is indeed true, that the powder prepared without attention, is produced in different quantities, varies in colour, and probably in strength. From analogy, I am disposed to think the white is the strongest; for it is well known, that black precipitates of mercury approach the nearest to the metallic state. The variation in quantity is remarkable; the smallest quantity I ever obtained from 100 grains of quicksilver being 120 grains, and the largest 132 grains. Much depends on very minute circumstances. The greatest product seems to be obtained, when a vessel is used which condenses and causes most ether to return into the mother liquor; besides which, care is to be had in applying the requisite heat, that a speedy and not a violent action be effected. One hundred grains of an oxide are not so productive as 100 grains of quicksilver.

This powder, struck on an anvil with a hammer, explodes with a stunning disagreeable noise, and with such force, as to indent both the hammer and the anvil. Half a grain or a grain, if quite dry, is as much as ought to be used on such an occasion. The shock of an electric battery, sent through five or six grains, produces a very similar effect. The powder explodes at the 368th degree of Fahrenheit's thermometer. A quantity of it, sufficient to discharge a bullet from a gun, with a greater force than an ordinary charge of gunpowder, always bursts the piece. Ten grains of the powder, exploded in a glass globe, produce only four cubic inches of air, consisting of carbonic acid gas and nitrogen, or azotic gas.

This powder is composed of sulphuric, nitric, and muriatic acids. When concentrated sulphuric acid is poured upon it, an immediate explosion takes place. According to the experiments of Mr Howard, this powder consists of oxalate of mercury, and nitrous etherised gas. But it appears that the nature of the component parts varies with the different modes which are followed in its preparation. When it is prepared with little heat, it consists of nitric acid, oxide of mercury, and a peculiar vegetable substance; but by continuing the heat during the fermentation, a greenish colour is communicated to the powder. It is then found to be composed of ammonia, oxide of mercury, and a greater proportion of the vegetable matter. Its detonating power is more feeble, and it gives out a blue flame when placed on hot coals." By boiling the mixture for half an hour, it is composed of oxalate of mercury, and a small proportion of vegetable matter; does not detonate, but decrepitates when it is heated.*

4. Muriate of Mercury.

Muriatic acid has no action whatever on mercury; but it combines readily with its oxides, and forms salts which have been the subject of research among chemists, almost in every age. The muriates of mercury were known to the Arabs in the 10th and 11th centuries. They were the first objects of study and examination with the alchemists, in their search after the philosopher's stone; and since chemistry assumed the form of a science, they have greatly occupied the attention of philosophers, in discovering their nature and properties.

There are two compounds of muriatic acid and two oxides of mercury, which possess very different properties, according to the degree of oxidation of the mercury.

Muriatic acid precipitates the oxides of mercury from their solutions in sulphuric and nitric acids. If muriatic acid be added to the yellow sulphate of mercury, or to the nitrate of mercury which is precipitable by water, a muriate of mercury is obtained, which is soluble in water, and which, on account of its properties, was formerly called corrosive sublimate, or corrosive muriate of mercury. But if muriatic acid be added to the acidulous sulphate of mercury, or to the nitrate of mercury which affords no precipitate with water, a white, insoluble, infusible precipitate is obtained, which was formerly called sweet mercury or calomel, and is now known by the name of submuriate, and sometimes sweet muriate of mercury.

The muriate of mercury, or corrosive sublimate, may be prepared by the following process. Boil two parts of mercury with two and a half of sulphuric acid in a matras, with the heat of a sand bath, to dryness. Let this dry mass be mixed with four parts of dried muriate of soda, and let the whole be sublimed in a glass vessel, by gradually increasing the heat. In the first part of this process, part of the sulphuric acid is decomposed; the mercury combines with the oxygen and forms an oxide, which is dissolved in the undecomposed part of the sulphuric acid, and a sulphate of mercury is thus obtained. The muriate of soda being mixed with this salt, produces another decomposition. The muriatic acid combines with the mercury, forming the muriate of mercury, which is sublimed; and the sulphuric acid of the sulphate of mercury combines with the soda, forming a sulphate of soda, which remains behind.

The muriate of mercury, thus obtained, forms a beautiful white, semitransparent mass, which is found to be composed of small prismatic crystals in the form of needles. It may be obtained by evaporation, in the form of cubes or rhombooidal prisms, or four-sided prisms, having the alternate sides narrower, and terminated by two-sided summits. The taste is extremely acrid and caustic, and the metallic impression remains long on the tongue. The specific gravity is 5.1398. It is soluble in 20 parts of cold water, and in less weight of boiling water. This salt is not altered by exposure to to the air; and, when it is sublimed by heat, it remains unchanged. It is soluble in sulphuric, nitric, and muriatic acids, and, when these solutions are evaporated, the muriate of mercury is obtained unaltered. It is precipitated by all the alkalies and earths, of an orange-yellow colour, which gradually changes to a brick-red. The carbonates of the fixed alkalies afford a permanent yellow colour. Ammonia forms with it a triple salt. The component parts of this salt, according to Mr Chenevix, are,

| Oxide of mercury | 82 | |------------------|----| | Acid | 18 | | | 100 |

Muriate of mercury is one of the most violent poisons known. When taken internally, it produces nausea and vomiting, with severe pain, and, in a short time, corrodes the stomach and bowels. Externally, it is employed as an emetic for destroying fungous flesh. It sublimes readily when heated, and is extremely injurious in the state of vapour, to those who breathe it.

**Submuriate of Mercury.**—This salt is prepared by triturating together in a glass mortar, four parts of muriate of mercury or corrosive sublimate, with three of mercury, till the latter disappear. When this is formed into a uniform mass, it is put into a matrix, of which it should fill 7, and it is to be sublimed with the heat of a sand bath. When the process is finished, the phial is broken; and the white matter at the upper part of the vessel, and the red matter at the bottom, are to be separated, and the remaining part of the mass is to be sublimed, and afterwards reduced to a fine powder, which is to be well washed with boiling water.

In this process, it is obvious, that the mercury which is added, combines with part of the oxygen of the oxide of mercury, formerly combined with the muriatic acid; and the whole of the oxide of mercury having now a smaller proportion of oxygen, is combined with a smaller proportion of muriatic acid. This will appear from the proportions of its component parts, as they have been ascertained by Mr Chenevix.

Oxide of mercury in calomel contains,

| Mercury | 89.3 | |---------|------| | Oxygen | 10.7 | | | 100.0 |

Calomel is composed of

| Oxide of mercury | 88.5 | | Muriatic acid | 11.5 | | | 100.0 |

Submuriate of mercury, or calomel, is generally in the form of a white, solid mass; but it is susceptible of crystallization in four-sided prisms, terminated by pyramids. It has scarcely any taste, has no poisonous property, and is very little soluble in water. The specific gravity is 7.1758. It becomes dark coloured by exposure to light, is phosphorescent when rubbed in the dark, and requires a higher temperature for its sublimation than the muriate of mercury. It is converted into muriate or corrosive sublimate, by the nitric and oxymuriatic acids.

This salt, which is now generally known in the shops, by the name of calomel or sweet mercury, was formerly described under a great variety of names, derived from its effects, or the mode of its preparation. In the beginning of the 17th century, it was regarded as an important secret. But, in the year 1608, Beguin described it very accurately, in his tyrocinium chemicum, under the name of the dragon tamed, on account of the corrosive sublimate from which it was prepared, being deprived of its poisonous and destructive qualities. At different periods it was distinguished by other names, as aquila alba, aquila mitigata, manna metallorum, panchymagogus quercetanus, &c. The use of this salt as a purgative, and indeed in all cases where mercurial preparations are required, is well known.

**5. Muriate of Ammonia and Mercury.**

If ammonia be added to a solution of muriate of mercury, or corrosive sublimate, a white precipitate is obtained, which is a triple salt, formed by the combination of the ammonia with the muriate of mercury. This white precipitate has at first an earthy taste, which becomes afterwards metallic and disagreeable. It seems to be insoluble in water. Sulphuric acid forms with this triple salt, corrosive sublimate, and sulphate of ammonia and mercury. Nitric acid converts it into corrosive sublimate and nitrate of ammonia and mercury. It is completely soluble in muriatic acid, and there is formed a muriate of mercury and ammonia. This preparation was known to the alchemists, and distinguished by the names of sal alembroth, and sal of wisdom. The component parts of this salt, according to Fourcroy, are

| Acid | 16 | | Oxide of mercury | 81 | | Ammonia | 3 | | | 100 |

*Fourcroy.*

**6. Hyperoxymuriate of Mercury.**

The salt was formed by Mr Chenevix, by passing a current of oxymuriatic acid gas through water, in which there was red oxide of mercury. The oxide became of a dark brown colour, and a solution appeared to have taken place. The liquor was evaporated to dryness, and a salt was obtained which consisted partly of corrosive sublimate, and partly of hyperoxymuriate of mercury. By separating the latter, and crystallizing it again, it was obtained nearly pure. This salt is more soluble than corrosive sublimate, four parts of water retaining it in solution. Hyperoxymuriatic acid is given out by the addition of sulphuric, or even weaker acids, and the liquid assumes an orange colour.

**7. Fluate of Mercury.**

Fluoric acid combines only with the oxide of mercury; or the soluble fluates mixed with a solution of nitrate of mercury, produce a precipitate of a white colour, which is the fluate of mercury, of which the properties are little known.

**8. Borate:** 8. Borate of Mercury.

Boracic acid has no direct action on mercury, but by mixing together a solution of borate of soda with a solution of nitrate of mercury, a yellowish precipitate is obtained, which is the borate of mercury. This salt acquires a greenish colour by exposure to the air. Lime water forms a precipitate of a red powder.

9. Phosphatate of Mercury.

Phosphoric acid has no action on mercury, but it combines with its oxide. This salt may be prepared by precipitating the nitrate of mercury in solution, by means of phosphatate of soda. A white precipitate is formed, which is phosphatate of mercury. This salt is insoluble in water, phosphoresces when rubbed in the dark, and is decomposed by heat, giving out phosphorus.

10. Carbonate of Mercury.

By precipitating the solutions of mercury in the other acids by means of the alkaline carbonates, a white precipitate is obtained, which is a carbonate of mercury.

11. Arseniate of Mercury.

When arsenic acid is distilled in a retort with mercury, it is partially decomposed. Arsenious acid is sublimed, with a portion of metallic mercury and a small quantity of yellow oxide. There remains behind a yellow mass, which is arseniate of mercury. It is insoluble in water, and in sulphuric and nitric acids. It is soluble in muriatic acid, and affords by evaporation and sublimation, the muriate of mercury, or corrosive sublimate. Arsenic acid precipitates the fulphate and nitrate of mercury in the form of a white powder, which is also arseniate of mercury.

12. Tungstate of Mercury.

This salt is formed by adding to a solution of nitrate of mercury, an alkaline tungstate. This salt is decomposed, and the tungstate of mercury is precipitated in the form of a white insoluble powder.

13. Molybdate of Mercury.

Molybdic acid precipitates mercury from its solution in nitric acid, in the form of a white flaky powder. It is also insoluble in water.

14. Chromate of Mercury.

An alkaline chromate in solution, added to a solution of nitrate of mercury, forms a precipitate of a fine reddish purple colour. This is the chromate of mercury, which is insoluble in water, and which Vauquelin, who discovered it, suggests to be employed as a pigment.

15. Columbate of Mercury.

Unknown.

16. Acetate of Mercury.

Acetic acid combines with the oxides of mercury, and forms different salts, according to the oxide which enters into the combination. With the red-oxide of mercury it forms a salt which does not crystallize; but when the liquid is concentrated, and evaporated to dryness, it affords a yellow deliquescent mass. When this salt is dissolved in water, it divides into two parts; the one falls down in the state of yellow powder, which is acetate of mercury with excess of base; and the other part remains in solution, because it contains an excess of acid.

2. But when nitrate of mercury is precipitated by means of alkalis, and the precipitate is dissolved in acetic acid, the solution yields by evaporation and cooling, acetate of mercury, in thin brilliant flakes. This salt may also be formed by mixing together solutions of acetate of potash and nitrate of mercury. The acetate of mercury appears in the form of large flat crystals, which have an acid taste, and are scarcely soluble in water. This latter salt is a compound of acetic acid and the oxide of mercury, with a smaller proportion of oxygen. It is employed in medicine, and forms the principal ingredient of Keyfer's pills.

17. Oxalate of Mercury.

Oxalic acid combines with the oxide of mercury, and forms an oxalate in the state of white powder, which is scarcely soluble in water. It becomes black by exposure to the light. When it is heated it detonates. This salt may also be obtained, by adding oxalic acid to a solution of the nitrate or sulphate of mercury.

18. Tartrate of Mercury.

Tartaric acid forms an insoluble salt of a white colour, with the oxide of mercury, which becomes yellow by exposure to the light.

19. Tartrate of Potash and Mercury.

This triple salt may be prepared by boiling together in water, one part of oxide of mercury, and five of tartar. Crystals of the triple salt are obtained by evaporating the liquid.

20. Citrate of Mercury.

Citric acid produces an effervescence with the red oxide of mercury, changes into a white colour, and then unites it in one mass. This salt is scarcely soluble in water. It has a metallic taste, and is decomposed by nitric acid.

21. Malate of Mercury.

When malic acid is added to a solution of nitrate of mercury, a white precipitate is formed, which is malate of mercury.

22. Benzoate of Mercury.

Benzoic acid forms with the oxide of mercury, a salt in the state of white powder, which is insoluble in water, and is scarcely altered by exposure to the air. It is decomposed by heat.

23. Succinate of Mercury.

Succinic acid combines with the oxide of mercury with the assistance of heat, and forms with it an irregular mass in which some crystals are observed.

24. Saccolate 24. Saccolate of Mercury.

By adding falcatic acid to a solution of nitrate of mercury, a white precipitate is formed, which is facolate of mercury.

25. Mellate of Mercury.

Mellitic acid added to a solution of nitrate of mercury, produces a copious precipitate, which is re-dissolved by the addition of nitric acid.

26. Prussianate of Mercury.

This salt is obtained by boiling the red oxide of mercury with Prussian blue. It forms crystals in four-sided prisms, terminated by four-sided pyramids. The specific gravity is 2.7612. It forms triple salts with sulphuric and muriatic acids, the properties of which are not known.

II. Action of Alkalies, &c.

There is no action between mercury and the alkalies or alkaline earths; but the alkalies combine with the oxides of mercury, and form with them compounds in which the latter seem to act the part of acids. Some of these compounds have been already treated of, in speaking of the action of ammonia on some of the mercurial salts.

Salts formed with the alkalies and earths, have no action on mercury or its oxides, if we except the muriates. By dissolving the muriate of mercury in a solution of muriate of ammonia, a triple salt, which is muriate of ammonia and mercury, and which has been already described, is obtained.

Mercury is one of the metals of the most extensive utility. In the metallic state it is applied to the construction of meteorological instruments, as the barometer and thermometer. Mercury is also applied to a great variety of purposes in arts; in gilding with silver and gold; in forming an amalgam with tin for covering the back of mirrors; and in metallurgy for the purpose of separating gold and silver from their ores. Mercury is also of considerable importance for the purposes of chemistry. Many of its preparations form some of the most effectual and most certain remedies in different diseases.

Sect. XV. Of Zinc and its Combinations.

1. Paracelsus is the first who speaks of zinc under its present name. It is supposed that the Greeks were acquainted with this metal in the state of compound with copper, which formed the famous Corinthian bronzes; but it does not appear that they made any distinction between it and other metals. It is particularly mentioned by Albertus Magnus, who died in 1280, and he seems to have known that it inflamed, and communicated a colour to metals with which it was combined. The method of obtaining zinc from the ore called calamine, is mentioned by Hennecel in his Pyrologia in 1721. Swab extracted it by distillation in 1742, and Margraaf was occupied with this process in 1746. Zinc was supposed by the earlier chemists to be a variety or compound of some of the other metals. Lemery thought it was a kind of bismuth, and Homberg took it for a mixture of iron and tin; while others supposed that it was tin rendered brittle by sulphur, or that it was a coagulated mercury.

2. Zinc is found in four different states: In the state of oxide, in the state of sulphuret, in that of sulphate, and in that of carbonate. 1. In the state of oxide it is known by the name of calamine, or lapis calaminaris, deposited in a regular form, or in that of incrustations and stalactites, in the cavities of metallic veins. 2. The sulphuret of zinc, known by the name of blende, is sometimes disposed in scales, and sometimes crystallized in tetrahedrons, or octahedrons. It is frequently found in lead mines, accompanying the ores of lead. 3. The phosphate of zinc, which is found native, is readily known by its white colour and transparency, its strong acid taste, and solubility in water. It is generally found in a stalactitical form, or in fine silky crystals, like those of amiantus. 4. The native carbonate of zinc, which is sometimes confounded with the oxide or calamine, forms another ore of zinc. It is transparent, white, or yellowish. It is infusible and insoluble in water, and dissolves with effervescence in nitric and muriatic acids.

3. To reduce oxides of zinc to the metallic state, the Analytical ore is pulverized and mixed with charcoal, and the mixture is heated in a crucible covered with a plate of copper. The zinc is sublimed in the metallic state, and combines with the copper, which it converts into brass; and in this rude process the richness of the ore is ascertained by the intensity of the colour. The sulphurets of zinc are reduced by roasting, by which process the sulphur is separated, and the residuum is then treated in the same way as the oxides. In the humid way Bergman has proposed to analyze the oxides of zinc by means of sulphuric acid, and then by precipitating the oxide by carbonate of soda, he has ascertained that 193 parts of this precipitate give 100 parts of the metal.

4. Zinc is of a brilliant white colour with a bluish tinge, which is very perceptible in its metallic state, and of a distinct lamellated texture; but the plates of which it is composed are smaller than those of bismuth and antimony. The specific gravity is 7.190. Zinc is not quite so brittle as the preceding metals. It requires a smart and sudden blow to separate its fragments. It is susceptible of a slight degree of malleability, for, by gradual and cautious pressure, it may be formed into thin plates, which have some degree of elasticity. It has a slight odour, and a peculiar taste, which is communicated to the fingers when they are rubbed on this metal.

5. When zinc is exposed to a heat of about 700° it melts, and by increasing the heat it evaporates, so that heat in close vessels it may be distilled. When allowed to cool slowly after being in fusion, it crystallizes in fine needles. When zinc is exposed to the air, it undergoes very little alteration in the cold. Its brilliancy is slightly tarnished, and it becomes at length covered with a thin gray oxide. When zinc is fused in close vessels and exposed to heated air, at the moment it becomes solid on the surface, it exhibits a great variety of shades of colour, which is the commencement of oxidation. When it is kept in fusion, in the open air, the surface becomes covered with a gray pellicle, which being removed, is succeeded by another, till the whole Zinc, &c. of the zinc is converted into this gray-coloured matter, which is an oxide of zinc. This process may be promoted by agitating the vessel, so that the metal in fusion may be exposed to the air. By heating together the gray pellicles which have been collected in an open vessel, the whole is converted into a uniform gray powder, which at last affumes a yellowish colour. The yellow oxide, thus formed, has acquired an additional weight of about 17 per cent. of the metallic zinc.

When this metal is heated to redness in an open vessel, by agitating the vessel, it suddenly takes fire, and burns with a very brilliant white and somewhat greenish flame. Zinc is at the same time reduced to a state of vapour, which is condensed in the air, in light, filamentous, white flakes, of a very delicate texture. This is an oxide of zinc. It has been distinguished by different names, as flowers of zinc, nihil album or white nothing, lana philosophica, or philosophic wool.

Thus, there are two oxides of zinc; the gray oxide, which consists of about 88 parts of zinc, and 12 of oxygen, and the white oxide, which, according to Proust, is composed of 80 parts of zinc, and 20 of oxygen.

6. There is no action between azote and this metal. Hydrogen gas, it is supposed, dissolves a small quantity of zinc; for by dissolving zinc in diluted sulphuric acid, the hydrogen gas which is obtained by the decomposition of the water, has been found to hold a little zinc in solution, which is deposited on the sides of the jars containing the gas. It is supposed too, that zinc is sometimes combined with carbure, because hydrogen gas obtained by the above process, is sometimes contaminated with carbonated hydrogen gas.

7. Zinc combines with phosphorus, and forms a phosphuret. This may be prepared by adding small bits of phosphorus to zinc in fusion, but previously throwing in a little resinous matter, to prevent the oxidation of the zinc. This was the process by which Pelletier formed the phosphuret of zinc. This phosphuret is of a white colour and metallic lustre. It has some degree of malleability. When it is hammered, it emits the odour of phosphorus, and when exposed to a strong heat, it burns like zinc. Phosphorus also enters into combination with the oxide of zinc, and forms with it a phosphorated oxide. This is formed by distilling in an earthen-ware retort, equal parts of oxide of zinc, and phosphoric glass, with one-sixth of charcoal powder. A strong heat is applied, and a metallic substance of a silvery white colour is sublimed, which has a vitreous fracture. When it is heated by the blow-pipe, the phosphorus burns, and there remains behind a vitreous matter, which is transparent while in fusion, but becomes opaque when it is cold.

8. Zinc has not been combined directly with sulphur. When they are heated together in a crucible, the sulphur separates without producing any other change on the zinc than that of being a little more fusible; but it has been observed that sulphur and zinc, when fused together in a crucible, enter into combination, as the zinc is oxidized. This compound affumes a brownish gray colour. Guyton afterwards discovered that sulphur and the oxide of zinc readily unite together by fusion, and that the compound is of a gray colour, similar to the native sulphuret of zinc, as it has been called, or the sulphurated oxide of zinc, according to this experiment; but according to Proust, the zinc, &c., ore of zinc, which is known by the name of blende, is a sulphuret, that is, sulphur combined with zinc in the metallic state.

9. The order of the affinities of zinc and its oxide is Affinities, the following:

| Zinc | Oxide of Zinc | |------|--------------| | Copper | Oxalic acid | | Antimony | Sulphuric acid | | Tin | Muriatic acid | | Mercury | Saltaëtic acid | | Silver | Nitric acid | | Gold | Tartaric acid | | Cobalt | Phosphoric acid | | Arsenic | Citric acid | | Platinum | Succinic acid | | Bismuth | Fluoric acid | | Lead | Arsenic acid | | Nickel | Lactic acid | | Iron | Acetic acid | | Boracic acid | Prussic acid | | Carbonic acid |

I. Salts of Zinc.

1. Sulphate of Zinc.

1. Sulphuric acid diluted with water, acts very powerfully on zinc. A violent effervescence takes place; the mixture is strongly heated, and a great quantity of hydrogen gas is evolved. In this process, which is usually followed for obtaining the purest hydrogen gas for chemical purposes, the water is decomposed; its oxygen combines with the metal and forms an oxide, which is then dissolved in the sulphuric acid, and forms a sulphate of zinc, while the hydrogen, the other component part of the water, escapes in the form of gas. A black powder is sometimes observed floating in the solution, which is carburet of iron, with which the zinc is frequently contaminated. As the effervescence ceases, a white powder is formed, which gradually disappears towards the end of the process, and with the addition of water forms a transparent solution. By evaporation and cooling, the sulphate of zinc is obtained crystallized.

2. The sulphate of zinc is frequently contaminated with other metals, as with lead, iron, and copper; but when it is pure, it crystallizes in four-sided prisms, terminated by pyramids with four faces. This salt has an acid, astringent, and strongly metallic taste. When it is exposed to the air it effloresces. It is soluble in less than two and a half parts of cold water, and more soluble in boiling water. The specific gravity of the crystallized salt is 1.912; but as it is generally met with in the shops, it is only 1.3275. When heated in a retort, it melts, loses its water of crystallization, and part of its acid in the state of sulphurous acid, and a little water. It is decomposed and precipitated in the state of white oxide by all the alkalies; and if the precipitate is formed by means of the carbonates, a white pigment is obtained. The sulphate of zinc is also decomposed with the assistance of heat, by means of nitre. The alkaline sulphurets and hydrofulphurets also precipitate the sulphate of zinc, Zinc, of a deep orange or brown colour. The component parts of this salt are, according to Bergman, Kirwan.

| Acid | 40 | 20.5 | |--------|----|------| | Oxide | 20 | 40.0 | | Water | 40 | 39.5 |

100 100.0

3. The salt, known in commerce by the name of white vitriol, is a sulphate of zinc, and is supposed to contain an excess of acid. It is in the form of white granular masses, resembling sugar, and often marked with yellow spots. This salt is usually prepared by roasting the sulphuret of zinc or blende, by which means the sulphuret is converted into sulphuric acid. It is then dissolved in water, which is purified and evaporated, and the salt is crystallized by sudden cooling. Part of its water of crystallization is afterwards driven off by heat, so that it is obtained in a regular, solid, and granulated mass. It is generally contaminated with iron and other metals; but it may be purified from these, by adding filings of zinc, which precipitate the other metals, and leave a pure sulphate of zinc.

2. Sulphite of Zinc.

Concentrated sulphurous acid readily combines with the white oxide of zinc, without any effervescence, but with the evolution of heat, and the acid being deprived of its odour. When the saturation is completed, white crystals appear on the surface of the liquid. This salt has a pungent, astringent taste. It crystallizes readily. It is decomposed by the acids, with effervescence. It is insoluble in alcohol. It forms white precipitates with the alkalies, and when exposed to the air, it is readily converted into sulphate of zinc.

Sulphurated fulphite of Zinc.—When sulphurous acid is added to zinc in the state of powder or filings, a great degree of heat is produced; sulphurated hydrogen gas is disengaged; the liquid becomes at first brown, sometimes muddy, and assumes a yellow colour, and towards the end of the process it becomes transparent. The solution has an acid, astringent, and sulphurous taste. Sulphuric and muriatic acids disengage with effervescence, sulphurous acid gas, and precipitate a yellowish white powder. Nitric acid at first separates sulphurous acid gas, and afterwards a flaky precipitate, which is pure sulphur. When this solution is exposed to the air, it becomes thick like honey, and affords crystals in the form of needles or fine four-sided prisms, terminated by four-sided pyramids. These are crystals of sulphurated fulphite of zinc, which become white by exposure to the air, and form a white powder insoluble in water. When this salt is heated by the blow-pipe, it fizzes up, gives out a bright light like burning zinc, and forms dendritic ramifications. This salt is partly soluble in alcohol. The part not dissolved, only gives out sulphurous acid gas by means of sulphuric acid, whilst the part which is dissolved affords, besides sulphurous acid gas, a copious precipitate of sulphur. When it is distilled in a retort, it gives out water, sulphurous acid, sulphuric acid, and sulphur sublimed. There remains behind oxide of zinc, mixed with a little of the sulphate.

In the solution of zinc in liquid sulphurous acid, water, and part of the sulphurous acid itself, are decomposed; for sulphurated hydrogen gas is disengaged, which is composed of the hydrogen of the water and part of the sulphur of the sulphurous acid. There is no precipitation of sulphur during the solution, for it combines with the sulphite of zinc, as it is formed; but this is not completely saturated, since alcohol dissolves only the portion of sulphurated fulphite which it contains, and separates the sulphite.

3. Nitrate of Zinc.

1. Concentrated nitric acid produces a violent action with zinc, and sometimes even inflames it. To effect this solution, with a moderate action, the acid should be diluted with water. Great heat is produced, with violent effervescence and the evolution of nitrous gas. The acid is decomposed; its oxygen combining with the metal, forms an oxide, which combines with the acid as it is formed.

2. This solution is of a greenish-yellow colour, and extremely caustic. By evaporation it affords crystals, in the form of four-sided, compressed, and striated prisms, terminated by four-sided pyramids. The specific gravity is 2.096. This salt is deliquescent in the air. When it is heated on burning coals, it melts, and detonates with a small red flame. When heated in a crucible, it gives out red vapour, and affirms a deep colour and gelatinous consistence. When cooled in this state, it retains its softness for some time. By continuing the heat, it dries, gives out nitrous and oxygen gases, and leaves behind a yellow oxide.

4. Muriate of Zinc.

Muriatic acid produces a rapid action on zinc. It is dissolved with effervescence, and with the evolution of pure hydrogen gas. The solution of zinc in muriatic acid is colourless; it does not crystallize, but assumes the form of a transparent jelly. It affords by distillation a small quantity of fuming acid, and a solid muriate of zinc, which is fusible with a moderate heat, and was formerly known by the name of butter of zinc. When this muriate of zinc is sublimed by heat, it becomes of a fine white colour, composing a mass of crystals in the form of small prisms. It is decomposed by sulphuric acid, and is precipitated by the alkalies. It is soluble in water, attracts moisture from the atmosphere, and is soon converted into a transparent jelly. The specific gravity is 1.577.

5. Muriate of Ammonia and Zinc.

This triple salt is formed by boiling white oxide of zinc in a solution of muriate of ammonia. The oxide of zinc is dissolved; part of which is afterwards deposited, when the solution cools, but what remains in the solution is not precipitated by the alkalies or the alkaline carbonates.

6. Fluate of Zinc.

Fluoric acid produces a violent action with zinc; there is considerable effervescence, with the evolution of... Zinc, &c., of hydrogen gas. The metal is oxidated, and then dissolves in the acid; but the properties of this salt are little known.

7. Borate of Zinc.

Boracic acid combines with the oxide of zinc, by adding the borate of potash or soda to the solution of zinc in nitric or muriatic acid. This salt is insoluble in water.

8. Phosphoric acid diluted with water, acts upon zinc with the evolution of hydrogen gas, owing to the decomposition of water. A white powder is deposited, which is phosphate of zinc. By exposing phosphoric acids and zinc to a strong heat, a phosphuret of zinc is formed, by the decomposition of the acid.

9. Carbonate of Zinc.

Zinc reduced to a fine powder, and added to liquid carbonic acid, is oxidated and copiously dissolved in the acid, at the end of 24 hours. This solution, exposed to the air, is covered with a pellicle of carbonate of zinc of different colours. The carbonate of zinc is found native, and has been distinguished by the name of calamine, thus confounding it with the oxide of zinc. Carbonate of zinc, according to the analysis of Bergman, is composed of:

| Acid | 28 | | Oxide | 66 | | Water | 6 |

100

10. Arseniate of Zinc.

When arsenic acid is added to zinc, it produces an effervescence, with the evolution of hydrogen gas, holding arsenic in solution. A black powder is deposited, which is metallic arsenic. In this process, the zinc decomposes part of the water, and combines with its oxygen, and at the same time deprives the arsenic acid of its oxygen, by which it is reduced to the metallic state. The arseniate of zinc may be obtained by adding a solution of an alkaline arseniate to a solution of the sulphate of zinc. A white precipitate is formed, which is the arseniate of zinc. It is insoluble in water.

11. Tungstate of Zinc.

12. Molybdate of Zinc.

These salts may be formed by a similar process. A white powder is obtained, which is insoluble in water.

13. Chromate of Zinc.

This salt is obtained by combining an alkaline chromate with a solution of zinc in nitric acid. A precipitate is formed of an orange red colour, which is chromate of zinc.

14. Columbate of Zinc.

Unknown.

15. Acetate of Zinc.

Acetic acid dissolves zinc, and the solution by evaporation crystallizes in the form of rhomboidal prisms and hexagonal plates. This salt has a bitter metallic taste, is not altered by exposure to the air, and is soluble in water. It burns with a blue flame when thrown on burning coals. When distilled, it yields water, an inflammable liquid, and some oil. At the end of the process, when the salt is completely decomposed, the oxide of zinc is sublimed, which being brought in contact with a candle, burns with a fine blue flame. The residuum is in the state of pyrophorus, but it has little combustibility.

16. Oxalate of Zinc.

Oxalic acid acts upon zinc with effervescence, and the evolution of hydrogen gas. Water is decomposed, and as the zinc is oxidated, it combines with the acid, forming an oxalate of zinc. It is in the state of white powder, of an acrid taste, and but little soluble in water.

17. Tartrate of Zinc.

Tartaric acid combines with zinc with effervescence, and the evolution of hydrogen gas. The properties of this salt have not been examined.

18. Citrate of Zinc.

Citric acid acts upon zinc with effervescence and the evolution of hydrogen gas. At the end of 24 hours the action ceases, and the liquid deposits on the sides of the vessel and on its surface, small, brilliant crystals in the form of plates, which are insoluble in water. The citrate of zinc has an astringent, metallic taste. It is composed of equal parts of acid and of oxide of zinc.

19. Malate of Zinc.

Malic acid dissolves zinc, and, by evaporating the solution, crystals may be obtained.

20. Benzoate of Zinc.

Benzoic acid readily dissolves zinc, and by evaporation the solution affords needle-shaped crystals. The benzoate of zinc is soluble in water and alcohol. When it is exposed to heat, the acid is sublimed.

21. Succinate of Zinc.

Zinc is dissolved in succinic acid with effervescence. By evaporation the solution affords slender, foliated crystals.

22. Lactate of Zinc.

Zinc is soluble in lactic acid with effervescence, and by evaporating the solution, the salt may be obtained crystallized.

II. Action of Alkalis, &c., on Zinc.

1. When zinc is immersed in a solution of potash fixed alkali or soda, it is tarnished, and becomes black, and when it is boiled in the solution, hydrogen gas is evolved. The solution assumes a dirty-yellow colour, from which an oxide of zinc may be precipitated by acids.

2. Ammonia. 2. Ammonia has a still more powerful action on zinc. Hydrogen gas is more copiously evolved, and the oxide which is formed is more abundantly dissolved in the liquid, and at the end of some time a considerable quantity of white oxide is deposited. These alkaline solutions become turbid by exposure to the air; its oxygen and carbonic acid, acting at the same time, precipitate the oxide.

3. The alkaline and earthy sulphates are readily decomposed by zinc, with the assistance of heat. It attracts the oxygen of the sulphuric acid, and thus decomposing it, separates the sulphur, which combines with the bases of the sulphates. Alum boiled in solution with zinc, is decomposed, and there is formed a triple salt, which is sulphate of zinc and alumina.

4. The nitrates produce a vivid inflammation with zinc at a red heat. The acid is decomposed, its oxygen combines with the metal, and by this rapid combination, a violent detonation is produced. The azotic gas is disengaged, and the zinc is fully oxidated. Three parts of nitre well dried, and one of zinc in fine powder, well mixed together and projected into a red-hot crucible, produce a very brilliant inflammation. The burning matter is sometimes thrown out to a considerable distance; so that the experiment should be made with caution. This compound is sometimes employed in fire-works.

5. Zinc has a considerable action on the muriates. Triturated with the muriate of ammonia, the salt is decomposed, and ammonia is disengaged. By distilling this salt with zinc, ammoniacal and hydrogen gases are obtained; the latter is obviously owing to the decomposition of the water contained in the salt, by means of the zinc, which combines with the oxygen, and then forms a muriate of zinc with the muriatic acid.

6. The phosphates and borates combine by fusion with the oxide of zinc, which communicates to the glass thus formed a greenish-yellow colour.

7. Zinc decomposes the greatest number of the metallic salts from their solutions, by its strong affinity for oxygen. They are precipitated in the metallic form, or in the state of oxide, but deprived of a portion of oxygen.

8. Zinc is employed in many of the arts. It forms useful alloys with some of the other metals, some of which will be mentioned afterwards. It is also employed in medicine. The sulphate of zinc is sometimes exhibited as an emetic, and frequently used in solution as an eye-wash. The oxide of zinc, or the flowers of zinc, have been prescribed as an antipathodic, and particularly in cases of epilepsy.

Sect. XVI. Of Tin and its Combinations.

1. Tin has been known from the earliest ages. It was much employed by the Egyptians in the arts, and by the Greeks as an alloy with other metals. Pliny speaks of it under the name of white lead, as a metal well known in the arts, and even applied in the fabrication of many ornaments of luxury. He ascribes to the Gauls the invention of the art of tinning, or covering other metals with a thin coat of tin. The alchemists were much employed in their researches concerning tin. They gave it the name of Jupiter, from which the salts or preparations of tin were called jovial. Since their time, the nature and properties of tin have been particularly investigated by many chemists, and it has proved the subject of some important discoveries in chemical science. So early as the year 1630, John Rey threw out a conjecture, that the air was fixed in this metal during its calcination. Boyle, towards the end of the same century, attempted to account for the increase of weight which this metal acquired during this process; but this was only fully ascertained by Lavoisier, who repeated the experiment of Boyle, and calcined the metal in close vessels; but the method of conducting this experiment and the result of it, have been already detailed.

2. Tin exists in nature in three different states. It ores, is found native, in the state of oxide, and in that of sulphurated oxide. Native tin is in brilliant plates, or regularly crystallized. The native oxide of tin, which is the most common ore of this metal, exists under a variety of forms. It is generally found crystallized. The sulphuret of tin is of a pale or dark gray colour, and when pure, has some resemblance to an ore of silver.

3. To obtain the metal from its ores, they are first analysed, roasted, and then treated with a flux, to reduce the metal. It has been recommended by some, to mix a small quantity of pitch with the fused mass, to prevent the oxidation of the tin. After the ore is roasted, it fuses readily with three times its weight of black flux, and a little decrepitated muriate of soda.

In the humid way, native tin may be dissolved in nitric acid, which readily oxidizes, and reduces it to the state of white powder, which is an oxide of tin; and if it contain iron and copper, these two metals remain in the solution.

4. Tin is of a white colour, nearly as brilliant as Properties-silver. The specific gravity of tin is 7.291. It is one of the softest of the metals. It may be scratched with the nail, and easily cut with a knife. It is extremely flexible, and produces a peculiar noise when it is bent or folded. It is so malleable, that it can be easily beaten out to \(\frac{1}{1000}\) part of an inch, which is the thickness of tinfoil. It has little elasticity or tenacity. A wire of this metal about \(\frac{1}{10}\) of an inch in diameter supports a weight of about 30 lbs. without breaking.

5. Tin is susceptible of very considerable expansion Action of by means of caloric, and on this account it has been heated. Proposed to employ it as a pyrometer. Tin is one of the most fusible of the metals, and melts at the temperature of 442°, but it requires a very high temperature to raise it in vapour. If it be allowed to cool slowly, and when the surface becomes solid, by pouring out part of the liquid metal, crystals are formed, in large rhomboids, composed of a great number of small needles.

6. Tin is a good conductor of electricity. It possesses a peculiar odour, which is communicated to the hands by friction. It has also a perceptible taste.

7. When this metal is exposed to the air, it is soon tarnished, and assumes a grayish white colour; but it undergoes no farther change. When it is melted in an open vessel, it is soon covered with a grayish pellicle, which is the commencement of the oxidation of the When this pellicle is removed, another forms, and so on successively till the whole is oxidated. By continuing the heat, and by agitation, the process goes on more rapidly, and the metal is converted into a whitish powder. This oxide contains about 20 parts of oxygen in 100 of the metal. With the addition of lead to promote the oxidation, this oxide is the putty of tin. It contains about two parts of oxide of lead, and one part of oxide of tin. But when tin is strongly heated, it is converted into a fine white oxide, which during the process gives out a vivid white flame. This oxide is condensed in the cold, and crystallizes in thinning transparent needles.

According to Proust, tin combines with two proportions of oxygen, thus forming two oxides. The yellow oxide, which has the smaller proportion of oxygen, may be prepared by dissolving tin in nitric acid diluted with water, without the aid of heat. By precipitating the oxide with pure potash, it is obtained in the form of a yellowish powder. Its component parts are those already stated, namely,

\[ \begin{align*} 20 \text{ oxygen}, & \\ 80 \text{ tin}, & \\ \hline 100 & \end{align*} \]

By dissolving tin in concentrated nitric acid, with the assistance of heat, the whole is converted with effervescence into a white powder, which falls to the bottom of the vessel. The component parts of this oxide are, 28 oxygen, and 72 of tin.

8. There is no action between tin and azote, hydrogen, or carbone, nor is there any perceptible action between tin or its oxides and water.

9. Phosphorus combines very readily with tin, by projecting bits of phosphorus on melted tin in a crucible. A phosphuret of tin is thus obtained, which crystallizes on cooling. This compound is of a silvery white colour, may be cut with a knife, and extended under the hammer, but soon separates into plates. The filings of this phosphuret are like those of lead, and when they are thrown on red-hot coals, they take fire, and burn with the smell and flame of phosphorus. By the action of the blow-pipe, the phosphorus only burns, and the small metallic button which remains is surrounded with a transparent glass. Pelletier distilled this phosphuret often with hyperoxymuriate of mercury, and obtained a fuming muriate of tin, with the mercury reduced to the metallic state, and phosphorated hydrogen gas, which exploded as it came in contact with the air. There remained in the retort a spongy inflammable matter, which he supposed to be a compound of tin and phosphorus.

10. Sulphur combines very readily with tin, by adding the sulphur to the metal while in a state of fusion. This compound forms a grayish or bluish matter, which has a metallic lustre, a lamellated structure, and crystallizes in cubes, or in octahedrons. It is decomposed by acids with effervescence. The component parts are, according to Bergman, Pelletier:

\[ \begin{align*} \text{Tin} & : 80 : 85 \\ \text{Sulphur} & : 20 : 15 \\ \hline 100 & 100 \end{align*} \]

11. If equal parts of oxide of tin and sulphur be fused together in a retort, sulphurous acid and some sulphur are disengaged, and there remains in the vessel a compound of a brilliant golden colour. It crystallizes in flat plates. It is not acted on by the acids. When it is strongly heated, it gives out sulphurous acid and sulphur, and there remains behind a black mass which is sulphuret of tin. This compound, which is a sulphurated oxide of tin, was formerly distinguished by the name of aurum myricum, myricum, or myricum. The component parts of this sulphurated oxide of tin are,

\[ \begin{align*} \text{Oxide of tin,} & 60 \\ \text{Sulphur,} & 40 \\ \hline 100 & \end{align*} \]

12. Tin enters into combination with many of the metals, and forms alloys with them, some of which are of great importance. It also combines with acids, and forms salts. The affinities of tin and its oxides are in the following order.

| Tin | Oxide of Tin | |-----|--------------| | Zine | Tartaric acid | | Mercury | Muriatic, | | Copper | Sulphuric, | | Antimony | Oxalic, | | Gold | Arsenic, | | Silver | Phosphoric, | | Lead | Nitric, | | Iron | Succinic, | | Manganese | Fluoric, | | Nickel | Selenic, | | Arsenic | Citric, | | Platinum | Lactic, | | Bismuth | Acetic, | | Cobalt | Boracic, | | Sulphur | Prussic. |

I. Salts of Tin.

1. Sulphate of Tin.

1. Sulphuric acid acts very feebly on tin in the cold. The acid, however, is at last decomposed; its oxygen combines with the metal, sulphurous acid gas is emitted, and the oxide falls to the bottom in the state of white powder. In this case, the oxide has the smaller proportion of oxygen, and then the solution is more permanent. There is no precipitation by water.

2. But when the solution of tin in sulphuric acid is promoted by the action of heat, the acid is still farther decomposed; a greater quantity of sulphurous acid is given out, and sulphur is deposited. In this case the white oxide of tin is formed. This compound, when evaporated, assumes the form of a jelly, and does not crystallize by the addition of water. It is precipitated in the form of white powder. The first might be called the yellow sulphate of tin, and the second the white sulphate of tin.

2. Sulphite of Tin.

When tin is immersed in liquid sulphurous acid, it assumes a yellow colour. At the end of some days it becomes Tin, &c., becomes black like charcoal, and there is deposited in the liquid a black powder. In this process part of the sulphurous acid is decomposed; its oxygen combining with the metal, forms an oxide, which enters into combination with another part of the acid, and forms the sulphite of tin. A portion of sulphur is deposited along with a white sulphite, which is not very soluble, and another portion remains in solution with part of the sulphite, forming a sulphated sulphite. A third portion of the sulphur combines with part of the metallic tin, and forms a black sulphuret, on which the acid has no action.

3. Nitrate of Tin.

1. Nitric acid produces a very violent action with tin. It is accompanied with great heat, and the evolution of nitrous gas. The metal is converted into a white oxide, which gives to the liquid the appearance of coagulated milk. It had been long observed by chemists, that the solution of tin in nitric acid was not permanent, for by evaporating or concentrating the solution, the oxide is always precipitated. This difficulty has been solved by the discoveries of modern chemistry.

2. If tin be dissolved in nitric acid, diluted with water, and the great increase of temperature moderated by the application of cold, as by immersing the vessel in cold water, a solution of a small quantity of the oxide of tin is effected. The solution is of a yellow colour, and contains the oxide of tin, with a smaller proportion of oxygen, which is the yellow oxide. In this process the tin is chiefly oxidized by the decomposition of the water. In this process too, ammonia is formed from the azote of the acid combining with the hydrogen of the water. This becomes perceptible by adding potash to the liquid. When the solution is heated, the oxide of tin is separated in great abundance.

3. But when nitric acid is more concentrated, a more violent action takes place between this acid and tin. The metal is oxidized, and the whole of it separates from the liquid. To one part of pure nitric acid Guyton added 1/4 of tin in a retort, when a violent effervescence took place, but no gas was given out. In this experiment a quantity of ammonia equal to 1/5 of the weight of the acid and tin employed, was formed. The acid and the water are decomposed, and the oxygen of both combines with the tin, and forms an oxide, while the azote of the acid and the hydrogen of the water combine together and form ammonia. In this state of oxidation, the tin does not combine with the acid.

4. Muriate of Tin.

1. Concentrated muriatic acid dissolves tin, either in the cold or with the assistance of a gentle heat. The acid is soon deprived of its fuming property, and of its yellow colour. A slight effervescence takes place, which is owing to the decomposition of water, and the evolution of a fetid hydrogen gas. This peculiar odour is supposed to be occasioned by the hydrogen gas holding in solution a portion of the metal. Muriatic acid dissolves more than 1/5 its weight of tin. No precipitate is formed, as with the other acids. When it is evaporated, it furnishes crystals in the form of brilliant needle-shaped prisms, which are deliquescent in the air.

2. This muriate of tin is precipitated by the alkalies in the form of a copious white oxide, which is re-dissolved with an excess of alkali. The alkaline solution is of a brownish yellow colour. The sulphuret of ammonia precipitates this salt in the form of powder, which becomes black as it dries, and by distillation yields ammonia and aurum myroon. The sulphuret of potash produces a yellow precipitate, which, by distillation furnishes sulphurous acid and sulphur, and what remains is converted into aurum myroon, or the sulphated oxide of tin. This oxide precipitated by means of soda, and distilled with its weight of sulphur, yields sulphurous acid gas, sulphur, and the residuum is aurum myroon.

3. This solution of tin absorbs oxygen, with the evolution of heat, from oxymuriatic acid, which is deprived of its odour. With nitric acid, a violent effervescence takes place. Nitrous gas is disengaged, and in both these cases, the oxide of tin combines with an additional portion of oxygen. With the addition of sulphurous acid, this solution of tin deposits the yellow sulphated oxide of a fine bright colour. This solution converts arsenic acid into the metallic state, and it produces the oxymuriate effect on the molybdic and tungstic acids, by combining with their oxygen. The red oxide of mercury, the hyperoxymuriate of mercury, the white oxide of antimony, the oxides of zinc and silver, are all reduced to the metallic state by being deprived of their oxygen by the muriate of tin. This muriate also precipitates from the solution of gold, the purple powder of Caffius, by attracting that portion of oxygen which renders the oxide of gold soluble. In all these processes, the results of which were ascertained by Pelletier, the muriate of tin is converted into an oxymuriate.

4. This oxymuriate of tin is formed by making a stream of oxymuriatic acid gas pass into a solution of another muriate of tin. It is also prepared by triturating equal parts of an amalgam, consisting of two parts of tin, and one of mercury, and muriate of mercury, or corrosive sublimate, and distilling this mixture in a glass retort, with a very moderate heat. A colourless liquor first passes over, which is followed with the sudden evolution of a white vapour, which lines the inside of the receiver. This vapour is condensed into a transparent liquid, which, in the air, exhales a copious, heavy, white vapour, from which this liquid has been called the smoking liquor of Libavus, or the oxymuriate of tin. When this liquor is included in a vessel, it no longer gives out any visible vapour, but it deposits at the top of the vessel needle-shaped crystals, while similar crystals are precipitated to the bottom. Water does not precipitate the fuming muriate of tin. When it is thrown into the water, it produces a noise similar to that which is occasioned by concentrated sulphuric acid. A number of transparent bubbles of air being evolved from the mixture, collect on the surface, and become white by the contact of air. By agitating the water, they are more readily diffused, and the liquid fumes no longer.

5. Nitromuriatic acid, which is composed of one part of nitric acid, and two or three of muriatic acid, muriate very readily dissolves tin. A strong heat is produced, which which may be moderated by immersing the vessel, in which the solution is made, in cold water. The metal should be added in small portions, and one part should be dissolved before the addition of another. In this way the acid will dissolve half its weight of tin. It is by this process that the muriate of tin is obtained for the purpose of dyeing scarlet; but it is found to vary considerably in its effects, which, no doubt, depends on the strength of the acids employed, and the different proportions in the mixture. This solution is almost always coloured. Sometimes it affords a gelatinous mass on cooling, which becomes in time more solid. Sometimes it is of a white colour like milk. This solution has not the fetid odour of the simple solution of tin in muriatic acid. It often happens, that it does not assume the viscid or solid form, without the addition of \( \frac{1}{2} \) its weight of water. It is then slightly opaque, which is owing to the precipitation of part of its oxide. When this solution is heated, an effervescence takes place; the tin is more strongly oxidated, and it is generally after this process that it assumes the form of a transparent jelly.

5. Fluate of Tin.

Fluoric acid has very little action on tin, but it dissolves its oxide, and forms with it a solution which assumes a gelatinous form. The fluate of tin may be also obtained by adding a solution of an alkaline fluate to a solution of tin in muriatic acid.

6. Borate of Tin.

By a similar process boracic acid combines with the oxide of tin, and forms a borate of tin, which is insoluble.

7. Phosphate of Tin.

This salt may be formed by precipitating the oxide of tin from its solution in muriatic acid, by means of an alkaline phosphate. A phosphate of tin is thus obtained, which is insoluble in water.

8. Carbonate of Tin.

This salt is prepared by precipitating the oxide of tin from its solution in muriatic acid, by means of the carbonates of the alkalies. When this carbonate of tin is dissolved in an acid, it effervesces; but, according to Bergman, the oxide of tin, precipitated by an alkaline carbonate, is not found to have received any sensible addition of weight, so that the effervescence occasioned by the action of an acid, on what is supposed to be a carbonate of tin, probably depends on the decomposition of the acid itself.

9. Arseniate of Tin.

Arsenic acid, with a moderate heat, dissolves a small quantity of tin, and the solution assumes the form of a jelly. Arseniate of tin is formed, by adding to a solution of tin in muriatic acid, an alkaline arseniate. A precipitate is formed, which is arseniate of tin in the state of insoluble powder.

All the metallic acids are decomposed by means of tin. They also combine with the oxide of tin, and form salts in the state of powder, which has little solubility.

10. Acetate of Tin.

Acetic acid dissolves only a small portion of tin; but when the acid is boiled on tin, the action is more powerful, and the solution, which is of a whitish colour, affords by evaporation small crystals. The solution of tin in acetic acid sometimes does not crystallize, but affords only a gelatinous mass; so that, by the action of acetic acid on tin, the metal is either in different degrees of oxidation, or there are different proportions of the acid and base.

11. Oxalate of Tin.

Oxalic acid added to tin in thin plates or filings, first blackens the surface, which is afterwards covered with a white powder. The oxalate of tin, which is soluble in water, has an austere metallic taste. By slow evaporation it furnishes needle-shaped or prismatic crystals. When it is more rapidly evaporated, it affords a transparent mass like horn.

12. Tartrate of Tin.

Tartaric acid dissolves the oxide of tin, but the nature of this salt has not been examined.

13. Tartrate of Potash and Tin.

This triple salt may be obtained by boiling together the oxide of tin and tartar, in water. It is a soluble salt, and crystallizes with difficulty. It is not precipitated by the alkalies or the alkaline carbonates.

14. Benzoate of Tin.

This salt is formed by adding to a solution of tin in muriatic acid, benzoate of potash. The benzoate of tin is precipitated, which is soluble in water, with the assistance of heat.

15. Succinate of Tin.

The oxide of tin is dissolved by succinic acid with the assistance of heat. When the solution is evaporated, it affords thin transparent crystals of succinate of tin.

II. Action of Alkalies, &c. on Tin.

1. Tin in the metallic state is little changed by the action of the alkalies; but the oxides of tin readily combine with these bodies. The combination of the oxide of tin with the fixed alkalies is effected, either in the dry or humid way; and with the assistance of heat the oxide of tin combines with liquid ammonia. This combination takes place most readily when the oxide is recently precipitated, when it is in the state of minute division.

2. The oxide of tin combines with the earths by fusion; and with the addition of a fixed alkali, forms an opaque vitreous mass, which is employed for the purposes of enamel.

3. Most of the salts are decomposed by means of tin, in consequence of the strong affinity of this metal for oxygen. All the sulphates, when heated with this metal are more or less rapidly converted into sulphurets. Equal parts of sulphate of potash and tin, heated together in a crucible, afford a greenish coloured mass, which has no metallic appearance, and which seems to be a sulphuret of potash and tin. The nitrates produce... duce deflagration with this metal, with the assistance of heat. If the tin be melted in a crucible, and brought to a red heat, and dried nitre in powder be projected into it, a white brilliant flame is produced, and when the detonation has entirely ceased, the tin is found to be oxidated. This experiment may be also made, by mixing together tin filings with three parts of nitre in powder, and projecting the mixture into a red-hot crucible. Muriate of ammonia is decomposed by tin; and by adding sulphur, the sulphurated oxide of tin, or aurum mufivum, is obtained. Eight parts of tin united to eight parts of mercury, with six of sulphur, and four of muriate of ammonia, afford, according to the process of Pelletier, a very beautiful aurum mufivum.

It was observed by this philosopher, that during the process, sulphurated hydrogen gas, sulphuret of ammonia, and muriate of tin, were produced; that the tin oxidated and united to the sulphur, formed aurum mufivum; and that a part of this matter, composed of the different substances, in a state of vapour, was deposited in lamellated, hexangular crystals, in the upper part and in the neck of the retort.

The alkaline hypoxymuriates, but especially that of potash, produce a violent detonation with this metal. Three parts of this salt mixed with one of tin in fine powder, rapidly deflagrates when brought into contact with a burning body. During this combustion, there is a brilliant and sudden flame, and the metal is reduced to the state of vapour. The same mixture by percussion produces a violent detonation with a considerable flame in the dark.

Many of the metallic solutions and metallic salts are decomposed by means of tin, and are either reduced to the metallic state, or deprived of a considerable portion of their oxygen.

III. Alloys.

1. Tin and arsenic form an alloy by fusion. The compound, when the proportion of arsenic is considerable, is white, brittle, more sonorous and harder than tin. In the proportion of 15 parts of tin and one of arsenic, the alloy crystallizes in large plates, is more fusible than tin, and more brittle than zinc. By exposure to the air, and with the assistance of heat, the arsenic is driven off.

2. With cobalt, tin forms an alloy which is in small grains, and of a light violet colour.

3. Tin combines with bismuth. The tin is then harder, more sonorous and brighter. The compound in certain proportions becomes more fusible than either of the two metals. The alloy of equal parts of tin and bismuth melts at $285^\circ$. Eight parts of tin and two of bismuth melt at $390^\circ$, and two of tin and one of bismuth at $330^\circ$.

4. Tin combines with antimony, and forms an alloy which is white and brittle, and has a specific gravity less than that of the two metals taken separately. The antimony gives hardness to the tin, and changes its texture. This alloy is employed in many arts, and particularly for the plates on which music is engraved.

5. Tin combines very readily with mercury, and in all proportions. The tin is even dissolved when the quantity of mercury is considerable. This union takes place in the cold, but it is greatly promoted by means of heat. The heated mercury is poured upon the tin in fusion. The amalgam of tin is susceptible of crystallization in the form of cubes. Sage observed the crystals of this amalgam in gray brilliant plates, thin towards the edges, and leaving between them polygonal cavities.

This amalgam is employed for covering mirrors. In applying it, tinfoil is spread on a smooth flat stone or table, and mercury, in which a certain proportion of tin has been already dissolved, is poured upon it. It is then spread equally over the whole with a feather or a piece of cloth. The plate of glass, one side of which is to be covered, is then applied to the edge of the table, and cautiously moved along the tinfoil, so that the redundant part of the mercury may be carried before it. What remains enters into union with the tin. The glass is then to be equally loaded with weights, to press out any part of the mercury which may yet remain uncombined with the tin. In the course of a few hours the amalgam of the two metals adheres so firmly to the glass, that the weights may be removed.

6. Zinc readily forms an alloy with tin by fusion. Zinc. The compound affords a hard metal with small grains, the ductility of which corresponds to the quantity of tin. The alloy of tin and zinc forms part of the compound which is known by the name of pewter.

Tin is applied to a great many important purposes. Uses. In the arts and domestic economy, it is formed into a great variety of vessels and instruments. The alloys of tin with other metals are not less important. It forms a component part of type metal, and bell metal. The oxides of tin are employed for the purpose of polishing glasses and metallic substances, and combined with the earths and alkalis for the fabrication of enamels. The salts of tin are employed for the preparation of colours in dyeing, or as a valuable mordant for fixing certain colours. Tin in the metallic state has been exhibited as a remedy against worms. It is then granulated by constant agitation while it cools after fusion; but it is supposed, if it produces any effect as a vermifuge medicine, that it is merely by its mechanical action.

Sect. XVII. Of Lead and its Combinations.

1. Lead has been known from the earliest ages. History. Pliny speaks of it under the name of black lead, probably to distinguish it from tin, with the properties of which he was also acquainted, for he observes that it was sometimes the practice to contaminate tin with lead.

2. Lead is found in great abundance in many parts of the world, and in a great variety of forms and combinations. Lead has rarely, if ever, been found native, and it is doubted whether it has yet been discovered in the state of oxide. The most common form of lead is in the state of sulphuret, when it is combined with sulphur. In this state it is of a gray, brilliant colour, of a lamellated texture, very brittle, and breaks into cubes. This is the most frequent combination of lead, and it is generally found in this state in veins. Lead is also frequently met with combined with several of the acids. The carbonate, phosphate, and arseniate of lead are not uncommon productions in the cavities of the veins of sulphuret of lead. The chromate, molybdate, and phosphate of lead, are more rare. 3. The sulphuret of lead, which is the most common ore, is reduced by roasting, and then fusing with black flux. The other ores of lead are to be analyzed according to the nature of the acid with which they are combined. To obtain lead in a state of purity, it may be dissolved in nitric acid, and precipitated by means of sulphate of soda. The precipitate, which is sulphate of lead, is well washed, and reduced in a crucible, by fusing it with three times its weight of black flux.

4. Lead is of a grayish or bluish white colour. It has considerable brilliancy, but it soon tarnishes when exposed to the air. The specific gravity of lead is 11.352. It gives out a peculiar odour when it is rubbed; it has at first scarcely any perceptible taste; but a disagreeable impression after some time remains on the tongue. When it is taken internally, it produces violent effects on the animal economy, even in very small quantity. The colic pectorum or dry belly-ach of the West Indies, or, as it is called in this country, mill-reek, which is a violent affection of the bowels, is occasioned by this metal being taken internally, either combined with some liquid, or in the state of vapour. This terrible disease often terminates in palsy. Lead stains the finger or paper of a bluish colour. It is one of the softest of the metals. It may be scratched with the nail or cut with a knife. It possesses considerable malleability, and may be reduced to plates thinner than paper. It has no great ductility, and its tenacity is less than that of the other metals. A lead wire of about \( \frac{1}{16} \) of an inch in diameter can support only a weight of about 18 lb.

5. Lead is very fusible. It melts at the temperature of 540°, or, according to the estimation of Guyton, at 594°. When it is kept a long time melted, and at a red heat, it sublimes, and evaporates in the air. By slow cooling it crystallizes in quadrangular pyramids composed of octahedrons.

6. When lead is exposed to the air, it soon tarnishes, is deprived of its lustre, and becomes first of a deep gray, and afterwards of a grayish white colour; but this process is extremely slow, for the white crust which is formed on the surface defends the metal from the action of the air, and its farther oxidation by absorption of oxygen.

When lead is melted in the open air, and heat continued, an iridescent pellicle is formed on the surface, which afterwards assumes a uniform gray colour. When this is removed, another pellicle is formed, and in this way the whole may be converted into an oxide. When these pellicles are heated and agitated together, the whole is converted into a grayish powder, mixed with yellowish or greenish spots. This is the gray oxide of lead, which is the first state of its oxidation.

When the gray oxide of lead is more strongly heated in contact with air, it absorbs a greater quantity of oxygen, and is converted into a yellow oxide, which is known in the arts by the name of maflicot. It contains about nine parts of oxygen in the hundred. This oxide, which is much employed in some of the arts, is prepared in the large way, by constantly agitating it while heated, in contact with air, without applying so great a heat as to reduce the metal to the state of the next oxide.

If this oxide of lead be reduced to a fine powder, and exposed to a strong heat in a furnace for about 50 or 60 hours, it is converted into a red powder, which is well known by the name of minium, or red lead. The heat necessary for this conversion is that of a cherry-red, in a reverberatory furnace.

Lead is susceptible of combining with another portion of oxygen, and of forming another oxide. If a quantity of red oxide of lead, according to the process of Proust and Vauquelin, be put into a vessel with water, and oxymuriatic acid gas be passed through it, the oxide assumes a deeper colour, and is dissolved. By adding potash to the solution, the lead is precipitated of a brown colour, which is the brown oxide of lead. It is of a shining brown colour, and is composed of

| Lead | 79 | | Oxygen | 21 |

By the action of the blow-pipe it becomes yellow, and melts. On burning coals it is reduced, and when heated in a retort, gives out pure oxygen gas, and is converted into a vitreous matter. It inflames sulphur by triturating it with the oxide, and gives out a bright flame.

7. When lead has been converted into an oxide, litharge, and when this oxide is exposed to a more violent heat, it melts into a kind of glass, or semifluid matter. In this state it is known by the name of litharge. It consists of small reddish brilliant scales, which from the colour is called litharge of gold. When it has been exposed to a greater degree of heat, and is more vitrified, it is distinguished by the name of litharge of silver.

8. There is no action between lead and azote, hydrogen or carbone. Water has no action on lead, but it seems to promote the oxidation of this metal, when it is in contact with air. Leaden vessels which are frequently moistened with water, are covered with a white crust when exposed to the air.

9. Lead combines with phosphorus, and forms phosphuret with it a phosphuret. This may be prepared by projecting phosphorus on lead melted in a crucible, or by distilling phosphorus with lead in a retort. The phosphuret of lead is of a silvery white colour, with a little of a bluish shade. It is of a lamellated structure, and may be separated in plates by hammering. It is so soft that it may be cut with a knife. It is somewhat less fusible than the component parts. During its fusion, a small quantity of phosphorus separates, and takes fire on the surface. The component parts of this phosphuret are,

| Lead | 88 | | Phosphorus | 12 |

10. Sulphur combines readily with lead, either by melting sulphur and lead together in a crucible, or by throwing sulphur on melted lead. A black matter is thus obtained, of a brilliant appearance, fibrous texture, and less fusible than lead. This compound is brittle, and resembles the native sulphuret of lead, or galena. The component parts of this sulphuret are, Lead enters into combination with the metals, and forms alloys, and with the acids, and forms salts. The order of the affinities of lead and of its oxide is the following:

| Lead | Oxide of Lead | |------|--------------| | Gold | Sulphuric acid, | | Silver | Saccharic, | | Copper | Oxalic, | | Mercury | Arsenic, | | Bismuth | Tartaric, | | Tin | Muriatic, | | Antimony | Phosphoric, | | Platina | Salphuric, | | Arsenic | Suberic, | | Zinc | Nitric, | | Nickel | Fluoric, | | Iron | Citric, | | Sulphur | Lactic, |

1. Salts of Lead.

1. Sulphate of Lead.

Sulphuric acid has no action on lead in the cold; but when lead is boiled with the acid concentrated, it decomposes it, and sulphurous acid gas is disengaged with effervescence. The lead is converted into a white thick mass, which remains at the bottom of the vessel. Sulphate of lead may also be obtained by adding sulphuric acid or an alkaline sulphate to acetate of lead. This salt is precipitated in the state of a white powder. The white mass obtained by the first process, being washed with water, separates into two portions, one of which is oxide of lead containing a little sulphuric acid, and the other portion, which is sulphate of lead, is soluble in water, and may be obtained crystallized in needles. The specific gravity of this salt is 1.8742. It has scarcely any taste. It is found native, and crystallized in regular octahedrons, or four-sided pyramids, or transparent tables. The component parts of native sulphate of lead are, according to

| Kirwan | Klaproth | |--------|----------| | Oxide | 75.00 | 70.50 | | Acid | 23.37 | 25.75 | | Water | 1.63 | 2.25 |

This salt is deprived of great part of its acid by means of the alkalis.

2. Sulphite of Lead.

Sulphurous acid has no action on lead; but it combines readily with the oxide of lead, with a smaller proportion of oxygen. The red oxide of lead added to liquid sulphurous acid, soon becomes white; the lead acid is deprived of its colour, and there is formed a saline mass of sulphate and sulphite of lead. The sulphite of lead cannot be obtained separately, but by treating the white oxide of lead separated from the nitrate by means of sulphurous acid. The sulphite of lead is tasteless and insoluble. By the action of the blow-pipe on charcoal, it melts, gives out a phosphoric heat, and becomes of a pale yellow colour on cooling. When it is heated for a longer time, it fuses up, and is entirely reduced to the metallic state. When distilled in clothe vessels, it gives out water, sulphurous acid, and sulphur, and there remains behind, sulphate of lead of a greenish yellow colour. It is decomposed with effervescence and the evolution of sulphurous acid, by means of sulphuric and muriatic acid. It is not decomposed by nitric acid, but is converted into a fulminate, and red fumes of nitrous gas are given out. If, in place of treating the red oxide with sulphurous acid, this oxide be exposed to a red heat, along with sulphite of soda, the oxide is reduced, and the sulphite of soda is converted into a sulphate, but with excess of soda, because the sulphuric acid formed, cannot saturate the same quantity of soda. Hence it appears, that the red oxide of lead gives up part of its oxygen to the sulphurous acid when it is uncombined, and the whole of its oxygen to the acid, when it is in combination with potash or soda.

3. Nitrate of Lead.

Nitric acid, a little diluted with water, acts upon lead, oxidizes it, and dissolves it with effervescence. If the acid be too strong, there remains behind a dry oxide. This oxide is equally soluble in nitric acid. No precipitate is formed in the solution by the addition of water. It has at first a sweetish, then an astringent, acid taste. By evaporating the solution, it affords on cooling, regular crystals in the form of flat triangles; and by flow, spontaneous evaporation, the angles are truncated. Sometimes six-sided truncated pyramids are obtained, with the faces alternately broad and narrow. These crystals decrepit strongly on burning coals, and give out brilliant sparks. The salt is decomposed, and a yellow or red oxide of lead remains behind. Nitrate of lead is decomposed by the alkalis, and precipitated in the form of white oxide. It is precipitated of a black colour, by means of the sulphuric and hydro-sulphuric acids; it is also decomposed by sulphuric acid and the sulphates, which form a thick, white, soluble precipitate of sulphate of lead. Sulphurous acid also precipitates this salt in the form of sulphate of lead.

2. The former salt is a compound of nitric acid and with the yellow oxide; but when nitric acid combines with white oxide, the salt crystallizes in yellow coloured brilliant scales, which are very soluble in water. This salt may also be prepared by boiling together a quantity of nitrate of lead with the yellow oxide, along with lead in the metallic state. The lead deprives the yellow oxide of part of its oxygen, and the whole is converted into the white oxide, and combines with the acid.

3. But if nitric acid be poured on the red oxide of lead, heat is produced, the oxide becomes white, part red oxide is dissolved, and part falls to the bottom in the form of Lead, &c., a black powder. This powder is the brown oxide of lead, with the greatest proportion of oxygen, part of which it has derived from the red oxide, which is then converted into the white. About $\frac{6}{7}$ of the red oxide are dissolved in the acid, but are previously reduced to the state of white oxide, and the oxygen which has been given out combines with the remaining $\frac{1}{7}$, and converts it to the state of brown oxide. Thus it appears, that the red and the brown oxides of lead do not form compounds with nitric acid. They must be deprived of a portion of their oxygen, and converted into the white or yellow oxides, before they are soluble in this acid.

4. Muriate of Lead.

1. Muriatic acid acts feebly on lead or its oxide; but when it is heated with the latter, part of the oxide combines with the acid, becomes soluble with excess of acid, and affords crystals in the form of thinning filky needles, which are not deliquescent in the air, but are soluble in water, and have an astringent taste. This salt may be formed by adding an alkaline muriate to a solution of nitrate of lead. A white thick precipitate is immediately formed. The muriate of lead thus obtained, has a sweetish taste, and is soluble in about 30 times its weight of water. When heated, it readily melts, and gives out a white vapour, which condenses into a crystalline powder. When this salt is melted, it assumes the appearance of a lamivitreous, shining, grayish mass, which has been called plumbum cornueum, or horny lead. This salt is decomposed by sulphuric acid. Its component parts are, according to Klapproth.

| Acid | 13.5 | | Oxide of lead | 86.5 |

2. When muriatic acid is slightly heated with the red oxide of lead, the acid is converted into oxymuriatic acid; while the oxide, deprived of part of its oxygen, unites to another portion of the acid, and forms muriate of lead in the state of white powder.

5. Hypoxymuriate of Lead.

When oxymuriatic acid gas is made to pass through water, having a white, yellow, or red oxide of lead, it is absorbed. The oxide becomes at first black or brown, and is then dissolved. The hypoxymuriate which is formed, remains in solution of a yellow colour. This solution being precipitated with potash or soda, the oxide of lead is deposited, of a reddish brown colour. This salt may be obtained by pouring oxymuriatic acid on nitrate of lead. No precipitate is at first formed, but in the end a brownish red powder appears. This salt is more soluble than muriate of lead, and is readily decomposed. The brown oxide of lead, which is obtained by decomposing this salt, according to the experiments of Vauquelin, possesses very different properties from those of the other oxides of this metal. It is of a deep shining, velvet-brown colour. Heated with the blow-pipe, it becomes yellow, and melts. On red-hot coals it is reduced; it gives out pure hydrogen gas, when it is heated in a retort, and there remains behind a little of lead. It dissolves in nitrous acid, but is insoluble in nitric acid. The addition of sugar, honey, lead, &c., or some vegetable matter, by depriving it of part of its oxygen, renders it soluble in this acid.

6. Fluate of Lead.

This salt may be formed by pouring a solution of an alkaline fluate into a solution of nitrate of lead. An insoluble infusible salt is thus formed, which is decomposed by sulphuric, nitric, and muriatic acids.

7. Borate of Lead.

This salt is formed in the same way as the last, and is in the state of white powder. It melts before the blow-pipe, into a colourless glass.

8. Phosphate of Lead.

1. Liquid phosphoric acid acts very slowly upon lead, and converts it into a white, insoluble phosphate. It may be formed, however, by adding an alkaline phosphate to the nitrate of lead. With an excess of acid this salt becomes fusible by heat, and when it cools, assumes the form of regular polyhedrons. It is decomposed by red-hot charcoal, which converts it into phosphorus and lead, while the carbons of the charcoal is converted into carbonic acid. It is decomposed by sulphuric, nitric, and muriatic acids, and by the alkaline carbonates.

2. This salt is frequently found native, crystallized in fix-sided prisms, of a green or yellow colour. It is soluble in pure soda, but insoluble in water. The component parts of a phosphate of lead from Wanlockhead in Scotland, according to the analysis of Klapproth, are the following.

| Oxide of lead | 80.00 | | Phosphoric acid | 18.00 | | Muriatic | 1.62 |

9. Carbonate of Lead.

1. Carbonic acid which has no action on lead, combines with its oxide, which is converted into the carbonate of lead; or this salt may be prepared by the decomposition of a soluble salt of lead by an alkaline carbonate. Thus precipitated, it is in the state of white powder, which has neither taste nor smell, and is insoluble in water, but it is soluble in pure potash.

2. This salt is frequently found native, of a whitish Native colour, and crystallized in tables, in fix-sided prisms, or in regular octahedrons. The specific gravity is 7.2357. It is insoluble in water. By the action of the blow-pipe on charcoal, the acid is driven off, and the lead is revived. The component parts of carbonate of lead, are, according to Bergman.

| Acid | 16 | | Yellow oxide | 84 |

3. Ceruse or white lead, which is employed as a paint, is a carbonate of lead, combined with a certain proportion proportion of oxide. It is prepared by exposing thin plates of lead to the vapour of vinegar. A range of pots are placed on tanners bark or horse dung, that they may receive a moderate heat. These are covered with plates of lead, which are full of holes. Another range of pots is placed above these, covered in like manner with plates of lead, and so on, till the whole chamber is filled. The acid is decomposed; part of the lead remains in the state of oxide, while the greatest proportion is converted into a carbonate, which is the white lead of commerce.

10. Arseniate of Lead.

When lead is digested in a solution of arsenic acid, the surface is blackened, and becomes covered with a white powder. When lead filings are distilled with double their weight of solid arsenic acid, the mixture melts into a transparent mass. A small quantity of arsenious acid is separated, and there remains behind a whitish glass, which being diluted with water, lets fall a white powder, whilst part of the arsenic acid is dissolved. The lead in this case has deprived the arsenic acid of part of its oxygen, and in the state of white oxide has combined with another portion of the acid. The arseniate of lead is not soluble in water. By heat it fuses into a white glass. This salt is found native, and by the analysis of Mr Chenevix it is composed of

| Acid | 33 | |------|----| | White oxide | 63 | | Water | 4 |

11. Tungstate of Lead.

Tungstic acid separates the oxide of lead from its solution in nitric acid, and forms a tungstate of lead, in the form of a white powder.

12. Molybdate of Lead.

When molybdic acid is added to the solution of lead in nitric acid, it forms a copious white precipitate, which is molybdate of lead. This salt is found native, and crystallized in cubes or rhombohedral plates. It is of a yellow colour, insoluble in water, but soluble in fixed alkalies and nitric acid. It is decomposed by muriatic acid. The component parts, as ascertained by Klaproth, are,

| Acid | 34.7 | |------|------| | Oxide | 65.3 |

13. Chromate of Lead.

An alkaline chromate mixed with the solution of nitrate of lead, forms a precipitate in the state of red powder, which is chromate of lead. This salt is found native, of a reddish yellow colour, and crystallized in four-sided prisms, terminated by four-sided pyramids. The specific gravity is about 6. It is soluble in the fixed alkalies, but insoluble in water. It is decomposed by muriatic and sulphuric acids, but dissolves without decomposition in nitric acid. According to the analysis of Vauquelin, it is composed of

| Acid | 34.9 | |------|------| | Oxide | 65.1 |

14. Acetate of Lead.

1. The combination of acetic acid and lead was formerly known by the names of extract of Saturn, salt of Saturn, sugar of Saturn, or sugar of lead. This acid oxidizes lead, and dissolves the oxides with great facility. It is formed by dissolving carbonate of lead or preparerite in acetic acid, or by exposing thin plates of lead to the action of acetic acid in earthen vessels. After the acid has been sufficiently saturated, and the solution concentrated by evaporation, the acetate of lead is deposited in small crystals.

2. This salt is in the form of small crystals, which are flat, four-sided prisms, terminated by two-sided units. It has an agreeable sweetish taste. The specific gravity is 2.345. It is not very soluble in water, without an excess of acid. It undergoes no change by exposure to the air. By its solution in water, a small quantity is deposited in the form of white powder, which is a carbonate of lead, formed by the carbonic acid which exists in the water.

3. Acetate of lead is decomposed by sulphuric, muriatic, fluoric, and phosphoric acids. It is decomposed by heat. By distillation it affords, according to the experiments of Proust, from 160 parts of the salt 12 parts of slightly acidulated water; with a greater heat, 72 parts of a yellow liquid, having the odour of alcohol, which had something of an empyreumatic smell. Ammonia was disengaged, by adding lime to the liquid; and when the liquid was saturated with potash, and remained at rest for 24 hours, a third part of oil separated, and floated on the surface. This oil, which had a strong odour, was removed, and the liquid distilled with a moderate heat. The first part that came over mixed with water like alcohol, and was almost as volatile as ether. When it was brought into contact with a burning body, it gave out a white flame.

15. Oxalate of Lead.

Oxalic acid very readily tarnishes lead, and at last corrodes it. It readily dissolves the oxide; and when it is saturated, the solution becomes thick, and deposits small shining crystals, which become readily opaque by exposure to the air. This salt may be formed by pouring oxalic acid into the solutions of nitrate, muriate, or acetate of lead. It is scarcely soluble in water, without an excess of acid. The component parts are,

| Acid | 41.2 | |------|------| | Oxide | 58.8 |

16. Tartrate of Lead.

Tartaric acid combines with the oxide of lead, or forms a precipitate in the state of an insoluble white powder, Lead, &c., powder, from the solution of lead in nitric and muriatic acids. It is composed of

| Acid | 34 | |------|----| | White oxide | 66 |

100.

17. Tartrate of Potash and Lead.

This triple salt is obtained by boiling the oxide of lead in tartar with water. It is insoluble, and is not decomposed by the alkalies.

18. Nitrate of Lead.

By adding citric acid to a solution of acetate of lead, a citrate of lead precipitates in the form of powder, which is scarcely soluble in water.

19. Malate of Lead.

This salt is obtained by adding malic acid to a solution of the nitrate or acetate of lead. The malate of lead precipitates in the form of fine light flakes. It is soluble in acetic and diluted nitric acids.

20. Benzoate of Lead.

Benzoic acid has but a feeble action on lead. By evaporating the solution, crystals of a brilliant-white colour are obtained, which are benzoate of lead. This salt undergoes no change by exposure to the air, is soluble in water and alcohol, is decomposed by heat, and by the sulphuric and muriatic acids.

21. Succinate of Lead.

Succinic acid combines with the yellow oxide of lead, and yields slender foliated crystals, which are nearly insoluble in water, but soluble in nitric acid.

22. Saccolate of Lead.

When salicylic acid is added to solution of nitrate of lead, a white precipitate is obtained, which is saccolate of lead.

23. Suberate of Lead.

Suberic acid forms a precipitate when added to the solution of lead in acetic and nitric acids.

24. Laclate of Lead.

Laetic acid, after it has been digested upon lead for some days, dissolves a portion of it. The solution has a sweet, astringent taste, but it does not crystallize.

II. Action of the Alkalies, &c. on Lead.

1. The alkalies and earths have no action whatever on lead. The alkalies, however, promote its oxidation by the air, on account of the attraction which they possess for the oxide of lead.

2. The alkalies and alkaline earths unite readily with the oxide of lead. Lime-water digested some time with oxide of lead in the state of litharge, dissolves this oxide better than the red. When the solution is evaporated, it affords small, transparent, iridescent crystals, not more soluble than lime. The alkaline sulphates decompose this compound of oxide of lead and lime. It is also decomposed by sulphurated hydrogen gas, and by sulphuric and muriatic acids, which latter convert the lead into a fulphate and muriate. This solution blackens wool, the nails, hair, the white of an egg; but has no action, and produces no change, on silk, on the skin, or the yolk of an egg. It has been observed, that the simple mixture of red oxide of lead and of lime, which latter converts it to white, produces a black colour on animal matters. It is sometimes employed for dyeing the hair. It had formerly been observed by Bergman, that the caustic fixed alkalies dissolve the oxide of lead, which takes place when these bodies are added in excess to the precipitate of this metal from its solution.

3. The earths, but especially alumina and silica, readily combine with the red oxide of lead, by the action of heat; and, when the proportion of oxide is considerable, the compound is a heavy, uniform, vitreous mass, which has been called glass of lead. It is on account of the strong tendency of the oxide of lead to vitrification, and which it communicates to earthly matters, that it is employed in the composition of glaas in the proportion of from $\frac{1}{3}$ to $\frac{1}{6}$. This oxide was only employed formerly, for the preparation of enamels, and for glazing pottery and stone ware; but it is now generally used after the example of the English manufacturers, in the fabrication of glaas, in most countries of Europe.

4. Lead has no action on the sulphates. It burns slowly with the assistance of the nitrates. When nitro, &c., in the state of fine powder, is thrown into melted lead, raised to a red heat, there is scarcely any perceptible flame; and, when the action has ceased, the oxide is found in small yellowish semivitrified scales, similar to those of litharge.

5. There is a perceptible action between lead and the muriates, some of which have given rise to several important processes in chemistry, and in the arts. It had been long observed, that a plate of lead immersed in water, saturated with muriate of soda, was soon covered with a crust of white oxide. It was also known, that the red oxide of mercury and litharge became white when kept in contact with muriate of soda dissolved in water. This process, which is promoted by agitation, is one of the great discoveries of modern chemistry, to be able to decompose common salt for the purpose of obtaining the soda. It was at first supposed, that this was a partial decomposition, from which a small quantity of muriate of lead only was obtained; that the decomposition was aided by heat; and that it was by this process that a brilliant yellow muriate of lead, much employed in painting under the name of English yellow, was prepared.

This subject has been greatly elucidated by the experiments and researches of Vauquelin. He took seven parts of litharge reduced to powder, and one of muriate of soda mixed together, and moistened with a sufficient quantity of water, to reduce them to the liquid state, and then agitated the mixture for several hours to promote the reciprocal action. The oxide became white, and increased in volume, and the mixture absorbing the water, became of a more solid consistence. Having added new quantities of water during four days, and diluted the whole in seven or eight parts of this Lead, &c. this liquid, it was filtered. The liquid, which was now sensibly alkaline, contained a little muriate of lead, but no trace of muriate of soda. When it was evaporated to \( \frac{1}{3} \) of its bulk, it yielded crystals of carbonate of soda, which were opaque, by being contaminated with muriate of lead. The oxide of lead which remained, had increased about \( \frac{1}{8} \) of the weight; it became of a fine citron-yellow colour, with a moderate heat, and lost 0.025 of its weight. It was insoluble in water. Soda dissolved a portion of this oxide, as did also diluted nitric acid. By this means the muriate of lead was separated pure and crystallized; and the mass which remained after the action of muriate of soda and lead, exhibited the characters of a muriate of lead containing an excess of oxide.

From these experiments Vauquelin concludes, that the litharge which has been employed in the decomposition of sea salt, is a muriate of lead with excess of oxide; that the caustic alkalies dissolve this salt, but do not decompose it; that the affinity of muriate of lead for an excess of the oxide of this metal, is the cause of the decomposition of muriate of soda by means of litharge; that the excess of oxide gives to the muriate of lead the property of affuming a brilliant yellow colour by heat, a property which the simple muriate of lead does not possess; that the same excess of lead renders it insoluble in water, and that this excess may be taken up by the nitric acid, which reduces it to the state of ordinary muriate of lead. The same philosopher has confirmed these inferences, by shewing that caustic soda decomposes the common muriate of lead, only by bringing it to the state of muriate with excess of oxide, which is characterized by being in the form of powder, and the yellow colour, which is communicated by heat, and its decomposition by nitric acid, which converts it into nitrate of lead, and simple muriate of lead. Thus, it appears, that the oxide of lead decomposes the muriate of soda, by double affinity; namely, by the affinity of the oxide for muriatic acid, and that of the muriate of lead for an excess of oxide. A considerable quantity of the latter, therefore, is necessary for the complete decomposition. Five-sixths, at least, are required to form the muriate with excess of oxide. Litharge then decomposes sea salt completely, when in sufficient quantity, while soda only decomposes the muriate of lead partially, and reduces it to the state of muriate with excess of oxide; but the carbonate of soda effects the entire decomposition of this salt.

6. The decomposition of muriate of ammonia by lead, and especially by its oxide, has been long known. The oxides of lead triturated with this salt in a mortar in the cold, disengage ammonia, which is very perceptible by its smell. By distilling a mixture of one part of red oxide of lead and two of muriate of ammonia in a retort, very pure caustic ammonia is obtained. If the red oxide has remained for any length of time exposed to the air, it gives out, during the process, a little carbonate of ammonia. The hypoxymuriate of potash produces a detonation with lead. A mixture of three parts of this salt with one of lead, gives out a vivid flame by percussion. The other salts, as the phosphates, fluates, &c. have no effect on lead. By the action of the blow-pipe, they combine with its oxides, and form yellowish, or gray, opaque, or transparent glasses.

III. Alloys.

1. Lead combines with arsenic by fusion, and the compound is a brittle lamellated alloy. When the oxides of these metals are combined together by means of heat, a vitreous mass of a red colour is formed.

2. The alloys of lead with tungsten, molybdenum, and the newly discovered metals, are not known.

3. Cobalt seems to have little affinity for lead. Cobalt Equal parts of the two metals being fused together, were found, when the mass cooled, to be in separate masses. The heaviest metal occupied the inferior part of the vessel, and the lighter the upper part. An alloy of lead and cobalt has been formed by introducing cobalt in powder within plates of lead, and covering them with charcoal, to exclude the air. A brittle mass, which assumed a better polish than lead, was obtained from equal parts of the two metals, by the application of heat. The two metals in different proportions afforded an alloy which differed in hardness, specific gravity and malleability, according as the one or the other metal predominated.

4. Lead forms with bismuth an alloy of a close grain, bismuth, and a dark gray colour. This alloy, when the bismuth is not in great proportion, possesses considerable ductility. Bismuth has the property of increasing the tenacity of lead. The specific gravity of the alloy of lead and bismuth is greater than the mean.

5. When lead is combined with one-eighth of its weight of antimony, it forms an alloy which possesses great tenacity. When they are combined in equal parts, the alloy is very brittle. Two parts of lead with one of antimony, give a brittle alloy in small grains similar to those of iron. Four parts of lead with one of antimony, afford an alloy of greater ductility, and in larger grains. Four parts of lead with one-half of antimony, give a very soft metal in fine grains like steel, and having the same colour. The alloy of 16 parts of lead and one of antimony, differs only from lead in hardness. This alloy has a greater specific gravity than the mean, and possesses considerable tenacity. It is employed in the fabrication of printing types.

6. Mercury combines with lead very readily, and mercury, in all proportions. An amalgam of lead and mercury may be formed by triturating the former in filings with the latter; or, by adding heated mercury to lead in fusion. This amalgam varies in solidity, according to the proportion of the two metals. It is of a white colour, is altered by exposure to the air, and affords crystals by cooling. The mercury is driven off by strong heat, and when it is triturated with water, a black powder, which is oxide of lead, separates. The amalgam of lead and mercury becomes very liquid, when it is triturated with the amalgam of bismuth. To equal parts of lead and bismuth melted in an iron vessel, half the quantity of the whole mass of muth, hot fluid mercury was added, and the mixture was agitated till it cooled. A fluid amalgam was thus obtained, which does not become solid by rest, or exposure to the air, and which almost entirely passes through leather like mercury itself. This liquidity of lead and bismuth is ascribed to their increased capacity for caloric in a state of combination. When mercury is thus sophistication, it may be detected by observing the Iron, &c., the smaller specific gravity, and subjecting it to the taff formerly mentioned, of pouring it along a smooth surface, when it is found to drag a tail.

7. An alloy of zinc and lead in equal parts is harder and whiter than lead, and is malleable. The lead is rendered volatile by the zinc, while the latter is in the proportion of 10 or 12 parts to one of the former; but if the zinc be in smaller proportion, it separates from the lead. The specific gravities of the alloys of zinc and lead are said to be greater than the mean of the two metals.

8. Lead combines with tin in all proportions. Lead, in general, is found to increase in density and hardness, when alloyed with tin. Three or four parts of tin with one of lead, according to Mutchenbroek, form an alloy which possesses twice the hardness of pure tin. The alloy of three parts of tin and one of lead possesses the greatest tenacity of any proportion of these metals. Two parts of lead and one of tin compose an alloy which is more fusible than either of the metals. This is the composition of common solder. Tin foil is a compound of tin and lead; and the sheet lead employed for lining the boxes in which tea is brought from China to Europe, contains a certain portion of tin, which gives it hardness. This, however, is also found to be alloyed with zinc and bismuth.

One of the most singular alloys of lead is that with bismuth and tin, which has been called, from its easy fusibility, the fusible alloy. Eight parts of bismuth, five of lead, and three of tin, are the proportions proposed by Darect for this alloy, which is so fusible, that it remains liquid at the temperature of boiling water. This alloy crystallizes by slow cooling.

Lead and its various preparations are applied to a great variety of purposes in the arts. In the metallic state it is employed in the construction of numerous vessels. In the state of oxide it is used as a paint, and in the fabrication of enamels for porcelain and pottery, and in the preparation of coloured glazes and artificial precious stones. Some of its salts are of great importance in the arts, as the acetate in dyeing, and the carbonate or ceruite in painting.

The greatest caution ought to be observed, however, in the use of leaden vessels in domestic economy, in which substances are preserved which are to be taken internally, particularly those which contain acids that are apt to dissolve the lead; and as the effects of lead are so deleterious to the animal economy when taken internally, this caution cannot be too strictly observed.

Sect. XVIII. Of Iron and its Combinations.

1. Iron is one of the most important and most useful of the metals, and it is fortunately one of the most abundant. It is supposed that it was not so early known as some of the other metals, which, on account of their scarcity and durability, have been held in higher estimation, and dignified with the name of precious metals. But perhaps the difficulty of extracting and working iron prevented it from being so generally applied to those purposes to which, on account of its valuable properties, it is peculiarly appropriated.

2. Iron, as it is the most useful of the metals, so as it has been observed, it is the most abundant, and at the same time the most universally diffused. Iron exists in five different states, but in these it exhibits the greatest variety of any other of the metals. It is found in the metallic state, in that of alloy with other metals; in the state of sulphuret, in the state of oxide, and combined with the acids forming salts.

1. Iron has only been found native in insulated masses, ores, one of which, discovered by Pallas in Siberia, and another, which was found in South America, long occupied the attention of philosophers in speculations and discussions concerning their origin. This point remained unsettled till the discovery of numerous other facts with regard to similar productions, which have proved, whatever may have been their origin or mode of formation, that these metallic masses have fallen from the atmosphere. 2. Iron is frequently found in the state of alloy with other metals; but in this state it is generally in very small proportion. 3. Combined with sulphur. This compound, or sulphuret of iron, which is known to mineralogists by the name of pyrites, is a frequent production among the ores of iron. Sulphuret of iron is found crystallized in a great variety of forms. Iron is also frequently found combined with carburet. This compound, now distinguished by the name of carburet of iron, was formerly known by the name of black lead, or plumbago. 4. But the most ordinary state of iron is that of oxide, and in this state it exhibits a great variety of forms. It is sometimes in irregular and insulated masses; sometimes regularly crystallized, and disposed in veins. 5. The native salts of iron are very numerous. It has been found in the state of sulphate, phosphate, carbonate, tungstate, and prussiate, and there is reason to believe, that it exists in combination with many other acids.

3. The method of assaying iron ores, or of extracting Analysis, the metal from these substances with which it is combined, varies according to the nature of the ore. It is first reduced into powder, and exposed to heat, to separate the moisture or sulphur, or other volatile matters. Four parts of the ore are then to be mixed with an equal quantity of decomposed muriate of soda, and the same quantity of a mixture of equal parts of fluor spar and lime, with one-half part of charcoal. This mixture is exposed to a red heat in a crucible nearly an hour, after which the iron is found in the metallic state at the bottom of the crucible. In the humid way, a given quantity of iron ore may be reduced to powder, and digested with six parts of muriatic acid, which combines with the iron, and other substances soluble in that acid, but leaves the sulphur and siliceous earth behind. The solution is then to be saturated with potash, by which the iron is precipitated in the state of oxide, along with the earths with which it had combined. The precipitate is to be well dried, and subjected to a red-heat. It is then to be reduced to powder, and digested with diluted nitric acid. The acid combines with the earths, but leaves the iron, because it is too highly oxidated to be soluble in this acid. The oxide, after being well washed, is mixed with charcoal, and exposed to a strong heat in a crucible, by which the oxygen is driven off, and the iron remains behind in the metallic state.

4. Iron has a peculiar metallic brilliancy. It is of a grayish or bluish-white colour. The specific gravity of Iron, &c., of iron is from 7.6 to 7.89, and according to some, even 8.16. It has an alluring taste, and when it is rubbed, gives out a peculiar smell. One of the singular properties of iron, is that of possessing the magnetic virtue, or of being attracted by the magnet. Iron possesses a considerable degree of malleability, but in this property it is inferior to gold or silver. It is extremely ductile. It may be drawn out into wire almost as fine as hair. The tenacity of iron is very great. A wire .078 of an inch in diameter will support a weight, without breaking, equal to more than 300 lb. avoirdupois*. The texture of iron seems to be fibrous; and to this, it is supposed, are owing its great ductility and tenacity.

5. Iron is one of the most infusible of the metals. It is said that it requires a temperature equal to more than 150° Wedgwood for its fusion. It becomes red long before it melts, and different degrees of temperature are distinguished by the different shades of red which it exhibits. The first is called a dull red, the second a cherry red, the third a bright red, and the fourth a white heat, or incandescence.

6. When iron is exposed to the air, the surface soon becomes tarnished, and is covered with a brown powder, which is called rust. This process is greatly promoted by the moisture of the atmosphere. This is the oxidation of the metal, and its conversion into an oxide, by combining with the oxygen of the atmosphere. The process of rusting, then, is the oxidation of the iron, and it is owing to the strong affinity which exists between iron and oxygen. But rust is not merely a compound of oxygen and iron. It has combined with a certain proportion of carbonic acid. This was formerly called saffron of mars.

7. There are two oxides of iron; the first, or that which contains the greatest proportion of oxygen, is common rust, or, as it is denominated from its colour, brown or red oxide of iron. This oxide may be formed by exposing iron filings in an open vessel to a red heat, and agitating them till they are converted into a red powder. This oxide consists of

\[ \begin{align*} \text{Oxygen} & : 48 \\ \text{Iron} & : 52 \\ \end{align*} \]

The red oxide of iron cannot be decomposed by heat; but when it is exposed to heat with its own weight of iron filings, there is no evolution of any gas, but the iron filings are converted into a black powder, and the red oxide is converted into a similar powder. This is the black oxide of iron, which contains the smaller proportion of oxygen. This oxide is composed of

\[ \begin{align*} \text{Oxygen} & : 28 \\ \text{Iron} & : 73 \\ \end{align*} \]

This oxide may also be obtained by heating iron filings for some time in water at a temperature not under 70°, or by making the vapour of water pass through a red-hot tube containing iron wire, or small fragments of iron. The water in these cases is decomposed, the hydrogen escapes in the form of gas, and the oxygen combines with the iron. This oxide was formerly called martial ethiops. It is this oxide which is obtained by burning iron wire in oxygen gas.

8. There is no action between iron and azote. Hydrogen gas, which is obtained from the decomposition of water by means of iron filings and sulphuric acid, holds a small quantity of iron in solution. When hydrogen gas is brought into contact with the red oxide of iron, it deprives it of that proportion of oxygen which it contains above the black oxide, and converts it into this oxide.

9. Iron combines very readily with carbone, and carburet. When the charcoal combines with one-tenth of its weight of iron, it constitutes a carburet, which is found native, and distinguished by the name of plumbago, or black lead. This compound has a metallic lustre, is of a bluish or dark-gray colour, has a greasy feel, and stains the fingers. It is well known as the substance of which black-lead pencils are composed. But there is another combination of iron with carbone, which forms one of the most important compounds, on account of its valuable properties, and the numerous uses to which it is applied. This is steel. The different states of iron are owing to its being perfectly free from contamination with other substances, or to its combination with carbone in different proportions. In these different states it is distinguished by the names of cast or crude iron, wrought iron, and steel.

Crude or cast iron.—When iron is first extracted from its ores, it is in the state of what is called crude iron. Iron is generally obtained from ores in the state of oxide, and this is frequently mixed with clay. It must therefore be separated from these substances. This is accomplished by reducing the ore to small pieces, and mixing it with a flux composed of limestone and charcoal. It is then exposed to a very strong heat. For this process, furnaces are constructed in such a way, that the heat can be raised to a very high temperature. The nature of the process must be obvious. The carburet of the charcoal combines with the oxygen of the iron, and forms carbonic acid, which is driven off in the state of gas. By the strong heat to which the lime and the clay are subjected, they are fused together, and form a vitreous matter, which being lighter than the iron, rises to the surface. The iron also is in a state of fusion at the bottom of the furnace. When the process is finished, a hole is opened, through which the fluid iron flows, and is received into moulds. This is crude or cast iron, or, in the language of the workmen, pig iron. In this state it is extremely brittle and hard, and possesses scarcely any malleability. It still contains a considerable proportion of carbone, and it is not entirely free from oxygen.

Wrought Iron.—The next process in the manufacture of iron, is to deprive it of these substances which alter its properties, and prevent its application to the purposes of pure or malleable iron. The crude iron is again introduced into a furnace, where it is melted by the flame of combustible substances, which is directed to its surface; and while it is in the state of fusion, it is constantly stirred, that the whole of it may be uniformly brought into contact with the air. At last it swells, and gives out a blue flame; and when this is continued for about an hour, the iron begins to acquire some consistency, and at last becomes solid. While it is hot, it is removed from the furnace, and hammered... Iron, &c., hammered by the action of machinery. It is then in the state of wrought or soft iron.

Steel.—This is soft iron or wrought iron combined with a certain portion of carbone. There are different processes for the preparation of steel; and the steel prepared by these processes has received different names. What is called natural steel, is prepared by exposing cast iron to a strong heat in a furnace, while its surface is covered with scoriae. In this process, part of the carbone of the crude iron combines with the oxygen, from which it is not entirely free, and is driven off in the state of carbonic acid gas. The iron remains combined with a small proportion of carbone. The steel prepared in this way is of an inferior quality.

Steel of cementation is prepared by arranging bars of pure iron and charcoal in powder in alternate layers, in large troughs or crucibles, which are carefully closed up with clay. These are exposed to heat in a furnace for the space of eight or ten days, when the bars of iron are found converted into steel. This is sometimes called blistered steel, from blisters which appear on the surface, or tilted steel, when it is drawn out into smaller bars by the hammer. By breaking it into pieces, and repeated welding in a furnace, and afterwards drawing it out into bars, it is converted into what is called German or sheer steel. Steel formed in this way is generally of a superior quality to natural steel.

Cast steel is prepared by fusing natural steel with charcoal powder, and pounded glaas, in a close crucible; or by melting together 30 parts of iron, one of pounded glaas, and one of charcoal. By this process the best kind of steel is obtained, and it is this which is generally used for the finer kinds of cutting instruments. Different opinions have been entertained concerning the proportions of iron and carbone in the composition of steel. According to some, the proportion of carbone amounts to $\frac{1}{2}$ part, though, according to others, it does not exceed $\frac{1}{4}$ part.

Steel possesses very different properties from iron. It is extremely hard and brittle, does not yield to the file, and retains the magnetic virtue for any length of time. When it is hammered, its specific gravity is greater than that of iron. It is not malleable when cold, but it has this property when red-hot, and it may be reduced to thinner plates than iron.

There is a very easy test by which steel may be distinguished from iron. If a drop of diluted nitric acid be let fall on steel, and allowed to remain for a few minutes, it leaves behind, after it is washed off, a black spot, which is owing to the conversion of the carbone of the steel into charcoal, by combining with the oxygen of the acid. But if nitric acid is dropped on iron, a whitish gray spot remains.

Phosphuret. Iron combines with phosphorus, and forms with it a phosphuret. It may be formed by melting in a crucible 16 parts of phosphoric glaas with 16 parts of iron, and one-half part of charcoal in powder. The phosphuret of iron is of a white colour when it is broken, and it is observed crystallized in some points in rhomboidal prisms. It is of a striated and granulated texture, and is magnetic. This phosphuret may be formed also, by dropping small bits of phosphorus into iron filings heated red-hot. This is the siderite of Bergman, in which he supposed he had discovered a new metal, to which he gave the name of siderum. Cold short iron is called cold short iron, from its being brittle when cold, but malleable when it is heated, contains a certain portion of phosphate of iron, to which this property is owing. It was in the investigation of the nature of this iron, that Bergman obtained, by means of sulphuric acid, a white powder, which was converted into a brittle metal of a dark-gray colour. By the experiments of Klaproth and Scheele it was proved, that cold short iron is a compound of phosphoric acid and iron.

11. Iron combines with sulphur by different processes. A sulphuret of iron may be prepared by fusing together in a crucible, equal parts of powdered sulphur and iron filings. This is a mass which is remarkably brittle and hard, and of a deep-gray colour. If this mass be reduced to powder, and moistened with water, the water is decomposed, its oxygen combines with the sulphur, which is converted into sulphuric acid, and the iron is oxidated. If equal parts of sulphur and iron-filings be well mixed together by trituration, and a sufficient quantity of water be added, to form the whole into a paste, and if this mixture be exposed to the air, it soon becomes hot, swells up and cracks, exhaling the vapours of sulphurated hydrogen gas, and sometimes spontaneously inflamed. During this action the water is decomposed, the iron is oxidated, and the sulphur is converted into sulphuric acid, while the hydrogen of the water combines with a portion of sulphur, and forms sulphurated hydrogen gas. By observing the phenomena of this process, which also takes place, it is said, when the mixture is buried under ground, Lomery supposed that he could explain the nature and cause of volcanic eruptions.

If a mixture of three parts by weight of iron filings, and one of powdered sulphur, be put into a glaas vessel on burning coals, a sulphuret of iron is obtained, with some remarkable phenomena. It first melts, and then all at once becomes red-hot, and sometimes, when the quantity is considerable, is accompanied with an explosion, at the moment when the combination takes place. According to the experiments of Proust, the component parts of sulphuret of iron are,

| Sulphur | 60 | |---------|----| | Iron | 40 |

According to the experiments of the same chemist, pyrites, which is found in great abundance in nature, and usually crystallized in cubes, is sulphuret of iron combined with an additional portion of sulphur. The component parts of pyrites are,

| Sulphuret of iron | 80 | |-------------------|----| | Sulphur | 20 |

12. Iron enters into combination with the acids, and forms salts, and with the metals, and forms alloys. The affinities of iron and its oxides are, according to Bergman, in the following order. Iron.

Oxide of Iron.

Nickel, Oxalic acid, Cobalt, Tartaric, Manganese, Camphoric, Arsenic, Sulphuric, Copper, Slaclastic, Gold, Muriatic, Silver, Nitric, Tin, Phosphoric, Antimony, Arsenic, Platinum, Fluoric, Bismuth, Succinic, Lead, Citric, Mercury, Lactic, Acetic, Boracic, Prussic, Carbonic.

I. Salts of Iron.

1. Sulphate of Iron.

1. Concentrated sulphuric acid has scarcely any action on iron. When it is heated, the acid is decomposed, part of its oxygen combines with the iron, and sulphurous acid gas is evolved. But when diluted sulphuric acid is added to iron filings, a violent effervescence takes place, and hydrogen gas is disengaged. In this process, the water, with which the acid is diluted, is decomposed, the oxygen of which combines with the iron, and converts it into an oxide, while the hydrogen escapes in the state of gas. The solution is of a green colour, and, by evaporation, it affords crystals of sulphate of iron, which are transparent, of a fine green colour, in the form of rhombohedral prisms, and having an acid astringent taste. This salt almost always reddens vegetable blues. It is very soluble: two parts of cold water, and less than its weight of boiling water, are sufficient for its solution.

2. This salt is, in many places of the world, a natural production. It is obtained from the decomposition of pyrites, which it is sometimes found necessary to promote by art. This is done by throwing them together into heaps, and watering them occasionally. Sometimes previous roasting is necessary, either to render them more brittle, and to separate the additional portion of sulphur above what is necessary to constitute a sulphuret. After a certain time an efflorescence takes place, and the surface is covered with the sulphate of iron, which is dissolved in water, concentrated by boiling, and evaporated, and then allowed to cool and crystallize. This salt, which was known to the ancients, was denominated myty, sory, and calchaniun. It is distinguished in commerce by a great variety of names, as martial vitriol, roman vitriol, and most commonly by the names of green copperas or green vitriol.

3. When sulphate of iron is strongly heated, it melts, and is deprived of its water of crystallization. Sulphurous acid gas is then given out; it assumes a red colour, and is reduced to the state of powder. This was formerly called coleothar, and colcothar of vitriol. It is the salt almost entirely decomposed. Part of the iron is strongly oxidated, and to this the red colour is owing. It is also mixed with sulphate of iron; but the iron in this case is also converted into the red oxide, with the greater proportion of oxygen. This change, it is obvious, depends on the strong affinity of iron for oxygen; for by the action of heat, the sulphate of iron, of which the green oxide forms the base, is decomposed; the oxygen of the acid combines with the iron, and converts it into the red oxide; part of which, as it is formed, unites with the acid, before the whole of it is decomposed; and in this way the product of this process is the red oxide of iron mixed with red sulphate.

The component parts of this salt are, according to Compoition:

| Acid | 39 | | Oxide | 23 | | Water | 38 |

These properties vary, according to the estimation of Mr Kirwan, who makes this salt to be composed of:

| Acid | 26 | | Oxide | 28 | | Water of composition | 8 | | of crystallization | 38 |

This distinction made by Mr Kirwan between the water of composition and that of crystallization is, that the former is combined with the oxide, and the latter with the salt.

4. When this salt is exposed to the air, it becomes action of a yellowish colour, opaque, and a powder forms on the surface. The same thing takes place, if the salt in solution in water be exposed to the air. From a fine transparent green colour, it becomes turbid, and is converted into a yellowish-red liquid, and there is precipitated a powder of the same colour. This change is owing to the absorption of oxygen, and the conversion of the green oxide with the smaller proportion of oxygen, into the red oxide with the greater proportion. This process is greatly promoted by the direct combination of oxygen, or by the addition of those substances which are readily decomposed, and give out their oxygen. When oxymuriatic acid is added to the solution, it becomes instantly yellow, and there is formed a red precipitate. The same change takes place when the salt is dissolved in water impregnated with carbonic acid. The iron decomposes the acid, and combines with its oxygen. Thus it appears, that the decomposition of the sulphate of iron is owing, in all these cases, to the absorption of oxygen, and to the higher degree of oxidation of the metal.

5. The sulphate of iron is converted into the red Decomposition sulphate by means of nitric acid. It is decomposed by the alkaline earths and the alkalis, which precipitate it in the form of oxide. The pure fixed alkalies and lime separate an oxide of a deep green colour, which, being exposed to the air, is converted into the red oxide. Ammonia affords a precipitate of a deeper green colour. The sulphurets and hydro-sulphurets precipitate from the solution of green sulphate of iron, a black sulphurated or hydrosulphurated oxide. Most of the salts decompose the sulphate of iron. When equal parts Iron, &c., parts of nitrate of potash and sulphate of iron are distilled together in a retort; a weak nitric acid at first passes over, then a nitrous acid, and at last a very small quantity of sulphurous acid. The muriate of soda is decomposed by the sulphate of iron, in consequence of the disengagement of sulphuric acid, which separates the muriatic acid from its base. Sulphate of soda, combined with the oxide of iron in the state of a vitreous mass, remains in the retort. The hyperoxymuriate of potash converts the green sulphate of iron into the red. This salt is also decomposed by the alkaline phosphates, borates, and carbonates.

Red fulphate of iron.—In the detail which has been given of the properties of the green sulphate of iron, it appears, that it has a strong affinity for oxygen. The oxide of the green fulphate contains 27 parts of oxygen; but by absorbing another portion of oxygen, it is converted into the red oxide, which contains 48 parts of oxygen. This salt may be obtained by the direct combination of the red oxide of iron with concentrated sulphuric acid, with the assistance of heat. The salt remains in the solution from which the green sulphate of iron has been crystallized. This solution has been called the mother water of vitriol. The red fulphate of iron is very different in its properties from the green fulphate. It does not afford crystals; it is distinguished by its red colour, and it deposits the oxide of iron, when brought into contact with the air, or by the action of heat. It deliquesces in the air, and at last becomes liquid. It is more soluble in water than the green fulphate; and also soluble in alcohol, by which it may be separated from the green fulphate, which is not affected by the alcohol. When iron filings are added to a solution of red fulphate of iron, part of the oxide is separated, another part gives up a portion of its oxygen to the iron, and is converted into the green fulphate. The same effect is produced, as M. Proust, by whom this subject has been greatly elucidated, observes, by means of other metals, as mercury, zinc, and tin. The two fulphates of iron are distinguished by other properties. The infusion of nut-galls produces no change in the green sulphate of iron, but gives a fine black precipitate with the red fulphate.

Prussiate of potash occasions no change of colour on the green fulphate of iron, but produces a deep blue precipitate with the red fulphate; from which it appears that there are two prussiates of iron, corresponding to the two oxides. The white prussiate contains the green oxide with the smaller proportion of oxygen; the blue prussiate, the red oxide with the greater proportion. Another characteristic property is, that the green fulphate of iron absorbs nitrous gas in considerable quantity, and assumes a yellowish colour; but no such absorption is effected by the red fulphate.

1. Sulphurous acid is decomposed by iron, and the portion of sulphur which is separated, remains in combination with the salt as it is formed. When liquid sulphurous acid is added to iron filings, it affumes a deep yellow colour; some hydrogen gas is evolved, with a production of heat, and the yellow colour soon changes to a greenish shade. Sulphuric or muriatic acid, added to this solution, produces an effervescence, but without any precipitation. It is necessary to add iron, &c., the acid in considerable quantity to obtain a precipitate of sulphur in white powder. Fuming nitrous acid separates the sulphur of a yellow colour, and in the form of a ductile mass. From these facts it appears, that the first portion of acids acts only on the simple fulphite of iron; but when a greater quantity is added, the sulphurated fulphite is decomposed, and the sulphur is deposited.

2. The solution of iron in sulphurous acid, exposed to the air, deposits a reddish-yellow powder, and affords crystals which are surrounded with this reddish powder. By adding water to this mass, it dissolves the crystallized part, and leaves the red powder, which being dissolved in muriatic acid, gives up its iron, and deposits sulphur, which is still mixed with a little iron. This precipitate dissolved in water, affords a sulphurated sulphite of iron, with a smaller quantity of sulphur than the first solution. Exposed to the air after the first precipitation is formed, the surface is soon covered with a red pellicle. A red powder is deposited, and afterwards crystals of fulphite of iron.

3. The sulphurated fulphite of iron remains permanent by exposure to the air. Its simple fulphite absorbs oxygen. The sulphurated fulphite deposits sulphur by the action of the acids. The fulphite gives out sulphurous acid. The sulphurated fulphite is soluble in alcohol; the fulphite is insoluble.

4. The red fulphate of iron with the greater proportion of oxygen, does not produce the same effect on sulphurous acid, by converting it into sulphuric acid, and thus to form a fulphate of iron, as the oxide of manganese, because iron has a stronger affinity for oxygen than sulphurous acid. Thus we have seen, in consequence of the same affinity of iron for oxygen, that nitric acid decomposes sulphuric acid, and converts part of it into sulphurous acid, and that it even decomposes sulphurous acid, by separating its sulphur, which combines with the oxide as it is formed, and constitutes the sulphurated fulphite of iron. Neither of these sulphites of iron give a black colour with the infusion of nut galls, nor a blue colour with the prussiate of potash; from which it is inferred that the iron is in its minimum state of oxidation, or in that of a green fulphate of iron.

3. Nitrate of Iron.

Nitric acid acts with great violence on iron; a great quantity of nitrous gas is disengaged, especially when the acid is a little diluted with water. When diluted acid has been employed, the solution is of a yellowish-green colour, and when it is exposed to the air, it affumes a pale colour, in consequence of the nitrous gas which it holds in solution, combining with oxygen, and being converted into nitric acid. When it is exposed to the air, or concentrated by evaporation, a precipitate of the red oxide of iron is formed, because it combines with another portion of oxygen, and is converted from the green to the red oxide. By means of the alkalis, the green oxide is precipitated from this solution.

Red nitrate of iron.—This is the salt formed with preparatory acid and the red oxide of iron. It is prepared by exposing the green nitrate of iron to the air, which absorbing oxygen, is converted into the red nitrate. If iron be dissolved in concentrated nitric acid, the iron is converted into the red oxide, and this combining with the undecomposed acid, also forms the red nitrate of iron. The solution of this salt, which is of a brown colour, does not crystallize; when it is evaporated, it assumes the form of a jelly, or deposits a red powder. When this salt is heated, the acid is driven off, and the red oxide remains behind. The red nitrate of iron gives a black colour with the infusion of galls, and a blue precipitate with prussiate of potash, from which it appears, that the iron is in its highest degree of oxidation. This has been fully demonstrated by an experiment made by Vauquelin. Concentrated nitric acid was kept for some months on black oxide of iron, without any apparent change. The nitric acid, however, lost its acidity, and acquired a neutral taste. The liquid had assumed a brown colour; and large crystals, transparent and white, with a slight tinge of violet by looking through them, were formed. The crystals were in square prisms, terminated by two-sided ridges. This salt was extremely deliquescent, and had a pungent inky taste. The solution in water becomes red, as is also the precipitate, by means of ammonia and potash. Prussiate of potash gives a fine blue precipitate.

4. Muriate of Iron.

1. When iron filings are exposed to muriatic acid gas they soon become black, and are converted into the state of red oxide. This is owing to the decomposition of the water which the gas holds in solution. The bulk of the gas is increased by the addition of hydrogen gas, from this decomposition of water. When the whole of the muriatic acid is absorbed by the iron in the state of oxide, hydrogen gas only remains in the vessel in which the process has been conducted. When a little water is added, it assumes a green colour, having combined with the muriate of iron in the liquid state.

2. Liquid muriatic acid acts upon iron in proportion to its degree of concentration, and the action is the more violent as it is less concentrated. An effervescence takes place, with the disengagement of hydrogen gas. As the iron is oxidized by the decomposition of the water, it is dissolved in the acid. This solution is of a pale yellowish colour, and of a strong acetic taste. When it is evaporated to the constancy of syrup, it forms on cooling, a viscid mass, in which are found needle-shaped, deliquescent crystals. When this solution is exposed to the air, or strongly heated, it assumes a brown colour, and deposits oxide of iron.

Red muriate of iron.—When the red oxide of iron is treated with muriatic acid, the acid dissolves the iron, and forms a solution of a deep brown colour. During the solution, oxymuriatic acid is formed and given out, which is owing to the combination of a portion of the oxygen of the oxide with the muriatic acid. The oxide thus deprived of a portion of its oxygen, combines with the muriatic acid, and forms red muriate of iron. When this solution is evaporated to dryness, it affords a yellow coloured mass, which is deliquescent in the air. This salt does not absorb nitrous gas, and it is converted into muriate of iron by the action of sulphurated hydrogen gas. When it is precipitated by the alkalies, the oxide is not farther changed by exposure to the air. The infusion of nut galls gives a black colour, and the prussiate of potash a blue.

5. Hyperoxymuriate of Iron.

This salt was formed by Mr Chenevix, by directing a stream of oxymuriatic acid gas into water, having red oxide of iron diffused in it; but its properties have not been ascertained.

6. Fluate of Iron.

Fluoric acid has a very powerful action on iron, which is owing to the evolution of hydrogen gas, and the decomposition of water. The iron is oxidized, and dissolves in the acid, forming a fluate of iron. The solution has a flaky, metallic state, does not afford crystals by evaporation, but assumes a gelatinous form. Evaporated to dryness, it becomes hard and solid; and when strongly heated, the acid is driven off, and there remains behind the red oxide of iron, so that this salt is the red fluate of iron. The red oxide of iron is also soluble in fluoric acid, and communicates to it, according to Scheele, an aluminous taste. The fluate of iron is decomposed by sulphuric acid, and is precipitated by the alkalies and the earths.

7. Borate of Iron.

Boracic acid promotes the oxidation of iron by water very slowly. The borate of iron may be obtained by precipitating the fulphate of iron by means of the borate of soda, or borax. The borate of soda is precipitated in the form of a whitish powder. It is insoluble in water, but its other properties have not been ascertained.

8. Phosphoric Acid of Iron.

Phosphoric acid combines very slowly with iron, but after the oxidation of the metal has taken place, it forms with its oxide an insoluble salt. The phosphate of iron may be prepared by adding a solution of an alkaline phosphate to a solution of fulphate or nitrate of iron. The alkali leaves the phosphoric acid, and combines with the sulphuric or nitric; while the phosphoric acid combines with the iron, and forms a phosphate of iron, which is in the state of white precipitate. Phosphoric acid combines with both oxides of iron, and constitutes either a green or a red phosphate. The red phosphate of iron may be obtained by precipitating the red muriate of iron in solution, by means of phosphate of potash or soda; and when this latter salt is treated with pure fixed alkalies, a brownish red powder is precipitated, which is the red phosphate of iron, with excess of base. It is nearly insoluble in acids and in water, but is soluble in the serum of blood, and the white of an egg, communicating to them a brown colour. This salt exists in the blood of animals, and to it the red colour of the blood is owing.

9. Carbonate of Iron.

Carbonic acid combines readily with the oxide of iron. This is the case when iron rusts in the air; for in proportion as the oxidation of the iron is effected, it combines with the carbonic acid of the atmosphere, and and forms a carbonate of iron. This acid dissolved in water, when brought in contact with iron, acts upon it slowly; and there is disengaged, but without effervescence, a perceptible odour of hydrogen gas, and the water acquires in the course of a few hours, an astrin- gent taste. When this solution is exposed to the air, as Bergman observed, it becomes covered with an iridescent pellicle, and is decomposed by lime and the alkalies. But the alkaline carbonates have no such effect. This solution of the carbonate of iron converts the syrup of violets to a green colour. When it is evaporated, it deposits the salt in the form of a reddish ochre. It is this carbonate of iron which exists in mineral waters, to which, for this reason, the name of char- lybate has been given to waters. Rust is a carbonate of iron, mixed with the oxide. Fourcroy found by distilling it, that it yielded carbonic acid gas, and a little water, and there remained black oxide of iron; and distilled with muriate of ammonia, it afforded carbonate of ammonia. The component parts of this carbonate, according to Bergman, are

| Acid | 24 | | Oxide | 76 |

10. Arseniate of Iron.

1. When iron is digested with arsenic acid, it is dissolved, and towards the end of the process the solution assumes the form of a jelly. But if it be conducted in a close vessel, no coagulation takes place. By exposing it to the open air for some hours, the surface becomes so solid, that the vessel may be inverted without any part of it dropping out. The solution which has not been exposed to the air, affords a precipitate with potash, of a greenish-grey colour, from which there is dis- engaged by heat, arsenious acid, and there remains behind a red oxide of iron. One part of iron-filings distilled with four of concrete arsenic acid, swells up and inflame; the metallic acid is sublimed, and brown spots appear on the sides of the retort. From this experiment it appears, that the iron has carried off the oxygen from the acid.

2. Arsenic acid does not precipitate iron from its solutions, but the arseniates or arsenites form a very soluble precipitate, which becomes yellow or red in contact with the air. This precipitate, which is fusible at a high temperature, exhales the odour of arsenic when it is melted, is converted into black scoria; when it is treated with charcoal, gives out a considerable quantity of arsenic, and is reduced to the state of black oxide of iron.

3. Arsenic acid combines with both the oxides of iron. The green arseniate of iron may be obtained by adding a solution of arseniate of ammonia to a solution of sulphite of iron. The arseniate precipitates in the form of powder which is insoluble in water. The component parts of this salt, according to Chenevix are

| Acid | 38 | | Oxide | 43 | | Water | 19 |

Red Arseniate of Iron.—This salt is prepared, either by boiling arseniate of iron in nitric acid, or by adding arseniate of ammonia to a solution of red sulphate of iron. It is composed of

| Acid | 42.4 | | Oxide | 37.2 | | Water | 20.4 |

Both these salts have been found native.

II. Tungstate of Iron.

Tungstic acid has no great effect on iron in the cold. Iron immersed in a solution of this acid in muriatic acid, communicates to it a beautiful blue colour, which is owing to the decomposition of the tungstic acid, and to its reduction to the metallic state by means of the iron. Tungstic acid precipitates from the solution of iron in sulphuric acid, tungstate of iron. Tungstate of iron exists native under the name of wolfram.

12. Molybdate of Iron.

The alkaline molybdates which are soluble, precipitate iron from its solution in acids, of a brown colour.

13. Chromate of Iron.

If chromic acid, combined with an alkali, be added to a solution of the red sulphate of iron, a precipitate is immediately formed, of a brown colour; but if an alkaline chromate is added to the green sulphate of iron, the precipitate is green, because the chromic acid is deprived of a portion of its oxygen, and is converted to the state of green oxide.

14. Columbate of Iron.

The columbite of iron is found native, and from the only specimen which has yet been discovered, Mr Hatchet extracted a new metal, which has been described under the name of columbium. It is of a dark-brownish grey colour, has a vitreous lustre, and a lamellated structure. According to Mr Hatchet, it is composed of

| Columbic acid | 77.5 | | Oxide of iron | 21.0 |

15. Acetate of Iron.

1. Acetic acid dissolves iron with effervescence, with the evolution of hydrogen gas. The liquid af- fumes a reddish-brown colour, and by evaporation be- comes a gelatinous mass, in which are found long brown crystals. This salt has a sweetish pungent taste. It is decomposed by heat, and is deliquescent in the air. When it is heated till it no longer gives out the odour of vinegar, it lets fall a yellowish oxide, which is easily reduced, and is attracted by the magnet. The alkalies separate the iron nearly in the state of black oxide. This solution affords a black precipitate with the infusion of nut-galls, and a blue with the alkaline prussiates. 2. The solution of this salt is prepared in the large way with old iron, and vinegar obtained from grain or molasses. They are exposed to the air in large vessels, and as the fermentation of the liquid goes on, it is converted into acetic acid, the iron is oxidized, and dissolved by the acid. This solution is employed in dyeing and calico-printing.

Green acetate of iron.—This salt has been formed by dissolving sulphuret of iron in acetic acid. It affords crystals by evaporation, in the form of prisms, and of a green colour. The taste is pungent and sweetish. It gives a white precipitate with the alkaline prussiates, and no change is effected by the infusion of galls. When the solution of this salt is exposed to the air, it very readily absorbs oxygen, and is converted into red acetate of iron.

16 Oxalate of Iron.

Oxalic acid produces a violent action on iron, with the evolution of hydrogen gas. This solution has a very pungent taste, and forms by evaporation prismatic crystals of a greenish yellow colour. When this solution is exposed to the air, or, when it is heated, it assumes a red colour, which is owing to the absorption of oxygen, and its conversion into red oxalate. The oxalate of iron is composed of

| Acid | 55 | | Oxide | 45 |

Red oxalate of iron.—Oxalic acid precipitates the red oxide of iron from the solution in sulphuric acid, and forms an oxalate of iron of a fine red colour. The red oxalate of iron does not crystallize, and has little solubility in water. This has been proposed to be employed as a pigment. None of the acids dissolve the oxides of iron more readily than oxalic acid, and especially the gallate of iron. On this account it answers well for removing spots of ink, for which purpose also the acidulous oxalate of potash, or salt of tartar, is also employed.

17 Tartrate of Iron.

1. Tartaric acid dissolves iron with effervescence, and the evolution of hydrogen gas. The solution becomes of a red colour, and assumes the form of a gelatinous mass, but does not crystallize. This is the red tartrate of iron.

2. But when tartaric acid is added to the solution of sulphate of iron, and heat applied, a precipitate is formed, which is not very soluble, but affords lamellated crystals. This is the compound of tartaric acid with the green oxide of iron, for it does not form a precipitate with the alkaline prussiates, without the addition of nitric acid.

18 Tartrate of Potash and Iron.

This triple salt, which was formerly called chalybeated tartar, and tartarized tincture of Mars, is prepared by forming into a paste with water, six parts of iron filings with 16 of tartar in powder. The mixture is left at rest for 24 hours; and being diluted with 192 parts of water, is boiled for two hours, when crystals are deposited of tartrate of potash and iron.

19 Citrate of Iron.

Citric acid acts upon iron with effervescence, occasioned by the emission of hydrogen gas. The solution becomes of a brown colour; it deposits, by spontaneous evaporation, small crystals of citrate of iron. By evaporating with heat, it becomes black as ink, and ductile while it is hot, but falls to powder, and becomes very black when it is cold. This salt has a very astringent taste, and is very soluble in water. It is composed of

| Acid | 69.62 | | Oxide | 30.38 |

The crystals which were obtained by spontaneous evaporation, were probably the green citrate; and the black mass, by the action of heat, is probably converted into the red citrate of iron.

20 Malate of Iron.

Malic acid gives a brown solution by its action on iron, but it does not crystallize.

21 Gallate of Iron.

It has frequently been mentioned, in describing the gallic acid salts of iron, that the infusion of nut-galls, or gallic acid, produces no precipitate or change of colour, nor only when it is added to salts of iron in solution, of which with the black or green oxide constitutes the base; but red oxide, when the acid is added to a solution of a salt of iron, having the red oxide for its base, a black precipitate is immediately formed. From this it appears, that the black precipitate can only be obtained from the red oxide of iron, or it is the gallate of iron in the highest degree of oxidation. Writing ink is a compound of the solution of gallate of iron and the tanning principle. The important qualities of good ink are, that it shall be durable, and have a black colour. On this subject Professor Robison observes, in his Notes on Dr Black's Lectures, that "the great art in ink-making is to have a superabundance of astringent matter to counteract the deposition of the iron to a farther calcination, which renders the ink brown. It would be a great improvement in the manufacture of writing paper, if some astringent matter could be introduced. A little ardent spirits effectually prevents the spoiling of ink by keeping, but makes it sink and spread."

A good Proportion for Writing-Ink.

Rasped logwood, 10 ounces; Best gall-nuts in coarse powder, 3 ounces; Gum arabic in powder, 2 ounces; Green vitriol, 1 ounce; Rain water, 2 quarts; Cloves in coarse powder, 1 drachm.

Boil the water with the logwood and gum to one half; strain the hot decoction into a glazed vessel; add the galls and cloves; mix and cover it up. When nearly cold, add the green vitriol, and stir it repeatedly. After some days, decant or strain the ink into a bottle, to be kept close corked in a dark place. Ink is sometimes of a very pale colour when first used, but becomes black by exposure to the air. This is owing to the absorption of oxygen. The green vitriol or sulphate of iron, which is employed in making ink, has not its base fully saturated with oxygen, or is not in the state of red oxide. It is the conversion of the green into the red oxide, which takes place when it is exposed to the air. The use of gum in the composition of ink is to prevent the precipitation of the black particles, and also, it is supposed, to act as a varnish, to defend it from the air, which might give it a brown colour by farther oxidation.

22. Benzoate of Iron.

Benzoic acid readily dissolves the oxide of iron, and forms with it yellowish crystals, which are sweet to the taste, effloresce in the air, and are soluble in water and in alcohol. Gallic acid produces a black precipitate, and the prussiates give a blue. It is decomposed by the alkalies, and by the carbonates of lime and barytes. The acid is driven off by heat.

23. Succinate of Iron.

Succinic acid combines with the oxide of iron; and the solution, by evaporation, affords small radiated crystals, which are transparent and of a brown colour. This salt is insoluble in water. It may be formed by adding an alkaline succinate to the solutions of iron in acids.

24. Suberate of Iron.

Suberic acid decomposes the fulphate of iron, and produces a deep yellow colour.

25. Mellate of Iron.

Mellitic acid produces a copious precipitate of an Isabella-yellow colour, in the solution of iron in nitric acid. This precipitate is readily dissolved in nitric acid.

26. Lactic acid produces a copious precipitate of an Isabella-yellow colour, in the solution of iron in nitric acid. This precipitate is readily dissolved in nitric acid.

27. Prussian Blue.

1. Prussian blue combines with both the oxides of iron. When the prussiate of potash is added to a solution of the green fulphate or muriate of iron, a white precipitate is obtained. This shows, as has been already observed, that the base of these salts is in its lowest degree of oxidation. It is in the state of green or black oxide. But if the prussiate of potash be poured into a solution of the red fulphate of iron, a fine blue precipitate is formed, which is Prussian blue, or a prussiate of iron in the state of red oxide.

2. When the white precipitate of iron is exposed to the air, it gradually absorbs oxygen, and is converted into the blue prussiate, or Prussian blue. On the other hand, the blue prussiate may be converted into the white, by preserving it in a close vessel, with plates of iron or tin. The metallic substance deprives the iron of part of its oxygen, and makes it pass to the state of green oxide; in which state, combined with prussic acid, it is colourless. Sulphurated hydrogen gas produces a similar effect, by depriving the iron of its iron, etc., oxygen. Nitric and oxymuriatic acids convert the white prussiate into blue, by giving up their oxygen, which combines with the iron, and forms the red oxide.

II. Action of the Alkalies, &c. on Iron.

1. Iron, in the metallic state, has a very feeble action on the alkalies and earths. The alkalies, in their pure and concentrated state, promote the decomposition of water by means of iron. Hydrogen gas is disengaged, and the metal is converted into the state of black oxide, or martial ethiops; but there seems to be no perceptible solution of the oxide of iron, which is thus formed in the liquid alkalies.

2. The brown oxides of iron readily combine with the earths suspended in water. This combination has been long employed on account of its properties of affuming a great degree of solidity and hardness, as a cement, and especially as a cement or mortar to be employed under water. Hence volcanic productions, as pumice-stone earths, which contain a considerable proportion of oxide of iron, are often employed for this purpose. The oxide of iron combines also with the earths by means of fusion, and communicates to them various shades of colour, according to the degree of oxidation, and the proportion of oxide employed. In this state it is used in the fabrication of enamels and coloured glazes.

3. The alkaline sulphates are decomposed by iron at a high temperature. The iron deprives the sulphuric acid of its oxygen, and reduces it to the state of sulphur. Fourcroix heated for an hour in a covered crucible, one part of sulphate of potash, with two of iron filings. He obtained a kind of granulated scoria, which had swelled up, and was of a deep green on the surface. It was extremely hard, and exhibited in some of the internal cavities, shining fixed plates of black oxide of iron. It had a hot, acrid taste. When reduced to powder, it exhaled the fetid odour of sulphurated hydrogen gas. It was not deliquescent in the air; and diluted with 10 parts of water, it was of a deep green colour. This was a solution of hydrochloride of potash, holding a small quantity of iron in solution. Sulphur was precipitated by the addition of acids, with the evolution of sulphurated hydrogen gas.

4. The nitrates are also decomposed by means of iron heated to redness. Two or three parts of nitre, with one of clean iron filings, well triturated together, and projected into a red-hot crucible, give out at each projection a great number of vivid sparks. After the detonation, a half-fused mass remains, of a reddish yellow colour, which, by washing with water, affords pure potash, and there remains an oxide of iron in its highest degree of oxidation. Steel also detonates with nitre, and gives out a very brilliant red flame. These mixtures are employed in artificial fireworks.

5. Some of the muriates are also decomposed by iron. The experiment of Scheele, in which the muriate of soda was decomposed by means of iron, has already been mentioned. The muriate of ammonia is readily decomposed by iron with the assistance of heat. Hydrogen and ammoniacal gases are disengaged. A preparation formerly known by the name of martial ammoniacal ammoniacal flowers, was made with 16 parts of muriate of ammonia and one of iron filings. This mixture is sublimed in two earthen vessels, the one being inverted over the other. A small quantity of the muriate of ammonia only is decomposed, and the salt assumes a yellowish colour, with a small portion of muriate of iron. The muriate of ammonia is also decomposed by triturating the red oxide of iron with this salt. Ammonia is disengaged, and the oxide combines with the acid.

6. Hyperoxymuriate of potash produces a violent detonation with iron. Two parts of this salt with one of iron filings, detonate strongly, and with a vivid red flame, by percussion, or even by sudden pressure, or by being brought in contact with a burning body.

7. There is no action between the fluates, borates, phosphates, or the carbonates, and iron, in the cold.

III. Alloys.

1. Iron combines with arsenic by fusion, forming a brittle alloy of a white colour, analogous to the native compound of arsenic and iron, known by the name of milspickel. It is more fusible than iron, and is therefore employed, on account of its lustre and fine polish, for different purposes to which iron is not applicable.

2. The alloys of iron with tungsten, molybdenum, chromium, columbium, titanium, and uranium, are scarcely known. With titanium iron affords an alloy of a gray colour, which is extremely infusible.

3. The alloy of iron and cobalt possesses some of the properties of steel. It is extremely hard, its texture is fine-grained, and it is attracted by the magnet.

4. Iron combines with nickel, and the affinity between these metals is so strong, that it is extremely difficult to deprive nickel entirely of iron.

5. Manganese is frequently found in combination with iron, to which it communicates a white colour, and renders it brittle.

6. Bismuth forms a brittle alloy with iron. It is attracted by the magnet, even when the proportion of bismuth amounts to three-fourths of the whole. Twenty parts of iron and one of bismuth, were broken by a weight of 15 lb.; but four parts of iron and three of bismuth only supported 35 lb. These were the experiments of Mulchenbroeck. Gellert has observed, that the alloy of iron and bismuth has an inferior specific gravity to the mean.

7. Iron combines readily with antimony by fusion. An alloy of equal parts of these metals is not attracted by the magnet, has no ductility, and scarcely any malleability. This alloy was formerly called martial regular. It is brittle and hard, and has a less specific gravity than the mean. Iron has a stronger affinity for sulphur than for antimony, for when the sulphuret of antimony is heated with iron, it is decomposed, and the iron combines with the sulphur.

8. Iron, it has been long supposed, has no action on mercury; but by triturating together the amalgam of zinc and mercury with iron filings, and by adding to the mixture a solution of iron in muriatic acid, and afterwards by kneading this mixture and heating it, Mr. Aiken obtained an amalgam of iron and mercury, having the metallic lustre*.

9. Zinc forms an alloy with iron, but combines with it in very small proportion. It has been observed that iron, &c., zinc may be applied to the surface of iron by fusion, so as to defend it from the action of the air, and thus to prevent it from rusting.

10. Iron combines with difficulty with tin. Berg-Tinman made a number of experiments on the alloy of iron and tin. He put a quantity of tin into a crucible, and covered it with iron filings. The crucible was then filled with charcoal, and closely covered. He exposed the apparatus to the heat of a forge for half an hour, and he always obtained two distinct alloys, corresponding to the weight of the metals which he had employed.

The one was iron combined with a small quantity of tin, and the other tin united to a small portion of iron. Tin alloyed with \(\frac{1}{2}\) of iron was very malleable, might be cut with a knife, had lost a little of its lustre, and was a little harder. With the fusible phosphates it gave a brown glass, which was less fusible; and by the addition of nitric acid, it became black, and there was separated an insoluble powder. Iron combined with half its weight of tin, exhibits some of the properties of the latter. It is slightly malleable, cannot be cut with a knife, unites with difficulty with mercury and with the phosphates, and in fusion with the latter, gives out brilliant sparks, which do not appear from the iron or tin alone. This inflammation is still more brilliant when the quantity of tin is increased to \(\frac{1}{2}\).

Tin combines with iron, and adheres strongly to its surface, forming a thin covering. This is one of the most useful combinations of tin, for it renders the iron fit for a great many valuable purposes, for which, otherwise, on account of its strong tendency to oxidation or rusting, it would be totally inapplicable. This is well known by the name of tinplate, or white iron. The process of tinning iron is the following: The plates of iron being reduced to the proper thickness, are cleaned by means of a weak acid. For this purpose the surface is first cleaned with sand, to remove any rust that may have formed. They are then immersed in water acidulated with a small quantity of sulphuric acid, in which they are kept for 24 hours, and occasionally agitated. They are then well rubbed with cloths, that the surface may be perfectly clean. The tin is fused in a pot, the surface of which is covered with an oily or resinous matter, to prevent its oxidation. The plates of iron are then immersed in the melted tin, and are either moved about in the liquid metal, or are dipped several different times. They are then taken out, and rubbed with saw-dust or bran, to remove the impurities from the surface.

It is said by some chemical writers, that the tin not only covers the surface, but penetrates the iron completely, so as to give the whole a white colour. This seems to be quite a mistake, which may be very easily proved by the test of experiment. If the surface of a piece of tin-plate be scraped with a knife, the metallic particles which are at first separated, are not attracted by the magnet. As the process is continued, some of the particles are magnetic, which shows that they are particles of iron, scraped off, after the coating of tin is separated, and this coating may be completely removed, that the whole of the particles are attracted by the magnet. This, perhaps, it may be said, would take Copper, &c., take place, even through the iron were alloyed with a certain proportion of tin; but when the coating of tin is entirely removed, and the iron is moistened, it is soon covered with rust, in the same way as if it never had been combined with a particle of tin.

11. Guyton has shown, that an alloy may be formed of iron and lead, which it was formerly supposed could not be effected. By melting together equal parts of lead and filings of iron, he obtained two separate metallic buttons, of which the lead occupied the lower part of the crucible, and the iron the upper part. When these were subjected to the test of experiment, it appeared that the lead contained a small proportion of iron, and the iron a small proportion of lead.

The uses of iron are extremely numerous and important, but they are so well known, that it is altogether unnecessary to enumerate them.

Sect. XIX. Of Copper and its Combinations.

1. Copper seems to have been known in the remotest periods of antiquity. It is among the first metals which were employed by the early nations of the world; and indeed this might have been expected, as it is not one of the scarce metals, is easily extracted from its ores, and not difficult to work. The Egyptians applied it to a great variety of uses, as it appears, from the earliest period of their history. The Greeks were acquainted with the mode of working copper, and employed it in many of the arts. It was the basis of the celebrated Corinthian metal. The Romans knew the uses of this metal, and it is generally supposed that of it they fabricated the greatest number of their utensils. The alloys which they made with copper, after the example of the Egyptians and Greeks, were very numerous, and applied to a great variety of uses.

2. Copper exists in considerable abundance in nature; it is found native, alloyed with other metals, combined with sulphur, in the state of oxide, and in that of salt. It is not unfrequently met with in the native state, sometimes crystallized in an arborecent form, and sometimes in more regular figures. Copper exists native, alloyed with gold and silver. The most abundant ores of copper are the sulphures, and of these there is a considerable variety, exhibiting various colours, and various forms of crystals. In the state of oxide, it has been found in Peru, of a greenish colour, mixed with white sand. In the state of salt, copper is combined with the sulphuric and carbonic acids, forming native sulphates and carbonates of copper. The latter present many varieties, but may chiefly be referred to the blue and green carbonates.

3. The extraction of the ores of copper is to be conducted according to the nature of the combination in which they exist. The following process is recommended for the treatment of the sulphures of copper. The ore is first reduced to powder, and then boiled with five parts of concentrated sulphuric acid. The solution is evaporated to dryness, and the ruddiness well washed with warm water, to remove all soluble matters. The solution being sufficiently diluted, a plate of copper is immersed in it, which precipitates the silver, and afterwards a plate of iron to precipitate the copper. It is boiled with the plate of iron, till no further precipitate takes place. The copper which is thus obtained, is dried with a gentle heat, so that it may not undergo oxidation. It is supposed that the copper is mixed with iron, the whole may be dissolved in nitric acid, and the process is again repeated by introducing the plate of iron. In this way it is easy to discover the quantity of copper in the sulphures of this metal.

4. Copper is a very brilliant metal, of a fine red colour, different from every other metallic substance. The specific gravity of copper is 8.584. When it is hammered, it acquires a greater density. It possesses a considerable degree of hardness, and some elasticity. It is extremely malleable, and may be reduced to leaves so fine that they may be carried about by the wind. It has also a considerable degree of ductility, intermediate, according to Guyton, between tin and lead. The tenacity of copper is also very great. A wire .078 of an inch in diameter, will support a weight without breaking equal to more than 300lbs. avoirdupois. Copper has a peculiarly agreeable and disagreeable taste. It is extremely deleterious, when taken internally, to the animal economy, and indeed may be considered as a poison. It is distinguished by a peculiarly disagreeable odour, which it communicates to the hands by the slightest friction.

5. Copper does not melt till the temperature is elevated to a red heat, which is about 270° Wedgwood, heat, or by citation 1450° Fahrenheit. When it is rapidly cooled after fusion, it afflumes a granulated and porous texture, but if it be cooled slowly, it affords crystals in quadrangular pyramids, or in octahedrons, which proceed from the cube, its primitive form. When the temperature is raised beyond what is necessary for its fusion, it is sublimed in the form of visible fumes.

6. When copper is exposed to the air, especially if it be humid, it is soon deprived of its lustre. It tarnishes, becomes of a dull brown colour, which gradually deepens, till it is converted into that of the antique bronze, and at last is covered with a shining green crust, which is well known under the name of verdigris. This process is the oxidation of the metal by the absorption of oxygen from the atmosphere; and it is promoted and accelerated, either by being moistened with water, or by the water which exists in the atmosphere. As this oxide is formed, the carbonic acid of the atmosphere combines with it, so that it is to be considered as a mixture of oxide and carbonate of copper.

7. But when copper is subjected to a strong heat, the oxidation proceeds more rapidly. If a plate of copper be made red-hot in the open air, it loses its brilliancy, becomes of a deep brown colour, and the external layer, which is of this colour, may be detached from the metal. This is the brown oxide of copper. This oxide may be obtained by immersing a plate of red-hot copper into cold water. The scales which are formed on the surface fall off by the sudden contraction of the heated copper. This may be repeated till the whole is converted into this oxide. The copper in this state is in the highest degree of oxidation. Sometimes it afflumes a black, and sometimes a green colour, which, according to Proult, are owing to the combination of carbonic acid with the oxide. This oxide of copper may also be obtained by dissolving Copper, &c., dissolving copper in nitric or sulphuric acid, and then by precipitating with an alkali, which precipitate is to be dried, to separate the water. The component parts of this oxide are,

| Oxygen | Copper | |--------|--------| | 25 | 75 |

But copper combines with a smaller proportion of oxygen, forming an oxide of an orange colour. If the black oxide of copper be mixed with less than an equal proportion of metallic copper in fine powder, triturated in a mortar, and introduced into a close vessel with muriatic acid, the whole of the copper is dissolved with the emission of heat, and the oxide is precipitated of an orange colour, by means of potash. This is the oxide of copper with the smaller proportion of oxygen. The component parts of this oxide, according to Mr Chenevix, are

| Oxygen | Copper | |--------|--------| | 11.5 | 88.5 |

This oxide changes colour the moment it is exposed to the air, by the absorption of oxygen, for which it has a very strong affinity.

8. There is no action between azote, hydrogen, or carbone, and copper.

9. Phosphorus readily combines with copper, and forms with it a phosphuret, which is prepared by fusing equal parts of copper and phosphoric glass, with \( \frac{1}{3} \) of the whole of charcoal in powder. Or, it may be formed by projecting phosphorus on red-hot copper in a crucible. The phosphuret of copper is of a whitish gray colour, with a metallic lustre, and of a close texture. It is much more fusible than copper; it melts by the action of the blow-pipe; the phosphorus burns with deflagration on the surface, and the copper remains behind in the flake of black iron. Exposed to the air, it loses its brilliancy, blackens, and is converted into a kind of efflorescence, which is phosphate of copper. It is composed of 20 parts of phosphorus, and 80 of copper.

10. Copper combines with sulphur by different processes. If sulphur in powder and filings of copper are mixed together, and formed into a paste with a little water, when they are exposed to the air, the mass swells up, becomes hot, and is converted into a brown matter, which effloresces slowly in the air, and is converted into sulphate of copper. This sulphuret may be also formed by heating together in a crucible, equal parts of sulphur and copper filings. A deep coloured mass is thus obtained, which is brittle, and more fusible than copper. This substance, which is employed in dyeing, is prepared by stratifying in a crucible plates of copper and sulphur. When the whole is melted, it is afterwards reduced to powder, and was formerly known by the name of æs veneris.

A singular and splendid experiment was first made by the society of Dutch chemists at Amsterdam, in the formation of sulphuret of copper. If three parts of flowers of sulphur, by weight, and eight parts of copper filings, be mixed together, introduced into a glass matras, and then placed upon red-hot coals, the mixture melts, and afterwards, with a kind of explosion, becomes almost instantaneously red-hot. If it be then removed from the fire, it continues red-hot for some time, and is converted into a sulphuret of copper. The singular part of this experiment is, that it succeeds equally well without the access of oxygen; or even it may be performed, when the mixture is under water. It seems, therefore, at first sight, to be a case of combustion, or apparent combustion, without oxygen. Various opinions have been entertained concerning the nature of this process, and different theories have been propounded to account for the phenomena, which are seemingly irreconcilable with the present theory of combustion. Indeed it was at first held up as an objection to the Lavoisierian theory. It has been explained by some, by supposing that a small quantity of air may have remained within the apparatus, or mixed with the materials; or that the quantity of air necessary might be supplied from the moisture, from which the materials and the apparatus may not have been sufficiently freed. But this affords no satisfactory explanation; for the quantity of air or water which could remain when the experiment has been carefully performed, is not sufficient to furnish the necessary portion of air for the support of such a vivid combustion. Fourcroy considers it as a case of simple phosphorescence, a change or sudden increase of capacity for caloric, or as merely the separation of light, or the conversion of caloric into light; and in support of this opinion he states, that the compound is always sulphuret of copper, which would not have been the case, had real combustion been effected, for then it would have been a sulphate of copper. But it is explained by others according to the principles of the theory of combustion, which has been given by Gren, and which we have already detailed, in treating of heat. According to this theory, the light exists in combination with the combustible, which in this case is the copper. When heat is applied to the mixture, the sulphur melts, and therefore combines with a great quantity of caloric; but, when the sulphur combines with the copper, it returns to the solid state, and therefore gives out a quantity of caloric. The light from the metal at the same time combines with the caloric, and both appear in the form of fire. It is at the instant of combination that the mass becomes red-hot, in consequence of the sudden extrication of heat and light from the two substances which form the compound.

Copper combined with sulphur, is one of the most common ores of this metal. According to the experiments of Proust, the natural production, known by the name of copper pyrites, is a sulphuret of copper, combined with an additional portion of sulphur. It is distinguished by its brittleness, metallic lustre, and yellow colour.

11. The order of the affinities of copper and its oxides, is according to Bergman the following:

| Copper | Oxide of Copper | |--------|----------------| | Gold | Oxalic acid | | Silver | Tartaric | | Arsenic| Muriatic | | Iron | Sulphuric | | Manganese| Sulfuric | | Zinc | Nitric |

Copper, Copper is reduced to the metallic state from its solutions in acids, by several metallic substances, as iron, zinc, tin. If a plate of iron be introduced into a solution of copper in an acid, the iron is in a short time covered with metallic copper. It is in this way that copper is obtained from its natural solutions in water.

2. Sulphite of Copper.

Sulphurous acid has no action whatever on copper but the oxide of copper readily combines with this acid. Or, the sulphite of copper may be formed by adding a solution of sulphite of soda, to a solution of sulphate of copper. An orange-yellow precipitate is formed, and small crystals of a greenish white are deposited. These become deeper coloured by exposure to the air. Both the yellow precipitate and the greenish white salt have been proved by experiment to be sulphites of copper. The first contains a greater proportion of copper, and therefore has an excess of base, to which its colour and insolubility are owing. The second is a saturated sulphite, which is soluble and crystallizes. When these salts are heated by the blow-pipe, they melt, blacken, assume a grayish colour, and are at last reduced to the metallic state. By the addition of nitric acid they are converted into sulphate of copper. By the sulphuric acid the sulphurous acid is driven off, and there remains behind a brownish-coloured matter in the state of powder, which is the oxide of copper mixed with a portion of that metal in the metallic state.

3. Nitrate of Copper.

1. Nitric acid is decomposed by copper with great rapidity. Nitrous gas is given out in great abundance, the metal is oxidized, and dissolved in the acid. The solution, which is at first of a pale blue, assumes a deep colour, and by slow evaporation yields crystals in the form of long parallelepipeds. This salt has an acid fleshy taste, is extremely caustic, and corrodes the skin. It is deliquescent, and very soluble in water. This salt exposed to a heat, even under 100°, melts; by increasing the heat, the water of crystallization is driven off; it detonates slightly on red-hot coals, and when mixed with phosphorus, by percussion.

2. If a quantity of this dried salt, reduced to powder, be spread on a sheet of tinfoil, it remains without action on any action; but if it be moistened a little with water, tin, and wrapped up, a violent action takes place. The salt is decomposed, and nitrous gas is disengaged with a great degree of heat. The tinfoil is burst to pieces, and sometimes it is even inflamed. In this process, the nitric acid of the nitrate of copper is decomposed, in consequence of the strong affinity of the tin for the oxygen of the acid. The tin is oxidated, nitrous gas is given out, and the copper is partly reduced to the metallic state.

3. The alkalis and earths precipitate the solution. Copper, &c., of nitrate of copper in the form of a bluish-white oxide, which becomes green by exposure to the air. When it is precipitated by means of potash, if the potash predominates, a bulky precipitate is formed, of a fine blue colour. The precipitate is composed of the oxide of copper and water, from which Proust, who particularly examined it, has denominated it hydrate of copper. Lime thrown into this solution, has the property of giving it a deeper shade of blue. It is by this process that the blue pigment known in commerce by the name of verditer, and which is employed for painting paper, is prepared.

4. If nitrate of copper be distilled in a retort, the salt becomes thick, and forms a green crust on the retort. It is then in the state of nitrate with excess of base, or subnitrate, which is insoluble in water.

5. The component parts of this salt are, according to Proust,

| Acid | 16 | | Oxide | 67 | | Water | 17 |

4. Muriate of Copper.

1. Concentrated muriatic acid, with the aid of heat, acts on copper and dissolves it. It produces a slight effervescence, with the evolution of hydrogen gas. The solution is of a fine green colour, by which it is distinguished from the sulphate and nitrate of copper. This salt may be formed by the direct combination of the green oxide of copper with muriatic acid, a little diluted with water. By evaporation and slow cooling, crystals may be obtained in the form of long small needles, or rectangular parallelepipeds, which are of a fine grass-green colour. This salt is extremely acid and caustic; it melts with a moderate heat; it is deliquescent in the air, and is soon converted into a thick liquid like oil. The salt fuses at a moderate heat, and becomes of a uniform mass by cooling. It is not decomposed by sulphuric or nitric acids. The alkalis precipitate a bluish white oxide, which becomes green in the air; the copper is precipitated by zinc and iron. The component parts of this salt, according to Proust, are,

| Acid | 24 | | Black oxide | 49 | | Water | 36 |

This salt is therefore the muriate of copper with the oxide in the highest degree of oxidation.

2. This salt, according to the experiments of Proust, may be distilled to dryness without any change; but by increasing the heat, a part of its acid is driven off in the state of oxymuriatic acid, and the copper remains behind in its lowest state of oxidation, and forms a muriate of copper of a white colour. This muriate may also be obtained by dissolving copper in nitro-muriatic acid. A greenish powder appears, which is a muriate of copper with excess of base. The component parts of this salt are,

| Acid | 12.5 | | Oxide | 79.0 | | Water | 8.5 |

3. Muriatic acid also forms a salt with the oxide of copper in its lowest degree of oxidation. Proust obtained this salt by mixing salts of copper with muriate of tin, which latter deprived the copper of a portion of its oxygen, and afforded a salt of a white colour; it may be formed also by introducing a plate of copper into a bottle filled with muriatic acid. This salt crystallizes in tetrahedrons. It may be precipitated in the state of white powder; by diluting the solution with water, and by repeated washings, the orange oxide of copper is obtained. When it is exposed to the air, it soon combines with oxygen, and is converted into muriate of copper with the oxide in its maximum state of oxidation. This salt is soluble in ammonia, and forms with it a colourless solution, which, after being for some time exposed to the air, assumes a fine blue colour by the absorption of oxygen.

5. Hyperoxymuriate of Copper.

The oxide of copper dissolved in water, is dissolved when a stream of oxymuriatic acid gas is directed through it. But the properties of this salt were not examined by Mr Chenevix, who formed it.

6. Fluate of Copper.

Fluoric acid readily oxidizes and dissolves copper; but the properties of this salt are little known. It forms a gelatinous solution, and affords by evaporation cubical crystals.

7. Borate of Copper.

This salt is most readily formed by adding a solution of an alkaline borate to the solution of nitrate or sulphate of copper. A greenish precipitate is formed, which has very little solubility in water.

8. Phosphate of Copper.

Phosphoric acid is not decomposed by copper; but when it remains for some time in contact with the metal, it promotes the oxidation, and there is thus formed a phosphate of copper, which has little solubility. Or it may be obtained by pouring an alkaline phosphate into a solution of sulphate or nitrate of copper. The phosphate of copper is formed, which is almost insoluble. When it is heated with charcoal in a crucible it affords a gray phosphuret of copper, which has some brilliancy. The component parts of phosphate of copper, as they have been ascertained by Mr Chenevix, are,

| Acid | 35.0 | | Oxide | 61.5 | | Water | 3.5 |

The above oxide is composed of 49.5 brown oxide, and 12 of water.

9. Carbonate 9. Carbonate of Copper.

Carbonic acid has no action on copper, either in the gaseous or liquid state; but it is very readily absorbed by the blue or green oxides of this metal. It may be formed by adding an alkaline carbonate to any of the solutions of copper in the other acids. To prepare this salt of the most brilliant and uniform colour, it should be precipitated with boiling water, washed carefully, and the vessel which contains it placed in the sun. The carbonate of copper is found native, and is known by the name of malachite. It contains the same proportions as the artificial carbonate. Its component parts are,

| Acid | 25.0 | |------|------| | Brown oxide | 69.5 | | Water | 5.5 |

100.0

10. Arseniate of Copper.

This salt may be formed by adding a solution of an alkaline arseniate to nitrate of copper; or, by digesting arsenic acid on copper. A green solution is obtained, and the arseniate of copper is precipitated in the form of a bluish-white powder. The arseniate of potash added to a solution of sulphate of copper forms a precipitate of a very rich green, which was propounded by Scheele as a paint, because it is unaltered by the air, and hence it obtained the name of Scheele's green. It is the arsenite of copper. This salt may be formed by the following process:

Diffuse a quantity of potash in water, and add white oxide of arsenic, till the potash is saturated. Filter the liquor, and add gradually a solution of sulphate of copper while it is hot, stirring the mixture during the addition. It is then left at rest for some time, after which the arsenite of copper precipitates in the form of a beautiful green powder. The precipitate is to be repeatedly washed with water, and dried. Several varieties of the arseniates of copper have been described, and analyzed by the Count de Bourbon and Mr Chevieux, and an account of them published in the Philosophical Transactions for 1801.

11. Tungstate of Copper.

Tungstic acid combines with oxide of copper, or forms a precipitate when added to a solution of sulphate of copper.

12. Molybdate of Copper.

Molybdic acid added to a solution of nitrate of copper, produces a green precipitate.

13. Chromate of Copper.

This is formed by adding chromic acid to a solution of nitrate of copper. A red precipitate is obtained.

14. Acetate of Copper.

Copper is readily oxidized and dissolved in acetic acid. The solution is aided by heat, and gradually assumes a green colour. The oxide of copper, which is thus formed, is the verdigris of commerce. It is usually prepared by exposing plates of copper to the action of vinegar. The surface of the plates is covered with this bluish-green powder, which being dissolved in acetic acid affords a solution of a fine greenish-blue colour. This solution by evaporation and cooling gives crystals of a deep blue colour, and in the form of quadrangular, truncated pyramids. The specific gravity is 1.779. This salt has a strong disagreeable taste, and is poisonous. It effloresces in the air, and is very soluble in water. It is decomposed by all the alkalis; and by means of heat, or by distillation, it is decomposed, and gives out acetic acid. This salt, according to the analysis of Proust, is composed of

| Acid and water | 61 | | Oxide | 39 |

15. Oxalate of Copper.

Oxalic acid readily acts upon copper, and forms with it needle-shaped crystals of a green colour. It readily combines with the oxide of copper, and is then in the state of a bluish green powder, which is little soluble in water. Oxalic acid precipitates the sulphate, nitrate, and muriate of copper, in the form of a bluish gray powder.

16. Tartrate of Copper.

Tartaric acid dissolves copper, when exposed to the air, and at last converts it into an oxide. It combines readily with the oxides of copper, and forms with them a salt of little solubility, and of a green colour. When this acid is added to the solution of sulphate or muriate of copper, it forms a tartrate of copper, which appears after some time in irregular greenish crystals.

17. Tartrate of Potash and Copper.

This triple salt may be prepared by boiling together oxide of copper and tartar in water. By evaporating the solution blue crystals are obtained, which have a sweetish taste. If the same solution be evaporated to dryness, a bluish green powder remains behind, which is employed as a paint, by the name of Brunswick green.

18. Citrate of Copper.

Citric acid dissolves the oxide of copper at the boiling temperature. The solution affords by evaporation greenish coloured crystals.

19. Benzoate of Copper.

Benzoic acid readily dissolves the oxide of copper. The solution yields small crystals of a deep green colour, which have little solubility in water. It is decomposed by the alkalis, the carbonates of lime, and barytes, and the acid is driven off by heat.

20. Succinate of Copper.

When succinic acid is long digested with copper, it dissolves a small portion, and the solution affords green crystals.

21. Suberate of Copper.

When suberic acid is added to a solution of nitrate Copper, &c., trate of copper, it produces a green colour; but there is no precipitate.

22. Mellate of Copper.

When mellitic acid is added to a solution of acetate of copper, it affords a precipitate, and the colour of verdigris, but it produces no change on muriate of copper.

23. Laftate of Copper.

Laftic acid, after digestion with copper, first affumes a blue colour, then changes to a green, and is afterwards converted into a dark brown. The solution does not yield crystals.

24. Prufiates of Copper.

The prufiates of potash precipitate the salts of copper of different colours. The prufiates obtained from sulphate, nitrate, and muriate of copper, Mr Hatchet observes, are very beautiful; but the finest and deepest colour he obtained from the muriate. He has proposed the prufiate of copper as a paint; and on trial with oil and water, it has been found to answer the purpose. The method which he recommends for the preparation of this pigment, is to take green muriate of copper with 10 parts of distilled or rain water, and to add prufiate of lime, which he thinks is preferable to prufiate of potash, until the whole is precipitated. The prufiate of copper is then to be well washed with cold water, and to be dried without heat.

II. Action of Alkalies, &c., on Copper.

1. The fixed alkalies in solution in water, digested with copper filings, and allowed to cool, promote the oxidation of the metal. The liquid affumes a slight blue colour, as well as the copper, but the action of the air is necessary for this process. It scarcely succeeds in clofe vessels.

Liquid ammonia, treated in the same way, becomes of a brilliant blue colour, but it diffuses only a very small quantity of the oxide. By the slow evaporation of this solution, the greatest part of the ammonia is separated in the form of gas; a very small quantity only remains combined with the oxide of copper. This solution, it has been said, yields transparent crystals of a fine blue colour. The dried mass affumes a green colour when it is exposed to the air, as the ammonia is dissipated, and the oxide absorbs carbonic acid. The green oxide of copper is instantly converted to a blue. This action is promoted by heat, and when the heat is increased, azotic gas is disengaged; the hydrogen of the ammonia combines with part of the oxygen of the oxide and forms water; the oxide becomes of a brown colour, and the metal is at last revived.

2. There is no action between the earths and copper, excepting by fusion. With the vitrifiable earths and the oxides of this metal, a glas is formed, which is most commonly of a fine green colour, with different shades of brown or red, according to the degree of oxidation. The oxides of copper are frequently employed to colour glas, porcelain, and pottery.

3. Copper seems to have but a feeble action on most of the salts. The sulphates are not decomposed by this metal, even with the assistance of heat. When copper is boiled with the solution of alum, it is oxidated and partially dissolved, by the excess of sulphuric acid copper, &c., which this salt contains. The sulphate of copper thus formed, seems to combine in the state of triple salt with the sulphate of alumina and potash. It has been observed that alumina precipitated from alum, the solution of which has been kept for some time in copper vessels, is slightly tinged with a blue colour. The nitrates, especially the nitrate of potash, when fused together, give out sparks, but without inflammation or detonation. A brown oxide of copper is thus formed, mixed with potash. When it is washed with water, the alkali is dissolved, and there remains the pure oxide of copper, which is often prepared in this way for the fabrication of enamels.

Muriate of ammonia is decomposed by copper with Muriates, the assistance of heat. Hydrogen gas and ammoniacal gas are disengaged, and there remains behind a muriate of copper. The solution of muriate of ammonia also acts upon copper, and becomes of a blue colour, when it is kept in vessels of this metal. When muriate of ammonia is sublimed with about $\frac{1}{5}$ of its weight of green oxide of copper, a small quantity of the muriate of ammonia is decomposed, and the muriate of copper which is formed, combines with the undecomposed salt. This was formerly called cuprous flowers of sal ammoniac, or ens veneris. If a quantity of lime water, with about $\frac{1}{6}$ of its weight of muriate of ammonia, be kept in a copper vessel for 10 or 12 hours, the liquid affumes a fine blue colour. This was formerly called celestial water. In this process a small quantity of ammonia is disengaged by the lime, and it diffuses some portion of the copper, which communicates a blue colour to the whole solution. This compound may also be formed, by adding a small quantity of copper filings to a mixture of the solution of muriate of ammonia and lime water.

4. The phosphates, fluates, borates, and carbonates, have no other action on copper than by means of the water in which they are dissolved. This action is greatly promoted by exposure to the air.

III. Alloys.

1. Copper readily combines with almost all other metals, by means of fusion; and many of the alloys which are thus formed, are of great importance in the arts.

2. When copper is combined with arsenic, by melting them together in a clofe crucible, and covering the surface with muriate of soda, to prevent oxidation, a white brittle alloy is formed, which has been called white tombac. With a certain proportion of zinc and tin, this alloy is employed in the fabrication of various utensils.

3. The alloys of copper with tungsten, molybdenum, chromium, columbium, titanium, and uranium, are either altogether unknown, or have not been examined.

4. Little is known of the alloy of copper and cobalt. It is said that it resembles cobalt itself in texture and brittleness.

5. Copper forms with nickel a white hard alloy, Nickel, which has no ductility, and which is soon altered by exposure to the air.

6. Copper unites with manganese, and gives an alloy of a red colour, which is very malleable.

7. Equal 7. Equal parts of copper and bismuth, melted together, form a brittle alloy of a pale red colour. With one-eighth of bismuth, the alloy is extremely brittle, of a very pale red colour, and exhibiting in its texture nearly cubical fragments. The specific gravity of this alloy is exactly the mean of that of the two metals; and, as the proportion of bismuth is increased, the tenacity of the alloy is diminished.

8. Copper combines readily with antimony by fusion. Equal parts of the two metals constitute an alloy of a beautiful violet colour, and of a greater specific gravity than the mean. This alloy is remarkable for its lamellated and fibrous texture. The alchemists gave it the name of regulus of Venus. A compound formed of equal parts of martial regulus and regulus of Venus, according to an alchemical prescription, the surface of which exhibits the appearance of meshes or cavities, was called Vulcan's net, because it seemed to envelope iron and copper, which were denominated Mars and Venus.

9. Copper enters into combination with mercury with some difficulty. This alloy may be formed by triturating very thin plates of copper which have been rubbed with vinegar or common salt, with mercury; or, by triturating copper filings with the solution of mercury in nitric acid. It is also formed by other processes; but whatever be the process, this amalgam is of a reddish colour, and sufficiently soft to receive the most delicate impressions when it is a little heated. It becomes hard by exposure to the air. It is decomposed by heat, and the mercury is separated.

10. The compound of copper and zinc constitutes one of the most important and useful alloys, of all the combinations of the metals. Muffchenbroeck has given a particular description of several of these alloys. Equal parts of copper and zinc afforded a metal of a fine golden yellow, whose specific gravity was 8.247; one part of copper and half a part of zinc, formed a compound of a pale golden colour; one part of copper and three-fourths of zinc, composed an alloy of a golden colour, which yielded to the file; one part of copper and one-fourth of zinc, gave a compound of a finer colour than that of bras. According to the proportions of the metals which are employed, the alloys have received different names. The usual process for combining them, is either by fusing copper with a mixture of calamine, or native carbonate of zinc and charcoal; or by stratifying plates of copper with the same mixture, and exposing them to heat.

The well known compound, distinguished by the name of bras, is an alloy of copper and zinc. The proportion of the zinc is about one-fourth of the copper. This alloy is of a fine yellow colour, less liable copper, &c., to tarnish, and more fusible than the copper. The density of this alloy is one-tenth more than the mean. It is malleable, and possesses considerable ductility. A compound applied to a great variety of ornamental purposes, and known by the names of Prince Rupert's metal, prince's metal or pinchbeck, is an alloy of zinc and copper in the proportion of three parts of the former to four of the latter. This alloy is less malleable than bras; but has a fine golden colour, which is pretty permanent, and little affected by exposure to air.

The compound of zinc and copper, called bras, it is supposed, was well known to the ancients. An ore of zinc was employed in the fabrication of it, although it does not appear that they were at all acquainted with zinc as a distinct metal. "It is probable," Professor Beckman observes, after Pliny, "that ore containing zinc, acquired the name of cadmia, because it first produced bras." "Ipse lapis est quo fit aes, cadmia vocata." "When it was afterwards remarked, that calamine gave to copper a yellow colour, the same name was conferred on it also. It appears, however, that it was seldom found by the ancients, and we must consider cadmia in general as signifying ore that contains zinc. Gold-coloured copper or bras was long preferred to pure or common copper, and thought to be more beautiful the nearer it approached to the best aurichalcum (c). Bras, therefore, was supposed to be a more valuable kind of copper; and on this account Pliny says that cadmia was necessary for procuring copper, that is, bras. Copper as well as bras was for a great length of time called aes, and it was not till a late period, that mineralogists, in order to distinguish them, gave the name of cuprum to the former. Pliny says, that it was good when a large quantity of cadmia had been added to it, because it not only rendered the colour more beautiful, but increased the weight (d)."

To discover the proportions of the two metals in this alloy, Vauquelin dissolved a quantity of bras in nitric acid. When the solution is completed, he precipitates the two metals by means of potash, which is added in large quantity, to dissolve the whole of the oxide of zinc; and as the oxide of copper is not soluble by this alkali, it remains in the form of black powder, which is separated, washed, and dried. A fifth part of the weight of this precipitate is deducted for the oxygen with which it is combined; the remainder gives the weight of copper in the alloy. What is deficient of the whole weight of the alloy, is the weight of the zinc.

(c) According to Bishop Watson, the aurichalcum, or orichalcum, of the ancients, is to be considered as the same with our bras. Mancheft. Transf. ii. 47.

(d) Mr Beckmann farther adds, "At first it was called aes cyprium; but in course of time only cyprium, from which at length was formed cuprum. It cannot, however, be ascertained at what periods these appellations were common. The epithet cupreus occurs in manuscripts of Pliny and Palladius, but we cannot say whether later transcribers may not have changed cyprium into cupreus, with which they were perhaps better acquainted. The oldest writer who uses the word cuprum, is Spartan, who says in the life of Caracalla, cancelli ex aere, vel cupro; but may not the last word have been added to the text as a gloss? Pliny, book xxxvi. 26, says, addito cypro et nitro, which Isidore, xvi. 15. p. 363, expressed by the words adjecto cupro et nitro." Hist. of Invent. iii. 75. 11. Copper combines very readily with tin. This is a very important alloy in the arts. It is with this alloy that bronze, metals for casting statues and cannons, bell-metal, and metallic mirrors, are formed. Tin diminishes the ductility of copper, and increases its tenacity, hardness, and sonorous quality. According to Mutchtenbroeck, copper acquires the greatest solidity with the addition of one part of tin to five or six of this metal. By increasing the quantity of tin, the alloy becomes hard and brittle.

To form the alloy employed for cannons, 12 parts of tin are united to 100 of copper. In fusing the two metals for this alloy, it is necessary to stir or agitate the mixture, otherwise they remain uncombined. Bronze, or the metal which is used for statues, is not different from that of which cannons are made, excepting in the proportion of tin being either more or less, to vary the colour.

The component parts of bell-metal are usually 75 of copper and 25 of tin, or three of copper and one of tin. A small quantity of other metals is sometimes detected by analysis, in fragments of bells that have been examined, such as zinc, antimony, bismuth, and even silver. But these metals are not considered as essential to the alloy. Bell-metal is of a grayish white colour, of a close grain, and so hard as to be scarcely touched with the file. It is also elastic and sonorous. The specific gravity is considerably more than the mean, and it is more fusible than copper. A mixture of three parts of tin and one of copper, fused with a little arsenious acid, and black flux, gives an alloy of the colour of steel, very hard, and susceptible of a fine polish, which is employed in the fabrication of mirrors for telescopes. But other proportions, with the addition of other metals, are employed by different opticians. Bismuth, antimony, and silver, are added, to increase the reflecting property of the mirror.

Copper vessels which are employed for the purposes of domestic economy are apt to be corroded or oxidized by the substances which are boiled or preserved in them. To defend them from the action of these substances, and to prevent the terrible accidents which would otherwise happen to those who employ any of these matters as food, the inside of such vessels is covered with a thin coating of tin. This is performed by the following process. The surface to be covered with tin, is scraped very clean with an iron instrument, or it is scoured with wine lees, or weak nitric acid and sand. The tin is then applied in two ways; in the first way, the tin is in a state of fusion, and the surface is covered with some resinous or oily matter, to prevent oxidation, in the same way as in tinning iron. The surface to be tinned is first immersed in a solution of muriate of ammonia, and dried, and then dipped into the melted tin. Another method is, to heat the copper vessel on charcoal, and then to apply to the inside of it a quantity of tin, which is then melted; a little muriate of ammonia being thrown in at the same time in powder. The surface is then rubbed with tow. The muriate of ammonia is employed, both to clean the surface of the copper, and also to prevent the tin from being oxidated. The coating of tin which can be applied to copper is extremely thin; and it cannot by any means be increased, to bear a heat greater than that which melts tin. Bayen in his researches concerning tin, found, that a vessel nine inches in diameter, and three lines in depth, acquired, by having its surface covered with tin, only 21 grains of additional weight.

In using vessels thus tinned, care should be taken not to allow acid substances to remain for any length of time in contact with them, because the tin would be corroded, and part of the copper afterwards dissolved, which would inevitably act as a poison. Pure tin ought only to be employed, at least without any mixture of lead.

12. Copper combines very readily with lead by fusion. With an excess of lead, the alloy is of a gray colour, is ductile, but brittle when it is hot, on account of the great difference of fusibility of the lead and copper. This alloy is employed in the fabrication of printing types for large letters. According to Savary, the proportion for this purpose is 100 of lead and 25 or 25 of copper.

13. Copper combines with iron, but with much greater difficulty than with the other metals. As the proportion of iron is increased, the alloy becomes of a darker gray, loses its ductility, and is more infusible. The alloy of copper with iron has been supposed to constitute that variety called hot short iron, which possesses greater tenacity than other kinds of iron, and on account of some peculiar properties is more applicable to a variety of purposes.

Next to iron, copper is of the greatest importance, uses and most extensive utility, of all the metals. In the metallic state it is employed for a great variety of instruments and utensils; some of its oxides and salts are much used in painting, dyeing, and enamelling; and the alloys with other metals, especially with zinc and tin, are applied to many valuable purposes in the arts, and in domestic economy. But the uses of copper in its different states, and in its various combinations, are so familiar and well known, that it must appear quite unnecessary to enumerate them.

Sect. XX. Of Silver.

1. Silver has been reckoned among the noble or perfect metals, and has been known from the earliest ages of the world. Its scarcity, beauty, and utility, have always rendered it an object of research among mankind, so that the nature and properties of this metal have been long studied and minutely investigated. In the midst of the rage for the transmutation of metals which for centuries fired the imaginations of the alchemists, silver occupied a great share of their attention and labour, with the hope of discovering the means of converting the baser and more abundant metals into this, which is more highly valued on account of its scarcity and durability. When the dawn of science commenced, and its light had diffused the follies and extravagancies of these pursuits, the earlier chemists were much employed in examining the properties and combinations of silver; nor has it been overlooked or neglected by the moderns.

2. Silver which is neither in such abundance nor so universally diffused as many other metals, exists in nature in five different states; in the native state; in that of alloy with other metals, especially with antimony; in that of sulphuric, sulphurated oxide, muriate, and carbonat. Silver, &c. carbonate. 1. Native silver, which is characterized by its ductility and specific gravity, is frequently tarnished on the surface, of a gray or blackish colour, and appears under a great variety of forms. In this state it is not perfectly pure. It is usually alloyed with a little gold or copper. 2. The alloy of silver and antimony, which is the most frequent, is distinguished by its brittle and lamellated structure from native silver, which it resembles in lustre and colour. It crystallizes in prisms which are six-sided and pretty regular. 3. The sulphuret of silver which is known to mineralogists by the name of vitreous silver ore, is of a dark gray colour, and has some metallic lustre. It is usually crystallized in the form of cubes, octahedrons with angular facets, or sometimes in the form of the dodecahedron. 4. The sulphurated oxide of silver and antimony. In this ore of silver the sulphur is combined with the metal in the state of oxide; in the former, in the metallic state. This ore is called red silver ore. It is of a deep red colour, sometimes transparent, and sometimes nearly opaque, frequently having the lustre of steel on the surface. The primitive form of its crystals is the rhomboidal dodecahedron. 5. The muriate of silver, which has been long known to mineralogists by the name of cornicose silver, is found in irregular masses of a grayish colour, frequently opaque, but sometimes semitransparent. It is soft and very fusible.

The analysis of silver ore varies according to its nature and combinations. Native silver, after being broken down and washed, is rubbed with liquid mercury, which by strong trituration dissolves, and combines with the silver. This amalgam is subjected to pressure, to separate the excess of mercury. It is then distilled, and afterwards heated in a crucible, to volatilize the mercury, and the silver remains pure. When silver is combined with antimony and sulphur, the ore is to be strongly roasted, to separate the antimony or sulphur. It is then melted with a proper quantity of alkaline flux. The sulphurated oxide of silver and antimony may be treated in the same way.

But by these processes the silver is not in a state of perfect purity. To obtain it pure, by the separation of other metals, as copper or iron, it is subjected to the process called cupellation. This depends on the peculiar property of lead, when it is oxidated and afterwards vitrified, of combining with the metals, and leaving the silver in a state of purity. A small flat cup made of the powder of burnt bones, which has received the name of cupel, is employed for this purpose. The silver to be purified is included in a plate of lead, usually double the weight of the silver. The cupel is introduced under a muffle in the middle of the furnace. The use of the muffle is to increase the heat, by allowing the metal to be surrounded on all sides with coals, and at the same time preventing the admixture of any part of the fuel with the fused matter. The heat is then to be applied sufficiently great, that every part of the metal may be in fusion, but not such as to sublime the lead too rapidly. As the process advances, the lead is oxidated and vitrified, and having combined with all the other metals except the silver, sinks into the porous cupel, and leaves the silver pure. The lead, which is now in the state of litharge, is extracted from the cupel, and applied to the usual purposes.

Silver is of a fine white colour, and great brilliancy. The specific gravity is 10.474, and according to some, when it is hammered, 10.535, and sometimes nearly 11. The hardness of silver is intermediate between iron and gold. The elasticity of silver is considerable, and it is one of the most famous of the metals. It possesses very great ductility and malleability. It may be beaten out into leaves of an inch thick, and a grain of silver may be so extended as to be formed into a hemispherical vessel of sufficient capacity to hold an ounce of water, or to be drawn out into a wire 400 feet in length. The tenacity of silver is very great. A wire .078 of an inch in diameter, will support a weight of 187 lbs. avoirdupois.

Silver is a good conductor of calorific. Its expansive power is less than that of lead and tin, and heat greater than that of iron. When it is exposed to a white heat it melts. The temperature necessary to bring it to fusion has been calculated at the 1000° of Fahrenheit; but, according to Kirwan, it requires a higher temperature than 28° Wedgwood to melt it, although at that temperature it continues in a state of fusion. When it is cooled slowly after fusion, it exhibits some marks of crystallization. It assumes the form of four-sided pyramids, or of octahedrons. If the heat be increased after the silver is melted, it boils, and may be reduced to vapour. The surface of melted silver is extremely brilliant, that it seems to throw out sparks, which is called coruscation by the workmen.

Silver is a good conductor of electricity. It has no perceptible taste or smell.

Silver is not altered by exposure to the air, although it is soon tarnished, which is owing, as Proust ascertained, to a thin covering of sulphuret of silver, which is formed by sulphurous vapours to which it is exposed; but when it is subjected to a strong heat for a long time, in an open vessel, it combines with the oxygen of the atmosphere, and is converted into an oxide. In the experiments of Macquer, the oxidation of silver was effected by exposing it for 20 times successively in a crucible, to the strong heat of a porcelain furnace. At last perceptible traces of oxidation were observed, and vitreous matter of an olive colour was obtained. In other experiments silver being acted on by the heat of a burning glass, was covered with a white powder, which was afterwards converted into a crust of a green colour. Van Marum passed electric shocks through silver wire, which was instantly reduced to a kind of powder, with a greenish white flame, and the oxide which was formed was dissipated in vapour. The oxide of silver, which is formed by these processes, is of a greenish or yellow colour. It is composed of about ten parts of oxygen, and 90 of silver. The oxide of silver is very easily reduced, for the affinity of oxygen for this metal is very feeble. It is decomposed by the application of heat, and even when it is exposed to the light. By heating it in clothe vessels, pure oxygen gas is obtained, and the metal is converted to the metallic state, by melting it in a crucible.

Azote, hydrogen, or carbure, have no action whatever on silver.

Silver combines with phosphorus, forming a phosphuret. One part of silver in filings, with two of phosphoric Silver, &c., phosphoric glafts, and half a part of charcoal, exposed to heat in a crucible, yielded a phosphuret of silver which had acquired one-fourth of its primitive weight of silver. This phosphuret is of a white colour, brittle, of a granulated texture, and may be cut with a knife. By throwing pieces of phosphorus on silver red hot in a crucible, the metal is instantly melted, and the phosphuret which is formed remains at the bottom. At the moment when the surface becomes solid, a quantity of phosphorus is thrown out with a kind of explosion, and the surface of the metal then exhibits a lamellated appearance. Pelletier, who first made this experiment, concludes from it, that silver is susceptible of retaining a greater proportion of phosphorus in combination with it, when it is in fusion than in the solid state, and that the separation of the phosphorus is owing to the sudden contraction of the silver. A hundred parts of silver in fusion retain 25 of phosphorus, but only 15 when it becomes solid. Phosphorus has the property of reducing the oxides of silver, and of precipitating them from this solution in acids, in the metallic form.

9. Sulphur combines readily with silver, both in the dry and humid way. By stratifying in a crucible plates of silver alternately with sulphur, and melting them rapidly, a deep violet-coloured mass is obtained, which is more fusible than silver, brittle, crystallized, and has a metallic lustre. It may be cut with a knife, and has a good deal of resemblance to vitreous ore of silver. When this sulphuret of silver is exposed to heat for a considerable time, the sulphur is gradually dissipated, and the silver remains pure and ductile. Silver combines very readily with sulphur, when it is long exposed to those matters which gradually deposit this substance. This effect is immediately produced, when silver is brought into contact with sulphurated hydrogen gas, or when it is immersed in water impregnated with this gas, as in natural sulphurous waters. It is owing to the same cause that a silver spoon is tarnished by a boiled egg, and particularly if the egg has begun to spoil. Sulphurated hydrogen gas which is exhaled by the egg, is decomposed, the sulphur combines with the silver, and forms a thin layer of sulphuret of silver, which is of a dark or violet colour. The same thing happens, when silver is exposed in places that are much frequented, as in churches and theatres.

10. Silver forms alloys with most of the metals, and fuses with the acids. The order of the affinities of silver and its oxide, as they have been arranged by Bergman, is the following.

| Silver | Oxide of Silver | |--------|----------------| | Lead | Muriatic acid | | Copper | Oxalic | | Mercury| Sulphuric | | Bismuth| Sulfuric | | Tin | Phosphoric | | Gold | Sulphurous | | Antimony| Nitric | | Iron | Arsenic | | Manganese| Fluoric | | Zinc | Tartaric | | Arsenic| Citric | | Nickel | Lactic |

Sulphurous acid combines readily with the oxide of silver. It affumes the form of small shining grains, often a pearly-white colour. It is not altered by exposure to light. Sulphurous acid precipitates the solution of silver in nitric acid, in form of a white powder of sulphite of silver. The same salt is obtained by adding a solution of sulphite of ammonia to a solution of nitrate of silver. An excess of this sulphite redissolves the precipitate, and forms a triple salt. This sulphite of ammonia and silver exposed to the sun's rays, is soon covered with a pellicle of silver, and the liquid contains sulphate of ammonia. Sulphurous acid, aided by the affinity of ammonia, deprives the oxide of silver of its oxygen, and is converted into sulphuric acid; which combines with the ammonia, and forms a sulphate. Sulphite of silver is decomposed by muriate of ammonia; and the precipitate, which is formed, affumes a black colour, and is partly reduced. When sulphite of silver is exposed to the action of the blow-pipe, it gives... Silver, &c., out sulphurous acid, melts into a yellow mass, and leaves behind a metallic button of pure silver. This salt has an acrid metallic taste; it is soluble in the caustic alkalies, and forms with them a triple salt.

3. Nitrate of Silver.

1. Silver dissolves nitric acid with effervescence, in consequence of the evolution of nitrous gas. If the solution be made in a tall conical vessel, the nitrous gas, which is disengaged from the bottom, is dissolved in the acid, and communicates a green colour to the lower part of the liquid. If the green colour is permanent, or passes to a blue, the metal is contaminated with copper; but if it be mixed with gold, a purple coloured powder is deposited at the bottom of the vessel.

2. Nitric acid dissolves more than \( \frac{1}{2} \) of its weight of silver. This solution is nearly colourless, very heavy, and extremely caustic. It colours the skin, first of a reddish purple, and then of a deep black. It produces the same effect on the nails, the hair, and all animal substances. It is employed to dye the hair of a black colour, but this should be done with great caution. When it is diluted with water, so as to deprive it of its causticity, it has an astringent bitter taste. By evaporating the solution till a pellicle is just formed on the surface, and by slow cooling, it crystallizes in transparent brilliant plates, sometimes of a metallic lustre, when the liquid has been exposed to the sun during the crystallization. These crystals are not very regular. They are sometimes six-sided, sometimes square, and sometimes triangular; but they seem to be composed of very fine small prisms. The taste is so extremely bitter, that it has been denominated the gall of the metals. It is not deliquescent in the air. When exposed to the light of the sun, it gradually blackens, and the silver is reduced. When it is heated in a crucible, it readily melts into a brown liquid, which swells up, as it is deprived of its water of crystallization; and in this state of fusion, if it be allowed to cool, it assumes the form of a deep grey, or black mass. When the nitrate of silver is thus fused, and cast into small cylindrical moulds, the cylinders thus formed, which exhibit a radiated fracture, are well known in surgery by the names of lunar caustic, or lapis infernalis. This is generally prepared by evaporating the solution of nitrate of silver to dryness, without previous crystallization.

3. When nitrate of silver is heated in a retort, it first gives out nitrous gas, then very pure oxygen gas, which is afterwards mixed with azotic gas. The silver is reduced at the bottom of the vessels. When a plate or crystal of nitrate of silver, well dried, is put upon burning coals, it produces a brilliant detonation; the silver is reduced, and adheres to the surface of the charcoal.

4. The nitrate of silver is very soluble in water, and in this state it may be reduced by hydrogen gas and phosphorus. By exposing paper or silk moistened with a solution of nitrate of silver to hydrogen gas, the paper or silk is coated with metallic silver, in consequence of the reduction of the salt by the hydrogen, which has a stronger affinity for the oxygen than the silver. The same effect takes place, if a cylinder of phosphorus be immersed in a solution of nitrate of silver. The phosphorus combines with the oxygen of the oxide, silver, &c., and the silver is deposited on the surface of the phosphorus in the metallic state. The phosphorus may be separated from the silver by melting it in boiling water. These experiments were made by Sage and Bouillon in France, and Mrs Fulham in England.

5. A mixture of this salt and phosphorus struck detonation. Inwardly with a hammer, produces a violent detonation. Nine grains of nitrate of silver and three of sulphur produce no detonation, but only an inflammation of the sulphur, when they are struck with a cold hammer; but with a hot hammer, a detonation takes place, with the reduction of the silver.

6. Nitrate of silver is decomposed by sulphuric acid, and forms a precipitate of sulphate of silver, in the state of white powder. It is also decomposed by sulphurous acid. Muriatic acid produces a copious white precipitate, which is very insoluble, and is deposited in the form of thick heavy flakes of muriate of silver.

7. Nitrate of silver is decomposed by all the alkaline and earthy matters. A white precipitate is at first formed, which afterwards passes to an olive green; but the carbonates of the alkalies give a white precipitate which remains unaltered. Ammonia occasions a sparing precipitate, which is re-dissolved by an excess of alkali, when there is formed a triple salt. But a very peculiar action takes place between ammonia and the oxide of silver, by which both the one and the other are decomposed with a violent detonation. This is the celebrated fulminating silver, which was discovered by Berthollet in 1788. It is prepared by the following process.

A solution of pure silver in nitric acid is precipitated-filmed by lime water. The precipitate is placed on graying silver paper, which absorbs the whole of the water and the nitrate of lime. Pure caustic ammonia is then added, which produces an effect somewhat similar to the flaking of lime. The ammonia dissolves only part of this precipitate. It is left at rest for 10 or 12 hours, when there is formed on the surface a shining pellicle, which is redissolved with a new portion of ammonia, but which does not appear, if a sufficient quantity of ammonia has been added at the first. The liquid is then separated, and the black precipitate found at the bottom, is put in small quantities on separate papers. This powder is fulminating silver, which, even while it is moist, explodes with great violence, when it is struck with a hard body. When it is dry, it is sufficient to touch, or rub it slightly, to produce an explosion. If the liquid decanted off this precipitate be heated in a glass retort, it effervesces, gives out oxygen gas, and there are soon formed small, brilliant, opaque crystals, which have a metallic lustre, and which fulminate with the slightest touch, though covered with liquid, and break with violence the vessels containing them. In this action the most obvious circumstance is the tendency of the compound to decomposition. The oxygen of the oxide combines with the hydrogen of the ammonia, and forms water, while the azote of the ammonia escapes in the form of gas, and the silver remains behind in the metallic state. The violence of the explosion is owing to the sudden expansion of the azotic gas. The shining pellicle which appears on the surface, is part of the silver, from Silver, &c., from which the ammonia has been separated by the action of the air; and to have the full effect, another portion of ammonia is necessary to dissolve it. Carbonate of ammonia dissolves the oxide of silver precipitated by lime, with effervescence, and the evolution of carbonic acid; but there remains enough of this acid to form a triple salt, which, when dried, is in the form of a yellow powder, but has no fulminating property. The preparation of this dangerous powder frequently fails. A mixture of copper, the absorption of carbonic acid by the oxide of silver, precipitated by means of lime, and left too long exposed to the air, and ammonia containing a little of this acid, either diminish or destroy its fulminating property.

7. Many of the salts decompose the nitrate of silver. All the sulphates produce a precipitate of sulphate of silver in the form of powder. The same effect is produced by the other salts, and the effect is similar to that which takes place with the acids of which they are composed.

8. Most metallic substances have a stronger affinity for oxygen than silver has; it is therefore precipitated from its solution in nitric acid, either partially or entirely deprived of its oxygen, and in the metallic state. In the precipitation which takes place by means of mercury, the silver is reduced in an arborecent form, which has long retained the name of Arbor Diana. Different processes have been recommended to effect this decomposition. One part of silver, according to Lemozy, is dissolved in diluted nitric acid. The solution is then to be farther diluted with 20 parts of distilled water, and then to add two parts of mercury. It is said, that it requires, by this process, about 40 days for the formation of the metallic tree. Homberg gives a shorter process, which succeeds sufficiently well. It consists in making an amalgam in the cold of four parts of silver-leaf and two of mercury. This amalgam is then to be dissolved in a sufficient quantity of nitric acid, and the solution to be diluted with 32 times the weight of the metals of water. By introducing into part of this liquid a small ball of soft amalgam of silver, the formation of the tree immediately takes place. It may be formed also by putting a soft amalgam of silver into five parts of a solution of nitrate of silver, and four of a solution of nitrate of mercury. In these processes one part of the mercury of the amalgam attracted by that of the solution, and carrying off the oxygen of the silver, precipitates the latter in the metallic state. The precipitation of the silver is still favoured by the affinity between it and the portion of undissolved mercury, and also part of the silver of the amalgam. All these attractions conspire to effect the separation of the silver, when it is deposited in prismatic needles, which arrange themselves in an arborecent form.

9. Silver is precipitated from its solution in nitric acid, by means of copper. When a plate of copper is immersed in this solution, diluted with its weight of distilled water, the silver is immediately separated in whitish gray-coloured flakes. If this precipitate is scraped off, and well washed with water, afterwards fused in a crucible, and subjected to the processes of cupellation with lead, pure silver may be obtained.

4. Muriate of Silver.

Muriatic acid has no action whatever on silver; but by adding muriatic acid to a solution of silver in sulphuric or nitric acid, the moment it comes in contact with these solutions, it decomposes them, carries off the oxide of the silver, and forms with it a white insoluble salt, which is precipitated in a kind of coagulated state. The muriates also produce a similar precipitate, and hence it is that the nitrate of silver is employed as a re-agent, and a most delicate test of muriates or muriatic acid in mineral water. The muriate of silver, which is called cornuous silver or horny silver, is extremely insoluble in water. Exposed to the light it becomes brown, violet, and black. By heating it gently in a matras, it melts like tallow, and when it becomes solid by cooling, it assumes the form of a transparent gray substance, similar to some kinds of horn, from which it derived its name of luna cornua, or horn silver. If it be fused on a stone, it is converted into a kind of friable matter, crystallized in beautiful, brilliant, and as it were metallic needles. When it is strongly heated in a crucible, it filters through it, and is lost in the fire. The component parts of this salt, composition, according to Proust,

| Acid | 18 | | Oxide | 82 |

This salt is not decomposed by any of the acids, or by the pure alkalies. It is decomposed by the alkaline carbonates. The muriate of silver is very soluble in caustic liquid ammonia. This solution, which is transparent and colourless, undergoes a remarkable change when it is exposed to the air. As the ammonia evaporates in the air, there is formed on the surface a pellicle which affumes a brilliant, bluish, or iridescent colour. This pellicle, which gradually increases in thickness, deepens in colour, and at last becomes of a dirty gray or black, by the contact of light. The substance thus separated is the muriate of ammonia, containing a small proportion of the metal reduced.

5. Hyperoxymuriate of silver.

This salt may be prepared by passing oxymuriatic acid gas through water having the oxide of silver diffused in it. It is soluble in two parts of warm water, and crystallizes in cooling in the form of small rhomboids. It is decomposed by muriatic acid, and by nitric and acetic acids. The muriate of silver remains behind. Exposed to a moderate heat, it melts, oxygen gas is given out, and the salt is reduced to the muriate of silver. With one-half its weight of sulphur, it produces violent detonation, by slight percussion. It gives out a white vivid flash.

6. Fluate of Silver.

Fluoric acid dissolves the oxide of silver, and forms with it an insoluble salt. It is decomposed by sulphuric acid.

7. Borate of Silver.

Boracic acid combines with the oxide of silver, by adding Silver, &c., adding a soluble borate to the solution of nitrate of silver. The whole of the silver is precipitated in the form of a white, heavy, insoluble powder.

8. Phosphate of Silver.

Phosphoric acid dissolves the oxide of silver, and precipitates it from its solution in nitric acid. The precipitate is a white heavy powder; with considerable heat it melts into a kind of greenish enamel. It is not soluble in water without an excess of acid. When it is heated in a retort with charcoal, it gives out a little phosphorus, and is reduced, in great part, to phosphuret of silver.

9. Carbonate of Silver.

Carbonic acid combines readily with the oxide of silver. It may be prepared by adding an alkaline carbonate to sulphate or nitrate of silver. The carbonate of silver is precipitated in the form of a white powder. This salt, which blackens by the action of light, readily gives out its carbonic acid by heat.

10. Arseniate of Silver.

Arsenic acid dissolved in water, and heated with silver, has no action upon it; but when the water is evaporated, and the heat is increased to produce vitrification, arsenic is sublimed, and there remains a white vitreous matter, which contains the silver oxidated, and is covered with a deep yellow-coloured glaze. By heating water on this glaze reduced to powder, the solution becomes of a brown red colour; the arsenic acid is dissolved, and carries with it a little oxide of silver, which is precipitated by adding muriatic acid. The brown insoluble powder is fused at a high temperature, and becomes semitransparent. By continuing the heat in a crucible, the silver is reduced. Arsenic acid gives a brown precipitate in the solution of nitrate of silver.

11. Tungstate of Silver.

Tungstic acid does not seem to have any action on silver; but, when added to a solution of nitrate of silver; it occasions a precipitate in the form of white powder, but its properties have not been examined.

12. Molybdate of Silver.

Molybdic acid produces a white, flaky precipitate in a solution of nitrate of silver. Nothing is known of the properties of this salt.

13. Chromate of Silver.

By adding chromate of potash to a solution of silver in nitric acid, a precipitate is formed, of a most beautiful crimson red, which the action of light changes to purple. The precipitate, which is the chromate of silver, is in the state of powder. When heated by the action of the blow-pipe, it become black, and is reduced in part to the metallic state. Reduced to powder in this state, it is still of a purple colour; but when it is heated with the blue flame of a candle directed by the blow-pipe, it becomes green, and the silver is separated in globules. The chromic acid, decomposed by the hydrogen of the blue flame, passes to the state of green oxide, and the oxide of silver is reduced.

14. Acetate of Silver.

Acetic acid dissolves the oxide of silver. The acetate of silver may be prepared, by adding acetate of potash to a solution of nitrate of silver. The solution affords, on cooling, small prismatic crystals. This salt is very soluble in water, and has an acrid metallic taste. When heated, it fuses up, and is decomposed. The acid is driven off, and the oxide remains behind.

15. Oxalate of Silver.

Oxalic acid dissolves a small portion of the oxide of silver, which is precipitated from nitric acid, by means of potash, or, by adding oxalic acid to a solution of nitrate of silver. A white, thick, insoluble precipitate is formed, which is oxalate of silver. This salt is soon changed by the action of light. When exposed to the rays of the sun, it becomes black; and when it is heated in a spoon, it undergoes a kind of detonation.

16. Tartrate of Silver.

Tartaric acid combines with the oxide of silver, and forms with it a tartrate of silver, which becomes black by exposure to the air. This acid has no action on silver itself, nor does it produce a precipitate in the solution of nitrate of silver.

17. Tartrate of Potash and Silver.

When tartar is added to a solution of nitrate of silver, there is formed, according to Thenard, a triple salt, which consists of tartaric acid, oxide of silver, and potash.

It is decomposed by the alkalis and alkaline carbonates, and by the fulphates, and muriates *.

18. Citrate of Silver.

Citric acid dissolves the oxide of silver, and forms with it an insoluble salt, which becomes black by being exposed to the sun. It has a harsh, strong, metallic taste. It affords by distillation concentrated acid, and leaves behind the silver reduced in an arboreal form, mixed with a little charcoal, at the bottom of the retort. This salt is decomposed by nitric acid. Its component parts are,

| Acid | 36 | | Oxide of sulphur | 64 |

19. Malate of Silver.

Malic acid added to a solution of nitrate of silver, produces a precipitate, the nature of which is unknown.

20. Benzoate of Silver.

Benzoic acid combines with the oxide of silver, and forms with it a salt which is soluble in water, is not deliquescent in the air, but becomes brown by exposure to the sun's rays, and is decomposed by heat; the acid being driven off, and the oxide reduced to the metallic state.

21. Succinate of Silver.

Succinic acid has no action on silver, but it combines with silver, &c. with its oxide. The succinate of silver crystallizes in thin oblong prisms, which are arranged in a radiated form.

22. Saccolate of Silver.

Saccharic acid poured into a solution of nitrate of silver produces a white precipitate, the nature of which has not been examined.

II. Action of Alkalies, &c. upon Silver.

1. The pure alkalies have no effect on silver. Its oxide is soluble in ammonia; but if this solution be long exposed to the light, the ammonia is decomposed, azotic gas is disengaged, water is formed by the combination of the hydrogen of the ammonia and the oxygen of the oxide, which is reduced to the metallic state.

2. Silver forms no compound with the earths; but in the state of oxide it combines with some of them, by vitrification, and in this state it colours glass and enamels of a yellow, olive green, or brownish shade. For this purpose the oxide of silver is employed in the arts.

3. None of the salts have any action on silver. It is not sensibly oxidized by the nitrates or hyperoxymuriates. The metals which are more easily oxidized, and with which silver is frequently contaminated, are acted on by these saline matters, and in this way it has been observed, silver may be refined or purified by means of nitre.

III. Alloys.

1. There are few metallic substances with which silver does not enter into combination, and form alloys. Few of these, however, are applied to useful purposes. Arsenic combines with silver, and forms an alloy, which is externally of a yellow colour, but internally of a dark gray. It is brittle; and, when it is exposed to heat, the arsenic is sublimed, and the silver remains behind in a state of purity.

2. Cobalt is with difficulty alloyed with silver. When they are melted together in a crucible, they separate from each other, according to their specific gravities, and each having a small proportion of the other.

3. Bismuth combines with silver very readily by fusion. The alloy is brittle, lamellated, and of an intermediate colour between bismuth and antimony. The specific gravity is greater than the mean. The two metals cannot be separated, but with difficulty. When this alloy is exposed to strong heat in the open air, the bismuth is oxidized, and vitrified at the same time that it is partially sublimed, so that it might be employed in place of lead for the cupellation of silver; and in some cases bismuth is preferred, on account of its more rapid oxidation.

4. The alloy of antimony and silver is easily effected by fusion. It is heavier than the mean of the two metals. This alloy is brittle, and has not been applied to any use.

5. Silver has a strong affinity for mercury. An amalgam may be formed of these two metals, by saturating silver leaf, or fine filings of silver, with mercury; or by adding to silver, while it is red-hot, heated mercury. The consistence of this amalgam varies according to the proportion of the two metals. In general it is white and soft, and the specific gravity is greater than the mean. It sinks to the bottom of liquid mercury. Exposed to a moderate heat for some time, it shoots out into a kind of vegetation, like the tree of Diana; and, if after fusion, it is allowed to cool slowly, it crystallizes in the form of small leaves, or in square prisms, terminated by four-sided pyramids. When it remains long exposed to the air, it becomes harder, and of a more solid consistence. This amalgam is much employed in gilding.

6. Silver combines readily with zinc, by means of zinc fusion, and forms with it a brittle alloy, which has not been applied to any use.

7. Silver combines easily with tin, and forms an alloy which is extremely brittle. The silver is entirely deprived of its ductility. This alloy, however, instead of being useless, is considered as one of the most troublesome in the working of silver, on account of the hardness and brittleness which it communicates, and it is found almost impossible to separate them entirely.

8. Lead, it has been already observed, readily combines with silver by means of fusion. It is employed for the purification of lead in the process of cupellation. This alloy is very fusible, resembles lead in colour, and is less sonorous, but not less ductile than silver. The specific gravity is greater than the mean.

9. An alloy of silver and iron in equal proportions has nearly the colour of silver. It is harder, has some ductility, and is attracted by the magnet. Steel is soldered with silver. Guyton fused together silver and iron, and obtained two buttons, which were placed by the side of each other, and strongly adhering, but sufficiently distinct. Each of the metals was found to be alloyed with a small proportion of the other. This silver renders the iron hard and compact, and the iron communicates to the silver properties which seem to render it applicable to many important uses.

10. Silver combines readily with copper, and forms copper with it one of the most useful alloys. This alloy gives hardness to the silver, and the colour of the latter is not diminished, unless the quantity of copper is considerable. These properties render it extremely useful in the fabrication of various utensils, and especially of money. The density of the alloy is less than the mean of the two metals. If 137 parts of silver be alloyed with 7 parts of copper, the mean specific gravity is 10.301, but it is only 10.175, which shows an increase of bulk of \( \frac{1}{37} \) part. This is the alloy of the silver coin of France*. The standard silver, which is employed in the British silver coin, is composed of 11 parts of silver and one of copper.

The uses of silver are as important and extensive as those of any of the metals, except iron, and especially when it is alloyed with copper; as it is applied as the medium of commerce by all civilized nations, and for various instruments and utensils, most of which are so familiar as to require no particular enumeration.

Sect. XXI. Of Gold and its Combinations.

1. Gold is spoken of in the earliest histories of the world. The peculiar properties of this metal, its scarcity, durability, and beauty, have rendered it always an object of pursuit, and have raised it high in the estimation. Gold, &c. tion of mankind. The alchemists regarded gold as the purest, the simplest, the most perfect, and very justly the most indestructible of all the metals with which they were acquainted. Hence it was esteemed the noblest and most perfect of what they considered as perfect metals, and dignified with the pompous name of king of the metals. It was the object of all their labours and researches, to discover the means of transmuting the baser and more abundant metals into this precious metal.

2. Gold is supposed to be, next to iron, the most uniformly diffused, but very rarely diffused in all the metals; but, at the same time it is found in such small quantities, that it is one of the rarest. It is most commonly found in the state of small grains, mixed with the sand or with the soil, almost in every part of the world. Gold is also found imbedded in stones, especially quartz, either in grains, or crystals, which are octahedrons; and it is probably from these that the grains found in the soil or in the sand of the beds of rivers, have been derived. Gold is, however, more abundant in the tropical regions of the earth, where it forms an article of commerce, under the name of gold dust. In this state it is found in the rivers of Africa, and exported to Europe. But although gold is always found in the metallic state, it is not absolutely pure. It is generally alloyed with copper or silver, and sometimes with iron and mercury.

3. To separate gold from the metals with which it is alloyed, the process recommended by Bergman may be employed. It is first dissolved in nitro-muriatic acid; the silver is deposited spontaneously in the form of nitrate of silver, which is insoluble; the gold is precipitated in fine powder by the sulphate of iron; the quantity of iron may be ascertained by prussian of potash; and the copper is separated by means of iron. Each of these processes is performed on different portions of native gold, so that the quantity of gold, and the different metals with which it is alloyed, may be determined. In the large way, the extraction of gold is a very simple process. The auriferous sand of rivers is first washed to carry off all extraneous matters. It is triturated in a vessel with water, with 10 or 12 times its weight of mercury. The water is poured off, and carries with it the earthy matters. The amalgam is pressed in skins, to separate the excess of mercury, and the solid portion which remains is exposed to heat in stoneware retorts, to drive off the mercury, and the gold remains behind. To separate the gold from other metals, it is subjected to the process of cupellation, which has been already described in treating of the purification of silver.

4. Gold is of a reddish yellow colour. It possesses considerable lustre, although other metals have this property in a superior degree. Gold, next to platinum, is the heaviest body in nature, having a specific gravity of 19.3 and 19.4. It is not very hard, but is extremely ductile and malleable. It may be beaten out into leaves so thin as to equal 1/100000 part of an inch. The method of extending gold, which is followed by the gold-beaters, is by hammering a number of thin rolled plates between skins or animal membranes. A single grain of gold may be beaten out in this way, so as to cover 564 square inches. The coating of gold which covers wire is still thinner. By computation it is found, from the diameter and length of the wire, and gold, &c., the quantity of gold employed, that it is only 1/1000 of the thickness of gold leaf. The tenacity of gold also is very considerable. A gold wire .078 of an inch in diameter will support a weight equal to more than 150 lbs. avoidupesis, without breaking. Gold has no perceptible taste or smell.

5. Gold melts, according to Guyton, at the temperature of 32° Wedgwood. It has been observed, that heat, gold, in the state of filings or grains, melts with more difficulty than in larger masses; and that the small fragments, even after they are fused, remain in separate globules. To make them run into one mass, a little nitre or borax is thrown into the crucible. It has also been observed, that gold, which has only been subjected to the degree of heat necessary for its fusion, is brittle after cooling. To preserve its ductility, therefore, the temperature must be raised much higher. It is brittle also, when it is too suddenly cooled after fusion. By increasing the temperature while the gold is in fusion, it seems to become convex on the surface, and when it cools, it sinks, which is ascribed to the expansion and contraction of the metal. When it is slowly cooled, it crystallizes in the form of quadrangular pyramids, or regular octahedrons. If the heat be continued while it is in perfect fusion, it seems to be agitated, and to undergo a kind of ebullition. This was observed by Homberg and Macquer, by the action of the burning glass, or when a small globule of gold was acted on by the blow-pipe. According to Macquer, it rose in vapour to the height of five or six inches, and attached itself to the surface of a silver plate, which it gilded completely.

6. Gold is the most indestructible, and the least altered of all the metals, by exposure to the air. It preserves its lustre, its brilliancy, and colour, for any length of time.

7. The strongest heat of a furnace, which has been applied to gold in fusion, has been found incapable of producing the smallest change, or the least tendency to oxidation; but, by the action of Tschirnhausen's powerful burning glass, Homberg having placed some gold in the focus, found that it rose in vapour; and that it was covered with a violet-coloured vitreous oxide. This change was at first ascribed to foreign bodies, particularly to the charcoal on which the gold was placed during the experiment. But Macquer repeated the same experiments with a more powerful glass, and obtained the same result. The vitrification after some time gradually extended, the gold diminished, and the support was impregnated with a purple coloured matter. The effect of electricity on gold leaf, placed between two cards, was observed by Camus in 1773. The gold was converted into a violet-coloured powder, which adhered to the paper. This seeming oxidation was regarded by some as merely a minute mechanical division of the gold; but this objection has been removed by the experiments of Van Marum on the combustibility of gold by means of the powerful electrical machine at Haarlem. A strong electrical shock was passed through a golden wire suspended in the air. It kindled, burned with a perceptible green flame, and was reduced to fine powder, which was dissipated in the air. It was supposed by this philosopher, that the inflammation of gold might be Gold, &c., effected without the excess of oxygen gas, as he found it to take place in hydrogen gas and other elastic fluids, which are incapable of supporting combustion. But the force of this objection is removed by recollection, that all gases hold in solution a quantity of water, and that water is very readily decomposed by electricity.

A similar oxidation has been observed to take place on the gilding in the inside of houses, or on the furniture, which has been struck with lightning. The purple oxide of gold, thus obtained, contains about five or six parts in the hundred of oxygen. Gold combines with a greater proportion of oxygen, forming a different oxide of a yellow colour; but this oxide is incapable of combining with any farther portion of oxygen. It remains therefore, unchanged in the air, and retains for a long time its brilliant rich colour. This oxide, however, is decomposed by the action of heat; the oxygen is driven off, and the gold remains behind in the metallic state.

When gold is dissolved in nitro-muriatic acid, or in a mixture of equal parts of nitric and muriatic acids, an effervescence takes place, and the solution becomes of a yellow colour. In this process the nitric acid is decomposed, its oxygen combines with the gold, and the oxide, as it is formed, is dissolved in the muriatic acid. By adding lime water, a precipitate is formed, which is the yellow oxide of gold, consisting of eight or ten parts of oxygen in the 100.

8. There is no action between gold and azote, hydrogen, carbone or sulphur. The oxides of gold, indeed, are readily decomposed by hydrogen.

9. Phosphorus, according to the experiments of Pelletier, combines with gold, by heating together in a crucible a mixture of one part of gold in filings, with two parts of phosphoric glais, and one-eighth part of charcoal. Great part of the phosphorus is separated from the acid, and driven off, but there remains a small quantity united with the gold, forming a phosphuret of gold. This phosphuret is whiter and more brittle than the gold, and has some appearance of crystallization. It may be formed also by adding phosphorus to gold in a red heat in a crucible. It becomes pale coloured, granulated, brittle, and a little more fusible. This phosphuret contains 1/4th part of phosphorus. It is decomposed by being kept some time in fusion; the phosphorus is driven off in the state of vapour, and inflamed.

10. The order of the affinities of gold and its oxides, as they have been arranged by Bergman, is the following:

| GOLD | OXIDE OF GOLD | |------|--------------| | Mercury | Muriatic acid | | Copper | Nitric | | Silver | Sulphuric | | Lead | Arsenic | | Bismuth | Fluoric | | Tin | Tartaric | | Antimony | Phosphoric | | Iron | Prussic |

II. Salts of Gold.

1. Nitrate of Gold.

When concentrated nitric acid is several times successively poured upon gold, boiled and distilled to dryness, the gold is dissolved, and the solution assumes a yellow colour. This effect was first observed by Brandt, in separating gold and silver, by means of this acid. But it appears from the observation of Deyeux on the solubility of gold in nitric acid, that the solution is more readily effected in proportion to the quantity of gas, or nitrous gas, which the acid contains. According to the experiments and observations of Fourcroy, gold leaf is dissolved in nitric acid, impregnated with nitrous oxide, and that it is owing to the nitrous oxide that the gold is oxidated, this oxide being more easily decomposed than nitric acid. Thus it happens that the acid is deprived of its colour as it acts on the gold, and the solution is more rapidly effected in the cold than with heat, because the nitrous gas is disengaged by heat. The acid which at first had been deprived of its colour, by the oxidation of the gold, as this oxide is dissolved, assumes an orange-yellow colour, holding in solution the nitrate of gold with excess of acid. The nitrate of gold cannot be obtained in crystals. It is decomposed by heat, or by exposure to the light of the sun. When this solution is filtered, it leaves fed by heat on the paper a violet-coloured trace, which is the oxide of gold. The nitrate of gold is also decomposed by the alkalies, or by introducing a plate of tin or silver into the solution, and the purple oxide is precipitated in the form of powder. It is also decomposed by muriatic acid, which, at the instant of combination, converts the orange colour to a pure yellow.

2. Muriate of Gold.

1. Muriatic acid has no action whatever on gold, or on its purple oxide, but gold is immediately oxidated, and dissolved by oxymuriatic acid; or if nitric acid be added to muriatic acid, the solution of gold is immediately effected. It is on account of this property that nitro-muriatic acid was distinguished by the name of aqua regia, because it dissolved gold, which was filled by the alchemists, the king of the metals. The nature of the action is obvious. Gold is oxidated with great difficulty. This is effected by oxymuriatic acid, which readily parts with its oxygen, or by the addition of nitric to the muriatic acid, the former of which is decomposed, giving up its oxygen to the gold, which being oxidated, is dissolved in the muriatic acid, forming a muriate of gold. This solution of the muriate of gold is of a deep yellow colour, extremely acid and caustic, has a very astringent, metallic taste, and attains the skin of a deep purple colour, which becomes darker by exposure to the air and the light. It continues permanent till the epidermis is renewed. It produces a similar effect on all vegetable and animal matters, and on marble and siliceous stones. By evaporating this solution, nitric acid is disengaged, and crystals are obtained, in the form of truncated octahedrons, or small quadrangular prisms, of a topaz colour. These crystals are easily procured by evaporating the solution to one half, and adding a little alcohol. They assume a red colour by the action of strong Gold, &c., strong light. They attract moisture from the air, and spontaneously become liquid. By gradually heating in a retort this solution of gold in nitro-muriatic acid, there passes over nitric acid, muriatic acid, which carries with it a portion of gold, and even reddish-yellow crystals of muriate of gold. To the nitro-muriatic liquid, which is of a high colour, and which rises during the distillation, the alchemists gave the name of red lion. By evaporating the solution to dryness, a dry muriate of gold is obtained, which may be reduced by a strong heat, previously giving out oxygen gas, and leaving the gold behind in the metallic state.

2. The muriate of gold is very soluble in water. It is decomposed by hydrogen gas. If a piece of silk be moistened with a solution of muriate of gold, the salt is decomposed, and the gold, reduced to the metallic state, attaches itself to the silk. Muriate of gold is also decomposed by phosphorus. If a stick of phosphorus be introduced into a saturated solution of muriate of gold, the salt is decomposed, and the gold being reduced to the metallic state, forms a cylindrical covering to the phosphorus, which may be separated by dissolving the latter in hot water. A similar effect is produced by burning sulphur, by sulphurated and phosphorated hydrogen gases, and by sulphurous acid. If a solution of muriate of gold be cautiously added to sulphurous acid, a fine pellicle of gold appears on the surface, which is instantly precipitated in the form of small grains. These curious and interesting experiments were made by Mrs Fulham. It is easy to see the nature of the process. All the substances which have been enumerated, have a stronger affinity for oxygen than gold, so that the oxide of gold in combination with the acid is decomposed; the oxygen combining with the hydrogen, for instance, and forming water, or with the phosphorus or sulphur, and forming sulphuric or phosphoric acid. The reduction of muriate of gold, Mrs Fulham has observed, does not take place except in the liquid state, and she supposes that the decomposition of water is necessary to produce this effect. But the liquid state of the salt, it is supposed by others, is only necessary, to expose it to the action of combustibles in a state of minute division, and that otherwise this theory does not account for the phenomena.

3. The muriate of gold is soluble in ether. It forms with it a solution of a golden yellow colour, which floats on the top of the fluid. By adding ether to a solution of gold, and agitating the mixture, as soon as it is left at rest, the two liquids separate, the ether rises to the top, and assumes a yellow colour, while the nitro-muriatic acid remains below and becomes white. By this process a tincture of gold, or what was formerly called potable gold, was prepared. The solution of gold in ether is not permanent. It is soon reduced to the metallic state, and is sometimes found crystallized on the surface.

4. The muriate of gold is decomposed by all the alkalies and earths, and is reduced to the state of yellow oxide. This decomposition is effected slowly by the fixed alkalies, and if the alkali be added in sufficient quantity, the precipitate is re-dissolved, and the liquid assumes a reddish colour. It is owing to this solution of the oxide of gold by these alkalies, that the precipitation is slow and difficult. Triple salts are gold, &c., formed, the nature of which is unknown. The oxide of gold, thus precipitated, becomes of a purple colour by exposure to the light; by the action of heat it gives out oxygen gas, and the gold is revived.

The most singular precipitate from the muriate of fulminating gold, is that by means of ammonia, which forms the ing gold compound called fulminating gold. It is prepared by the following process. To a solution of gold in nitro-muriatic acid, and diluted with three or four times its weight of distilled water, gradually add pure ammonia, as long as any precipitate is formed. No excess of alkali must be added, because the precipitate is redissolved. It is then washed and dried in the air on paper, and afterwards put into a phial, which should be covered only with a bit of cloth or paper, as the powder is apt to explode with the slightest friction.

Fulminating powder may also be obtained, by dissolving gold in a solution of two parts of nitrate of precipitate ammonia, and one of muriatic acid. The oxygen of the nitric acid combines with the gold, and forms an oxide, which is dissolved in a portion of the muriatic acid; nitrous gas is disengaged, and there remain in the liquid, muriate of gold, and muriate of ammonia. By precipitating this solution by means of a fixed alkali, fulminating gold is obtained. The alkali combines with the muriatic acid of the gold and ammonia, and the oxide of gold uniting with the ammonia, forms the fulminating gold. The precipitate is washed and dried as in the former process. Basil Valentine, who first described this singular preparation, had observed that it produced detonation equally by means of heat, by friction, and percussion. When a small quantity of fulminating powder is exposed to heat, it produces a violent detonation; or, if it be rubbed with a hard body, a similar effect takes place. It explodes also, by being smartly struck with a hammer. These astonishing effects long excited the attention of philosophers, but received no satisfactory explanation, till the nature of the composition of this substance was discovered by modern chemists. It was examined by Scheele and Bergman; and at last the theory of its violent action was fully developed by Berthollet. This compound consists of the oxide of gold and ammonia, and as the oxide performs the part of an acid, it is sometimes denominated aurate of ammonia. During the explosion which takes place, whether by the application of heat, or by friction or percussion, the hydrogen of the ammonia combines with the oxygen of the oxide of gold, and forms water. This water being suddenly raised to the state of vapour, and the azote, the other component part of ammonia, being at the same time suddenly converted into gas, produce the explosion. The gold is reduced to the metallic state.

This substance may be deprived of its fulminating property, by being exposed for some time to a very gentle heat. It is then converted into a blackish brown powder. A similar effect is produced, by subjecting it for a long time to the temperature of boiling water. Its fulminating property is at least greatly diminished by the latter process. It appears too, that the contact of air promotes this action; for when it was heated in an iron globe, in an experiment which which Birch performed before the Royal Society of London, or in a sphere of strong copper, in an experiment by Bergman, no detonation took place. Berthollet applied a gentle heat to a quantity of fulminating gold, in copper tubes; and he obtained ammonia-cal gas, and the gold was reduced to the state of purple oxide. By these experiments it appears, that this substance is decomposed without detonation, when the sudden dilatation of the gases which are disengaged is resisted by strong vessels, or when the heat is too moderate as to separate the ammonia without decomposition.

5. The muriate of gold is decomposed by almost all metallic substances. Some metals decompose it completely, and reduce it to the metallic state, while others deprive it of a portion of oxygen, and reduce it to the state of purple oxide. Bismuth, zinc, iron, copper, and mercury, reduce the gold to the metallic state. Lead, silver, and tin, occasion a precipitate in the form of purple oxide. The most singular of all these precipitates, and which has long occupied the attention of chemists, is that which is produced by means of tin. This is called the purple precipitate, or powder of Caffius. It was at first particularly described by Caffius, from whom it derived its name; but it was known long before, even so early as the time of Basil Valentine, by whom it is mentioned. If a plate of tin be immersed in a solution of muriate of gold, the surface of the metal is soon covered with a deep-colored violet or purple powder, which is gradually diffused through the whole liquid. This is usually prepared by adding to a solution of gold in nitro-muriatic acid, a solution of muriate of tin recently prepared. The theory of this process is the following. The gold in solution is in the state of yellow oxide. It is deprived of part of its oxygen, and reduced to the state of purple oxide by the tin. The purple oxide is no longer soluble in the acid, and is therefore precipitated. The same effect is produced when a salt of tin is added, provided this salt be not fully saturated with oxygen, for in that case no precipitate is obtained. This is the reason, as Pelletier has shown, that muriate of tin, after it has been for some time exposed to the air, loses the property of producing the purple precipitate, because it has absorbed oxygen from the atmosphere, and is not susceptible of combining with a greater quantity. For the same reason no precipitate is obtained by the oxymuriate of tin, or the smoking liquor of Libavius, or the red sulphate of iron, because both these salts have their bases fully saturated with oxygen. Other metallic solutions have also the property of decomposing and precipitating the muriate of gold. The nitrate of silver produces a reddish precipitate, which is a mixture of white muriate of silver and purple oxide of gold. The nitrate of lead deposits a dark colored substance, composed of muriate of lead and oxide of gold.

6. The metallic acids have no effect whatever on gold. Vauquelin found that chromic acid, mixed with muriatic acid, gave it the property of dissolving gold. This is owing to the chromic acid giving up part of its oxygen, which appears to be the case, from its passing from its natural color, which is orange, to the state of green oxide.

II. Action of Alkalies, &c. upon Gold.

1. None of the alkalies have any action upon gold or on its purple oxide; but the yellow oxide precipitated from its solution by means of the fixed alkalies, and digested for some time with ammonia, is readily converted into fulminating gold.

2. The earths have no action on gold in the metallic state; but in the state of purple or yellow oxide, it combines with the earths which are vitrified by means of the alkalies, and forms with them enamels, which are of a violet or purple colour, or glaze of a golden-yellow colour. It is on account of the latter property that the yellow oxide is employed in the fabrication of artificial topazes. It has been observed that glass coloured by means of gold, and which contains a considerable proportion of oxide of lead or of manganese, has a remarkable property of changing to a permanent purple or ruby-red colour, when it is slightly heated, and long before fusion. This is supposed to be owing to some change in the state of the oxidation of the different metals.

3. The most powerful salts, as the nitrates, the hy-Salts, peroxymuriates, have no action on pure gold. It has, however, been observed, that borax diminishes its colour, and that nitre, which is employed in its purification, renders it more brilliant.

III. Alloys of Gold.

1. Gold is susceptible of combination with most metallic substances, which produce a very particular nic. change on its properties. The alloy with arsenic is brittle, hard, of a granulated texture, and of a very pale colour. According to Mr Hatchett's experiments, arsenic readily combines with gold raised to a common red heat, when the former is in the state of vapour, and particularly when the combination is made in close vessels.

2. The alloys of gold with tungsten, molybdenum, Tungsten, chromium, titanium, and uranium, have not been examined.

3. The combination of gold and cobalt is not perceptibly different from pure cobalt. This alloy reduces to a fine powder, and heated in contact with air, gives, after its oxidation, and by strong heat, a deep blue glaze. In Mr Hatchett's experiments, one part of cobalt and 14 of gold form a brittle alloy of a dull yellow colour. With 1/10 of cobalt the alloy was brittle, but became ductile with 1/10 part.

4. Gold forms with nickel a white and brittle alloy. Nickel. In Mr Hatchett's experiments 1/8 of nickel rendered the alloy brittle. It was scarcely, if at all, brittle with 1/7 part, and with 1/10 of nickel it was completely ductile. One part of nickel and 16 of gold give an alloy of the colour of brass.

5. Mr Hatchett formed an alloy of gold with manganese. It was of a pale yellowish-gray colour, had something of the lustre of polished steel, and some ductility, although it was very hard. It contained about one-ninth of manganese. Acids produced no effect, nor was it altered by exposure to the air.

6. Bismuth fused with gold, yields an alloy which is brittle in proportion to the quantity of bismuth employed. The specific gravity of this alloy is greater than... Gold, &c., than the mean. In Mr Hatchett's experiments, this alloy was brittle, when the proportion of bismuth amounted only to $\frac{1}{32}$ part.

7. Antimony combines with gold, and renders it hard and brittle. Equal parts of these metals form an alloy not much different in appearance from gold itself. This compound was frequently employed by the alchemists in their researches. Antimony was called the royal bath. They pretended that the quantity of gold was increased when it was separated from the alloy, after having been fused with this metal. But it appears that this increase of weight was owing to part of the antimony, which was not separated from the gold. The sulphuret of antimony was formerly much employed for the purification of gold, to separate, by means of the sulphur, the metals which were combined with it; and from this property of acting on all the metals then known, excepting gold, the sulphuret of antimony was called by the alchemists, the wolf of the metals.

8. Gold unites very readily with mercury. If gold be brought into contact with this metal, it is instantly covered with it; and if gold leaf be triturated with mercury, it totally disappears, and is dissolved in the mercury; so that even in the cold, mercury combines with the whole quantity of gold with which it can be alloyed. When the proportion of gold is increased, the amalgam becomes solid. When this operation is performed in the large way, the combination is promoted by means of moderate heat. This amalgam is of a yellowish white colour; it is fusible at a moderate heat, and crystallizes in the form of quadrangular prisms. It is decomposed by a strong heat, and the mercury is dissipated. This amalgam is much employed in gilding.

9. Gold combines with zinc by means of fusion. This alloy is paler than gold, has little malleability, and if the proportion of the zinc be considerable, is very brittle. An alloy consisting of equal parts of the two metals, is of a greater specific gravity than the mean, is very hard, susceptible of a fine polish, and is not much altered by the air. It has been recommended, on account of these properties, for the fabrication of the mirrors of telescopes.

10. Gold combines easily with tin by means of fusion. This alloy, it is said, is the dread of the workmen, because it deprives gold of its ductility. They are even cautious in preserving gold from the contact of the vapour of tin in fusion, which renders the gold so brittle, that it may be reduced to powder in a mortar. It is extremely difficult to purify gold after it has been alloyed with tin, for it does not pass into the cupel with lead or with bismuth. Nitre, borax, and even the hypoxymuriate of mercury, which are often employed with this view, do not always succeed. The most successful method is by treating the alloy with sulphuret of antimony, or with muriatic acid, which dissolves the tin when it is in considerable proportion. But in the experiments of Mr Hatchett and Mr Bingley, it appears that the universal opinion which has hitherto prevailed, of tin being so injurious to the ductility of gold, is to a certain extent, erroneous; and it appears probable, that the ductility of gold being destroyed, as was supposed, even by the fumes of tin, ought to have been ascribed to other metals, as bismuth, lead, antimony, or zinc, with which the tin was contaminated.

11. Lead very readily combines with gold by fusion; this alloy deprives the gold of its ductility, and diminishes the colour. So small a proportion as $\frac{1}{32}$ part of lead destroys the ductility of gold. This alloy, it has been already stated, is made for the purpose of purifying gold from other metals, in consequence of the easy oxidation and vitrification of the lead.

12. Gold is easily alloyed with iron, and forms with it a hard brittle mass. Some of these alloys are so hard, that Dr Lewis found them fit for cutting instruments. Equal parts of iron and gold form an alloy of a gray colour. Four parts of iron and one of gold afford an alloy nearly of the colour of silver, and the specific gravity of this alloy has been ascertained to be less than the mean. One part of iron alloyed with 12 of gold, according to Mr Hatchett, was of a pale-yellowish gray colour, and was so ductile that it might be rolled and cut. When gold is fused, it adheres readily to iron; and hence it has been proposed to solder small pieces of steel with gold, which seems to be preferable to copper.

13. Gold readily combines with copper by fusion. Copper. This is one of the most important alloys, on account of the hardness which copper communicates to gold, without diminishing its colour. This alloy, according to Muenchenbroeck, possesses the greatest hardness, without sensibly diminishing its ductility, when the proportions are one part of copper and seven of gold. This alloy is more fusible than gold, and on that account it is employed as a solder for that metal. The gold coin of most countries consists of this alloy. The proportions in the gold coin of Britain and France are 11 parts of gold to one of copper. According to Briffon, the specific gravity of this alloy is greater than the mean. It is 17.486, but it ought to be 17.153. But, according to Mr Hatchett's experiments, there is no mutual penetration in the alloy of these metals, and therefore no increase of density. On the contrary, some degree of expansion was observed. Four hundred and forty-two grains of gold of specific gravity 19.172, were alloyed with 38 grains of copper of specific gravity 8.875. The specific gravity of the alloy was found to be 17.157. The bulk of the alloyed mass amounted to 27.98, while the natural bulk of the two metals before combination was 27.32, which shows an increase of expansion of the alloyed mass equal to $\frac{66}{100}$. Mr Hatchett observes that Briffon's experiment was probably made on part of a large bar or ingot, in which it generally happens, that the two metals are very unequally diffused, and this inequality, which is greater according to the quantity of the metal, is found to vary with the form, nature, and position of the mould, and therefore to produce variations in the specific gravity.

14. Silver forms an alloy with gold. Homberg found, that equal parts of these metals fused together in a crucible, formed an alloy which contained $\frac{1}{4}$ of its weight of silver. One part of silver and two of gold, according to Muenchenbroeck, give to the alloy the greatest degree of hardness. One-twentieth part of silver changes the colour of gold very sensibly. This alloy is employed for soldering gold, being more fusible than this metal. Mr Hatchet observes, that the obvious inference to be deduced from his experiments is, that only two metals are proper for the alloy of gold coin. These are, silver and copper. All other metals either considerably alter the colour, or diminish the ductility of gold. According to the same philosopher, the ductility of gold is diminished by different metallic substances, nearly in the following decreasing order:

Bismuth, Lead, Antimony, Arsenic, Zinc,

These are nearly equal in effect.

The uses of gold, many of which have been already detailed, in describing its properties and combinations, are too familiar to require particular enumeration (f).

Sect.

(f) Mr Hatchet supposes that the platina not being quite pure, the place he has assigned to it is perhaps not precisely that which it ought to occupy.

(f) The metals which were earliest known, were long distinguished by particular names and characters, of which the following account is taken from the elaborate researches of Professor Beckmann. The following table exhibits their names and characters.

| Metals | Names | Characters | |---------|-------|------------| | Gold | Sun | ☉ | | Silver | Moon | ♦ | | Mercury | Mercury | ♈ | | Copper | Venus | ♋ | | Iron | Mars | ♌ | | Tin | Jupiter | ♍ | | Lead | Saturn | ♎ |

It cannot be doubted, Professor Beckmann observes, that these names were first given to the heavenly bodies, and the metals which were then known, amounting to the same number, were supposed to have some affinity or relationship to the planets, and with them to the gods, and were accordingly named after them. "To each god was assigned a metal, the origin and use of which was under his particular providence and government; and to each metal were ascribed the powers and properties of the planet and divinity of the like name; from which arose, in the course of time, many of the ridiculous conceits of the alchemists.

"The oldest trace of the division of the metals among the gods is to be found, as far as I know, in the religious worship of the Persians. Origen, in his refutation of Celsus, who asserted that the seven heavens of the Christians, as well as the ladder which Jacob saw in his dream, had been borrowed from the mysteries of Mithras, says, 'Among the Persians the revolutions of the heavenly bodies were represented by seven stairs, which conducted to the same number of gates. The first gate was of lead; the second of tin; the third of copper; the fourth of iron; the fifth of a mixed metal; the sixth of silver; and the seventh of gold. The leaden gate had the flow tedious motion of Saturn; the tin gate the lustre and gentleness of Venus; the third was dedicated to Jupiter; the fourth to Mercury, on account of his strength and fitness for trade; the fifth to Mars; the sixth to the Moon, and the last to the Sun.' Celsus of quidquidam Perarum doctrina Mithraeique eorum mysteriis vestigium. In illis enim duae celestes conversiones, alia stellarum fixarum, errantium alia, et animae per eas transitus quodam symbolo repraesentantur, quod hujusmodi est. Scala altas portas habens, in summa autem octava porta. Prima portarum plumbea, altera flaminea, tertia ex aere, quarta ferrea, quinta ex aere mixto, sexta argentea, septima ex auro. Κλειστή ὑπνολόγος, ἐπὶ διαφορὰ πυλῶν εὐθύνη. Ἡ πρώτη τῶν πυλῶν καλεῖται, ἡ δεύτηρα μακρινότερον, ἡ τρίτη ἡ καλύτερον, ἡ τέταρτη ἐνδέχεται, ἡ πέμπτη καρποῦ νομισμάτων, ἡ ἕκτη αργύριον, ἡ ἑβδόμη. Primum assignant Saturno, tarditatem illius fideris plumbico indicantes; alteram Veneri, quam referunt, ut ipsi quidem putant, stanni splendor et mollitutes; tertiam Jovi, aheneam illam quidem et foliadam; quartam Mercurio, quia Mercurius et ferrum, uterque operum omnium tolerantes, ad mercaturam utiles, laborum patiensissimi. Marti quintam, inaequalem illam et variam propter mixturam. Sextam, quo argentae est, luna; septimam auream foli tribunt, quia folis et lunae coloris hic duo metalla referunt." Contra Celsum, lib. vi. p. 161. Here there is an evident trace of metallurgical alchemy, as Borrichius calls it, or of the astronomical or mythological nomination of metals, though it differs from that used at present. According to this arrangement, tin belonged to Jupiter, copper to Venus, iron to Mars, and the mixed metal to Mercury. The conjecture of Borrichius, that the transcribers of Origen have, either through ignorance or design, transposed the names of the gods, is highly probable: for if we reflect that in this nomination men, at first, differed as much as in the nomination of the planets, and that the names given them were only confirmed in the course of time, of which I shall soon produce proofs, it must be allowed that the causes assigned by Origen for his nomination do not well agree with... Sect. XXII. Of Platina and its Combinations.

Platina in most of its properties is equal to gold, but in others, it is superior. It was first clearly ascertained to be a distinct metal, by Scheffer, a Swedish chemist, in the year 1752. It had been indeed taken notice of at an earlier period. A quantity of it was brought from Jamaica in 1741, by Mr Wood. It is particularly mentioned by Antonio de Ulloa, a Spanish mathematician, in the account of his voyage to Peru with the French academicians, to measure a degree of the meridian, which was published in 1748. After this period numerous experiments were made upon this new substance, all of which tended to prove that it is a different metal from any formerly known; Scheffer

with the present reading, and that they appear much juster when the names are disposed in the same manner as that in which we now use them. Borrichius arranges the words in the following manner: Secundam pertam faciunt Jovis, comparantes ei flanni splendorem et mollitatem; tertiam Veneris aeratam et solidam; quartam Martis, eft enim laborum patiens, æque ac ferrum, celebatus hominibus; quintam Mercurii, propter mituram inaequam ac variam, et quia negotiator ef; sextam Lunæ argenteam; septimam Solis auream. Ol. Borrichius de ortu et progressu chemice. Hafniae 1668, 4to. p. 29.

"This astrological nomination of metals appears to have been conveyed to the Brahmins in India; for we are informed that a Brachman sent to Apollonius seven rings, distinguished by the names of the seven stars or planets, one of which he was to wear daily on his finger, according to the day of the week. This can be no otherwise explained than by supposing that he was to wear the gold ring on Sunday; the silver one on Monday; the iron one on Tuesday, and so of the rest. Allusion to this nomination of the metals after the gods occurs here and there in the ancients. Dydimus, in his explanation of the Iliad, calls the planet Mars the iron star. Those who dream of having had anything to do with Mars are by Artemidorus threatened with a chirurgical operation; for this reason, he adds, because Mars signifies iron. Heraclides says also in his allegories, that Mars was very properly considered as iron; and we are told by Pindar that gold is dedicated to the sun.

"Plato likewise, who studied in Egypt, seems to have admitted this nomination and meaning of the metals. We are at least assured by Marcellus Ficinus; but I have been able to find no proof of it, except where he says of the island Atlantis, that the exterior walls were covered with copper and the interior with tin, and that the walls of the citadel were of gold. It is not improbable that Plato adopted this Persian or Egyptian representation, as he assigned the planets to the demons; but perhaps it was first introduced into his system only by his disciples. They seem, however, to have varied from the nomination used at present; as they dedicated to Venus copper, or brass, the principal component part of which is indeed copper; to Mercury tin, and to Jupiter electrum. The last-mentioned metal was a mixture of gold and silver; and on this account was probably considered to be a distinct metal, because in the early periods mankind were unacquainted with the art of separating these noble metals.

"The characters by which the planets and metals are generally expressed when one does not choose to write their names, afford a striking example how readily the mind may be induced to suppose a connection between things which in reality have no affinity or relation to each other. Antiquaries and astrologers, according to whose opinion the planets were first distinguished by these characters, consider them as the attributes of the deities of the same name. The circle in the earliest periods among the Egyptians was the symbol of divinity and perfection; and seems with great propriety to have been chosen by them as the character of the sun, especially as, when surrounded by small strokes projecting from its circumference, it may form some representation of the emission of rays. The semicircle is, in like manner, the image of the moon, the only one of the heavenly bodies that appears under that form to the naked eye. The character η is supposed to represent the scythe of Saturn; θ the thunderbolts of Jupiter; δ the lance of Mars, together with his shield; ρ the looking-glass of Venus; and ξ the caduceus or wand of Mercury.

"The expression by characters adopted among the chemists agrees with this mythological signification only in the character assigned to gold.—Gold, according to the chemists, was the most perfect of metals, to which all others seemed to be inferior in different degrees. Silver approached nearest to it, but was distinguished only by a semicircle, which, for the more perspicuity, was drawn double, and thence had a greater resemblance to the most remarkable appearance of the moon; the name of which this metal had already obtained. All the other metals, as they seemed to have a greater or less affinity to gold or silver, were distinguished by characters composed of the characters assigned to these precious metals. In the character ρ the adepts discover gold with a silver colour. The cross placed at the bottom, which among the Egyptian hieroglyphics had a mysterious signification, expresses, in their opinion, something I know not what, without which quicksilver would be silver or gold. This something is combined also with copper, the possible change of which into gold is expressed by the character ρ. The character θ declares the like honourable affinity also; though the semicircle is applied in a more concealed manner; for, according to the properest mode of writing, the point is wanting at top, or the upright line ought only to touch the horizontal, and not to intersect it. Philosophical gold is concealed in itself; and on this account it produces such valuable medicines. Of tin one half is silver, and the other consists of the something unknown: for this reason the cross with the half moon appears in η. In lead this something is predominant, and a similitude is observed in it to silver. Hence in its character η the cross stands at the top, and the silver character is only suspended on the right hand behind it.

"The mythological signification of these characters cannot be older than the Grecian mythology; but the chemical..." Platina, Scheffer, gave it the name of white gold, because it resembled this metal in many of its properties. In the year 1754, Dr Lewis published an account of a very full and elaborate set of experiments on platina, in the Philosophical Transactions. The properties of this new metal were still farther investigated by Margraaf in 1757, and by Macquer and Beaumé in 1758. It became afterwards the subject of research with many other philosophical chemists. Among these may be mentioned Buffon, Bergman, Sickingen, and more lately Guyton, Lavoisier, and Pelletier. It was at last denominated platina, signifying little silver, from the Spanish word plata, silver.

2. Platina has only been found among the gold ores of South America, and especially in the mine of Santa Fe near Carthagena, and in the district of Choco in Peru. It is found in the form of small grains or scales, of a white or grayish colour, intermediate between that of silver and iron. These grains are mixed with several other substances, as particles of gold, a black ferruginous sand, and some particles of mercury. Some of these grains extend under the hammer; others, which seem to be hollow, containing particles of iron and a whitish powder, break to pieces. To these grains of iron is ascribed the magnetic property which platina seems to possess (c).

3. To obtain platina in a state of purity, it is first separated from the substances with which it is contaminated. Mercury is driven off by exposing it to a red heat, and the particles of iron are separated by the magnet. The grains of platina are then heated with muriatic acid, which dissolves the remaining part of the iron. By this process, Bergman has observed, that the platina diminishes in weight about 0.05. The platina is now only alloyed with gold, which is to be separated by dissolving both in nitro-muriatic acid, and by precipitating the gold by means of the green sulphate of iron. But even after these processes, the platina is not in a state of absolute purity, as will appear afterwards (h).

4. This metal is of a white colour, but less bright than silver, and it possesses nothing of the brilliancy of either silver or gold. Platina is the densest body, and therefore the heaviest yet known. Its specific gravity, when it is hammered, is 233 or, according to Chabaneau, 24. According to Guyton, it comes next to iron and manganese in hardness. It possesses very considerable malleability, for it may be hammered

mical may be traced to a much earlier period. Some, who consider them as remains of the Egyptian hieroglyphics, pretend that they may be discovered on the table of Isis, and employ them as a proof of the high antiquity, if not of the art of making gold, at least of chemistry. We are told also that they correspond with many other characters which the adepts have left us as emblems of their wisdom.

"If we are desirous of deciding without prejudice respecting both these explanations, it will be found necessary to make ourselves acquainted with the oldest form of the characters, which, in all probability, like those used in writing, were subjected to many changes before they acquired that form which they have at present. I can, however, mention only three learned men, Saumaise, Du Cange, and Huet, who took the trouble to collect these characters. As I am afraid that my readers might be disgusted were I here to insert them, I shall give a short abstract of the conclusion which they form from them; but I must first observe that the oldest manuscripts differ very much in their representation of these characters, either because they were not fully established at the periods when they were written, or because many supposed adepts endeavoured to render their information more enigmatical by wilfully confounding the characters; and it is probable also that many mistakes may have been committed by transcribers.

"The character of Mars, according to the oldest mode of representing it, is evidently an abbreviation of the word Θεος, under which the Greek mathematicians understood that deity; or, in other words, the first letter Θ, with the last letter Σ placed above it. The character of Jupiter was originally the initial letter of Ζων, and in the oldest manuscripts of the mathematical and astrological works of Julius Firmicus the capital Z only is used, to which the last letter Σ was afterwards added at the bottom to render the abbreviation more distinct. The supposed looking-glass of Venus is nothing else than the initial letter, distorted a little, of the word Φαντασμα, which was the name of that goddess. The imaginary feet of Saturn has been gradually formed from the two first letters of his name Κρόνος, which transcribers, for the sake of dispatch, made always more convenient for use, but at the same time less perceptible. To discover in the pretended caduceus of Mercury the initial letter of his Greek name Σεληνη, one needs only look at the abbreviations in the oldest manuscripts, where they will find that Σ was once written as C; they will remark also that transcribers, to distinguish this abbreviation from the rest still more, placed the C thus Ω, and added under it the next letter τ. If those to whom this deduction appears improbable will only take the trouble to look at other Greek abbreviations, they will find many that differ still farther from the original letters they express than the present character Ω from the C and τ united. It is possible also that later transcribers, to whom the origin of this abbreviation was not known, may have endeavoured to give it a greater resemblance to the caduceus of Mercury. In short, it cannot be denied that many other astronomical characters are real symbols, or a kind of proper hieroglyphics, that represent certain attributes or circumstances, like the characters of Aries, Leo, and others quoted by Saumaise."

Hist. of Invent. iii. 53.

(c) Collet Desfontaines observes, that among the metallic substances which are usually found accompanying platina, there are two kinds of ferruginous sand; of which one is attracted by the magnet, and soluble in acids. This contains titanium. The other has no magnetic property, and is only partially soluble in acids. This last contains a considerable proportion of chromic acid. Ann. de Chim. xlviii. 154.

(h) A new metal, or several new metals, have been discovered in platina, by some late experiments. These will be mentioned in a future section. Platina, &c.

mered out, although with difficulty, into very thin plates; and it is so ductile, that it may be drawn out into wire \( \frac{1}{32} \) of an inch in diameter. The tenacity of platina is very considerable. A wire of .078 of an inch in diameter will support a weight, without breaking, equal to more than 274 lbs. avoirdupois.

5. Platina is the most infusible of all the metals. The temperature at which it enters into fusion is unknown. But small particles of platina have been fused by means of the blow-pipe, or by directing a stream of oxygen gas on red-hot charcoal. Guyton also succeeded in fusing it by means of a flux, composed of eight parts of pounded glass, one of calcined borax, and one-half part of charcoal in powder. When platina has been exposed to a white heat, it may be welded by hammering, like iron.

6. As platina is infusible in the strongest furnace heat, so it remains otherwise unchanged (1). It does not appear to undergo, like most other metals, any degree of oxidation; but if platina be dissolved in 16 times its weight of nitro-muriatic acid, by boiling the solution becomes at first of a yellow, and then changes to a brown colour. This solution is precipitated by means of lime, and the precipitate is in the form of a yellowish powder, which is the oxide of platina. The proportion of oxygen in this oxide is supposed not to exceed .07. But according to the experiments of Mr Chenevix, it is composed of

\[ \begin{align*} \text{Platina}, & \quad 87 \\ \text{Oxygen}, & \quad 13 \\ \end{align*} \]

The same chemist also found, that in the reduction of this oxide of platina, it became of a green colour, and remained for some time in that state. Ammonia assumes a green colour when it holds oxide of platina in solution. This Mr Chenevix considers as a second oxide of platina, and it contains

\[ \begin{align*} \text{Platina}, & \quad 93 \\ \text{Oxygen}, & \quad 7 \\ \end{align*} \]

Platina has also been oxidated by means of electricity. In Van Marum's experiments, a wire of this metal through which electric sparks were sent, burnt with a white flame, and was dissipated in the form of fine powder or dust.

7. Azote, hydrogen, and carbone, have no action whatever on platina.

8. Phosphuret of platina was formed by Pelletier, by mixing together equal parts of platina and phosphoric glass, with one-eighth of charcoal. This mixture being exposed to the temperature of 32° of Wedgwood for an hour, yielded a small button of phosphuret of platina, of a silvery white colour, part of which had assumed the form of cubic crystals. It was so hard as to strike fire with steel, and was not attracted by the magnet. It was covered with a dark coloured glass, which afterwards became green, bluish, and white. By exposing this phosphuret to a strong heat, the phosphorus is separated, and burns on the surface, and the metal remains behind very pure and malleable. Pelletier has proposed this process for the purification of platina from other metals.

9. Sulphur has been found in combination with natrophuretive platina. When native platina is exposed to the action of the blow-pipe on charcoal, it exhales the penetrating odour of sulphur, accompanied with a vapour which does not render gold white, and which requires a higher temperature to sublime it than mercury.

I. Salts of Platina.

1. Sulphate of Platina.

By adding sulphuric acid to a solution of platina in muriatic acid, Mr Chenevix obtained an insoluble salt, which he found to be composed of

\[ \begin{align*} \text{Oxide of platina}, & \quad 54.5 \\ \text{Acid and water}, & \quad 45.5 \\ \end{align*} \]

This triple salt is formed by adding a solution of potash to sulphate of platina. The component parts of this salt are, sulphuric acid, oxide of platina, and potash; but the proportions have not been ascertained by Bergman, who examined it.

3. Sulphate of Platina and Ammonia.

This triple salt is formed in the same way as the former, by adding ammonia to the sulphate of platina.

4. Nitrate of Platina.

Nitric acid has no action on platina, but it dissolves the yellow oxide. Mr Chenevix precipitated the oxide of platina from its solution in nitro-muriatic acid by means of lime, and although it was added in excess, a great portion of platina remained in the liquor. The precipitate was redissolved in nitric acid, and evaporated to dryness. The result was, a subnitrate of platina, which consisted of

\[ \begin{align*} \text{Yellow oxide}, & \quad 89 \\ \text{Nitric acid and water}, & \quad 11 \\ \end{align*} \]

5. Nitrate of Platina and Potash.

When potash is added to a solution of nitrate of platina, crystals are deposited forming a triple salt, composed of nitric acid, oxide of platina and potash.

6. Nitrate of Platina and Ammonia.

This triple salt is formed by adding ammonia to a solution of nitrate of platina.

---

(1) Guyton proposes to construct a pyrometer of platina. See Ann. de Chim. xlvii. 276. 7. Muriate of Platina.

Muriatic acid has no action on platina, but the muriate of platina may be obtained by dissolving the metal in nitric acid. Boiled in 16 parts of a mixture consisting of one part of nitric acid and three parts of muriatic acid, it is gradually dissolved with effervescence. It may also be dissolved in oxymuriatic acid. The solution of platina in muriatic acid is of a reddish or deep brown colour. It is extremely acid and caustic, corrodes and burns animal matters, and leaves a dark brown spot on the skin. When the solution is concentrated, it deposits, on cooling, small irregular crystals, nearly in the state of powder, and of a brownish-yellow colour. When these crystals are washed and dried, they are found to be less soluble by boiling in water, than even the sulphate of lime. The solution is of a yellow colour. The muriate of platina has a harsh, astringent taste; it is decomposed by heat; the acid is driven off, and the oxide remains. It is also decomposed by concentrated sulphuric acid. Potash produces in this solution, small reddish crystals, frequently in the form of octahedrons, constituting the triple salt already described. The same triple salt is formed by the sulphate of potash. Ammonia, or the muriate of ammonia, also forms a triple salt, by being added to the solution of muriate of platina. Soda in sufficient quantity occasions a precipitate of the yellow oxide of platina, and a triple salt also is formed. Mr. Chenevix found that the insoluble muriate of platina is composed of

| Oxide of platina | 70 | |-----------------|----| | Acid and water | 30 |

8. Muriate of Platina and Soda.

Till the experiments of Collet-Desfontaines, little was known of this triple salt. It may be obtained by adding to a solution of platina a salt with base of soda. By concentration and cooling it crystallizes in the form of long prisms, and sometimes in that of triangular tables, of a yellow or red colour. It is very soluble in water, and also in alcohol. It is decomposed by muriate of ammonia, and by a solution of soda; but an excess of this salt re-dissolves the precipitate. It may be reduced by the action of the blowpipe on charcoal. This crystallized triple salt, if it has no excess of acid, changes from a red colour to a green by exposure to the air. If in this state it be dissolved in water, and oxymuriate of lime be added to it, a deep blue precipitate is formed, which being washed and collected, is soluble in muriatic acid, and communicates to it a beautiful blue colour. The addition of alcohol deprives the solution of its colour, but the oxymuriate of lime restores it.

9. Muriate of Platina and Potash.

This salt is formed by adding potash to a solution of muriate of platina. Small crystals of a red colour, in the form of octahedrons, are precipitated, which are a triple salt, consisting of muriatic acid, oxide of platina and potash.

10. Muriate of Platina and Ammonia.

1. A similar triple salt is formed by adding ammonia to the solution of muriate of platina. This triple salt is precipitated in the form of crystalline grains, of a reddish yellow colour, which are soluble in water. By evaporating the solution of these triple salts to dryness, and by exposing it to a strong heat, the platina is reduced. This fact with regard to the fusibility of platina by means of potash or ammonia, was observed by Bergman, and it is by this process that platina is purified and wrought.

2. When this salt is precipitated by means of potash, a fulminating platina is obtained. This, according to Fourcroy and Vauquelin, by whom it was prepared, is a compound of oxide of platina and ammonia. When it is exposed to sudden heat, it decrepitates and is agitated with a rapid motion, but when the heat is gradually applied, it detonates violently.

11. Oxalate of Platina.

Oxalic acid combines with the oxide of platina, and affords by evaporation crystals which are of a yellow colour.

12. Benzoate of Platina.

Benzoic acid, according to Trommsdorf, dissolves a small quantity of the oxide of platina. When this solution is evaporated, it crystallizes. This salt undergoes no change by exposure to the air, and is not very soluble in water. The acid is driven off by heat, and the oxide of platina remains behind.

II. Alloys.

1. Platina combines with many of the metals, and forms with them alloys, some of which are of considerable importance in the working of this metal.

Platina forms an alloy with arsenic, which is brittle and very fusible. It is in this state of alloy that platina is susceptible of being formed into different utensils and instruments for which it is peculiarly fitted. It is first fused with this metal, and then cast into moulds, at first in the form of square plates. It is then exposed to a red-heat, and hammered into bars. By the heating and hammering, the arsenic is driven off, and the metal is purified and becomes infusible, but retains its ductility, so that it may be wrought like iron.

2. The alloys of tungsten, molybdenum, chromium, columbium, titanium, uranium, and manganese, are unknown; nor have the alloys of cobalt and nickel with this metal been examined.

3. Platina combines with bismuth by means of fusion. Bismuth. This alloy is fusible and hard in proportion to the quantity of bismuth. It is altered by exposure to the air; it becomes yellow, purple, and black.

4. Platina readily combines with antimony, and antimony forms a very brittle alloy. The antimony may be separated by means of heat, but not completely. Some part remains, which diminishes the weight and ductility of the platina.

5. It has been found extremely difficult to combine mercury, platina and mercury. Guyton had observed that the adhesive force of platina and mercury is greater than that that of metals which do not combine with it, and that it is not inferior even to those which readily form alloys; from which he conjectured that the alloy of platinum and mercury might be effected by the following process. He placed a very thin plate of pure platinum at the bottom of a matra containing a quantity of mercury. The matra was put upon a sand bath, and heat applied, till the mercury boiled and the matra became red-hot. When the platinum was taken out, it was found to have acquired additional weight, and to have become very brittle. But this combination is different from the other combinations of mercury with the metals, for the platinum did not lose its solid form.

Mr Chenevix, in the course of experiments and researches respecting a supposed new metal called palladium, succeeded in forming an amalgam with platinum and mercury. He heated purified platinum in the form of fine powder, with ten times its weight of mercury, and rubbed them together for a long time. The result was an amalgam of platinum, which being exposed to a violent heat, lost all the mercury it contained, and the original weight of the platinum remained.

6. Platinum readily combines with zinc, and forms with it a fusible alloy, of a bluish colour, brittle, and hard. By heating, the zinc is sublimed, and burns on the surface.

7. Platinum alloys readily with tin. This alloy is one of the most fusible. It is hard and brittle, when the two metals are in equal proportions; but tin in the proportion of 12 parts to one of platinum, affords a very ductile alloy, which becomes yellow by exposure to the air. From this it appears that platinum diminishes the ductility of tin.

8. Platinum readily combines with lead, by means of fusion. An alloy of equal parts of these metals is of a purplish colour, granulated in its fracture, brittle, and easily altered by exposure to the air. The cupellation of platinum by means of lead has been an object of considerable importance with chemists, in the view of being able to purify it in the same way as gold and silver; but on account of the infusibility and refractory nature of platinum, the attempts that have been made have rarely succeeded.

9. Dr Lewis failed in his attempt to combine platinum with iron, but he obtained an alloy by fusing together platinum and cast iron. This alloy was extremely hard, and possessed some degree of ductility. Platinum, as it is found native, is frequently alloyed with iron.

10. Platinum combines with copper by means of fusion, and gives it hardness. When the proportion of copper is three or four times greater than that of platinum, the alloy is ductile, susceptible of a fine polish, and is not altered by exposure to the air. This alloy has been employed in the fabrication of mirrors for telegraphs.

11. Platinum readily combines with silver by fusion, although a very strong heat is required. The platinum greatly increases the hardness of silver, but diminishes its whiteness. When this alloy is kept in fusion for some time, the two metals are separated. During this fusion, Dr Lewis observed the silver forced towards the sides of the crucible with a kind of explosion.

12. Gold combines readily with platinum, but it requires a very powerful heat for the fusion of these two metals. Platinum diminishes the colour of gold, unless it Palladium, be in very small quantity. When the proportion of platinum is above \( \frac{1}{7} \), the colour of the gold begins to be altered. There is no perceptible change in the specific gravity or the ductility of gold from this alloy.

Platinum, on account of its peculiar properties, its infusibility, density, and indestructibility, could it be obtained in sufficient quantity, and at a moderate price, would undoubtedly prove one of the most useful and most important of the metals yet known. The importance and utility of platinum, on account of its scarcity, have been hitherto limited to chemical purposes; and for different chemical instruments and utensils, it has been found peculiarly appropriate, as there are few chemical agents whose effects it cannot resist. There is indeed little doubt but it might be employed with equal advantage in the construction of instruments and utensils, in various arts and manufactures.

Sect. XXIII. Of Palladium, a supposed new metal; and of Iridium and Osmium, two new Metals obtained from crude PLATINA.

1. In the month of April 1803, the discovery of a new metal, to which the name of Palladium was given, was announced in London. It was said to possess the following properties: "1. It dissolves in pure nitric acid, and makes a dark-red solution. 2. Green sulphate of iron throws it down in the state of a regulus from the solution. 3. If you evaporate the solution, you get a red calx, which dissolves in muriatic or other acids. 4. It is thrown down by quicksilver, and by all the metals but gold, platinum, and silver. 5. Its specific gravity by hammering, is only 11.3; but by flattening as much as 11.8. 6. In a common fire the face of it tarnishes a little, and turns blue; but becomes bright again, like other noble metals, on being stronger heated. 7. The greatest heat of a blacksmith's fire would hardly melt it. 8. But if you touch it while hot, with a small bit of sulphur, it runs as easily as zinc." Nothing was said of the history of the discovery; but from the unusual manner in which it was announced, Mr Chenevix conceiving it to be an imposition, procured a specimen, which being subjected to various tests, he found could not be referred to any of the known metals. He afterwards purchased the whole quantity which was offered for sale. The substance had been wrought by art, had been rolled out in flattening mills, and was offered for sale in thin laminae. The largest, about three inches in length, and half an inch in breadth, weighing about 25 grains, were sold at a guinea. When this substance was polished, it could scarcely be distinguished from platinum. It was flexible, but not very elastic. The specific gravity of some pieces was 10.972, while others were only 11.482.

The effects of galvanic electricity upon palladium were the same as upon gold and silver. Exposed to the blow-pipe, the side removed from the immediate action of the flame became blue. Exposed in an open vessel to a greater degree of heat than the fusing temperature of gold, no appearance of fusion or oxidation was observed. When the heat was increased, a melted button was obtained, which had lost a little of its weight, but was increased in specific gravity. The addition of sulphur renders it more fusible, and ex- Palladium, extremely brittle. There seems to be no action between charcoal and palladium. Mr Chenevix found that this substance formed alloys with gold, platina, silver, copper, lead, and some other metals. The alloy with lead was the hardest of all, but extremely brittle, and its specific gravity was 12. He also subjected this substance to other experiments, with alkalies, some of the earths, several of the acids, and some of the salts; and from the whole he concludes that it would be difficult to say what metal, or what combination of metals, palladium consists.

2. Mr Chenevix still prosecuted his experiments, and he concluded at last, that this supposed new metal is an alloy of platina and mercury. It must however, be observed, that he did not arrive at this discovery by analyzing palladium, for he failed in every attempt with that view. It was by combining platina and mercury in certain proportions, that he composed a substance which he considered as exactly similar in all its properties to palladium. The process by which he succeeded in forming palladium, or a substance exactly similar, was by dissolving 100 grains of platina in nitro-muriatic acid, and then adding 200 grains of red oxide of mercury. This being insufficient to saturate the excess of acid, more was added till it ceased to be dissolved. A quantity of green sulphate of iron was then poured into a long-necked retort, to which the mixed solution of platina and mercury was added, and the whole placed upon a sand bath. In less than half an hour, a precipitate formed, and the inside of the retort was lined with a thin metallic coat. The liquor was passed through a filter, and the precipitate, after being digested with muriatic acid, was well washed and dried. The whole quantity collected amounted to 276 grains, which were composed of 92 of platina, and 184 of mercury. It was in the form of a fine powder, with a metallic lustre. It was put into a charcoal crucible, and fused into a button. The specific gravity was 11.2. It was entirely soluble in nitric acid, easily fused by sulphur, and precipitated by green sulphate of iron; thus exhibiting all the properties of palladium, which Mr Chenevix concludes, is composed of two parts of mercury, and one of platina.

3. One of the most singular circumstances with regard to this alloy, if such it can be called, is its specific gravity, which is not only far below the mean of the specific gravity of the two metals, but considerably inferior to either of its elements. The specific gravity of platina is 22, according to some greater, and that of mercury is nearly 14, and yet the specific gravity of the compound is only 10.972, little more than the half by calculation. But although we have no reason to doubt the accuracy and precision of Mr Chenevix's experiments, and although we are little disposed to place any confidence in the assertion of the unknown discoverer of this substance, from the extraordinary circumstances under which it has been announced, yet we do not consider the result of these experiments fully satisfactory, in proving palladium to be an alloy of palladium, platina and mercury (k). Every attempt which Mr Chenevix made to analyze this supposed new metal, failed. It is true, he was equally unsuccessful in decomposing the alloy of platina and mercury which he had formed, and which resembled palladium in most of its properties which were compared. The attempts which his experiments have been made to repeat the experiments of Mr Chenevix, have not succeeded. No other chemist has yet been able to form the compound of platina and mercury, which possesses the properties of palladium. Till, therefore, Mr Chenevix shall have extended his researches concerning this alloy, or till it shall have been examined by some other chemist, we must remain in suspense with regard to its nature.

4. Two other metals have been just announced. Iridium. They were discovered in crude platina by Mr Tennant, in analyzing the black powder which remains after dissolving platina. To the first of these metals Mr Tennant has given the name of iridium, from the various colours it assumes in solution. It possesses the following properties. It is soluble in all the acids, but less soluble in muriatic acid, with which it forms octahedral crystals. The solution with much oxygen is deep red; with a smaller proportion, green or deep blue. It is partially precipitated by the alkalies, and by all the metals except gold and platina. Infusion of galls and prussiate of potash deprive this solution of its colour, but without any precipitate; thus affording an easy test of its presence. The oxide, therefore, loses its oxygen by water alone. When combined with gold or silver, it cannot be separated by the usual process of refining these metals. The same substance was examined by Defoëtis and Vauquelin, and the properties which they ascribe to this metal are the following. 1. It reddens the precipitates of platina made by muriate of ammonia. 2. It is soluble in muriatic acid. 3. It is precipitated by the infusion of galls and prussiate of potash.

5. The other new metal is obtained by heating the black powder with pure alkali in a silver crucible. The oxide of this metal combines with the alkali, and may be expelled by an acid, and obtained by distillation, being very volatile. It does not reddish vegetable blues, but stains the skin of a deep red or black. The oxide in solution with water has no colour; but by combining with alkali or lime, becomes yellow. With the infusion of nut-galls it gives a very vivid blue colour. It is precipitated by all the metals excepting gold and platina. An amalgam may be formed with mercury, by agitating it with the aqueous solution of this oxide. When this amalgam is heated, the mercury is driven off, and the pure metal remains behind in the state of black powder. To this metal Mr Tennant has given the name of osmium, on account of the strong smell of the oxide.

Such is the account of these metals which we have received. Should a fuller detail reach us in time, we shall

(k) Fourcroy and Vauquelin have thrown out a conjecture that palladium is probably an alloy of platina, and a new metal discovered in crude platina by Collet-Defoëtis and Mr Tennant. Ann. de Chim. xlviii. 185. Component shall not fail to lay it before our readers, either in an appendix to this treatise, or under the names of the metals themselves, in the order of the alphabet, in the course of the work.

**CHAP. XV. OF THE ATMOSPHERE.**

The atmosphere is that invisible elastic fluid which surrounds the earth. Its physical properties, such as density, elasticity, and pressure, have been long known; but its composition and constituent parts must be ranked among the discoveries of modern chemistry. In the present chapter, we propose only to take a short view of the nature, constitution, and changes of the atmosphere, referring the full discussion of the latter to meteorology, to which it properly belongs.

**SECT. I. Of the COMPONENT PARTS of the ATMOSPHERE.**

1. The air of the atmosphere was considered by the ancients as one of the four elements of which all bodies are composed. The same opinion was held by all philosophers, previous to the discoveries of modern chemistry. It was universally admitted to be a simple homogeneous substance, till the discovery of oxygen gas by Dr Priestley, and that of azotic gas by Scheele, it was fully demonstrated that these two substances are the chief ingredients in atmospheric air.

2. This compound possesses all the physical properties of the different kinds of air which we have hitherto examined. It is invisible, elastic, and may be indefinitely expanded and compressed. The specific gravity of atmospheric air is 0.0012, or it is 816 times lighter than water. A hundred cubic inches weigh 31 grains troy; but in consequence of the elasticity of the air, the absolute weight and the density must vary with the temperature and pressure. The estimation which we have here given, is taken at the ordinary temperature of the atmosphere, between 50° and 60°, and when the barometer, which indicates the pressure, stands at 30 inches. The density must vary by diminishing, according to the height above the surface of the earth. The experiments of naturalists, whose attention has been particularly directed to this subject, have shown that the diminution of density is in the ratio of the compression; and therefore, that the increase of density is in geometrical progression, while the heights increase in arithmetical progression.

3. After the discovery of the composition of atmospheric air, it became an object with philosophers to determine the proportions of its component parts. It was observed by Priestley and Scheele, and other philosophers who were occupied in the prosecution of their discoveries, that a certain portion of a given quantity of atmospheric air only was absorbed during the processes of combustion and respiration. It was observed too, that certain substances combined with the portion of atmospheric air which disappeared during these processes, and that the same quantity of atmospheric air suffered no farther diminution, whatever length of time it was exposed to the action of these substances. The portion of the air absorbed is the oxygen gas, and on this principle is founded the construction of those instruments which have been denominated eudiometers, because they are employed to measure the purity of a given portion of air, by ascertaining the quantity of oxygen gas which it contains. Different eudiometers have been proposed for this purpose, but all depending on the same principle, namely, the abstraction of oxygen gas from a given quantity of air. The reader will probably recollect the effects which take place by mixing together nitrous gas and the air of the atmosphere, or oxygen gas. When these gases come into contact, red fumes are produced; the atmospheric air is partially diminished; but the oxygen gas entirely disappears. This is owing to the combination of the nitrous gas with the oxygen gas, forming nitric acid, which, if the experiment be made over water, is absorbed; thus diminishing the bulk of the air by the quantity of oxygen gas abstracted. This is the principle of the first eudiometer, which was proposed by Dr Priestley; but it has been found that the results and experiments with this kind of eudiometer are far from being uniform and constant. It is subject to variation from the difference of purity of the nitrous gas employed, the water over which the experiment is made, and even the form and construction of the apparatus. The variations in the results of different experiments by different philosophers, are from 22 to 30% of oxygen gas in 100 parts of atmospheric air.

Scheele proposed a different eudiometer. A mixture of iron filings and sulphur formed into a paste with water, absorbs the whole of the oxygen gas of any given portion of atmospheric air. The diminution of bulk of a portion of air, exposed to the action of this substance, therefore, indicates the proportion of oxygen gas which it contains; but this absorption goes on slowly, and is therefore an objection to this mode of ascertaining the proportions of atmospheric air. This objection has been removed by an improvement of this eudiometer, in which hydrogenated sulphuret of potash or lime is substituted for the iron filings and sulphur. This is prepared by boiling together sulphur and lime water, or a solution of potash in water. By the use of this sulphuret, the absorption takes place in a few minutes. A given portion of air is agitated in a bottle with this sulphuret, taking care to exclude the external air with a ground stopper. The diminution of the bulk of this quantity of atmospheric air shows the proportion of oxygen gas which it contained.

Volta proposed to explode a given portion of atmospheric air with hydrogen gas, by means of the electric spark. The hydrogen and oxygen combine together and form water; and the diminution of the bulk of the airs employed is in proportion to the quantity of water formed. But to this method of ascertaining the quantity of oxygen gas in a given portion of atmospheric air, it has been objected, that the proportion of hydrogen gas requires to be accurately adjusted; for if it exceed, the superabundant quantity increases the bulk of the remaining air; and, if the proportion be too small, the oxygen and azote will form nitric acid by the action of electricity, and thus the residuary quantity of air will be too much diminished.

When phosphorus is exposed to the air, it absorbs the oxygen readily, and is converted into phosphorous acid. This, which was first proposed by Achard, has been improved by Berthollet, for the purpose of a cu-

A given portion of air is exposed to the action of phosphorus, in a vessel over water; when the absorption has ceased, the remaining air is measured, the diminution of which indicates the quantity of oxygen gas which it contained.

Mr Davy has proposed the green sulphate or muriate of iron dissolved in water, impregnated with nitrous gas. This solution is prepared by transmitting nitrous gas through green muriate or sulphate of iron dissolved to saturation in water. All the apparatus necessary is a small graduated tube, having its capacity divided into 100 parts, and greatest at the open end, and a vessel for containing the fluid. The tube is filled with the air to be examined, and then introduced into the solution. To promote the absorption, it is gently moved from a perpendicular to a horizontal position. In a few minutes the experiment is completed, and the whole of the oxygen condensed by the nitrous gas in the solution, in the form of nitric acid. But in this process it is necessary to observe the period at which the diminution stops, for after this the volume of residual gas is increased by the decomposition of the nitric acid, by means of the green oxide of iron.

From a number of comparative experiments made by Mr Davy with different eudiometers, and from other experiments on air in different places, and collected under different circumstances, it appears that the component parts of atmospheric air are always nearly the same. These proportions are from .21 to .22 of oxygen gas, and from .78 to .79 of azotic gas. The constituent parts therefore of atmospheric air by bulk may be taken at

| Oxygen gas | Azotic | |------------|--------| | 22 | 78 |

But in estimating the proportions of given bulks of atmospheric air, it is necessary, as we have already hinted, to take into account the density and temperature, otherwise very great anomalies must happen.

4. It is universally admitted, that water exists in the atmosphere; but philosophers are greatly divided with regard to the quantity of water, and the state in which it exists in the air. To ascertain the quantity of water, instruments called hygrometers, or measures of moisture, have been contrived; the quantity of which is indicated by certain changes which take place by its absorption; but none of these instruments that have yet been invented are susceptible of great accuracy, and perhaps to this is owing the very different results in estimating the quantity of water in the atmosphere. There is also a very great difference of opinion whether this water exists in the atmosphere in the state of water, or whether it has been converted into vapour. According to the first opinion, the water is held in solution by the air, and the quantity increases as the temperature of the air is increased. But according to others, the water of the atmosphere is in the state of vapour. According to the experiments of naturalists, the quantity of water in the atmosphere varies in different climates, and at different seasons of the year, from \( \frac{1}{100} \) to \( \frac{1}{500} \) part of the weight of the atmosphere.

5. When lime-water, or an alkaline solution, is exposed to the air, it is soon covered with a crust or pellicle. This is owing to the absorption of carbonic acid, and the conversion of the alkali or lime, to the state of carbonate. This shows that carbonic acid gas exists in the atmosphere. This gas has been found not only on the surface of the earth, where the density of the atmosphere is greatest, but also on the tops of some of the highest mountains. The quantity of carbonic acid gas in the atmosphere is supposed to vary from .01 to .05 parts.

Sect. II. Of the Constitution of the Atmosphere.

1. The component parts of the atmosphere are, Different azotic gas, oxygen gas, water, and carbonic acid gas. Here a question has arisen among philosophers, whether these parts are chemically combined, or merely form a mechanical mixture. According to one set of philosophers, the oxygen and azotic gases of the atmosphere are in chemical union, because their proportions are always found to be uniform and constant, which it is supposed could not be the case from the inequality of the causes acting in diminishing the quantity of oxygen gas, by the different processes of combustion and respiration, which are going on in the surface of the earth, if the component parts of the air were not in chemical combination. The air of the atmosphere in chemistry, it is said, possesses properties very different from combination, the artificial mixture of its component parts. The processes of combustion and respiration continue for a greater length of time in the latter, because it parts with a greater proportion of its oxygen, and for the same reason it is more diminished by nitrous gas. According to others, the air of the atmosphere is merely a mechanical mixture. This opinion is supported by Mr Dalton, in some ingenious speculations on the constitution of mixed gas, and particularly of the atmosphere. The principle on which Mr Dalton's hypothesis is founded is, that the particles of homogeneous elastic fluids only mutually act upon each other, and that the particles of an elastic fluid of one kind are neither attracted nor repelled by the particles of an elastic fluid of a different kind, when they are mixed together. According to this hypothesis, therefore, the particles of the oxygen gas of the atmosphere mutually act on each other, or are only attracted and repelled by those of their own kind.

2. Difference of opinion also prevails, whether the vapour of water, as it exists in the atmosphere, be merely a mechanical mixture, or chemically combined. The former opinion is also supported by Mr Dalton, upon the principle that all gases mixed with vapour, expand in a proportional degree to the elasticity of the vapour in that temperature.

Sect. III. Of the Changes of the Atmosphere.

1. The changes which are produced in the atmosphere by heat and cold, are too obvious to escape observation; but it was not till the invention of the thermometer that these changes could be observed and marked with any degree of accuracy; and even after the invention and improvement of this instrument, it was long before any scientific application was made of the Changes of the changes of the temperature which it indicated.

The variable temperature of the same day, the great difference between midnight and midday, and the still greater difference between the heat of summer and the cold of winter, seem to hold out a number of insulated facts, without resemblance or connexion, and incapable of being arranged under any general law. But more comprehensive views, and more extended observations, have not only shewn the possibility of establishing a general principle, but have enabled philosophers to arrange and classify phenomena which were otherwise seemingly unconnected.

2. The great source of heat is the sun. This is fully demonstrated by the increase of temperature being in proportion to the duration and greater or less obliquity of the sun's rays. It has been imagined that the earth is heated by central fires; but this opinion seems to be fully disproved, by observing that the temperature depends invariably on the absence or presence of the sun; that this temperature is diminished, at least to a certain extent, by going deeper into the earth; and that the cold is greatest in places most distant from the sun's rays; so that the temperature which is most uniform within the tropics, diminishes, other things being equal, in proportion to the distance from the equator towards the poles.

3. In considering the difference of temperature which is observed in different places, it became an object with philosophers to discover some fixed points from which the whole amount of the changes for any given period could be ascertained. This was first thought of by Mayer, who proposed the method used by astronomers, of finding the mean of certain large periods, as for years and months; and he made the discovery by which the mean annual temperature of two latitudes being known, the mean annual temperature for every other degree of latitude may be also found. The application of this rule has been greatly improved and extended by Mr Kirwan, and upon this principle he constructed tables which exhibit the mean annual temperature for all degrees of latitude from the equator to the poles. These tables were constructed by finding from observation the temperature of what he calls a standard situation, that is, a place least liable to be affected by adventitious causes, but where the cause of temperature, or the communication of heat from the source, was most uniform and constant; and having discovered this standard situation, to compare the temperature of every other situation with it. The land, Mr Kirwan thought, owing to the operation of causes which occasion variations least easily appreciable, would not afford results sufficiently uniform. This situation, he then concluded, was to be sought for on the water; and that part of the ocean, which he chose, was the immense tract of water which includes that part of the Atlantic lying between the 85° of north latitude, and the 45° of south latitude, extended westward as far as the gulf stream, and to within a few leagues of the coast of America; and all that part of the Pacific ocean reaching from the 45° north latitude to the 40° south latitude, and from the 20° to the 27° of longitude east from London. This includes the greater part of the surface of the globe. But for the method of constructing these tables, and for the tables themselves, we refer our readers to the article Meteorology, where they will be informed.

The difference of temperature, it may be observed, within 10° of the equator and within the same distance from the poles, is very small; and the variation of temperature for different years within the same space, is also found to be very little; but as the distance increases from the equator towards the poles, the difference of temperature is greater. In latitudes under 35°, it scarcely ever freezes, excepting in very elevated situations, and it scarcely ever hails in latitudes higher than 60°. In places near the sea, between the latitudes of 35° and 60°, it generally thaws when the sun's altitude is 40°, and seldom begins to freeze till the meridian altitude be below 40°.

4. Mr Kirwan has also constructed tables to mark Monthly, the mean monthly temperature. In every latitude the mean temperature of the month of April approaches nearly to the mean annual heat of that latitude. And from this analogy he proceeded, supposing that the temperature is always regulated by the direct action of the solar rays, unconnected with the other circumstances which occasion considerable variations. Taking all these into the account, and endeavouring to reduce them to strict calculation, he found it impracticable; and therefore he constructed his tables, partly from principle, and partly from the best observations he could procure from sea journals, and similar sources of information. The mean monthly temperature in these tables also refers to the standard ocean.

5. The coldest weather also prevails about the middle of January in all climates, and the warmest in July; but if it depended immediately on the sun's heat, the greatest heat should prevail in the latter end of June, and the greatest cold in the latter end of December. But as the earth requires a considerable time to absorb heat, so also it is some time before what has been absorbed is given out. All these observations and calculations refer to the surface of the ocean, which is least subject to variation from causes, the influence of which could not be ascertained with precision.

6. But as the earth is the chief source of heat in the atmosphere that surrounds it, the temperature must heats the decrease with the elevation above the earth, and in the highest regions of the atmosphere, where the air is perfectly free from clouds, the greatest cold must prevail. Hence, in consequence of this elevation above the level of the ocean, the highest mountains, even under the equator, are covered with perpetual snow. Mr Bouguer found the cold on the top of Pinchincha in South America, immediately under the line, to vary from 7° to 9° below the freezing point every morning before sunrise, and hence, at a certain height, which varies in almost every latitude, it constantly freezes at night in every season; although in some latitudes, in the warmer climates, it thaws next day. This height he calls the lower term of congelation, and he places it at the height of 15,577 feet between the tropics. In latitude 28° he thinks it should commence in summer at the height of 13,440 feet above the level of the sea. But at still greater heights it never freezes at all, because the vapours do not ascend so high. This height M. Bouguer denominates the upper term of congelation; and immediately under the equator he fixes it at 28,000 feet. As the weather is not subject to great variations under the equator, the height of both these terms is nearly constant; but in other latitudes this height is variable, both in summer and winter, in proportion to the degree of heat which prevails; and as there is a mean annual temperature peculiar to each latitude, so is there a mean height for each of these terms peculiar to each latitude. By taking the differences between the mean temperatures of every latitude, and the point of congelation, it will appear that whatever proportion the difference under the equator bears to the height of either of these terms, the same proportion will the difference peculiar to every other latitude bear to their height.

7. But there is not the same uniformity or capacity in air, land, and water, for receiving and returning heat. Hence arise very considerable deviations in the temperature of places, as they are more or less connected with these bodies. Air, when it is perfectly transparent, receives very little heat from the rays of the sun as they pass through it. Air which is over seas or large tracts of water, is generally many degrees warmer in winter, and colder in summer, than air which is incumbent on land, because the land receives the heat much more readily than the water; in general the air participates of the temperature of those substances with which it is in contact. Land, if dry, receives heat rapidly, but transmits or conducts it to great depths very slowly; but water receives it more slowly, and diffuses it more rapidly. From experiments made by Dr Hales, it appears that the earth is much heated during the summer, but that this heat descends very slowly, great part of it being communicated to the air; that during winter, the earth gives out to the air the heat it had received during the summer, and that wet summers must be succeeded by cold winters, because the heat is carried off by the greater proportion of evaporation during the wet season. At the depth of 80 or 90 feet below the surface of the earth, the temperature is found to vary very little, and it generally approaches to the mean annual heat. The temperature of the cave at the observatory of Paris, which is 90 feet below the pavement, is about 53.5°. The greatest variation which has been observed, does not exceed half a degree, and this only happens in very cold years. Hence, too, the temperature of springs is almost uniformly the same throughout the year, and corresponds with the mean annual temperature of the climate.

8. There is not only a considerable difference in the temperature of land and water; but this variation also holds with regard to the land itself, according as it is elevated above the surface, and according to the nature of the surface, whether it is covered with vegetables, or only exhibits bare rocks, or sterile sand. A considerable deviation also is observed to take place, in proportion to the distance from the ocean. All these causes, however, are greatly modified by the relative situation of places with regard to seas and oceans, mountainous regions, and extensive tracts of level country, covered with thick forests, or improved by cultivation. These causes too are modified by particular winds, which produce considerable deviations, as they proceed from the ocean, from low, flat countries, or elevated regions.

9. Another remarkable change to which the atmosphere is subject, is the difference of its weight or pressure. The air, like all other matter, is influenced by the law of gravitation, by which it presses with a certain force on the surface of the earth. It has been found that the measure of this force is nearly equal to 15 lb. on every square inch. The variations which take place in the atmosphere are measured by the barometer. The mercury in the barometrical tube is supported by a column of air of an equal base, and since this column of air and the mercury in the tube mutually balance each other, it follows that they are of the same weight, and therefore the barometer may be employed as a measurer of the weight or pressure of the air.

10. The first general fact with regard to the weight of the atmosphere is, that in all places at the level of the sea, the barometer stands nearly at the same point, and the mean height is about 30 inches. But as the elevation is increased, the barometer sinks, because then there is a shorter column of air to support it, which is therefore lighter. In no place does the weight of the air continue always the same. It is subject to daily variations, which are greater or smaller according to the latitude of the place, or the influence of particular causes. In all places within the tropics, the variations of the barometer have been observed to be smallest, and in elevated situations the variations are considerably smaller than on the level of the sea. The deviations of the mercury from its mean annual altitude are more frequent and extensive in the neighbourhood of the poles than in that of the equator, and they are greater and more frequent without the tropics in winter than in summer.

11. The causes which have been proposed to account for these variations, are changes of temperature, velocity of winds, and the agency of vapours. The air is subject to the action of heat, by which it is rarefied or condensed, according to the increase or diminution of temperature. Dense air is heavier than that which is rarer; but if the masses of air remain the same, the weights must be the same, and consequently the heights to which they elevate the mercury will also be equal. If, therefore, a change of temperature occasion a variation of the barometer, it must be by increasing or diminishing the mass of the atmosphere. But it appears from observation, that a variation of the mass of the atmosphere is not a necessary consequence of a change of temperature, for the mercury is often at the same height at different seasons, and at different places at the same time, when the difference of temperature is very great. But even when the mercury changes with the temperature, this variation is often directly contrary to what it ought to be. The barometer has sometimes risen with an increase of temperature, instead of falling by the rarefaction of the air. The changes of temperature are very inconsiderable in the higher regions of the atmosphere, so that it would appear that the barometer can be little affected by changes of temperature. Mr Kirwan has endeavoured to show, that the influence of winds, or a greater or smaller quantity of vapours existing in the atmosphere, can... Changes can have little effect in elevating or depressing the barometer. According to Mr Kirwin, the variations of the barometer, or the difference of pressure of the air of the atmosphere, can only be accounted for from an accumulation of air over those places in which the mercury exceeds its mean height, and from the diminution or subtraction of the natural quantity of air, over those regions in which the mercury falls below its mean height.

12. The winds constitute another remarkable change in the atmosphere. The winds in general are subject to great irregularity; but in some parts of the world they are pretty regular and uniform. Between the 30° of N. Lat. and the 30° S. Lat. the wind, when it is not counteracted by local causes, continues to blow constantly from the same points. On the north side of the equator, that is, from the equator to the 30° N. Lat. it blows from the north-east, and from the equator to the 30° S. Lat. it blows from the south-east. This is called the trade-wind. Immediately under the equator the wind is observed to be pretty nearly from the east; that is, about the place where the two currents meet, the one from the north-east, and the other from the south-east; but receding from the equator, the direction of it deviates more and more from the easterly point, till it reaches the intermediate point between north and south, and then constitutes the north-east trade-wind on the north side of the equator, and the south-east trade-wind on the south side of the equator. Were the causes which produce the constancy and uniformity of the trade-winds uninfluenced by others, these winds would prevail without variation within the limits or near the boundaries of the torrid zone; but they are greatly counteracted, and subject to great variations, from the unequal influence of land and water, in rarefying or condensing the air.

13. As the air of the atmosphere is a fluid body, and therefore subject to all the laws of fluids, if any part be removed, the remainder rushes in to restore the equilibrium, and hence an agitation or wind is produced, as air is capable of indefinite dilatation and compression. The denser air being heavier, must sink, and the rarefied air ascends, when air of unequal densities is mixed together. The greatest degree of mean temperature is within the torrid zone, in consequence of the sun's rays being more perpendicular, and acting with greater force on the earth's surface. The air therefore round the equator undergoes the greatest degree of rarefaction, and this extends to the north and south, in proportion to its distance from the equator, or rather its distance from the sun's place. Thus, when the sun is perpendicular to the equator, or middle part of the torrid zone, the air in that place being most rarefied, becomes lighter, ascends, and its place is filled with the colder air from the north and south. And thus, as long as the sun's influence continues to rarefy the air, would a north and south wind blow to that quarter where the rarefied air, being rendered lighter, had ascended. But as the earth has a diurnal motion on its axis from west to east; those parts of the earth's surface to the westward are first heated, and consequently the incumbent air is first rarefied. The denser air from the east must therefore rush in to restore the equilibrium. Thus, there is produced an easterly wind. But there is another current of air from the north and south: the two currents coming from the north-east trade-wind on the north side of the equator, and the south-east trade-wind on the south side. Such are the causes which are generally supposed to produce the regular trade-winds.

14. These winds are regular and uniform in open oceans, such as the Pacific or Atlantic, but they are subject to considerable variation from the unequal rarefaction of the air over land and water. Thus, islands situated within the very course of the trade-winds have regular land and sea breezes, which are often directly contrary to the trade-wind. In consequence of the air incumbent on the land being more rarefied during the day, the wind blows from the sea, constituting the sea breeze; but the air over the sea being warmer during the night, the wind blows from the land, from which it is called the land wind. To a similar cause is owing another remarkable deviation from the uniformity of the trade winds, which is observed in the great Indian ocean. Here the winds called monsoons blow from one quarter during six months of the year, and from an opposite direction during the remaining six months. While the sun is in the northern tropic, the air over the extensive Indian continent is greatly rarefied; and, in consequence of this rarefaction, the denser air from the ocean rushes in to restore the equilibrium, and hence the current of the air or wind continues during this period of the year, constituting the south-east monsoon. But when the sun passes the equator to the southward, the air over the southern hemisphere is more influenced by his rays, and therefore more rarefied. The denser air then rushes in from the north, and thus produces the north-west monsoon, which blows during our winter, when the sun is in the southern tropic.

15. But even a superficial observation will show, that the phenomena of the winds cannot be satisfactorily accounted for, merely upon the general principle of the unequal rarefaction of the air over land and water. Thus sudden changes of wind often happen in particular places, which are extremely limited, and altogether unconnected with the difference of density of the air over land and water. The hurricane has swept the land, whose effects have not been felt on the neighbouring ocean, and the storm frequently agitates the ocean without reaching the land. These and other phenomena of the winds, equally inexplicable, have been ascribed by naturalists to the abstraction or sudden destruction of a certain quantity of the air of the atmosphere in particular places. But for the full discussion of this subject and the other phenomena of the atmosphere, we must refer our readers to Meteorology.

**CHAP. XVI. OF WATERS.**

1. We have already treated of the component parts of water, of the discovery of its composition, and of its most remarkable properties, and especially those which it exhibits by a change of constitution, as in the solid state or that of ice, in the liquid state, and in the state of vapour. In these views water was considered as perfectly pure; but this is rarely or never the case, as it is found in nature. Rain water, which is the purest, is not entirely free from impregnation, even when collected. It is slightly contaminated with certain substances, which it held in solution, as it existed in the clouds, or with which it combined in its passage through the atmosphere. But waters as they flow on the surface of the earth, or are carried through the strata under the surface, must dissolve those soluble substances with which they come in contact. It is the object of our present investigation to examine the waters as they are found in nature, and the substances with which they are impregnated.

2. The properties of pure water are almost obvious to the senses, so that few substances, at least in any quantity, can be dissolved in water, without being easily recognized. Thus, the saline, nauseous taste of sea-water, the fetid odour, or the astringent taste of mineral springs, must readily be distinguished by their striking qualities. But although it is probable that the remarkable diversity of waters, from their obvious properties, could not fail to be early observed by mankind, it is only by chemical investigation that the nature of the substances to which they owe these properties, can be ascertained; and indeed we are indebted to the discoveries and improvements of modern chemistry for the knowledge which we possess of the nature and proportion of the ingredients which enter into the composition, either of sea water or mineral springs.

This subject has been particularly investigated by Bergman, Wohler, Black, Fourcroy, Klaproth, and Kirwan. In the three following sections we propose to treat, 1. Of sea-water; 2. Of mineral waters; 3. Of the method of analyzing them.

**Sect. I. SEA-WATER.**

1. The saline taste of sea-water, we have already observed, could not fail to make it be distinguished from pure water; and this taste, it is well known, is chiefly derived from common salt which it holds in solution. Sea-water is also distinguished by a nauseous bitter taste, which is ascribed to the animal and vegetable matters which are floating in it. This taste has been considered as in some measure foreign to it; for it is only found in the water on the surface of the ocean or near the shores. Sea-water taken up at considerable depths, contains only saline matters. The specific gravity of sea-water varies from 1.0269 to 1.0285. Its greater density is owing to the salts which are dissolved in it; and to this impregnation also it is owing, that it is not frozen till the temperature is reduced nearly to 28°.

2. The salts which are chiefly found in sea-water, are muriate of soda, or common salt, muriate of magnesia, sulphate of magnesia, sulphate of lime and soda. The quantity of saline ingredients in the waters of the ocean varies from \( \frac{1}{4} \) to \( \frac{1}{2} \) part. Mr Kirwan makes the average quantity about \( \frac{1}{4} \) of its whole weight. The quantity of saline contents of water, taken up by Lord Mulgrave at the back of Yarmouth sands, in latitude 53°, amounted nearly to \( \frac{1}{4} \); while Bergman found the water taken up in the latitude of the Canaries to contain about \( \frac{1}{4} \) of its weight of saline matter. These quantities, however, vary, even in the same latitude, during rainy and dry seasons, near the land, or the mouths of great rivers. The difference of latitude does not seem to make any considerable difference in the proportion of saline matter. In latitude 80° north, 60 fathoms under ice, sea-water taken up by Lord Mulgrave, yielded about \( \frac{1}{4} \); in latitude 74° nearly the same; and in latitude 60°, \( \frac{1}{4} \). Pages obtained four per cent. from water taken up in latitude 81°, and the same quantity of saline matter from water taken up in latitude 45° and 30° north. In southern latitudes, the proportion was still greater; he found it to contain the following proportions:

| Lat. | Long. | Sp. Gr at 62° | |------|-------|--------------| | 49° 50' S. | 4.1666 per cent. of saline matter. |

In the Mediterranean the proportion is said to be still greater; but the Euxine and Caspian seas are found to be less salt than the ocean. This also is the case with the Baltic. If the saline matters of the waters of the ocean did not consist of different kinds, the proportion of salts which it contains might be ascertained by the specific gravity. In the following table the specific gravity of sea-water taken up in different latitudes has been determined by Mr Bladh. The temperatures are reduced by Mr Kirwan to 62° of Fahrenheit; and the longitude is reckoned by Bladh from Teneriffe.

| Lat. | Long. | Sp. Gr at 62° | |------|-------|--------------| | N. | E. | | | 50° 30' | 8° 48' | 1.0272 | | 57° 18' | 18° 48' | 1.0269 | | 57° 1' | 1° 22' | 1.0272 | | 54° 00' | 4° 45' | 1.0271 | | 44° 32' | 2° 04' | 1.0276 | | 44° 07' | 1° 00' | 1.0276 | | 45° 41' | 0° 30' | 1.0276 | | 34° 40' | 1° 18' | 1.0280 | | 29° 50' | 0° 00' | 1.0281 | | W. | | | | 24° 00' | 2° 32' | 1.0284 | | 18° 28' | 3° 24' | 1.0281 | | 16° 36' | 3° 37' | 1.0277 | | 14° 56' | 3° 46' | 1.0275 | | 10° 30' | 3° 49' | 1.0272 | | 5° 50' | 3° 28' | 1.0274 | | 2° 20' | 3° 26' | 1.0271 | | 1° 25' | 3° 30' | 1.0273 | | S. | | | | 0° 16' | 3° 40' | 1.0277 | | 5° 10' | 6° 00' | 1.0277 | | 10° 00' | 6° 05' | 1.0285 | | 14° 40' | 7° 00' | 1.0284 | | 20° 06' | 5° 30' | 1.0285 | | 25° 45' | 2° 22' | 1.0281 | | E. | | | | 35° 25' | 7° 12' | 1.0279 | | 37° 37' | 68° 13' | 1.0276 |

Specific gravity in different latitudes. From this table it appears that the proportion of saline matter is greatest near the tropics; and the smaller quantity near the equator is ascribed to the great quantity of rain that usually falls on that part of the globe.

3. The experiments of Mr Wilcke show that the proportion of saline matter in the Baltic is less than that of the ocean; and that it is saltier during the prevalence of a westerly wind, by which the water is driven from the ocean, than during an easterly wind. The following is the specific gravity of the waters of the Baltic, taken during the prevalence of different winds, and reduced by Mr Kirwan to the temperature of 62°.

| Wind | Specific gravity | |---------------|------------------| | East | 1.0039 | | West | 1.0067 | | West, a storm | 1.0118 | | North-west | 1.0098 |

From this it appears, that the proportion of saline matters in the Baltic is increased by the influx of water from the ocean, and is considerably influenced during a storm, when the wind blows from that quarter.

4. Dr Watson has estimated the quantity of salt in water of different specific gravities. It is also reduced to the temperature of 62° by Mr Kirwan, as in the following table.

| Salt | Specific gravity | |--------------|------------------| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |

These experiments were made with solutions of common salt, which was not perfectly pure, and therefore it is allowed that they may correspond pretty nearly with the proportions of saline matter in sea-water of the same specific gravities.

5. The proportions of the different salts in an analysis by Bergman, are the following.

- Muriate of soda, 30.911 - Muriate of magnesia, 6.222 - Sulphate of lime, 1.000

In 1000 parts of water taken up near Dieppe, Lavoisier found the following salts.

- Muriate of soda, 1375 - Of lime and magnesia, 256 - Of magnesia, 156 - Lime, 87 - Sulphate of soda and magnesia, 84

The name of mineral waters has been given to those waters which are distinguished by the smell, taste, or colour, from pure water, the obvious properties of which are transparency and infusibility. These peculiarities of taste, smell, and other properties, are owing to the impregnation of certain mineral substances which they have acquired in their passage through the soil or strata of the earth. The effects which such waters produce on the animal economy, early attracted the attention of mankind, and led to their application as remedies in the cure of diseases. It was long indeed before any other distinction of mineral waters was made, except what was indicated by their sensible qualities, and their effects on the human constitution. From these classes, properties mineral waters have been divided into four classes: 1. Acidulous or gaseous waters; 2. Saline waters; 3. Sulphureous or hepatic waters; and, 4. Chalybeate waters.

(1.) Acidulous waters are distinguished by their penetrating acid taste, the facility with which they boil; by sparkling when they are poured into a glass; and by the emission of bubbles of air, by agitation. The acid with which they are impregnated is generally the carbonic. These waters reddish the tincture of turpentine, and precipitate lime-water.

(2.) The second class, or the saline waters, are sufficiently characterized by their taste, which varies according to the nature of the salt with which they are impregnated.

(3.) The sulphureous or hepatic waters are at once recognized by their fetid odour, and by blackening some metallic substances, as lead and silver. Some of these waters are impregnated with sulphurated hydrogen gas, while in others it is combined with lime, or with an alkali.

(4.) The fourth class, or the chalybeate waters, are Chalybeate distinguished by an astringent taste. With the prussiate taste of lime they give a blue colour, or a black with the infusion of nut galls. This property is owing to a portion of iron which is held in solution, either by carbonic or sulphuric acid. Sometimes carbonic acid is in excess, and then the water has a penetrating slightly acid taste.

2. The substances which have been found in mineral waters, as they have been enumerated by Mr Kirwan, belong either to the class of gaseous bodies, acids, alkalies, earths, or salts.

3. Oxygen gas was first discovered in waters by Gales Scheele. It is generally in small proportion, and does not exist in waters with sulphurated hydrogen gas, or iron, because it is incompatible with these substances. Azotic gas has been found in the waters of Buxton, Harrogate, and Leamington Priors. Common air was first discovered in mineral waters by Mr Boyle; the quantity scarcely exceeds 1/8 of the bulk of the water. Fixed air or carbonic acid was first discovered in Pyrmont waters by Dr Brownrigg. The proportions are very variable; but there are few mineral waters which are entirely free from it. A hundred cubic inches of most waters contain from 6 to 40 of carbonic acid gas. A hundred cubic inches of Pyrmont waters contain, according to Bergman, 95 of fixed air; according

ing to Dr Higgins, 160, and according to Westrum, 187 cubic inches. Sulphurated hydrogen gas is the principal ingredient in sulphureous or hepatic water. Carbonated hydrogen gas is said to have been detected in some mineral waters in Italy.

4. The next class of substances found in mineral waters, are the acids. Sulphuric acid has never been found, except in combination with other substances, forming salts in mineral waters. With some of these salts it exists in excess. Sulphurous acid has been detected in many of the hot mineral springs in Italy, in the vicinity of volcanoes. Muriatic acid has only been found in mineral waters, in combination with other substances. Nitric acid is said also to exist in mineral waters in Hungary, in a combined state. Boracic acid has been found in a separate state, in some lakes in Italy.

5. The alkalies are rarely found combined in mineral waters. In the state of carbonate they are frequent. Soda only was detected in the hot mineral springs of Iceland, by Dr Black.

6. Few of the earths, except in combination, have been found in mineral waters. Lime, it is said, exists uncombined in some waters; but Bergman observes that it must be in hot, and not in cold mineral waters. Dr Black detected silica in the waters of Geyser and Rykum in Iceland. It has been found in those of Carlsbad by Klaproth, and it has not unfrequently been observed by others in different mineral waters.

7. The salts which have been found in mineral waters, are sulphates, nitrates, muriates, and carbonates.

Sulphates.—Sulphate of soda is frequently found in the waters of springs and lakes. Sulphate of ammonia has been found in mineral waters, in the neighbourhood of volcanoes. Sulphate of lime is one of the most common substances in most springs. Sulphate of magnesia, or Epsom salt, is not unusual in many mineral springs. Sulphate of alumina is rarely found in mineral waters; it is more commonly found in the state of triple salt or alum. Sulphate of iron is frequent in the springs and lakes of volcanic countries. It has also been found in other places. Sulphate of copper has only been detected in the waters which issue from copper mines.

Nitrates.—Nitrate of potash or nitre is rarely found in mineral waters. It has, however, been detected in several springs in Hungary; some traces of it have been observed in wells in Berlin, and in some felspar springs in Germany. Nitrate of lime has been detected in springs in the sandy deserts of Arabia. Nitrate of magnesia is said also to have been found in mineral waters.

Muriates.—Muriate of potash is but rarely found in mineral waters. It has been detected in the springs of Uleaburg in Sweden. Muriate of soda or common salt exists in almost all waters, as well as in the ocean. Muriate of ammonia is not very frequent in waters; it has been detected, however, in some mineral lakes in Italy, and also in Siberia. Muriate of barytes is very rare, but according to Bergman, it has been found in some mineral waters. Muriate of lime is very generally found in mineral springs. Muriate of magnesia is very common in mineral waters. Muriate of alumina has been detected in some mineral waters by Dr Withering. Muriate of manganese was found by Bergman in some mineral waters in Sweden, and it has lately been discovered, in small proportion, in the waters of Lemington Priors, by Mr Lambe.

Carbonates.—Carbonate of potash, it is said, has been found in some mineral waters. Carbonate of soda exists very frequently in the waters of many springs and lakes. Carbonate of ammonia has been found in the waters of Rathbone Place in London, by Mr Cavendish, and in some waters in France. Carbonate of lime is commonly found in almost all waters, and it is held in solution by an excess of carbonic acid. Carbonate of magnesia very frequently exists in mineral waters. When it is fully saturated with carbonic acid, it is soluble in water, without any excess of acid. Carbonate of alumina is said to have been found in the waters of Avon in Anjou, in France. Carbonate of iron is frequently found in mineral waters. It is to this that chalybeate waters owe their distinguishing properties.

8. Borax, or the subborate of soda, is found in some lakes in Tibet and Persia.

9. Sulphurated alkali and sulphurated lime, or the Hydro-sulphurates of soda and of lime, have been found in mineral waters. It is to these substances that hepatic or sulphureous waters owe their distinctive properties.

10. Bituminous substances have also been discovered bitumen, in some mineral waters. Sometimes they have been found combined with an alkali. Waters also sometimes contain vegetable and animal matters; but these are not, properly speaking, to be considered as ingredients in these waters.

SECTION III. Of the Analysis of Mineral Waters.

In the analysis of mineral waters, the first thing to physical be attended to is to ascertain the temperature and physical properties of the springs from which they are obtained. The sensible properties are then to be examined, such as colour, transparency, smell and taste. Of the physical properties of mineral waters, one of the most important and the first to be ascertained, is the specific gravity. By this means, although not with perfect accuracy, the quantity of saline ingredients may be known; but it is only by means of chemical operations that the nature of the substances with which mineral waters are impregnated, can be determined; and by obtaining these substances in a separate state, or forming new combinations, that their quantity or proportions can be accurately ascertained. In the analysis of mineral waters, therefore, after discovering their physical properties, the object of the chemist is first to detect the nature of the substances, and then the quantity or proportion of these substances which they contain. In both we shall follow the method pointed out by Mr Kirwan, in his Essay on the analysis of mineral waters.

I. Of the Method of Discovering the Substances in Mineral Waters.

1. The nature of the component parts of mineral waters is discovered by the addition of certain substances which produce changes of different kinds. The substances Analysis of substances employed for this purpose are known in chemistry by the name of tests or re-agents, because they act upon the substances with which the waters are impregnated, by decomposing them, and forming new combinations.

2. Gaseous substances are easily detected, either by their escaping in the form of bubbles when the water is exposed to the air, or, if they are more permanently held in solution, by boiling a quantity of the water in a retort, and receiving the gas over water or mercury. The nature of the gas, thus collected, may then be examined by the usual tests for gases.

3. Carbonic acid is detected by the infusion of litmus, not, however, when the acid is saturated with any base, unless the acid be in excess. Saturated lime water may also be employed as a test for carbonic acid. One cubic inch of carbonic acid gas in 7000 grains of water, may be discovered by this test. These effects are not produced by carbonic acid, after the water has been boiled.

4. The infusion of litmus, or paper tinged with it, is also employed as a test for mineral acids existing in waters. A red colour is produced, either when the acid is combined, or united with a base in excess. In this case the redness is permanent, and is not destroyed by boiling.

5. Sulphurated hydrogen gas reddens the infusion of litmus, and blackens silver or lead, or the solutions of these salts. It is also easily recognized by its peculiar odour.

6. Carbonated hydrogen gas burns with common air without explosion; it is not absorbed by lime-water, and has no peculiar smell.

7. The fixed alkalies produce a reddish brown colour with the infusion of turmeric. The same change takes place with the alkaline and earthy carbonates. The infusion of Brazil wood assumes a blue colour. Paper tinged blue with litmus, and reddened with vinegar, may be also employed as a test for alkalies; and by all the alkaline and earthy carbonates, the original blue colour is restored. The muriate of magnesia is precipitated only by the fixed alkalies. Potash forms with nitric acid a prismatic salt; with acetic acid a salt which does not deliquesce, and with sulphuric acid, a salt which effloresces. Ammonia, when in considerable quantity, is detected by the smell. If the proportion be small, it may be discovered by distilling part of the water with a gentle heat.

8. The carbonates of the earths and the metals are precipitated by exposure to the air, or by boiling and evaporation. Carbonates of lime, of alumina, and of iron, are precipitated by boiling for a quarter of an hour. Carbonate of magnesia is only partially precipitated by the same process.

9. Iron either in the state of carbonate, or combined with some other acid, is detected by tincture of galls, which produces a black or purple colour. A very minute portion of iron is detected by this test. Three grains of crystallized sulphate of iron dissolved in five pints of water, strike a purple colour in five minutes, with a single drop of this tincture. With this test the colour affirms different shades, according to the nature of the other substances which are in combination. If the water contains a carbonate of an alkali or an earthy salt, the colour is violet; it is dark purple with other alkaline salts; with sulphate of lime it is first whitish, and afterwards black; and with sulphurated hydrogen gas, the colour is purplish red. The latter, Mr Kirwan suspects, is occasioned by manganese. Iron dissolved by carbonate of ammonia, is at first whitened, and afterwards blackened by tincture of galls. In the caustic fixed alkalies the precipitate is at first crimson red, but afterwards becomes black. Prussian alkali is a sensible test of iron; the precipitate is blue; but if an alkali exists in the water, it prevents a small portion of iron from striking a blue colour with this test, until it be saturated with an acid.

10. Sulphuric acid is detected by muriate, nitrate, or acetate of barytes, nitrate or acetate of lead, nitrate of mercury, nitrate, muriate, or acetate of ironites, and nitrate, muriate, or acetate of lime.

11. Muriatic acid is readily detected by nitrate of silver. It forms a white precipitate, or a cloud in the water. If there are any carbonates of alkalies or earths in the water, they must be previously saturated with nitric acid. Sulphuric acid, or the sulphates, must be precipitated by nitrate or acetate of barytes. Acetate and sulphate of silver may be also employed for the same purpose.

12. Boracic acid, when it is uncombined, is detected by acetate of lead; but the alkaline and earthy carbonates must be previously saturated with acetic acid. The sulphates must be decomposed by means of acetate of strontites, and the muriates by acetate of silver.

13. Lime is readily detected with oxalic acid; but if the water contains any mineral acid, it must be previously saturated with an alkali. Barytes, if any exists in the water, must be precipitated by sulphuric acid. Magnesia is precipitated very slowly with oxalic acid, by which it is readily distinguished from lime.

14. Barytes is detected by diluted sulphuric acid, with which it instantly forms an insoluble white precipitate.

15. Magnesia and alumina are both precipitated by means of pure ammonia and lime water; but it is necessary that carbonic acid, if any exists in the water, be previously separated by means of a fixed alkali, and by boiling. If lime-water is employed, the sulphuric acid must be first precipitated with nitrate of barytes. If the two earths are precipitated together, the alumina may be separated from the magnesia, by boiling them with pure potash, which combines with the alumina.

16. Siliceous earth may be discovered by evaporating a large quantity of water nearly to dryness, and then by redissolving the precipitate in nitric or sulphuric acid, and afterwards evaporating to dryness. The dry mass, redissolved in water and filtered, leaves the silica on the filter.

17. Mr Kirwan gives the following directions for discovering the sulphates.

Sulphate of soda is detected by separating ammonia by gentle distillation, and then by evaporating to one-half, and afterwards by adding lime-water, while any precipitate is formed. By this means all the other sulphates are precipitated. By farther evaporation, and the addition of a few drops of alcohol and oxalic acid, the whole of the lime is separated. To the filtered residue add a strong solution of nitrate of lime; and if the alkaline sulphates exist in the quantity of eight grains... Analysis of grains in 1000 of the liquid a precipitate will appear. To ascertain whether the base of this alkaline salt be potash or soda, add to an equal quantity of the water acetate of barytes; filter the solution, and evaporate to dryness. Add alcohol to separate the other salts. This solution, filtered and evaporated to dryness, gives an acetate of potash or soda; if the former, if dequiesces, but if it be the latter it effloresces by exposure to the air.

18. Sulphate of lime is decomposed by evaporation to a few ounces, if it be contained in the proportion of four grains to 1000. It affords a precipitate with muriate of barytes, oxalic acid, or alcohol; the latter of the specific gravity of 0.848 produces a cloud instantaneously, in a solution of one grain of the salt in 1000 of water.

19. The test for alum is carbonate of lime. With this, alum forms a precipitate. If the water contain muriate of barytes, it must be precipitated with diluted sulphuric acid. A sulphate of any of the metals may be precipitated by means of an alkaline prufiate.

20. The hydrofulphuret of strontites affords a good test for sulphate of magnesia, and it does not give an immediate precipitate with any other salt; but the water should be free from any excess of acid.

21. Sulphate of iron is detected by exposing it in an open vessel to the air for a few days; or it may be precipitated from the water by means of alcohol.

22. To detect the muriate of potash and of soda, it is necessary, first, to separate the sulphates, if any exist in the mineral water, which is done by means of alcohol and nitrate of barytes. The earthy nitrates and muriates are decomposed by diluted sulphuric acid, and the nitric and muriatic acids are expelled by heat. The salts formed with sulphuric acid may be separated by alcohol and barytic water, so that nothing can now remain but alkaline nitrates and muriates. The last is decomposed by acetate of silver, and if a precipitate is thus formed, the water contains muriate of soda or of potash. To separate these from potash or soda, evaporate to dryness, and treat the dry mass with strong alcohol for 24 hours in a temperature of 60°. The acetates are thus dissolved and deposited by evaporation. The acetate of potash is known by its deliquescence, and the acetate of soda effloresces.

23. Muriate of ammonia is to be detected by first separating the sulphates by the acetate of barytes, and then evaporating the solution to dryness. The mass can only consist of acetates and alkaline muriates. Dissolve the dry mass in alcohol, and let it remain for 24 hours in the temperature of 60°. All the salts are dissolved, except the alkaline muriates. The residuum diffused with quicklime will give out ammonia, which will precipitate the solutions of iron, alum or lead, previously introduced into the receiver.

24. Muriate of barytes is discovered by sulphuric acid. This is the only barytic salt yet found in mineral waters.

25. To detect muriate of lime, first separate the sulphate of lime by evaporation, to a few ounces; add alcohol, and afterwards nitrate of barytes. Evaporate the filtered solution to dryness, treat the mass with alcohol; evaporate the solution to dryness, and re-dissolve the residuum in water. If a precipitate be formed, by adding nitrate of silver, oxalic or sulphuric acid, the solution then may contain muriate of lime; if to a portion of the solution, carbonate of lime be added, alumina is precipitated, if the muriate of alumina exist in the water, but not muriate or nitrate of magnesia. Pure ammonia will precipitate magnesia from its combination with the nitric or muriatic acid. And if none of these earths appear, the muriatic acid detected in the water must be united to lime.

26. Muriate of magnesia is discovered by decomposing the sulphates by means of nitrate of barytes. Filter the solution, evaporate to dryness, and dissolve the residuum in alcohol. Evaporate this solution to dryness, and dissolve the residuum in water. The nitrates of lime and magnesia, and the muriates of lime, magnesia and alumina, can only exist in the solution. Carbonate of lime precipitates alumina; pure ammonia precipitates magnesia. Muriatic acid is detected by nitrate of silver. To ascertain whether the muriatic acid be united to magnesia, treat another portion of the solution with sulphuric acid and alcohol. If no alumina has been found, and no precipitate now appears, magnesia is the only earth retained in the solution.

27. To detect the muriates of alumina and iron, of alumina and iron, the alkaline carbonates, if they exist in the water, should be saturated with nitric acid, and the sulphates decomposed with nitrate of barytes. By adding carbonate of lime to a portion of the water filtered and purified, the muriates of alumina and iron will be precipitated. Muriate of manganese is also separated by carbonate of lime.

28. To discover the nitrates of potash and of soda, nitrate of precipitate the sulphates with acetate of barytes, and potash and the muriates with acetate of silver. Evaporate to dryness, and dissolve the residuum in alcohol. The alkaline nitrates, and a portion of acetate of lime, remain undissolved. Filter off the undissolved nitrates, wash them with alcohol, and redissolve them in water. Carbonate of magnesia decomposes nitrate of lime. To separate the nitrate of magnesia thus formed, evaporate to dryness, add alcohol to the dried mass; the nitrate of magnesia is dissolved, but the alkaline nitrates remain untouched.

29. To detect nitrate of lime, evaporate the water considerably to separate the sulphate of lime which it may contain, and add alcohol to separate the other sulphates. The sulphates being filtered off, and the alcohol expelled by heat, oxalic acid added to the solution, will produce a precipitate, if there be any lime in it. Decompose the muriates with acetate of silver; filter the solution, and evaporate it to dryness; dissolve the dry mass in alcohol; evaporate this to dryness, and redissolve it in water. If nitrate of lime exist in the solution, sulphuric acid will discover it.

30. To discover nitrate of magnesia, the sulphates and muriates are first to be separated; the solution being filtered, and evaporated to dryness, the residuum is to be dissolved in alcohol. Evaporate this solution to dryness; dissolve the residuum in water. Add to the solution pure potash, which precipitates the earthy acetate and the nitrate of magnesia. Filter the solution, evaporate to dryness, and treat the residuum with alcohol, which dissolves the alkaline acetates. Analysis of tates, and leaves the nitrate of potash untouched; by which proceeds it must appear, that nitrate of magnesia previously existed in the water.

31. Alkalies combined with bitumen are sometimes found in mineral waters. These mineral soaps, or bituminated alkalies, as they are called by Mr Kirwan, form a coagulum with the acids. This coagulum is insoluble in the alkalies.

32. Extractive matter, which is sometimes found in mineral waters, is discovered by means of nitrate of silver, with which it forms a brown precipitate, but the water containing it must be freed from fulphuric and muriatic acids with nitrate of lead. Three grains of the precipitate, according to Weitrum, indicate one grain of extractive matter.

33. Animal extractive matter gives a very disagreeable taste and smell to water. It is soluble in alcohol.

34. The following is a list of salts which are incompatible with each other, or which cannot exist together in the same water.

1. Alkaline carbonates; and earthy or metallic sulphates, muriates, or nitrates.

2. Sulphuric acid; and earthy nitrates, muriates, or carbonates.

3. Alkaline sulphates; and earthy nitrates, or muriates.

4. Sulphate of soda; and muriate of potash.

5. Sulphate of potash; and nitrate of soda.

6. Sulphate of ammonia; and nitrate of potash, and muriate of potash.

7. Sulphate of magnesia; and nitrate or muriate of lime.

8. Alum; and nitrate of lime and of magnesia, or muriate of magnesia.

9. Nitrate of lime; and muriate of potash, muriate of ammonia, of barytes, or magnesia.

10. Nitrate of magnesia; and muriate of barytes, and of potash.

11. Muriate of magnesia; and nitrate of soda or lime*.

II. Of the Method of ascertaining the Proportions of Substances in Mineral Waters.

1. In examining any mineral water, it has been already mentioned, that it is necessary, first to ascertain the physical properties, and especially the specific gravity, from which the quantity of saline matter, as Mr Kirwan observes, may be estimated. The method he proposes is the following. He subtracts 1000, the specific gravity of pure water, from the specific gravity of the mineral water to be examined, expressed in whole numbers, and multiplying the product by 1.4, which gives the weight of the salts freed from their water of crystallization. Thus, a solution of common salt, whose specific gravity is 1.079. A thousand subtracted from this leaves 79, which multiplied by 1.4 is equal to 110.6, which is the quantity of saline matter in 1000 parts of the solution of common salt.

2. After ascertaining the physical properties, the first step in the analysis is to estimate the quantity of gaseous bodies which the water contains. These are, oxygen gas, azotic gas, atmospheric air, sulphurated hydrogen gas, and sulphurous acid. They are to be collected by heating a quantity of the water in a retort, and receiving the gas over water, or over mercury, if it is absorbed by water. The nature of the gas will be ascertained by the different tests which have been already mentioned for detecting the gases, and the quantity of it may be ascertained, by calculating the bulk, taking care to make the proper allowance for the difference of pressure of the air and temperature. But for this see Mr Kirwan's method of calculation, in his Essay on the Analysis of Min. Wat. p. 178.

3. To discover the carbonates which may exist in the water, is the next step in the analysis. There may be carbonate of lime, of magnesia, of alumina, or iron. If the water contains sulphurated hydrogen, it must be separated by exposure to the air, or by means of litharge. Filter and boil a quantity of the water for half an hour. In this way it is deprived of the earthy or metallic carbonates, if the water contains no sulphurated hydrogen. It is to be boiled for a quarter of an hour, exposed to the air till it is cool, and filtered. Dissolve the precipitate in diluted muriatic acid. The whole are soluble in this acid, excepting alumina and sulphate of lime. Let the residuum be exposed to a red heat; mark the weight, and boil it in carbonate of soda. Saturate the soda with muriatic acid, and boil the mixture for half an hour. Carbonate of lime and alumina are thus precipitated. Dissolve the dried precipitate in acetic acid. The lime is dissolved, but the alumina remains. The weight of the lime, after being dried, subtracted from the original weight, gives the proportion of sulphate of lime. To separate the iron, add ammonia to the muriatic solution, as long as a reddish precipitate is perceived. If magnesia be precipitated with the iron, expose the precipitate in the open air for some time, to a heat of about 200°; add acetic acid in small quantities, to dissolve the magnesia; the iron thus separated, is to be re-dissolved in muriatic acid, precipitated by an alkaline carbonate, and gently dried and weighed. The acetate of magnesia is next to be precipitated and estimated as above. The muriatic solution is thus freed from iron and part of the magnesia. Add sulphuric acid as long as any precipitate appears; heat the solution slightly, and add alcohol. The sulphate of lime is separated and heated to redness. A hundred grains are = 70 of carbonate of lime. The ammonia is to be precipitated by carbonate of soda, dried and weighed. The whole of the carbonate of magnesia is not precipitated by boiling. Evaporate the boiled water nearly to dryness. The carbonate of magnesia and sulphate of lime will be deposited. Add a large quantity of boiling distilled water, which will dissolve the sulphate of lime, and other substances. The carbonate of magnesia remains behind, and may be collected, dried, and weighed. The carbonate of alumina and sulphate of lime are to be estimated by weighing them, after they have been dried in a red heat.

4. To ascertain the proportion of sulphuric acid, sulphuric acid add barytic water to saturation, and weigh the precipitate after it has been exposed to a red heat. A hundred parts of the sulphate of barytes contain 33 parts of real sulphuric acid. To determine the quantity of muriatic acid, likewise add barytic water, till it is neutralized, then precipitate the barytes with sulphuric acid. A hundred parts of barytes take up 31.8 of real Analysis of real muriatic acid. The proportion of boracic acid may be ascertained by precipitating it with acetate of lead. The precipitate is to be digested in a heat of 230° for an hour with sulphuric acid. Evaporate the solution to dryness, and add to the dried mass 10 or 12 times its weight of alcohol. Distil and evaporate this solution; the boracic acid remains behind, which may be dried and weighed.

5. The alkaline sulphates are precipitated by means of nitrate of barytes. A hundred and seventy parts of ignited sulphate of barytes indicate 100 of dried sulphate of soda; and 136.86 of sulphate of barytes indicate 100 of dry sulphate of potash.

6. Sulphate of lime is most conveniently determined by evaporating to a few ounces, and adding a few drops of alcohol, which will precipitate the sulphate of lime. It is then to be dried and weighed. The proportion of alum in a mineral water is ascertained by evaporating to one-half, and precipitating by means of carbonate of lime. Acetic acid added to the precipitate, combines with the excess of lime which may have been added. The alumina thus freed from the carbonate of lime, is to be heated to incandescence for half an hour. Twelve parts denote 100 crystallized alum, or nearly 49 of the dried salt.

7. If no other sulphate exists in the water, sulphate of magnesia may be estimated by precipitating the acid with barytic salt. A hundred grains of sulphate of barytes indicate 52.11 of sulphate of magnesia. But if the water contains sulphate of lime, without any other sulphate, it may be decomposed by means of carbonate of magnesia. The lime thus obtained being weighed, shows the quantity of sulphate of lime. By adding barytes, the whole of the sulphuric acid is precipitated, and thus the quantity of this acid may be estimated. Then by subtracting the quantity of sulphuric acid belonging to the sulphate of lime, the remaining portion indicates what was combined with the magnesia. If the water is found to contain sulphate of soda, none of the earthy nitrates or muriates can exist along with it. If, therefore, no other earthy sulphate has been detected, the magnesia is to be precipitated by means of soda, and is then to be dried and weighed; 36.68 parts indicate 100 of dried fulphate of magnesia. If fulphate of lime accompany these two sulphates, the precipitate consists both of lime and magnesia. It is then to be dissolved in sulphuric acid, and evaporated to dryness. By adding twice its weight of cold water, the sulphate of magnesia is dissolved; the sulphate of lime is insoluble. Evaporate the sulphate of magnesia to dryness, expose it to a heat of 400°, and weigh it. If the water contain alum instead of sulphate of lime, the same process may be followed. But the precipitate being dried, must first be treated with acetic acid to dissolve the magnesia, but the alumina remains untouched. Sulphate of iron is separated by exposing the water to the air for some days, and then adding alumina. The iron is precipitated in the state of oxide, and the sulphate of alumina, being insoluble, is precipitated at the same time. These earths being previously separated, the proportion of sulphate of magnesia may be estimated in the way which has been already described.

8. The proportion of sulphate of iron may be estimated by the following process. Let the weight of a precipitate formed with prussiate of potash in a solution of a known weight of sulphate of iron in water, be previously ascertained. Then with the same prussiate precipitate the sulphate of iron in the water. But if muriate of iron has been detected in the water; evaporate to dryness, and add to the residuum alcohol, in which the muriate, but not the sulphate, is soluble.

9. Muriate of potash or of soda, unaccompanied with Muriate of other salts, may be estimated by precipitating by means potash and of nitrate of silver. 217.65 grams of muriate of filo, denote 100 of muriate of potash; and 235 grams of muriate of silver denote 100 of muriate of soda. If the water contains any of the alkaline carbonates, they must be previously separated by saturating with sulphuric acid. The muriatic acid is then to be precipitated by sulphate of silver. Muriate of ammonia is decomposed by means of barytic water; the ammonia is expelled by boiling, the barytes is precipitated by sulphuric acid, and the muriatic acid is saturated with soda. The sulphate of barytes denotes the quantity of muriate of ammonia.

10. If the common salt be accompanied with muriate of lime, of magnesia, of alumina, or of iron, these &c., may be precipitated with barytic water, and each earth washed, but not dried, re-dissolved in muriatic acid. If only one of these salts be found, saturate the excess of acid with a known quantity of an earth of the same kind, and evaporate to dryness. Then deduct from the weight that of the muriate formed by the earth added: thus 50 grams of lime denote 100 of muriate of lime heated to redness; 31 grams of magnesia indicate 100 of muriate of magnesia; and 21.8 grams of alumina indicate 100 of muriate of alumina. The barytes is precipitated by sulphuric acid; and the muriatic acid is driven off by heat. The muriate of soda may then be estimated by evaporation; but the proportion of muriate of soda, which the known quantity of muriatic acid separated from the earths denotes, must be deducted.

If sulphates and muriates are found accompanying each other, the former may be precipitated by alcohol, or by evaporating the whole to dryness. The earthy muriates may then be dissolved in alcohol. Sulphate of lime, accompanying alkaline and earthy muriates, is decomposed by muriate of barytes, and the precipitate of sulphate of barytes indicates the proportion of sulphate of lime.

If muriates of soda, magnesia, and alumina, accompany the sulphates of lime and magnesia, the water to be examined is to be divided into two equal portions. To precipitate the whole of the lime and alumina, add to the one portion carbonate of magnesia. The proportion of lime in sulphate of lime is then to be ascertained; and, by precipitating the sulphuric acid, by means of muriate of barytes, the quantity contained in the sulphates of magnesia and of lime is ascertained. The proportion of sulphate of magnesia is determined by deducting this last portion. The whole of the magnesia and alumina is precipitated from the second portion of water by lime water. The quantity of these earths indicates the proportion of muriate of magnesia and alumina, deducting that portion of magnesia which was discovered in the state of sulphate in the first portion of water. The sulphuric acid is then precipitated. Vegetables precipitated by barytic water, and the lime by carbonic acid; the common salt is obtained by evaporating the water to dryness.

Nitrate of potash.

11. Nitre may exist in water with all sulphates and muriates which are not incompatible with each other. After sufficient evaporation, the sulphates are to be precipitated by acetate of barytes, and the muriates by acetate of silver. Filter and evaporate to dryness; and add to the residuum alcohol, which dissolves the acetates. The nitrate of potash, which remains undissolved, may then be estimated. If soda be found in the water, it must be previously saturated with sulphuric acid.

If nitre be accompanied with common salt, nitrate of lime, muriate of lime, muriate of magnesia, evaporate to dryness, and add alcohol, which dissolves the earthy salts. Re-dissolve the dry residuum in water, from which the nitre and common salt may be separated by acetate of silver. Evaporate the spirituous solution to dryness, and re-dissolve the residuum in water. The weight of muriate of magnesia is ascertained by precipitating by means of nitrate of silver. The weight of the nitrate of lime is determined by precipitating by means of sulphuric acid; 35 grains denote 100 of dry nitrate of lime.*

* See Anal. Min. Waters, 175—

Chap. XVII. Of MINERALS.

In following out the arrangement which we have laid down at the beginning of this treatise, we should now enter upon the consideration of mineral substances. To preserve the chemical investigation of the different departments of nature unbroken, we propose to employ this chapter in a general view of the characters of mineral bodies, of their composition and methods of analysis; but as this article has been unavoidably extended to so great a length, we shall reserve the whole to the article MINERALOGY, where they will be fully detailed.

Chap. XVIII. Of VEGETABLES.

1. Natural bodies may be properly divided into organized and inorganized, each of which exhibit characters sufficiently discriminative. The substances included under the 17 preceding chapters, belong to the latter class. Organized substances are vegetables and animals, which are to be treated of in this and the following chapters. The distinction between these two classes of bodies, although in some cases it is less obvious, in general is easily recognized. The most perfect forms of inorganized matter afford no marks of resemblance to the varied and complicated structure of a plant or an animal. In the mode of formation, or the growth and increase of the individuals of these two classes, there is the most striking diversity, which exhibits plain and certain characters of distinction. In the one class the growth or increase takes place by the mere aggregation of the particles of matter already prepared, and according to the laws of affinity between the particles; and no new properties exist in the aggregate, which did not exist in the minutest particles of which it is composed. The other class of bodies, comprehending vegetables and animals, exhibits a very different process. The substances which enter into their composition are received into tubes or vessels, are conveyed by them to every individual part of the vegetable or animal, are subjected to peculiar changes, and assume new forms, possessing properties and qualities which could not be previously detected in the simple elements, by any chemical or mechanical operation. This is indeed the essential characteristic of vegetables and animals. The particles which compose a crystal, formed by the evaporation of water, were held in solution by the water, and invariably and uniformly arranged according to certain laws; but the almost infinite variety of substances which compose vegetables and animals, are not to be found in the materials which are necessary to promote their growth and health; neither in the water, the earth, the air, the heat, nor the light, all which contribute their share to the same end. These undergo new changes, and enter in new combinations, none of which existed in the simple elements, and none of which can be effected by any mechanical or chemical process. Indeed the laws which regulate vegetable and animal operations, seem to be totally different from the established laws of chemical action. Hence, from observing this difference of action, the existence and influence of a different principle have been inferred in animals and vegetables. This has been called the vital principle, or the principle of life, because by its influence the varied and complicated phenomena of animals and vegetables are exhibited, which cannot be accounted for on mechanical or chemical principles. It is by the influence of this principle that the animal or vegetable seems to possess the remarkable power of resisting or counteracting to a certain degree the effects of chemical or mechanical agents which may prove injurious to its existence; the power of regulating and selecting what is beneficial and necessary, of supplying what is deficient, and of curtailling what is redundant. Organized substances admit of a natural division into vegetables and animals. The bodies included under each of these divisions have some points of resemblance; but in general are sufficiently characterized and distinguished from each other, by their form, structure, power of motion, component parts and peculiarities of habits. The first of these divisions, namely vegetables, forms the subject of the present chapter.

2. A vegetable is composed of a root, stem, leaves, flowers, fruits, and seeds; and when all these different parts are fully developed, the vegetable is said to be perfect. When any are deficient, or at least less obvious, the vegetable is said to be imperfect.

The root is that part of the plant which is concealed in the earth, and which serves to convey nourishment to the whole plant. The stem, which commences at the termination of the root, supports all the other parts of the plant. When the stem is large and solid, as in trees, it is denominated the trunk, which is divided into the wood and the bark. The bark constitutes the outermost part of the tree, and covers the whole of the plant from the extremity of the roots, to the termination of the branches. The bark is composed of three parts, namely, the epidermis, the parenchyma, and cortical layers. The epidermis, which is a thin transparent membrane, forming the external covering of the bark, is composed of fibres crossing each other. When the epidermis is removed, it is reproduced. Vegetables. The parenchyma, which is immediately below the epidermis, is of a dark green colour, composed of fibres crossing each other in all directions, and is succulent and tender. The cortical layers, which constitute the interior part of the bark, are composed of thin membranes, and increase in number with the age of the plant.

The wood immediately under the bark, is composed of concentric layers, which increase with the age of the plant, and may be separated into thinner layers which are composed of longitudinal fibres. The wood next the bark, which is softer and whiter, is called the alburnum. The interior part of the trunk is browner and harder, and is denominated the perfect wood.

In the middle of the stem is the pith, which is a soft spongy substance, composed of cells, or utriculi, as they are called. In old wood, this part entirely disappears, and its place is occupied by the perfect wood. The leaves are composed of fibres arranged in the form of net-work, which proceed from the stem, and footstalks by which they are attached to the branches. These fibres form two layers in each leaf, which are destined to perform different functions. The leaves are covered with the epidermis, which is common to the whole of the plant. Each surface of a leaf has a great number of pores and glands, which absorb or emit elastic fluids. Flowers are composed of different parts. The calyx or cup is formed by the extension of the epidermis; the corolla is a continuation of the bark, and the filaments and pistils, the internal parts of fructification, are composed of the woody fibres and pith of the plant. Fruits are usually composed of a pulpy, parenchymatous substance, containing a great number of utriculi or vessels, and traversed by numerous vessels. Seeds are constituted of the same utricular texture, in the vessels of which is deposited a pulverulent or mucous substance. These cells have a communication with the plant by means of vessels, and by these is conveyed the necessary nourishment during germination.

Plants contain different orders of vessels, which are distinguished from each other by their course, situation, and uses. Lymphatic vessels serve for the circulation of the sap. They are chiefly situated in the woody part of the plant. The peculiar vessels, which generally contain thick or coloured fluids, are placed immediately under the bark; they are smaller in number than the sap-vessels, and have their interstices filled up with utriculi or cells, with which they form a communication. Some of these proper vessels are situated between the epidermis and the bark, which are readily detected in the spring. Some are situated in the interior part of the bark, forming oval rings, and filled with the peculiar juices of the plant. Another set of proper vessels is placed in the albumen, nearer the centre of the stock or trunk, and sometimes in the perfect wood. The utriculi or cells constitute another set of vessels, which seem to resemble a flexible tube, slightly interrupted with ligatures at nearly equal distances, but still preserving a free communication through its whole length. They vary in form, colour, and magnitude, in different vegetables, and exist in the roots, the bark, leaves, and flowers. The tracheae or spiral vessels, which are readily detected in succulent plants, appear in the form of fine threads, and may be drawn out to a considerable length without breaking.

These vessels are very numerous in all plants, especially under the bark, where they form a kind of a ring, and are disposed in distinct bundles, in trees, shrubs, and stalks of herbaceous plants.

After these preliminary observations on the characters of organized substances, and the general structure of plants, we now proceed to give a short view of the functions, decomposition, and component parts of vegetables. These shall form the subject of the three following sections.

Sect. I. Of the Functions of Vegetables.

I. Of Germination.

1. When the perfect seeds of a vegetable are placed in certain circumstances, they produce plants exactly like those from which they originated. The requisite circumstances for the germination of seeds are heat, air, and moisture. It is well known that no vegetation goes on when the temperature of the air is at the freezing point, and very little till it rises a considerable number of degrees above it. The seeds of different plants, it is observed, require different degrees of heat for their germination, and hence the various seasons and climates in which different plants and seeds are found to vegetate.

2. But whatever the temperature may be, no seeds will germinate, unless they are exposed to the action of the air. It is found that it is the oxygen of the air which is necessary for the production of this change; for when it is entirely excluded no change takes place, and when it is in greater quantity, vegetation is more rapid and more vigorous.

3. Moisture is also necessary for the vegetation of seeds. But although water be necessary for this purpose, it must be applied in moderate quantity, for except the seeds of aquatic plants, which are possessed of peculiar habits, most seeds are deprived of their vegetative power, and entirely decomposed, when they are kept in water. Hence it is that many seeds do not vegetate in stiff clay soils, which retain too much water, nor in sandy lands, which allow the whole of the water to filter through them. Many seeds, although they are exposed to the favourable action of these agents, do not vegetate when they are exposed to the action of light. It is on this account, and also, no doubt, for the proper application of moisture, that seeds are covered with the soil, by which means germination is found to be greatly promoted.

4. A seed is composed of three principal parts, which have been denominated the cotyledons or lobes, the radicle, and plumula. The greatest number of seeds have two cotyledons. Some, however, as many of the farinaceous seeds and seeds of grasses, have only one. Other seeds have three, and some four. Hence plants have been distinguished into mono-cotyledinous, di-cotyledinous, and poly-cotyledinous.

5. The first change which takes place on a seed placed in circumstances favourable to germination, is the increase of size by the absorption of moisture. The radicle is then formed, which stretches downwards into the earth. The plumula shoots upwards, and expands into leaves and branches. The peculiar function of the root is to convey nourishment from the earth Functions for the future growth of the plant; but from what source is the nourishment derived for the formation of the root itself?

6. The very first change which takes place within the feed is the combination of the oxygen of the air which is absorbed, with the carbure which exists in the lobes of the feed, and the formation of carbonic acid, which is given out in the state of gas. The farinaceous matter of the feed being deprived of part of its carbure, is converted into a saccharine substance, which is destined for the nourishment of the embryo plant, till its parts are so far evolved, and its structure completed, as to derive nourishment from the earth.

7. The first chemical change, therefore, which is observed in the germination of seeds, is the absorption of oxygen, the emission of carbonic acid gas, and the conversion of the farinaceous matter into a saccharine substance. This is the process of germination, as it has been described by chemical physiologists. But if oxygen gas be entirely excluded, no change takes place; no part of the process of germination goes on; or even if it has proceeded so far as that the plumula shall have appeared above the surface in the form of seminal leaves; if these leaves are removed before others have been unfolded, the plant dies. The seminal leaves are the lobes which have been pushed out of the earth along with the plumula, so that if they are destroyed the plant is cut off from the necessary source of nourishment for the evolution of its parts, and the formation of roots and leaves, which are destined to perform the different functions of vegetation.

II. Of the Food of Plants.

1. But air, heat, and moisture are not only necessary for the formation of the different parts of the plant; their action must be continued, and is absolutely requisite for its future health and growth. It could not long escape observation, that plants cease to vegetate when they are entirely deprived of water. Hence it became the opinion of the earlier physiologists, that water constituted the chief or the only food of plants; but it has been proved by experiments in analyzing plants which grew in pure water, that they received no increase of one of the necessary principles in their constitution, farther than what previously existed in the seeds or roots from which they sprang. In a series of experiments instituted by Hassenfratz, on the roots of hyacinths, the seeds of kidney beans and other seeds, he found that the quantity of carbonaceous matter in the full-formed plant, was even less than what previously existed in the bulb or seed.

2. But although pure water seems not to contribute to the growth of plants, yet it is necessary as a solvent for those substances which are considered as the proper food of vegetables. But when water is impregnated with certain saline and earthly, but especially with carbonaceous matter, it is then found to be most proper for promoting the growth and increase of vegetables. We have observed plants growing in a soil which was frequently moistened with the water from a dunghill, advance with a more rapid and vigorous growth, and attain to a larger size, than similar plants in the same soil, which received only the usual supply of rain and dew from the clouds. It has been found by experiment, that this water holds in solution a considerable portion of carbure. It is not improbable that it also contains some of those saline matters which have been detected by analysis in plants in the greatest health and luxuriance. The waste of the soil must be repaired with frequent additions of manure, which may be considered as necessary supplies of food or nourishment.

3. But whatever may be the food of plants, it is peculiarly taken up by the roots in the state of solution in water, and conveyed by the vessels to every part of the vegetable. For this purpose it would appear that there is a peculiarity of structure in the extremities of the roots; for, if part of the fibre of a root be cut off, the plant ceases to vegetate till new fibres are formed, which are so constructed, as to be capable of absorbing the necessary quantity of water.

4. This fluid, which is found in plants, is called the Sap. It is most abundant in the spring, as the season of vegetation advances; and during that season, when the plant is wounded, it flows out copiously, and it is then said to bleed. This is particularly the case with some trees, such as the birch and a species of maple; the sap of which, by certain processes, yields wine or sugar. The sap is contained in what is called the lymphatic or common vessels of the plant.

5. The fluids taken up by vegetables, it is probable, is prepared no sooner enter the plant, than they undergo some change. Vauquelin has directed his attention to this subject, and has analyzed the sap at different periods during the season of vegetation. The sap of the common elm (Ulmus campestris Lin.) extracted from the tree early in the spring, was of a brown colour, had a sweet mucilaginous taste, but scarcely reddened the tincture of turpentine. Ammonia produced in this fluid a copious yellow precipitate, soluble with effervescence in acid. Barytes and lime-water produced a similar effect. Oxalic acid and nitrate of silver gave a white precipitate. Sulphuric acid, diluted with water, occasioned a brisk effervescence, with the evolution of the odour of acetic acid from the mixture. Oxymuriatic acid destroyed the colour of the sap, and formed in the liquid a yellow precipitate. Hydrofluosulphate of potash and sulphate of iron effected no change, but acetic acid threw down a flaky precipitate. A quantity of this sap being evaporated with a moderate heat, there was found on the surface a brownish pellicle; a brown matter separated in the form of flakes, and an earthy matter deposited on the sides of the vessel, which was dry to the touch. After evaporation to a certain degree, and cooling, a yellow earth was deposited, which dissolved with effervescence in muriatic acid. When the solution was completed, the liquid was filtered, to separate the insoluble vegetable matters. The muriatic solution mixed with carbonate of potash, yielded carbonate of lime. The liquid which had deposited the vegetable matter being evaporated with a gentle heat afforded a grayish extract, which strongly attracted moisture from the air, and had a very pungent, saline taste. It effervesced with the addition of concentrated sulphuric acid, and gave out the odour of radical vinegar. Distilled with three parts of sulphuric acid, it furnished very concentrated acetic acid, and there remained in the retort sulphate of potash with excess of acid.

6. From this analysis it follows, that the extract of the sap Functions sap of the elm is chiefly composed of acetate of potash. One thousand and thirty-nine parts of this sap yielded nearly the following proportions.

| Acetate of potash | 9.24 | |-------------------|------| | Vegetable matter | 1.06 | | Carbonate of lime | .796 |

The deficiency was made up of water and some volatile matter.

When the season was farther advanced, the sap of the same tree was again subjected to analysis, and it was found that the quantity of acetate of potash and carbonate of lime had diminished, but that the quantity of vegetable matter was nearly double. At a still more advanced period of the season, the experiment was repeated, the result of which was, that the increase of the vegetable matter, and the diminution of the acetate of potash and carbonate of lime were still greater. It appeared too, that carbonic acid existed in excess in the sap, and that the carbonate of lime was held in solution by it.

7. The same chemist analyzed the sap of the beech, and it was found to be composed of water, acetate of lime with excess of acid, acetate of potash, gallic acid, tan, mucous, extractive matter, and acetate of alumina; but the proportions of these parts have not been mentioned. From this analysis it appears, that the sap of the beech is different from that of the elm, in containing acetic acid uncombined, besides gallic acid and tan, but at the same time having no carbonate of lime. When the sap of the same plant was examined later in the season, the proportion of gallic acid and tan had increased. Vauquelin also examined by analysis, the sap of the carpinus fylvetris or hornbeam, and the betula alba or birch *. The component parts of the sap of the former were found to be, acetate of potash and lime, mucilage, sugar, and extract, with water; and the latter were found to be water, acetates of lime, alumina and potash, sugar, and vegetable extract. From these experiments it appears that the fluids which are taken up by plants, are immediately changed by certain processes within the plant; for some of the substances which are component parts of the sap of plants, are either not found in the liquids before they enter the plant, or exist in them in very small quantity. These changes, it appears too, from the same experiments, are considerably greater, at the later periods of the season of vegetation. Some of the component parts are greatly increased, while others are much diminished.

8. The sap ascends from the root to the extremities through the branches, which has been proved by making incisions in the trunk of a tree at different heights in the spring season. The sap is observed to flow, first, from the lowest incision, and successively to the highest. It is through the vessels in the woody part of the tree, that the sap ascends, for no sap flows from an incision unless it has penetrated the wood, and in some trees it is necessary to make the incision nearly to the centre. It has been observed that coloured infusions always pass from that part of the wood called the alburnum.

9. The sap of plants is conveyed through those vessels which were described under the name of tracheae or spiral vessels. These were denominated tracheae or air-

vessels by the earlier physiologists, because being found empty, when they were cut across and examined, they were supposed to convey nothing but air.

10. As the sap of vegetables moves with very considerable force, it has given rise to much speculation about the nature of that power, or the cause by which this is effected. Malpighi ascribed the ascention of the sap to the dilatation and contraction of the air in the air-vessels; while Grew supposed, that it was owing to the lightness of the vapour, in which state he conceived the sap entered the plant, and was conveyed through it. By many others the ascent of the sap in vegetables has been ascribed to the force of capillary attraction; but the nature of this action, as it is demonstrated and explained by mechanical philosophers, seems to be incompatible with the phenomena of the circulation of the sap in vegetables, and has therefore been rejected as a hypothesis equally unsatisfactory with those which have been just mentioned. It has been ascribed with more probability to the action of the vessels themselves. This is owing, in the language of physiologists, to the irritability of the vessels, or a certain power by which they are enabled to contract, by the action or influence of certain substances. This is supposed to be the case with the sap, and the action which takes place when it enters the roots, is owing to the irritability of the vessels. As the sap is carried a certain length by the first contraction, it is carried still farther by the second; and thus by successive contractions it is propelled through every part of the plant, while at the same time new additions continue to enter the extremities of the root.

III. Of the Functions of the Leaves.

1. Whatever be the nature of the process, the sap is carried to every part of the vegetable, and we have seen that it has no sooner entered it than it undergoes certain changes, which become more considerable according to the length of time after its absorption. But the greatest changes which take place in the sap of plants, are effected in the leaves. The leaves are to be considered among the essential organs of vegetables, for in them the sap is totally changed, and converted into the peculiar juice, or succus proprius, of the plant. As the functions of the leaves are of great importance in vegetation, it will be necessary to consider the nature of their action.

2. During the day, the leaves of plants transpire a very considerable quantity of moisture, the proportion of which, it appears from some experiments, was not much inferior to the quantity absorbed. From similar experiments it appears that the quantity evaporated was in proportion to the extent of surface of the leaves. The quantity has been observed to be greatest too, during sunshine and warm weather. It is greatly interrupted during the night, and entirely checked by cold. When the quantity of moisture transpired is diminished, the moisture imbibed is also found to be less in proportion. This indeed might have been expected, for when the transpiration of a plant ceases, this being an essential function of vegetation, the whole process must be interrupted. In experiments made on this transpired matter, by evaporating to dryness a quantity which had been collected, a small portion of carbonate of lime was obtained; from the residuum, Functions a still smaller proportion of sulphate of lime, with a little gummy and resinous matter. It has been found that the transpiration of moisture takes place chiefly on the upper surface of the leaves, and this seems to be performed by a particular set of organs.

Oxygen gas given out. During the day, and especially during bright sunshine, oxygen gas is given out by the leaves of plants.

Carbonic acid gas absorbed. The quantity of oxygen gas emitted by leaves, as appears from the experiments of naturalists, depends on the quantity of carbonic acid gas which is absorbed by the plant; for it has been ascertained that vegetables grow rapidly and vigorously when they are exposed to this gas; nay, it is found essentially necessary to their health and growth. If the water with which plants are supplied be deprived of the whole of its air by boiling, no oxygen gas is emitted, and water which is impregnated with the greatest proportion of carbonic acid gas, gives out the greatest quantity of oxygen gas.

Action of light. This process goes on only during the day, and it is more vigorous during bright sunshine; from which it is natural to conclude, that light performs some necessary part in it. It is well known that plants which grow in the dark do not acquire a green colour; and it is found that these plants contain a smaller proportion of carbons than similar plants, in the same circumstances, exposed to the light. From this it may appear what is the nature of the process when carbonic acid gas is absorbed by plants, and oxygen gas emitted. It is the decomposition of the former, which is effected; the carbons being retained in the plant, and the oxygen given out; but light being a necessary agent in this decomposition, the process must be interrupted when it is excluded.

Parenchyma of the leaf gives out the oxygen gas. This decomposition takes place in the parenchymatous substance of the leaf, and the quantity emitted, it appears, is in proportion to the thickness of this substance. The green colour of plants, it has already been mentioned, depends on the action of light. Plants which vegetate in the dark, have not only a smaller proportion of carbons, but also continue of a white colour; but in a short time after they are exposed to the light, the green colour is restored.

Vegetables the great source of oxygen. Thus it appears, that it is one part of the functions of leaves of plants to exhale a considerable proportion of the moisture taken in by the roots; to absorb carbonic acid gas; to decompose this gas, by which its carbons are retained in the plant, and the oxygen is given out. Thus too, it appears, that vegetables are one of the great sources of supply of oxygen gas, which is essentially necessary in the numerous processes of combustion, and the respiration of animals, which are constantly going on on the surface of the earth; and thus the waste of this vital fluid is repaired, and the balance preserved between its destruction and supply.

Function of leaves during the night. The leaves of plants perform a very different function during the night. Instead of emitting moisture and oxygen gas, and absorbing carbonic acid gas, which takes place during the day, the process is reversed. Carbonic acid gas is emitted, and moisture and oxygen gas are absorbed. The absorption of moisture seems to be chiefly performed by the under surface of the leaves, at least in many plants. It has been found by experiment, that plants, which have been made to grow in oxygen gas give out a greater quantity of carbonic acid gas, than when they grow in common air.

From this circumstance it has been supposed, that the carbonic acid gas, emitted by plants during the night, is owing to the combination of the oxygen absorbed, with the carbons of the sap; for it is at the same time that oxygen is absorbed. It has also been ascribed to the decomposition of the water.

8. By these different processes which are carried on in the leaves of plants, by the abstraction of some of its principles, and by entering into minute combinations with others, the sap undergoes very great changes. It peculiarly there converted into the peculiar juice of the plant, juice, from which are derived, by other processes, the different substances, which are produced in the different parts of plants, the nature of which will be afterwards examined. The leaves of plants have been compared to the lungs and stomach of animals. How far this analogy is just, it is not necessary to inquire; but there can be no doubt that the leaves are essential organs in the economy of vegetables. In the very first step in the process of vegetation, during the germination of seeds, the moisture absorbed by the roots is carried to the seminal leaves, and there undergoes certain changes, before it is fit for the formation of the stem and other leaves of the plant; for, if these leaves are removed, vegetation is entirely interrupted, and the plant dies. Even when plants have made farther progress, and are in full vigour, if they are entirely stripped of their leaves, the powers of vegetation cease, till these necessary organs are restored, and new leaves are formed. The progress of vegetation is also stopped when the surface of leaves is varnished over, so that the absorption and emission of the necessary fluids are interrupted.

9. The sap of plants, it has been already observed, flows from the roots towards the branches and leaves from the plant. In the leaves it undergoes peculiar changes, in consequence of part being exhaled, and in consequence of the absorption of different principles which combine with it, and no doubt contribute by this combination to the changes which take place. The sap, as we have already said, is then converted into the succus proprius, or peculiar juice. It is the sap of the plant, which is so far prepared to be converted into the different parts of the plant, corresponding to its nature and properties; and, as the different parts, both of liquids and solids in plants, possess properties totally distinct from each other, and have derived these from the same nourishment, the processes by which these different substances are produced in different plants, and even in the same plant, must undoubtedly be different.

10. The peculiar juice of plants flows from the leaves towards the roots. If a ligature is fastened round the juice from the leaves immediately above the ligature, that is, between it and the leaves, swells out by the accumulation of this juice. Or if a wound be made in the bark, the peculiar juice flows in greater abundance from that side of the wound next to the leaves, than from the other side.

11. The peculiar juice of plants has a greater consistence than the other juices. It is readily recognized by some peculiarity of colour. In a great many plants it is milky, in some it is of a green colour, and in others Decomposition of Vegetables.

The component parts of the peculiar juice of plants are little known; but from some experiments which have been made on this subject, it appears that some part of the vegetable is ready formed. In the experiments of Chaptal on the peculiar juice of plants, he detected a substance which possessed the properties of the woody fibre. In similar experiments on the seeds of plants, it was found that they contained a greater proportion of the woody fibre, from which it is inferred, that the peculiar juices of plants contain their nourishment ready prepared, and in that state in which it is found in the seed. The peculiar juices of plants contain a greater proportion of these elements which constitute the different parts of plants, than what is found to exist in the sap. These are carbon, hydrogen, and oxygen.

12. Many plants cease to vegetate as soon as they have perfected their seeds, which is accomplished by some in one season, by others in two, and hence such plants have been called annuals and biennials. Other plants, however, continue to yield seeds and fruit for many successive seasons, and to live for a great length of time. What is the cause of this remarkable diversity among the vegetable tribes,—why the humble annual springs up, flowers, and forms perfect seeds within the short period of a few months, while the stately oak rears its lofty head, and continues to be the pride and glory of the forest for hundreds of years, it would be difficult to say. At present, however, it is not our province to enter into the speculation.

Sect. II. Of the Decomposition of Vegetables.

1. As soon as the plants have ceased to vegetate, they undergo a new set of changes. The whole plant is broken down; the elements of which it is composed enter into new combinations, and new substances make their appearance, which did not previously exist in the plant. This decomposition is owing partly to the affinities between the component parts of the vegetable themselves, and partly to the affinities which exist between some of the elementary principles of the plant, and the heat, air, and moisture, without which no decomposition takes place. While the plant continued to exhibit the phenomena of vegetation, that is, while it continued to live, it possessed a power of resisting this chemical action between the elements of which it is composed, and also to a certain extent the action of external agents. During this decomposition of vegetables, air, heat, and moisture, are necessary. Gaseous bodies are generally given out, and new compounds are formed. Some plants, and some parts of the same plant, have a greater tendency to undergo this decomposition than others, because they either possess a greater proportion of the substances which promote the decomposition, or a greater proportion of the substances of which the new compounds are formed.

2. The changes or spontaneous decompositions of vegetables, as they are almost always accompanied with an intestine motion, have received the name of fermentation. The nature of these changes is very different, both with regard to the gaseous bodies which are absorbed or emitted, and the nature of the products which are obtained after the process is finished. Hence, fermentations have been usually distinguished into three kinds; namely, the vinous, so called, because the product is wine, when certain substances are subjected to this process, or beer, when other substances are employed; the acetic fermentation, because during this part of the process vinegar is produced; and the putrid or putrefactive fermentation, because the substances are still further decomposed, and run into the state of putridity. But these different kinds of fermentation might perhaps be considered merely as different stages of the same process; for unless it is checked at certain periods, it runs through the different stages without interruption. According to some, these three species of fermentation do not include all the changes which have the characters of this process to which vegetables are subject. To these it has been proposed to add the saccharine fermentation, or that change which is induced on farinaceous seeds by heat and moisture, which is the germination of seeds or the process of malting; and the colouring fermentation, or that process by which the colouring matter of vegetables, as indigo, is developed. In the present section we propose to treat, 1. Of the vinous fermentation; 2. Of the acetic or acid fermentation; 3. The panary fermentation, or the formation of bread; and, 4. Of the putrid fermentation.

I. Of the Vinous Fermentation.

1. The vinous fermentation, otherwise denominated History, the spirituous, has been so called, because the first product is wine, which by distillation yields spirits. Boerhaave was the first who directed his attention to trace the causes, and to observe the phenomena of fermentation. The same subject was afterwards prosecuted by other chemists, and much was written on the nature and manufacture of wine; but till the discoveries of modern chemistry, and especially the important one of the composition of water, nothing was ascertained with precision concerning the nature of fermentation, or the changes which take place on the fermenting substances. To the experiments and researches of Lavoisier on the formation and decomposition of alcohol, chemistry is indebted for some of the most important facts with regard to the process of fermentation.

2. Certain conditions are necessary to promote the vinous fermentation. The first indispensable condition is the presence of some saccharine matter. Experience has shown that no vegetable substances are susceptible of this fermentation, which do not contain sugar. Thus, the sweet juices of fruits are usually employed in this process; and particularly, for the production of wine, the juice of the grape.

But sugar in a state of purity, or uncombined with other substances, is not susceptible of any change. A certain quantity of water, therefore, is necessary that the saccharine matter may be in the liquid state. Water, therefore, is one of the essential conditions of the vinous fermentation; and it seems necessary that the water should neither be in too great quantity, nor deficient. In the latter case the fermentation is interrupted; in the former it is promoted too rapidly, and is apt to be converted into the next stage, the acetic or acid fermentation. When the concentration is too great, water must be added, and when it is too fluid, the addition of sugar becomes necessary. The vinous fermentation scarcely commences, if the temperature be below 60°, but at the temperature of 70° the process goes on briskly.

But sugar and water alone do not ferment, without the addition of some other substances. In the liquid expressed from grapes, which has received the name of must, there are, besides sugar, a portion of jelly, some glutinous matter, and tartar.

The contact of air has been considered as one of the requisites of the vinous fermentation; but this is not necessary, on account of the fermenting liquid deriving any addition from the atmosphere, for the process goes on equally well, when it is excluded, provided the gaseous bodies which are formed are permitted to escape.

A large mass is also favourable for promoting the vinous fermentation. A small quantity of saccharine matter scarcely at all undergoes this change, while it runs speedily to the acid fermentation.

3. When the substances which are susceptible of this fermentation, are placed in proper circumstances, the process commences in a few hours, or a few days, according to the temperature and the quantity of liquid employed. The liquid is then agitated with an intestine motion; it becomes thick and muddy; the temperature increases, and carbonic acid gas is disengaged. The liquid is increased in bulk, and the surface is covered with a voluminous, frothy matter, which is owing to the carbonic acid gas adhering for some time to the viscid matters in the liquid. The quantity of carbonic acid gas disengaged during this process is very considerable. It begins to be evolved at the commencement of the fermentation, and continues till its termination. At the end of a few days, or a longer or shorter time, according to the temperature and other circumstances, the fermentation ceases. The liquid becomes transparent, the matters which occasioned the muddiness having precipitated to the bottom, and from having a sweet taste, it becomes sharp and hot, and from having been viscid and glutinous, it becomes more liquid and lighter. It is now converted into wine.

4. Such are the phenomena of fermentation, from which, and from the nature of the product, very considerable changes must have taken place on the component parts. One change has been observed during this process; namely, that the quantity of sugar is always diminishing, and, at the end of the process, is entirely decomposed. The liquid is now more fluid, is specifically lighter, and has obtained a vinous taste; which new properties are ascribed to the formation of alcohol which exists in all wine. It would appear, from the experiments of M. Lavoisier, that it is the sugar only which has suffered decomposition. It is divided into two portions, one of which separates, and is carried off in the form of carbonic acid gas, while the other, containing a greater proportion of hydrogen, remains in the liquid, in the form of alcohol. Part of the alcohol is carried off, and the alcohol which remains in the liquid is combined with the acids of the wine and the colouring matter, from which it must be separated by distillation. The tartaric acid, it has also been found, is partially decomposed during the process, and a portion of malic acid is formed. It appears from other experiments, that azotic gas is disengaged during this process, from which it is inferred, that some others of the constituents of the fermenting liquid have been decomposed, since sugar contains no azotic.

5. There is great variety in the colour, flavour, and strength of wines. These differences depend on Component the nature of the soil and of the grapes, and very often on the manner in which it is manufactured. But the component parts of wine are generally some acid matter, alcohol, extractive matter, oil, and colouring matter. It has been ascertained by experiment, that all wines redden the tincture of turmeric. The acid which exists in greatest abundance in wine, was found by Chaptal to be the malic acid; some portion of citric acid also has been detected. Some wines, as champagne, contain a considerable portion of carbonic acid.

It is to a certain portion of alcohol contained in wines that they owe their strength; and, when wines are subjected to the process of distillation, the alcohol passes over, and the spirit which is thus obtained is known by the name of brandy.

The extractive matter found in wines has been observed to diminish in proportion to the age of the wines, as it separates gradually from the liquid, and is precipitated to the bottom.

The flavour and odour of wines have been ascribed to a small quantity of volatile oil; but this quantity is so small, that no means hitherto employed have succeeded in obtaining it in a separate state. Wines are distinguished by a peculiar colour, which is owing to the colouring matter originally derived from the husk of the grape.

6. The juices of other fruits also afford materials for fermentation, as that of cider from apples, and perry from pears. These are distinguished from wines properly so called by containing a greater proportion of mucilaginous matter. The juice of the sugar cane also affords a fermenting liquid from which is obtained by distillation the spirit called rum.

7. Beer or malt liquors, as they are called in Britain, are fermented liquors obtained from farinaceous seeds. Different kinds of corn are employed for the purpose of making beer. In Britain, barley is the most common grain in the preparation of this liquid. It is first steeped in water, and afterwards thrown together in a heap for about 24 hours. During this period, in consequence of the moisture which has been absorbed by the grain, the process of germination commences, oxygen gas is absorbed, carbonic acid gas is given out and heat is evolved, while the radicle is protruded. The process having advanced thus far, is checked by slowly drying the grain. For this purpose it is spread out on a floor, and in this state it is known by the name of malt. It is afterwards exposed to heat, fully dried, and ground to a coarse powder. An infusion is then made with water about the temperature of 160°, which is drawn off; more water is added till the whole soluble part of the malt is extracted. This infusion, which has a sweet taste, from having a portion of saccharine matter, is called wort. After being boiled with some bitter substances, as hops, it is allowed to ferment, and the process of fermentation is in a great measure similar to that which has been already described of the fermentation of wine. The temperature most proper for this fermentation is about 60°; the fermentation... mentation of wort is greatly promoted, and the quantity of the fermented liquor is more abundant with the addition of yeast.

It has been found also, that the infusion of malt ferments in close vessels, and equally well as when exposed to the open air. During this fermentation carbonic acid gas is disengaged, which is mixed with a portion of the wort. By the distillation of the liquid obtained after the fermentation has ceased, alcohol is obtained; the nature and properties of which have been already described in treating of that liquid under inflammable substances.

II. Of the Acetous Fermentation.

1. In treating of acetic acid, which is the product of this fermentation, we have already detailed the method proposed by Boerhaave for the manufacture of vinegar, and we have also described the properties of that acid. All that is now necessary, therefore, is shortly to state the general phenomena which are exhibited during this fermentation. When wine or beer, which is the product of the vinous fermentation, is exposed to a temperature between 70° and 90°, it becomes gradually turbid, the temperature is increased; it is agitated with intestine motions, and flaky substances are seen floating through it in all directions. The intestine motions at last subside, the liquid becomes transparent by the matters which rendered it turbid precipitating to the bottom of the vessel. The liquid has now assumed different properties; it is converted into acetic acid or vinegar.

2. The conditions necessary for the acetous fermentation are, a considerable elevation of temperature, and exposure to the air of the atmosphere. During this fermentation oxygen is absorbed from the air, and unless this absorption takes place, the fermentation does not go on. It is necessary that the substances to be subjected to this fermentation contain a certain proportion of extractive matter; for if they are entirely deprived of it, the process does not go on. Weak wines or beer are more readily converted into vinegar than strong wine; but when the process of fermentation has commenced on the latter, the product is a stronger and better vinegar.

3. In examining the products of this fermentation, it has been found that the malic acid and the alcohol which previously existed in the wine, have entirely disappeared, so that by their decomposition they have contributed to the formation of the vinegar. Some portion of the extractive matter also has been decomposed. The acetic acid is formed also during the decomposition of many vegetable substances, either by means of heat, or other chemical agents.

III. Of the Panary Fermentation, or of Bread.

1. The fermentation which takes place in making bread is supposed to be peculiar; but the phenomena and product have not been sufficiently examined to be able exactly to ascertain its nature. The process is extremely simple. Wheat flour, which is generally employed, is formed into a paste with water, the proportions of which vary according to the age and quality of the flour. After some time it is agitated with an internal motion, similar to the other fermentations, in consequence of the action of the component parts upon each other, the formation of new compounds, and the evolution of gaseous matter. Water is essentially requisite in this fermentation. One of the changes which have taken place during the process, is, that the gluten which constitutes a part of the flour, has disappeared. It is entirely decomposed. This matter has acquired a foul disagreeable taste, and if it is made into bread, it is found unfit to be eaten.

A quantity of new paste is then prepared, and a small quantity of the old flour paste is added to it. This produces rapid fermentation. The flour paste, thus added, to promote the fermentation, is called leaven, and the bread prepared by this process has received the name of leavened bread; a distinction which has been known to mankind from the earliest ages of the world. It is frequently mentioned in Scripture, in the Jewish history. It requires some attention to be able to determine the exact quantity of leaven necessary for the proper fermentation of the paste. When it is deficient in quantity, the process of fermentation is interrupted, and the bread thus prepared is solid and heavy, and if too much leaven be used, it communicates to the bread a disagreeable sour taste. When the fermentation succeeds, the paste swells up, and is greatly enlarged in bulk, which is owing to the formation of a quantity of gas, which is confined within the mass, by the viscosity of the glutinous part of the flour.

Other substances are employed to promote the fermentation of paste for the purpose of making bread; one of the most common is the matter which collects on the surface of fermenting liquids from farinaceous matters. This substance, which is called barm or yeast, is equally efficacious in producing fermentation, and is less apt to contaminate the bread with any disagreeable taste. As it is collected on the surface of fermenting beer, it was examined by Weitbruch, and was found to contain a great variety of ingredients. Besides the water, which was in greatest proportion, it consisted of gluten, sugar, and mucilage, with a quantity of alcohol, and a small portion of malic, acetic, and carbonic acids. The essential components of barm or yeast were found, by the same chemists, to be gluten mixed with a vegetable acid; and therefore yeast, which has been collected and put into bags strongly pressed and dried, by which means it is obvious many of the component parts must be separated, has been found equally fit for fermentation.

2. When the paste has undergone the proper degree of fermentation, it is formed into loaves, and introduced into an oven, which has been previously heated. The same temperature is as nearly as possible employed for the baking of bread. This is regulated by throwing a little flour on the bottom of the oven. If it becomes black, without taking fire, the oven is supposed to have acquired a proper temperature. This is found to be about 448°.

3. If the fermentation has been properly conducted, the bread during the process of baking enlarges in bulk, becomes light and porous, and is full of eyes or cavities, in consequence of the extrication of the gas which was confined by the viscid, glutinous matter, and now driven off by means of heat. It is also considerably. Decomposition of vegetable matters. In some parts they are completely separated, and resolved into their primary elements by the escape of those substances by which they were mutually held together. In others, new compounds are formed, by a new set of attractions and combinations.

2. Several conditions are necessary to promote putrefaction. The first requisite is water, without which the process does not go on. When vegetables are kept perfectly dry, they undergo no change. The contact of air is also necessary, and a moderate temperature. When the temperature is too high, the moisture is carried off by evaporation, before the changes in which this process consists can be effected; but when the moisture is not carried off, the higher the temperature, the more rapid is the putrefaction.

3. When vegetables are placed in proper circumstances to favour this process, the colour and consistence are soon changed; the texture is destroyed, the fibres are separated; the soft and liquid parts swell up and are covered with froth; elastic fluids are discharged, the temperature is increased, and sometimes so high as to produce actual inflammation. The gases which are discharged, are, after the process has fairly commenced, accompanied with a fetid odour. They are composed of a mixture of carbonated hydrogen, carbonic acid, and azotic gases. After these phenomena have continued for some time, which is longer or shorter, according to the nature and consistence of the vegetable matters, great part, it appears, has been dissipated by evaporation. There remains a dark coloured substance, containing the more fixed materials of the vegetable, as the earths combined with the acids and part of the carbons.

4. In observing the necessary conditions, the phenomena, and the products of the putrid fermentation of vegetables, the influence of the numerous attractions of the different materials which enter into their composition is manifest. Part of the hydrogen combines with the oxygen, and is carried off in the state of water, part cicatrices in the state of gas combined with a portion of carbons, and another portion of hydrogen unites with the azote of those plants which contain it, and forms ammonia. A fourth part remains behind, and communicates odour and colour to the residuary mass. The carbons combine partly with the discharged hydrogen, partly with the oxygen, forming carbonic acid, and part remains behind. The oxygen is divided between the hydrogen and carbons, forming compounds of which these elements are the base.

Sect. III. Of the Component Parts of Vegetables.

1. Having in the two former sections given a short view of the functions and spontaneous decomposition of plants, we are now to consider the nature and properties of those substances which enter into their composition. Some of these substances are obtained from plants, while they continue to exhibit the phenomena of vegetation; such are saccharine matters obtained from the sap, which is extracted by wounding the bark and wood, without much seeming injury to the health and growth of the plant; and such too are gummy and resinous matters, which many plants throw off by spontaneous exudation; and which, so far from being injurious, is perhaps necessary in some degree to vegetation; but, in general, the substances formed during the process of vegetation, or which are constituent parts of vegetable matters, can only be obtained by the destruction of the vegetable itself. These are procured by different processes, which we shall shortly describe, in treating of the nature and properties of each individual substance.

2. The component parts of vegetables, so far as they have been examined, and sufficiently characterized by distinct properties, may be enumerated under the following heads:

1. Gum, 2. Sugar, 3. Jelly, 4. Acids, 5. Starch, 6. Albumen, 7. Gluten, 8. Extractive matter, 9. Colouring matter, 10. Bitter matter, 11. Narcotic matter, 12. Oil I. Of Gum.

1. Gum exudes from many trees during the process of vegetation, in the form of a viscid, transparent, insipid fluid. The finer kind of gum is obtained chiefly from the *mimosa nilotica*, a plant which is very common in many parts of Africa. This gum is usually distinguished by the name of gum arabic. After it separates from the tree, the watery part evaporates, and the gum remains behind. It has then some degree of hardness, and is so brittle that it may be reduced to fine powder. It retains its transparency, is generally of a yellow colour; but, when pure, it is entirely colourless. It has neither taste nor smell. The specific gravity is from 1.316 to 1.481.

2. Gum is not changed by exposure to the air, but it is deprived of its colour by the action of the sun's light. When it is exposed to heat, it becomes soft, swells up, gives out air-bubbles, blackens, and is reduced to charcoal. During the change it gives out very little flame, and is greatly enlarged in volume. It readily dissolves in water. The solution is thick and adhesive, and well known as a paste, under the name of mucilage. This solution is little disposed to decomposition. By evaporation the whole of the gum may be obtained unchanged.

3. Gum is soluble in the vegetable acids without decomposition. Sulphuric acid decomposes it, and converts it into water, acetic acid, and charcoal. With the assistance of heat, muriatic acid produces a similar effect. Oxymuriatic acid converts it into citric acid.

Gum is soluble in nitric acid with the assistance of heat. Nitrous gas is emitted during the solution, and, when it cools, acetic acid is deposited. Malic acid appears at the same time; and by continuing the heat, the gum is at last converted into oxalic acid. Four hundred and eighty grains of gum digested with five ounces of nitric acid, afforded Mr Cruickshank 210 grains of oxalic acid, and five grains of oxalate of lime.

4. By pouring alcohol into a mucilaginous solution, the gum is precipitated, so that it is insoluble in this liquid. It is also insoluble in ether.

5. Mr Cruickshank distilled, 480 grams of gum arabic by exposing it to a red heat in a glass retort, and obtained the following products:

- Acetic acid mixed with some oil: 210 g. - Carbonated hydrogen and carbonic acid gases: 164 - Charcoal: 96 - Lime and a little phosphate of lime: 20

Thus the constituent parts of gum are, oxygen, hydrogen, carbone, azote, and lime.

6. Besides gum arabic, the properties of which we have now described, there are different species of gum obtained from different plants, which, however, in their constituent properties resemble gum arabic. In some instances they seem to be different, but these differences have not been distinctly ascertained. Gum tragacanth, the produce of the *Afragalus tragacantha*, which is in the plants of vermicular masses, is less transparent than gum arabic, less soluble in water, and more adhesive; but yields by distillation similar products. Gum obtained from the cherry and plum tree, is of a brownish colour, softer and more soluble in water, but seems otherwise to possess nearly the same properties as gum arabic.

7. Gum in the state of mucilage exists in a great number of plants, and especially in the roots and leaves, exits in It seems to be most abundant in bulbous roots, as those of the hyacinth, which contain such a quantity that they may be advantageously employed in place of gum arabic. It is obtained also in considerable quantity from many of the lichens, and most of the fuci. Mucilage is found in greatest proportion in young plants, but this proportion diminishes with the age of the plant. It is a principal constituent in the leaves and roots of esculent vegetables.

8. In the state of mucilage, gum constitutes a nutritious aliment. On account of its adhesive properties, it is employed as a paste, and by the calico-printers to mix with their colours to give them consistence. It is well known as a component part of ink, to prevent the precipitation of its more insoluble ingredients, and it forms a very valuable article in the Materia Medica.

II. Of Sugar.

1. Sugar exists in every part of plants. It is found in all parts of plants, as those of the carrot and beet root; in the stems, as in the birch, the maple, some palms, and especially the sugar-cane; in the leaves, as those of the ash; in the flowers, the fruits, and seeds.

2. But the sugar which now forms a very extensive article of commerce, and may be considered as a necessary of life, is entirely obtained from the juice of the sugar-cane, which is chiefly cultivated in the East and West Indies for the purpose of extracting the sugar. When the plants have arrived at their full growth, which in the West Indies is in the course of 12 or 14 months, they are cut down and bruised by means of machinery; the juice which is collected, is conveyed to iron boilers, where it is boiled, with the addition of a small quantity of quicklime, and the impurities which rise to the surface are scummed off. The boiling is continued till it acquires the consistence of syrup, after which it is put into shallow vessels, where it is allowed to cool and granulate. In general, it is afterwards put into hogheads, in which it is imported to Europe, the bottoms of which are perforated, that the molasses with which the sugar is mixed, may be allowed to drain off. Sometimes it is put into conical earthen vessels, open at both ends, the base of which is covered with moist clay, so that the water filters through the sugar, and carries with it a greater quantity of the molasses and other impurities. The fur... Component sugar thus treated, is called clayed sugar. It is not different from the former, but in being somewhat purer.

The addition of quicklime in the boiling is supposed to take up some vegetable acids which prevent the granulation of the sugar.

3. In this state the sugar is known in commerce by the name of raw Muscovado sugar. It is still farther purified by dissolving it in water, and boiling, when the impurities which rise to the surface are again removed; a quantity of lime is also added, and it is clarified with blood. When boiled down to a proper consistency, it is put into unglazed earthen vessels of a conical shape, and inverted, to allow the water from the moist clay with which the base of the cone is covered, to pass through the sugar, and carry off its impurities. It is still farther purified by again dissolving it in water, and subjecting it to a similar process. According to the number of processes to which it has been subjected, it is called single or double refined sugar.

4. Sugar in this state is of a white colour; it is well known for its sweet taste; it has no smell. It has some degree of transparency when it is crystallized. It is considerably hard; but it is brittle, and may be easily reduced to powder. It is phosphorescent in the dark. When the solution of sugar in water is concentrated, it crystallizes in the form of six-sided prisms, terminated by two-sided summits. The specific gravity of sugar is 1.4045.

5. When sugar is exposed to heat, it melts, swells up, becomes of a dark brown or black colour, emits air bubbles with a peculiar smell, which has been called caramel. If a red heat be applied, it suddenly bursts into flames, with a kind of explosion.

6. Neither oxygen nor azote have any action on sugar. It is not altered by exposure to the air. If the air be moist, it absorbs a little water. There is no action between hydrogen and sugar. It is very soluble in water; at too low a temperature as 48°, water dissolves its own weight of sugar. This power increases with the temperature of the water. When water is saturated with sugar, it is called syrup, which by concentration and rest affords crystals.

7. Sugar is soluble in many of the acids. It is decomposed by sulphuric acid; when heat is applied, the acid itself is decomposed, and converted into sulphurous acid; and a great quantity of charcoal is deposited.

Nitric acid acts on sugar with considerable violence; an effervescence is produced, nitrous gas is emitted; and the sugar is converted into oxalic and malic acids.

Muriatic acid gas is slowly absorbed by sugar, which becomes of a brown colour, and acquires a very strong smell. Sugar is instantly dissolved when it is thrown in the state of powder into liquid oxymuriatic acid; it is converted into malic acid, while the oxymuriatic acid is deprived of its oxygen, and reduced to the state of muriatic acid. Alcohol readily dissolves sugar. One part of sugar is soluble in four of boiling alcohol. Sugar also combines with the oils, and by this means they may be mixed with water.

8. The fixed alkalies combine with sugar, and deprive it of its sweet taste; but by adding sulphuric acid, and precipitating the sulphate which is formed by means of alcohol, the taste is restored. Some of the earths, as lime, combine with sugar, and form similar compounds.

9. The sulphurets, hydro-sulphurets, and phosphurets of the alkalies and some of the earths, decompose sugar, and reduce it to a state somewhat similar to gum. Sulphuret, Mr Cruickshank dissolved a quantity of sugar in alcohol, and added to it phosphuret of lime. After exposing the mixture to the open air for some days, it was evaporated, and water was added. There was no evolution of gas, and the phosphuret was found converted into a phosphate. By filtering the liquid, and by evaporation, a tenacious substance, resembling gum, remained behind.

10. By distilling sugar in a retort, the first part of the product is water, nearly in a state of purity. Acetic acid with a little oil next comes over, and afterward empyreumatic oil. A bulky carbonaceous matter, which sometimes contains a little lime, remains behind. Mr Cruickshank obtained by the distillation of 480 grains of pure sugar, by means of a red-heat,

| Acetic acid and oil | 270 grs. | | Charcoal | 120 | | Carbonated hydrogen and carbonic acid gases | 90 |

Sugar, therefore, is composed of oxygen, carbene, and hydrogen. The proportions of its constituent parts, according to Lavoisier, are the following:

| Oxygen | 64 | | Carbene | 28 | | Hydrogen | 8 |

100

11. Sugar is also obtained from the juice of the maple tree in North America. The juice is extracted sugar from the tree during the ascent of the sap in the spring season. A single tree, it is said, yields from 20 to 30 gallons of sap, from which are contained five or six lbs. of sugar. It is manufactured in the same way as the juice of the sugar-cane.

It has lately been proposed to extract sugar from the root of the beet; and the attempt has been made, even in the large way, by Achard of Berlin. The process which he followed is to boil the roots, cut them into slices, and extract the juice by pressure. The roots are again put into water for 12 hours, and again subjected to the press. The liquids thus obtained are filtered through flannel, boiled down to 3, and filtered a second time. The remaining liquid is reduced by boiling to 1 of the original quantity, and again filtered. It is then evaporated to the consistence of syrup. The crust which forms on the surface must be broken from time to time, and the spontaneous evaporation allowed to continue till the surface is covered with a viscid pellicle, instead of the crystals which first form on it. The whole mass is then introduced into woollen bags, and the mucilage is separated by pressure. This sugar, which in many respects possesses the properties of common sugar, is contaminated with some matter, which communicates a bitter nauseous taste. Many other plants also contain sugar, either in the roots, the sap, or the seeds. It exists in wheat, barley, beans, pease, Component parts of vegetables, and other leguminous seeds, especially when they are young, in considerable quantity.

12. The uses of sugar are so familiar, that it is scarcely necessary to enumerate them. In most countries where it can be obtained, it may be considered in some measure as a necessary of life. It contains a great proportion of nutritious matter. It is not changed by the action of the air, so that it may be preserved for any length of time. It is employed to preserve other vegetable matters from putrefaction, and sometimes it is also advantageously applied to a similar purpose, in the preservation of animal substances.

III. Of Jelly.

1. Jelly is a soft tremulous substance which is obtained from the juice of different fruits, especially from currants and bramble berries. The juice is extracted by expression, and when it is allowed to remain at rest, it coagulates. It is still mixed with a portion of aqueous liquid; but this being poured off, and the coagulated part washed with water, the jelly remains nearly pure.

2. It is sometimes perfectly colourless, but frequently tinged with the colouring matter of the fruit. It is of a soft, tremulous consistence, and has an agreeable, slightly acid taste. It dissolves readily in hot water, and again coagulates on cooling. In cold water it is nearly insoluble. It is deprived of the property of coagulating by boiling, and then it is similar to mucilaginous matter.

3. By coagulating the juices of the fruits which yield jelly, separating the liquid parts by filtration, afterwards washing the coagulum with cold water, and by allowing the mass to dry, it is found diminished in bulk, and is transparent and brittle, having many of the properties of gum; so that it has been supposed that jelly is this latter substance in combination with some vegetable acid.

4. Jelly is converted into oxalic acid by means of nitric acid. It combines readily with the alkalies; and when it is distilled, it yields a considerable portion of acetic acid mixed with oil, but no perceptible quantity of ammonia. Jelly is found in all the acid fruits, as in gooseberries, oranges, and lemons.

IV. Of Acids.

1. The acids which exist in many vegetables are at once recognized by their taste. These acids were formerly denominated essential salts of vegetables, and it was supposed, that all essential salts were the same, and were composed of tartar, or vinegar. But Scheele's discovery of the citric, malic, and gallic acids, which possess distinct properties from those of tartaric and acetic acids, proved the contrary. Some vegetables contain only one acid, as oranges and lemons, which contain citric acid only. In other vegetables two acids are found, as in gooseberries and currants, the malic and citric acids; and sometimes three, as the tartaric, citric, and malic acids, which exist together in the pulp of the tamarind. As the acids which exist in vegetables have been already described, with the method of preparing them, it is now only necessary to enumerate the vegetable acids, specifying at the same time some of the plants from which they are obtained.

2. Acetic acid has been discovered in the sap of some trees, and in the acid juice of cicer arietinum. In the latter it is mixed with oxalic and malic acids. Acetic acid was detected by Scheele in the sambucus nigra or elder.

3. Oxalic acid exists in combination with potash, in the leaves of the oxalis acetosella or wood-foxtail. In other species belonging to the same genus, and in some species of rumex, it is in the state of acidulous oxalate of potash. Oxalate of lime has been found in the root of rhubarb.

4. The following vegetable substances contain tar-Tartaric acid; in which, however, it is combined with potash, in the state of acidulous tartrate of potash. In this state it is found in the pulp of the tamarind, the juice of grapes, of mulberries, of rumex acetosa or sorrel, of rheum raponticum, or rhubarb, and of agave americana. It is found also in the roots of tritium repens, or couch-grass, and in leontodon taraxacum, or dandelion.

5. Citric acid is found in the juice of oranges and lemons, in the berries of two species of vaccinium, the oxyococos or cranberry, and the vitis idea or red whortleberry, the prunus padus, or bird-cherry, solanum dulcamara, bitter-sweet, or nightshade, rofa canina, or wild rose.

6. Malic acid exists unmixed with other acids, in Malic, the apple, the barberry, plum, floe, elder, rowan, or fruit of the mountain ash.

In the gooseberry, in the cherry, strawberry, currants, and some other fruits, malic and citric acids are found nearly in equal proportions.

Malic acid has been found mixed with tartaric acid in the agave americana, and in the pulp of tamarinds, along with citric acid. Vauquelin found it combined with lime, forming a malate of lime, in the sempervivum tectorum or house-leek; in three species of sedum or stone-crop, namely the album, acre, and telephium; in different species of crassula and mesembryanthemum, and in arum maculatum.

7. Gallic acid is found in a great number of plants, Gallic, and in them it exits chiefly in the bark. The following are the relative proportions of the quantity of gallic acid in different plants, as they have been ascertained by Mr Biggin.

| Plant | Quantity | |----------------|----------| | Elm | 7 | | Oak cut in winter | 8 | | Horse-chestnut | 6 | | Beech | 7 | | Willow boughs | 8 | | Elder | 4 | | Plum-tree | 8 | | Willow trunk | 9 | | Sycamore | 6 | | Birch | 8 | | Cherry-tree | 4 | | Sallow | 8 | | Mountain ash | 8 | | Poplar | 8 | | Hazel | 9 | | Ash | 10 | | Spanish chestnut | 10 | | Smooth oak | 10 | | Oak cut in spring | 10 | | Huntingdon or Leif | 10 | | Celer willow | 10 | | Sumac | 14 |

8. Benzoic acid is found in benzoin, balsam of To-Benzoic, lu and Peru, liquid flyrax, cinnamon, and vanilla. Fourcroy and Vauquelin suspect that it exists in the anthoxanthum odoratum, or sweet-scented grass, which communicates the aromatic flavour to hay. Component 9. Prussic acid has been found in the leaves of the Parts of laurocrafus and peach, in bitter almonds, in the Vegetables kernels of apricots; and it is supposed that it exists also in the kernels of peaches, of plums, and cherries.

Prussic. It is obtained from the kernels of apricots by distilling water off them with a moderate heat; and if lime be added to the concentrated infusion of bitter almonds, a prussiate of lime is formed.

Phosphoric. 10. Phosphoric acid has been found in different parts of plants; but it is generally combined with lime, forming a phosphate of lime. This salt exists in the leaves of many trees, in the aconitum napellus, or monks-hood, and in all kinds of grain.

V. Of Starch.

1. If a paste be formed of wheat flour and water, and this be washed with additional quantities of water, till it is no longer turbid, but comes off pure and colourless, the mass which remains becomes tenacious and ductile. This is called gluten, which will be afterwards described. If the water with which the paste was washed be allowed to remain at rest, it deposits a white powder, which is distinguished by the name of fecula or starch.

2. Starch is of a fine white colour, and is usually in the state of concrete columnar masses. It has no perceptible smell, and scarcely any taste. It is little altered by exposure to the air; when it is exposed to heat on a hot iron, it melts, swells up, becomes black, and burns with a bright flame. The charcoal which remains, contains a little potash. When it is distilled, it gives out water mixed with acetic acid, which is contaminated with oil. It gives out also carbonic acid and carbonated hydrogen gas.

3. Starch is not soluble in cold, but forms a thick paste with boiling water, and when this paste is allowed to cool, it becomes semitransparent and gelatinous; it is brittle when dry, somewhat resembling gum. If this paste be exposed to moist air, it is decomposed, for it acquires an acid taste.

4. Sulphuric acid dissolves starch slowly; sulphurous acid is dilengaged, and a great quantity of charcoal is formed.

Muriatic acid also dissolves starch, and the solution resembles mucilage of gum arabic. When left at rest, a thick, oily, mucilaginous liquid appears above, and a transparent straw-coloured fluid below. The odour of muriatic acid remains; but when water is added, it is destroyed, and a strong peculiar smell is emitted.

Starch is also soluble in nitric acid, with the evolution of nitrous gas. The solution assumes a green colour, and when heat is applied, the starch is converted into oxalic and malic acids. Some part of the starch, however, is insoluble in nitric acid, and when this is separated by filtration, and washed with water, it has a thick oily appearance like tallow, is soluble in alcohol, and when distilled, yields acetic acid, and an oily matter similar to tallow in colour and consistence.

5. Starch is insoluble in alcohol, but is soluble in the alkalies; impure potash if swells up, becomes transparent and gelatinous, and is then susceptible of solution in alcohol. The component parts of starch, as appears by distilling it, and by the action of re-agents, are oxygen, hydrogen, and carbon.

6. Starch exists in a great number of vegetable substances, but chiefly in the roots and seeds, and particularly those which are employed as food.

Starch, it is well known, may be obtained from the potato. If the potato be grated down and washed with water till it comes off pure and colourless, this water roots and being left at rest, deposits a fine white powder, which assumes something of a crystallized appearance, and is heavier than wheat starch.

Sago, which is well known on account of its nutritious qualities, is obtained from the pith of different species of palms which grow within the tropics. The stem is cut into pieces, which are split into two; the pith is washed out with cold water, which being left at rest deposits the starch. The water is poured off, and before the remaining mass is fully dried, it is forced through a perforated vessel, and granulated, in which state it is brought to Europe.

Saloup, which is chiefly composed of starch, is prepared from the roots of different species of orchis. It is mostly imported from Persia.

Caffava, or caffada, is a kind of bread chiefly composed of starch, which is much used as an article of food in the West Indies. It is prepared from the roots of the jatropha menihot. The roots are well washed, grated down, and put into bags, which are subjected to strong pressure. By this process the whole of the juice is separated. This juice, or something at least which it holds in solution, when taken internally, is a deadly poison to most animals. The matter remaining in a bag is dried and sifted, and without any other addition, when it is spread thin on a hot stone, it forms a cake, which is the caffada bread, found to be of a very nutritious quality, in consequence of the great proportion of starch which it contains.

Some species of the tribe of lichen contain a considerable proportion of starch, as the lichen rangiferinus, or rein-deer lichen, which affords food to the rein-deer, and the lichen illandicus which is formed into bread by the Icelanders, and is found to be extremely nutritious. The latter has lately been recommended as a remedy in consumption; but it probably possesses no other virtue in the cure of that fatal disease, than affording a great proportion of nutritious matter in small bulk.

VI. Of Albumen.

1. The existence of albumen in vegetable substances had begun to be doubted by chemists, till it was lately discovered, by Vauquelin, in the juice of the carica papaya, or papaw-tree, which grows in different countries within the torrid zone. The juice which exudes from this tree, was brought home in the liquid state, mixed with an equal quantity of rum, and another portion of the juice was in the state of extract. The first was of a reddish brown colour, was semitransparent, and had the odour and taste of boiled beef. The second was of a yellowish white colour, semitransparent, and of a sweetish taste; had no perceptible smell, but was of a firm consistence, and in the form of small irregular masses. When the dried portion was macerated in cold water, it was almost entirely dissolved. When nitric acid was added, a copious white precipitate was formed. This was the albumen in the state VII. Of Gluten.

1. When a paste is formed with flour and water, and washed with more water till it pastes off pure and colourless, a tenacious, ductile, soft, elastic mass remains behind, which is gluten.

2. This substance is of a gray colour, extremely ductile and tenacious, and possesses considerable elasticity. It has a peculiar smell, but no perceptible taste. When it is suddenly dried, it increases much in volume, and, when it is exposed to heat, it cracks, swells, blackens, and burns like horn, exhaling a fetid odour. When it is distilled, it yields water impregnated with ammonia, and an empyreumatic oil; charcoal remains behind. When moist gluten is exposed to the air, it gradually dries, becomes hard, brittle, slightly transparent, and of a brownish colour, having some resemblance to glue. When it is broken, it resembles the fracture of glass. It is insoluble in water, but retains a portion of it, which it absorbs, and to which the elasticity and tenacity are owing. It is deprived of these properties by boiling.

3. When it is kept moist, it ferments with the evolution of hydrogen and carbonic acid gases. An offensive putrid odour is given out at the same time. The gluten afterwards, if the process be allowed to go on, exhales the smell, and acquires the taste of cheese. In this state it is found to contain ammonia and acetic acid.

4. Gluten is soluble in all the acids. It is precipitated from this solution by all the alkalis, and is then nearly in the state of extractive matter, being deprived of its elasticity. It is decomposed by concentrated sulphuric acid; hydrogen gas is emitted, and water, charcoal, and ammonia are formed. It is also decomposed by nitric acid; azotic gas is emitted, and if the heat be continued, a portion of oxalic acid is formed. Yellow coloured oily flakes are precipitated. After gluten is fermented, it is soluble in acetic acid, and this solution may be employed as a varnish.

5. Gluten is insoluble in alcohol and in ether; but if fermented gluten be triturated with a little alcohol, and afterwards mixed with a quantity of the same liquid, part of it is dissolved and forms a varnish, which may be employed either for paper or wood, for cementing china, or for mixing with vegetable colours that are used as paints. Pieces of linen dipped in this varnish, adhere strongly to other bodies, and if lime be added to the solution, it constitutes a good glue.

6. With the assistance of heat gluten is soluble in the alkalies; and when they are much concentrated it is decomposed, and formed into a kind of soap, consisting of oil and ammonia.

7. It appears from the distillation of gluten, and from its spontaneous decomposition, that it consists of oxygen, hydrogen, carbure, and azote. The vapour which is evolved during the fermentation of gluten, blackens silver, from which it is inferred that sulphur is one of its constituent parts. From the properties and composition of gluten, the resemblance between this substance and animal matter is sufficiently obvious.

8. Gluten exists in greatest abundance in wheat flour, but it is found in a great number of plants, and in different parts of vegetables. It exists in considerable proportion in the juice of the leaves of many plants, as those of the cabbage, cresses, &c. When this juice is procured by expression, filtered through a cloth, and allowed to remain at rest, it deposits in the course of some days, a greenish powder, which has been called the green fecula of plants. This fecula is chiefly composed of gluten mixed with a resinous matter, which gives it its colour, and a portion of woody fibre. If this juice be exposed to the temperature of about 130°, the fecula coagulates in the form of large flakes. It dries when separated from the water, and assumes the appearance of horn. When it is treated like gluten, it also acquires the smell and taste of cheese.

Gluten has been found in acorns, chestnuts, and horse-chestnuts, in barley, rye, peas, and beans; in apples, fruits, and quinces; in the leaves of sedum of different species, hemlock, borage, saffron; in the petals of the rose, in the berries of the elder, and in the grape. None was detected in the potato by Proust, although he found it in several other roots.

A substance which resembles the fibrina of the blood, was found by Vauquelin in the juice of the pawpaw tree. When this juice is mixed with water, part is dissolved, and part remains insoluble. The latter has a greyish appearance, becomes soft in the air, viscid, brown, and semitransparent. It melted when thrown on burning coals, while drops of grease exuded. It was entirely consumed, without leaving any residuum. But according to some, this substance is exactly similar to gluten, and therefore, is not to be considered as one of the constituents of vegetable matter.

9. Gluten is one of the most important of the component parts of vegetable substances. It is one of the chief ingredients in wheat, and to this it is owing that wheat flour is fit for being formed into bread.

VIII. Of Extractive Matter.

1. The word extract was formerly employed to signify the infusorial juices of vegetables, but of late it has been limited to a peculiar principle possessed of distinct properties. If saffron be infused in water for some time, and if the infusion be filtered and evaporated to dryness, the residuum is that substance to which the name of extractive principle is given.

2. The following properties of extract were ascertained by Vauquelin. 1. All extracts have an acid taste. 2. If a few drops of ammonia be added to a solution of extract, a brown precipitate is formed, which consists of lime, and part of the extract becomes insoluble. 3. Sulphuric acid engenders a penetrating acid vapour, which is found to be acetic acid. 4. When quicklime Component quicklime is added to a solution of extractive matter. Parts of ammonia is disengaged. A solution of sulphate of alumina without excess of acid, being poured into a solution of extractive matter, and boiled, there is formed in the liquid a flaky precipitate which is composed of alumina and vegetable matter, and rendered infusible in water. 6. Almost all metallic solutions produce a similar effect. With muriate of tin an infusible brown precipitate is formed, which is composed of the oxide of tin and vegetable matter. 7. Oxymuriatic acid poured into a solution of extractive matter, forms a copious, dark yellow precipitate. Muriatic acid remains in the solution. 8. If wool, cotton, or thread, be impregnated with alum, and boiled with a solution of extractive matter, these substances become charged with a great quantity of the extractive substance, they assume a fawn-brown tint, and the solution loses a great deal of its colour. The same effect is produced by immersing the substances to be dyed in a solution of muriate of tin. The effect is still better, if oxymuriatic acid be employed instead of alum, or the solution of muriate of tin. 9. When extractive matter is distilled in an open fire, it yields an acid liquid, which contains a greater portion of ammonia than when it is distilled in the humid way with lime or alkaline. 10. When extractive matter is dissolved in water, and is left exposed to the open air, it is completely decomposed. The carbonates of potash, of ammonia, and of lime, and some other mineral salts which previously existed in the extractive matter, and are indestructible by putrid fermentation, remain behind.

3. It appears that extractive matter is found in greater proportion in old plants. It is found in different parts of the plant. It frequently forms one of the constituents of the sap. It is this extractive matter which precipitates during the evaporation of the sap, or when oxymuriatic acid is added to it.

Extractive matter has been found in the bark of many trees, and it is supposed that it exists in all barks which possess an astringent property. It has been found in the bark of the common willow, the Leicestershire willow, the oak, and the elm.

Extractive matter has been obtained from the infusion of catechu, in which it is united with tan. If the powder of catechu be repeatedly washed with water, the liquid which passes off no longer precipitates gelatine. The residuum is extractive matter, of a reddish-brown colour, has no smell, but a slightly astringent taste. The solution in water is at first yellowish-brown, but acquires a red colour by exposure to the air. Many of the metallic salts form a precipitate with the solution of this matter. Linen boiled in it almost extracts the whole, and becomes of a light red brown colour. Extractive matter softens when exposed to heat; the colour becomes darker, but it does not melt. When it is distilled, it yields carbonic and carbonated hydrogen gases, acetic acid, and a small portion of extractive matter unchanged. A light porous charcoal remains behind.

The infusion of the leaves of senna is of a brown colour, has a peculiar aromatic odour, and a bitter taste. When the air of the atmosphere or oxygen gas is made to pass through this infusion, a yellow coloured precipitate is formed. It is produced also by adding to the solution muriatic or oxymuriatic acid. In this state the extractive matter has combined with oxygen, and has assumed a yellow colour, and being no longer soluble in water, it is precipitated. The taste is slightly bitter. It is soluble in alcohol, but when water is added, it is thrown down. It is soluble also in alkalies, and forms with them a deep brown solution. When placed on burning coals, it gives out a dense smoke, exhales an aromatic odour, and leaves behind a fleshy mass of charcoal.

Extractive matter is obtained from the infusion of Peruvian bark, which being united with oxygen, becomes of a fine red colour. It is obtained by boiling water on it, and by slow evaporation, and then dissolving what remains in alcohol. By evaporating the alcohol, the peculiar extractive matter is deposited. The matter thus obtained was of a brown colour, of a bitter taste, soluble in hot water and alcohol, but insoluble in cold water. It is of a black colour when dry, and brittle. It breaks with a polished fracture. With the addition of lime-water it was precipitated in the form of a fine red powder, which combined with alkalies, but is insoluble in water and alcohol.

IX. Of Colouring Matter.

1. Colouring matter is extracted from a number of plants for the purposes of dyeing, as from madder, carthamus, brazil wood, logwood, yellow weed or redia plants, luteola, tufic or yellow-wood, annatto, and indigo.

2. The colouring matter of madder or rubia tinctorum, is soluble in alcohol. By evaporation it leaves a residuum of a dark red colour. A violet precipitate is formed in this solution by a fixed alkali. Sulphuric acid produces a fawn-coloured precipitate, and sulphate of potash, a beautiful red. Precipitates of different shades of colour are obtained with alum, nitre, chalk, acetate of lead, and muriate of tin.

3. Carthamus (tinctorius) contains two colouring matters, the one yellow and the other red. The first only is soluble in water, but the solution is turbid. It becomes transparent with the addition of acids; with alkalies it inclines to an orange colour; a fawn-coloured precipitate is formed, and then the solution becomes clear. Alum produces a dark yellow precipitate, but not very copious. A slight tincture is extracted from the flowers of this plant by means of alcohol, after the whole of the yellow matter has been dissolved by water.

4. Brazil wood, or fernambouc, is much employed in dyeing. A recent decoction of this wood gives a wood-red precipitate inclining to fawn colour with sulphuric acid. The liquid in which the solution was made remains transparent and of a yellow colour. With the first addition of nitric acid the tincture first passes to a yellow colour; but with a greater quantity, becomes of a dark orange yellow and transparent, after having depoited a matter similar in colour to the former, but more copious. The same changes take place with the muriatic acid as with the sulphuric.

5. Logwood or Campeachy wood yields its colouring matter to water and to alcohol, but more copiously to the latter. The tincture of logwood, or the solution in alcohol, is of a beautiful red colour, inclining to violet or purple. These different shades are more obvious in the decoction in water. When the aqueous solution is Component left to itself, it first becomes yellow, and then changes to black. The addition of acids produces a yellow colour; alkalies deepen the colour and restore the purple or violet. Sulphuric, nitric, and muriatic acids throw down a light precipitate which separates slowly. Sulphate of iron communicates a bluish colour somewhat resembling ink. A copious precipitate of a similar colour is formed at the same time.

6. Yellow weed, or dyers weed (refeda latroba, Lin.) in solution in water yields a yellow colour inclining to brown. When it is diluted with a greater quantity of water, the yellow colour which was more or less bright changes a little to green. The colour becomes paler with the addition of acids. It becomes deeper by the action of alkalies.

7. Fustic, or yellow wood (morus tinctoria, Lin.) contains a great proportion of colouring matter. A strong decoction in water is of a dark reddish yellow colour. When water is added to this solution the colour becomes orange-yellow. The liquid grows turbid with the addition of acids. Alkalies render it much deeper and nearly red.

8. Anatto is in the form of a dry hard paste, externally brown, and internally of a beautiful red colour. It is prepared from the seeds of the bixa orellana by reducing them to powder, mixing them with water, and allowing them to ferment. Anatto is more soluble in alcohol than in water. With the addition of an alkali the solution is promoted, and the colour inclines less to red.

Beside these, a great variety of other vegetable substances give out their colouring matter to water or alcohol, and are employed in dyeing. To what has now been said, however, we shall only add a short account of one of the most important, namely indigo.

9. Indigo is a colouring matter which is obtained from several plants, and has some resemblance to fucus or starch. The indigo of commerce is chiefly obtained from the indigofera tinctoria, a shrubby plant which is cultivated in the East and West Indies, for the purpose of extracting the colouring matter.

10. When the indigo plant has arrived at maturity, it is cut down, and conveyed to large wooden vessels, where it is covered with water, and soon commences a fermentation. When the plant is cut down at the period of its maturity, it produces a more beautiful colour, but in smaller quantity. If it be too late, the quantity is still diminished, and the indigo is of a bad quality. The putrefactive process soon commences, and succeeds best about the temperature of 80°. The water becomes turbid, and of a green colour. The smell of ammonia and carbonic acid gas are evolved. The fermenting process is finished in the period of from 6 to 24 hours, according to the temperature and state of the plant. The liquid is then poured off into flat vessels, in which it is constantly agitated till blue flakes appear. With the addition of a quantity of lime-water these flakes precipitate to the bottom. A yellowish liquid is poured off, and the blue precipitate is collected in linen bags, from which the water drains off. When the matter in the bag has acquired sufficient consistence, it is formed into small cakes, which are slowly dried in the shade. This is the indigo of commerce.

11. Indigo may be also extracted from the neriun tinctorium, or rosebay, a plant which grows in abundance in the East Indies, from the leaves of which Dr. Roxborough extracted it, by the following process. He digested the leaves in a copper vessel with water, from other kept at the temperature of 165° till they assumed a plants yellowish colour. The liquid becomes of a deep green; it is then poured off, and with the addition of lime-water is agitated till the indigo is precipitated. To produce one pound of indigo, two or three hundred pounds weight of green leaves were found necessary; but this quantity varies according to the season and state of weather in which they are collected.

12. The jatis tinctoria, or woad, which is a British plant, also yields indigo, by treating it in the same way as the indigo plant.

13. The history of indigo is curious. It was early known in India, but its value as a dye-stuff was not of indigo, understood in Europe before the middle of the 16th century. But what is most singular, the use of this substance was either restricted or entirely prohibited in different countries, from some prejudice that its effects in dyeing were injurious. The use of it was prohibited in England from the time of Queen Elizabeth till the reign of Charles II. It was also prohibited in Saxony. It is described in the edict as a corrosive substance, and denominated food for the devil! In France during the administration of Colbert, the dyers were restricted to the use of a certain quantity. For some time after, indigo was generally employed as a dye stuff in Europe, and was chiefly cultivated in the West Indies, and some parts of the American continent. This indigo was generally preferred in the market. What is now cultivated in the East Indies is found to be equal in quality.

14. Indigo is a light, friable substance, of a compact texture, and a deep blue colour. The shade varies from copper, violet, and blue tints. The lightest indigo is the best. It is always contaminated with extraneous matters. Bergman found in the purest indigo which he could procure, the following component parts.

| Component | Percentage | |-----------------|------------| | Pure indigo | 47 | | Gum | 12 | | Resin | 6 | | Barytes | 10.2 | | Lime | 10.0 | | Silica | 1.8 | | Oxide of iron | 13.0 |

100.0

Other earths have been found in indigo. In some specimens Proult detected magnesia.

15. Pure indigo is a soft powder of a deep blue colour, which has neither taste nor smell. When exposed to heat, it emits a bluish red smoke, and then burns away with a faint white flame. The earthy part remains behind in the state of ashes. It undergoes no change by exposure to the air. It is infusible in water, but if kept some time under it, a fetid odour is exhaled, owing to some change.

16. Diluted sulphuric acid poured upon indigo dif- Component solvcs only the earthy and mucilaginous matters; but if concentrated sulphuric acid be added, in the proportion of eight parts of acid to one of indigo, the latter is dissolved with the evolution of heat, in about 24 hours. The mixture is black and opaque; but if water be added, it becomes clear, and of a fine blue colour, producing various shades, according to the quantity of water. This solution of indigo in sulphuric acid is called liquid blue, or according to Bancroft, sulphate of indigo.

Bergman made a great number of experiments on the effect of different substances on this solution, some of which we shall now mention, in which the colour was either changed, or entirely destroyed. When it was dropped into sulphurous acid, the colour which was at first blue, became green, and was at last destroyed. In diluted tartaric acid the colour became gradually green, and was at last converted into a pale yellow. In acetic acid it became green, and was at last destroyed. In potash, carbonate of potash, soda, ammonia and its carbonate, the colour became green, and at last disappeared. In sulphate of soda, the solution being diluted, after some time became green. It also became green in sulphate of iron, and at last disappeared. In the sulphurets the colour was very soon destroyed. Black oxide of manganese produced the same effect. These experiments have been mentioned, to show that indigo is deprived either partially or totally of its colouring matter, by those substances which have a strong affinity for oxygen. From this it is inferred that indigo owes its colour to oxygen; and that it becomes green when it is deprived of it.

Nitric acid. Concentrated nitric acid attacks indigo with such violence, that it sometimes inflames it. By diluting the acid, the action is greatly moderated. The solution becomes of a brown colour; crystals appear, which are supposed to be oxalic acid, and a brown viscid substance remains behind.

Muriatic acid dissolves indigo precipitated from sulphuric acid, and forms a liquid of a dark-blue colour. The other acids, as the phosphoric, acetic, and tartaric, exhibited similar phenomena. They readily dissolve indigo, which has been precipitated.

Oxymuriatic acid has little action on indigo in substance, but it destroys the colour of it in the state of solution.

Alkalies. 17. Neither alcohol, ether, nor oils, have any action on indigo. Common indigo, when digested with alcohol and ether, communicates a yellow colour; but this, it is supposed, is owing to the solution of the resinous substance.

18. The solution of the fixed alkalies readily dissolves indigo, when it is precipitated from its solution. The colour of the solution is at first green, and is at last destroyed. Liquid ammonia and its carbonate produce a similar effect, from which it appears, that indigo is decomposed by the alkalies.

19. Lime water also dissolves indigo precipitated from its solution. The colour is at first green, becomes gradually yellow; when exposed to the air, the green returns, and at last disappears.

20. Bergman subjected indigo to the process of distillation; from 576 grains he obtained the following products:

| Component | Parts of Vegetables | |-----------|---------------------| | Carbonic acid gas | 19 | | Yellow acid liquid containing ammonia | 173 | | Oil | 53 | | Charcoal | 33 |

The component parts of indigo, therefore, appear to be oxygen, carbons, hydrogen, and azote.

X. Of Bitter Matter.

1. A great number of vegetable substances are distinguished by a very bitter taste, such as quassia, a sub-substance used in medicine, gentian, hops, chamomile. This taste is ascribed to a peculiar matter, called from this property bitter matter. It may be obtained by infusing quassia for some time in water. This solution, which is of a yellow colour, has an extremely bitter taste, but no smell. If the water be evaporated with a moderate heat to dryness, a brownish yellow substance, which has some degree of transparency and ductility, remains behind. After some time it becomes brittle.

2. When this substance, which has a very bitter taste, and a brown yellowish colour, is heated, it softens, swells, and blackens, then burns away without much flame, and leaves a small quantity of ashes. It is very soluble in water and alcohol. Nitrate of silver renders it turbid, and afterwards produces a yellow precipitate in the form of flakes. Acetate of lead produces a copious white precipitate.

XI. Of Narcotic Matter.

1. A peculiar substance has been detected in opium, found in which it is supposed the properties it possesses of producing sleep, are owing. On account of this property this substance has received the name of narcotic matter. It is obtained from the milky juices of some plants, as those of the poppy, lettuce, and some others. Opium, which is extracted from the poppy, is prepared by the following process.

The heads of the papaver album or white poppy, which is cultivated in India and different countries of opium, the cask for this purpose, are wounded with a sharp instrument; a milky juice flows out, which concretes, and is collected and formed into cakes.

2. In this state opium is a tenacious substance, of a brownish colour, has a peculiar smell, and a disagreeable bitter taste. It becomes soft with a moderate heat. It readily takes fire, and burns rapidly. By the analysis of opium, it appears to be composed of the sulphates of lime and of potash, extractive matter, gluten, mucilage, resinous matter, and an oil, besides the narcotic matter to which its peculiar properties are owing.

3. By digesting opium in water, part of it is dissolved, and by evaporating the solution to the consistence of syrup, a gritty precipitate appears, which becomes more copious with the addition of water. This precipitate is composed of resinous and extractive matter, besides the peculiar narcotic matter which is crystallized. When alcohol is digested on this precipitate, the resinous and narcotic matters are dissolved, and the Component the extractive matter remains behind. As the solution cools, the narcotic matter crystallizes, but the crystals are coloured with a portion of resin. By repeated solutions and crystallizations it may be obtained tolerably pure.

If alcohol be digested on the residuum, it becomes of a deep-red colour; the same crystals are depoited on cooling, and may be purified in the same way from the resinous matter with which they are contaminated.

4. The narcotic matter, or, as it is called by Derofine, the essential salt of opium, when properly purified, is of a white colour, crystallizes in right-angled prisms, with a rhomboidal base, and has neither taste nor smell. It is insoluble in cold water, and requires 400 parts of boiling water for its solution, from which it is precipitated by cooling. The solution does not redden the tincture of turpentine. It is soluble in 24 parts of boiling alcohol, and requires about 100 parts when it is cold. When water is added to the solution in alcohol, it is precipitated in the form of a white opaque matter.

Ether and the volatile oils dissolve this salt with the assistance of heat; but on cooling it is deposited in the form of an oily liquid, and some time after crystals appear at the bottom of the vessel.

5. One of the most decided characters of this substance is its easy solubility in all the acids, and without the aid of heat. It is precipitated from these solutions by means of an alkali, in the form of white powder. Pure alkalies increase the power of its solubility in water; and the acids, when not added in excess, occasion a precipitate. When nitric acid is poured on the crystals reduced to a coarse powder, it communicates to them a red colour, and readily dissolves them. When the solution is heated and evaporated, it yields crystals of oxalic acid in considerable quantity. The residuum has a very bitter taste.

6. When it is thrown on burning coals, it gives out a copious flame. When heated in a spoon, it gradually melts like wax. Distilled in a retort with a moderate heat, it melts, and afterwards swells up, with the evolution of white vapours, which condense on the sides of the vessel, in the form of a yellow oily matter. There passes over, at the same time, a little water impregnated with carbonate of ammonia. Towards the end of the process, carbonic acid and carbonated hydrogen gas, with some ammonia, are disengaged. There remains in the retort a light, spongy, voluminous mass of charcoal, which, by burning, gives some traces of potash. The oily matter deposited in the neck of the retort is very viscid, and has a strong aromatic odour, with a pungent, acrid taste.

7. Derofine tried the effects of this substance on animals, and in very small quantity. The symptoms which appeared, when it was given to dogs, were exactly similar to those which are produced, when a large quantity of crude opium is swallowed. They were recovered from its effects by means of vinegar, which he accounts for on the principle of the easy solubility of this substance in acids.

8. From the effects of heat and of nitric acid on this substance, it appears to be composed of oxygen, hydrogen, carbons, and azote.

9. This narcotic substance is also found in the milky juice, and in the extracts which are obtained from several other plants, as from different species of lactuca or lettuce, hyoscyamus niger, or henbane. The leaves of some plants also produce similar effects, as those of the deadly nightshade, foxglove, and conium maculatum or hemlock.

XII. Of Oils.

1. The nature, properties, and component parts of Fixed oils, have already been detailed, when treating of inflammable substances. Oils are of two kinds, fixed and volatile. Fixed oil exists chiefly in the seeds of plants, as linseed oil, almond oil, and rape-seed oil. Fixed oil is also found in the pulp of some fruits, as in that of the olive. Fixed oils are found in those seeds which have double lobes, or two cotyledons, and in these they are mixed with a quantity of mucilage. These oils are extracted from seeds by expression and boiling.

2. Volatile oils are found in all parts of plants, excepting the seeds. In some plants they exist in the root, or the stem, and in others in the leaves, the flower, the pulp and rind of the fruit. The peculiar odour by which almost all plants are distinguished, is supposed to be owing to a volatile oil. These oils are also extracted by expression, and sometimes by distillation.

XIII. Of Wax.

1. Wax, of which bees form their combs for containing honey, is collected from vegetables; and a similar substance being found in different parts of plants, it is to be considered as vegetable matter. The varnish with which the upper surface of the leaves of some trees is covered, possesses the properties of bees wax. If the bruised leaves are digested in water, and afterwards in alcohol, till the soluble part is extracted, and the residuum be mixed with six times its weight of a solution of ammonia, and after maceration, the solution being poured off and filtered, diluted sulphuric acid be added in excess to saturate the alkali, constantly stirring it, the varnish precipitates in the form of a yellow powder. It is then to be washed with water, and melted with a moderate heat. This substance is wax.

2. Pure wax is of a white colour, has no taste, and scarcely any smell. The aromatic smell of bees wax is owing to some substance with which it is mixed, for it is entirely removed by exposure to the air, when the colour at the same time disappears. Pure wax undergoes no change by exposure to the air. The specific gravity is 0.96. It is insoluble in water.

3. Wax becomes soft by the application of heat. Unbleached wax melts at the temperature of 142° heat. When it is pure it requires the temperature of 155°, and then melts into a colourless, transparent fluid. By increasing the heat, the wax boils and evaporates; with a red heat the vapour takes fire, and burns with a bright flame.

4. The acids have scarcely any action on wax. It is bleached by means of oxynitric acid, but no other effect is produced.

5. Wax is soluble in boiling alcohol. It requires 20 parts of alcohol to dissolve one of wax, and as the solution cools, the greater part is precipitated. With the addition of water the whole is thrown down. Component the assistance of heat ether dissolves wax nearly in the Parts of same proportion, but on cooling it is also precipitated.

Wax is soluble in the fixed oils with the aid of heat. This compound is known by the name of cerate, which is much employed to form plasters for dressing wounds. It is soluble also in some of the volatile oils, as those of turpentine, with the assistance of heat. As the solution cools, part of the wax is precipitated.

6. Wax combines with the fixed alkalies, and forms with them substances similar to soap.

7. According to the analysis of Lavoisier, wax is composed of

| Component | Percentage | |-----------|------------| | Carbone | 82.28 | | Hydrogen | 17.72 |

100.00

8. When wax is distilled with a temperature above 212°, water comes over, some acid, and a little fluid and odorous oil. The oil in the course of the process becomes thicker, and at last assumes the consistency of butter; and hence it has been called butter of wax. This substance by repeated distillation is converted into a volatile oil. A coaly matter remains in the retort.

9. Wax is extracted from a number of plants, possessing different degrees of consistency, as that from the cacao, called the butter of cacao; from the croton fimbriata, called the tallow of croton; and the myrtle wax extracted from the myrica cerifera, or candle-berry myrtle of America. The myrtle wax is obtained from the berries of this plant. They are collected and put into a kettle, and covered with water to the depth of half a foot. Heat is applied, and the berries are pressed against the sides of the vessel. The wax melts, and swims on the top. It is collected, passed through a cloth, dried and melted again, and then cast into cakes. The wax, it appears, exists chiefly in the outer covering of the berries. Myrtle wax is of a pale-green colour; the specific gravity is 1.015. When heated to the temperature of 100°, it melts; with stronger heat it burns, giving out a white flame with little smoke; an agreeable aromatic odour is at the same time emitted. In its other properties it resembles beeswax.

Proust has detected wax in the rind of plums, oranges, and similar fruits, and in the green fecula of many plants.

XIV. Of Camphor.

1. Camphor is obtained from the laurus camphorata, a species of laurel which grows in China and Japan. It is extracted by sublimation in an iron pot. The Dutch afterwards purify it by a second sublimation.

2. It is a white, brittle substance, possessing a hot acrid taste. The specific gravity is 0.9887. It is not altered by exposure to the air, but it is extremely volatile, that it disappears entirely if left in an open vessel. It crystallizes by sublimation in close vessels in the form of hexagonal plates or pyramids. It is insoluble in water, although at the same time it communicates some of its odour.

3. When a heat about the temperature of 300° is suddenly applied, it melts, and then is volatilized. It readily catches fire, and burns with a bright flame, without leaving any residuum. It even burns on the surface of water. When a small quantity of camphor in a state of inflammation is introduced into a large glass vessel filled with oxygen gas, it bursts out into a vivid flame; the inside of the vessel is covered with a black powder, and a great deal of carbonic acid gas is discharged. If a little water has been previously put into the vessel, it is impregnated with carbonic and camphoric acid.

4. Camphor is soluble in the acids, but with the addition of water or an alkali, it is precipitated unchanged. Camphor in sulphuric acid forms a red solution; in nitric acid, a yellow solution, which was formerly called oil of camphor. By the repeated distillation of nitric acid off camphor, it is converted into camphoric acid.

Sulphurous acid, muriatic acid, and fluoric acid, in the state of gas, dissolve camphor. If oxymuriatic acid gas be made to pass into a solution of camphor in nitric acid, it is immediately changed to a rose colour, and instantly afterwards it becomes yellow, which is permanent during the process. When water is added to the solutions of camphor in acids, it is separated. Camphor is also soluble in water impregnated with carbonic acid gas, and in acetic acid. The latter compound constitutes Henry's aromatic vinegar.

5. Alcohol readily dissolves camphor, but it is precipitated with the addition of water. By diluting alcohol which holds camphor in solution with water just so much as not to precipitate the camphor, the latter crystallizes in the form of feathers. The fixed and volatile oils dissolve camphor with the assistance of heat, but on cooling the camphor is precipitated, and crystallized, as in the solution with alcohol.

6. Camphor communicates to the alkalies a little of its colour, but is not otherwise soluble in these bodies.

7. According to the analysis of Bouillon Lagrange, by distilling one part of camphor with two of alumina, formed into a paste with water in a glass retort, the component parts of camphor are carbone and hydrogen; the proportion of carbone being much greater than in oils.

In the course of the distillation, he obtained a volatile oil of camphor, of a golden yellow colour, which floated on the surface of the water in the receiver. It had an acid burning taste, and aromatic odour, similar to that of thyme or rosemary.

8. Camphor has been detected in many other plants. Found in it has been extracted from the roots of thyme and many fagaceae, and in these plants it seems to be combined with volatile oil. If the oil be exposed to a temperature below 54° in the open air, it evaporates, and the camphor crystallizes. It may be also obtained by distilling the oil in a water bath, under the temperature of 212°, till a third part of the oil passes over. Part of the camphor is found crystallized in the vessel, and by repeating the process, the whole may be extracted from the oil. By mixing the camphor with a little dry lime, and subliming it, it may be purified.

XV. Of Caoutchouc.

1. Caoutchouc is a soft elastic substance, chiefly obtained Component tained from the inspissated juice of two trees, the *hevea caoutchouc* and *jatropha elatia*, which are natives of South America. This substance was first brought from America about the beginning of the 18th century. It is called by the inhabitants of *Elmeraldas*, a province of Quito, *heve*, and by the natives of the province of Mainas, *caoutchouc*.

2. It is extracted by making incisions in the bark of the tree. A milky juice flows from it, which is collected in proper vessels. The juice is then applied, one stratum above another, on earthen moulds, and suffered to dry in the sun, or before a fire. Various figures are formed on the surfaces of the different pieces by means of a pointed instrument. They are then exposed to smoke, and, when perfectly dry, the moulds are broken. In this state it is brought to Europe. It is generally in the shape of bottles, but sometimes in other forms.

3. When caoutchouc is pure, it is of a whitish colour; it is soft and pliable like leather, extremely elastic, and possesses great tenacity. The specific gravity is 0.9335.

4. When caoutchouc is exposed to heat, it readily melts into a matter of the consistence of tar. It burns with a bright white flame, and diffuses a fetid odour.

5. Sulphuric acid decomposes caoutchouc; charcoal is precipitated, and the acid is partially converted into sulphurous acid. It is also decomposed by nitric acid; carbonic acid gas, azotic gas, and prussic acid gas are disengaged, and oxalic acid is formed. Muriatic acid has no action upon it; but if oxymuriatic acid is poured upon the milky juice, the caoutchouc is immediately precipitated, and the acid is converted into uric acid. If a given quantity of air be confined in a vessel over a quantity of this milky juice, the oxygen of the air is absorbed, and a pellicle of caoutchouc is formed on the surface, from which it appears that the formation of caoutchouc is owing to the combination of its base with oxygen.

6. Caoutchouc is insoluble in alcohol. It is soluble in ether, but it is necessary that the ether be previously washed with water. By this treatment it is formed into syringes, catheters, and other instruments. It is soluble in the volatile oils, but it remains somewhat glutinous after the evaporation. A mixture of volatile oil and alcohol forms a good solvent for caoutchouc, and in this state it may be employed as a varnish for paper or stuffs. A varnish may also be formed with it by dissolving it in boiling wax. It is also soluble in rectified petroleum, and when the solution is evaporated, the caoutchouc remains unchanged.

7. According to some, caoutchouc is insoluble in the alkalies; but according to others, all of these bodies are capable of dissolving it.

8. By distillation caoutchouc yields ammonia; and from this, and its decomposition by means of sulphuric and nitric acids, its constituent parts must be carbons, hydrogen, azote, and oxygen.

9. Caoutchouc has been detected in different parts of many other plants, but it is mixed with resinous, gummy, and extractive matters. It has been found in different species of the milletoe, in opium and ma-

**XVI. Of Resins.**

1. Resinous bodies form a very numerous class of vegetable substances. When volatile oils are exposed to the air, they become thicker after a shorter or longer time, and are then found to be converted into a resin. The oil absorbs oxygen from the air, and is deprived of part of its carbons, which combining with the oxygen of the atmosphere, forms carbonic acid. Resinous substances, therefore, are generally considered as volatile oils saturated with oxygen. The general properties of resinous substances are the following.

2. They are solid, brittle, and commonly of a yellowish colour, with some degree of transparency. The taste resembling volatile oils, is hot and acrid. They have no smell. The specific gravity is from 1.018 to 1.2289. All resinous bodies are electrics, and when excited by friction, the electricity is negative; hence it is called resinous electricity.

3. They melt by being exposed to heat, and burn with a yellow flame, giving out a great quantity of heat and smoke. Resins are insoluble in water.

4. Resinous substances are soluble in nitric acid; acids, &c., are precipitated by the addition of water, and the whole by means of the alkalis. With the affluence of heat they are all soluble in alcohol, and in sulphuric ether. Resins are soluble in some of the fixed oils, and also in volatile oils.

5. Resinous substances have been found to be soluble in the fixed alkalis.

6. We shall now enumerate some of the resins which are best known.

**Resin.—** This substance is extracted from different species of the fir, and the resinous matter obtained from it has received different names. That procured from the *pinus sylvestris* is the common turpentine; from the *pinus larix*, venice turpentine; and from the *pinus balsamea*, balsam of Canada. The turpentine is obtained by stripping the bark off the trees; a liquid juice flows out, which gradually hardens. This juice consists of oil of turpentine and resin. By distilling the turpentine the oil passes over, and the resin remains behind. By distilling to dryness common rosin is obtained. When water is added, while it is yet fluid, and incorporated by agitation, what is called yellow rosin is formed.

**Pitch—** Is a resinous juice obtained from the *pinus picea*, or pitch pine. It is purified by melting and squeezing it through linen bags, and it is then known by the name of white or Burgundy pitch. White pitch mixed with lamp-black forms black pitch.

**Mastic—** This is a resinous substance obtained from the *pistacia lentiscus*, a tree which grows in the Levant. The fluid which exudes from the tree, concretes into yellowish transparent brittle grains. It has little taste, melts and exhales a fragrant odour when heated, and readily dissolves in alcohol and fixed oils. It contains a little volatile oil.

**Sandarac—** This resinous substance is extracted from Sandarac. Component the juniper. It is a spontaneous exudation from this plant in the form of brown tears, which are semitransparent and brittle.

Labdanum, or Ladanum.—This is the produce of the *cylus creticus*, a shrub which grows in Candia. It is the exudation of a viscid juice, which concretes by exposure to the air. It has a fragrant odour and a bitter taste.

Dragons-blood.—This resinous substance is a production of the *dracaena draco*, and some other plants. It is of a dark-red colour, opaque and brittle. The powder is of a crimson colour. It melts when it is heated, and readily burns. It has no taste, is insoluble in water, but soluble in alcohol, to which it communicates a crimson colour. It is also soluble in the fixed oils, and gives them a red colour.

Resina anime.—This resin is the produce of a species of *hymenea*, or locust tree, a native of North America. It is soluble in alcohol, and is employed as a varnish.

Copal.—This resinous substance is obtained from a tree, the *rhus copallinum*, a native of North America. The copal most preferred is brought from Spanish America. It is a light brown, transparent substance. It melts when heated, but is not directly soluble in alcohol, or in oil of turpentine, and it is with difficulty soluble in fixed oils. Copal forms an excellent varnish. Indeed it is one of the best that is known for beauty and durability.

If copal be treated with oil of turpentine in a close vessel, from which the vapours are not allowed to escape, they exert a great pressure, which prevents the boiling, and thus the mixture acquires a higher temperature. A considerable portion of the copal is thus dissolved, and with the addition of a little poppy oil it forms an excellent elastic varnish.

If copal be kept melted till a four-smelling aromatic odour ceases to proceed from it, and if it be then mixed with an equal quantity of linseed oil previously rendered colourless by exposure to the sun, it combines with the oil, and thus forms a varnish. The substances varnished with this preparation must be dried in the sun.

Copal may be dissolved in alcohol, by previously dissolving half an ounce of camphor in 16 ounces of alcohol. This solution is poured on 4 ounces of copal in a matraf, which is stopped with a cork, and perforated with a pin. When the copal is nearly dissolved, the process is stopped, and the matraf allowed to cool, before the cork is removed. This solution forms a colourless varnish.

Copal, it is said, may be dissolved in alcohol, by exposing it to the action of the vapour. This process is conducted by boiling a quantity of alcohol in the bottom of a vessel, at the top of which a piece of copal is suspended. During the process the copal softens, and falls down like oil into the alcohol.

Elemi.—This resinous substance is the produce of the *amyris elemifera*, a tree which grows in the East and West Indies. It is semitransparent, of a pale yellow colour, softish, and hardens by keeping. It has a strong fragrant smell, and when distilled it yields a fragrant oil.

Opobalsamum, or balm of Gilead.—This resin is procured from another species of *amyris*, the *Gileadensis*, a tree which is a native of Arabia. The best kind, which is highly valued by the Turks, is never seen in Europe.

Copaviva, or balsam of Copaviva.—This resinous substance is obtained from the *copaviva officinalis*, a tree which is a native of South America. It exudes by wounding the trunk of the tree. It is transparent, of a yellowish colour, has a pungent taste, and an agreeable smell. It is at first of the consistence of oil, but afterwards becomes as thick as honey. By distillation the volatile oil, with which it is mixed, may be separated, and the resinous matter remains behind.

Guaiac.—This resin is the produce of the *guaiacum officinale*, a tree which is a native of the West Indies. The resin exudes spontaneously in tears, but it is chiefly obtained by cutting the wood into billets, and boring them longitudinally. When one of these is heated on the fire, the resinous matter is melted, and runs through the hole as the wood burns. This resin is of a brownish-yellow colour, and has some degree of transparency. It is soluble in alcohol, and has neither smell nor taste. It melts when heated, and when it is thrown on hot coals, it diffuses an agreeable odour. When swallowed in the state of powder, it produces a strong sensation of heat in the throat.

Lac.—This resinous substance is obtained from the *Lac croton lacciferum*. It is of a deep red colour, with some degree of transparency. It is the basis of the finer kinds of sealing wax, and is employed as a varnish.

Amber.—This substance possesses many of the properties of the resins, and it has been considered by some of vegetable origin. It is a brittle hard substance, transparent, sometimes colourless, but often yellow or deep brown. The specific gravity is 1.065. It has neither taste nor smell, except when it is heated, and then it becomes soft, and gives out a fragrant odour. It burns with a strong heat, leaving only a small residue. It is insoluble in water, but alcohol dissolves a small quantity of it. When the solution is concentrated, it becomes milky with the addition of water. The precipitate which is formed is a resinous substance. It is soluble in the fixed alkalies at a boiling temperature.

Sulphuric acid converts amber into a black resinous mass. It is also soluble in nitric acid.

By the distillation of amber, carbonic acid gas and carbonated hydrogen gas, an acid liquor, and an oil, which is at first thin and transparent, but afterwards larger and thicker, is obtained. Succinic acid sublimes towards the end of the process.

When amber is roasted, it becomes soluble in the oils, and forms a varnish. This varnish may be formed by spreading the amber on a flat-bottomed iron pan, and exposing it to heat till it melts. It is then covered up, and let by to cool. One part of this roasted amber, which has lost half of its weight, if the process be properly managed, is then to be mixed with three parts of linseed oil. The mixture is to be exposed to a gentle heat till the amber is dissolved. It is then to be removed from the fire, and four parts of the oil of turpentine are to be added when it is nearly cold. The clear part, after it has settled, is strained through a linen cloth.

Benzoin.—This substance contains a resinous matter combined Component Parts of Vegetables.

Combined with an acid, and is commonly ranked among ballams. Benzoin is obtained from the *Styrax benzoin*, a tree which is a native of Sumatra. It is a brittle substance, has a fragrant odour when rubbed, and, when it is heated, the acid escapes. It may be dissolved in alcohol, but it is insoluble in water.

**Styrax.**—This substance, which is in a half-fluid state, exudes from a tree in Arabia. It is of a greenish colour, has an aromatic taste, and an agreeable odour. The benzoic acid, which is one of its component parts, dissolves in water. The whole of it is soluble in alcohol. It absorbs oxygen, and becomes harder by exposure to the air.

**Storax.**—This substance is procured from the *Styrax officinale*, a tree which is a native of the Levant. It is of a brown colour and brittle, has an aromatic taste, fragrant odour, and is soluble in alcohol. It gives out benzoic acid by heat.

**Balsam of Tolu.**—This substance is obtained from the *Tolufera balsamum*, a tree which is a native of South America. It is of a reddish-brown colour, becomes solid and brittle when exposed to the air, and has a very fragrant smell.

**Balsam of Peru.**—This is obtained from the *Myroxylon peruforum*, a plant which is a native of South America. The resin is extracted by boiling the twigs in water. It is of the consistence of honey, has a brown colour, an agreeable smell and an acrid taste. It is soluble in alcohol. The acid part is soluble in water. Benzoic acid is driven off by heat.

**XVII. Of Gum-Resins.**

1. This class of substances seems to be composed of a mixture of resinous matter with a portion of gummy and extractive matter. They are never obtained from plants by means of spontaneous exudation, but are procured by wounding the plants which contain them. The general properties of gum-resins are the following:

2. They are always in the solid state, and commonly brittle and opaque. They are softened by heat, but do not melt, and are less combustible than the resins. They burn with flame. They have an acrid taste, with a strong smell, somewhat resembling garlic. They are partially soluble in water, and in alcohol. The solution in water is opaque and milky, and the solution in alcohol is transparent. They are partially soluble in vinegar and wine. They are soluble in nitric acid, and also in the alkalies, with the assistance of heat.

3. The gum-resins by distillation yield a portion of ammonia, which shows that azote forms one of their constituent parts.

4. Many of the gum-resins have been long known in medicine, and some of them are of considerable importance. We shall specify the peculiar properties of the following.

**Olibanum.**—This gum-resin is chiefly collected in Arabia, from the *Juniperus lycia*. It is brought from Mecca to Cairo, and from thence to Europe, in the form of transparent brittle grains, not larger than a chestnut, of a yellow colour, a peculiar aromatic smell, but with little taste. With water it forms a milky fluid, but it is entirely soluble in alcohol. When heated it does not melt, but inflames and burns with an agreeable smell. It is the frankincense of the ancients, and is still employed to diffuse an agreeable fragrance in the Greek and Roman churches.

**Scammony.**—This substance is extracted from the *Cynoglossum scammonia*, a climbing perennial plant which grows in Syria. By cutting the roots, a milky juice flows out, which is collected and dried in the sun. It is of a dark-gray colour, a bitter acid taste, and a nauseous smell. It forms a greenish milky fluid with water. It is soluble in alcohol. It is employed in medicine as a cathartic.

**Euphorbium.**—This substance is obtained from the *Euphorbia officinalis*, which is a native of Ethiopia. The bium, milky juice which flows from incisions made in the plant, is dried in the sun. It is in the form of small yellow tears. It has no smell, and at first no perceptible taste, but it communicates afterwards a burning sensation to the mouth. It is soluble in alcohol. It has been considered as poisonous.

**Affafetida.**—This gum-resin is obtained from the *Affafetida ferula affafetida*, a perennial plant, which is a native of Persia. It is extracted from the roots by cutting off the extremity. The milky juice flows out, which is dried in the sun. It is brought to Europe in large irregular masses, which are of a whitish, reddish, or violet hue. It has a strong fetid, alliaceous smell, and a bitter acid taste. It is but partially soluble, both in alcohol and in water. It is much employed in medicine as a stimulant and antispasmodic.

**Ammoniac.**—This gum-resin is supposed to be obtained from another species of the *Ferula*, a plant which grows in Abyssinia and in the interior parts of Egypt. It is brought from the East Indies, usually in large masses, which are composed of little lumps or tears, of a milky colour. When exposed to the air, it is changed to a yellow colour. It has a nauseous, sweet taste, which is succeeded by a bitter. It has a peculiar smell. It is not fusible; but when placed on hot coals, it burns away in flame. It forms a milky solution with water and vinegar, and it is partially soluble in alcohol.

**Myrrh.**—It is not yet known from what plant this Myrrh substance is obtained. It is brought from the East Indies in the form of tears; is light and brittle, of a reddish-yellow colour, and an unctuous feel. It has a bitter aromatic taste, and a strong, but somewhat grateful odour. It does not melt, and burns with difficulty. It is more soluble in water than in alcohol. With the former the solution is yellow and opaque; with the latter it is transparent.

**Sarcocon.**—This substance is supposed to be the product of the *Ponca sarcocon*. It is brought from Persia and Arabia, in the form of small whitish-yellow grains. It has a bitter and somewhat sweetish taste. It is almost entirely soluble in water.

**Gallanum.**—This substance is obtained from the *Galbanum bubon galbanum*, a perennial plant which grows in Africa. The milky juice sometimes exudes from the joints of the old plants, but is most commonly procured by cutting them aeros. This juice becomes hard, and is the galbanum brought to Europe. It is in the form of whitish-yellow tears, has a bitterish acid taste, and a peculiar smell. It forms a milky solution with water, wine, and vinegar. It is scarcely soluble in alcohol. Component It does not melt, but yields a considerable proportion of oil by distillation.

**Sagapenum.**—It is only conjectured that this gum-resin is obtained from the *ferula perfica*. It is brought in large masses or distinct tears from Alexandria. It is of a yellow colour, becomes hot in the hand, but is not fusible. It has a hot, nauseous, bitterish taste, and a disagreeable garlic smell. It is sparingly soluble in alcohol, but dissolves almost entirely in water. It yields by distillation a fetid volatile oil.

**Opoponax.**—This gum-resin is obtained from the *Ajinaca opoponax*, a perennial plant which grows wild in the south of Europe. It is obtained by wounding the stock or root, and is in the form of round drops or tears, or in irregular masses of reddish-yellow colour. It has a bitter, acrid, and somewhat nauseous taste, with a strong peculiar smell. It forms a milky solution with water, and yields an essential oil by distillation.

**Gamboge.**—This gum-resin is obtained from the *Alamagotis gambogioides*, a tree which grows wild in Siam and Ceylon. In Siam it is procured in drops by breaking the leaves and young shoots, from which it is supposed to derive the name of *gum guttae*. In Ceylon it is obtained by wounding the bark and collecting the juice, which is afterwards dried in the sun. It is brought from the East Indies in cakes or rolls. It is of a yellow-orange colour, opaque and brittle, has no smell, and little taste, leaving only a slight sense of acrimony when it has been kept in the mouth. It forms a turbid yellow solution with water, and is almost entirely soluble in alcohol. It is employed in medicine, and is a violent cathartic.

**Bdelium.**—Little is known of this substance, or of the tree from which it is obtained. It is in the form of small pieces or tears of different sizes, of a golden-yellow colour, with a reddish tint. This substance, or a substance with the same name, was long celebrated among the ancient physicians.

### XVIII. Of Wood.

1. If a piece of wood be boiled in a great quantity of water till it no longer gives out taste or smell, and if it be afterwards digested in alcohol, the substance which remains is the woody fibre.

2. It is either in a fibrous, lamellated, or pulverulent form. This substance, which is more or less coloured, has neither taste nor smell, is not altered by exposure to the air, and is insoluble in water and alcohol.

3. When it is heated in contact with air, it blackens, exhales dense, acrid, pungent fumes, and leaves behind a coaly matter, which does not change its form. By reducing it to ashes, it is found to contain a little potash, sulphate of potash and lime, phosphate of lime. When it is distilled in a retort it yields water, acetic acid contaminated with oil, a thick oily matter, carbonated hydrogen and carbonic acid gases, and a portion of ammonia, combined with acetic acid.

4. By the action of nitric acid on quinquina, which resembles the woody fibre, Fourcroy obtained from 100 parts, the following products:

- Oxalic acid, 56.250 - Citric acid, 3.995 - Malic acid, 0.388 - Acetic acid, 0.486 - Azotic acid, 0.867 - Carbonate of lime, 8.330

A quantity of carbonic acid gas was also discharged, which was not estimated. The increase of weight is ascribed to the oxygen which combined with the bases of the acids which were formed during the decomposition of the woody fibre by the nitric acid. The residuum, by distillation, yielded a yellowish fluid mixed with alcohol and some acetic acid, a concrete oil soluble in alcohol, charcoal, and carbonate of lime, besides carbonic acid and carbonated hydrogen gases. The component parts of wood, therefore, appear to be, oxygen, carbons, hydrogen, azote, and lime.

The relative proportion of wood in plants has been estimated by the proportion of charcoal which they afford. From different woods, Proust obtained charcoal in the following proportions.

| Substance | Proportion | |-------------|------------| | Black ash | 25 | | Guaiac | 24 | | Pine | 20 | | Green oak | 20 | | Heart of oak| 19 | | Wild ash | 17 | | White ash | 17 |

### XIX. Of Tan.

1. Tan is obtained from a great number of vegetable substances. It exists in considerable proportion in oak bark and nut-galls; and it is obtained from the latter by the following process.

Reduce a quantity of nut-galls to a coarse powder, infuse them in water till it is saturated, pour off the liquid, and boil it to dryness. A black matter remains, which is tan, nearly in a state of purity. It is proposed also to extract tan from nut-galls by other processes. If a solution of muriate of tin be added to the infusion of nut-galls, a copious precipitate of a yellow colour is produced. When this is separated by filtration, and dried, it is in the form of a buff-coloured powder. It is a compound of oxide of tin and tan. It is then mixed with water, and a stream of sulphurated hydrogen gas is passed through it. An insoluble sulphuret of tin is formed, and the tan is dissolved in water. By filtration and evaporation of this water to dryness, a brown substance remains, which is tan; but by this process it is not perfectly pure, being mixed with a portion of extractive matter. It has also been proposed to separate tan from the infusion of nut-galls by means of concentrated sulphuric or muriatic acid, carbonate of potash, or lime water.

2. Tan is a brittle substance, of a brown colour, has a very astringent taste, is soluble in water and alcohol, to both of which it communicates a brown colour and very astringent taste.

3. When it is heated, it becomes black, gives out carbonic acid gas, and burns in the open air, leaving behind a small quantity of lime.

4. Tan is precipitated from the infusion of galls, by The following proportions of tan were found by adding a solution of glue to the infusion of the plant in water.

| Proportion of Tan | Proportion of Tan | |-------------------|-------------------| | Elm | Sallow | | Oak cut in winter | Mountain ash | | Horse chestnut | Poplar | | Beech | Hazel | | Willow boughs | Ash | | Elder | Spanish chestnut | | Plum tree | Smooth oak | | Willow trunk | Oak cut in spring | | Sycamore | Leicester willow | | Birch | Sumach | | Cherry tree | |

XX. Of Suber.

1. The vegetable substance denoted by the name of Coniferae suber, is, according to Fourcroy, the epidermis or outer covering of trees. This substance is analogous to common cork, which is the epidermis of the quercus suber, from which the name of this peculiar vegetable substance is derived.

2. It is a light, soft, elastic substance, is insoluble in water, but readily absorbs this liquid. Common cork is the same substance, having greater density, and accumulated in greater quantity.

3. This matter is very combustible, and burns with a white vivid flame, leaving behind a very black, light, heat-voluminous coaly matter. When this matter is distilled, it yields ammonia.

4. When cork is treated with nitric acid, carbonic acid gas and nitrous gas are evolved. The cork is acid decomposed, and converted partly into a yellow, soft, unctuous matter, which floats on the surface, and partly into suberic acid; the nature and properties of which have been already described.

XXI. Of Alkalies.

1. The fixed alkalies only have been detected in plants, and there are few plants which do not yield alkalies only smaller or greater proportion of one of these alkalies. It is supposed that they exist in plants, in combination with acetic and carbonic acids.

2. Potash, formerly called vegetable alkali, because potash, it was supposed to exist only in vegetables, is found in all plants except those which grow near the sea. The process for extracting it has been already described. The vegetables are reduced to ashes by burning; the ashes washed with water, which is filtered and evaporated to dryness. The potash remains behind.

3. Shrubby and herbaceous plants yield a greater proportion of ashes than trees. The branches of trees afford more ashes than the trunk, and the leaves yield more than the branches. Other salts are found mixed with the potash, such as the sulphates of potash and of lime, muriate of potash, phosphate of lime, and phosphate of potash; the latter of which has been detected in maize and wheat. In the following table the proportion of ashes obtained from 100 parts of different plants, and the quantity of potash which these ashes yield, are exhibited.

| Component by means of sulphuric, nitric, and muriatic acids, and forms with them compounds which are soluble in water. | |------------------------------------------------------------------------------------------------------------------| | 5. The alkalies combine with tan, and form compounds which are soluble in water. A reddish brown colour is produced in the liquid by the addition of potash or soda, and it loses the property of precipitating gelatine. Ammonia forms a similar compound with the infusion of galls. | | 6. Most of the earths combine with tan, and form with it compounds which are chiefly insoluble in water. Lime water, added to the infusion of galls, produces an olive-coloured precipitate. A similar precipitate is obtained by means of barytes, strontites, and magnesia. | | 7. The metallic oxides combine with tan, and form compounds which are nearly insoluble in water. Similar precipitates are obtained by means of many of the metallic salts. The green sulphate of iron produces no precipitate; but the red sulphate gives a deep-blue precipitate, which becomes black by exposure to the air, or when it is dried. This is the base of writing ink, as was formerly described in treating of the sulphate of iron. | | 8. Tan forms an insoluble compound with gelatine, which is the principle of the important process of tanning leather, and is nothing more than the combination of tan with the animal matter called gelatine or glue. | | 9. Tan is chiefly found in the bark of trees; it is also found in the leaves, the wood, the sap, and sometimes it is obtained by spontaneous exudation, as is the case with the substance called kino. Several varieties of tan have been found in different vegetable substances, as in catechu, dragon's blood, fumach, and fustic. | | 10. The quantity of tan varies with the age and size of the tree, and at different seasons. The greatest proportion has been found in the inner bark. Mr Davy ascertained the quantity of tan obtained from the solid matter extracted by water, from an ounce of different vegetable substances. |

| Solid Matter. Tan. | |-------------------| | White inner bark of old oak | 108 grs. 72 grs. | | young oak | 111 77 | | Spanish chestnut | 89 63 | | Leicester willow | 117 79 | | Coloured or middle bark of oak | 43 19 | | Spanish chestnut | 41 14 | | Leicester willow | 34 16 | | Entire bark of oak | 61 29 | | Spanish chestnut | 53 21 | | Leicester willow | 71 33 | | elm | 13 | | common willow | 11 | | Sicilian fumach | 165 78 | | Malaga fumach | 156 79 | | Souchong tea | 48 | | Green tea | 41 | | Bombay catechu | 261 | | Bengal catechu | 231 | | Nut-galls | 180 127* |

Sallow,

| Component Parts of Vegetables | Ashes | Potash | |-------------------------------|-------|--------| | Sallow | 2.8 | 0.285 | | Elm | 2.36727 | 39.1 | | Oak | 1.35185 | 0.15343 | | Poplar | 1.23476 | 0.07481 | | Hornbeam | 1.1283 | 0.1254 | | Beech | 0.58432 | 0.14572 | | Fir | 0.34133 | 0.00000 | | Vine branches | 3.397 | 0.35 | | Common nettle | 10.67186 | 2.5933 | | Common thistle | 4.04265 | 0.53734 | | Fern | 5.00781 | 0.6259 | | Cow thistle | 10.5 | 1.96003 | | Great river rush | 3.85395 | 0.72234 | | Feathered rush | 4.33593 | 0.50811 | | Stems of Turkey wheat | 8.86 | 1.75 | | Wormwood | 9.744 | 7.3 | | Fumitory | 21.9 | 7.9 | | Red clover | | 0.078 | | Vetches | | 2.75 | | Beans with their stalks | | 2 |

Herbaceous plants, it appears, contain a greater proportion of earths than trees. In all the kinds of grain which Bergman examined, he found all the four earths. From 100 parts of oat grain, Vauquelin obtained a residuum of 3.1591, which by analysis he found to be composed of:

- Silica, 60.7 - Phosphate of lime, 39.3

By burning the stem and seeds of the same grain, the residuum by analysis afforded the following substances:

- Silica, 55 - Phosphate of lime, 15 - Potash, 20 - Carbonate of lime, 5

Some traces of oxide of iron were also detected.

XXII. Of Earths.

1. Four of the earths have been detected in vegetables, namely lime, silica, magnesia, and alumina. Few plants have been found which do not contain some portion of lime. It is the most abundant of all the earths in plants.

2. Silica has been found in several plants, and chiefly in the epidermis, some of which are almost entirely composed of this earth. A hundred parts of the epidermis of the following plants yielded the annexed proportions of this earth:

- Bonnet cane, 90 - Bamboo, 71.4 - Common reed, 48.1 - Stalk of corn, 6.5

3. Magnesia is more rarely found in vegetables. It has been detected in considerable proportion in the fuci and other sea plants. The greatest proportion yet discovered is found in the falfola soda. A hundred parts of this plant have yielded 17.929 of magnesia.

4. Alumina is found in plants in very small quantity.

5. In the following table is exhibited the quantity of earths in general, found in 100 parts of different plants.

| Proportion of earths | Oak | Beech | Fir | |----------------------|-----|-------|-----| | | 1.03| 1.453 | 0.003 |

Turkey wheat, 7.11 Sunflower, 3.72 Vine branches, 2.85 Box, 2.674 Willow, 2.515 Elm, 1.96 Aspen, 1.146 Fern, 3.221 Wormwood, 2.444 Fumitory, 14.000

XXIII. Of Metals.

The only metallic substances which have certainly been found in plants are iron and manganese. Iron and manganese has been detected in the ashes of falfola; and manganese has been found in the ashes of the pine, green oak, calendula, vine, and fig-tree. Gold, it is said, has been found in some plants, but in very minute proportion.

CHAP. XIX. OF ANIMALS.

Animals constitute the second division of organized matter. They are distinguished from vegetables by texture, form, and component parts. The more characteristic differences between animals and vegetables are, the locomotive power of animals, irritability, and sensibility. Animal matters pass to the putrid fermentation, and they are all soluble in the alkalis. Sulphuric acid reduces animal substances to a carbonaceous matter. Charcoal is precipitated, and ammonia is discharged. Nitric acid acts violently on animal substances, with the evolution of azotic gas.

In treating of animal matters, we shall first consider the functions of living animals; 2. Their decomposition; and, 3. Their component parts. These subjects shall occupy the three following sections.

Sect. I. Of the Functions of Animals.

In taking a view of animal substances, it is necessary to consider the function of the living animal, so on chemical principles.

far at least as these functions admit of explanation on chemical principles. It is beyond the reach of human sagacity fully to understand the simplest processes in the animal economy. These cannot be explained on chemical or mechanical principles; but to comprehend clearly and fully, even what is known of the functions of living animals, it would be necessary to enter into a description of the structure and nature of the organs which are employed in these functions. But this is not the province of chemistry; it belongs to the sciences of ANATOMY and PHYSIOLOGY. We must therefore content ourselves with giving a short account of the chemical changes which take place by the action of living animals. The functions of animals which have occupied the attention of chemical physiologists, and which we propose to treat of in this section, are respiration, digestion, secretion, and assimilation.

I. Of Respiration.

1. Respiration is to be considered as one of the vital functions of animals. No animal can exist when it is interrupted, nor indeed can it be suspended, even for the shortest time, without the hazard of life. In the mechanical part of the function of respiration, the air is alternately drawn into the lungs and expelled.

2. It is well known that all gases are not fit for respiration. Some indeed, as carbonic acid gas, the moment they are inhaled, are destructive to life. The respiration of others, although they are not productive of such sudden effects, yet at last they prove fatal to the animal which is forced to respire them. Animals are very differently constituted, both with regard to the structure of their respiratory organs, and with regard to the quantity of air which must be respired in order to support life. In these respects, the hot and cold-blooded animals are very different from each other; and even among the latter class, namely the cold-blooded animals, there are some tribes which require a very small quantity of air, and can bear without much seeming inconvenience a temporary interruption of this function; but for all animals, whatever be their nature, whatever be their structure, or whatever be the modifications of their respiratory system, the air of the atmosphere is the most proper for the support of life. It is the oxygen of atmospheric air which is necessary for the breathing of animals; but although animals live longer in a given quantity of oxygen gas than in atmospheric air, as appears from the experiments of Count Morozzo, related in the chapter on oxygen gas, yet it is too powerful, or too stimulating for their organs; for to such as have been confined to breathe it, it has been found highly injurious.

3. Some of the gases prove immediately fatal to life; such for instance is carbonic acid gas. It seems to be certain that no animal ever made a full inspiration of this gas, without being destroyed. Nay, it is so noxious to animal life, that the organs themselves, by an involuntary action, obstruct it in its passage to the lungs. Other gases are equally fatal after a few inspirations, such as hydrogen and azotic gases; and indeed it is probable, if the lungs were completely emp-

Vol. V. Part II.

tied of air, before the inspiration of any gas whatever, excepting oxygen gas or atmospheric air, a single inspiration would prove fatal. This, however, is never the case; for after the fullest expiration, a considerable quantity of air remains in the lungs. We may conclude, therefore, that the air of the atmosphere alone is proper for the respiration of animals, and the support of life.

4. After the same quantity of atmospheric air or the same oxygen gas has been once respired by animals, it becomes totally unfit for farther respiration either by the same animals or any other. It is then not only deprived of the whole of the oxygen, but is also contaminated with noxious gases. This even happens to fishes and insects which require a very small quantity of air. If the water in which the former live be deprived of its air, it is equally fatal to them, as being immersed under water is to those animals which live in the air of the atmosphere.

5. Attempts have been made by physiologists to ascertain the quantity of air respired by animals. This quantity will appear at first sight, must be extremely different in different classes of animals. Even in the same class of animals, it is probable that it varies much. The difference of the results of experiments on man to ascertain this point are enormous. No conclusion whatever can be drawn from the number of respirations made in a given time, even if this could be determined with any degree of accuracy, which is scarcely to be expected. For no function of the body is sooner influenced by mental affections than the breathing. The very attention to the circumstance of reckoning the number of respirations will have some effect in occasioning considerable deviations from the natural number. The number of respirations which have been reckoned by some is 14 in a minute, while others make the number amount to 27, which shews that little dependence can be placed on this mode of calculating the quantity of the air respired in a given time. But even if this could be accurately ascertained, still it would not enable us to ascertain the quantity of air respired. For it is extremely probable that this quantity varies greatly in different men and in different animals, and in the same animal at different times, arising from causes the effects of which either entirely elude observation, or are altogether inappreciable. And accordingly we find that the differences of the results of the quantity of air taken in at a single inspiration, or of the quantity calculated in the lungs after expiration, are not less than those of the number of respirations.

6. The nature of the changes which the air inspired undergoes has been ascertained with more accuracy, although the experiments made to determine the amount of these changes vary considerably. Part of the air which is respired disappears; and it has been generally supposed that it is only the oxygen gas which is taken up. But according to the experiments of Mr Davy, part of the azotic gas also disappears and is absorbed along with the oxygen. Dr Menzies estimates the quantity of oxygen gas absorbed by a man in 24 hours at rather more than 41 oz. troy. Lavoisier fixes the quantity consumed by a man in the same time at 32 oz. nearly; and Mr Davy gives as the result of his his experiments and calculations about \(3\frac{1}{2}\) oz. of oxygen gas, and \(4\frac{1}{2}\) oz. of azotic gas, amounting together to about 38 oz.

7. The air thrown out of the lungs by expiration contains a quantity of carbonic acid gas. But here the results of experiments to determine the quantity are as widely different as in other points relating to respiration. By one it is reckoned at 15 oz. in 24 hours; by another at not less than 37 oz.

8. Water in the state of vapour is also thrown out of the lungs during respiration. The quantity estimated by different philosophers exhibits the same difference of results as in the other substances. According to Hales it is \(20\frac{1}{2}\) oz. nearly; according to Lavoisier it amounts to \(28\frac{1}{2}\) oz.

9. But although it seems difficult, or perhaps impossible, to ascertain with perfect accuracy the proportions or quantity of each of the substances thrown out of the lungs, yet it is clearly proved by experiment, that the component parts of the air expired are azotic gas, carbonic acid gas, and water in the state of vapour.

10. The blood, as it flows from the left side of the heart, is of a bright red colour. It is conveyed by the arteries to every part of the body. It is then taken up by the veins, and carried back to the heart, by means of the venous system. The blood having thus circulated through the body, enters the right side of the heart, and has totally changed its colour. It is now of a dark purplish red, instead of the bright red colour which it possessed when it passed out of the heart, to be distributed through the body. But before the blood can pass to the left side of the heart, again to enter the circulation, it must pass through the lungs, where it again acquires the bright red colour. From the lungs it passes to the left side of the heart, from which it flows as before through the arterial system to all parts of the body. The blood then acquires this florid red colour in the lungs. Let us now see in what this change consists.

11. This change was ascribed by some of the earlier chemical physiologists to the absorption of air. Dr Priestley observed that venous blood, which was of a dark colour, became of a bright red when exposed to oxygen gas, and that hydrogen gas produced a contrary effect. The same thing has been ascertained since, by many other chemists. According to Dr Priestley, the blood was deprived of its phlogiston as it passed through the lungs; but according to the theory of Lavoisier and others, no part of the air inspired is absorbed; the blood gives out hydrogen and carburetted water, combining with the oxygen of the air, form water and carbonic acid. He supposed that the quantity of oxygen in the water and carbonic acid expired was equal to that which had disappeared during respiration. According to another theory, the oxygen gas combines with the blood, and while this combination takes place, the carbonic acid gas and water which are expelled from the lungs along with the azotic gas, are given out. According to later experiments, it has been ascertained that not only the whole of the oxygen of atmospheric air, but part of the azote, is absorbed during respiration; and indeed some have supposed that the whole of the atmospheric air is absorbed by the blood unaltered, and that it is only after this absorption that the decomposition takes place. The whole of the oxygen and part of the azote are retained, and the remaining part of the azote is thrown out, along with the carbonic acid gas and water, which are expired; but this opinion, as well as most others with regard to the nature of the changes that take place during respiration, rests in a great measure on plausible conjecture.

12. A question has arisen among chemists regarding the formation of the carbonic acid and the substances water which are expired; whether it takes place immediately in the lungs, by the direct combination of the oxygen of the air with the carburetted water of the blood, or whether these substances previously existed in the blood in a state of combination, and are thrown out during respiration.

13. What are the purposes of these changes? What are the uses of respiration in the animal economy? As respiration, the blood is the source from which are derived the materials for repairing the constant waste of the body, it is necessary that means should be provided, to supply this waste, to which the blood is constantly subjected. This is accomplished, as we shall find afterwards, by the process of digestion, the product of which is conveyed to the blood. But before it can be converted into blood, it must undergo certain changes, which take place in the lungs. There is an essential part of the blood, and an essential part of animal bodies, namely the fibrina, which does not exist in the chyle and lymph, which are the substances conveyed to the blood, to repair its waste, before they have passed through the lungs along with the blood. Hence it is supposed that one purpose of respiration is to form the fibrina of the blood.

14. But another great purpose of respiration in the animal economy is to preserve the proper degree of temperature necessary for the health and life of the animal. It is well known that the temperature of animals is not regulated like inorganic matter by the surrounding medium. In whatever temperature animals are placed, except in those extreme degrees of heat or cold which destroy life altogether, the temperature of their bodies continues almost uniformly the same, and this temperature, it appears, corresponds to the quantity of air inspired. Hence it is that the temperature of the lower orders of animals which require but a small proportion of air, as insects, fishes, and amphibious animals, is not much higher than that of the medium in which they live, and on this account they constitute a division of animals which have been distinguished by physiologists by the name of cold-blooded animals. The temperature of warm-blooded animals, whatever be the temperature in which they live, is from 96° to 104°. The temperature of man is about 98°, while that of birds which require a greater proportional quantity of air, is usually 5° or 6° higher.

15. The manner in which the temperature of the body is kept up by means of respiration, has been thus accounted for, on the principles of Dr Black's theory of latent heat. Part of the latent heat of the air, which was inspired and combined with the blood, is given out, and thus raises the temperature of the blood, and that of the whole body through which it circulates. But if this change took place in the lungs, and all the latent heat of the air inspired was extricated in that organ, it was urged as an objection to this theory, that the temperature in them would be much higher than in other parts of the body. According to the theory of Lavoisier and Crawford, the oxygen gas of the air inspired combines with the hydrogen and carbon which are given out by the blood, forming carbonic acid and water. During this process, which takes place in the lungs, the latent heat of the oxygen becomes sensible. Part of it combines with the water and the carbonic acid, and converts them to the state of gas; the remainder combines with the blood, to preserve the temperature of the body. The capacity of arterial blood for caloric, or the specific caloric of arterial blood, that is, the quantity of caloric which is necessary to raise it to a given temperature, is much greater than that of venous blood. According to this theory, therefore, the specific caloric of arterial blood, as it circulates through the body, is more and more diminished, till it is at last converted into venous blood. In this way it has been proposed to obviate the objection of the temperature of the lungs being highest, if, as it has been supposed, the whole of the caloric is here evolved; and to account for the uniformity of temperature which exists in every part of the body.

But if the difference of the specific caloric of arterial and venous blood be not sufficiently great to account for the phenomena, this objection has been attempted to be removed, by supposing that the air is absorbed by the blood in the state of gas, and that the greatest part of the changes which it undergoes, is effected in the course of the circulation. Part of the caloric, it is supposed, is evolved, when the air combines with the blood, and this portion combining with the carbonic acid and water thrown off, raises them to the state of gas, in which state they are emitted during respiration. The air absorbed by the blood gives out the remaining portion of its caloric in the course of the circulation, when the oxygen combines with the carbonic acid and forms carbonic acid, and with the hydrogen and forms water; and thus the caloric is gradually evolved during the course of the circulation. Such then are two of the important purposes which seem to be accomplished by means of the function of respiration; namely, the preservation of animal temperature, and the complete formation of the blood.

II. Of Digestion.

1. The animal body is subject to continual waste, and the quantity of this waste varies according to the nature and age of the animal. This waste is repaired by the blood, which must consequently receive some supplies, to make up for its continual consumption. On this account, all animals require food or nourishment, to compensate for the waste of the body, and directly for the consumption of the blood from which this waste is supplied.

2. Different animals, according to their nature, constitution, and circumstances in which they are placed, require different kinds of food. Some animals live entirely on vegetables, others feed exclusively on animals, while a third class feed indiscriminately both on vegetables and animals. But whatever be the kind of food, or whatever be the nature of the animal, it is all converted, by the process of digestion, into the same uniform substance. In most animals the food, as it is taken into the mouth, is broken down, mixed with the saliva, and conveyed to the stomach, and after it has remained there for a short time, it is totally changed, and is converted into the uniform substance above alluded to, called chyme.

3. In attempting to account for the functions of the Falce animal body, chemists and physiologists have beenalogies of ways too much disposed to consider the changes which physiologists take place within the body, as analogous to those which take place on inorganic or dead matter, in supposed similar circumstances. Accordingly we find among the speculations of philosophers, concerning the nature of the function of digestion, that it has been ascribed to fermentation. By one set it was ascribed to one kind of fermentation, namely to the vinous or acetous; and by another set this conversion of the food was supposed to be effected by the putrefactive fermentation. But now, that the nature and circumstances of the processes of fermentation and digestion have been more accurately observed, this opinion, it is probable, is universally exploded. The experiments of physiologists, also, have led to more rational views concerning this function.

4. It is now generally admitted, that the conversion Gastric of the food into chyme, is effected by the action of a juice, peculiar fluid secreted in the stomach, from which it has been denominated gastric juice. This liquid seems to possess different properties in different animals, for those animals which live entirely on vegetables cannot digest animal food, and the gastric juice of those which have been accustomed to live entirely on animals, has no effect on vegetables. It is true, indeed, that the nature of animals in this respect, as well as in most of their habits, may be completely reversed, when it is affected by slow degrees. All substances taken into the stomach, are not equally acted upon by the gastric juice. Some of the hardest are readily dissolved, while others, seemingly less compact and durable, remain unaltered. The hulls of grain in the stomachs of many animals resist its action, while the hardest bone is entirely consumed.

5. No accurate knowledge has yet been obtained concerning the nature of the gastric juice. According to some it is of an alkaline nature, and according to others it possesses acid properties. But this difference of opinion is by no means to be wondered at, if we consider the difficulty, or perhaps the impossibility of obtaining the gastric juice in a state of purity, to subject it to chemical examination. If it even were possible to collect it perfectly pure, its effects could not be the same as within the body, since all animal matters, the moment they are separated from the living body, begin to undergo new changes, and therefore must exhibit new properties. All experiments, therefore, which have been made, to ascertain the nature of the gastric juice, and the process of digestion out of the body, must be considered as entirely inconclusive. Such experiments show us the effects of this liquid in the state of dead matter, but can lead to no knowledge of its na-

6. But whatever be the nature of this liquid, or the process of digestion, the food, as we have already observed, is broken down in the mouth and mixed with the saliva, which, in the first instance, probably contributes much to favour its commencement; for it has been observed that the process of digestion is considerably deranged when the secretion of saliva is interrupted, or its usual quantity diminished. All, then, that is certainly known concerning this change is, that the food conveyed to the stomach is in a very short time converted into the substance called chyme.

7. The chyme, which is a soft, pulpy matter, after being formed in the stomach, is carried to the intestines, where it is mixed with other substances, and undergoes new changes. As soon as the chyme has passed into the intestines, it is converted partly into a milky fluid called chyle, and partly into excrementitious matter. Thus it is decomposed by some process, and separated into two parts, one of which is destined for the nourishment of the body, and for repairing its waste, while the other is ejected.

8. The chyle, soon after it is formed from the chyme, mixes with the bile which flows from the liver into the intestines. In consequence of this combination, it is supposed the excrementitious matter is separated from the chyle, and is thrown out of the body; while the chyle itself is taken up by a set of vessels called lacteals, which open on the inner surface of the intestines, and receiving the fluid, convey it to a large trunk in which they all terminate, denominated, from its situation in the thorax, the thoracic duct. The use of the bile is supposed to be, to separate the excrementitious matter which might prove injurious to the system, if it were absorbed along with the chyle; and for this purpose the bile, it is supposed, is decomposed; one part, namely its saline and alkaline constituents, combines with the chyle, by which it becomes more liquid, while another part, namely the resinous and albuminous matter, combines with the excrement, and in this state acts as a stimulant to the intestines, so that the contents, which might otherwise prove injurious, if long retained, are ejected.

9. As a proof that the food which has been taken into the body has been totally changed, substances have been detected in the excrement of different animals which did not previously exist in the food. According to Vauquelin, excrementitious matter is always distinguished by an acid property. Benzoic acid has been detected in that of horses and cows. An acid of a peculiar nature has been found in the dung of pigeons; but in general this matter is much disposed to ferment, and at last gives out ammonia.

In the analysis of the excrement of a hen by Vauquelin, compared with the nourishment, he found that the oats which were taken in were composed of phosphate of lime and silica, and that the shells of the eggs, and the excrements which were examined, consisted of phosphate of lime, carbonate of lime, and silica. The proportion of silica which was found in the excrement was less than the quantity taken in; but the quantity of phosphate of lime was increased, and a quantity of carbonate of lime which did not previously exist in the food, was formed.

10. The chyle, it has been observed, is taken up by the lacteals, and conveyed to the thoracic duct. Little of chyle is known of its properties, excepting that it possesses some in common with milk. Like milk, it coagulates, and divides into a serous and oily matter. In the thoracic duct the chyle is mixed with another fluid called the lymph, which is conveyed from all parts of the body by a set of vessels which have been denominated lymphatics. This fluid is in considerable quantity, is of lymphatic and colourless, but from the difficulty of collecting it, little is known of its properties. The lymph and the chyle, thus mixed together, are conveyed by the thoracic duct to the blood-vessels. It is mixed with the blood in the veins, and conveyed by them to the right side of the heart, from which it is carried to the lungs, where it undergoes the changes already described in the account of respiration, and the whole is converted into arterial blood, which returns to the heart, from whence it is distributed to all parts of the body.

III. Of Secretion.

1. In the course of the circulation of the blood, different substances are separated from it, some of which are destined for the growth and nourishment of the body, as in young animals, or for the repair and supply of parts that are destroyed; while other substances, which seem either to be superfluous, or if retained, would be injurious, are thrown out of the body. These secretions are performed by peculiar organs, the description and operation of which belong to ANATOMY and PHYSIOLOGY. At present we will give a short account of two of the most important of these secretions, namely, the secretion of urine, and that of perspirable matter.

Secretion of urine.—The urine, which is an excrementitious matter, is separated from the blood by the kidneys, according to the observations of anatomists and physiologists on the structure and office of these organs, a great proportion, or even, as some suppose, the whole, of the blood passes through them. As the urine secreted by these organs seems to serve no purpose in the animal economy, since the whole of it is thrown out, it is probable that the substances of which it is composed, or at least their constituents, would have proved injurious if they had been retained.

2. Whatever the change be which takes place in the blood by the action of the kidneys, it is of the utmost importance to the health and even to the life of the animal.

(b) The stomach of young animals contains some substance which has the property of coagulating milk. Acids also have this property, from which it has been concluded that the substance in the stomach of young animals, which produces this effect on milk, is of an acid nature; but it ought to be recollected, that it is out of the body, and that it has undoubtedly undergone new changes; and besides, it is not known exactly what substances may have the property of inducing this change on milk. the animal; for if these organs are destroyed by disease or accident, the death of the animal is the certain consequence.

3. By the action of the kidneys on the blood, new substances make their appearance. Such, for instance, are urea and uric acid, which exist in the urine, but cannot be detected in the blood; but the bases or constituents of these substances must have formed part of some of the matters of the blood, which are therefore decomposed for their evolution; and this decomposition must take place in these organs. But although the urine, the secreted matter, has been accurately analyzed, and its component parts, after it is thrown out of the body, pretty well ascertained, it is yet unknown what are the peculiar changes which the blood undergoes by the action of the kidneys.

Perspiration.—1. A considerable quantity of matter is separated from the blood by means of a set of vessels on the skin of animals. This action is called perspiration, and the substance emitted, perspirable matter. The attention of physiologists and chemists has been long directed to ascertain the quantity and nature of the matter thus thrown off. To ascertain the first point, many experiments have been made. Sanctorius, an Italian physician, was the first who made this attempt, by weighing himself, and estimating the quantity of food which was taken in, and the quantity of excrementitious matter thrown off. The difference, he supposed, indicated the quantity of matter perspired; but neither in his experiments, nor in those of many others, who endeavoured to ascertain the same thing, was any estimate made of the quantity of matter given out by the lungs.

2. With this distinction in view, a set of experiments was instituted by Lavoisier and Seguin. The latter was inclosed in a varnished bag, which prevented the escape of everything thrown off from the body, excepting what was lost by respiration. Having previously weighed himself, and having continued the experiment for some time, the quantity of matter thrown off by respiration was ascertained, by weighing a second time. By weighing himself afterwards without the covering, and repeating the operation at the end of a similar interval, he was thus enabled to ascertain the quantity lost by transpiration from the skin, by subtracting what had been previously ascertained by transpiration from the lungs, from the whole diminution of weight which was indicated in the last experiment. From these experiments, the following conclusions were drawn.

a. In a state of health, and when there is no disposition to corpulence, the body returns to the same weight once every 24 hours.

b. Indigestion retards transpiration. The weight is increased for four days, and on the fifth the body returns to its original weight.

c. Drink only, and not solid food, increases the perspiration. It is least at the moment of taking food, and immediately after.

d. The perspiration is greatest during digestion.

e. The greatest quantity of matter perspired amounted in a minute to 26.25 grains troy; the least to nine grains.

f. The pulmonary transpiration is proportionally greater than that of the skin. It is greater in winter, on account of the necessity of preserving the temperature of the body.

3. The quantity of matter perspired is greatest during hot weather, and in hot climates. The quantity too bears a relation to the quantity of urine. The following are the results of the experiments of Rye made in Ireland, on the relative proportion of urine and perspirable matter, which were excreted in the course of one day at different seasons of the year.

| Matter perspired | Urine | |------------------|-------| | Winter | 53 | 42 | | Spring | 62 | 40 | | Summer | 63 | 37 | | Autumn | 59 | 37 |

4. When the temperature to which the body is exposed is much elevated, the quantity of perspired matter is greatly increased, and it then appears in a visible liquid form called sweat. This answers a very important purpose in the animal economy, for by this means the equilibrium of temperature is preserved. The heat which is absorbed is carried off along with the matter which evaporates from the surface of the body, and thus the increase of temperature which would otherwise prove fatal, is prevented.

5. The next object of chemical physiologists was to Component ascertain the nature of the substance which is perspirable. This has been found extremely difficult, on account of the small quantity which it has been possible to collect. But it has been ascertained that it consists chiefly of water and carburet, with an oily matter. Phosphoric acid also, and phosphate of lime, have been detected in the perspirable matter. In the air which has been confined in contact with the skin, carbonic acid gas has been detected; from which it is concluded, that either the carburet must have been evolved, and combined with the oxygen of the air, or the oxygen gas must have been absorbed, and combining with the carburet, is given out in the state of carbonic acid. The oily matter which is emitted by the skin, is supposed to occasion the peculiar smell by which animals are distinguished. The remarkable circumstance of a dog being able to trace another animal to a great distance by the smell, or to discover his master by the same means to a much greater distance, is ascribed to the emission of this matter. The matter perspired, according to Berthollet, possesses acid properties, and the acid he supposes, is the phosphoric. Phosphate of lime has been detected in the skins of horses by Fourcroy and Vauquelin.

Besides these, there are other secretions which are Other secretions defined for peculiar purposes in the animal economy, or immediately connected with the functions of particular organs, or parts of the system. Such is the secretion of saliva in the mouth, of tears in the eyes, of mucous in the nose, and wax in the ears. The secretion of milk in the female is defined for the nourishment of the offspring; but we shall not enter into the description of the organs employed in these secretions. The nature and properties of the matters secreted will come under our consideration in treating of the different parts of animals. IV. Of Assimilation.

1. The continual waste and decay of the body require to be repaired. This, as we have already seen, is the purpose of taking nourishment into the body; part of which being subject to the processes of digestion and respiration, is converted into blood, from which source are derived those supplies of new matter which are wanted in the formation of new parts, or to make up the general decay of the system. New supplies of matter are peculiarly necessary, in young animals, in which the parts already formed increase in size and constancy, and in which, in the progress of the growth of the body, entirely new parts are evolved. But if there be anything in the speculations of physiologists, of the whole matter in the body being periodically changed, even after it has arrived at its full growth, a constant supply of new matter becomes absolutely necessary. All these supplies are furnished by the blood, and for this purpose it is distributed to every part of the body. The materials for repairing the general waste, for increasing those parts which are already formed, or for the formation of new parts, are all derived from it. From this source are derived the most fluid, as well as the most solid parts of the body; the saliva of the mouth, and the gastric juice of the stomach, so necessary in the function of digestion, by which the health and life of the animal are preserved, as well as the bones and muscles, which give it strength, firmness and motion. The process by which the different substances which are furnished by the blood for the repair of some parts and the formation of others, has been distinguished by the name of assimilation, because, in consequence of new actions and combinations, matter exactly similar to the parts repaired or renewed, is deposited, which did not previously exist in the blood.

2. These changes are effected by the action of peculiar organs or vessels. Whatever be the nature of the food taken into the stomach, it is converted into chyme by the process of digestion. This again, by a farther change, as it passes into the intestines, forms the chyle, which is conveyed to the blood, and after this fluid has undergone the changes which are induced on it by respiration, it has acquired those properties which render it fit for the important purposes to which it is destined.

3. By the action of the different secretory organs, the same matter is always separated from the blood, while the animal continues in the healthy state. The perspirable matter is separated by the glands or vessels on the skin, and the saliva is prepared by the glands of the mouth. The matter of bones, of muscles, or of nerves, is separated and deposited in those places where it is required, and no other. In the healthy state of the body, muscular matter is not deposited among the bones, nor is effusive matter mixed with the muscles.

4. The most astonishing part of the animal system is that power which it possesses of accommodating itself to particular circumstances. It would be less surprising that the same actions and the same functions, after they have commenced, should continue to be performed with uniformity and regularity. But, in the animal system, new actions take place, or at least those which were comparatively feeble and limited, become more powerful and more extensive. Thus, a part of the body which has been destroyed or removed is by this new or extended action, completely renovated. A large piece of muscle in the healthy state of the body is soon renewed; and, what is more surprising, the constituent parts of bone are prepared, when necessary, and deposited in those places where large pieces of this substance have been removed.

5. But although some, or perhaps all these changes are regulated by which take place in the different processes going on in the animal system, are of a chemical nature, yet the living principle is subject to the control of some power, the characteristics of which are totally different from those of a chemical or mechanical agent. This is the living principle which counteracts, regulates, and directs the effects of chemical agents. It is by means of this power, that the materials of which the different parts of the body are composed, are deposited in their proper places. It is by means of the same power that a greater quantity of matter necessary for the renovation of any particular part which has been destroyed, is prepared and deposited exactly in that place where it is wanted; but the power of this agent is limited. Certain substances taken into the stomach, which are unfit for digestion or nourishment, are immediately rejected; but others are too powerful, and destroy the organ itself. As the strongest proof of the existence and control of this power, the constituent parts of animal bodies begin immediately to decompose each other as soon as its action has ceased. The gastric juice of the stomach, which acts only on the substances introduced into it in the living state, has been sometimes found to corrode and destroy the stomach itself, after death. But the investigation of the nature of this agent, and of its influence on the animal body, belong to Physiology.

Sect. II. Of the Decomposition of Animal Substances.

1. As soon as an animal has ceased to live, its frame and texture are destroyed, the constituent parts are separated, they enter into new combinations, new substances are formed, and the component parts are totally changed. The rapid spontaneous decomposition of animal matters, which has been called putrefaction, is one of the most striking characters by which they are distinguished. Vegetable matters, we have seen, when vegetation ceases, are also subject to decomposition; but in them the process is slow and gradual, and many of the products are totally different.

2. The remarkable difference between the spontaneous decomposition of vegetables and animals, depends on the difference of the constituent parts of these two classes of organized substances. Animal matters are composed of a greater variety of constituent principles, and thus originates a greater variety of action, when the different component parts begin to act on each other. By the numerous and complicated attractions which exist among these constituent principles, decomposition is more readily effected, and a greater variety of new products make their appearance.

3. But notwithstanding the variety and complicated structure of animal substances, total decomposition or putrefaction Decomposition does not take place, except in certain circumstances, by which the mutual action of the constituent principles is promoted. The chief circumstances necessary for the putrefaction of animal matter are, moisture and moderate heat. Dry animal matters do not undergo any change. Bones, when moistened with water, the soft parts of animals, but especially the liquid parts, run rapidly on to putrefaction. Heat is also necessary to promote this change. No putrefaction takes place in animal matters, at or below the freezing temperature. Before it commences, the temperature must be elevated some degrees above this point, and as the temperature rises, the rapidity of the process is proportional. This condition, however, has its limits; for when the heat reaches a certain point, far from promoting the process of putrefaction, it is retarded, or altogether interrupted, by carrying off the moisture. The contact of air was thought necessary to favour this process; but although it appears that this is not an essential condition, putrefaction goes on more rapidly in the open air, perhaps by receiving and carrying off the elastic fluids as they are formed. Matters which have already undergone this change, brought in contact with recent animal substances, promote and accelerate putrefaction.

4. When animal matters are placed in favourable circumstances, the solid parts become soft, and the liquid parts become more fluid. The colour changes, and is converted into a reddish brown, or deep green. The odour, which is at first disagreeable, becomes fetid and insupportable. An ammoniacal smell is also diffused, but this is only temporary, while the putrid odour continues during the whole process. The liquids become turbid, the soft parts are melted into a kind of jelly, accompanied with an intestine motion, and an enlargement of the bulk of the whole mass, owing to the escape of elastic fluids, which are slowly discharged. The whole matter is then reduced to one mass, the swelling ceases, the bulk is diminished, and the colour deepens. Towards the end of the process, a peculiar odour, somewhat aromatic, is emitted. When it ceases entirely, there remains behind an unctuous, viscid, and fetid earthy mass.

5. The duration of this process is extremely various, according to the nature of the substances and the circumstances in which they are placed; but it has been divided by some into different stages. In the first there is merely a tendency to putrefaction, accompanied with a very slight change of texture and colour. The second change, or incipient putrefaction, exhibits some traces of acidity; the parts are more softened, a furred matter begins to flow from the relaxed fibres; the colour is more altered, and the putrid fetid odour exhaled. In the third or more advanced stage of putrefaction, the fetid odour is more or less mixed with the smell of ammonia; the diffused putrid matter becomes of a deeper colour, and is diminished in weight by the escape of a great quantity of volatile matter. In the last stage, or when the process is completed, the ammoniacal odour vanishes, the fetid smell becomes less, and is often succeeded by something of an aromatic smell. The animal matter has diminished greatly in bulk, and has lost all appearance of organized structure. There remains only a dark brown, earthy substance, unctuous to the feel, which has been called animal earth. But these changes are regulated by the particular circumstances in which the process takes place.

6. In the course of the putrefactive process of animal substances, different gases are successively emitted. These are chiefly carbonated, sulphurated, and phosphorated hydrogen gases, water in the state of vapour, ammonia, and carbonic acid gas. These bodies are evolved and volatilized, carrying with them some of the principal constituents. Other products, formed at different periods of the process, and of a more fixed nature, make their appearance; such, for instance, is an unctuous matter, and a kind of soap, formed of this matter and ammonia; such too is nitric acid, which is frequently formed during this decomposition, and is combined with an earthy or alkaline base; and such finally is the unctuous earth which remains after the evolution and separation of the former products.

7. The process of putrefaction, then, consists in a change produced by the action of affinities, more powerful than those which hold together the constituent principles of the animal matter. These constituents are, hydrogen, azote, carbure, and oxygen, with a certain proportion of sulphur, phosphorus, and different species of phosphates. During the decomposition, a portion of the hydrogen combines with azote to form ammonia, while another portion combines with part of the oxygen to form water; part of the carbure is united with a portion of oxygen, and forms carbonic acid; the union of azote with a third portion of oxygen constitutes nitric acid; a combination of hydrogen, carbure, and azote, yields a volatile or fixed oil, according to the proportion of the constituents; and finally, the saline, earthy, and metallic substances, which are little susceptible of change, during this process, remain unaltered, and constitute the residuum. Thus, in taking a general view of the affinities which come into action during this process, the amount of those which tend to combine the hydrogen with the azote to form ammonia; the oxygen with the carbure, to form carbonic acid; the carbure with the ammonia, to form carbonate of ammonia; the hydrogen, carbure and oxygen, to form oil, and this latter with ammonia to constitute soap, beside the hydrogen and oxygen to form water, is greater than the sum of the forces which retain in combination, the hydrogen, the azote, the carbure and oxygen, which are the principal constituents of animal compounds.

8. Such are the results when the process is conducted in clothe vessels; but when the process takes place in the open air, similar results are obtained, but in a manner somewhat different, according to the nature of the compounds which are formed. In this case part of the animal substance is dissolved and carried off by the air and the water. The ammonia and carbonic acid are dissipated as they are formed; part of the carbonated hydrogen is also volatilized by the increase of temperature, and there is no unctuous matter or ammoniacal soap formed.

9. It is well known that the odour which proceeds from putrid animal matters is extremely offensive. This is owing in a great measure, to the sulphurated and phosphorated hydrogen gases discharged; but it is not merely offensive, but noxious to the health, and sometimes destructive to the life of animals. These effects are Component parts of Animal Substances.

1. Gelatine, 2. Albumen, 3. Fibrina, 4. Urea, 5. Sugar, 6. Oils, 7. Resins, 8. Phosphorus, 9. Sulphur, 10. Acids, 11. Alkalies, earths, and metals.

I. Of Gelatine.

1. Glue, a well-known substance in the arts, is gelatinous in a state of impurity. This may be obtained pure by repeatedly washing the fresh skin of an animal in cold water, afterwards boiling it, reducing it to a small quantity by a slow evaporation, and allowing it to cool. It then assumes the form of a solid tremulous substance called jelly. When this substance is dried in the air, it becomes hard and semitransparent.

2. Gelatine has different degrees of hardness, and properties when pure, it is colourless and semitransparent. It is brittle, breaks with a vitreous fracture, and has neither taste nor smell.

3. When it is exposed to heat, in the dry state, it becomes white, then blackens, and is converted into heat. A coaly matter. Tremulous gelatine melts before it undergoes these changes. When it is distilled, it affords a watery fluid, impregnated with ammonia and a fetid oil. A voluminous mass of charcoal remains behind.

4. Gelatine remains unaltered in the dry state and exposure to the air; but the solution in water is soon decomposed, giving out an acid, the nature of which is unknown, a fetid odour, and some ammonia. It is not very soluble in water; it increases in bulk, and becomes soft and tremulous. In this state it soon dissolves in warm water; but as the solution cools, it returns to its former state.

5. With the affluence of heat gelatine is readily dissolved by the acids. Sulphuric acid acts slowly on this substance, and forms a brown solution, which becomes gradually darker with the evolution of sulphurous acid. Nitric acid by digestion on gelatine, is decomposed; azotic gas is evolved, and afterwards a great quantity of nitrous gas. The gelatine is dissolved, and converted partly into oxalic and malic acids, and an oily matter which remains on the surface. Muriatic acid readily dissolves gelatine, and forms a brown-coloured solution, from which a white powder is gradually precipitated. When this solution is added to the solution of tan in water, a copious precipitate is formed.

6. Gelatine is readily dissolved by the alkalies, with alkalies, the aid of heat. There is no action between any of the earths and this substance.

7. Some of the metallic oxides form precipitates with gelatine in its solution in water. The compound thus formed is insoluble. Similar precipitates are occasioned by some of the metallic salts.

8. Gelatine forms a copious white precipitate with tan. A brittle compound is thus produced, which is insoluble in water, and is not changed by exposure to the air.

9. The component parts of gelatine are carbons, hydrogen, azote, and oxygen, with some traces of phosphate of lime and of soda, but the proportions of these substances have not been determined.

10. There are various kinds of gelatine, probably arising from slight variations of the proportions of its constituents, or from the addition of other substances, the nature of which has not been distinctly ascertained. Glue is extracted from different animal substances, as bones, muscles, membranes, but especially from skins, by first steeping them in lime-water, to purify them from all extraneous substances, and afterwards boiling them with pure water. The strongest glue is obtained from the skins of old animals. What is called size, is a weaker kind of glue, which is colourless and transparent, and is extracted from the skins of eels, horses, cats, rabbits, and from some kinds of white leather. It is this which is employed in the manufacture of paper, and in gilding and painting. Ifinglaf, another kind of glue, is extracted from different parts of the sturgeon, and some other fish.

11. Gelatine forms a principal part, both of the solid and fluid parts of animals. It is found in blood and in milk, in the bones, ligaments, skin, and other solid parts.

12. Animal jelly, which is gelatine, is well known as a very nutritious food, and is much employed in the state of glue, size, and ifinglaf, in numerous arts.

II. Of Albumen.

1. The white of an egg consists chiefly of albumen. It is combined with a portion of soda and sulphur. From these substances it cannot be separated without decomposition, so that its properties are probably modified by them.

2. When albumen is exposed to a heat of about 165° it coagulates into a solid white mass, of different degrees of consistence, according to the duration of the heat applied. This is the characteristic property of albumen. In this state it has totally changed its properties. Formerly soluble in water, it cannot now be dissolved in that liquid, either hot or cold.

Different opinions have been formed concerning the nature of this change, or the cause of the coagulation of albumen. It has been ascribed by some to the abstraction of caloric, and by others to that of oxygen. The former opinion was that of Scheele, and the latter is supported by Fourcroy; but this coagulation is found to take place when air is entirely excluded, or without any change being produced in the surrounding air. It has been supposed by others, that the coagulation is produced by the extraction of caloric, as in other cases when fluid bodies are converted into solids. According to an experiment of Fourcroy, this extraction of caloric actually takes place; but it is ascribed by others to a different arrangement of the particles of the albumen, which is induced by the action of the heat applied.

3. The properties of albumen, it has been observed, are very different after coagulation. Before coagulation it is a glairy liquid which has scarcely any taste, and no smell. When dried in a moderate heat, it becomes brittle and transparent, and by being spread thin, forms a varnish. When thus dried, it is not changed by exposure to the air, but otherwise it soon becomes putrid.

4. Albumen is coagulated by means of the acids. With the aid of heat, sulphuric acid dissolves it, and forms a solution of a green colour. By the action of nitric acid, azotic gas is disengaged: the albumen is then dissolved; nitrous gas is given out, and oxalic and malic acids are formed, besides a thick oily substance which appears on the surface. The coagulation of albumen does not take place when it is dissolved in a great proportion of water. Albumen is also coagulated by means of alcohol and ether, but if the quantity of water in which it is dissolved be considerable, the coagulation is not effected.

5. By trituration with a concentrated solution of potash, albumen left at rest for some time, coagulates, and is converted into a substance resembling jelly, which is brittle and transparent when it is dried. No change takes place on albumen by the action of the earths.

6. Albumen is precipitated, from its solution in water, by many metallic salts. The precipitate is white, yellow, or brown, according to the metal employed.

7. Tan precipitates albumen from its solution in tan water, in the form of a copious yellow substance, which is insoluble in water. It becomes brittle when dry, and is not changed by exposure to the air.

Coagulated albumen.—1. Albumen, when it is coagulated, acquires new properties. It is then a tough, opaque substance, of a pearly-white colour, and of a sweetish taste. It is insoluble in water, and is less subject to change. When it is dried in the temperature of 215°, it is converted into a hard, brittle, yellowish substance, of the transparency of horn. When it is some time digested in water, it becomes soft, white, and opaque, like albumen newly coagulated. By long action a small part seems to be dissolved, but no precipitation is formed in this solution by the infusion of tan.

2. The mineral acids largely diluted with water, dissolve a portion of coagulated albumen; but by the addition of the same acids in their concentrated state, it is again precipitated. If coagulated albumen be kept in diluted nitric acid for several weeks, the acid acquires a yellow colour, which gradually deepens; the albumen becomes more opaque, but is not dissolved. By saturating the yellow-coloured acid with ammonia, no precipitate is formed, but it assumes a deep orange colour. If the albumen be then introduced into liquid ammonia, the latter assumes a deep orange colour, inclining to red. The albumen dissolves slowly, and after the solution is completed, it is of a yellowish-brown colour. By washing and boiling in water, the albumen thus treated with nitric acid, is dissolved, the liquid becomes of a pale yellow, and assumes the form and appearance of jelly, when it is concentrated. If this mass be dissolved in boiling water, the solution is precipitated by tan; so that nitric acid has the property of converting coagulated albumen into gelatine.

3. Coagulated albumen is readily dissolved in a solution of potash by boiling. Ammonia is disengaged, and

Component and a soap is formed. If this soap be dissolved in water, and muriatic or acetic acid be added, a precipitate is formed, which also has the properties of soap. When it is moderately heated, a portion of oil flows out, and a viscid brownish substance remains behind.

4. Albumen is composed of carbon, hydrogen, azote, and oxygen, but the proportions have not been determined. It is supposed by some that it contains a greater proportion of azote than gelatine.

5. Albumen constitutes an essential part in the composition of bones and muscles. Cartilage, horns, and hair consist almost entirely of this substance, as well as the membranous portion of shells and sponge.

6. Albumen is advantageously employed for clarifying liquids. The liquid to be purified is mixed with the white of eggs, the serum part of the blood, or other substances containing albumen, and then heated. By the action of heat the albumen is coagulated, and falls to the bottom, carrying with it those substances which were mixed with the liquid, and occasioned the opacity, and which, on account of the minuteness of the particles, could not be otherwise separated.

III. Of Fibrina.

1. Fibrina is readily obtained by allowing blood to remain at rest for some time after it has been drawn from an animal. The clot, which has formed and falls to the bottom, is to be separated, put into a linen cloth, and repeatedly washed with water, till the liquid come off infusible and colourless. The fibrous part of the blood, as it has been called, or the fibrina, remains behind. Mr Hatchett obtained it by cutting lean beef into small pieces, macerating in water for fifteen days, changing the water daily, and squeezing it out at the same time by pressure. The mucilaginous substance was boiled every day five hours for three weeks in a fresh portion of six quarts of water. The fibrous substance was then pressed, and dried with the heat of a water bath. What remained is considered as fibrina nearly pure.

2. Fibrina is of a white colour, soft and elastic, when it is recently extracted from blood; and, as it dries, the colour becomes deeper. When it is extracted by boiling and maceration from mucilaginous matter, it is brittle, has some degree of transparency, and does not become too deep in the colour. It has neither taste nor smell. It is insoluble in water and alcohol, and is not changed by exposure to the air.

3. When it is exposed to heat, it contracts suddenly, and emits the smell of burning feathers. It melts with an increase of temperature. It yields by distillation, water, carbonate of ammonia, a thick fetid oil, carbonic acid, and carbonated hydrogen gas, with some traces of acetic acid. The coaly matter which remains behind burns with difficulty, on account of the phosphate of soda, phosphate and carbonate of lime, with which it is mixed.

4. Fibrina is soluble in the acids. The solution in sulphuric acid is of a deep brown colour; charcoal is precipitated, and acetic acid formed. When diluted nitric acid is added to fibrina, azotic gas is copiously discharged. Fibrina kept by Mr Hatchett for 15 days in nitric acid diluted with 3 times its weight of water, gave to the solution a yellow colour, and it resembled in its properties the solution of albumen in the same acid. By this process, after being dissolved in boiling water, and concentrated by evaporation, the fibrina is converted into gelatine, which is soluble in hot water, and is precipitated by tan. The fibrina in this state also is almost entirely dissolved by ammonia, and the solution is of an orange colour. Fibrina is dissolved in boiling nitric acid, in which ammonia produces a precipitate, composed chiefly of oxalate of lime. During the action of the nitric acid, prussic acid passes over, with carbonic acid gas and nitrous gas. Oxalic acid is formed, and a fatty matter appears on the surface. Fibrina is also soluble in muriatic acid, with which it forms a green-coloured jelly. It is dissolved also in acetic, oxalic, tartaric, and citric acids, with the assistance of heat; and is converted by concentrating the solutions, into a gelatinous mass. Alkalies precipitate fibrina from its solution in the acids, in the form of flakes, which have the properties of gelatine, and are soluble in hot water.

5. Concentrated potash or soda, boiled upon fibrina, forms a deep brown coloured solution, which has the properties of soap. During the process ammonia is given out.

6. Fibrina is composed of carbon, hydrogen, azote, and oxygen, but the proportions are unknown. It is found only in the blood and muscular parts of animals.

IV. Of Urea.

1. The nature and properties of urea have been chiefly investigated by Fourcroy and Vauquelin. It is obtained from urine. It may be extracted by the following process.

If a quantity of human urine which has been passed Method of a few hours after taking food, be evaporated with a preparing gentle heat, to the confluence of a thick syrup, and allowed to cool, it concretes into a crystalline mass. Add to this mass in separate portions four times its weight of alcohol; with the application of a gentle heat, great part is dissolved, and what remains consists of different saline substances. Separate the solution from the undissolved part, and introduce it into a retort. Dilute with the heat of a sand-bath, and continue the boiling till the liquid is reduced to the form of a thick syrup. The matter which remains in the retort crystallizes as it cools. The crystals thus formed are urea.

2. Urea, which is prepared by this process, is crystallized in the form of plates, crossing each other. It is viscid, resembling thick honey, and of a yellowish white colour. It has a strong acrid taste, and a fetid alliaceous smell. It deliquesces in the air, and by attracting moisture is converted into a thick brown liquid. It is very soluble in water, and also in alcohol. The solution in water concentrated is of a brown colour. This solution is gradually decomposed, air is emitted, which is partly composed of ammonia, and acetic acid is formed in the liquid. If the solution in water be boiled, and as the evaporation goes on fresh portions of water be added, the urea is decomposed; carbonate of ammonia is discharged, while acetic acid is formed and charcoal precipitated.

3. By the action of heat urea soon melts, enlarges in bulk, and evaporates, emitting an extremely fetid heat, smell, Component smell. By distillation, benzoic acid first passes over, afterwards carbonate of ammonia, carbonated hydrogen gas, with a small portion of prussic acid and oil. What remains behind consists of charcoal, muriates of ammonia and of soda. The benzoic acid, the muriate of ammonia and muriate of soda, are considered as extraneous matter, so that the products of urea by distillation consist of the carbonate of ammonia, carbonated hydrogen gas, and charcoal. The component parts of urea, therefore, are supposed to be,

| Component | Parts | |-----------|-------| | Oxygen | 39.5 | | Azote | 32.5 | | Carbome | 14.7 | | Hydrogen | 13.3 |

100.0

4. If one-fourth of its weight of diluted sulphuric acid be added to the solution of urea, and heat be applied, an oily matter appears on the surface, which concretes on cooling. Acetic acid is found in the liquid which is collected in the receiver, and sulphate of ammonia remains in the retort. The whole of the urea may be converted into acetic acid and ammonia by repeated distillation.

Nitric acid produces a violent effervescence with the crystals of urea. The liquid becomes dark red, and during effervescence nitrous gas, azotic gas, and carbonic acid gas are evolved. A concrete white matter remains after the effervescence has ceased, mixed with a small portion of the red liquid. The refi- duum produces a detonation with the application of heat.

Urea is soluble in muriatic acid, but it remains unchanged. A diluted solution of urea absorbs very rapidly oxymuriatic acid gas. Whitish flakes appear, which soon become brown, and adhere to the sides of the vessel. After the absorption, the solution gives out carbonic acid and azotic gases. Muriate and carbonate of ammonia remain in the liquid after the effervescence ceases.

5. Urea is readily dissolved in solutions of potash or soda. Ammonia is also disengaged, when urea is dissolved in solutions of barytes, lime, or magnesia. It is also disengaged by triturating pure potash in the solid state, with urea. Heat is produced at the same time. The mixture assumes a brown colour, and an oily matter is deposited.

Muriate of soda dissolved in a solution of urea in water, affords by evaporation crystals in the form of regular octahedrons; but muriate of ammonia, dissolved in the same way, crystallizes in the form of cubes.

V. Of Sugar.

1. Sugar has only been discovered among animal matters in milk and in the urine of persons labouring under diabetes. Sugar is obtained from milk by evaporating fresh whey to the consistence of honey. When it cools, it concretes into a solid mass. This is to be dissolved in water, and being previously clarified with the white of eggs, to be filtered and evaporated to the consistence of syrup. Crystals of sugar of milk are deposited on cooling.

2. When sugar of milk is pure, it is of a white colour, has a sweetish taste, but no smell. It crystallizes in the form of regular parallelopipeds, terminating in four-sided pyramids. The crystals are semitransparent. The specific gravity is 1.543. It is soluble in seven times its weight of water.

3. When it is burnt, it exhibits the same appearances as vegetable sugar, giving out at the same time the odour of caramel. Similar products are obtained by distillation as from vegetable sugar; but the empyreumatic oil has the odour of benzoic acid.

4. By means of nitric acid the sugar of milk is partly converted into saccharic acid.

Sugar from diabetic urine.—This is obtained by evaporating the urine of persons labouring under diabetes, obtaining One twelfth of the weight of urine of a sweet-tasted substance of the consistence of honey has been obtained by this process. When this substance is treated with nitric acid, it affords oxalic acid in the same proportion as vegetable sugar; but no saccharic acid is formed, as when sugar of milk is treated in the same way. It has not been crystallized.

VI. Of Oils.

1. The oils which have been detected in animals have the characters of fixed oils. Sometimes they exist in the solid state, and sometimes they are liquid. Fat is a copious animal production, which has different degrees of consistence, as it is obtained from different animals. To purify it, it is cut into small pieces, which are to be well washed with water, and the membranous and vascular parts separated. It is then put into a shallow vessel along with some water, and kept melted till the whole of the water is evaporated. It is then of a pure white colour, without taste or smell.

2. It melts at different temperatures. Hogs lard requires only a temperature of 97°, while the fat extracted from meat by boiling requires a temperature of 127°. When the heat is raised to 400°, a white smoke is given out; as the heat increases it is decomposed, and becomes black. When hogs lard is distilled in a retort, carbonated hydrogen and carbonic acid gases, accompanied with a very offensive smell, pass over. A portion of water is also obtained, and a white oil which concretes in the receiver. Acetic acid and a portion of sebacic acid are also found in the receiver. A black mass remains behind in the retort.

3. Fat is insoluble in water and alcohol. It is dissolved and decomposed by the strong acids. If nitric acid be poured upon fat, and a moderate heat applied, the acid is decomposed, and the fat is converted into a yellow coloured ointment. Fourcroy calls this an oxide of fat; the oxygen of the acid having combined with the oily matter.

4. Fat combines with the alkalies in the same way as other oily substances, and with them it forms soap.

5. The constituent parts of fat, as appears from the products which are obtained from its decomposition, are oxygen, hydrogen, and carbome.

There are besides some other oily substances obtained from different parts of animals, as spermacti from the head of the spermacti-whale, spermacti-oil, which is separated in the purification of the spermacti, and train VII. Of Refins.

1. Resinous substances are found in different parts of animals, or rather they exist in those substances which are secreted by animals.

2. A resinous substance is extracted from the bile of animals. It is extracted from the fresh bile of the ox, by muriatic acid, in the proportion of one part of the latter to 32 of the former. The mixture remains for some hours, is filtered, and a white coagulated substance is separated. The filtered liquid, which has a fine green colour, is to be evaporated in a glass vessel with a gentle heat. The evaporation is continued till a green-coloured substance precipitates, which is to be separated, and washed with pure water. This substance is the resin of bile.

3. It is of a dark-brown colour, but when spread thin, is of a fine green. The taste is extremely bitter.

4. When it is heated to the temperature of 122°, it melts. By increasing the heat, it takes fire and burns. It is soluble in cold and hot water, and also in alcohol; but it is precipitated from the latter by water. The alkalies also dissolve this substance, and form a compound which has the properties of soap. This substance is precipitated from all these solutions by means of diluted acids.

A resinous substance has also been discovered in human urine, in ambergris, which will be afterwards described, and in caffor, civet, and musk.

VIII. Of Phosphorus.

During the putrefaction of animal matters, phosphorus is given out in the state of phosphated hydrogen gas, so that it must have entered as a constituent into these matters.

IX. Of Sulphur.

Albumen is always mixed with a portion of sulphur. It has been detected in the white of eggs and in milk, in the blood, in the urine and faeces, in the muscles and in the hair. According to Proust sulphur exists in the blood, in combination with ammonia, forming a hydrofulphuret of ammonia.

X. Of Acids.

No less than 12 different acids have been detected ready formed in animal bodies. These are,

- Sulphuric, - Muriatic, - Phosphoric, - Carbonic, - Acetic, - Oxalic, - Malic, - Benzoic, - Lactic, - Uric, - Rofaciac, - Amniotic.

1. Sulphuric acid has been found combined with soda, forming sulphate of soda, in the liquor of the amnios of cows. Sulphate of lime has been detected in the urine of quadrupeds.

2. Muriatic acid exists in combination with soda in almost all the animal fluids, forming muriate of soda.

3. Phosphoric acid is found in great abundance in different parts of animals. The phosphate of lime constitutes the basis of the bones, and it exists also in almost all the solid parts of animals, and in most of the fluids. In the blood it is combined with iron.

4. Carbonic acid is found combined with lime in the urine of horses and cows. It has also been detected in fresh human urine.

5. Acetic acid is found in urine; but it has been detected in great abundance in the red ant, and was formerly called formic acid, at least combined with malic acid.

6. Oxalic acid has been found in urinary calculi.

7. Malic acid has been found in the liquid obtained from the red ant. This is obtained by bruising the ants, and macerating them in alcohol. The alcohol is driven off by distillation, and an acid liquid remains behind. By saturating this liquid with lime, and adding acetate of lead to the solution, a copious precipitate is formed, which is soluble in acetic acid, so that this liquid contains something besides acetic acid. If nitrate of lead be mixed with the acid liquid after it is saturated with lime, a precipitate is formed, which is the malic acid combined with lead.

8. Benzoic acid has been detected in human urine, and in considerable quantity in the urine of cows. It has been found in the blood, white of eggs, in glue, silk, or wool, in the sponge, and in mushrooms.

9. Lactic acid is obtained from milk, when it becomes sour. It is also said, that it has been found in new milk.

10. Uric acid exists in human urine, and forms one of the constituents of urinary calculi. One species of calculus, indeed, is composed entirely of this substance.

11. Rofaciac acid is obtained from the urine of persons labouring under fevers and other disorders, when the urine deposits what is called a lateritious sediment.

12. Amniotic acid is obtained from the liquor of the amnios of the cow.

XI. Of Alkalies, Earths, and Metals.

1. The different alkalies have been found in animal fluids. Potash has been found in considerable abundance in the urine of quadrupeds. It has also been detected in the milk of cows. Soda is found in all the fluids. It is usually mixed with albumen. It is frequently combined with the phosphoric and muriatic acids. Ammonia also has been detected in urine.

2. The earths which have been detected in animals are lime, magnesia, and silica. Lime forms, in combination with phosphoric acid, the basis of bones. It is also found in the same state in the other solid parts, as well as in most of the fluids. The shells of animals are composed chiefly of carbonate of lime. Magnesia has been found in human urine, combined with phosphoric acid and ammonia. It forms also one of the component parts of urinary calculi. Silica has only been found in similar concretions.

3. The only metal which has been detected in animals is iron, in combination with phosphoric acid, which forms a constituent part of the blood. II. Fluid parts of Animals.

We shall treat of the animal fluids in the following order:

1. Blood, 2. Bile, 3. Urine, 4. Milk, 5. Saliva, 6. Tears and mucus of the nose,

7. Humours of the eye, 8. Wax of the ear, 9. Synovia, 10. Semen, 11. Liquor of the amnios, 12. Fluids secreted by different organs.

1. Of the Blood.

1. The blood is a fluid of a red colour, which circulates through the body, and is distributed by means of the arteries to every part of it, communicating, as we have seen, heat and nourishment. It is then reconveyed by the veins from the extremities to the heart. Human blood, and that of some other animals, is of a fine, purplish-red colour, has some degree of consistence, soft and foamy to the feel, of a sweetish saline taste, and a peculiar odour. The blood is found to vary in consistence, so that its specific gravity also varies from 1.033 to 1.126.

2. When blood, after it has been separated from the body, remains for some time at rest, it separates into two parts. One part, called the clot or cruror, is coagulated, and continues of a red colour; the other part called the serum, remains fluid. The usual proportion of cruror to serum, is about one part of the former to three of the latter. This proportion, however, is subject to considerable variation.

3. The acids also coagulate blood, and decompose it. Concentrated sulphuric acid occasions a brown colour, with the production of charcoal. It is coagulated by nitric acid, with the evolution of azotic gas, and the production of carbonic and oxalic acids, besides some unctuous matter. Muriatic acid also coagulates blood, but without any perceptible change of colour. Oxymuriatic acid renders it as black as ink. Acetic acid also produces a coagulation.

4. The caustic alkalies dissolve the coagulum of blood, even when it has been produced by acids. If they are mixed with blood recently drawn, the coagulation is interrupted. Many saline bodies produce a similar effect by preventing coagulation, or decomposition.

5. The metallic oxides have little perceptible action on blood, except those which readily part with their oxygen. It is then coagulated. Almost all metallic solutions coagulate blood, and have the property, as well as the alkaline salts, of preserving it from putrefaction.

6. Many vegetable substances, when mixed with blood, prevent its putrefaction, such as sugar, volatile oils, camphor, resins. It is coagulated by solutions of gum and of starch. Tan produces a copious precipitate in blood, and gallic acid gives a black colour, owing to the iron which is contained in blood. The latter precipitate may be obtained by diluting the blood with a considerable proportion of water.

7. Blood, by remaining at rest, it has been observed, separates into two parts, the serum and the cruror. The serum is of a pale, greenish yellow colour, of a thinner consistence than blood; but retains its taste, smell, and foamy feel. The specific gravity is about 1.0287. In consequence of its containing a portion of soda, it gives a green colour to syrup of violets. Serum coagulates at the temperature of 156°.

The same effect is produced by adding boiling water. This coagulum is of a grayish white colour, resembling the white of eggs. By breaking the coagulum to pieces, a fluid may be expressed from it, which has been called the ferocity of blood. The residuum, being washed with boiling water, exhibits the properties of albumen.

8. By diluting serum with six times its weight of gelatine water, and boiling it, the albumen is coagulated. If the remaining liquid be evaporated with a gentle heat, till it is considerably concentrated, it assumes the form of jelly, and this possesses the properties of gelatine.

9. By heating the coagulated serum in a silver vessel, the silver is blackened, in consequence of its conversion into a sulphuret, by combining with sulphur contained in the coagulum. It has been already mentioned, that this sulphur exists in the blood, in combination with ammonia, in the state of hydrofulphuret.

10. The serum of blood contains muriate of soda, carbonate of soda, phosphate of soda, and phosphate of salts, lime. These salts may be obtained by mixing serum with double its weight of water, applying heat to coagulate the albumen, which being separated, and the remaining liquid filtered and evaporated, crystals are deposited on cooling. The soda exits in blood combined with gelatine and albumen, and is in its caustic state. It unites with the carbonic acid of the air during the evaporation. The component parts of serum, therefore, are the following:

Albumen, Gelatine, Hydrofulphuret of ammonia, Soda, Muriate of soda, Phosphate of soda, Phosphate of lime.

11. The cruror or clot of the blood, the other portion into which it spontaneously separates, is of a red colour, and has considerable consistence. Its specific gravity is about 1.245. By washing this substance with a small quantity of water, and continuing the process till the water passes off colourless, part of it is dissolved in the water, and part remains in the state of a solid white elastic substance, which is the fibrina of the blood. That part which is held in solution by the water contains the colouring matter. This solution converts the syrup of violets to a green colour. By exposure to the air it deposits albumen in the form of flakes. By the evaporation of this solution to dryness, and the addition of alcohol, part is dissolved. If this solution be evaporated, the residuum converts vegetable blues to green, and mixes with water like soap and soda. This residuum contains albumen and soda.

12. If the watery solution be evaporated to dryness, iron, with a moderate heat, a quantity of iron remains behind, which may be separated by the magnet. It has been said that the quantity of iron in the blood of a healthy man amounts to more than two ounces; but this... Component this is little better than conjecture, founded on vague Parts of Animal Substances.

Quantity conjec- tured.

2656

If the watery solution be evaporated to dryness, and the residuum obtained be calcined in a crucible, a red mass remains, which amounts to 0.0045 of the blood which was employed. Part of this residuum, which is phosphate of iron, is dissolved by digestion in nitric acid. From this it is precipitated of a white colour, by ammonia. With the addition of pure potash, the precipitate becomes red. By adding lime water to the solution which contains the potash, a precipitate is formed, which is phosphate of lime. By the action of these re-agents, it appears that the iron in the blood combined with phosphoric acid, is in the state of sub-phosphate. Phosphate of iron is insoluble in water, but soluble in the acids. It is partially decomposed by the alkalis, which carry off part of its acid, and leave the remainder with excess of iron. Thus it is that this salt is preserved in the state of sub-phosphate, by means of the soda which exists in the blood.

13. The method of obtaining fibrina from blood has been already described. This substance may be separated by agitating, or stirring rapidly with a stick, the blood which has been newly drawn from the animal. The fibrina or fibrous matter being well washed and dried on paper, loses about two-fifths of its weight, and becomes hard and brittle. The mean proportion of fibrina in the blood of man has been estimated at 0.0028. The fibrina is formed in the blood as it passes through the lungs, and is deposited in the muscular part of animal bodies, of which it forms one of the principal constituents. When the fibrina is separated from the blood, the latter is no longer disposed to coagulate when it is left at rest. A flaky matter only is separated, which appears on the surface.

14. Blood dried with a moderate heat, exhales a quantity of water which possesses a peculiar odour, owing to a portion of animal matter which it holds in solution. If the blood thus dried be distilled in a retort, a watery fluid passes over, afterwards carbonic acid gas, carbamate of ammonia, which crystallizes in the neck of the retort, a fluid oil, carbonated hydrogen gas, and an oily matter of the consistence of butter. A green powder is precipitated from sulphate of iron by the watery fluid. A portion of this powder is soluble in muriatic acid, and a small quantity of Prussian blue remains behind, from which it appears that prussic acid and an alkali are contained in the watery liquor.

A quantity of dried blood amounting to 9216 grs. was introduced into a large crucible, and being gradually heated, it became at first nearly fluid; it then swelled up, gave out abundance of yellowish-coloured fetid fumes, and at last took fire, and burnt with a white flame. The flame and the fumes ceasing to be emitted, were succeeded by a light, acrid smoke, which had the odour of prussic acid. When the matter had been deprived of about five sixths of its weight, at the end of five hours it melted again; a purple flame appeared on the surface, with the evolution of dense acrid fumes, which being collected were found to possess the properties of phosphoric acid. One hundred and eighty-one grains of a deep black colour and metallic brilliancy constituted the Component residuum. It was attracted by the magnet. From these observations it appears that the constituent parts of the blood are the following:

1. Water. 2. Fibrina. 3. Albumen. 4. Gelatine. 5. Hydrosulphuret of ammonia. 6. Soda. 7. Subphosphate of iron. 8. Muriate of soda. 9. Phosphate of soda. 10. Phosphate of lime. 11. Benzoic acid.

15. The constituent parts of blood vary considerably at different periods of life, and in different states of the body. The colouring matter of the blood periods of the fetus has been found to be darker and more copious. It contains no fibrina or phosphoric acid.

16. The blood of persons labouring under inflammatory disorders seems to possess different properties, from that of persons in health. It then exhibits, soon after it is drawn from the body, what has been called by physicians the buffy coat, which is considered to be the characteristic of inflammation. This inflammatory crust has been found to consist of fibrina, so that the erector deprived of this matter, becomes soft, and is almost entirely soluble in water. The albumen of the fleshy part has also undergone some changes. It assumes a milky appearance when mixed with hot water, and does not coagulate when it is heated.

17. The serum of the blood of persons labouring under diabetes, is deprived of its saline taste, has the appearance of whey, and somewhat of a saccharine taste.

II. Of Bile.

1. Bile is an important fluid in the animal economy. It seems to perform an essential part in the function and process of digestion. It is secreted from the liver, and is of a yellowish-green colour, has a soapy feel, a bitter taste, and a peculiar odour; but it varies in colour, and in some other of its properties, in different animals. It varies also in its specific gravity. It has been estimated at 1.0246. The experiments which have been made on bile relate chiefly to that obtained from the gall-bladder of the ox, hence denominated ox-gall. When bile is strongly agitated, it forms a lather like soap; and hence it has been called an animal soap. It mixes in all proportions with water, to which it communicates a yellow colour.

2. When bile is exposed to a moderate heat, it becomes thick, having lost a great part of its weight. The vapour it exhales has a peculiar offensive odour. A solid brown mass is thus obtained, which has a bitter, with somewhat of a sweetish taste, becomes soft with the heat of the hands, is ductile, attracts moisture from the air, and is soluble in water. This substance effervesces slightly with acids, and acquires a perceptible odour of musk or amber, when kept for some time. This has been called the extract of bile. When this process is conducted in close vessels, with the heat of a water bath, it gives out a clear aqueous fluid of disagreeable odour, which undergoes no particular change by means of re-agents, if the distillation has not been carried too far, or the bile has not become in some degree putrid. If this latter circumstance has taken place, Component place, the watery product has frequently a strong odour of musk, and becomes turbid on cooling.

When this extract of bile is heated in a retort, it is decomposed with peculiar appearances. When heat is gradually applied, a watery fluid, which is slightly muddy, and of a fetid odour, passes over. This fluid precipitates metallic salts, and contains almost always sulphurated hydrogen. The matter in the retort enlarges in volume, and the fluid which then comes over is of a brown colour, extremely fetid, and contains carbonate and zoonate of ammonia. Soon after an oil is evolved, which is at first liquid, and afterwards becomes of a brownish colour, thick, and empyreumatic, and of a most offensive fetid odour. At the same time carbonate of ammonia crystallizes on the sides of the receiver. There is then a copious evolution of an elastic fluid, composed of carbonic acid, carbonated and sulphurated hydrogen gases, holding in solution a small portion of oil. The carbonate of ammonia thus obtained, does not amount to the one-eighth part of the quantity which is extracted from the blood and from the bones of animals, from which it is supposed that the bile is less animalized than many other animal substances. There remains behind a black spongy mass of coal, which is easily burnt. This coaly matter, by exposure to the air, effloresces on the surface, which is found to be carbonate of soda. When it is well burnt, it preserves a deep gray colour; and there is separated, by means of cold water, nearly half its weight of carbonate of soda, a little muriate of soda, phosphate of soda, phosphate of lime, with some traces of iron.

3. Bile is decomposed by all the acids. A precipitate is formed, which is always of a green colour. Part of this precipitate remains suspended in the solution, and is even dissolved by agitation. The solution being filtered, leaves on the filter a portion of coagulated albumen. By evaporation the liquid deposits a deep green flaky substance like pitch, which has considerable tenacity, swells up when put upon hot coals, readily takes fire, and burns like refractory matter. After the separation of this matter, the liquid affords by evaporation, a salt with a base of soda.

Three different saline substances have been obtained by the action of acids on bile; the first with a base of soda, the second which crystallizes in small needles has lime for its base, and the third is a crystalline matter, of a slightly sweet taste, which is supposed to be similar to sugar. Thus it appears that acids act on bile in three different ways; they coagulate the albumen, which is precipitated; they combine with the soda, by separating the oily matter which constituted the fatty part of the bile; and they decompose the phosphoric salts.

Concentrated sulphuric acid coagulates bile in the form of dense floccus, and communicates to it a deep colour. Nitric acid, after having formed a precipitate of a green colour in the cold, affumes a golden yellow colour, when it is heated for a sufficient length of time. It converts a portion of bile into oxalic and prussic acids. Muriatic acid at first produces a green precipitate, which afterwards affumes a shade of a reddish violet colour, especially by means of heat. Oxymuriatic acid renders it white and turbid like milk. It changes the properties of the different constituents of bile, and occasions a precipitate similar to that matter which frequently constitutes biliary calculi.

4. When the precipitate from bile by means of the acids is treated with alcohol, and everything soluble in this liquid separated, there remains a whitish matter, which is infusible, nearly infipid, insoluble, whether with cold or hot water, but soluble in solutions of lime. The caustic fixed alkalies, which burns on red-hot coals with the odour of horn, and which gives by analysis, similar products, especially carbonate of ammonia in considerable quantity. The coal which remains contains a portion of phosphate of lime.

5. The alkalies deprive bile of its bitter taste; but action of the alkalis do not coagulate it.

6. Thus it appears that the constituent parts of bile are the following:

| Water, | Saccharine matter, | |--------------|--------------------| | Albumen, | Muriate of soda, | | Refin, | Phosphate of lime, | | Soda, | Phosphate of soda, | | Sulphurated hydrogen, | Iron. |

7. Bile, it has been already observed, performs an important part in the function of digestion. The albuminous and saline parts combine with the chyle, and are conveyed to the blood. The refractory portion combines with the excrementitious part of the chyle, and is thrown out of the body.

Bile is employed in the arts for removing spots of grease and oil from woollen stuffs. It is also employed as a pigment. It is evaporated and reduced to the form of extract, and diluted with a little water, in which state it gives a brown colour.

III. Of Urine.

1. The properties of urine vary considerably, according to the constitution and health of the body, and the period when it is voided after taking food. The urine of a healthy person is of a light orange colour, and uniformly transparent. It has a slightly aromatic odour, in some degree resembling that of violets. It has a slightly acrid, saline, bitter taste. The specific gravity varies from 1.005 to 1.033. The aromatic odour, which leaves it as it cools, is succeeded by what is called the urinous smell, which latter is converted to another, and finally, to an alkaline odour. Urine converts the tincture of turpentine into a green colour, from which it is concluded, that it contains an acid.

2. By adding a solution of ammonia to fresh urine, a precipitate is formed in the state of white powder, of lime, which is found to be phosphate of lime. But if lime water be employed in place of ammonia, a more copious precipitate, of phosphate of lime, is obtained, from which it is concluded, that the phosphate of lime is held in solution with an excess of acid.

3. A small portion of magnesia is also found mixed with the phosphate of lime which has been precipitated, derived from phosphate of magnesia, which has been decomposed by the alkali or lime.

4. The froth which appears when urine is evaporated is ascribed to the evolution of carbonic acid gas.

5. Urine which has been kept in new casks, deposits carbonates of lime. Component fits finall crystals, which efloresce in the air. These crystals have been found to possess the properties of carbonate of lime.

6. A brick-coloured precipitate is frequently formed in urine as it cools. This substance is uric acid, which exists in all urine, and may be obtained by evaporating fresh urine, dissolving it in pure alkali, and precipitating by means of acetic acid.

7. The urine of persons labouring under intermittent fevers, and some other diseases, deposits a copious sediment called the lateritious sediment, which consists of rofacic acid.

8. Benzoic acid also exists in urine. It is obtained by evaporating fresh urine to the consistence of a syrup, and adding muriatic acid. A precipitate is thus formed, which is benzoic acid. But it may be obtained by evaporating urine to dryness, separating the saline substances, and applying heat to the residuum. By this process the benzoic acid is sublimed, and crystallized in the receiver. The quantity of benzoic acid is more considerable in the urine of horses and cows than in human urine.

9. Albumen or gelatine has been found in urine, and is precipitated by means of an infusion of tan. The cloud which appears as urine cools, consists of these substances, which are increased in proportion during different diseases. The urine of persons labouring under dropsy contains a large quantity of albumen; and in the urine of those persons who are subject to indigestion, the albumen and gelatine are greatly increased.

10. Urea is the principal constituent of urine. The method of obtaining it from urine has been already described. It is to this substance that the taste, smell, and peculiar characters of urine are owing. If concentrated nitric acid be poured upon urine, evaporated to the consistence of syrup, crystals appear, which are the nitrate of urea. The quantity of urea secreted is very different in different circumstances.

11. A resinous substance resembling the resin of bile has been detected in urine, to which its colour is ascribed. Urine evaporated to the consistence of extract, mixed with sulphuric acid and distilled, gives out this resinous matter, which is soluble in water and in alcohol. When urea has been separated from urine by evaporation and crystallization, a saline mass remains. If this be dissolved in hot water, and spontaneously crystallized in a close vessel, two kinds of crystals are deposited. Those at the bottom are in the form of rhombohedral prisms, and consist of phosphate of ammonia mixed with a little phosphate of soda. The crystals in the upper part of the vessel are in the form of rectangular tables, composed chiefly of phosphate of soda. These were formerly called sable salt of urine, microcosmic salt.

12. Muriate of soda was the first saline substance detected in urine. It may be obtained by slowly evaporating it to the consistence of syrup. The salt crystallizes upon the surface, but in this case the form of the crystal is that of an octahedron, and not the cube, the usual form. The cause of this deviation is ascribed to the urea.

13. Muriate of potash is also found among the crystals which are formed during the evaporation of urine.

14. Muriate of ammonia is one of the salts which are found in urine. The crystals of this salt which are usually octahedrons, when they are formed in urine assume that of the cube, a deviation which is also ascribed to the action of the urea.

15. Urine contains sulphur, which may be detected by holding paper stained with acetate of lead over urine when it becomes putrid. The paper is blackened, which is owing to sulphur exhaled with the carbonic acid. Sulphate of soda and sulphate of lime have also been detected in urine.

16. No less than 30 different substances have been detected in urine by chemical analysis, the principal parts which are the following:

Water, Phosphoric acid, Phosphate of soda, Phosphate of soda and ammonia, Phosphate of ammonia, Phosphate of lime, Phosphate of magnesia, Phosphate of magnesia and ammonia, Carbonic acid, Carbonate of lime, Uric acid, Urate of ammonia, Rofacic acid, Benzoic acid, Benzoate of ammonia, Gelatine, Albumen, Urea, Refin, Muriate of potash, Muriate of soda, Muriate of ammonia, Sulphur, Sulphate of lime, Sulphate of soda.

17. Urine is much disposed to spontaneous decomposition. The time when this process commences, and of the rapidity of the changes which take place, depend on the quantity of the gelatine and albumen. When the proportion of these substances is considerable, the decomposition is very rapid. This is owing to the great number of substances, and the united force of their attractions overcoming the existing affinities of the different compounds of which fresh urine consists, and especially to the facility with which urea is decomposed. This substance is converted during putrefaction into ammonia, carbonic acid, and acetic acid. Hence the smell of ammonia is always recognized while urine is undergoing these changes. Part of the gelatine is deposited in a flaky form mixed with mucilage. Ammonia combines with phosphoric acid, and the phosphate of lime is precipitated. It combines also with phosphate of magnesia, and forms a triple salt. The other acids, the uric, benzoic, the acetic and carbonic acids, are all saturated with ammonia. The following substances, therefore, are obtained from urine by putrefaction:

Ammonia, Phosphate of ammonia, Phosphate of magnesia and ammonia, Carbonate of ammonia, Urate of ammonia, Acetate of ammonia, Benzoate of ammonia, Muriate of ammonia, Muriate of soda. Products nearly similar are obtained by distillation of urine.

18. Such are the properties of human urine in its healthy state; the changes to which it is subject, and the products which are obtained, either by means of chemical analysis or spontaneous decomposition. But the nature and properties of urine vary considerably, according to the period of life, the time it is voided after taking food, different seasons of the year, the nature of the food, the influence of passions, and disease.

In the urine of infants no phosphate of lime is found. The proportion of benzoic acid is considerable, and the quantity of urea is small. There is less acrimony, odour, and colour. As the period of life advances, the saline matters increase, especially the phosphate of lime, which is no longer required for the formation of bone.

The urine, which is passed immediately after taking food, is white and colourless, and seems to contain little else but water. It is not till seven or eight hours after a repast, that the urine is completely formed.

Urine voided during the warmer seasons of the year, or by persons who inhabit hot climates, is high-coloured and acrid, which is ascribed to a greater proportion of saline matter and urea. In winter also the urine is red and high-coloured, owing to a greater proportion of the earthy phosphates and of uric acid, which it then contains. It is no doubt considerably influenced by the modification of the action of the skin.

The food frequently communicates its properties to the urine. The odour of garlic, of resinous substances and some aromatics, is often perceptible in the urine a few minutes after these substances are taken into the stomach, or even only applied to the skin. The fetid odour of the urine of those who have eaten asparagus, is well known. The colouring matters of some substances are communicated to the urine; such as the red colour of beet-root, the orange-yellow of rhubarb, or the colour of madder.

The passions of the mind have great influence on the secretion of urine, both in changing its properties and increasing its quantity. In these cases the urine is generally colourless, insipid, and without odour.

But the nature and properties of urine undergo still greater changes during disease. From these changes the empiric has attempted to form prognostics of the nature, progress, and termination of diseases.

At the commencement of fevers and inflammatory disorders, the urine is high-coloured and extremely acrid, scarcely becomes turbid on cooling, and deposits no sediment. In affections of the liver, such as jaundice, it is of a yellow orange colour, like saffron, and communicates its colour to the vessels into which it is received, or to those substances which are immersed in it. It is then called bilious urine. It seems to contain a portion of the colouring matter of bile. Towards the termination of febrile disorders, the quantity of urine is increased; and it deposits, as it cools, a crystalline or scaly matter, of the colour of peach flowers, which is called critical urine. The sediment is composed of phosphate of lime, rofacic and uric acids. During nervous affections, as in hysteria, the urine is perfectly limpid and colourless, inodorous and insipid.

It has been observed, that the urine of gouty persons contains a smaller proportion of acid than usual. At the commencement of a paroxysm, the quantity of phosphoric acid seems to be diminished; but it gradually increases towards the termination of the fit, and is then in greater proportion than in ordinary health. The urine of persons labouring under rickets deposits a great portion of lime. The urine of an infant who died of worms, was found on analysis to contain oxalate of lime. In some cases of diabetes, the urine is colourless and insipid; in others it contains a great proportion of saccharine matter.

19. The urine of other animals exhibits different characters from that of man, according to their nature, the diversity of their organs, their food, manner of respiration, and the medium in which they live.

The urine of the horse has a strong peculiar odour. The horse. It is turbid when voided, or soon after becomes muddy. A pellicle, which is carbonate of lime, forms on the surface when it is exposed to the air. It changes the syrup of violets to a green colour, effervesces with acids, and is precipitated by the alkaline carbonates. The urine of the horse yields no phosphorus. The component parts of the urine of this animal, as they have been ascertained by Fourcroy and Vauquelin, are the following:

| Component | Parts | |----------------------------|-------| | Carbonate of lime | 0.011 | | Carbonate of soda | 0.009 | | Benzotate of soda | 0.024 | | Muriate of potash | 0.009 | | Urea | 0.007 | | Water and mucilage | 0.940 |

* Mem. de l'Inst. ii. P. 445.

The urine of the cow possesses nearly the same properties as that of the horse. It has a foamy feel, and a strong peculiar odour. It gives a green colour to syrup of violets, effervesces with acids, but is not altered by the alkaline carbonates. When it is exposed to the air, small crystals form on the surface. Its component parts are,

- Carbonate of potash, - Sulphate of potash, - Muriate of potash, - Benzoic acid, - Urea.

The urine of the camel is more distinguished by its odour than any other, but it is analogous to that of the cow. It is not mucilaginous, and does not deposit carbonate of lime. The specific gravity of this urine is greater than any other. It produces a slight change on the infusion of violets, communicating a green colour. It effervesces with acids, and furnishes nitre, sulphate and muriate of potash, with the addition of sulphuric, nitric, and muriatic acids. It contains

- Carbonate of potash, - Sulphate of potash, - Muriate of potash, - Urca.

The urine of the rabbit, examined by Vauquelin, exhibits... Component exhibits similar characters with that of the horse, the cow, and the camel. It becomes milky, and deposits carbonate of lime by exposure to the air. It converts vegetable blues to a green colour, and effervesces with acids. It contains the following substances:

- Carbonate of lime, - Carbonate of magnesia, - Carbonate of potash, - Sulphate of potash, - Sulphate of lime, - Muriate of potash, - Urea, - Gelatine, - Sulphur.

The urine of the Guinea pig is analogous in its nature and properties to that of the larger animals already described.

It appears that the urine of graminivorous animals belonging to the class of mammalia, or which live on vegetables in general, contains no phosphoric salts, or uric acid; that it is loaded with carbonate of lime, salts having a base of potash, and benzoic acid. The only substance which the urine of these animals possesses in common with human urine, is urea. The urine of carnivorous animals, of which indeed scarcely anything is known, is supposed to possess different properties from that of the animals just mentioned. The strong fetid odour of the urine of the cat is well known. Muriate of ammonia has been obtained from the urine of this animal by evaporation; but it is supposed, from the peculiar odour, that it contains urea.

The urine of birds affords a copious sediment, which seems to be carbonate of lime.

A substance which was found in the urinary bladder of the turtle in the form of paste, and which was examined by Vauquelin, was composed of

- Muriate of soda, - Phosphate of lime, - Animal matter, - Uric acid.

IV. Of Milk.

1. Milk, which is secreted in particular organs by the females of viviparous quadrupeds and cetaceous fishes, included under the class mammalia, and destined for the nourishment of the offspring, is a white opaque fluid, varying in its properties according to the different species of animals, and the nature of their food. The milk of the cow, which is most easily and most abundantly procured, has been chiefly the subject of chemical investigation. To it, therefore, the following observations are chiefly applied.

2. Milk is distinguished by an agreeable sweet taste, and a peculiar smell. But these properties belong to it only when it is just separated from the cow; for in the course of a few hours they are considerably different. The specific gravity varies at different periods. It is greater than that of water, and has been found to amount to 1.0324. The boiling and the freezing points of milk are also variable.

3. If milk be left at rest for some time, it separates into two parts; an unctuous matter, which floats on the surface, called cream, and a denser fluid which still retains many of the properties of milk. The quantity of cream obtained from milk, and the time it requires to separate, vary according to the nature of the milk and the temperature.

4. Cream thus obtained is of a yellow colour, and acquires a greater consistence by being exposed to the air. It is lighter than water, has an unctuous feel, and becomes rancid like oils, by keeping. When it is boiled, a small portion of oil appears on the surface. Cream is not soluble in alcohol or in oils. When cream is agitated for a longer or shorter time, according to the temperature to which the milk has been exposed during its separation, and perhaps to some circumstances which have not yet been observed, it separates into two parts; one, which has a solid consistence, is butter, and another which remains fluid.

5. Butter is of a yellow colour, and has all the properties of an oil, combined with a portion of the curd and serum of the milk. It melts at the temperature of 96°, and mixes readily with other oily matters. When butter is kept for some time, it is decomposed; it becomes rancid, which is ascribed to the whey and the curd with which it is combined; for when these substances are previously separated, it may be preserved much longer. Butter yields by distillation water, an acid liquid, an oily substance, which is at first fluid, but becomes afterwards concrete. A small portion of carbonaceous matter remains behind.

6. When fresh cream, or the whole of the milk fresh drawn from the cow, is churned, it requires the proceeds to be continued a much longer time than when the cream or milk is left to repose, as is usually the case, till it has acquired a slightly acid taste. But when cream, which has become sour, is churned, the butter separated has no acid properties, and the milk which remains is even less sour than the cream previous to the commencement of the process. An acid, therefore, has been evolved, and this acid is supposed to be the carbonic. When fresh cream or fresh milk is subjected to this process, in which the acid has not been formed, it requires greater agitation to complete this previous part of the change which the cream or milk must undergo, before the separation of the oily part or the butter. The milk which remains after the butter has been separated, or, as it is called, the butter-milk, has all the properties of milk from which the cream has been separated.

7. The milk which remains after the separation of the cream, may be coagulated by the addition of several substances, particularly by the addition of rennet, which is in most common use, and which is prepared by digesting the inner coat of the stomach of young animals, especially that of the calf. This coagulum separates into two parts, the curd and the serum or whey.

Curd is a white solid substance, and somewhat brittle, when the whole of the whey is expressed. It is soluble in acids, but it is necessary that the mineral acids be greatly diluted, and the vegetable acids concentrated.

Cheese is prepared from curd, by separating the whey by expression. The quality of the cheese depends upon the quantity of cream which remains in the milk. The best cheese is obtained by coagulating the milk at the temperature of about 100°, and expressing the whey slowly and gradually, without breaking down the curd.

If milk be not too much diluted with water, it may be coagulated by a great number of different substances. Among this number are acids, alcohol, neutral salts, gum arabic, and sugar.

Whey expressed from coagulated milk is of a yellowish green colour, and has an agreeable sweet taste. If it is boiled, a quantity of curd separates, and after being left at rest for some time, the whole of it is precipitated, and the liquid remains transparent and colourless. By slow evaporation it deposits white-coloured crystals of sugar of milk, with some muriate of potash, muriate of soda, and a little phosphate of lime. The liquid which remains after the separation of the salts, is converted, by cooling, into a gelatinous substance. If whey be kept for some time, it becomes sour, by the formation of an acid, which is lactic acid. It is to this acid that the spontaneous coagulation of milk, after it remains at rest for some time, is owing.

If milk, after it has become sour, be kept in a proper temperature, it ferments, emitting carbonic acid gas, and exhibiting the other phenomena of fermentation. A vinous intoxicating liquor is thus prepared, which has been long known among the Tartars, and called by them koumis. They prepare it from the milk of the mare.

Milk is susceptible of the acetous fermentation. If about six spoonfuls of alcohol be added to eight pints of milk, and the liquid be excluded from the air, vinegar will be formed in four or five weeks. Although the air is to be excluded, yet the carbonic acid gas must be allowed to escape as it is disengaged.

By the distillation of milk with the heat of a water-bath, water passes over, after which the milk coagulates, and an oily yellowish white substance remains behind, which, by increasing the heat, yields a transparent liquid, a fluid oil, ammonia, an acid, a thick black oil, and in the end carbonated hydrogen gas. The coaly matter in the retort contains potash, muriate of potash, phosphate of lime, and sometimes muriate of soda, with a small portion of magnesia and iron.

The constituent parts which enter into the composition of milk, are the following:

1. Water, 2. Oil, 3. Curd, 4. Gelatine, 5. Sugar of milk, 6. Muriate of soda, 7. Muriate of potash, 8. Phosphate of lime, 9. Sulphur.

Although the milk of different animals be composed nearly of the same substances, the proportions vary so much, as to give them very different properties.

The following are the results of the investigations of Deyeux and Parmentier with regard to the properties of the component parts of the milk of different animals compared together.

A. Every kind of milk when left at rest, produces cream on the surface, but it is different in the milk of different animals.

a. In the milk of the cow it is copious, thick, and of a yellow colour.

b. In woman's milk it is more liquid, white, and in small quantity.

c. In goats milk it is more abundant than in that of the cow, thicker and whiter.

d. In ewes milk it is nearly as abundant, and of the same colour as that of the cow, but has a peculiar taste.

e. In asses milk it is thick, less abundant, and in a great measure resembles that of women's milk.

f. In mares milk it is very fluid, and similar in colour and consistence to good cows milk before the cream appears on the surface.

B. Butter obtained from the milk of different animals, has the following comparative properties.

a. That of the cow is sometimes of a deep yellow, sometimes pale or white, and has always a considerable consistence.

b. It is difficult to separate the butter from the cream of women's milk. It is in small quantity, infipid, and of a pale yellow. It has been erroneously supposed that no butter could be obtained from this milk.

c. The butter of asses milk is always very white, soft, and readily disposed to become rancid.

d. The butter from goats milk is easily separated from the cream. It is abundant, always white, soft, and disposed to become rancid.

e. The butter from ewes milk is of a yellow colour, soft, and soon becomes rancid.

f. The butter of mares milk is difficult to be obtained and in small quantity. It has little consistence, and is readily decomposed.

C. The curd of milk varies in different animals.

a. That from the milk of the cow is bulky, tremulous, and retains a great deal of the serum.

b. That from women's milk is in small quantity, little coherent, has an unctuous feel, and retains but a small portion of the whey.

c. The curd of asses milk is similar to the former, but without being unctuous.

d. Curd from the milk of the goat is in great proportion, of a firmer consistence than that of the cow, and retains less whey.

e. Curd from ewes milk is fat, viscid, and communicates a soft pasty to cheesy.

f. The curd from mares milk is in very small quantity, and similar to that from women's milk.

D. The serum or whey constitutes a very great proportion of the milk, and exhibits the following varieties.

a. Whey from the milk of the cow is of a greenish-yellow colour, a sweet taste, and contains sugar of milk and neutral salts.

b. The whey from women's milk has little colour, but has a very sweet taste, containing a considerable proportion of saccharine matter.

c. The whey of asses milk is colourless, and contains less salts and more sugar than that of the cow.

d. Whey of the goat is of a slight yellow colour, and contains very little sugar and saline matter. The latter consists almost entirely of muriate of lime.

e. The whey of ewes milk is always colourless, and contains the smallest quantity of sugar, and but a small portion of muriate and phosphate of lime.

f. The whey of mares milk has little colour, and contains a great proportion of saccharine matter and of saline substances. V. Of Saliva.

1. The saliva which is secreted by peculiar glands, and which flows into the mouth, is a clear, viscid fluid, without taste or smell. Its specific gravity varies from 1.0167 to 1.080. It has generally a frothy appearance, being mixed with a quantity of air.

2. Saliva has a strong attraction for oxygen, which by trituration it communicates to some metallic substances, as mercury, gold, and silver. When saliva is boiled in water, albumen is precipitated; and when it is slowly evaporated, muriate of soda is obtained. A vegetable gluten remains behind, which burns with the odour of prussic acid.

3. Saliva becomes thick by the action of acids. Oxalic acid precipitates lime. Saliva is also inspissated by alcohol. It is decomposed by the alkalies; and the nitrates of lead, of mercury, and of silver, precipitate muriatic and phosphoric acids.

4. By distillation in a retort, it froths up, affords near four-fifths of its quantity of water nearly pure, a little carbonate of ammonia, some oil, and an acid. What remains behind consists of muriate of soda, phosphate of soda, and of lime. The constituent parts of saliva are the following:

- Water - Mucilage - Albumen - Muriate of soda - Phosphate of soda - Phosphate of lime - Phosphate of ammonia

5. The saliva of the horse is of a greenish yellow colour, a disagreeable smell, a saline taste, and foamy feel. It is coagulated by the acids, alcohol, and boiling water. A black earthy residuum remains after spontaneous evaporation. By distillation it yields an insipid watery liquid, carbonate of ammonia, carbonated hydrogen and carbonic acid gases, and a black empyreumatic oil.

6. The pancreatic juice, it is supposed, possesses properties analogous to those of saliva, and is destined for similar purposes, namely, to contribute to the solution of alimentary substances, and to their conversion into chyme; but very little is known of its nature and uses.

VI. Of the Humours of the Eye.

1. The eye is composed of three substances, which in anatomy have received the name of humours. These are the aqueous, the vitreous, and the crystalline humours or lens. The following observations are from Mr Chenevix's experiments on this subject.

2. The aqueous humour of the eye of the sheep is transparent like water, and has scarcely any taste or smell. The specific gravity is 1.0090. It evaporates slowly when exposed to the air; a coagulum is formed by boiling. When 100 parts are evaporated to dryness, eight parts remain behind. None of the metallic salts produce any precipitate except nitrate of silver, which throws down the muriate of silver. Tan also produces a precipitate in the aqueous humour. The component parts, therefore, of this substance, are albumen, gelatine, and muriatic acid, or rather muriate of soda, as the acid is in combination with soda. The vitreous humour exhibited the same properties.

3. The crystalline lens of the sheep is solid, composed of concentric coats, and transparent. The specific gravity is 1.1. It has scarcely any taste when it is fresh. It is soluble in water, and the solution is coagulated by heat. Tan produces a copious precipitate, both before and after coagulation. Its component parts are, therefore, albumen and gelatine, with water.

4. The human eye was found to be composed of human the same substances. The specific gravity of the aqueous and vitreous humours is 1.0053; of the crystalline lens, 1.0790. The specific gravity of the aqueous and vitreous humours of the eye of the ox is 1.008; the crystalline lens 1.0765. The composition is the same as that of the sheep.

VII. Of Tears and Mucus.

1. The tears are secreted by the lachrymal gland, for the purpose of lubricating the eye. This liquid is transparent and colourless, has no perceptible smell, but a saline taste. It communicates to vegetable blues a permanent green colour. When it is evaporated nearly to dryness, cubic crystals are formed, which are muriate of soda. Soda is in excess, because vegetable blues are converted by it to a green colour. A portion of mucilaginous matter, which becomes yellow as it dries, remains after the evaporation. This liquid is soluble in water and in alkalies. Alcohol produces a white flaky precipitate, and when it is evaporated, muriate of soda and soda remain behind. By burning the residuum, some traces of phosphate of lime and of soda are detected. The component parts of tears, are, therefore,

| Water | Muriate of soda | |-------|----------------| | Mucilage | Phosphate of lime | | Soda | Phosphate of soda |

The mucilage of tears absorbs oxygen from the atmosphere, and becomes thick, viscid, and of a yellow colour. It is then infusible in water. Oxymuriatic acid produces a similar effect. It is converted into muriatic acid, so that it has been deprived of its oxygen.

2. The mucus of the nose consists of the same substances as the tears; but being more exposed to the air, it acquires a greater degree of viscidity from the mucilage absorbing oxygen.

VIII. Of the Wax of the Ear.

1. The wax of the ear, or cerumen, is a liquid secreted by glands, which are situated in the internal ear. It is of a viscid yellow colour, and becomes concrete by exposure to the air. The taste is bitter; it melts with a moderate heat, gives out an aromatic smell, and stains paper like oil. When thrown upon burning coals, it gives out a white smoke, melts, swells, becomes dark-coloured, and gives out the odour of ammonia. A light coaly matter remains behind. It forms a kind of emulsion by agitation with water.

2. Alcohol dissolves a portion of cerumen; the undissolved part exhibits the properties of albumen mixed with oil. By evaporating the alcohol, an orange-coloured residuum, similar to turpentine, is left behind. It has the properties of resin of bile. This matter is also soluble Component: Iuble in ether. By burning the albumen of the cerumen, some traces of soda and phosphate of lime are detected. The component parts of cerumen are,

Albumen, Refin, Colouring matter, Soda, Phosphate of lime.

IX. Of Synovia.

1. The liquid secreted within the capsular ligaments of the joints, to facilitate motion by lubricating these parts, is called synovia. The synovia of the ox is a viscid, semitransparent fluid, of a greenish-white colour, which soon acquires the consistence of jelly, and not long after becomes again fluid, depositing a filamentous matter.

2. Synovia mixes with water, and renders it viscid. When this mixture is boiled, it becomes milky, and some pellicles are deposited on the sides of the vessel. Alcohol produces a precipitate when added to synovia. This precipitate is albumen. After this matter is separated, the liquid still remains viscid; but if acetic acid be added, the viscidity disappears, and it becomes transparent, depositing a white filamentous substance, which resembles vegetable gluten. It is soluble in cold water, and in concentrated acids and pure alkalies. This fibrous matter is precipitated by acids and alcohol in flakes.

3. The concentrated mineral acids produce a flaky precipitate, which is soon redissolved; but the viscidity of the liquid is not destroyed till they are too much diluted with water, that the acid taste is only perceptible.

4. When synovia is exposed to dry air, it evaporates, and cubic crystals remain in the residuum with a white saline efflorescence. The first are muriate of soda, and the latter carbonate of soda. This substance soon becomes putrid, giving out ammonia during its decomposition. By distillation in a retort, it yields water, which soon becomes putrid; water containing a portion of ammonia, and an empyreumatic oil, with carbonate of ammonia; by washing the residuum, muriate and carbonate of soda may be obtained. A small portion of phosphate of lime is found in the coaly matter. The constituent parts of synovia are the following:

| Component | Percentage | |-----------------|------------| | Fibrous matter | 11.86 | | Albumen | 4.52 | | Muriate of soda | 1.75 | | Soda | 0.71 | | Phosphate of lime| 0.70 | | Water | 80.46 |

*Annal de Chim. xiv. p. 123.*

X. Of Semen.

1. Semen is secreted in the testes of male animals; but when it is ejected it is composed of two substances; the one is fluid and milky, and the other of a thick mucilaginous consistence, in which appear a great number of white silky filaments, especially if it be agitated in cold water. It has a disagreeable odour, and an acrid irritating taste. The specific gravity varies considerably, but is always greater than that of water. When it is rubbed in a mortar, it froths up, and acquires the consistence of potamum from the air with which it mixes. It converts the flowers of mallow and of violets to a green colour, and it precipitates the calcareous and metallic salts; which shews, that it contains an uncombined alkali. The thick part of the semen, as it cools, becomes transparent, and affumes a greater degree of consistence; but it afterwards becomes entirely liquid, even without absorbing moisture from the air. This change takes place in about twenty minutes from the time of its emission.

2. If semen be exposed to the air after it has become liquid at the temperature of 60°, it becomes covered with a transparent pellicle, and at the end of three or four days deposits fine transparent crystals of a line in length, crossing each other like radii from a center. When they are magnified, they appear to be four-sided prisms, terminated by long four-sided pyramids. When semen is exposed to a warm air, in considerable quantity, it is decomposed; it affumes the colour of the yolk of egg, and becomes acid, either by absorbing the oxygen from the atmosphere, or by a different combination and arrangement of its own constituent principles. It then emits the odour of putrid fish, and is covered with the hyssus septica.

3. Heat accelerates the liquefaction of semen; and of heat, when it has undergone this change it is no longer susceptible of coagulation. It is decomposed by the application of strong heat. Water is first separated; it then blackens, swells up, and emits yellow fumes, having an empyreumatic, ammoniacal odour. A light coal remains behind, which burns readily to white ashes.

4. Before it has become fluid, semen is not soluble in water, in water either cold or hot. To the latter it communicates an opal colour. But in the fluid state it combines readily with either hot or cold water, from which it is separated by alcohol or oxymuriatic acid in the form of white flakes. The alkalies promote the solution of semen in water.

5. No ammonia is disengaged from fresh semen by means of quicklime; but when it has been exposed for some time to a warm and moist air, it is separated in great abundance, so that ammonia is formed during its exposure to the air.

6. The acids readily dissolve semen, and this solution is not decomposed by the alkalies; nor indeed is the alkaline solution of semen decomposed by the acids. Wine, cider, and urine also dissolve semen, but it is in consequence of the acid which is combined with these liquids. Water acidulated with sulphuric acid acquires the same property. Oxymuriatic acid coagulates semen in white flakes which are insoluble in water and in acids. The same acid produces the coagulation of fluid semen. This is owing to the absorption of oxygen derived from the acid which is converted into muriatic acid.

7. Barytic, salts are not decomposed by the seminal fluid which has been liquefied in a clothe vessel; but when it has undergone this change in the open air, rhomboidal crystals are formed with the addition of these salts. The calcareous and metallic salts are decomposed by semen in both conditions. From these facts Component facts it appears that semen contains an uncombined al- kali, which has not the property of decomposing the barytic salts till it has combined with the carbonic acid from the atmosphere.

8. The crystals which form in semen by spontane- ous evaporation in the open air, and which are en- tangled in the viloid matter, may be separated by add- ing water. These crystals have neither smell nor taste. They melt under the blow-pipe into a white opaque globule, which is surrounded with a yellowish flame. This salt is insoluble in water, and is not acted on by the alkalies; but is soluble in the mineral acids with- out effervescence, from which solutions, lime water, the alkalies, and oxalic acid, throw down a precipitate. Alcohol added to the concentrated muriatic solution of this substance, diffuses part of it, which exhibits all the characters of muriate of lime; and there remains another substance which melts under the blow-pipe in- to a green transparent glass soluble in water, which precipitates lime water and reddens vegetable blues. This salt, therefore, as is demonstrated from these ex- periments, is phosphate of lime. After the formation of the above salts, a great number of small, white, opaque bodies appear on the surface. They are also phosphate of lime.

9. By burning 40 grains of dried semen in a cru- cible, it first became soft, and then gave out the odour of burnt horn accompanied with yellow fumes. It blackened and emitted the odour of ammonia. The coaly matter which remained was lixiviated with water. This was evaporated, and afforded crystals in the form of rhomboidal plates, which effervesced with acids; with sulphuric acid afforded sulphate of soda, and with muriatic acid formed muriate of soda. The alkali, therefore, was soda.

10. The alkaline matter being separated, the resi- due was still exposed to strong heat, and furnished 13 grs. of white ashes which had the following pro- perties. By the action of the blow-pipe it is conver- ted into an opaque white enamel which attracts moisture from the air, is soluble in acids, and the solution has all the characters of phosphate of lime. The component parts of semen, therefore, are,

| Component | Parts of Animal Substances | |-----------|-----------------------------| | Water | 90 | | Mucilage | 6 | | Soda | 1 | | Phosphate of lime | 3 |

100.

XI. Of the Liquor of the Amnios.

1. This liquid is secreted in the amnios or bag which surrounds the fetus in the uterus. It is very different in different animals, so far at least as its nature and properties have been investigated. The liquor of the amnios of women and cows only has been examined. The following are the results of the experiments of

* Vauquelin, Ann. de Chim. IX. 64—80.

2. This liquid in women is of a milky colour, an agreeable odour and a saline taste. It becomes trans- parent by filtering and separating some coagulated matter which is suspended in it, and which communi- cates the white colour. The specific gravity is 1.005. It seems to contain both an acid and an alkali; for it converts syrup of violets to a green colour, and red- dons the tincture of turnsole. It froths when agitat- ed, becomes opaque when heated, and exhales the odour of the white of egg.

3. It is rendered more transparent by acids; but alcohol and the alkalies occasion a flaky precipitate, which is like glue when it is dried. The infusion of nut-galls gives a copious brown precipitate; and ni- trate of silver produces a white precipitate, which be- ing insoluble in nitric acid, is muriate of silver.

4. By slow evaporation this liquid assumes a milky appearance; a transparent pellicle forms on the sur- face, and a very small residuum is left. By adding water to the residuum, and evaporating the solution, muriate and carbonate of soda are obtained. The ashes which remain, after burning the residuum, consist of carbonate of soda, phosphate and carbonate of lime. During the burning a strong, fetid, ammoniacal odour is exhaled.

5. From these experiments, it appears that this li- quid consists of a great proportion of water, of albu- men, muriate of soda, of soda, phosphate of lime, and lime.

6. A white shining soft substance, somewhat resem- bling soap, is deposited on the body of the fetus in the uterus. It is insoluble in water, alcohol, and oils. The caustic alkalies dissolve a portion of it, and form a kind of soap. It decrepitates on burning coals, then dries, blackens, and gives out the odour of an em- pyreumatic oil. It leaves behind a coaly matter, which burns with difficulty. When it is heated in a crucible of platina, it decrepitates, while an oily matter exudes. It then curls up like horn, inflames, and leaves behind gray ashes, which effervesce with acids, and which seem to be composed chiefly of car- bonate of lime.

7. This matter seems to be a mixture of animal mu- cilage and fat, originating from the albumen, which has undergone some peculiar change. The parts of a fetus which have remained in the uterus after death, have been found converted into a fatty matter.

Liquor of the amnios of the cow.—1. This liquid differs from the former in being of a reddish brown colour, in having an acid bitter taste, an odour resem- bling the extracts of some vegetables, and the viscid- ity of a solution of gum. The specific gravity is 1.028. It reddens the tincture of turnsole, forms a copious precipitate with muriate of barytes, and with alcohol a precipitate of a reddish matter.

2. When it is evaporated, a thick scum forms on the surface, which is easily separated, and which, on ac- cooling, is found to contain white crystals of a slight- ly acid taste. A viloid matter like honey appears, by continuing the evaporation. When this matter is treated with boiling alcohol, it furnishes, on cooling, an acid which crystallizes in shining needles. This is the amniotic acid which has been already described. The matter which remains after the separation of the crystals is insoluble in alcohol, and is firm and tena- cious.

3. Having extracted the whole of the acid, if the evaporation be continued till the liquid acquire the confinement of a syrup, large transparent crystals are obtained, which have a bitter taste, and are soluble in water. These crystals were found to be sulphate of soda,

Component soda, which are obtained in a state of purity, by burning the residuum of a quantity of the liquid evaporated to dryness, dissolving the coaly residuum in water, and evaporating.

4. The animal matter which accompanies the saline substances, is of a reddish brown colour and a peculiar taste, very soluble in water, but insoluble in alcohol, which even separates it from water. It neither combines with tan, nor is it susceptible of being converted into jelly, so that it does not possess the properties of animal mucilage. When it is heated strongly, it swells up; exhales, at first the odour of burning mucilage; afterwards that of ammonia and an empyreumatic oil; and, at last, that of prussic acid. When it is burnt, there remains behind a bulky coal, the ashes of which are white, and contain phosphate of magnesia and a small portion of phosphate of lime.

5. The constituent parts of the liquor of the amnios of the cow, are the following:

Water, Acid, Sulphate of soda, Animal matter.

XII. Of Fluid Morbid Secretions.

1. During the diseased action of the vessels of different parts of the body, liquids are secreted, as, for instance, when the muscular or bony parts are wounded, a matter is exuded, which continues to flow till the wound is healed up; in tropical diseases a liquid is secreted in the different cavities of the body; and when the skin is irritated by the action of blisters, a fluid collects between the cuticle and true skin.

Liquor of droppings.—This liquid is of a yellowish green colour, has sometimes considerable transparency, but is sometimes turbid. In its chemical properties it seems to correspond with the serum of the blood.

Liquor of blisters.—The liquor which is secreted by the action of blisters is usually transparent. The constituent parts are the same as those of the serum of the blood. Two hundred parts of this liquid yielded

Albumen, 36 Muriate of soda, 4 Carbonate of soda, 2 Phosphate of lime, 2 Water, 156 200 *.

Pus.—What is called healthy pus is about the consistence of cream, and of a yellowish-white colour, an insipid taste, and when it is cold, without smell. It produces no change on vegetable blues.

2. When pus is exposed to a moderate heat, it dries, and assumes the appearance of horn. By distillation it gives out water in considerable proportion, ammonia and some gaseous substance and an empyreumatic oil; a shining coaly matter remains behind, the ashes of which, after being burnt, afford some traces of iron.

3. When this liquid is exposed to the air, it becomes acid. It is soluble in sulphuric acid, forming with it a purple-coloured solution. With the addition of water the pus separates, and the dark colour disappears. With concentrated nitric acid it forms a yellow coloured solution, which effervesces during the combination. Water produces a precipitate. Pus is also soluble in muriatic acid, and is separated by means of water. Pus is not soluble in alcohol, but is thickened; nor is it soluble in the oils.

4. A whitish ropy fluid is formed by the addition of a solution of the fixed alkalies, and by adding water the pus is precipitated. Pure ammonia forms with pus a transparent jelly, and dissolves it in considerable proportion.

5. A precipitate is occasioned by means of nitrate of metallic silver, and it is still more copious with nitrate and oxy-muriate of mercury.

6. The following tests have been given to distinguish To distinguish pus from mucus, which is of considerable importance guida pus in cases where the formation of pus is suspected in the lungs.

(1.) Pus is insoluble in sulphuric acid, and precipitated by water. Mucus floats. (2.) Pus may be diffused through water, diluted sulphuric acid, and brine; but mucus is not. (3.) Pus is soluble in alkaline solutions, and is precipitated by water; but this is not the case with mucus.

7. These are the properties of pus when it is secreted from a sore which is said to be in good condition, or in a disposition to heal. Its properties are very different in what are called ill-conditioned sores. In these cases the matter secreted is thin, fetid, and acrid. Matter secreted by cancerous sores, which has been examined, converts the syrup of violets to a green colour, and from this matter sulphurated hydrogen gas is separated by means of sulphuric acid. This gas is supposed to exist in combination with ammonia.

Subdivision III. Of the Solid Parts of Animals.

The following are the solid parts of animals, which we shall treat of in the order in which they are enumerated.

1. Bones, 2. Skin, 3. Muscles, 4. Cartilage, tendons, &c. 5. Brain and nerves, 6. Hair and nails, 7. Morbid concretions.

I. Of the Bones.

1. The bones are those parts of animals which give Of different firmness, strength, and shape to the body. Bones are density very different with regard to solidity and density, not only in different parts of the body, but even in the same bone. The specific gravity, therefore, of bones, must be various. They are of a white colour, of a lamellated structure, and inflexible.

2. When bones are burnt, they are converted into Action of a white, porous, insipid substance, which still retains the heat shape of the bone.

3. When bones are broken into small pieces, and boiled in water, a considerable quantity of fat rises to the surface; an oily matter, therefore, is one of the constituent parts of bones.

4. If the boiling be continued for a greater length Gelatine of time, the water dissolves another substance, which, being concentrated and left at rest, assumes a gelatinous form. Component form. Bones, therefore, contain a portion of gelatine.

5. If bone is kept for some time in diluted muriatic acid, it is converted into a white flexible substance, which retains the shape of the bone. It becomes brittle and semitransparent when dried; it is soluble in nitric acid, and when this acid is diluted, it is converted by its action into gelatine. It forms a soap with the fixed alkalies. From these properties it resembles coagulated albumen. This substance, which is called cartilage, is the first part of the bone which is formed.

6. Besides these substances, bones contain a considerable proportion of earthy salts. These are phosphate of lime, which is in great proportion; carbonate of lime in smaller proportion, with a still smaller of sulphate of lime.

7. The component parts of bones, therefore, are earthy salts, cartilage, gelatine, and fat. The following table exhibits the proportions of these constituent parts in the bones of different animals. It was drawn up by Merat-Guillot. A hundred parts of bone were employed, and as much dried as possible, and to this quantity the proportions specified refer *.

| Names | Gelatine | Phosphate of lime | Carbonate of lime | Lofs | |------------------------|----------|-------------------|------------------|------| | Human bones taken from a burying ground | 16 | 67 | 1.5 | 15.5 | | Human bones dried but not buried | 23 | 63 | 2 | 2 | | Bones of the ox | 3 | 93 | 2 | 2 | | calf | 25 | 54 | | 21 | | horse | 9 | 67.5 | 1.25 | 22.25| | fucep | 16 | 70.0 | 0.5 | 13.5 | | elk | 1.5 | 90.0 | 1.0 | 7.5 | | hog | 17.82 | 52.0 | 1.0 | 30.0 | | hare | 9 | 80.5 | 1.0 | 5.0 | | pullet | 6 | 72.0 | 1.5 | 20.5 | | pike | 12 | 64.0 | 1.0 | 23.0 | | carp | 6 | 45.0 | 0.5 | 28.5 |

8. The human teeth have been analyzed by Mr Pepys, and he found the constituents of different teeth, and different parts of the teeth, to be the following.

| Teeth of adults | Shedding teeth of children | Roots of the teeth | |-----------------|----------------------------|--------------------| | Phosphate of lime | 64 | 62 | 58 | | Carbonate of lime | 6 | 6 | 4 | | Cartilage | 20 | 20 | 28 | | Lofs | 10 | 12 | 10 |

He found the following to be the component parts of the enamel of the teeth.

But according to Fourcroy and Vauquelin the enamel is composed of

| Phosphate of lime | 72.9 | | Gelatine and water | 27.1 |

II. Of the Skin.

1. The skin, which forms the external covering of animals, consists of three parts; the epidermis or cuticle, the true skin, and a soft substance called the rete mucosum, which lies between the cuticle and true skin.

2. The epidermis, which may be separated from the cutis, by macerating the skin in hot water, is a thin elastic substance, which is insoluble in water and in alcohol.

3. Sulphuric and muriatic acids have little action for some time on this substance; but it is immediately converted into a yellow colour by means of nitric acid, and at last entirely decomposed. It is entirely soluble in the caustic fixed alkalies. From these properties the epidermis is supposed to be coagulated albumen in a peculiar state of modification.

4. The cutis or true skin is denser and thicker. When it is heated, it first contracts, then swells, exhaling a fetid odour, and leaving behind a dense mass of charcoal. By distillation the same products are obtained as from fibrina.

5. The skin is softened by weak acids, is rendered transparent, and is at last dissolved. It is converted heat into oxalic acid and fat by nitric acid, with the evolution of azotic gas and prussic acid. It is converted by means of the concentrated alkalies into oil and ammonia.

6. After maceration for some time in water, a small proportion of gelatine may be obtained, by evaporating gelatine. The water; but if the skin be boiled for a considerable time in water, it is entirely dissolved, and the liquid, by evaporation, assumes the consistence of jelly. The skin is thus converted into glue. It is from the skin of animals that glue is chiefly extracted; and it is obtained of different degrees of strength from the skin of different animals.

7. As skin consists chiefly of gelatine, it combines readily with tan. This compound forms leather; and the process by which it is effected is called tanning, for the detail of which see the article TANNING.

8. The mucous substance, or rete mucosum, lies between the epidermis and true skin. It is this which gives the black colour to the skins of negroes. It is deprived of its colour, even in the living body, by means of oxynuratic acid. The foot of a negro became nearly white by being kept for some time in water impregnated with this acid. The black colour, however, returned in a few days.

III. Of III. Of the Muscles.

1. The muscular, or fleshy parts of animals, are of a reddish-white colour, and fibrous structure. If a quantity of muscular substance is separated into small pieces, it becomes white. If the water be heated, it coagulates. Albumen and a portion of fibrina are obtained. It becomes glutinous by farther evaporation; and, when the process is carried on to dryness, and alcohol added, a peculiar matter is distilled; which, after the alcohol is expelled by heat, appears of a reddish-brown colour, has an aromatic smell, and a very acid taste; and it is soluble both in water and alcohol. The gelatine formed in the mass evaporated to dryness, with a little phosphate of soda and ammonia, remains undissolved by the alcohol. When this extractive matter is distilled, it affords an acid, which is combined with ammonia.

By boiling the same muscular matter for some time in water, another portion of albumen is obtained; and, when the water is concentrated by evaporation, it is converted into a jelly; and by treating with alcohol as before, after evaporating to dryness, the extractive matter is taken up, and the gelatine and phosphoric salts remain undissolved. The fibres of the muscle are then of a gray colour, insoluble in water, and become brittle when dry. This substance is fibrina, which constitutes the chief part of muscular matter.

2. If muscular matter be dissolved in nitric acid, and ammonia added to the solution, a precipitate of phosphate of lime is obtained; but no phosphate of lime is obtained, when treated in this way, after being long boiled in water, for it is either combined with the gelatine, or is thus rendered soluble. Carbonate of lime, however, is found after boiling the muscular substance, and is converted into oxalate of lime by means of nitric acid.

3. The constituent parts of muscular matter are the following:

- Fibrina, - Phosphate of soda, - Albumen, - Phosphate of ammonia, - Gelatine, - Phosphate of lime, - Extractive, - Carbonate of lime.

4. From the difference of solubility of the substances which enter into the composition of muscular matter, and the different effects of heat on these substances, the sensible qualities at least must vary considerably, according to the manner in which this matter is prepared for food. Accordingly, when the flesh of animals is boiled, those parts which are soluble in water combine with it. These are, the gelatine, the extractive matter, and part of the saline bodies. It is to these that the nutritious property of soups is ascribed. But when the flesh of animals is roasted, it has a much higher flavour, in consequence of these substances not being separated from it, and particularly the extractive matter, on which the odour and flavour depend. This extractive matter, according to Fourcroy, composes the brown crust which is formed on flesh during its roasting.

5. The muscular part of different animals, from its sensible qualities at least, seems to possess very different properties. Hence the difference in the taste, flavour and nutritious quality, of the flesh of different animals.

6. When the muscular parts of animals are exposed for a considerable length of time to the action of running water, they are converted into a peculiar substance, resembling in some measure spermaceti. The same change, indeed, in similar circumstances, takes place on the other soft parts of animals. This was first observed in the year 1786, in the Innocents burying-ground in Paris, where great numbers of bodies were thrown together into the same pit. The time which was required for this conversion was supposed to be in general about thirty years. But it has since been found, that animal matters are converted into a substance exactly similar, and in a much shorter period, by exposing them to the action of running water.

7. The matter produced by this change is of a Properties, white colour, soft and unctuous to the feel, and melts like tallow. It is decomposed by diluted acids; and an oily matter, with which it is mixed, is separated. By the action of alkalies and lime, ammonia is evolved. By exposure to the air, it is deprived of its white colour; the ammonia is almost entirely carried off, and a substance resembling wax remains behind. The oily matter which is separated by a diluted acid, is of a white colour, and concrete. It becomes of a grayish brown colour by drying, and assumes a crystalline, lamellated texture, like spermaceti. At the temperature of 120° it melts. It is soluble in alcohol at the temperature of 120°. It forms a soap with alkalies, and burns like oil; but exhales a disagreeable odour, which is the chief objection to its use as a substitute for oil, as it is supposed it may be obtained at a cheaper rate. A manufacture indeed has been established at Bristol for the preparation of this substance.

IV. Of Membranes, Tendons, and Ligaments.

1. Membranes are those parts of the body which include some of the internal parts of animals. Many of them are extremely thin, and they possess different degrees of transparency. They become pulpy by maceration in water, and by boiling are almost entirely converted into gelatine, so that they are chiefly composed of this substance. No phosphate of lime or other saline matter has been detected in the membranous substances hitherto analyzed.

2. Tendons are reduced by boiling to a gelatinous substance, so that they are composed of a similar matter with membranes.

3. The ligaments afford a portion of gelatine by boiling, but are not, like the two former, entirely reduced to jelly, so that some other substance besides gelatine enters into the composition of ligaments.

V. Of the Brain and Nerves.

1. The matter of the brain and nerves has a soft, Action of foamy feel, and a close texture. When exposed to the water, &c., air at the temperature of 65°, it soon becomes putrid, exhaling an offensive smell, and giving out a considerable quantity of ammonia. It is not soluble in cold water; but triturated with water in a mortar, a part is dissolved, and if this be heated moderately, it coagulates. If sulphuric acid be added to this solution, white flakes appear on the surface, and the liquid af-

Vol. V. Part II. Component fumes a red colour. Similar flakes are produced by Parts of the action of nitric acid, but the colour of the liquid Animal Substances is yellow. If nitric acid be added till a flight acidity is produced, a coagulum of a white colour separates, which is insoluble in water and alcohol, is softened by heat, and becomes transparent when it is dried. This matter, therefore, possesses many of the properties of albumen.

2. If a quantity of brain be triturated with diluted sulphuric acid, part is dissolved, and part is coagulated. The liquid part is colourless, and when it is evaporated, it becomes black, while sulphurous acid is exhaled, and crystals are formed. When it is evaporated to dryness, a black mass remains behind. By diluting this with water, charcoal separates. The matter therefore is entirely decomposed, ammonia is discharged, and combines with the acid, forming sulphate of ammonia. By evaporating the water, sulphate of ammonia and sulphate of lime, phosphoric acid, and phosphates of soda and ammonia, are obtained; and these salts may be separated by means of alcohol. These salts, however, exist in brain in small proportion. By treating in the same way a quantity of brain with nitric acid, part is dissolved, and part coagulated. When the solution, which is transparent, is evaporated till the acid is concentrated, carbonic acid and nitrous gases are evolved; a great quantity of ammonia is separated with effervescence, and charcoal remains behind, mixed with oxalic acid.

3. If a quantity of brain be evaporated to dryness with a gentle heat, a portion of transparent liquid separates, and the residuum assumes a brown colour when it is dried. The weight of this residuum does not exceed one-fourth of the quantity employed. If the residuum be repeatedly boiled with alcohol, more than one-half is dissolved; and when the alcohol cools, it deposits a yellowish white substance in the form of thinning plates, which may be reduced to a kind of ductile paste. It becomes soft with the heat of boiling water, and blackens with an increase of temperature, exhaling empyreumatic and ammoniacal fumes; a charred matter remains behind. By evaporating the alcohol, a yellowish black matter is deposited, which reddens paper stained with turpentine.

4. Brain is soluble in concentrated caustic potash; and during the solution, a great quantity of ammonia is given out.

VI. Of Hair and Nails.

1. If we include all those substances which form the covering of animals, as brittle, hair, wool, and down, under the general name of hair, and particularly as they possess nearly the same properties, we shall find that it varies greatly in size, in length, and colour, in different animals, and even in different parts of the body of the same animal.

2. If hair be boiled in water, a quantity of gelatine is obtained, and, by continuing the boiling, the hair becomes brittle, that it crumbles to pieces. The part which remains, after the gelatine has been separated, seems to be coagulated albumen. But besides gelatine and albumen, it appears from the combustion of hair, that it contains a portion of oily matter. Berthollet obtained by the distillation of a quantity of hair, carbonate of ammonia, water having the smell of burnt hair, some oil, and elastic fluids which were probably carbonated hydrogen and carbonic acid gases. The oil was of a brownish colour, and was concrete in the ordinary temperature of the atmosphere. It was soluble in alcohol, and burnt with a vivid flame. The charcoal which remained could scarcely be calcined, but some of its particles were attracted by the magnet.

3. The acids soften and destroy the colour of hair. Acids. It is decomposed by sulphuric acid with the assistance of heat; charcoal is deposited, and carbonic acid gas given out. Nitric acid communicates a yellow colour to hair, and dissolves it with the aid of heat. An unctuous matter is separated, and oxalic acid is formed. Muriatic acid at first whitens hair; but it becomes yellow when it dries. Oxymuriatic acid also bleaches hair; but at the same time destroys its texture. It is converted into a pulp when it is introduced into oxymuriatic acid gas.

4. Hair is soluble in the alkalies, and is converted into a reddish-coloured soap, with the evolution of ammonia. If muriatic acid is added to the solution of hair in potash, sulphurated hydrogen gas is evolved, from which it appears that hair contains sulphur. Silver is blackened by the same solution.

5. The metallic oxides also have the effect of blackening hair. It is in this way that the hair is dyed black. The red oxide of lead, the acetate of lead, and sometimes even the nitrate of lead, and the nitrates of mercury and silver, are employed for this purpose.

Nails.—The nails are considered as an elongation of the epidermis. They are attached to it, and separate when it is removed. They become soft by long maceration in water. There is no precipitate formed in this solution with tan. Nails are soluble in the acids and the alkalies. They are stained with metallic oxides, and combine with colouring matters. From these properties the nails are considered as a kind of coagulated albumen, with a small proportion of phosphate of lime, and, according to some, carbonate of lime.

VII. Of Morbid Concretions.

1. Earthy matters are frequently found in different parts of animal bodies, which are to be considered as extraneous, and occasioning, at least in the human body, some of the feverish disorders to which it is subject. These earthy matters are generally combined with an acid, and in some cases entirely composed of an acid. These substances, which have been called concretions and calculi, are formed, sometimes in the solid parts of the body, but chiefly among the fluids.

Pineal concretions.—These concretions are almost always found in the pineal gland of the human brain. They are indeed so rarely wanting in the brain, that they are considered as natural, as they do not seem to produce any inconvenience or disease. They have been found to consist of phosphate of lime, mixed with some animal matter.

Salivary concretions.—Concretions form in the salivary glands, and in the ducts which convey the secreted ed fluid from these glands to the mouth. The component parts of these concretions have been found to be also phosphate of lime and animal mucilage.

The tartar of the teeth is composed of the same substance. When this was examined with the microscope, it seemed to be composed of small shining grains united to each other, and containing a great number of pores or small angular cavities, resembling the cells of polypi, on account of which some naturalists have ascribed its formation to insects; but it is more natural to suppose, that it is a crystalline arrangement of the saline matter of which it is composed.

Concretions have also been found in the pancreas, and its ducts, and are supposed to consist of the same materials.

Pulmonary concretions.—These concretions are formed in the lungs during asthmatic and phthisical disorders. They are small hard bodies, unequal and rough, of a gray or reddish colour, which become white as they dry in the air. They are also composed of phosphate of lime mixed with animal matter.

Intestinal concretions.—These are more rarely met with in the human body. When they are found, they have been generally formed on the stones of fruits, or some other hard body which has been swallowed. They are more frequent in the intestines of the inferior animals, as in those of the horse. Some that have been examined were of a gray colour, and of a radiated or crystallized structure. The component parts of a stone of this description, analyzed by Berthollet, were the following:

| Component | Parts | |-----------|-------| | Magnesia | 18.0 | | Phosphoric acid | 26.0 | | Ammonia | 3.2 | | Water | 46.0 | | Animal matter | 4.0 |

97.2 *

Biliary concretions.—Biliary concretions, or calculi, are formed, either in the liver itself, in the gall-bladder or in the gall ducts, hence they have also been called gall-stones. Some found in the liver itself, are composed of phosphate of lime combined with some animal matter. The calculi which have been found in the gall-bladder, are different, both in structure and composition. Some of them seem to be composed of concentric layers of inspissated bile. These have different degrees of consistence; they are sometimes friable, and of a brown or reddish colour. The gall-stones of the ox, which are used by painters, are of this kind. Another kind of biliary calculi differ only from the former in having a smooth, whitish or grayish covering, resembling spermaceti. They are sometimes found in considerable numbers in the gall-bladder.

A third species is of a white or gray colour, opaque, or semitransparent. These are composed of thinning crystalline plates, or have a radiated structure. They are frequently solitary, and are then about the size, and have the form of a pigeon's egg. The nucleus of this kind of gall-stone is composed of inspissated bile.

A fourth species is composed of different proportions of the spermaceti substance and the concrete bile. These are the most frequent of all the kinds of gallstones, and are also the most numerous. They are of a deep green or olive colour. Sometimes they exhibit, internally, small shining plates of a deep yellow colour.

All these calculi are soluble in the caustic alkalies, in solutions of soap, in fixed and volatile oils, in alcohol, and partially in ether.

Urinary concretions.—1. These concretions, which are frequently formed in the urinary bladder of man, and produce one of the most excruciating disorders to calculi, which he is subject, have long attracted attention, with a view to prevent their formation, or to effect their dissolution after they have been formed. Little, however, has yet been done, to accomplish either of these ends; but the nature of the concretions themselves has been carefully investigated, and their component parts minutely examined by different chemists. Among these the labours of Fourcroy and Vauquelin are not the least conspicuous. Urinary calculi are found in the kidneys, the ureters, or the urinary bladder itself. Calculi, as found in the kidneys, vary considerably in size, form, colour, and internal structure. They are usually small, round, concrete bodies, smooth and shining externally, of a reddish-yellow colour, and so hard as to be susceptible of a polish. They pass readily along the ureters to the bladder, and from thence are ejected along with the urine. It is the formation of these small concretions which constitutes the disease called gravel. Some of these concretions sometimes remain in the kidneys, and increasing in volume by receiving new additions of matter, form large calculi. This happens, however, but rarely. The calculi which have been found in the ureters, have originated from the kidneys, and being too large to pass along the ureters, receive new additions of matter as it is deposited from the urine, and enlarge in size, at the same time dilating the ureter.

But by far the most common are those which are found in the bladder itself. These calculi have either originated from small concretions formed in the kidneys, and these passing along the ureters into the bladder, form a nucleus on which successive layers of matter are deposited from the urine; or they have their origin and complete formation in the bladder itself, or have been formed on some extraneous substance introduced into the bladder through the urethra. The first are the most frequent.

2. The form of urinary calculi is various, but they are frequently of a spheroidal or egg-shape, or compound properties, fed on two sides. Sometimes they are polygonal, which happens when there are several in the bladder at the same time. Some have been found of nearly a cubical form. Their extremities are frequently either pointed or obtuse. Their size is extremely various. Sometimes they are not larger than small beans, while some have been of such an extraordinary size as to fill the bladder itself; but they are most frequently from the size of a pigeon's egg, to that of a hen's egg. Some are of a yellowish-brown colour, resembling wood. These are composed of uric acid. Those which are white, or grayish-white, consist of the earthy phosphates, and those which are of a deep gray or blackish colour, are composed of oxalate of lime. Some exhibit all these different shades mixed together. The surface of urinary calculi calculi is sometimes smooth and polished; sometimes it is rough and unequal, and tuberculated. Some urinary calculi having their surface mammilated, are called mulberry stones, from some resemblance to a cluter of mulberries. Some of the white calculi are soft and smooth, semitransparent, and covered with thinning crystals. The specific gravity varies from 1.213 to 1.976. The odour of urinary calculi is sometimes perceptibly urinous and ammoniacal, which is discovered by rasping or sawing them; sometimes it is faint and earthy, as in the white calculi; and sometimes it resembles that of ivory sawed or rasped, and is analogous to the odour of semen. Mulberry calculi are distinguished by this odour.

3. The following substances have been discovered in urinary calculi.

| Uric acid, | Oxalate of lime, | |-----------|----------------| | Urate of ammonia, | Carbonate of lime, | | Phosphate of lime, | Silica, | | Phosphate of magnesia and ammonia, | Animal matter. |

Uric acid exists in almost all urinary calculi. Many calculi indeed are entirely formed of it; but it is found in greater or smaller proportion, in almost all that have been analyzed. The nature and properties of this acid have been already described. The calculi composed of it are of a brown colour, are smooth and polished, and have the appearance of wood. When this substance is triturated with a concentrated solution of potash or soda, it forms a thick saponaceous matter, which is precipitated by diluted acids. It is dissolved by nitric acid, and is converted into a red colour. This acid is a compound of azote, carbone, hydrogen, and oxygen; and when decomposed by chemical agents, it is converted into ammonia, malic, oxalic, prufic, and carbonic acids.

Urate of ammonia, the next substance found in urinary calculi, is also soluble in potash and soda, but the solution is accompanied with a copious evolution of ammonia. Calculi composed of this substance, consist of thin layers, and are not always smooth. They are generally of a small size, and resemble an infusion of coffee. The earthy phosphates are frequently interposed between the layers of calculi composed of this substance, and it is often mixed with phosphate of ammonia and magnesia.

Phosphate of lime frequently enters into the composition of calculi. It is usually in thin layers, which are friable, and have little consistancy. They are of a grayish-white colour, and opaque, without taste or smell. The phosphate of lime is usually mixed with gelatinous matter; is soluble in different acids, and is precipitated by the alkalies. Some calculi have been discovered entirely composed of phosphate of lime.

Phosphate of ammonia and magnesia is in the form of white, semitransparent layers, and it is sometimes found crystallized on the surface of calculi in the form of prisms. When it is reduced to powder it is of a brilliant white, very soluble in diluted acids, and is decomposed by the fixed alkalies.

Oxalate of lime is usually mixed with phosphate of lime and uric acid, but sometimes it is combined only with animal matter in mulberry calculi. The calculi composed of it are of a dark green colour, and extremely hard. It dissolves with difficulty in diluted nitric acid, and is decomposed by the carbonates of potash and soda.

The carbonate of lime constitutes the greatest part of some urinary calculi.

Silica has been rarely found in calculous concretions. It was detected mixed with phosphate of lime, only in two mulberry calculi, which were extremely hard.

In all calculous concretions there is a quantity of animal matter, which unites or cements together the matter, layers or particles of the hard substances of which they are composed. This animal matter seems to possess the properties of albumen. Sometimes it seems to be composed of albumen mixed with urea, or coagulated albumen, or gelatine.

4. Fourcroy and Vauquelin have analyzed more than 600 calculi, and by comparing the properties of each, they have arranged them into three genera and 12 species. The first genus comprehends those species which are composed of one substance. These are the three following:

1. Uric acid, 2. Urate of ammonia, 3. Oxalate of lime.

The second genus includes those species which are composed of two substances. It consists of the following seven species:

1. Uric acid and the earthy phosphates, in distinct layers. 2. Uric acid and the earthy phosphates intimately mixed together. 3. Urate of ammonia, and the phosphates in distinct layers. 4. The two preceding intimately mixed. 5. Earthy phosphates mixed or in thin layers. 6. Oxalate of lime and uric acid in layers. 7. Oxalate of lime and earthy phosphates in layers.

The third genus consists of two species, which are composed of three or four substances.

1. Uric acid or urate of ammonia, earthy phosphates, and oxalate of lime. 2. Uric acid, urate of ammonia, earthy phosphates, and silica.

We shall now state the general characters of these different species.

Genus I.

Species 1. Uric acid.—These calculi are easily known by their colour, which resembles wood. It is reddish, or yellowish. They are of a radiated, dense, fine texture, completely soluble in pure alkalies, without emitting any odour. They vary greatly in size, and have generally a smooth polished surface. The specific gravity is from 1.276 to 1.986. It usually exceeds 1.5. Of 600 calculi which were analyzed by Fourcroy and Vauquelin, 150 consisted of pure uric acid. The sand or gravel which is formed in the kidneys, usually belongs to this species.

2. Urate of ammonia.—Calculi composed of this substance, are usually of small size, soluble in caustic fixed alkalies, with the evolution of ammonia, of the colour of of the infusion of coffee, and are composed of fine layers which are easily separated. The surface is commonly smooth, and sometimes shining and crystalline. The specific gravity is from 1.225 to 1.720. They are soluble in hot water, at least when reduced to powder. The external layer is sometimes pure uric acid. This species is rare.

Oxalate of lime.—This species is easily recognized by its rough, mamellated surface, from which those calculi have received the name of mulberry stones. The colour is brown, they are of a close hard texture, and when rasped or sawed, emit the odour of fenem. They are soluble with difficulty in acids, and are insoluble in the pure alkalies. The specific gravity is from 1.428 to 1.976. This species frequently constitutes the nucleus of other calculi.

Genus II.

Species 1. Uric acid and earthy phosphates in distinct layers.—This species is known by its surface, which is white like chalk, friable and semitransparent. The external layer is composed of the phosphate of lime, or of ammonia and magnesia. The nucleus consists of uric acid, and when the calculus of this species is sawed asunder, two substances of which it is composed are distinctly seen. It is indeed only then that the species can be recognized. Calculi of this description are not uncommon, and they are generally of the largest size of all the urinary calculi. The specific gravity is very variable.

2. Uric acid and earthy phosphates intimately mixed.—This species contains numerous varieties, from the different proportion of the constituent parts. Sometimes the uric acid and the earthy phosphates are arranged in layers so thin, that they are scarcely perceptible. Sometimes they are so mixed together that they can only be detected by analysis. But sometimes the layers are sufficiently distinct. The specific gravity is from 1.213 to 1.739. This species of calculus is common.

3. Urate of ammonia and the phosphates in distinct layers.—In this species the nucleus consists of urate of ammonia; and the external layers are most frequently composed of the earthy phosphates mixed together, or more rarely of phosphate of ammonia and magnesia. This species is usually of small size; its specific gravity is from 1.312 to 1.701. It is not very common.

4. Urate of ammonia and earthy phosphates mixed.—The calculi belonging to this species are very rare. They are of a pale-yellow colour, and of less specific gravity than the second species of this genus, which they resemble in external characters. When they are treated with potash, ammonia is disengaged. This species is usually of small size.

5. Earthy phosphates mixed, or in thin layers.—This species is distinguished by its pure white colour. They are of a friable texture, insoluble in alkalies, and soluble in diluted acids. This species is pretty common, and often of a large size. The concretions formed on extraneous matters introduced through the urethra into the bladder, are of this kind. The specific gravity varies from 1.138 to 1.471.

6. Oxalate of lime and uric acid in distinct layers.—In this species the nucleus consists of oxalate of lime, and it is covered with a layer of uric acid. From external appearance they are not distinguished from those entirely composed of uric acid, till they are sawed asunder. The specific gravity varies from 1.341 to 1.754.

7. Oxalate of lime and earthy phosphates in layers.—The oxalate of lime constitutes the nucleus, and the earthy phosphates compose the external covering in this species of calculus. It can only be distinguished by being sawn asunder. The calculi belonging to this species vary greatly in form and size, but they are always white externally. The specific gravity is from 1.168 to 1.752.

Genus III.

Species 1. Uric acid, urate of ammonia, the earthy phosphates and oxalate of lime.—In this species there are frequently three distinct layers. The centre or nucleus is composed of oxalate of lime; the next of uric acid or urate of ammonia; and the outermost of the earthy phosphates, which are usually mixed with uric acid, or urate of ammonia. The calculi of this species can only be distinguished by sawing them in two. There are many varieties of this species, from the different proportions and the different arrangement of the constituent parts.

2. Uric acid, urate of ammonia, earthy phosphates, and silica.—In the calculi belonging to this species, the silica seems to hold the place of the oxalate of lime. It is mixed with uric acid and urate of ammonia, and covered with the phosphate of lime. This is the rarest species of all that have been examined.

3. The investigation of the cause of the formation of calculous concretions has occupied a great deal of attention of physiologists and physicians, and undoubtedly it is one of the most important on which the researches of man can be employed; for by obviating the cause of this disorder, its terrible effects might be prevented. Unfortunately, however, little is yet known on this intricate subject. In many cases, indeed, the formation of urinary calculi is obviously owing to the introduction of some extraneous substance into the bladder by the urethra. But this mode of formation is comparatively rare, and the calculi thus formed are composed of the earthy phosphates, which are deposited from the urine. All urine contains uric acid. This forms one of the most common species of calculi. The particles of gravel which are formed in the kidneys, consist of this acid, so that it very often forms the nucleus of calculous concretions. But the production of an excessive quantity of uric acid, in whatever way this takes place, seems to be the most powerful cause of the production of urinary calculi. It has been observed too, that the urine of those persons in whom these concretions are most frequent, is loaded with an unusual proportion of animal matter. This forms the cementing substance of these concretions. In the formation of these concretions it would appear that the different substances of which they are composed, are secreted at different times, or in different proportions, since the different successive layers of calculi are composed of totally distinct substances. It is perhaps difficult or impossible to explain the formation of those calculi in which oxalic acid is a constituent part. This acid has scarcely ever been detected in the urine, at least of adults, so that it must be produced by some morbid action. Component by which some of the animal fluids are converted into this substance.

4. It has long been an object with physicians, to discover the means of dissolving these substances after they have been formed; and the empiric has not been idle in offering his nostrums which are held out as solvents of the stone, and which it is no wonder are eagerly received with the hope of relief from one of the most dreadful maladies which can afflict mankind. Nothing, however, can be done with this view on rational principles, without previously knowing the nature and properties of the substances which are to be dissolved; and even when this is known, it must appear, from considering the function of digestion, and the changes which all substances taken into the stomach, undergo, that little can be expected from the exhibition of remedies in this way. After being subjected to the different processes of digestion, respiration, and secretion, the properties of these substances are totally changed, so that they can only produce some general effect on the system, and can have no specific action on particular organs. It has therefore been proposed by the French chemists, to employ these substances which possess the property of dissolving urinary calculi out of the body, by injecting them through the urethra into the bladder.

It has been found by experiment, that calculi composed of uric acid, or urate of ammonia, are soluble in solutions of pure potash and soda, even when these solutions are so much diluted with water that they may be taken internally, without producing any inconvenience.

Experiments have also shown, that calculi composed of the earthy phosphates are soluble in nitric and muriatic acids, so much diluted that they may be taken internally without the smallest injury.

Calculi composed of oxalate of lime are less easily dissolved. They are, however, soluble in diluted solutions of carbonate of potash or soda.

The first difficulty, however, which presents itself in the use of these solvents, is to discover the nature and composition of the concretion to be dissolved. This can only be done by employing some of the solutions, and examining them after they have remained for some time, or as long as they can be retained in the bladder. If a weak solution of potash has been injected, it is to be filtered, as soon as it is thrown out; and if on the addition of a little diluted muriatic acid, or vinegar, a white precipitate appears, the calculus is to be considered as composed of uric acid. But if this solution has been employed for some time, and no precipitate is produced in this way, the solution for the phosphates is then to be employed, and when it is passed, after remaining some time in the bladder, a precipitate will be formed with the addition of ammonia. This precipitate will be phosphate of lime.

If no effect is produced by any of these solutions, and if the severity of the symptoms continues, there is some probability that the calculus consists of oxalate of lime. This, it has been observed, is the most difficult of solution. It may be dissolved, however, although slowly, in nitric acid greatly diluted with water, or in weak solutions of the carbonates of potash or soda. These solutions, therefore, must be employed when the others have failed. The effects of these solutions must be judged of by the alleviation of the symptoms, or by the actual examination of the stone itself at different times, by means of the catheter, or found. Whatever solution is employed, it ought to be of the temperature of the body, and so much diluted as not to irritate or injure the internal surface of the bladder to which it is applied. Before the injection is made, the urine should be evacuated, and the injection retained, for at least a quarter of an hour, from that to an hour, or as long as it can be done without inconvenience. The injections should be repeated at first three or four times a day, and afterwards increased to six or eight times. As calculous concretions are frequently several years in forming, it is obvious that they must require a long time to dissolve them, so that the use of injections, if any relief is to be obtained from them, must be long continued.

5. Calculous concretions are not unfrequent in the urinary organs of other animals. They have been found in the horse, in the dog, the rabbit, the hog, and the rat. They are most frequently composed of carbonate of lime with some animal matter; sometimes of phosphate of lime, of phosphate of ammonia, and of carbonate of lime and phosphate of lime; but no traces of uric acid have yet been detected in these concretions.

Gouty concretions.—1. Concretions, which are commonly called chalk stones, are sometimes formed in the joints of those who have been long subject to the gout. They have been discovered by chemical analysis to be composed of uric acid and soda.

2. These concretions are of a white colour, irregular in their form, and of a fine granulated texture. When they are boiled for a few minutes, in 100 times their weight of water, they are entirely dissolved. Sulphuric acid added to this solution, produces a white precipitate, which assumes the form of small needles, which are crystals of uric acid. The remaining liquid, by being evaporated, affords sulphate of soda.

3. By treating a quantity of gouty concretion with 100 times its weight of a concentrated solution of pot-alkalies, ash with the aid of heat, it is almost entirely dissolved, exhaling at the same time the faint odour of animal matter. When the liquid is filtered, and muriatic acid added, it produces a white precipitate, which is uric acid. From this it appears, that gouty concretions possess similar properties with those formed in the urinary organs, excepting that they contain a greater proportion of animal matter.

4. When it is dissolved in a small quantity of diluted nitric acid, it tinges the skin with a rosy colour, and when evaporated, leaves a rosy-coloured deliquescent residuum. By distillation this substance yields ammonia, prussic acid, and an acid sublimate.

5. If a small portion of uric acid be triturated with artificial soda and a little warm water, they combine; and after the superfluous alkali has been washed out, the remainder has all the chemical properties of gouty matter.*

Subdivision IV. Of Substances peculiar to Different Animals.

Having briefly detailed the nature and properties of those substances which are common to animals, we shall now take a general view of some substances which are peculiar peculiar to different animals, and we shall treat of these according to the order in which they are arranged in natural history.

1. Of Substances peculiar to the Class Mammalia.

The substances peculiar to this class of animals are the following:

1. Ivory, 2. Horn, 3. Hartthorn, 4. Wool, 5. Musk,

6. Civet, 7. Caftor, 8. Ambergris, 9. Spermaceti, 10. Bezoards.

1. Ivory.—This is the teeth of the elephant, is a bony substance, of a fine compact texture, white colour, and so hard as to be susceptible of a fine polish. It is composed, like the bones, of gelatinous matter and phosphate of lime, and when it is distilled, it furnishes water, a thick oil, and carbonate of ammonia; and when calcined to whiteness, it leaves pure phosphate of lime.

The component parts of ivory are, according to Merat-Guillot, the following:

| Substance | Percentage | |--------------------|------------| | Phosphate of lime | 64.0 | | Carbonate of lime | 0.1 | | Gelatine | 24.0 | | Lofs | 11.9 |

100.0

2. Horn.—This substance called horn, possesses different properties from that of bone. This matter is produced in the horns of different animals, as those of oxen, sheep, and goats. It has some degree of transparency, and when heated it becomes so soft and flexible, that it may be made to assume different shapes, and formed into different instruments and utensils. Horn yields a very small proportion of earthy matter. The other constituent parts seem to be coagulated albumen and gelatine.

The following are the proportions of the constituents of hartthorn:

| Substance | Percentage | |--------------------|------------| | Phosphate of lime | 57.5 | | Carbonate of lime | 1.0 | | Gelatine | 27.0 | | Lofs | 14.5 |

100.0

3. Hartthorn.—The constituent parts of hartthorn, from the analysis which has been made, are exactly the same as those of bone, but they contain a greater proportion of gelatinous matter.

4. Wool is a kind of long hair, very fine and soft, which is a covering to different animals, especially the sheep. It has been considered as nearly analogous in its nature and properties to hair. It is entirely soluble in the caustic alkalies, and forms with them a foamy matter, which has been employed, it is said, with advantage, as a substitute for soap, in different manufactures.

5. Musk is a substance which is secreted in a bag situated near the umbilical region of the musk deer (moschus moschifer). It has an unctuous feel, is of a dark-reddish brown colour, has a very bitter taste, and is distinguished by a strong aromatic smell. It is partially soluble in water, to which it communicates the odour. A small portion of it also may be dissolved in alcohol, but it does not retain the odour. Musk is soluble in sulphuric and nitric acid; but in these solutions the odour is dissipated. The smell of ammonia is given out by the action of the fixed alkalies on musk. When it is laid on red hot iron, it takes fire, and is almost entirely consumed, leaving only a small portion of gray ashes. During its combustion it gives out the fetid odour of urine. Musk seems to possess many of the properties of the volatile oils, but its component parts have not been determined.

6. Civet.—This substance is extracted from a small bag near the anus of the civetta civeta, or civet cat. It is of a yellow colour, and of the consistence of butter. When first extracted it is said to be white. It has a very strong smell, and slightly acid taste; it combines readily with oils, and is much employed as a perfume.

7. Caftor.—This substance is extracted from two bags situated near the anus of the beaver. The best caftor is obtained from the large bag; that which is secreted in the small bag is said to be of an inferior quality. When eaten at first taken from the animal, it is nearly fluid, and of a yellow colour. After it is exposed for some time to the atmosphere, it becomes hard, and of a darker colour, assuming a resinous appearance. It has an acid, bitter, and nauseous taste, and a strong aromatic smell, which it loses by drying. It becomes lost in water, and communicates to it a pale yellow colour. This infusion converts vegetable blues to a green colour. When it has been long macerated in water, the infusion becomes of a deeper colour, and yields by evaporation extractive matter, which is soluble in alcohol and in ether. A resinous matter is precipitated from the solution in alcohol, by means of water, which has similar properties with the resin of bile. According to the analysis of Lagrange, the component parts of caftor are the following:

- Carbonate of potash, - Lime, - Ammonia, - Iron, - Resin, - Mucilaginous extractive matter, - Volatile oil.

8. Ambergris.—This is a substance which is supposed to be formed in the intestines of the spermaceti whale. It is frequently found floating in the sea. For its natural history, see Ambergris, and Cetology Index.

It is a soft light substance, of an ash-grey colour, with brownish-yellow and white streaks. It has an insipid taste, but an agreeable odour. The specific gravity is from 0.844 to 0.849. It melts at the temperature of 122°, and with the heat of boiling water is completely dissipated in white smoke, leaving a small trace of charcoal. By distillation an acid fluid is first obtained, and a light volatile oil; and there remains behind a voluminous mass of charcoal. By sublimation benzoic acid is separated.

Ambergris is insoluble in water. Concentrated sulphuric acid separates a small portion of charcoal. It is dissolved in nitric acid. During the solution, nitrous gas, azotic gas, and carbonic acid gas, are evolved. A resinous matter is obtained by evaporating the solution. Ambergris is soluble in the alkalies, with the assistance of heat. It is also soluble in the oils, in alcohol and ether. By the analysis of Bouillon la Grange, the constituent parts of ambergris are the following:

| Component | Parts | |-----------------|-------| | Adipocire | 52.7 | | Refin | 30.8 | | Benzoic acid | 11.1 | | Charcoal | 5.4 |

The substance called adipocire possesses the mixed or intermediate properties of fat and wax. This name was first given by Fourcroy to the matter into which the dead bodies found in the Innocents burying-ground were converted. In appearance and some of its properties it also resembles spermaceti.

9. Spermaceti.—This is a production of the same whale which yields the preceding substance. It is an oily matter which surrounds the brain. It is separated from a fluid oil, with which it is mixed, by expression. Spermaceti is also found in other cetaceous fishes, and in other parts of the body, mixed with the oil.

It is a fine white substance of a crystallized texture, very brittle, and has little taste or smell. It crystallizes in the form of shining silvery plates. It melts at the temperature of 112°. With a greater heat it may be distilled without change; but, by repeated distillation, it is decomposed, and partly converted into a brown acid liquid. It is soluble in boiling alcohol, but it separates when the solution cools. It is also soluble in ether, both cold and hot. In the hot solution it concretes on cooling into a solid mass.

Spermaceti is scarcely at all soluble in the acids. It combines readily with the pure alkalies, with sulphur, and with the fixed oils. By exposure to the air it becomes rancid. The uses of spermaceti are well known, and particularly in the manufacture of candles.

10. Bezoards.—These are calculous concretions which are found in the intestines of different animals belonging to this class, particularly the horse. Some of very large size have been found in the elephant and the rhinoceros. These substances were once celebrated on account of their medical virtues, and they were formerly distinguished into oriental and occidental. The first were most highly valued, and frequently bore a high price, especially the bezoards obtained from a species of goat which inhabits the Asiatic mountains. Some that have been examined were composed entirely of vegetable matter. In general the nucleus is of vegetable matter, on which phosphate of ammonia and magnesia or phosphate of lime have been deposited. These substances are distinguished by a strong aromatic odour when they are rubbed or reduced to powder. The brown or golden-coloured matter which has been observed on the grinding teeth of ruminating animals is found to be of the same nature with the bezoards which are formed in the intestines.

II. Of Substances peculiar to the Class of Birds.

The substances which are peculiar to this class of animals are the following:

1. Eggs, 2. Feathers, 3. Excrement, 4. Membrane of the stomach.

1. Eggs.—In a chemical view, three parts of an egg merit attention. There are the shell or external covering, the white, and the yolk. The white of egg, which consists of albumen, has been already described, so that it now only remains to give some account of the shell and the yolk.

The shells of the eggs of birds which have been analyzed are composed of similar constituents with bone, but in very different proportions. The following is the result of the analysis of Vauquelin.

| Component | Parts | |--------------------|-------| | Carbonate of lime | 89.6 | | Phosphate of lime | 5.7 | | Animal matter | 4.7 |

The yolk of egg is of a soft consistence, a yellow colour, and of a mild oily taste. It becomes solid by boiling, and crumbles easily into small particles. By heating gently after it has been boiled, and by expression, an oily liquid of a yellow colour, and insipid taste, is obtained. It is distinguished by the proprieties of fixed oil. What remains after separating the oil is albumen, still coloured with a small portion of oil. By boiling this residuum in water, a portion of gelatine is obtained, so that the yolk of egg is composed of oil, albumen, gelatine, and water.

2. Feathers—are considered as possessing similar properties with hair. According to some, the solid part, or quill, may be reduced to the gelatinous state by boiling; but according to others, no gelatine whatever can be detected. The quill part is therefore supposed to consist chiefly of coagulated albumen. It becomes soft by the action of acids and alkalies.

3. Excrement.—This matter in birds is very different from that of the animals included in the class mammalia. It is generally of a white colour, less liquid, and less fetid. It is commonly accompanied with a glairy matter of different degrees of transparency, analogous to the white of egg. This seems to be owing to a quantity of albumen which is secreted in the oviduct. The white part of this matter is composed of carbonate and phosphate of lime and albumen. The colouring matter seems to be part of the food.

4. Membrane of the stomach.—The internal surface of the gizzard, or muscular part of the stomach of birds, of the fowl is covered with a wrinkled membrane, which is susceptible of considerable extension, and through the pores of which gastric juice is copiously secreted. This membrane is easily separated from the muscular part. When it is boiled in water, it is converted into jelly, and communicates to the water the property of reddening vegetable blues, and coagulating milk. When it is dried and reduced to powder, it produces the same effect.

III. Of III. Of Matters peculiar to Animals in the Amphibious Clafs.

1. Poison of the Viper.—Some of the animals belonging to the snake tribe, secrete a peculiar fluid in the mouth, which is of a poisonous quality. The poison of the viper is a yellow, viscid liquid, somewhat resembling oil. It is secreted in two small bags, and from them conveyed to the fangs of the animal, which are hollow and perforated, and when it bites, the liquid is squeezed out of the bag, and flows through the teeth into the wound. It has no smell. It becomes thick by exposure to the air, and is converted into a transparent jelly; but it retains its poisonous property long after it is separated from the animal. It is soluble in water by agitation, but if thrown into the water when extracted from the vehicle, it falls instantly to the bottom like a heavy oil. It is soluble in warm water after it is dried, but not soluble in alcohol, or coagulated by boiling water. Acids and alkalies produce no perceptible change upon this matter. It is precipitated from its solution in water by alcohol. It resembles gum in so many of its properties, that it has been called an animal gum.

2. Liquid secreted from the tubercles on the head of the Toad.—It has been long supposed that the liquid secreted on the head of the toad is of a poisonous quality; but although it is said by some naturalists, that this fluid, brought in contact with the skin, produces inflammation, yet there seems to be no positive proof of this effect.

3. Tortoise-shell.—This substance, which forms a strong covering and defense to the body of the turtle, possesses many of the properties of horn; for it may be softened with heat, or in boiling water, and shaped into any form which may be wanted. It is composed of a number of hard plates or membranes, of different degrees of thickness, closely applied to each other. It becomes soft by maceration in nitric acid, and by burning it yields a very small proportion of phosphate of lime and soda, with some slight traces of iron.

IV. Of Substances peculiar to Fishes.

1. Scales.—Generally possess a silvery whiteness, and are composed of different laminae. In many of their properties they resemble horn. By long boiling in water they become soft, and when they are kept for some hours in nitric acid, they are converted into a transparent membranous substance. By saturating the acid with ammonia, a precipitate is formed, which is phosphate of lime. The constituent parts of scales, therefore, are membrane and phosphate of lime.

2. Bones of fisher.—These are composed of the same constituents as those of other animals, but have a greater proportion of animal matter. In some they are soft, flexible, and semitransparent, and hence they are called cartilaginous. In others they are hard and solid, having the usual appearance of bone.

3. Fish oil.—A great quantity of oil is extracted from the soft parts of different kinds of fish, and especially from the blubber of the whale. It is usually denominated train oil. It is obtained, either by expression, or by boiling. It is supposed that the oil obtained from the blubber of the whale, and from other fishes, possesses different properties, which are ascribed to the difference in the function of respiration of cetaceous and other fishes; but how far this difference really exists, does not seem to have been accurately ascertained. Fish oil is distinguished by a disagreeable smell, and it has long been an object to deprive it of this odour, as it is much employed in domestic economy and in many arts. By agitating the oil with a small portion of sulphuric acid, and adding water, the oil when left at rest, rises to the surface considerably purified. A portion of coagulated matter has separated, and the water is milky.

V. Of Substances peculiar to Insects.

1. Wax.—The nature and properties of this substance have already been described as a vegetable production.

2. Propolis.—This is a substance collected by bees, Propolis, and with which they cover the bottom of the hive, or any foreign matters which happen to be introduced into it, which they cannot remove. It is the substance which they collect on their legs and thighs. It is perhaps more properly to be considered as a vegetable production. It possesses more tenacity than wax, but has much of its ductility. It is insipid to the taste, but is distinguished by an aromatic odour. It is partially soluble in alcohol, to which it communicates a red colour. Another portion is dissolved in boiling alcohol, and part precipitates as the solution cools, which has the properties of wax. A resinous mass is obtained by concentrating the solution in alcohol and boiling in water. It is semitransparent and brittle. An acid was detected in the water in which it was boiled. The resinous substance is soluble in fixed and volatile oils. The following are the constituent parts of propolis.

| Component Parts of Animal Substances | |--------------------------------------| | Pure resin | 57 | | Pure wax | 14 | | Extraneous matter | 14 | | Loss and acid | 15 |

* Nikol. Jour. v. p. 49.

3. Honey.—This also has been considered as a vegetable production, as it is collected from plants by bees. It is of a white or yellowish colour, of a granular soft consistence, and has an aromatic smell; but these properties vary according to the plants from which it is collected, or the climate in which they grow. By distillation honey yields nearly the same products as sugar. It is converted into oxalic acid by means of nitric acid. It is very soluble in water, and is even somewhat deliquescent. It readily passes to the vinous fermentation, and affords a fermented liquor which has been called hydromel. It is partially soluble in alcohol, and by this means sugar may be extracted from it. The component parts of honey are sugar, mucilage, and an acid. If pure honey be melted, and carbonate of lime be added till the effervescence ceases, the sugar is separated, and is deposited in crystals.

4. Cantharides are a species of fly, (the meloe ves. Cantharis catorius, Lin.) which are much employed, from a peculiar property they possess, to raise blisters on the skin. For this purpose the whole of the insect is reduced. Component duced to powder. Cantharides have been subjected to analysis; and by successive treatment with water, alcohol, and ether, four different substances have been extracted.

1. Three-eighths of their weight consist of extractive matter, of a reddish-yellow colour, very bitter, and which yields by distillation an acid liquor.

2. A little more than one-tenth of the weight consists of a concrete oil, something of the nature of wax, which is of a green colour and very acrid taste. To this is owing the peculiar odour of cantharides. This substance yields by distillation, a very pungent acid substance and a thick oil.

3. About one-fiftieth of a yellow concrete oil, which seems to communicate the colour to the insect, is also obtained.

4. About one-half the weight of a solid matter remains, the nature of which has not been ascertained. The blistering effect of cantharides seems to depend on the green waxy matter, part of which is extracted by means of warm water, and it is entirely soluble in ether.

Millepedes.—These insects, which are different species of oniscus, were formerly employed in medicine. By distillation with the heat of a water bath, they yield a watery liquid, which converts the syrup of violets to a green colour, and by this process they are deprived of five-eighths of their weight. By treating them afterwards with water and alcohol, they furnish one-fourth of their weight of an extractive and waxy matter; the latter is soluble in ether. The muriates of potash and lime have been detected in the expressed juice of these insects.

Ants.—These insects contain an acid liquid, which they emit from the mouth when they are irritated, or when they are bruised on paper. This liquid converts vegetable blues to red; and it has been observed that streaks of the same colour are communicated to blue flowers, over which the insects creep. The acid obtained from ants, and particularly from the formica rufa, or red ant, was formerly considered as possessing peculiar properties, and thence denominated formic acid; but it has been lately ascertained to consist of a mixture of acetic and malic acids.

Lac.—This is a substance which is formed on the branches of several plants, as the ficus indica, the ficus religiosa, and especially the croton laciferum. It is produced by the puncture of an insect, but is considered as belonging to vegetable substances, among which the general properties have been already described, as well as the properties of an acid obtained from it, among the acids.

Silk.—This is the production of several insects, either for the purpose of covering up their eggs, or forming a net to catch their prey, as is the case with many of the spider tribe, or to cover up the insect during one of the stages of its metamorphosis. The silk of commerce is usually obtained from the phalena bombyx, or silk-worm. This substance is prepared in the body of the larva of the insect, from which it is protruded through several small orifices in very fine threads; and with this it forms a covering for itself while it remains in the state of chrysalis or pupa.

Silk is a very elastic substance, and is of a white or reddish yellow colour, when it is produced by the insect. The elasticity of silk has been ascribed to a varnish with which it is covered, of a gummy or gelatinous nature, which is precipitated by tan and muriate of tin. The yellow colour of silk is ascribed to a resinous matter which is soluble in alcohol. By distillation silk yields a large proportion of ammonia. It is soluble in sulphuric, nitric, and muriatic acids. By nitric acid it is partly converted into oxalic acid, and a fatty matter which floats on the surface.

Cochineal.—This is an insect which breeds on the leaves of the cactus coccinelliferus Lin. sometimes called opuntia or nopal. The plant is cultivated in Mexico, for the purpose of rearing the insects, which are collected, dried, and employed as a beautiful dye stuff. By burning, the same results are obtained as from other animal matters; but with boiling water it gives a crimson violet colour, which becomes red and yellow by the action of acids, while a precipitate is formed of the same colour. The metallic solutions added to this decoction, also produce a coloured precipitate. The muriate of tin throws down a beautiful red precipitate. The evaporated residuum of the decoction of cochineal treated with alcohol, gives a fine red colour, and this, by evaporating the alcohol, assumes the form of a resin. Oxymuriatic acid converts the solution of this substance into a yellow colour, from which the proportion of colouring matter may be in some measure estimated, by the quantity of acid requisite to destroy its colour. Cochineal is well known by its producing a beautiful scarlet colour. It may be kept for any length of time, at least in a dry place, without being deprived of its colouring matter. It has retained this property for 130 years. Cochineal is employed in the preparation of the beautiful lake called carmine.

Kermes.—This also is an insect which is employed in dyeing, from whence it has been called coccus infectarius. It is the coccus ilicis Lin. and is produced on a small kind of oak, the quercus cocifera. The insect attaches itself to the bark of the tree by a soft substance, which possesses many of the properties of caoutchouc.

When the living insect is bruised, it gives out a red colour. It has a slightly bitter, rough, pungent taste, but its smell is not unpleasant. The dried insect, or the kermes, imparts this odour and taste to water and to alcohol, and communicates also to these liquids a deep red colour. By evaporation, an extract of the same colour is obtained. It is employed in dyeing, and has been also used in medicine.

Crabs eyes.—The substance which has received this name, merely from its form, is a concrete body, convex on one side, and concave on the other. Two of these bodies are usually found in the stomach of the crab, about the time that it changes its shell. After the shell is fully formed, they are no longer found, so that they are supposed to furnish the materials of the new shell. They are entirely composed of carbonate of lime, a small proportion of phosphate of lime, and gelatine.

The crustaceous coverings of the crab, lobster, and similar animals, are composed of carbonate of lime, phosphate of lime, and animal matter, or cartilage.

VI. Of Substances peculiar to Testaceous Animals.

The only substances to be mentioned peculiar to this

Component this class of animals are shells, mother of pearl, and pearl.

1. Shells.—Such as have been particularly examined by Mr Hatchett are divided into two classes. In the one he includes those which have the appearance of porcelain, and have an enamelled surface, which he calls porcellaneous shells. Such are the various species of voluta and cypraea. These shells were found by analysis to be composed of carbonate of lime, with a small portion of animal gluten.

2. Mother of pearl.—The second class comprehends those which are generally covered with a strong epidermis, under which is the shell, composed chiefly of the substance called nacre, or mother of pearl. Such are the oyster, the river mussel, the halibut iris, and the turbo olearius. In these the proportion of carbonate of lime is smaller, and that of the animal matter greater.

3. Pearl.—This is a concretion formed in several species of shells, as in some species of the oyster and the mussel. It is considered by some as a morbid concretion, owing to an excess of the flaky matter, or to a wound of the shell containing the animal. Pearls are of a silvery or bluish-white colour, iridescent and brilliant. The refraction of the light is ascribed to the lamellated structure, for they consist of concentric layers of carbonate of lime and membrane alternately arranged. The constituent parts of pearl are the same as mother of pearl.

VII. Substances peculiar to Zoophytes.

The zoophytes, many of which have been examined by Mr Hatchett, are composed of carbonate of lime, phosphate of lime, and animal matter of different degrees of consistency. In some the constituents are only carbonate of lime and a gelatinous matter. Such are some species of the madrepora, as the madrepora muricata, virginea, and labyrinthica; some species of millepore, as the millepora cervula and alcicornis, and the tubipora myfica. Others again are composed of carbonate of lime and a membranaceous substance. Such are the madrepora fascicularis, the millepora celulosa and fascialis, and the iris hippuris. White coral and articulated coralline are composed of similar substances. Another division of zoophytes is composed of carbonate of lime, a small portion of phosphate of lime and membrane. Such are the madrepora polymorpha, the gorgonia nobilis or red coral, and the gorgonia setosa; but some of the zoophytes are also found to consist chiefly of animal matter, with scarcely any portion of earthy substance. To this division belong some species of gorgonia and many species of sponge.

CHAP. XX. Of Arts and Manufactures.

In this chapter it was intended to give a general view of the application of the principles of chemistry to different arts and manufactures, such as the manufacture of soap, of glass and porcelain; the arts of dyeing, bleaching and tanning. In this view it was proposed to explain the principles of these arts and manufactures, so far as they depend upon chemistry, leaving the detail to the different treatises on those subjects in the course of the work. But the unavoidable length to which this article has extended, obliges us to refer our readers for the whole to the different treatises.

APPENDIX.

After the chapter on earths was printed off, we received the account of a new earth discovered by Klapproth.

Of Ochroit. This earth was discovered in a mineral to which Klapproth has given the name of ochroites, of which the external characters are the following:

1. The colour of this mineral is between carminof red, clove brown, and reddish brown. It is compact, breaks splintering in irregular but not very sharp or angular pieces. It is perfectly opaque, the powder is reddish-grey; it is not very hard, but brittle. The specific gravity is 4.65. This mineral is found in the mine of Bainetze, near Riddarhytta in Westfalenland.

A. "c. A piece of the mineral, after having been ignited to redness, lost two per cent. Its reddish colour had been changed to brown. Its figure had suffered no alteration.

"B. One hundred grains of the finely levigated mineral ignited for half an hour, lost five grains. Its colour was changed to a dark brown.

B. a. One hundred grains of ochroit, after being mixed with 200 grains of carbonate of potash, were strongly ignited, the mass which could not be rendered fluid, was reddish gray, and brittle. On being diffused through water as usual, the obtained solution was colourless. It remained perfectly transparent; a proof that it did not contain tungsten oxide; nitrate of silver, mercury, lead, barytes, &c. proved the absence of acids.

b. The insoluble residue of the last process was boiled in nitro-muriatic acid, the filceous earth being separated, the solution was decomposed by potash, and the whole boiled for some time. The alkaline fluid, after being neutralized with muriatic acid, and then mingled with carbonate of potash, suffered no change.

C. a. Two hundred grains of the finely pulverized mineral were first boiled in two ounces of muriatic acid, to which half an ounce of nitric acid was gradually added, and the digestion continued for some time. The whole became thus dissolved except the filce contained in the mineral. Its quantity amounted to 68 grains.

b. To the solution obtained in the last process, carbonate of ammonia was added so long, till no permanent precipitate was produced. On letting fall into it succinate of ammonia, a curdly precipitate fell, which vanished again on agitation, leaving merely a pale red precipitate. precipitate of succinate of iron. This being collected, washed, dried, and strongly ignited, yielded nine grains of oxide of iron.

c. The fluid, thus freed from iron, and now colourless, was decomposed by carbonate of ammonia. The precipitate obtained was white, and weighed 168 grs. on being deprived of water and carbonic acid by heat, its white colour changed to cinnamon brown. It weighed 109 grams.

d. All the water employed for washing the different precipitates was mingled, evaporated to dryness, and the ammoniacal salt volatilized; a minute quantity of a muriate was obtained, the basis of which could not be determined.

From what follows it will become evident, that the cinnamon-brown precipitate (c.) which forms the principal part of the fossil, is a peculiar earth, distinct from all the others hitherto known. The characteristic property which it possesses, of acquiring a light-brown colour after being heated, has induced me to call it ochroit earth (A), which may also serve for the mineral itself.

According to this analysis, 100 parts of the ochroit of Riddarhytta contain:

| Component | Parts | |--------------------|-------| | Ochroit earth | 54.50 | | Silica | 34 | | Oxide of iron | 4 | | Water, &c. (A. b.) | 5 | | Loss | 2 |

Characteristic Properties of Ochroit Earth.

1. Ochroit earth is capable of combining with carbonic acid during its precipitation from acids by carbonated alkalies, and strongly consolidating a portion of water.

One hundred grains of the earth, precipitated by carbonate of ammonia, and strongly dried, lost on being neutralized by nitric acid, 23 grams; 100 grams of the same earth lost, after being strongly ignited, 35 grams; 100 parts of carbonate of ochroit, therefore, consist of:

| Component | Parts | |--------------------|-------| | Ochroit earth | 65 | | Carbonic acid | 23 | | Water | 12 |

2. Ochroit earth, after being freed from carbonic acid and water by heat, always appears in the form of a cinnamon-brown powder. The intensity of the colour is in proportion to the heat applied. This colour is not owing to the presence of iron or manganese, &c., but it is a characteristic property of the earth.

3. Ochroit earth, included in a charcoal crucible, and exposed to the heat of the porcelain furnace, suffered no change whatever.

4. Urged by the blowpipe, it becomes phosphorescent; fused with phosphate of soda and ammonia, it becomes tinged by it, without effecting a solution of the earth. The salt acquires merely a marbled lemon-yellow colour. Borax has likewise no chemical effect. This fact only effects a mechanical division. The earth always appears diffused through the borax in minute flocculi.

5. Ochroit earth, mixed in different proportions with proper fluxes, and applied for painting of porcelain, proved unsuccessful. The painted articles were light-brown; but the colour was not uniform; a proof that no combination had been effected.

6. Ochroit earth, combined with carbonic acid is easily soluble with effervescence in acids. The taste of the solution is very rough and astringent. The concentrated solution is of an amethyst-red colour; diluted with water, it becomes colourless. Ignited ochroit earth, on the contrary, is difficultly soluble in acids in the cold; if nitric acid be employed, the solution is yellowish red.

7. The combination of ochroit earth with sulphuric acid is crystallizable. The figure of the crystals formed in the mass of the fluid is the octahedron. They are heavy, of a pale amethyst colour, and difficultly soluble in water; but the sulphate of ochroit, with excess of acid, is more soluble; the figure of the crystals formed on the sides of the vessel, is needle-shaped, radiating from a centre. They are more soluble than the former.

8. If a solution of sulphate of soda be mingled with a solution of muriate or nitrate of ochroit, a mutual decomposition takes place. A white insoluble precipitate is formed, consisting of sulphuric acid united to the ochroit earth. This combination may be decomposed by boiling it with double its weight of carbonate of soda. By this means ochroit earth may be obtained very pure.

9. Ochroit earth is likewise soluble in sulphurous acid; the solution crystallizes in needles of a pale amethyst colour.

10. Muriatic acid dissolves ochroit earth, and yields crystals, the figure of which is the prism. It is soluble in alcohol, without imparting to its flame any particular colour.

11. Acetite of ochroit could not be crystallized, but yielded an adhesive mass.

12a Nitrate and muriate of ochroit are decomposable by carbonated earths and alkalies, the precipitate is milk-white. Alkalies and earths, freed from carbonic acid, occasion a yellowish-gray precipitate.

13. Prussiate of potash precipitates ochroit from all its neutral solutions, milk-white. The precipitate is soluble in muriatic and nitric acid (b).

14. Tincture of galls occasions no change in the solutions of this earth.

15. Hydroguretted hydrofulphuret of ammonia precipitates the solution of ochroit earth yellowish white.

16. Water impregnated with sulphurated hydrogen occasions no change in the solutions of ochroit earth.

17. Succinates precipitate ochroit earth white.

18. Phosphate

(a) From the Greek word ἀγκες, (flavescens), brownish yellow.

(b) If the earth contained the muriates and quality of iron, it becomes by this means manifested. 18. Phosphate of soda occasions in the solutions of this earth a white precipitate, which again vanishes by the addition of nitric or muriatic acid.

19. Tartrites of potash also precipitate this earth white.

20. Oxalates effect a like decomposition; the oxalite of ochroit, however, is not soluble in nitric or muriatic acids.

21. Alkalies and alkaline carbonates do not act on ochroit earth.

22. Ammonia feebly acts on it, under certain circumstances, as may be evinced from the following experiment:

A solution of nitrate of ochroit, prepared by dissolving 100 grains of carbonate of ochroit (not absolutely free from iron), in nitric acid, was decomposed by carbonate of ammonia, and digested in the fluid, containing a considerable quantity of carbonate of ammonia in excess, for some days. The fluid, which had acquired a yellow colour, was separated and neutralized by sulphuric acid, and then set in a warm place. A gray precipitate was thus obtained, which, on being dried, weighed 1½ grains. This precipitate, after being dissolved in nitric acid, yielded a blue precipitate by prussiate of potash; this being separated, a white flocculent precipitate fell down by dropping into the remaining fluid carbonate of potash. This method is, therefore, applicable for separating a minute quantity of iron, that may be contained in the fluid.

"From what has been stated, it becomes obvious, that General re-ochroit earth bears the nearest relation to yttria; marks and for, like this, it forms a connecting link between the characters of the ochroids and the metallic oxides. Like yttria, it has roit earth the property of forming a reddish-coloured salt with sulphuric acid, and is precipitable by prussiate of potash; but differs from yttria, in that it does not form sweet farts, that it is not (at least very sparingly) soluble in carbonate of ammonia, and that, when ignited, it acquired a cinnamon-brown colour. It farther differs from yttria by not being soluble in borax or phosphate of soda when urged upon charcoal before the blow-pipe, which fails easily effect a solution of yttria, and melt with it also into a pellucid pearl."*

ERRATUM in CHEMISTRY.

P. 508. l. 10. col. 2d. It is said that Mr Keir found that sulphuric acid froze at 45° Fahrenheit. This is only inferred from the thermometer being stationary at 45° during the melting of the frozen acid. A greater degree of cold was also found necessary for its congelation.

Phil. Trans. 1787. p. 279.

EXPLANATION OF THE PLATES.

Plate CXLII.

Fig. 1. Represents Harrison's pendulum constructed on the principle of the unequal expansion of metals.

Fig. 2. The calorimeter of Lavoisier and Laplace, see page 476.

Fig. 3. Iron bottle and bent gun-barrel for procuring oxygen gas from manganese. The black oxide is reduced to powder, and introduced into the bottle A. The bent tube is put on the mouth of the bottle at C, and fitted with the materials described at the foot of page 490. The bottle is then exposed to a red heat, and the gas which comes over is received in jars on the pneumatic apparatus.

Fig. 3. and 4. represent the apparatus for the decomposition of water. See page 496.

Fig. 5. Pneumatic trough for collecting gaseous bodies. Suppose a quantity of sulphurated hydrogen gas is to be collected, which is described in page 505. The iron filings and sulphur which were melted together in a crucible, and which then form a black brittle mass, are to be introduced into the glass vessel. Fig. 6. B is a bent tube ground to fit the mouth D, and is air-tight. To the other mouth C is fitted the ground stopper A. One end of the bent tube is fitted into the mouth D, and the other placed under the glass jar F on the shelf of the pneumatic trough E, which is filled with water about an inch above the surface of the shell. The jar is also previously filled with water, cautiously inverted, and set on the shelf. The apparatus being thus adjusted, muriatic acid is poured into the opening C, and the ground stopper is immediately replaced. A violent effervescence takes place, a great quantity of gas is disengaged, and as there is no other way for it to escape it passes into the glass jar. When this is filled, it is removed to another part of the shelf; another jar which was previously filled with water is put into its place, and so on till the whole gas is collected.

Fig. 7. Papin's digester. A is the body of the vessel, which has been generally made of copper or iron, very thick and strong. BB are two strong bars fixed to the sides of the vessel. To the upper end of these bars is fixed the cross bar C, through which passes a strong screw D, which presses on the lid of the vessel at E, so that it is enabled to resist the elastic force of the vapour; and the water can thus be raised to a higher temperature than the ordinary boiling point.

Fig. 8. This represents an apparatus for distillation. A is the furnace, B is the body of the still, which is generally made of copper; C is the top or head, made of the same metal. The vapour as it rises from the liquid by the application of heat, passes along the tube D, which communicates with a spiral tube in the refrigeratory E, which being filled with cold water, the vapour is condensed, and passes out at the other extremity of the tube F, and is received in the vessel G. Plate CXLIII.

Fig. 9. Glass Retort. Fig. 10. Tubulated retort. Fig. 11. Glass Alembic. Fig. 12. Solution glass. Fig. 13. Crucible.

Fig. 14. Apparatus for obtaining muriatic acid from muriate of soda by sulphuric acid. The muriate of soda is introduced into the retort A, and by means of the bent tube B the sulphuric acid is added. The mats C is adapted to the retort, to receive the portion of impure sulphuric acid and muriatic acid which passes over towards the end of the operation. D, E, and F, are bottles containing water; the quantity of which should be equal in weight to that of the salt employed. These bottles are furnished with tubes of safety GG; or the tube of safety may be applied as H in the bottle E.

Fig. 15. Apparatus for impregnating fluids with gases. A is a tubulated retort which is joined to B, a tubulated receiver, from which a bent tube C passes to the second receiver D. This last communicates with the bottle F by means of the bent tube E. The end of the tube C which enters the receiver D, is furnished with a valve which prevents the return of any gas from the receiver D to the receiver B, in case a vacuum should take place in the course of the operation in the receiver B, or in the retort A. The gas which is not absorbed by the water in the receiver D, passes through the tube E to the bottle F.

Fig. 16. A gazometer, which is a convenient apparatus for holding gases. It is usually made of tin plate. A is an inverted vessel, which exactly fits another, which is fixed within the cylinder B. When it is pressed down to the bottom of the cylinder, water is poured in, by which means the small quantity of air which remains in the intermediate spaces, is forced out, and the gas to be preserved may be introduced at the lower stop-cock C. The vessel A is nearly balanced by the weights DD, which are connected with it by means of the cords a a a a, which move on the pulleys b b b b. As the gas enters the apparatus, it forces up the vessel A, and in this way it may be completely filled. It is forced out by turning the stop-cock E, and pressing down the vessel A, and may be conveyed into a pneumatic apparatus, and received in jars by means of the flexible tube F.

INDEX.

A.

Acetate of potash, No 987 Acetic acid, history of, properties, analysis, Acids, distinctive character of, importance, found in animal bodies, Adhesion, how it happens, accounted for, Affinity, history of, action of, explained, limited, Laws of, force of, examples of, Albumen from eggs, uses, Alchemists, most eminent of, Alchemy, history of, useful, declines, not fruitful in discoveries, the reason, Alkali, calcined, silicated, Alkalies, origin of the name, characters, Alum, history of, preparation, properties, Alumina, history of, properties, gelatinous, uses, spongy, Amber, Ambergris, composition of, Ammonia, history of, properties, composition, faults, Ammoniac, Ammoni, liquor of, properties, composition, of the cow, composition, Amniotic acid, properties of, Animals, functions of, decomposition, component parts, Anime, Antimony, history of, properties, uses, Ants, Apparatus described, Application of chemistry to the arts, Argil, Argillaceous earth, Arseniate of potash, Arsenic acid, properties of, action of water on, affinities, Asafoetida, Atmosphere, component parts of, constitution, changes, Atmospheric air, properties of, Azotic gas, discovery of, Azotic gas, properties of, combines with oxygen, B. Bacon's theory of heat, Balm of Gilead, Barites, history of, properties, Bdellium, Becher's elements, Benzoic acid, history of, properties, component parts, affinities, Benzoin, Bergmann's explanation of affinity, Bezoards, Bile, properties of, composition, Bismuth, history of, properties, Bitter matter, Black, Dr., on caloric, fixed air, Blister, liquor of, Blood, properties, ferum, Cruor, Fibrina, constituents of, Inflammatory, Diabetic, Blue, liquid, what, | Bodies, capacities of, for caloric, | No 261 | | Boerhaave, his distribution of bodies, | 256 | | Boiling, point constant, | 229 | | Bones, composition, | 2772 | | of different animals, | 2778 | | of the teeth, | 2729 | | of fishes, | 2872 | | Boracic acid, discovery of, | 566 | | preparation, | 567 | | properties, | 568 | | affinities, | 574 | | Borate of lime, | 1213 | | Borax, history of, | 1067 | | properties, | 1069 | | ufs, | 1073 | | Bofcovich's theory of cohesion, | 72 | | Brain and nerves, | 2802 | | Britain, chemistry first studied in, | 36 | | Brugnatelli on combustion, | 325 | | Butter of antimony, | 1685 | | of bismuth, | 1670 | | of zinc, | 1775 |

| C. | | Calamine, | 1752 | | Calcis of metals, | 1518 | | Calomel, | 1738 | | Caloric, what, | 159 | | Bacon's theory of, | 161 | | velocity of, | 165 | | minute particles, | 166 | | reflection, | 170 | | rays of, | 172 | | effects of, | 303 | | modifications of, | 334 | | elastic fluids, effects on, | 181 | | radiated, | 241 | | refracted, | 242 | | reflected, | 243 | | Camel, urine of, | 2698 | | Cameleon, mineral, | 1652 | | Camphor, | 2441 | | Camphorate of potash, | 1006 | | Camphoric acid, history of, | 733 | | properties, | 740 | | affinities, | 744 | | Cantharides, | 2875 | | Canton's pyrophorus, | 144 | | Caoutchouc, | 2449 | | Carbonate of potash, | 974 | | Carbone, nature of, explained, | 397 | | Carbonic acid, formation of, | 595 | | names of, | 596 | | method of obtaining, | 598 | | properties, | 599 | | affinities, | 606 | | fatal effects of, | 608 | | Caster, | 2856 | | Cavendish, Mr, his experiments on water, | 389 | | Cerumen of the ear, | 2735 | | properties, | 2736 | | composition, | 2738 |

| Cheese, | No 2713 | | Chemistry, definition of, | 1 | | importance of to man, | 7 | | application of, to the arts, | 13 | | an art among the Egyptians, | 17 | | Greeks, | 18 | | Phoenicians, | 19 | | Chinese, | 20 | | Romans, | D. | | Chromate of potash, | 986 | | Chromic acid, discovery of, | 635 | | ufs, | 641 | | Churning, process of, | 2710 | | Cinnabar, | 1701 | | Citrate of potash, | 1005 | | Citric acid, found in fruits, | 680 | | compounds of, | 690 | | affinities, | 691 | | Civet, | 2855 | | Coagulation, caule of, | 2598 | | Cobalt, | 1593 | | Cochineal, | 2880 | | Cohesion, force of, | 68 | | Newton's theory of, | 70 | | Defaguliers', | 71 | | Bofcovich's, | 72 | | Cold reflected, | 272 | | accounted for, | 273 | | Colour, | 150 | | Colouring matter, | 2394 | | Columbate of potash, | 986 | | Columbic acid, discovery of, | 642 | | properties, | 644 | | Columbium, history of, | 1572 | | analysis, | 1574 | | Combustion, | 155 | | Concretion, morbid, | 2815 | | found in pineal gland, | 2816 | | salivary, | 2817 | | pulmonary, | 2819 | | composition of, | 2821 | | biliary, | 2822 | | urinary, | 2828 | | properties of, | 2830 | | constituents, | 2831 | | solvents, | 2842 | | how used, | 2843 | | gouty, properties of, | 2846 | | action of alkalies on, | 2847 | | Copaiva, | 2473 | | Copal, | 2469 | | Copper, history of, | 1958 | | ores, | 1959 | | properties, | 1961 | | alloys, | 2005 | | Corrosive sublimate, | 1738 | | Cow, urine of, | 2697 | | Crabs eyes, | 2882 | | Crawford, Dr, his method of ascertaining the capacity of bodies for caloric, | 262 | | Cruor of blood, | 2653 |

| Cruor of blood contains albumen and soda, | No 2654 | | iron, | 2655 | | Crystallization accounted for, | 82 | | by Newton, | 83 | | Haury, | 84 | | Curd, | 2712 | | of milk of different animals, | 2721 | | Cutis or true skin, | 2783 | | Dalton on caloric, | 269 | | Decomposition of animals, | 2572 | | Definition of chemistry, | 1 | | Defaguliers' on cohesion, | 71 | | Detonation, what, | 337 | | Diamond, | 397 | | found in the torrid zone, | 399 | | form of, | 400 | | properties, | 401 | | production of its combustion, | 402 | | a simple substance, | 403 | | compared with charcoal, | 404 | | Different affinities among bodies, | 412 | | Digestion, | 2548 | | nature of, unknown, | 2552 | | Discoveries of the alchemists, | 30 | | importance of, | 39 | | Dragon's blood, | 2467 | | Dropfy, liquor of, | 2764 | | E. | | Earths, properties of, | 1165 | | Effects of light on metallic oxides, | 151 | | calorific, | 175 | | solubility, | 100 | | Egg yields albumen, | 2596 | | Eggs, | 2863 | | Egyptians, their knowledge of chemistry, | 17 | | Elastic fluids, | 183 | | Eleme, | 2471 | | Elements of bodies, | 41 | | Epidermis of the skin, | 2781 | | Epsom salt, | 1343 | | Ether, formation of, | 832 | | names, | 833 | | fulphuric, | 834 | | nitric, | 844 | | muriatic, | 853 | | Evaporation explained, | 80 | | Euphorium, | 2489 | | Examples of affinity, | 94 | | Excrement, | 2867 | | Expansion, | 178 | | quantity of, | 202 | | ExtraStive matter, | 2387 | | Eye, humours of, | 2730 | | of sheep, | 2731 | | human, | 2732 | | F. | | Fat, | 2628 | | Fermentation, acetous, | 2310 | | vinous, | 2300 | | panary, | 2313 | | Fibrina obtained from blood, | 2612 | | Fibrina | | Topic | Page | |----------------------------------------------------------------------|------| | Fibrina obtained from muscle, properties, composition | 2613 | | Flint and steel, effects of | 277 | | Flowers of bismuth, of zinc | 1661 | | Fluate of potash, lime | 968 | | Fluoric acid, history of, properties, composition, affinities | 562 | | Fluidity, owing to an increase of caloric | 212 | | Fluids, elastic | 101 | | Fustus, crust on, nature of | 2758 | | Fourcroy's experiments on water | 392 | | France, chemistry studied in | 37 | | Freezing mixture, how used | 275 | | Friction | 290 | | Frigorific particles | 271 | | Fulminating gold, mercury, platina, powder, silver | 1731 | | Galbanum | 2494 | | Gallic acid, properties of, affinities | 706 | | Gamboge | 2497 | | Gases not luminous, expand equally, azotic, nitrous oxide, nitrous | 157 | | Gelatine | 2584 | | Glafs of antimony | 1684 | | Gold, history of, properties, affinities | 2077 | | Gluten, properties of | 1465 | | Good conductors, what, use of | 2337 | | Greeks, their knowledge of chemistry | 18 | | Guinea pig, urine of | 2700 | | Gum, properties, distillation of, resins | 2327 | | Gun-powder, preparation, nature of | 947 | | Guaiac | 2474 | | Hair and nails, action of water on | 2807 | | Hair and nails, action of acids on, distillation of, composition | 2810 | | Hartshorn | 84 | | Hauy's theory of crystallization | 156 | | Heat explained, latent | 224 | | from condensation, by friction, animal | 278 | | History of chemistry | 16 | | Honey | 2874 | | Hooke's theory of light | 312 | | Horn from sheep, &c. | 2851 | | Horse, urine of | 2696 | | Howard's fulminating powder | 1731 | | Hulme's experiments on light | 149 | | Hydrogen gas, history of, properties | 373 | | Hyperoxymuriatic acid, how obtained, composition of, affinities | 556 | | Ice, water in the state of | 394 | | Importance of chemistry | 7 | | Inflammable substances, names of, history, properties, constituents | 818 | | Inflection of light | 135 | | Ink, black, how to make, sympathetic | 1936 | | Iridium examined | 2153 | | Iron, history of, ores, properties, cast, its properties, falts, alloys | 1880 | | Irvine, Dr, his confirmation of Black's theory | 236 | | Ivory from the elephant | 2850 | | Kermes | 2881 | | Kirwan's method of estimating the force of affinity | 110 | | objections to it by Morveau and Berthollet | 111 | | Koumifs | 2715 | | Labdanum | 2466 | | Lac | 2473 | | Lactic acid, discovery of, properties of | 768 | | Lactic acid, affinities of, Lana philosophica | 767 | | Lavoirier on calorific laws | 92 | | Lead, properties of, falts of, alloys of | 1824 | | Ligaments | 2801 | | Light, velocity of, particles | 130 | | effects, reflection of, rays of, inflection, refraction, transparency | 134 | | Limbourg's idea of affinity | 55 | | Lime, properties of, affinities, falts | 1169 | | Liquid, water in the state of | 395 | | Liquor silicum, of the amnios | 2753 | | Litharge | 1834 | | Magister of bismuth | 1669 | | Magnesia, history of, properties, uses | 1332 | | Malate of potash | 1005 | | Malic acid, history of, properties | 692 | | Manganese, history of, ores, properties, oxides | 1632 | | Majestic | 2404 | | Matter, solid, fluid | 75 | | Mayow's theory of light | 313 | | Medicine | 9 | | Mellitic acid, discovery of, properties, composition | 754 | | Membranes | 2799 | | Mercury, history of, analysis, properties, affinities, fulminating | 1700 | | Metals, importance of, brilliancy, density, ductility, fusibility, imperfect, perfect | 1504 | | Milk, properties of cow's, separates into two parts, coagulation of | 2716 | | Milk | | | Topic | Page | |----------------------------------------------------------------------|------| | Milk, ferments, composition, comparison of different kinds | 2715 | | Millepeder | 2876 | | Mineral cameleon, waters, classes of, gases, salts, analysis | 1652 | | Minerals | | | Mixture, source of, Mixture, freezing | 291 | | Molybdate of potash | 985 | | Molybdena, history of properties | 1555 | | Molybdic acid, history of properties | 627 | | Mother of pearl | 2884 | | Mucus of the nose | 2735 | | Muriate of potash, uses of, properties, composition, lime | 938 | | Muriatic acid, names of, properties, supposed formation | 525 | | Muscles, structure of, composition, boiled, roasted | 537 | | Musk | 2492 | | Myrrh | | | Narcotic matter | 2418 | | Natural history, philosophy | 3 | | Newton's theory of cohesion, crystallization | 70 | | Nickel, history of, properties, alloy | 1615 | | Nitrate of potash, properties | 942 | | Nitric acid, names of, history, properties | 497 | | Nitrous gas, how prepared, properties | 309 | | Nitrous oxide gas | 303 | | Nomenclature, new | | | Ochroit earth, analysis of, combines with carbon | 2889 | | Oil, of two kinds | 861 | | Oils, fixed, preparation of, properties | 866 | | Olibanum | | | Opobalsamum | | | Opoponax | | | Osmium | | | Oxalate of potash | | | Oxalic acid found in plants, properties of, component parts | | | Oxidation | | | Oxide | | | Oxygen, discovery of, how obtained, properties | | | Oxygen, effects of, in combustion, animals live in, combines with bodies | | | Palladium, properties of | | | Paracelsus, account of | | | Particles, frigorific | | | Pearl | | | Percussion, source of caloric | | | Pewter | | | Phosphorus stone | | | Phosphate of lime, ammonia | | | Phosphorous acid, properties, composition, affinities | | | Physicians | | | Phlogiston, supposed to be light | | | Phosphated hydrogen gas | | | Phosphoric acid, properties of | | | Phosphorus, history of, exits in bones, how obtained | | | Piclet on caloric experiments | | | Pinchbeck | | | Pitch | | | Plates, explanation of | | | Platina, properties of, farts, fulminating, alloys | | | Potash, names of, preparation, purification, properties | | | Powder, fulminating | | | Priestley on air, on water | | | Propolis | | | Prussic acid, history of discovery, examined by Macquer | | | Pyrites | | | Pyrophorus of Canton | | | Quicklime, silver | | | Rabbit urine of | | | Radiation not the only cause of cooling | | | Rays, solar, of three kinds, coloured and heated, invisible | | | Red precipitate | | | Reflection of light | | | Refraction | | | Reflection of caloric | | | Repulsion | | | Refraction | | | Refins, vegetable, from bile | | | Respiration, changes on the air | | | Rofacic acid, origin of, properties | | | Rosin | | | S. | | | Saccharic acid, history of | | | Sagapenum | | | Saliva, properties of, composition, of the horse | | | Sandarac | | | Sarcocol | | | Saturation, what | | | Scales | | | Scammony | | | Sea-water, properties of | | | Sebacic acid, properties of | | | Secretions, morbid | | | Semen, properties of, composition | | | Serum of blood, contains gelatine, fulphur, fats | | | Sheep eyes of | | | Shells, of egg | | | Silica, properties of | | | Silk | | | Topic | Page | |--------------------------------------------|------| | Silk | 2879 | | Silver, history of | 2023 | | ores, analysis | 2024 | | falls, alloys | 2025 | | fulminating | 2035 | | Skin, epidermis of | 2067 | | cutis retie mucosum | 2048 | | Smell, earthy | 2781 | | Soda, names of | 2783 | | purification, fats | 2787 | | Spectrum | 1401 | | Spermaceti, properties of | 1018 | | Stahl improves Beccher's theory | 1022 | | Starch, properties of | 1030 | | Steam, nature of | 137 | | caloric of | 2865 | | Storax | 2365 | | Stomach, membrane of | 228 | | Strontites, history of | 237 | | properties, fats | 2482 | | Suber, | 2867 | | Suberate of potash | 1312 | | Suberic acid, properties of | 1314 | | Succinic acid, history of | 1319 | | properties | 747 | | Sugar, manufacture of | 723 | | properties | 2338 | | component parts | 2340 | | Sulphuric acid, properties | 2346 | | purification | 465 | | Sulphurous acid, history of | 464 | | Sulphur, properties | 479 | | Sun, chief source of light | 433 | | Styrax | 154 | | Synovia | 2481 | | T. | 2739 | | Tables of affinity invented | 52 | | enlarged | 53 | | Tan, | 2504 | | Tartaric acid, history of | 670 | | properties | 673 | | component parts | 678 | | affinities | 679 | | Tartrate of potash | 997 | | Tears, | 2735 | | properties | 2733 | | composition | 2734 | | Teeth, bones of | 2779 | | enamel of | 1692 | | Tellurium, history of | 1693 | | properties | 1696 | | action of alkalis on metals | 1698 | | Temperature, change of | 103 | | Tendons | 2800 | | Thermometer, construction of | 194 | | Vegetable acids | 203 | | Fahrenheit's, Reaumur's | 199 | | Celsius's, Delisle's | 200 | | Tin, history of | 201 | | ores, properties | 1787 | | affinities | 1788 | | fats, alloys | 1790 | | Tinfoil | 1799 | | Tinning, process of | 1800 | | Tintplate | 1817 | | Titanium, properties | 1790 | | Tungstate of potash | 1956 | | Tungsten, properties | 1955 | | alloys | 1517 | | Tungstic acid, history | 2869 | | properties | 2870 | | Turpeth mineral | 984 | | nitrous | 1551 | | Urate of ammonia | 1554 | | Urea how obtained | 618 | | properties | 620 | | Urine, | 1720 | | properties | 1728 | | Wedgwood's pyrometer | 24 | | Whey from milk of different animals | 1586 | | Wilcke, Mr., his method of ascertaining | 1587 | | the capacity of bodies for caloric | 1589 | | Wood, | 2833 | | Wool, | 2617 | | Yolk of egg, | 2618 | | composition | 2620 | | Uric acid, history of | 806 | | properties | 809 | | found in urinary calculi | 2832 | | Urine, | 2670 | | properties | 2686 | | component parts | 2687 | | products by spontaneous decomposition | 2697 | | of the horse | 2698 | | cow | 2699 | | camel | 2700 | | rabbit | 2701 | | Guinea pig | 2702 | | granivorous animals | 2703 | | carnivorous | 2704 | | birds | 2705 | | turtle | 2706 | | Vapour, elasticity of water | 239 | | water in the state of | 399 | | Varnish, copal | 2470 | | amber | 2479 | | Vegetables, root of | 2257 | | bark | 2258 | | pith | 2260 | | vessels | 2262 | | germination | 2263 | | food | 2270 | | leaves | 2284 | | decomposition | 2298 | | Zinc, history of | 1751 | | properties | 1754 | | phosphuret of | 1760 | | sulphuret of | 1762 | | sulphate of | 1764 | | sulphite of | 1768 | | nitrate of | 1773 | | muriate of | 1775 | | phosphate of | 1777 | | carbonate of | 1778 | | acetate of | 1779 | | action of alkalis on | 1780 | | Zirconia, history of | 1484 | | properties | 1486 | | affinities | 1490 | | salts | 1492 | | Zoophytes | 2886 |

CHEMNITZ.

Potash, thus obtained, is a white solid substance, which is susceptible of crystallization, in long, compressed, quadrangular prisms, terminating in sharp-pointed pyramids. These crystals, which are only obtained from very concentrated solutions, are soft and deliquescent. The taste is extremely acrid; and it is so corrosive, that it destroys the texture of the skin, the moment it touches it. It is from this property that it has derived the name of caustic; and in surgical language it has obtained the name of potential cautery, because it is employed for the purpose of opening abscesses, or for destroying excrescences. According to Haffner, the specific gravity of potash is 1.7085. It converts vegetable blues into a green colour.

Light has no action on potash. When it is heated in clofe vessels, it becomes soft and liquid, and is afterwards converted into a white, opaque, and granulated mass, when it cools. If the heat be increased

(t) By deliquescence is meant the melting of substances in the water which they attract from the air. Such salts are said to be deliquescent. Potash, &c., to redness, it swells up, and rises in vapour. If the vessel be opened, there arises a white smoke, which is extremely acrid, and condenses on cold bodies with which it comes in contact. But though it is thus sublimed, it undergoes no other change than assuming a slight green colour.

7. There is no action between potash and oxygen or azotic gases, nor is there any direct action between potash and carbons. Phosphorus and sulphur enter into combination with potash, and form peculiar compounds, the nature of which we shall consider, after having detailed the general properties of potash.

8. Potash has a very strong affinity for water. Water at the ordinary temperature dissolves double its weight of potash. The solution, when the potash is pure, is colourless and transparent, and is nearly of the consistence of oil.

9. Potash combines readily with the acids, and forms compounds with them, having different properties, according to the nature of the acid which is employed. Its affinities for the acids are in the following order:

- Sulphuric, - Nitric, - Muriatic, - Phosphoric, - Phosphorous, - Fluoric, - Oxalic, - Tartaric, - Arsenic, - Succinic, - Citric, - Lactic, - Benzoic, - Sulphurous, - Acetic, - Sulfuric, - Boracic, - Carbonic, - Prussic.

10. Potash is employed for a great variety of purposes; it enters into combination with many substances, and forms with them valuable and important compounds. It is employed in medicine as a useful and powerful remedy; in many arts and manufactures, as in bleaching, dyeing, and glass-making.

11. Potash is to be considered as a simple substance. No attempts yet made have succeeded in decomposing it. But although not the slightest proof has been adduced of its formation or decomposition, it is considered by some as a compound substance. This opinion is founded on the analogy of its properties with ammonia; the composition of which has been fully demonstrated. According to some, it is composed of lime and azote; and, according to others, of hydrogen and lime; but all these are mere conjectures, which have probably had their origin in that eagerness of the human mind, which leads it to fancy what it wishes to be true.

12. But we shall now consider more particularly the action of the different substances which have been already treated of, on potash, and the different combinations which it forms with them.

I. Action of Phosphorus on Potash.

1. There is no direct combination between potash and phosphorus; but although these two bodies have had but little tendency to unite, they have a very powerful effect upon each other when they are heated together with water. It was in this way that Gengembre first obtained the singular gas, which has been already described, when treating of phosphorus, under the name of phosphorated hydrogen gas.

2. If one part of phosphorus and ten parts of concentrated solution of pure potash be introduced into a small retort, and exposed to heat till it boils, phosphorated hydrogen gas will pass over, which may be received in jars over water; or if the beak of the retort be kept under the surface of water, the bubbles of the gas, as they rise to the surface, explode, and form the beautiful coronet of white smoke, formerly mentioned. In making this experiment, the retort should not be larger than to hold the solution, or, it should be filled with hydrogen or azotic gases, in which the phosphorated hydrogen gas will not inflame and explode, with the risk of breaking the vessel; for the inflammation can only take place when it comes in contact with the oxygen of the atmosphere.

3. In this process, the water which holds the potash in solution, is decomposed. The oxygen combines with the part of the phosphorus, and forms phosphoric acid, while another part of the phosphorus unites with the hydrogen, and passes over in the form of phosphorated hydrogen gas. Thus, without any perceptible action between the phosphorus and the potash, the decomposition of the water is aided by means of the potash, in consequence of its attraction for the phosphorus, combined with the oxygen in the state of phosphoric acid. For it is found, that a quantity of phosphorus of potash is formed, corresponding to that of the phosphorated hydrogen gas which is obtained. The decomposition is also assisted by the affinity of the phosphorus for the oxygen and hydrogen of the water. The whole of the phosphorated hydrogen gas which is formed, being disengaged, shows that no combination takes place between it and the potash.

II. Action of Sulphur on Potash.

1. Sulphur and potash very readily combine together. If one part of potash and three of sulphur be triturated together in a glass or porcelain mortar, the mixture becomes hot, the sulphur loses its yellow colour, and acquires a greenish tinge. There is disengaged a fetid smell of garlic; the mixture attracts moisture from the air, becomes soft, and is almost entirely soluble in water.

If two parts of potash and one of sulphur be well mixed together, and heated in a crucible, the mixture of potash fuses; and by this process is obtained sulphuret of potash in the dry state. This was formerly called hepatic sulphuris, or liver of sulphur, from its resemblance to the liver of animals. The same substance may be obtained by treating sulphur with the potash of commerce, with this precaution, not to apply too strong a heat, to occasion a sublimation of the sulphur, and the too rapid evolution of the carbonic acid from the potash. When the fusion is completed, it is poured out. 2. The solid sulphuret of potash, thus prepared, is of a shining brown colour like that of the liver of animals, from which it derived its former name. Exposed to the air it becomes green, then palles to gray, and even to white. It is dense, smooth and has a vitreous fracture. It has no other smell than that of heated or sublimed sulphur; it is acrid, caustic, and bitter to the taste, and leaves a brown spot on the skin. With a strong heat, in a porcelain retort, the sulphur is sublimed, and the potash remains in a state of purity at the bottom of the vessel. The sulphuret of potash converts vegetable blue colours to green, and afterwards destroys them.

3. But the sulphuret of potash possesses these properties, only while it is recently prepared, and very pure. When exposed to the air, it is readily decomposed, and more so, as the air is loaded with moisture. It absorbs water with avidity, acquires a green colour, and exhales the fetid odour of sulphured hydrogen gas. This change is owing to the decomposition of the water which has been absorbed. Part of the sulphur combines with the hydrogen, and forms sulphured hydrogen gas, which combines with the sulphuret, and forms hydrogenated sulphuret of potash.

4. This may also be formed by passing the sulphured hydrogen gas into a solution of potash. The gas is absorbed and condensed, till the potash is fully saturated. To this substance Berthollet, who particularly investigated the nature of these compounds, gave the name of hydro-sulphuret of potash.

This compound crystallizes, and is more permanent than the sulphuret. The crystals are transparent and colourless, while those of the sulphuret are brown and opaque. The crystals are large and in the form of four-sided prisms, terminating in four-sided pyramids. It is decomposed by heat, and by the action of the acids. Sulphured hydrogen gas is disengaged, but there is no deposition of sulphur. The oxymuriatic acid decomposes the sulphured hydrogen, and then sulphur is precipitated. The pure hydro-sulphuret has no smell, when it has no addition of sulphur beyond the saturation of the hydrogen. The alkali seems to have a stronger affinity for the sulphured hydrogen than for the sulphur, so that when it is saturated with the first, that is, in the state of hydro-sulphuret of potash, which is in the form of crystals, and without smell or inodorous, it combines with no more sulphur; but when sulphured hydrogen gas is made to pass into a solution of the sulphuret of potash, already hydrogenated by its solution in water to a certain degree of saturation, the sulphured hydrogen acts in the manner of acids, precipitates the sulphur like them, renders the liquid colourless, and leaves behind nothing but the hydro-sulphuret of potash.

5. Sulphur combines with the latter compound, and forms a new compound, which may be obtained by pouring a liquid hydro-sulphuret upon sulphur. The sulphur is dissolved without the affluence of heat; the liquid assumes a darker colour, and then it is converted into the hydrogenated sulphuret. Hydrogenated sulphuret of potash is prepared by boiling together a mixture of pure potash and sulphur in water. This solution is of a deep greenish yellow colour, has a very acid bitter taste, and a powerful action on many substances. It readily absorbs oxygen when exposed to the air. When it is kept in close vessels, sulphur is deposited; the liquid becomes transparent, and the smell is dissipated. Thus, there are three different compounds of sulphur with potash; namely, sulphuret of potash, hydro-sulphuret of potash, and hydrogenated sulphuret, which are all distinguished by peculiar properties.