Definition. Is a science, the object of which is to ascertain the ingredients that enter into the composition of bodies, to examine the nature of these ingredients, the manner in which they combine, and the properties resulting from their combination.
As an art, it has been in some measure coeval with the human race; for many of the most important branches of manufactures could not have been conducted without at least some knowledge of chemical combinations. As a science, it can hardly be dated farther back than the middle of the 17th century; but since that time it has advanced with a rapidity altogether unprecedented in the annals of philosophy. Newton laid its foundation; and since his days an almost incredible number of the most distinguished names in Europe have enlisted under its banners. So rapid has this progress been, that though the article Chemistry in the Encyclopaedia Britannica was written only about ten years ago, the language and reasoning of chemistry have been so greatly improved, and the number of facts have accumulated so much, that we find ourselves under the necessity of tracing over again the very elements of the science.
Importance Indeed, if we consider the importance of chemistry, we shall not be so much surprised at the ardour with which it has been cultivated. As a science, it is intimately connected with all the phenomena of nature; the causes of rain, snow, hail, dew, wind, earthquakes; even the changes of the seasons can never be explored with any chance of success while we are ignorant of chemistry; and the vegetation of plants, and some of the most important functions of animals, have received all their illustration from the same source. No study can give us more exalted ideas of the wisdom and goodness of the Great First Cause than this, which shows us everywhere the most astonishing effects produced by the most simple though adequate means, and displays to our view the great care which has everywhere been taken to secure the comfort and happiness of every living creature. As an art, it is intimately connected with all our manufactures: the glass-blower, the potter, the smith, and every other worker in metals, the tanner, the soap-maker, the dyer, the bleacher, are really practical chemists; and the most essential improvements have been introduced into all these arts by the progress which chemistry has made as a science. Agriculture can only be improved rationally, and certainly by calling in the assistance of chemistry; and the advantages which medicine has derived from the same source are too obvious to be pointed out.
It is evident from the definition of chemistry that it must consist in a history of the simple substances which enter into the composition of bodies, in an investigation of the manner in which these substances combine, and in a description of the properties of the compounds which they form. And this is the arrangement which we mean to pursue; referring to ourselves, however, the liberty of deviating a little from it, whenever it may appear necessary for the sake of perspicuity. All our classifications are in fact artificial; nature does not know them, and will not submit to them. They are useful, however, as they enable us to learn a science sooner, and to remember it better; but if we mean to derive the advantages from them, we must renounce a rigid adherence to arbitrary definitions, which nature disclaims.
We shall begin by an account of the simplest bodies, and proceed gradually to those which are more compound. By simple bodies, we do not mean what the ancient philosophers called the elements of bodies, but merely substances, which have not yet been decomposed. Very possibly the bodies which we reckon simple may be real compounds; but till this has actually been proved, we have no right to suppose it. Were we acquainted with all the elements of bodies, and with all the combinations of which these elements are capable, the science of chemistry would be as perfect as possible; but at present this is very far from being the case.
We shall divide this article into four parts. The first part shall treat of those bodies which are at present considered as simple; the second, of those bodies which are formed by the union of two simple bodies, and which for want of a better word we shall call compound bodies; the third, of those bodies which are formed by the union of two compound bodies; and the fourth, of bodies such as they are presented to us by nature in the mineral, vegetable, and animal kingdoms.
PART I. OF SIMPLE BODIES.
Classes of All the bodies which are at present reckoned simple, because they have never been decomposed, may be reduced into six classes.
1. Oxygen, 2. Simple combustibles, 3. Metals, 4. Earths, 5. Caloric, 6. Light.
These shall form the subjects of the six following chapters.
CHAP. I. Of Oxygen.
Take a quantity of nitre, or saltpetre as it is also called, and put it into a gun barrel A (fig. 1.), the touch-hole of which has been previously closed up with metal. This barrel is to be bent in such a manner, that while the close end, in which the nitre lies, is put into the fire E, the open end may be plunged below the surface of the water, with which the vessel B is filled. At the same time, the glass jar D, previously filled with water, is placed on the support C, lying at the bottom of the vessel of water B, so as to be exactly over the open end of the gun barrel A. As soon as the nitre becomes hot, it emits a quantity of air, which issuing from the end of the gun barrel, ascends to the top of the glass jar D, and gradually displaces all the water. The glass jar D then appears to be empty, but is in fact filled with air. It may then be removed in the follow- ing manner: Slide it away a little from the gun barrel and the support, and then dipping any flat dish into the water below it, raise it on it, and bear it away. The dish must be allowed to retain a quantity of water in it; (see fig. 2.) Another jar may then be filled with air in the same manner; and this process may be continued either till the nitre ceases to give out air, or till as many jarsfuls have been obtained as are required. This method of obtaining and confining air was first invented by Dr Mayow, and afterwards much improved by Dr Hales. All the airs obtained by this or any other process, or, to speak more properly, all the airs differing from the air of the atmosphere, have, in order to distinguish them from it, been called gases, and this name we shall afterwards employ.
The gas which we have obtained by the above process was discovered by Dr Priestley on the 1st of August 1774, and called by him dephlogisticated air. Mr Scheele of Sweden discovered it in 1775, without any previous knowledge of what Dr Priestley had done: he gave it the name of empurpled air. Condorcet, so conspicuous during the French revolution, gave it first the name of vital air; and Mr Lavoisier afterwards called it oxygen gas; a name which is now generally received, and which we shall adopt.
Oxygen gas may be obtained likewise by the following process:
D (in fig. 3.) represents a wooden trough, the inside of which is lined with lead or tinned copper. A.B is a shelf running along the inside of it, about three inches from the top. C is the cavity of the trough, which ought to be a foot deep. It is to be filled with water at least an inch above the shelf A.B. In the body of the trough, which may be called the cistern, the jars destined to hold gas are to be filled with water, and then to be lifted, and placed inverted upon the shelf at B, with their edges a little over it. This trough, which was invented by Dr Priestley, has been called by the French chemists the pneumatico-chemical, or simply pneumatic apparatus, and is extremely useful in all experiments in which gases are concerned. Into the glass vessel E put a quantity of the black oxide of manganese in powder, and pour over it as much of that liquid which in commerce is called oil of vitriol, and in chemistry sulphuric acid, as will somewhat more than cover it. Then insert into the mouth of the vessel the glass tube F, so closely that no air can escape except through the tube. This may be done by covering the jointing with a paste made of wheat flour and water, or any other paste, as substances used for similar purposes are called. The end of the tube C is then to be plunged into the pneumatic apparatus D and the jar G, previously filled with water, to be placed over it on the shelf. The whole apparatus being fixed in that situation, the glass vessel E is to be heated by means of a lamp or a candle. A great quantity of oxygen gas rushes along the tube F, and fills the jar G. As soon as the jar is filled, it may be slid to another part of the shelf, and other jars substituted in its place, till as much gas has been obtained as is wanted.
1. Oxygen gas is colourless, and invisible like common air. Like it too, it is elastic, and capable of indefinite expansion and compression.
2. If a lighted taper be let down into a jar of oxygen gas, it burns with such splendour that the eye can scarcely bear the glare of light, and at the same time produces a much greater heat than when burning in common air. It is well known that a candle put into a well closed jar filled with common air is extinguished in a few seconds. This is the case also with a candle inclosed in oxygen gas; but it burns much longer in an equal quantity of that gas than of common air.
3. It was proved long ago by Boyle, that animals cannot live without air, and by Mayow that they cannot breathe the same air for any length of time without suffocation. Dr Priestley and several other philosophers have shewn us, that animals live much longer in the same quantity of oxygen gas than of common air. Count Montozzo placed a number of sparrows, one after another, in a glass bell filled with common air, and inverted over water.
| The first sparrow lived | 3 | |------------------------|---| | The second | 0 | | The third | 0 |
He filled the same glass with oxygen gas, and repeated the experiment.
| The first sparrow lived | 5 | |------------------------|---| | The second | 2 | | The third | 1 | | The fourth | 1 | | The fifth | 0 | | The sixth | 0 | | The seventh | 0 | | The eighth | 0 | | The ninth | 0 | | The tenth | 0 |
He then put in two together; the one died in 20 minutes, but the other lived an hour longer.
4. Atmospheric air contains about 27 parts in a hundred of oxygen gas. This was first discovered by the atmosphere. Scheele. It has been proved by a great number of experiments, that no substance will burn in common air previously deprived of all the oxygen gas which it contained; but combustibles burn with great splendour in oxygen gas, or in other gases to which oxygen gas has been added. Oxygen gas, then, is absolutely necessary for combustion.
5. It has been proved also, by many experiments, that no breathing animal can live for a moment in any air or gas which does not contain oxygen mixed with it. Oxygen gas then is absolutely necessary for respiration.
6. When substances are burnt in oxygen gas, or in any other gas containing oxygen, if the air be examined after the combustion, a great part of the oxygen will be found to have disappeared. If charcoal, for instance, be burnt in oxygen gas, there will be found, instead of part of the oxygen, another very different gas, known by the name of carbonic acid gas. Exactly the same thing takes place when air is respired by animals; part of the oxygen gas disappears, and its place is occupied by substances possessed of very different properties.
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(a) This substance shall be afterwards described. It is now very well known in Britain, as it is in common use with bleachers and several other manufacturers. gas then undergoes some change during combustion; as well as the bodies which have been burnt; and the same observation applies also to respiration (a).
7. The specific gravity of oxygen gas, as determined by Mr Kirwan*, is \( \frac{1}{8} \), that of water being \( \frac{1}{1000} \), as is always the case when specific gravity is mentioned absolutely. It is therefore 740 times lighter than the same bulk of water. Its weight to atmospheric air is as 1103 to 1000: 116 cubic inches of oxygen gas weigh 39.03 grains troy, 116 cubic inches of common air, 35.38 grains.
8. Oxygen is capable of combining with a great number of bodies, and forming compounds. As the combination of bodies is of the utmost importance in chemistry, before proceeding farther we shall attempt to explain it. When common salt is thrown into a vessel of pure water, it melts, and very soon spreads itself through the whole of the liquid, as any one may convince himself by the taste. In this case the salt is combined with the water, and cannot afterwards be separated by filtration or any other method merely mechanical. It may, however, by a very simple process: Pour into the solution a quantity of spirit of wine, and the whole of the salt instantly falls to the bottom.
Why did the salt dissolve in water, and why did it fall to the bottom on pouring in spirit of wine? These questions were first answered by Sir Isaac Newton. There is a certain attraction between the particles of common salt and those of water, which causes them to unite together whenever they are presented to one another. There is an attraction also between the particles of water and of spirit of wine, which equally dispose them to unite, and this attraction is greater than that between the water and salt; the water therefore leaves the salt to unite with the spirit of wine, and the salt, being now unsupported, falls to the ground by its gravity. This power, which disposes the particles of different bodies to unite, was called by Newton attraction, by Bergman, elective attraction, and by many of the German and French chemists, affinity; and this last term we shall employ, because the other two are rather general.
All substances which are capable of combining together are said to have an affinity for each other; those substances, on the contrary, which do not unite, are said to have no affinity for each other. Thus there is no affinity between water and oil. It appears from the influence of the common salt and spirit of wine, that substances differ in the degree of their affinity for other substances, since the spirit of wine displaced the salt and united with the water. Spirit of wine therefore has a stronger affinity for water than common salt has.
In 1719 Geofroi invented a method of representing the different degrees of affinities in tables, which he called tables of affinity. His method consisted in placing the substances whose affinities were to be ascertained at the top of a column, and the substances with which it united below it, each in the order of its affinity; the substance which had the strongest affinity next it, and that which had the weakest farthest distant, and so of the rest. According to this method, the affinity of water for spirit of wine and common salt would be marked as follows:
| Water | Spirit of wine | Common salt | |-------|---------------|-------------|
This method has been universally adopted, and has contributed very much to the rapid progress of chemistry.
We shall proceed therefore to give a table of the affinities of oxygen.
| Oxygen | Carbon | Zinc | Iron | Manganese | Hydrogen | Azot | Sulphur | Phosphorus | Cobalt | Nickel | Lead | Tin | Phosphorous acid | Copper | Bitum | Antimony | Mercury | Silver | Arsenic | Sulphurous acid | Oil | Nitrous gas | Gold | White oxyd of arsenic | Muriatic acid | Oxyd of tin | |--------|--------|------|------|----------|----------|------|---------|-----------|--------|--------|------|-----|-----------------|--------|-------|-----------|---------|--------|---------|-----------------|-----|-------------|------|-------------------|--------------|------------| | | | | | | | | | | | | | | | | | | | | | | | | | | | |
(b) Mayow had in the last century made considerable progress towards the discovery of oxygen gas. He knew that only a part of the air supported combustion: This part he called particula igneo-aerea. He knew that this part was contained in nitre: "Pars nitri aeris nihil aliud quam particulas ejus igneo-aereas est." He adds, "At non efflantandum pabulum igneo-aerum ipsum aerem effe, sed tantum partem ejus major activum subtiliorem. Quippe lucerna vitro inclusa expirat cum tamen copia seris fatis ampla in eodem continetur." He knew also that it was this part of the air which was useful in respiration. After mentioning several experiments to prove this, he adds, "Ex dictis certo conicit animalia respirando particulas quasdam vitales easque elasticas ab aere hauires." See his Tractatus quingue Medico-Physici, p. 12, and 106.—He knew also that this part of the air was necessary to combustion: "Et tamen certo conicit, particulas nitro-aereas non minus quam sulphureas ad ignem confundam necesse esse." Ibid. p. 26.
(c) We are not certain that the phrase affinity for is warranted by classical authority; we have ventured, however, to use it, because, as the word affinity in this article signifies a species of attraction, we thought it would be more perspicuous to put after it the preposition for, which usually follows the word attraction, than to or with, which come after affinity when used in its ordinary acceptation. White oxyd of lead? Nitrous acid, White oxyd of manganese, Water.
The reason of this order will appear when we treat of these various substances.
**Chap. II. Of Simple Combustible Bodies.**
By combustibles, we mean substances capable of combustion; and by simple combustibles, bodies of that nature which have not yet been decomposed. These are only five in number, sulphur, phosphorus, carbon, hydrogen, and azot. Were we to adhere strictly to our definition indeed, we should add all the metals; for they are also combustible, and have not yet been decomposed: But for the reasons formerly given, we shall venture to deviate a little from strict logic, and consider them afterwards as a distinct class of substances.
**Sect. I. Of Sulphur.**
Sulphur, distinguished also in English by the name of brimstone, was known in the earliest ages. As it is found native in many parts of the world, it could not fail very soon to attract the attention of mankind. It was used by the ancients in medicine, and its fumes were employed in bleaching wool.
Sulphur is a hard brittle substance, commonly of a yellow colour, without any smell, and of a weak though perceptible taste.
It is a non-conductor of electricity, and of course becomes electric by friction.
If a considerable piece of sulphur be exposed to a sudden though gentle heat, by holding it in the hand, for instance, it breaks to pieces with a cracking noise†.
Its specific gravity is 1.990.
When heated to the temperature of 185° of Fahrenheit, it melts and becomes very fluid. If the temperature be still farther increased, the fluidity diminishes; but when the sulphur is then carried from the fire and allowed to cool, it becomes as fluid as ever before it congeals‡.
When sulphur is heated to the temperature of 170°, it rises up in the form of a fine powder, which may be easily collected in a proper vessel. This powder is called flowers of sulphur. When substances fly off in this manner on the application of a moderate heat, they are called volatile; and the process itself, by which they are raised, is called volatilization.
Sulphur undergoes no change by being allowed to remain exposed to the open air.
When thrown into water, it does not melt, as common salt does, but falls to the bottom, and remains there unchanged; it is therefore insoluble in water. If, however, it be poured, while in a state of fusion, into water, it assumes a red colour, and retains such a degree of softness, that it may be kneaded between the fingers; but it loses this property in a few days*.
There are a great many bodies which, after being dissolved in water or melted by heat, are capable of affuming certain regular figures. If a quantity of common salt, for instance, be dissolved in water, and that fluid, sulphur, by the application of a moderate heat, be made to fly off in the form of steam; or, in other words, if the water be slowly evaporated, the salt will fall to the bottom of the vessel in cubes. These regular figures are called crystals. Now sulphur is capable of crystallizing. If it be melted, and as soon as its surface begins to congeal, the liquid sulphur beneath be poured out, the internal cavity will exhibit long needle-shaped crystals of an octahedral figure. This method of crystallizing sulphur was contrived by Rouelle.
When sulphur is heated to the temperature of 302° in the open air, it takes fire spontaneously, and burns by combustion with a pale blue flame, and at the same time emits a vast quantity of fumes of a very strong suffocating odour. When heated to the temperature of 570°, or a little higher, it burns with a bright white flame, and at the same time emits a vast quantity of fumes. If the heat be continued long enough, the sulphur burns all away without leaving any ashes or residuum. If the fumes be collected, they are found to consist entirely of sulphuric acid. By combustion, then, sulphur is converted into an acid. This fact was known several centuries ago, but no intelligible explanation was given of it till the time of Stahl. That chemist undertook the task, and founded on his experiments a theory so exceedingly ingenious, and supported by such a vast number of facts, that it was in a very short time adopted with admiration by all the philosophic world, and contributed not a little to raise chemistry to that rank among the sciences from which the ridiculous pretensions of the early chemists had excluded it.
According to Stahl, there is only one substance in nature capable of combustion, which therefore he called phlogiston; and all those bodies which can be set on fire contain less or more of it. Combustion is merely the separation of this substance. Those bodies which contain none of it are of course incombustible. All combustibles, except those which consist of pure phlogiston (if there be any such), are composed of an incombustible body and phlogiston united together. During combustion the phlogiston flies off, and the incombustible body remains behind. Now when sulphur is burnt, the substance which remains is sulphuric acid, an incombustible body. Sulphur therefore is composed of sulphuric acid and phlogiston.
To establish this theory completely, it was necessary to show that sulphur could be actually made by combining sulphuric acid and phlogiston; and this also Stahl undertook to perform. Sulphat of potash is a substance composed of sulphuric acid and potash (p), and charcoal is a combustible body, and therefore, according to the theory of Stahl, contains phlogiston: when burnt, it leaves a very inconsiderable residuum, and consequently contains hardly any thing else than phlogiston. He melted together in a crucible a mixture of potash and sulphat of potash, stirred into it one-fourth part by weight of pounded charcoal, covered the crucible with another inverted over it, and applied a strong heat to it. He then allowed it to cool, and examined its contents. The charcoal had disappeared, and there only remained in the crucible a mixture of potash and sulphur combined together,
(p) The nature of potash shall afterwards be explained. It is the potash well known in commerce in a state of purity. together, and of a darker colour than usual, from the residuum of the charcoal. Now there were only three substances in the crucible at first, potash, sulphuric acid, and charcoal; two of these have disappeared, and sulphur has been found in their place. Sulphur then must have been formed by the combination of these two. But charcoal consists of phlogiston and a very small residuum, which is still found in the crucible. The sulphur then must have been formed by the combination of sulphuric acid and phlogiston. This simple and luminous explanation appeared so satisfactory, that the composition of sulphur was long considered as one of the best demonstrated truths in chemistry.
There are two facts, however, which Stahl either did not know or did not sufficiently attend to, neither of which were accounted for by his theory. The first is, that sulphur will not burn if air be completely excluded; the second, that sulphuric acid is heavier than the sulphur from which it was produced.
To account for these, or facts similar to these, succeeding chemists refined upon the theory of Stahl, deprived his phlogiston of gravity, and even assigned it a principle of levity. Still, however, the necessity of the contact of air remained unexplained. At last Mr Lavoisier, who had already distinguished himself by the extensiveness of his views, the accuracy of his experiments, and the precision of his reasoning, undertook the examination of this subject, and his experiments were published in the Memoirs of the Academy of Sciences for 1777. He put a quantity of sulphur into a large glass vessel filled with air, which he inverted into another vessel containing mercury, and then set fire to the sulphur by means of a burning glass. It emitted a blue flame, and gave out thick vapours, but was very soon extinguished, and could not be again kindled. There was, however, a little sulphuric acid formed, which was a good deal heavier than the sulphur which had disappeared; there was also a diminution in the air of the vessel proportional to this increase of weight. The sulphur, therefore, during its conversion into an acid, must have absorbed part of the air. He then put a quantity of sulphuret of iron, which consists of sulphur and iron combined together, into a glass vessel full of air, which he inverted over water (x). The quantity of air in the vessel continued diminishing for eighteen days, as was evident from the ascent of the water to occupy the space which it had left; but after that period no farther diminution took place. On examining the sulphuret, it was found somewhat heavier than when first introduced into the vessel, and the air of the vessel wanted precisely the same weight. Now this air had lost all its oxygen; all the oxygen of the air in the vessel must therefore have entered into the sulphuret. Part of the sulphur was converted into sulphuric acid; and as all the rest of the sulphuret was unchanged, the whole of the increase of weight must have been owing to something which had entered into that part of the sulphur which was converted into acid. This something we know was oxygen. Sulphuric acid therefore must be composed of sulphur and oxygen; for as the original weight of the whole contents of the vessel remained exactly the same, there was not the smallest reason to suppose that any substance had left the sulphur.
It is impossible, then, that sulphur can be composed of sulphuric acid and phlogiston, as Stahl supposed; since sulphur itself enters as a part into the composition of that acid. There must therefore have been some want of accuracy in the experiment by which Stahl proved the composition of sulphur, or at least some fallacy in his reasonings; for it is impossible that two contradictory facts can both be true. Upon examining the potash and sulphur produced by Stahl's experiment, we find them to be considerably lighter than the charcoal, sulphuric acid, and potash originally employed. Something therefore has made its escape during the application of the heat. And if the experiment be conducted in a close vessel, with a pneumatic apparatus attached to it, a quantity of gas will be obtained exactly equal to the weight which the substances operated on have lost; and this weight considerably exceeds that of all the charcoal employed. This gas is carbonic acid gas, which is composed of charcoal and oxygen, as will afterwards appear. We now perceive what passes in this experiment: Charcoal has a stronger affinity for oxygen at a high temperature than sulphur has. When charcoal therefore is presented to sulphuric acid in that temperature, the oxygen of the acid combines with it, they fly off in the form of carbonic acid gas, and the sulphur is left behind.
The combustion of sulphur, then, is nothing else than the act of its combination with oxygen; and, for anything which we know to the contrary, it is a simple substance.
The affinities of sulphur, according to Bergman, are as follows:
- Lead - Tin - Silver - Mercury - Arsenic - Antimony - Iron - Fixed alkalies - Ammonia - Barytes - Lime - Magnesia - Phosphorus? - Oils - Ether - Alcohol
Sect. II. Of Phosphorus.
Let a quantity of bones be burnt, or, as it is termed in chemistry, calcined, till they cease to smoke, or of phosphorus to give out any odour, and let them afterwards be reduced to a fine powder. Put this powder into a glass vessel, and pour sulphuric acid on it by little at a time, till further additions do not cause any extrication of air bubbles (y). Dilute the mixture with a good deal of water, agitate it well, and keep it hot for some hours; then pass it through a filter. Evaporate the liquid slowly.
(x) This experiment was first made by Scheele, but with a different view. (y) The copious emission of air bubbles is called in chemistry effervescence. slowly till a quantity of white powder falls to the bottom. This powder must be separated by filtration and thrown away. The evaporation is then to be resumed; and whenever any white powder appears, the filtration must be repeated in order to separate it. During the whole process, what remains on the filter must be washed with pure water, and this water added to the liquor. The evaporation is to be continued till all the moisture disappears, and nothing but a dry mass remains. Put this mass into a crucible, and keep it melted in the fire till it ceases to exhale sulphurous odours; then pour it out. When cold it assumes the appearance of a brittle glass. Pound this glass in a mortar, and mix it with one-third by weight of charcoal dust. Put this mixture into an earthenware retort, and apply a receiver containing a little water. Put the retort into a bath, and increase the fire till it becomes red hot. A substance then passes into the receiver, which has the appearance of melted wax, and which congeals as it falls into the water of the receiver. This substance is phosphorus.
It was discovered by Brandt, a chemist of Hamburg, about the year 1667; while he was employed in attempting to extract from human urine a liquid capable of converting silver into gold.
Kunkel, another German chemist, hearing of the discovery, was anxious to find out the process, and for that purpose associated himself with a friend of his named Kraft. But the latter procured the secret from the discoverer; and expecting by means of it to acquire a fortune, refused to give any information to his associate. Vexed at this treachery, Kunkel resolved to attempt the discovery himself; and though he knew only that phosphorus was obtained from urine, prosecuted the inquiry with so much zeal, that he succeeded, and has been deservedly considered as one of the discoverers.
Boyle likewise discovered phosphorus. Leibnitz indeed affirms that Kraft taught Boyle the whole process, and Kraft declared the same thing to Stahl. But surely the assertion of a dealer in secrets, and one who had deceived his own friend, on which the whole of this story is founded, cannot be put in competition with the affirmation of a man like Boyle, who was one of the honestest men, as well as greatest philosophers, of his age; and he positively assures us, that he made the discovery without being previously acquainted with the process.
Gahn, a Swedish chemist, discovered, in 1769, that phosphorus was contained in bones, and Scheele very soon after invented a process for obtaining it from them. Phosphorus is now generally procured in that manner. The process described in the beginning of this section is that of the Dijon academicians; it differs from that of Scheele only in a single particular.
Phosphorus, when pure, is of a clear, transparent, yellowish colour; but when kept some time in water, it becomes opaque, and then has a great resemblance to phosphorus white wax. Its consistence is nearly that of wax: it may be cut with a knife or twisted to pieces with the fingers. It is insoluble in water. Its specific gravity is 1.714.
It melts at the temperature of 99°, and even at 67° Pelletier, it gives out a white smoke, and is luminous in the dark; that is to say, it suffers a slow combustion: so that it can only be prevented from taking fire by keeping it at a very low temperature, or by allowing it to remain always plunged in water. If air be excluded, it evaporates at 219°, and boils at 554°. When heated to 122° (H), it burns with a very bright flame, and gives out a great quantity of white smoke, which is luminous in the dark; at the same time it emits an odour which has some resemblance to that of garlic. It leaves no residuum; but when the white smoke is collected, it is found to be an acid. Stahl considered this acid as the muriatic (1). According to him, phosphorus was composed of muriatic acid and phlogiston, and the combustion of it was merely the separation of phlogiston. He even declared, that to make phosphorus, nothing more was necessary than to combine muriatic acid and phlogiston; and that this composition was as easily accomplished as that of sulphur itself.
These assertions gained implicit credit; and the composition and nature of phosphorus were considered as completely understood, till Margraf of Berlin published his experiments in the year 1743. That great man, one of those illustrious philosophers who have contributed so much to the rapid increase of the science, distinguished equally for the ingenuity of his experiments and the clearness of his reasoning, attempted to produce phosphorus by combining together phlogiston and muriatic acid; but though he varied his processes a thousand ways, presented the acid in many different states, and employed a variety of substances to furnish phlogiston, all his attempts failed, and he was obliged to give up the combination as impracticable. On examining into phosphoric acid produced during the combustion of phosphorus, he found that its properties were very different from those of muriatic acid. It was therefore a distinct substance. The name of phosphoric acid was given to it; and it was concluded that phosphorus was composed of this acid united to phlogiston.
But it was observed in 1772 by Morveau*, that phosphoric acid was heavier than the phosphorus from which it was produced (x); and Boyle had long before shown that phosphorus would not burn except when in contact with air. These facts were sufficient to prove the inaccuracy of the theory concerning the composition of phosphorus; but they remained themselves unaccounted for, till Lavoisier published those celebrated experiments, which threw so much light on the nature and composition of acids.
He exhausted a glass globe of air by means of an air-pump;
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(a) Crell, in his life of Scheele, informs us, that Scheele was himself the discoverer of the fact. This, he says, clearly appears from a printed letter of Scheele to Gahn, who was before looked upon as the discoverer. See Crell's Annals, English Transl. I. 17.
(b) Morveau, Encyc. Method. Chimie, art. Affinités.—According to Nicholson at 16°. See his Translation of Chapter.
(1) This acid shall be afterwards described.
(x) The same observation had been made by Margraf, but no attention was paid to it. Phosphorus pump; and after weighing it accurately, he filled it with oxygen gas, and introduced into it 100 grains of phosphorus. The globe was furnished with a stopcock, by which oxygen gas could be admitted at pleasure. He set fire to the phosphorus by means of a burning glass. The combustion was extremely rapid, accompanied by a bright flame and much heat. Large quantities of white flakes attached themselves to the inner surface of the globe, and rendered it opaque; and these at last became so abundant, that notwithstanding the constant supply of oxygen gas, the phosphorus was extinguished. The globe, after being allowed to cool, was again weighed before it was opened. The quantity of oxygen employed during the experiment was ascertained, and the phosphorus, which still remained unchanged, accurately weighed. The white flakes, which were nothing else than pure phosphoric acid, were found exactly equal to the weights of the phosphorus and oxygen, which had disappeared during the process.
Phosphoric acid therefore must have been formed by the combination of these two bodies; for the absolute weight of all the substances together was the same before and after the process. It is impossible then that phosphorus can be composed of phosphoric acid and phlogiston, as phosphorus itself enters into the composition of that acid (l).
Thus the combustion of phosphorus, like that of sulphur, is nothing else than its combination with oxygen: for during the process no new substance appears except the acid, accompanied indeed with much heat and light.
Phosphorus combines readily with sulphur, as Margraf discovered during his experiments on phosphorus. This combination was afterwards examined by Mr. Pelletier. The two substances are capable of being mixed in different proportions. Seventy-two grains of phosphorus and nine of sulphur, when heated about four ounces of water, melt with a gentle heat. The compound remains fluid till it be cooled down to 77°, and then becomes solid. These substances were combined in the same manner in the following proportions:
| Phosphorus | Congeals at | |------------|-------------| | 72 | 59° | | 18 | Sulphur | | 72 | Phosphorus | | 36 | Sulphur | | 72 | Phosphorus | | 72 | Sulphur | | 72 | Phosphorus | | 216 | Sulphur |
Phosphorus and sulphur may be combined also by melting them together without any water; but the combination takes place so rapidly, that they are apt to rush out of the vessel if the heat be not exceedingly moderate.
Phosphorus is capable of combining also with many other bodies: the compounds produced are called phosphurets.
(l) The quantity of phosphorus consumed was 45 grains
The quantity of oxygen gas 69,375
Weight of the phosphoric acid produced 114,375
Phosphoric acid therefore is composed of 100 parts phosphorus and 154 oxygen.
The affinities of phosphorus have not yet been ascertained.
Sect. III. Of Carbon.
If a piece of wood be put into a crucible, well covered with sand, and kept red hot for some time, it is converted into a black shining brittle substance, without either taste or smell, well known under the name of charcoal. This substance contains always mixed with it several earthy and saline particles. When freed from these impurities it is called carbon.
Charcoal is insoluble in water. It is not affected (provided that all air be excluded) by the most violent heat of carbons which can be applied, excepting only that it is rendered much harder.
New-made charcoal absorbs moisture with avidity. When heated to a certain temperature, it absorbs air copiously. La Mettrie plunged a piece of burning charcoal into mercury, in order to extinguish it, and introduced it immediately after into a glass vessel filled with common air. The charcoal absorbed four times its bulk of air. On plunging the charcoal in water, one-fifth of this air was disengaged. This air, on being examined, was found to contain a much smaller quantity of oxygen than atmospheric air does. He extinguished another piece of charcoal in the same manner, and then introduced it into a vessel filled with oxygen gas. The quantity of oxygen gas absorbed amounted to eight times the bulk of the charcoal; a fourth part of it was disengaged on plunging the charcoal into water. It appears from the experiments of Sennebeger, that charcoal when exposed to the atmosphere absorbs oxygen gas in preference to azot†, as the other portion of common air is called.
When heated to the temperature of 370°, it takes fire, and, provided it has been previously freed from the earths and salts which it generally contains, it burns without leaving any residuum. If this combustion be performed in close vessels filled with oxygen gas instead of common air, part of the charcoal and oxygen disappear, and in their room is found a particular gas exactly equal to them in weight. This gas has the properties of an acid, and is therefore called carbonic acid gas. Mr. Lavoisier, to whom we are indebted for this discovery, ascertained, by a number of very accurate experiments, that this gas was composed of about 28 parts of carbon and 72 of oxygen.
Carbon is susceptible of crystallization. In that state it is called diamond. The figure of the diamond varies considerably; but most commonly it is a hexagonal prism terminated by a fixed pyramid. When pure it is colorless and transparent. Its specific gravity is from 3.44 to 3.55. It is one of the hardest substances in nature; and as it is not affected by a considerable heat, it was for many ages considered as incombustible. Sir Isaac Newton, observing that combustibles refracted light more powerfully than other bodies, and that the diamond possessed this property in great perfection, suspected, pected, from that circumstance, that it was capable of combustion. This singular conjecture was verified in 1694 by the Florentine academicians, in the presence of Cosmo III., grand duke of Tuscany. By means of a burning-glass, they destroyed several diamonds. Francis I., emperor of Germany, afterwards witnessed the destruction of several more in the heat of a furnace. These experiments were repeated by Rouelle, Macquer, and D'Arrect, who proved that the diamond was not merely evaporated, but actually burnt, and that if air was excluded it underwent no change.
No attempt, however, was made to ascertain the product, till Lavoisier undertook a series of experiments for that purpose in 1772. He obtained carbonic acid gas. It might be concluded from these experiments, that the diamond contains carbon; but it was reserved for Mr Tennant to show that it consisted entirely of that substance.
Into a tube of gold, having one end closed and a glass tube adapted to the other to collect the product, that gentleman put 2½ grains of diamonds and a quarter of an ounce of nitre (m). This tube was heated slowly; the consequence of which was, that great part of the nitric acid passed off before the diamond took fire, and by that means almost the whole of the carbonic acid formed during the combustion of the diamond remained in the potash, for which it has a strong affinity. To ascertain the quantity of this carbonic acid, he dissolved the potash in water, and added to the solution another salt composed of muriatic acid and lime. Muriatic acid has a stronger affinity for potash than for lime; it therefore combines with the potash, and at the same time the lime and carbonic acid unite and fall to the bottom of the vessel, because they are nearly insoluble in water. He decanted off the liquor, and put the lime which contained the carbonic acid into a glass globe, having a tube annexed to it. This globe and tube he then filled with mercury, and inverted into a vessel containing the same fluid. The lime by that means occupied the very top of the tube. It now remained to separate the carbonic acid from the lime, which may be done by mixing it with any acid, as almost every other acid has a stronger affinity for lime than carbonic acid has. Accordingly on introducing muriatic acid, 10.3 ounce measures of carbonic acid gas, or nearly 9,166 grains, were separated. But, according to the experiments of Lavoisier, this gas is composed of 72 parts of oxygen and 28 of carbon; 9,166 grains therefore contain 2,556 grains of carbon, which is almost precisely the weight of the diamond consumed. It follows, therefore, that it was composed of pure carbon. The difficulty of burning the diamond is owing entirely to its hardness. Mefris Moreau and Tennant rendered common charcoal so hard by exposing it for some time to a violent fire in close vessels, that it lost much of its natural tendency to combustion, and endured even a red heat without catching fire.
Charcoal possesses a number of singular properties,
Suppl. Vol. I. Part I.
(m) Nitre is composed of potash and nitric acid; and nitric acid contains a great quantity of oxygen, which is easily separated by heat. Diamond, when mixed with nitre, burns at a much lower heat than by any other process.
(n) It was formerly called inflammable air, and by some chemists phlogiston.
which render it of considerable importance. It is in Hydrogen, capable of putrifying or rotting like wood, and is not therefore liable to decay through age. This property has been long known. It was customary among the ancients to char the outside of those flake which were to be driven into the ground or placed in water, in order to preserve the wood from spoiling. New made charcoal, by being rolled up in cloths which have contained a disagreeable odour, effectually destroys it. It takes away the bad taint from meat beginning to putrefy, by being boiled along with it. It is perhaps the best teeth powder known. Mr Lowitz of Peterburgh has shown, that it may be used with advantage to purify a great variety of substances.
Carbon unites with a number of bodies, and forms Carburets, with them compounds known by the name of carburets. Its affinities have not yet been ascertained.
Sect. IV. Of Hydrogen.
Put into a glass vessel furnished with two mouths a quantity of fresh iron filings, quite free from rust. Lute into one of these mouths the end of a crooked glass tube. Insert the other end of this tube below a glass procuring jar filled with water, and inverted into a pneumatic apparatus. Then pour upon the iron filings a quantity of sulphuric acid, diluted with twice its own weight of water, and close up the mouth of the vessel. Immediately the iron filings and acid effervescence with violence, a vast quantity of gas is produced, which rushes through the tube and fills the jar. This gas is called hydrogen gas (n).
It was obtained by Dr Mayow and by Dr Hales from various substances, and had been known long before in mines under the name of the fire damp. Mr Cavendish* was the first who examined its properties with most attention. They were afterwards more fully investigated by Priestley, Scheele, and Fontana.
Hydrogen, like air, is invisible and elastic, and capable of indefinite compression and dilatation. Its specific gravity differs according to its purity. Kirwan found it 0.000107; Lavoisier 0.0000941, or about 12 times lighter than common air.
All burning substances are immediately extinguished by being plunged into this gas. It is incapable therefore of supporting combustion.
Animals, when they are obliged to breathe it, die almost instantaneously. Scheele indeed found that he could breathe it for some time without inconvenience; but Fontana, who repeated the experiment, discovered that this was owing to the quantity of common air contained in the lungs when he began to breathe; for on expiring as strongly as possible before drawing in the hydrogen gas, he could only make three respirations, and even these three produced extreme feebleness and oppression about the breast.
If a phial be filled with hydrogen gas, and a lighted candle be brought to its mouth, the gas will take fire, and burn gradually till it is all consumed. If hydro-
* Encycl. Method. Chemie art. Acier. gen and oxygen gas be mixed together and kindled; they burn instantaneously, and produce an explosion like gunpowder. The same effect follows when a mixture of hydrogen gas and atmospherical air is kindled, but the explosion is less violent. Hydrogen gas will not burn except in contact with oxygen gas, nor will it burn even in contact with oxygen gas, unless a red heat be applied to it. If 85 parts by weight of oxygen gas, and 15 of hydrogen gas, be mixed together, and set on fire in a close vessel, they disappear, and in their place there is found a quantity of water exactly equal to them in weight. This water must be composed of these two gases; for it did not previously exist in the vessel, and no other substance except the gases was introduced. Water then is composed of oxygen and hydrogen; and the combustion of hydrogen is nothing else but the act of its combination with oxygen (o).
It had been supposed, in consequence of the experiments of Dr Priestley and several other philosophers, that when hydrogen gas was allowed to remain in contact with water, it was gradually decomposed, and converted into another gas; but Mr de Morveau*, Mr Hasenfratz†, and Mr Lister‡, have shown, that it undergoes no change, provided sufficient care be taken to exclude every other gas.
Hydrogen gas dissolves sulphur, phosphorus, and carbon. The compounds are called sulphurated, phosphorated, and carbonated hydrogen gas.
1. Sulphurated hydrogen gas was first examined with attention by Scheele, who, together with Bergman, discovered many of its properties. Mr Kirwan likewise published a very valuable paper on the same subject. If equal parts of sulphur and potash be melted together in a covered crucible, they combine together, and form a compound known by the name of sulphuret of potash, but formerly called, from its red colour, hepatic sulphurite, or liver of sulphur. When this substance is moistened with water, it gives out a quantity of sulphurated hydrogen gas; hence this gas was at first called hepatic gas.
Mr Gengembre enclosed a bit of sulphur in a glass vessel filled with hydrogen gas, and melted the sulphur by means of a burning glass. A quantity of it disappeared, and the hydrogen assumed all the properties of hepatic gas. Hence it follows that this gas is merely sulphur dissolved in hydrogen gas.
The safest method of obtaining it is to pour an acid, the muriatic for instance, on a quantity of the sulphuret reduced to powder. An effervescence takes place, the gas is extricated, and may be collected by means of a pneumatic apparatus. The theory of this effervescence is obvious. The sulphur is gradually converted into sulphuric acid, by decomposing the water, which is always united with acids, and seizing its oxygen; the hydrogen of the water is thus set at liberty; it assumes the gaseous form, and at the same time dissolves part of the remaining sulphur, for which it has a considerable affinity.
The specific gravity of sulphurated hydrogen gas is 0.935; it is to common air as 1.166 to 1.000.
It has a very fetid odour, precisely similar to that emitted by rotten eggs, which indeed is owing to the emission of the very same gas.
It is not more respirable than hydrogen gas. When set on fire, in contact with oxygen gas, it burns with a light blue flame, without exploding, and at the same time a quantity of sulphur is deposited. The combustion of this gas, then, is merely the union of its hydrogen, and perhaps part of its sulphur, with oxygen.
This gas turns syrup of violets to a green colour*. It does not seem capable of existing in atmospherical air without decomposition; for the moment it comes into contact with oxygen gas, sulphur is deposited†.
2. Phosphorated hydrogen gas was discovered by Mr Gengembre in 1783, and by Mr Kirwan some time after, before he became acquainted with the experiments of that gentleman. It may be procured by mixing phosphorus with potash dissolved in water, and applying a boiling heat to the solution. The phosphorus is gradually converted into an acid by decomposing the water, and uniting with its oxygen. The hydrogen assumes the form of a gas, and flies off after dissolving a little of the phosphorus. This gas may be collected by means of a pneumatic apparatus.
Phosphorated hydrogen gas has a smell resembling that of putrid fish. When mixed with oxygen gas or common air, it becomes luminous; and on the application of the smallest heat, it burns with astonishing rapidity‡. The products are water and phosphoric acid. The combustion of this gas therefore is nothing else than the union of its phosphorus and hydrogen with oxygen, attended by an emission of heat and light.
Phosphorated hydrogen gas may also be formed by introducing a bit of phosphorus into a jar containing hydrogen gas; but care must be taken to make this gas as dry as possible; for its affinity with phosphorus is weakened in proportion to its moisture §.
3. Carbonated hydrogen gas arises spontaneously in hot weather from marshes, but always mixed with several other gases. Several species of it have been lately discovered by the associated Dutch chemists Bondt, Dieman, Van Troostwyck, and Lauwerensberg§. When 75 parts of sulphuric acid and 25 of spirit of wine are mixed together, a gas is extricated which suffers no alteration from standing over water. Its specific gravity is 0.93111, or it is to common air as 931 to 1000. It has a fetid odour, and burns with a strong compact flame. When passed through sulphur it is converted into sulphurated hydrogen gas, and at the same time a quantity of carbon is deposited in the form of a fine powder; it must therefore be composed of carbon and hydrogen gas. When burnt, the product is carbonic acid.
(o) The history of this great discovery, and the objections which have been made to it, we reserve for the chapter which treats of Water, where they will be better understood than they could be at present. This substance was called hydrogen by the French chemists, because it enters into the composition of water, from which it is derived; and I am born. Objections have been made to the propriety of the name, into which we shall not enter. It ought never to be forgotten, that Newton had long before, with a sagacity almost greater than human, conjectured, from its great refracting power, that water contained a combustible substance. acid gas and water*. By making ether (r) pass through a red hot glass tube, another carbonated hydrogen gas was formed; the specific gravity of which was 0.0086. Spirit of wine, passed in the same manner, afforded a gas, the specific gravity of which was 0.0053, and which burned with a paler flame than the other two. These gases were found to contain from 80 to 74 parts of carbon, and from 20 to 26 of hydrogen. The first species was found to contain most carbon, and the last to contain least†.
The affinity of hydrogen gas for these three combustibles is as follows:
- Sulphur, - Carbon, - Phosphorus (q).
Dr Austin found, that by repeatedly passing electric explosions through a small quantity of carbonated hydrogen gas, it was permanently dilated to more than twice its original bulk. He rightly concluded, that this remarkable expansion could only be owing to the evolution of hydrogen gas. On burning air thus expanded, he found that it required a greater quantity of oxygen than the same quantity of gas not diluted by electricity: An addition therefore had been made to the combustible matter; for the quantity of oxygen necessary to complete the combustion of any body, is always proportional to the quantity of that body. He concluded from these experiments, that he had decomposed the carbon which had been dissolved in the hydrogen gas; and that carbon was composed of hydrogen and azot (n), some of which was always found in the vessel after the dilated gas had been burnt by means of oxygen†. If this conclusion be fairly drawn, we must expunge carbon from the list of simple substances, and henceforth consider it as a compound.
There was one circumstance which ought to have prevented Dr Austin from drawing this conclusion, at least till warranted by more decisive experiments. The quantity of combustible matter had been increased. Now, if the expansion of the carbonated hydrogen gas was owing merely to the decomposition of carbon, no such increase ought to have taken place, but rather the contrary; for the carbon, which was itself a combustible substance, was resolved into two ingredients, hydrogen and azot, only the first of which burnt on the addition of oxygen and the application of heat. Dr Austin's experiments have been lately repeated by Mr William Henry with a great deal of accuracy*. He found, that the dilatation which Dr Austin describes actually took place, but that it could not be carried beyond a certain degree, a little more than twice the original bulk of the gas. Upon burning separately by means of oxygen, two equal portions of carbonated hydrogen gas, one of which had been expanded by electricity to double its original bulk, the other not, he found that each of them produced precisely the same quantity of carbonic acid gas. Both therefore contained the same quantity of carbon; consequently no carbon had been decomposed by the electric shocks.
Mr Henry then suspected that the dilatation was owing to the water which every gas contains in a larger or smaller quantity. To ascertain this, he endeavoured to deprive the carbonated hydrogen gas of as much water as possible, by making it pass over very dry potato, which attracts water with avidity. Gas treated in this manner could only be expanded one-fifth of its bulk; but on admitting a drop or two of water, the expansion went on as usual. The substance decomposed by the electricity, then, was not the carbon, but the water in the carbonated hydrogen gas. Nor is it difficult to see in what manner this decomposition is effected. Carbon at a high temperature has a greater affinity for oxygen than hydrogen; for if the steam of water be made to pass over red hot charcoal, it is decomposed, and carbonic acid and hydrogen gas are formed. The electric explosion supplies the proper temperature; the carbon unites with the oxygen of the water, and forms carbonic acid; and the hydrogen, thus set at liberty, occasions the dilution. Carbonic acid gas is absorbed with avidity by water; and when water was admitted into 799 measures of gas thus dilated, 100 measures were absorbed; a proof that carbonic acid gas was actually present. As to the azot which Dr Austin found in his dilated gas, it evidently proceeded from the admission of some atmospheric air, about 73 parts of which in the 100 consist of this gas; for Dr Austin's gas had flooded long over water; and Drs Priestley and Higgins have shewn that air in such a situation always becomes impregnated with azot.
The affinities of hydrogen have not yet been ascertained, but perhaps they are as follows:
- Oxygen, - Carbon, - Azot.
Sect. V. Of Azot.
If a quantity of iron filings and sulphur, mixed together and moistened with water, be put into a glass vessel full of air, it will absorb all the oxygen in the course of procuring a few days; but a considerable residuum of air still remains.
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(r) Ether is a very volatile and fragrant liquid, obtained by mixing spirit of wine and acids, and distilling. It shall be afterwards described.
(q) Sulphur decomposes carbonated hydrogen gas; therefore its affinity is greater than that of carbon. The Dutch chemists melted phosphorus in carbonated hydrogen gas, but no change was produced; therefore the affinity of phosphorus is inferior to that of carbon.
(n) See next Section.—His theory was, that carbonated hydrogen gas was composed of hydrogen, and azot, and carbon of azot, and carbonated hydrogen gas, which comes nearly to the same thing with regard to the elements of carbon. It is singular enough, that though Dr Austin would not allow the presence of carbon in carbonated hydrogen gas, he actually decomposed it by melting sulphur in it: the sulphur combined with the hydrogen gas, and a quantity of carbon was precipitated. This experiment he relates without making any remarks upon it, and seems indeed not to have paid any attention to it. Azot.
It was discovered in 1772 by Dr Rutherford, now professor of botany in the university of Edinburgh (s). Scheele procured it by the above process as early as 1776, and proved that it was a distinct fluid. Mr Lavoisier afterwards proved the same thing, without any previous knowledge of Scheele's discoveries.
The air of the atmosphere contains about 73 parts of azotic gas; almost all the rest is oxygen gas. The safest method of procuring azotic gas is to put some sulphuric acid into a glass vessel filled with air, and accurately closed, and then to apply heat to the sulphuric acid. All the oxygen is absorbed almost instantly. This method was first pointed out by Moreau (t).
Mr Kirwan examined the specific gravity of azotic gas obtained by Scheele's process; it was 0.9825; it is therefore somewhat lighter than the atmospheric air, it is to atmospheric air as 985 to 1000.
It tinged delicate blue colours slightly with green.
It is exceedingly noxious to animals; if they are obliged to respire it, they drop down dead almost instantly (r). No combustible will burn in it. This is the reason that a candle is extinguished in atmospherical air as soon as the oxygen near it is consumed.
Mr Goettling, indeed, published, in 1794, that phosphorus alone, and was converted into phosphoric acid, in pure azotic gas. Were this the case, it would not be true that no combustible burns in this gas; for the conversion of phosphorus into an acid, and even its burning, is an actual though slow combustion. Mr Goettling's experiments were found after repeated by Drs Scherer and Jaeger, who found, that phosphorus does not shine in azotic gas when it is perfectly pure; and that therefore the gas on which Mr Goettling's experiments were made had contained a mixture of oxygen gas, owing principally to its having been only confined by water. These results were afterwards confirmed by Professor Lampadius and Professor Hildebrandt. It is therefore proved beyond a doubt, that phosphorus does not burn in azotic gas, and that whenever it appears to do so, there is always some oxygen gas present.
Azotic gas is capable of dissolving phosphorus, as has been proved by the experiments of Fourcroy and Vanquelin.
It diffuses also a little carbon; for azotic gas obtained from animal substances, which contain a great deal of azot, when confined long in jars, deposits on the sides of them a black matter which has the properties of carbon.
These two solutions the properties of which have not yet been accurately examined, are called phosphorated azotic gas and carburetted azotic gas.
Azotic gas is capable of combustion. Take a glass tube, the diameter of which is about the fifth part of an inch; shut one of its ends with a cork, through the middle of which passes a small wire with a ball of metal at each end. Fill the tube with mercury, and then plunge its open end into a basin of that fluid. Throw up into the tube as much of a mixture, composed of 13 parts of azotic and 87 parts of oxygen gas, as will fill 3 inches. Through this gas make, by means of the wire in the cork, a number of electric explosions pass. The volume of gas gradually diminishes, and in its place there is found a quantity of nitrous acid. This acid, therefore, is composed of azot and oxygen; and these two substances are capable of combining, or, which is the same thing, azotic gas is capable of combustion in the temperature produced by electricity, which we know to be pretty high. The combustibility of azotic gas, and the nature of the product, was first discovered by Mr Cavendish, and communicated to the Royal Society on the 2d of June 1785 (v).
The affinities of azot are still unknown. It has never yet been decomposed, and must therefore, in the present state of our knowledge, be considered as a simple substance. Dr Priestley, who obtained azotic gas at a very early period of his experiments, considered it as a compound of oxygen gas and phlogiston, and for that reason gave it the name of phlogisticated air. According to the theory of Stahl, which was then universally prevalent, he considered combustion as merely the separation of phlogiston from the burning body. To this theory he made the following addition: Phlogiston is separated during combustion by means of chemical affinity: Air (that is, oxygen gas) has a strong affinity for phlogiston: Its presence is necessary during combustion, because it combines with the phlogiston as it separates from the combustible; and it even contributes by its affinity to produce that separation: The moment the air has combined with as much phlogiston as it can receive, or, to use a chemical term, the moment it is saturated with phlogiston, combustion necessarily stops, because no more phlogiston can leave the combustible.
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(s) See his thesis De Aere Mephitico, published in 1772.—"Sed aer salubris et purus respiratione animali non modo ex parte fit mephiticus sed etiam indolis sui mutationem inde patitur. Postquam enim omnis aer mephiticus (carbonic acid gas) ex eo, ope lixivi caustici secretus et abductus fugit, qui tamen reficit nullo modo salubrior inde evadit; nam quamvis nullam ex aqua calcis precipitationem faciat haud minus quam antea et flammam et vitam extinguat." Page 17.
"Aer qui per carbones ignitos folle adactus fuit, atque deinde ab omni acre mephitico (carbonic acid gas) expurgatus, malignus tamen adhuc reperitur et omnino finibus est ei qui respiratione inquinatur. Immo ab experimentis patet, hanc solam effe aeris mutationem que inflammationis adeoque potest. Si enim accedunt materies quaelibet que ex phlogisto et basi fixa atque simplici conlata, aer inde natu ne minimum acris mephitici quantitate in se continere videtur. Sic aer in quo sulphur aut phosphorus urinse combustus fuit, licet maxime malignum, calcem tamen ex aqua minime precipitat. Interdum quidem ex phosphoro natus foemit, nubealum aquae calcis inducit sed tenuissimum, nec aeris mephitico attribuendam, fed potius acido illi quod in phosphoro inefect, et quod, ut experimenta docuerunt, hoc singulare dote pollet." Page 19.
(t) Hence the name azot, given it by the French chemists, which signifies destructive to life, from a and t.
(v) It is remarkable enough, that the acidity of nitric acid was ascribed by Mayow, in 1674, to the presence of oxygen. Indoles caustica spiritus nitri (says he) a particularis ejus igneo-aerei provenit. Tract. p. 19. combustible (v): Air saturated with phlogiston is azotic gas. This was a very ingenious theory, and, when Dr Priestley published it, exceedingly plausible. A great number of the most eminent chemists accordingly embraced it; but it was soon after discovered, that during combustion the quantity of air, instead of increasing, as it ought to have done, had phlogiston been added to it, actually diminished both in volume and weight. There was no proof, therefore, that during combustion any substance whatever combined with air, but rather the contrary. It was discovered also, that a quantity of air combined with the burning substance during combustion, as we have seen was the case with sulphur, phosphorus, carbon, and hydrogen; and that this air had the properties of oxygen gas. These discoveries entirely overthrew the evidence on which Dr Priestley's theory was founded; accordingly, as no attempt to decompose azot has succeeded, it has been given up by almost every chemist except Dr Priestley himself. Atmospheric air, as Scheele first found, is composed of about 27 parts of oxygen, and 73 of azotic gas. During combustion, the oxygen is abstracted and the azotic gas remains behind.
La Methiere made an attempt to prove that azot was composed of oxygen and carbon (w). He took a bit of burning charcoal, extinguished it in mercury, and then plunged it while hot into oxygen gas. On being plunged into water, one fourth of the gas was disengaged, and part of it was found to consist of azotic gas. From this he concluded, that he had formed azotic gas by combining oxygen and carbon; but it was proved by Mr Lavoisier, beyond the possibility of doubt, that oxygen and carbon form carbolic acid gas. They cannot then certainly form azot; for two contradictory facts cannot both be true. There must then have been something overlooked in the experiment. Indeed the experiment itself does not warrant the conclusion which De La Methiere drew from it. He did not ascertain whether the weight of the charcoal was diminished; and, besides, there was azot mixed with the oxygen gas which he employed, as he himself has informed us: And how was it possible for him to admit the charcoal into water without, at the same time, admitting some atmospheric air?
We have now described all the combustibles which are at present reckoned simple, except the metals. We have found, that during combustion all of them combine with oxygen; that no part of them is disengaged, no part of them lost; we have therefore concluded, that the combustion of these substances is nothing else but the act of their uniting with oxygen. We have seen, however, that none of them, except phosphorus, was capable of uniting with oxygen at the common temperature of the atmosphere; that, in order to produce the union, heat was necessary, and that the degree of this heat was different for each. Hydrogen required a red heat, and azot a still greater. We have seen,
(v) This ingenious theory was first conceived by Dr Rutherford, as appears from the following passage of his thesis. "Ex idem etiam deducere licet quod aer illi malignus (azotic gas) componitur ex aere atmospherico cum phlogisto unio et quasi saturato. Atque idem confirmatur eo, quod aer qui metallorum calcinationi jam inservit, et phlogiston ab illo abripiat, ejusdem plane fit indolis." De aere Mephitisco, p. 20.
(w) Or rather of hydrogen, for he considered carbon itself as a compound.
too, that during these combinations a quantity of heat and light escaped. Now why is heat necessary for these combinations? and whence come the heat and the light which we perceive during the combustion of these bodies? These questions are of the highest importance, and can only be answered by a particular investigation of the nature and properties of heat and light. This investigation we shall attempt, as soon as we have described the metals and earths, which form the subject of the two following chapters.
CHAP. III. Of Metals.
Metals may be considered as the great instruments Properties of all our improvements: Without them, many of the arts, sciences could hardly have existed. So sensible were the ancients of their great importance, that they raised those persons who first discovered the art of working them to the rank of deities. In chemistry, they have always filled a conspicuous station: at one period the whole science was confined to them; and it may be said to have owed its very existence to a rage for making and transmuting metals.
1. One of the most conspicuous properties of the metals is a particular brilliancy which they possess, and which has been called the metallic lustre. This proceeds from their reflecting much more light than any other body; a property which seems to depend partly on the closeness of their texture. This renders them peculiarly proper for mirrors, of which they always form the basis.
2. They are absolutely opaque, or impervious to light, even after they have been reduced to very thin plates. Silver leaf, for instance, though of an inch thick, does not permit the smallest ray of light to pass through it. Gold, however, may be rendered transparent; for gold leaf, though of an inch thick, transmits light of a lively green colour *. And it is not improbable that all the other metals, as Sir Isaac Newton has supposed, would become transparent, if they could be reduced to a sufficient degree of thinness. It is to this opacity that a part of the excellence of the metals, as mirrors, is owing; their brilliancy alone would not qualify them for that purpose.
3. They may be melted by the application of heat, Fusibility, and even then still retain their opacity. This property enables us to cast them in molds, and then to give them any shape we please. In this manner many elegant iron utensils are formed.
4. Their specific gravity is greater than that of any other body hitherto discovered.
5. They are better conductors of electricity than any other body.
6. But one of their most important properties is Malleability, by which is meant the capacity of being extended and flattened when struck with a hammer. This property enables us to give the metallic body any form we think proper, and thus renders it easy for us to to convert them into the various instruments for which we have occasion. All metals do not possess this property; but it is remarkable that almost all those which were known to the ancients have it. Heat increases this property considerably.
Another property which is also wanting in many of the metals, is ductility; by which we mean the capacity of being drawn out into wire by being forced through holes of various diameters. This property has by some been called tenacity; and it doubtless depends upon the tenacity of the various metals.
When exposed to the action of heat and air, most of the metals lose their lustre, and are converted into earthy-like powders of different colours and properties, according to the metal and the degree of heat employed. Several of the metals even take fire when exposed to a strong enough heat; and after combustion the residue is found to be the very same earthy-like substance. If any of these calces, as they are called, be mixed with charcoal-powder, and exposed to a strong heat in a proper vessel, it is changed again to the metal from which it was produced. From these phenomena Stahl concluded, that metals were composed of earth and phlogiston. He was of opinion, that there was only one primitive earth which not only formed the basis of all those substances known by the name of earths, but the basis also of all the metals. He found, however, that it was impossible to combine any more earth with phlogiston; and concluded, therefore, with Becher, that there was another principle besides earth and phlogiston which entered into the composition of the metals. To this principle Becher gave the name of mercurial earth, because, according to him, it existed most abundantly in mercury. This principle was supposed to be very volatile, and therefore to fly off during calcination; and some chemists even affirmed that it might be obtained in the foot of those chimneys under which metals have been calcined.
A striking defect was soon perceived in this theory. The original metal may be again produced by heating its calx along with some other substance which contains phlogiston; now, if the mercurial earth flies off during combustion, it cannot be necessary for the formation of complete metals, for they may be produced without it; if, on the contrary, it adheres always to the calx, there is no proof of its existence at all. Chemists, in consequence of these observations, found themselves obliged to discard the mercurial principle altogether, and to conclude, that metals were composed of earth only, united to phlogiston. But if this be really the case, how comes it that these two substances cannot be united by art? Henkel was the first who attempted to solve this difficulty. According to him, earth and phlogiston are substances of so opposite a nature, that it is exceedingly difficult, or rather it has hitherto been impossible, for us to commence their union; but after it has been once begun by nature, it is an easy matter to complete it. No calcination has hitherto deprived the metals of all their phlogiston; some still adhere to the calces. It is this remainder of phlogiston which renders it so easy to restore them to their metallic state.
Were the calcination to be continued long enough to deprive them altogether of phlogiston, they would be reduced to the state of other earths; and then it would be equally difficult to convert them into metals, or, to use a chemical term, to reduce them. Accordingly we find, that the more completely a calx has been calcined, the more difficult is its reduction. This explanation was favourably received. But after the characteristic properties of the various calces had been ascertained, and the calces of metals were accurately examined, it was perceived that the calces differed in many particulars from all the calces, and from one another. To call them all the same substance, then, was to go much farther than either experiment or observation would warrant, or, rather, it was to declare open war against both experiment and observation. It was concluded, therefore, that each of the metals was composed of a peculiar earthy substance combined with phlogiston. For this great improvement in accuracy, chemistry is chiefly indebted to Bergman.
But there were several phenomena of calcination which had all this time been unaccountably overlooked. The calces are all considerably heavier than the metals from which they are obtained. Boyle had observed this circumstance, and had ascribed it to a quantity of fire which, according to him, became fixed in the metal during the process. But succeeding chemists paid little attention to it, or to the action of air, till Mr. Lavoisier published his celebrated experiments on calcination, in the Memoirs of the Paris Academy for 1774. He put eight ounces of tin into a large glass retort, the point of which was drawn out into a very slender tube to admit of easy fusion. This retort was heated slowly till the tin began to melt, and then sealed hermetically. This heat was applied to expel some of the air from the retort; without which precaution it would have expanded and burst the vessel. The retort, which was capable of containing 250 cubic inches, was then weighed accurately, and placed again upon the fire. The tin soon melted, and a pellicle formed on its top, which was gradually converted into a grey powder, that sunk by a little agitation to the bottom of the liquid metal; in short, the tin was partly converted into a calx. This process went on for three hours; after which the calcination stopped, and no farther change could be produced on the metal. The retort was then taken from the fire, and found to be precisely of the same weight as before the operation. It is evident, then, that no new substance had been introduced, and that therefore the increased weight of calces cannot, as Boyle supposed, be owing to the fixation of fire (x).
When the point of the retort was broken, the air rushed in with a hissing noise, and the weight of the retort was increased by ten grains. Ten grains of air, therefore, must have entered, and, consequently, precisely that quantity must have disappeared during the calcination. The metal and its calx being weighed, were found just ten grains heavier than before; therefore, the air which disappeared was absorbed by the metal; and as that part of the tin which remained in a metallic state was unchanged, it is evident that this air
(x) This experiment had been performed by Boyle with the same success. He had drawn a wrong conclusion from not attending to the state of the air of the vessel. Shaws's Boyle, II. 394. air must have united with the calx. The increase of weight, then, which metals experience during calcination, is owing to their uniting with air (y). But all the air in the vessel was not absorbed, and yet the calcination would not go on. It is not the whole, then, but some particular part of the air which unites with the calces of metals. By the subsequent discoveries of Priestley, Scheele, and Lavoisier himself, it was ascertained, that the residuum of the air, after calcination has been performed in it, is always pure azotic gas: It follows, therefore, that it is only the oxygen which combines with calces; and that a metallic calx is not a simple substance, but a compound. Mr Lavoisier observed, that the weight of the calx was always equal to that of the metal employed, together with that of the oxygen absorbed. It became a question, then, Whether metals, during calcination, lost any substance, and consequently, whether they contained any phlogiston? Mr Lavoisier accordingly proposed this question; and he answered it himself by a number of accurate experiments and ingenious observations. Metals cannot be calcined, excepting in contact with oxygen, and in proportion as they combine with it. Consequently they not only absorb oxygen during their calcination, but that absorption is absolutely necessary to their assuming the form of a calx. If the calx of mercury be heated in a retort, to which a pneumatic apparatus is attached, to the temperature of 120°, it is converted into pure mercury; and, at the same time, a quantity of oxygen separates from it in a gaseous form. As this process was performed in a close vessel, no new substance could enter: The calx of mercury, then, was reduced to a metallic state without phlogiston. The weights of the metal, and the oxygen gas, are together just equal to that of the calx; the calx of mercury, therefore, must be composed of mercury and oxygen; consequently, there is no reason whatever to suppose that mercury contains phlogiston. Its calcination is merely the act of uniting it with oxygen (z). The calces of lead, silver, and gold, may be decomposed exactly in the same manner; and Mr Van Marum, by means of his great electrical machine, decomposed also those of tin, zinc, and antimony, and restored them into their respective metals and oxygen. The same conclusions, therefore, must be drawn with respect to these metals. All the metallic calces may be decomposed by presenting to them substances which have a greater affinity for oxygen than they have. This is the reason that charcoal-powder is so efficacious in reducing them; and if they are mixed with it, and heated in a proper vessel, furnished with a pneumatic apparatus, it will be easy to discover what passes. During the reduction, a great deal of carbonic acid gas comes over, which, together with the metal, is equal to the weight of the calx and the charcoal: it must therefore contain all the ingredients; and we know that carbonic acid gas is composed of carbon and oxygen. During the process, then, the oxygen of the calx combined with the charcoal and the metal remained behind: It cannot be doubted, therefore, that all the metallic calces are composed of the entire metals combined with oxygen; and that calcination, like combustion, is merely the act of this combination. All metals, then, in the present state of chemistry, must be considered as simple substances; for they have never yet been decompounded.
The words calx and calcination are evidently improper and per, as they convey false ideas; we shall therefore afterwards employ, instead of them, the words oxyd and what oxydation, which were invented by the French chemists. A metallic oxyd signifies a metal united with oxygen; and oxydation implies the act of that union.
Metals are capable of uniting with oxygen in different proportions, and, consequently, of forming each of them different oxyds. These are distinguished from one another by their colour. One of the oxyds of iron, for instance, is of a green colour; it is therefore called the green oxyd; the other, which is brown, is called the brown oxyd.
The metals at present amount to 21; only 11 of which were known before the year 1730. Their names are gold, silver, platinum, mercury, copper, iron, tin, lead, zinc, antimony, bismuth, arsenic, cobalt, nickel, manganese, tungsten, molybdenum, uranium, tellurium, titanium, chromium.
The first eight of these were formerly called metals by way of eminence, because they are possessed either of malleability or ductility, or of both properties together; the rest were called semimetals, because they are brittle. But this distinction is now pretty generally laid aside; and, as Bergman observes, it ought to be altogether, as it is founded on a false hypothesis, and conveys very erroneous ideas to the mind. The first four metals were formerly called noble or perfect metals, because their oxyds are reducible by the mere application of heat.
(y) It is remarkable that John Rey, a physician of Perigord, had ascribed it to this very cause as far back as the year 1630: But his writings had excited little attention, and had sunk into oblivion, till after his opinion had been incontrovertibly proved by Lavoisier. Mayow also, in the year 1674, ascribed the increase of weight to the combination of metals with oxygen. Quippe vix concipi posset (says he), unde augmentum illud antimonii (calciniti) nisi a particulis nitro-aereis igneique inter calcinandum visis procedat. Tract. p. 28. Plane ut antimonii fixatio non tom a fulphuris ejus externi assumptione, quam particulis nitro-aereis, quibus flamma nitri abundat, ei intixis prove- nire videatur. Ibid, p. 29.
(z) This experiment was performed by Mr Bayen in 1774. This philosopher perceived, earlier than Lavoisier, that all metals did not contain phlogiston. "Ces experiences (says he) vont nous détrouper. Je ne tiendrai plus le langage des disciples de Stahl, qui seront forcés de restreindre la doctrine sur le phlogistique ou d'avouer que les précipités mercuriaux, dont je parle, ne font pas des chaux métalliques, ou enfin qu'il y a des chaux qui peuvent se réduire sans le concours du phlogistique. Les experiences que j'ai faites me force de conclure que dans la chaux mercuriale dont je parle, le mercure doit son état calcinaire, non à la perte du phlogistique qu'il ne pas effluée, mais à sa combinaison intime avec le fluide élastique, dont le poids ajouté à celui du mercure est la seconde cause de l'augmentation de pesanteur qu'on observe dans les précipités que j'ai fournis à l'examen." Jour. de Phys. 1774, pages 288, 295. It was in consequence of hearing Bayen's paper read that Lavoisier was induced to turn his attention to the subject. Gold seems to have been known from the very beginning of the world. Its properties and its scarcity have rendered it more valuable than any other metal.
It is of an orange red, or reddish yellow colour, and has no perceptible taste or smell.
No other substance can be compared with it in ductility and malleability. It may be beaten out into leaves so thin, that one grain of gold will cover 564 square inches. These leaves are only \( \frac{1}{2000} \) of an inch thick. But the gold leaf with which silver wire is covered has only \( \frac{1}{100} \) of that thickness. An ounce of gold, upon silver wire, is capable of being extended more than 1300 miles in length.
Its tenacity is such, that a gold wire \( \frac{1}{2} \) of an inch in diameter, is capable of supporting a weight of 500 pounds without breaking.
Its hardness is 6 (A); its specific gravity 19.3. It melts at 32° of Wedgwood's pyrometer (B). When melted, it assumes a bright bluish green colour. It expands in the act of fusion, and consequently contracts while becoming solid more than most metals; a circumstance which renders it less proper for casting into moulds.
It requires a very violent heat to volatilize it; it is therefore, to use a chemical term, exceedingly fixed. Boyle and Kunkel kept it for some months in a glass-house furnace, and yet it underwent no change; nor did it lose any perceptible weight, after being exposed to the air for some hours to the utmost heat of Mr Parker's lens*. Diderot, l. 7. Mr Lavoisier, however, observed, that a piece of silver, held over gold melted by a fire blown by oxygen gas, which produces a much greater heat than common air, was sensibly gilt: Part of the metal, then, must have been volatilized.
After fusion, it is capable of assuming a crystalline form. Tillet and Mongez obtained it in short quadrangular pyramidal crystals.
It is capable of combining with oxygen, and forming an oxyd of gold. There are two methods of producing this combination, the application of heat, and solution in acids. When it is exposed to a very violent heat in contact with air, gold absorbs oxygen. But the temperature must be very high; so high, indeed, that hardly any certain method of oxidating gold by heat is known, except by electricity. When the electric explosion is transmitted through gold leaf placed between two plates of glass, or when a strong charge is made to fall on a gilded surface—in both cases the metal is oxidated, and assumes a purple colour. It has been said also, that the same effect has been produced by a very violent fire; but few of the instances which have been adduced are well authenticated.
The other method of oxidating gold is much easier. For this purpose, equal parts of nitric and muriatic acids are mixed together (C), and poured upon gold; an effervescence takes place, the gold is gradually dissolved, and the liquid assumes a yellow colour. It is easy to see in what manner this solution is produced. No metal is soluble in acids till it has been reduced to the state of an oxyd. There is a strong affinity between the oxyd of gold and muriatic acid. The nitric acid furnishes oxygen to the gold, and the muriatic acid dissolves the oxyd as it forms. When nitric acid is deprived of the greater part of its oxygen, it assumes a gaseous form, and is then called nitrous gas. It is the emission of this gas which causes the effervescence. The oxyd of gold may be precipitated from the nitro-muriatic acid, by pouring in a little potash dissolved in water, or, which is much better, a little lime, both of which have a stronger affinity for muriatic acid than the oxyd has. This oxyd is of a yellow colour.
It is probable that gold is capable of two different degrees of oxidation, and of forming two different oxyds, the yellow and the purple: But neither the quantity of oxygen contained in these oxyds, nor the differences between them, have been accurately ascertained. The oxyds of gold may be decomposed in close vessels by the application of heat. The gold remains fixed, and the oxygen assumes the gaseous form. They may be decomposed, too, by all the substances which have a stronger affinity with oxygen than gold has. The affinities of the oxyds of gold, according to Bergman†, are as follows:
- Muriatic acid, - Nitro-muriatic, - Nitric, - Sulphuric, - Arsenic, - Fluoric,
Tartarous,
---
(A) We have borrowed from Mr Kirwan the method of denoting the different degrees of hardness by figures, which we think a great improvement. These figures will be understood by Mr Kirwan's own explanation, which we here subjoin.
1. Denotes the hardness of chalk. 2. A superior hardness, but yet what yields to the nail. 3. What will not yield to the nail, but easily, and without grittiness, to the knife. 4. That which yields more difficulty to the knife. 5. That which scarcely yields to the knife. 6. That which cannot be scraped by a knife, but does not give fire with steel. 7. That which gives a few feeble sparks with steel. 8. That which gives plentiful lively sparks. *Kirwan's Mineralogy*, I. 38. 9. According to the calculation of the Dijon academicians, it melts at 1298° Fahr.; according to Bergman, at 1301°.
(c) This mixture, from its property of dissolving gold, was formerly called aqua regia (for gold, among the alchymists, was the king of metals); it is now called nitro-muriatic acid. Gold is not changed either by air or water. It does not seem capable of combining either with fulphur or carbon. Mr Pelletier combined it with phosphorus, by melting together in a crucible half an ounce of gold and an ounce of phosphoric glass (x), surrounded with charcoal. The phosphuret of gold thus produced was brittle, whiter than gold, and had a crystallized appearance. It was composed of 23 parts of gold and one of phosphorus. He formed the same compound by dropping small pieces of phosphorus into gold in fusion.
Gold is also capable of combining with most of the metals. Its affinities are placed, by Bergman, in the following order:
- Mercury, - Copper, - Silver, - Lead, - Bismuth, - Tin, - Antimony, - Iron, - Platinum, - Zinc, - Nickel, - Arsenic, - Cobalt, - Manganese, - Phosphorus? - Sulphurets of alkalies.
Sect. II. Of Silver.
Silver appears to have been known almost as early as gold. It is a metal of a shining white colour, without either taste or smell.
It is the most malleable and ductile of all metals except gold, and perhaps platinum. It can be reduced to leaves about \( \frac{1}{5000} \) of an inch thick, and drawn into wire much finer than a human hair.
Its tenacity is such, that a wire of silver, \( \frac{1}{2} \) of an inch in diameter, is capable of sustaining 270 pounds without breaking.
Its hardness is 6.5*. Its specific gravity, before hammering, is 10.474; after hammering, 10.510†: for it is remarkable that the specific gravity of almost all the metals is increased by hammering.
It continues melted at 28° Wedgwood (v), but requires a greater heat to bring it to fusion.
The experiments of the French academicians have
Suppl. Vol. I. Part I.
(d) Have the alkalis any affinity for the yellow oxyd? Is not their affinity confined to the purple oxyd alone? And does not this oxyd act as an acid?
(e) Phosphoric acid evaporated to dryness, and then fused.
(f) According to the Dijon academicians, it melts at 1044° Fahr.; according to Bergman, at 1000°.
(g) Metallic oxyds, after fusion, are called glaifs, because they acquire a good deal of resemblance, in some particulars, to common glaifs.
When cooled slowly, it assumes a crystalline form. Tillet and Mongez obtained it in quadrangular pyramidal crystals, both insulated and in groups.
Silver may be combined with oxygen, and converted oxyds of into an oxyd by exposure to a very violent heat. By this method Junker partly converted it into a glaif; and Macquer, by exposing it 20 times successively to the heat of a porcelain furnace, obtained a glaif (q) of an olive green colour. The oxyd of silver may also be formed by dissolving the metal in an acid, and precipitating it from its solution by potash, lime, &c.: for, during its solution, the metal becomes oxidated. Little is known at present concerning the oxyds of silver, nor whether there be more than two, the black and the blue. From the experiments of Wenzel and Bergman, it follows, that one oxyd of silver is composed of about 90 parts of metal and 10 of oxygen. The affinities of the oxyds, according to Bergman, are as follows:
- Muriatic acid, - Sebatic, - Oxalic, - Sulphuric, - Saccharic, - Phosphoric, - Sulphurous, - Nitric, - Arsenic, - Fluoric, - Tartaric, - Citric, - Formic, - Lactic, - Acetous, - Succinic, - Prussic, - Carbonic, - Ammonia.
When silver is melted with sulphur in a low red heat, it combines with it and forms sulphuret of silver. It is of silver, very difficult to determine the proportion of the ingredients which enter into the composition of this substance, because there is an affinity between silver and its sulphuret, which dispose them to combine together. The greatest quantity of sulphur which a given quantity of silver is capable of taking up is, according to Wenzel, \( \frac{1}{2} \). Sulphuret of silver is of a black or very deep violet colour, brittle, and much more fusible than silver. If sufficient heat be applied, the sulphur is volatilized, and the metal remains behind in a state of purity.
If one ounce of silver, one ounce of phosphoric glass, and two drams of charcoal, be mixed together, and of silver heated in a crucible, sulphuret of silver is formed. Silver is of a white colour, and appears granulated, or as it were crystallized. It breaks under the hammer, but may be cut with a knife. It is composed of four parts of silver and one of phosphorus. Heat decomposes it by separating the phosphorus. Pelletier has observed, that silver in fusion is capable of combining with more phosphorus than solid silver; for when phosphuret of silver is formed by projecting phosphorus into melted silver, after the crucible is taken from the fire a quantity of phosphorus is emitted the moment the metal congeals.
Silver does not seem capable of combining with carbon.
Silver is capable of combining with gold, and forming an alloy (ii) composed of one part of silver and five of gold. That this is the proportion of the ingredients, was discovered by Homberg. He kept equal parts of gold and silver in gentle fusion for a quarter of an hour, and found, on breaking the crucible, two masses, the uppermost of which was pure silver, the undermost the whole gold combined with \( \frac{1}{5} \) of silver. Silver, however, may be mixed with gold in almost any proportion. But there is a great difference between the mixture of two substances and their chemical combination. Metals which melt nearly at the same temperature, may be mixed from that very circumstance in any proportion; but substances can combine chemically only in one proportion. This observation, which is certainly of importance, was first made, as far as we know, by Mr Keir. The alloy of silver and gold is of a greenish colour; but its properties have not yet been accurately examined.
Silver is not affected by water, nor by exposure to the air; but Mr Proult has remarked, that when long exposed in places frequented by men, as in churches, theatres, &c., it acquires a covering of a violet colour, which deprives it of its lustre and malleability. This covering, which forms a thin layer, can only be detached from the silver by bending it, or breaking it in pieces with a hammer. It was examined by Mr Proult, and found to be sulphuret of silver. He accounts for this transition of the silver into a sulphuret, by supposing that a quantity of sulphur is constantly formed and exhaled by living bodies.
The affinities of silver, according to Bergman, are as follows:
- Lead, - Copper, - Mercury, - Bismuth, - Tin, - Gold, - Antimony, - Iron, - Manganese, - Zinc, - Arsenic, - Nickel, - Platinum, - Sulphurets of alkalies, - Sulphur, - Phosphorus.
Sect. III. Of Platinum.
The metals hitherto described have been known to mankind from the earliest ages, and have been always in high estimation on account of their beauty, scarcity, ductility, and indestructibility. But platinum, though perhaps inferior to them in none of these qualities, and certainly far superior in others, was unknown, as a distinct metal, before the year 1752 (i).
It has been found only in America, in Choco in Peru, and in the mine of Santa Fe, near Carthagena. The workmen of these mines must no doubt have been early acquainted with it; but they seem to have paid very little attention to it. It was unknown in Europe till Mr Wood brought some of it from Jamaica in 1748. Soon after it was noticed by Don Antonio de Ulloa, a Spanish mathematician, who had accompanied the French academicians to Peru in their voyage to measure a degree of the meridian. In the year 1752, it was examined by Scheffer of Sweden, and discovered by him to be a new metal, approaching very much to the nature of gold, and therefore called by him aurum album.
(ii) Metals combined together are called alloys or allays.
(i) Father Cortinovis, indeed, has attempted to prove, that this metal was the electrum of the ancients. See the Chemical Annals of Brugnatelli, 1790. That the electrum of the ancients was a metal, and a very valuable one, is evident from many of the ancient writers, particularly Homer. The following lines of Claudian are alone sufficient to prove it:
Atria cinxit ebur, trabibus solidatur abenis. Culmen et in celis surgunt electra columnas. L. I. v. 164.
Pliny gives us an account of it in his Natural History. He informs us that it was a composition of silver and gold; and that by candle-light it shone with more splendor than silver. The ancients made cups, statues, and columns of it. Now, had it been our platinum, is it not rather extraordinary that no traces of a metal, which must have been pretty abundant, should be perceptible in any part of the old continent?
As the passage of Pliny contains the fullest account of electrum to be found in any ancient author, we shall give it in his own words, that every one may have it in his power to judge whether or not the description will apply to the platinum of the moderns.
"Omni auro inept argentum vario pondera.—Ubicunque quinta argenti portio est, electrum vocatur. Scrobes rerum sunt in Canaliensi. Fit et cura electrum argento addito. Quod si quintam portionem excedit, incidibus non reficit. Et electro auctoritas, Homero tefta, qui Menelai regiam aurum, electro, argento, ebore fulgere tradit. Minervae templum habet Lindos infusa Rhodiiorum in quo Helena sacravit calicem ex electro.—Electri natura est ad lucernarum lumina clariss argento splendere. Quod est nativum, et venena deprehendit. Namque discurrent in calicibus arcus coelestibus similes cum igne aridore, et gemina ratione praedicant."—Lib. xxxiii. cap. iv. Platinum, when pure, is of a white colour like silver, but not so bright (x). It has no taste nor smell.
It is both ductile and malleable; but the precise degree has not yet been ascertained. It has been drawn into a wire of \( \frac{1}{32} \) of an inch in diameter. This wire admitted of being flattened, and had more strength than a wire of silver or gold of the same size \( \frac{1}{4} \).
It is exceedingly difficult to fuse it. Macquer and Beaumé succeeded by means of a powerful burning-glass. It melts more easily when mixed with other substances. Its fixity is still greater than its inflammability. If the strongest fires cannot melt it, much less can they volatilize it.
Its hardness is 75 ||. Its specific gravity, after being hammered, is 23,000; so that it is by far the heaviest body known.
Some of the experiments which have been made on platinum seem to prove that it may be oxidized by the application of a violent heat. The oxyd of this metal may be easily formed by dissolving platinum in nitric acid, and precipitating it by means of an earth or potash. The various oxyds of platinum have never yet been examined with accuracy. The one at present best known possesses, as Mr Berthollet has proved, the properties of an acid.
The sulphuret of platinum is unknown.
By mixing together an ounce of platinum, an ounce of phosphoric glass, and a dram of powdered charcoal, and applying a heat of about 32° Wedgwood, Mr Pelletier formed a phosphuret of platinum weighing more than an ounce. It was partly in the form of a button, and partly in cubic crystals. It was covered above by a blackish glass. It was of a silver white colour, very brittle, and hard enough to strike fire with steel. When exposed to a fire strong enough to melt it, the phosphorus was disengaged, and burnt on the surface \( \frac{1}{4} \).
He found also, that when phosphorus was projected on red hot platinum, the metal instantly fused and formed a phosphuret. As heat expels the phosphorus, Mr Pelletier has proposed this as an easy method of purifying platinum \( \frac{1}{4} \).
Platinum does not seem capable of combining with carbon.
It is not in the least affected by the action of water or air.
1. When gold and platinum are exposed to a strong heat, they combine, and form an alloy of a much whiter colour, but nearly as ductile as gold. The proportions of the ingredients are not known. When only the alloy is platinum, the gold is scarcely altered in colour.
2. Whether silver and platinum combine chemically has not yet been properly ascertained. When fused together (for which a very strong heat is necessary), they form a mixture, not so ductile as silver, but harder and less white. The two metals are separated by keeping them for some time in the state of fusion; the platinum sinking to the bottom from its weight. This circumstance would induce one to suppose that there is very little affinity between them.
Sect. IV. Of Mercury.
Mercury, called also quicksilver, was known to the ancients, and seems to have been employed by them in gilding.
It is of a white colour, exactly like that of polished silver. It has no taste, but acquires a slight odour when mercury rubbed between the hands.
Its specific gravity is 13.68 \( \frac{1}{4} \).
It differs from all other metals in always existing, at the common temperature of the atmosphere, in a state of fluidity. It freezes at -39° \( \frac{1}{4} \); or, which is the same thing, it ceases to be a solid, and melts whenever it is placed in a temperature above -39°. It boils at the temperature of 600°.
From the experiments made on frozen mercury in Russia, Hudson's Bay, and Britain, we know that this metal, when solid, is malleable; but the extreme difficulty of examining it in that state, on account of the lowness of the temperature, has rendered it hitherto impossible to ascertain the precise degree either of its malleability, ductility, or hardness.
Mercury is capable of combining with oxygen, and forms oxyds differing from each other in the quantity of oxygen which they contain. The oxyds of mercury, at present known, are the black, the yellow, and the red.
1. When mercury is agitated for some time in contact with oxygen gas, or atmospheric air, it is partly converted into a greyish-black powder, and at the same time part of the oxygen disappears. This is the black oxyd of mercury. It is not known how much oxygen it contains, nor even whether the whole of the mercury which composes it is actually combined with oxygen.
2. The best way of forming the yellow oxyd is to dissolve mercury, either in boiling sulphuric acid or in oxalic acid, nitric acid. During its solution, it deprives these acids of just as much oxygen as is necessary to convert it into a yellow oxyd; and if potash or lime be afterwards added to the solution, it precipitates, and may be obtained pure by washing it with water. It is a bright yellow-coloured powder, which acts very powerfully as an emetic. From the observations of Bergman, it appears, that it is composed of about 97.8 parts of mercury, and 3.2 of oxygen \( \frac{1}{4} \).
3. The red oxyd of mercury may be prepared, either by distilling nitric acid off the metal repeatedly, or by keeping mercury for a long time exposed to a heat sufficient to evaporate it while it is in contact with air. When formed by the first process, it was formerly called red precipitate; when by the last, precipitate per se. It is a beautiful red powder, or rather small red crystals, which have some elastic qualities. When prepared by the second process, the heat must not be much below 600°, nor much above 800°, otherwise no union would take place; and it must be continued for some weeks.
(x) To this colour it owes its name. Plata, in Spanish, is silver; and platina, little silver, was the name first given to the metal. Bergman changed that name into platinum, that the Latin names of all the metals might have the same termination and gender. It was, however, first called platinum by Linnæus. From the experiments of Mr Kirwan, it appears to contain 92.6 parts of mercury and 7.4 parts of oxygen.
These oxyds may be decomposed by the application of a heat amounting to 1200°. The oxygen flies off in the form of gas, and running mercury remains behind.
The affinities of the oxyds of mercury, according to Bergman, are as follows:
- Sebacic acid, - Muriatic, - Oxalic, - Succinic, - Arsenic, - Phosphoric, - Sulphuric, - Benzoic (L), - Saccharotic, - Tartarous, - Citric, - Sulphurous, - Nitric, - Fluoric, - Zoonic (M), - Acetous, - Boracic, - Prussic, - Carbolic.
When two parts of mercury and three parts of flowers of sulphur are triturated for some time together, or when equal parts of mercury and melted sulphur are mixed together—they combine, and form a black powder, formerly called ethiops mineral, and now black sulphuret of mercury.
When 300 grains of mercury and 68 of sulphur, with a few drops of solution of potash to moisten them, are triturated for some time in a porcelain cup by means of a glass pestle, black oxyd of mercury is produced. Add to this 160 grains of potash, dissolved in as much water. Heat the vessel containing the ingredients over the flame of a candle, and continue the trituration without interruption during the heating. In proportion as the liquid evaporates, add clear water from time to time, so that the oxyd may be constantly covered to the depth of near an inch. The trituration must be continued about two hours; at the end of which time the mixture begins to change from its original black colour to a brown, which usually happens when a large part of the fluid is evaporated. It then passes very rapidly to a red. No more water is to be added; but the trituration is to be continued without interruption. When the mass has acquired the consistence of a jelly, the red colour becomes more and more bright, with an incredible degree of quickness. The instant the colour has acquired its utmost beauty, the heat must be withdrawn, otherwise the red passes to a dirty brown. This red powder is the red sulphuret of mercury, called formerly cinnabar, and, when reduced to a fine powder, vermilion (N). The process above described has been lately discovered by Mr Kirchhoff, and is by far the simplest and cheapest mode of forming red sulphuret with which we are acquainted. Count De Moulin Pouchin has discovered, that its passing to a brown colour may be prevented by taking it from the fire as soon as it has acquired a red colour, and placing it for two or three days in a gentle heat, taking care to add a few drops of water, and to agitate the mixture from time to time. During this exposure, the red colour gradually improves, and at last becomes excellent. He discovered also, that when this sulphuret is exposed to a strong heat, it becomes instantly brown, and then passes into a dark violet; when taken from the fire it passes instantly to a beautiful carmine red.
The difference between these two sulphurets has not yet been ascertained. One would be apt to suspect at first that the black sulphuret consists of the real sulphuret of mercury combined with sulphur; the red, of the sulphuret of mercury combined with mercury, and that the real sulphuret of mercury was not yet accurately known. But it cannot be doubted that, during the formation of the red sulphuret, according to Kirchhoff's process, there is an absorption of oxygen. The phenomena above described point out that almost incalculably; and we observed, on attempting to repeat the experiment, that the black sulphuret, during its trituration, emitted sulphured hydrogen gas. Perhaps, then, the mercury may be oxidized. We suspected at first that part of the sulphur might be converted into an acid; but on attempting an alteration of the process in consequence of that supposition, we could not succeed.
The red sulphuret of mercury is found naturally in several parts of the world. It used to be prepared by forming a black sulphuret with three parts of sulphur and one of mercury, and then setting fire to it. Part of the sulphur is burnt, and there remains behind a violet-coloured body, which is powdered and put into a glass vessel, to the bottom of which a red heat is applied. A reddish brown sublimate sublimes, which is red sulphuret of mercury; but its colour is not nearly equal to that which is prepared by Kirschhoff's process.
Mr Pelletier, after several unsuccessful attempts to form phosphuret of mercury, at last succeeded by distilling a mixture of red oxyd of mercury and phosphorus. Part of the phosphorus combined with the oxygen of the oxyd, and was converted into an acid; the rest combined with the mercury.
Phosphuret of mercury is of a black colour, of a pretty solid consistence, and capable of being cut with a knife. When exposed to the air, it exhaled vapours of phosphorus.
Mercury does not seem capable of combining with carbon.
The combinations of mercury with the other metals are called amalgams.
1. The amalgam of gold forms very readily, because there is a very strong affinity between the two metals. If a bit of gold be dipped into mercury, its surface, by combining with mercury, becomes as white as silver.
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(L) Benzoin of mercury is decomposed by sulphuric acid.
(M) Zoonic acid decomposes the acetite of mercury.
(N) The word vermilion is derived from the French word vermeil, which comes from vermiculus or vermiculum, names given in the middle ages to the kermes or coecus ilicis, well known as a red dye. Vermilion originally signified the red dye of the kermes. See Beckmann's Hist. of Discoveries, II, 180. The easiest way of forming this amalgam is to throw small pieces of red hot gold into mercury. The proportions of the ingredients are not easily determined, because the amalgam has an affinity both for the gold and the mercury; in consequence of which they appear to combine in any proportion. Most probably it is composed of two parts of gold and one of mercury. The combination is formed most readily in these proportions; and if too much mercury be added, it may be separated by filtration. The amalgam is of a white colour, and of the consistence of butter. This amalgam crystallizes in quadrangular prisms; which crystals, according to the Dijon academicians, are composed of six parts of mercury and one of gold. It is much used in gilding.
2. The amalgam of silver is made in the same manner. It forms dendritical crystals, which, according to the Dijon academicians, contain eight parts of mercury and one of silver. Gellert was the first who remarked that its specific gravity was greater than that of mercury, though that of silver be less.
3. Dr Lewis attempted to form an amalgam of platinum, but hardly succeeded, after a labour which lasted for several weeks. Mr Morveau succeeded by means of heat. But a much more expeditious method has been lately discovered by Count Mouffin Poutchkin. He took a dram of the orange-coloured salt, composed of oxyd of platinum and ammonia (o), and triturated it with an equal weight of mercury in a mortar of chalcedony. In a few minutes the salt became brown, and afterwards acquired a greenish shade. The matter was reduced to a very fine powder. Another dram of mercury was added, and the trituration continued: The matter became grey. A third dram of mercury began to form an amalgam; and six drams made the amalgam perfect. The whole operation scarce lasted 20 minutes. Mercury was added till it amounted to nine times the weight of the salt, and yet the amalgam continued very tenacious. It was easily spread out under the pellie; it received the impression of the most delicate seals, and had a very close and brilliant grain. This amalgam is decomposed, and the mercury passes to the state of black oxyd by the simple contact of several of the metals and a great number of animal matters. This effect even takes place on rubbing it between the fingers.
The affinities of mercury, as ascertained by the experiments of Morveau (r), are as follows:
- Gold, - Silver, - Tin, - Lead, - Bismuth, - Zinc, - Copper, - Antimony, - Arsenic (a), - Iron.
Sect. V. Of Copper.
Except gold and silver, copper seems to have been more early known than any other metal. In the first ages of the world, before the method of working iron was discovered, copper was a principal ingredient in all domestic utensils and instruments of war. Even during the Trojan war, as we learn from Homer, the combatants had no other armour but what was made of bronze, which is a mixture of copper and tin. The word copper is derived from the island of Cyprus, where it was first discovered, or at least wrought to any extent, by the Greeks.
Copper is of a pale red colour with a shade of yellow. Its taste is acrid and nauseous; and when rubbed copperbed it emits a disagreeable smell. It possesses a considerable degree of malleability, though less than silver. Its tenacity is such, that a wire of 1/8 of an inch in diameter can sustain a weight of 299 pounds without breaking.
Its hardness is 8 1/2. Its specific gravity, when not hammered, is 7,788; when wire-drawn, 8,878. The specific gravity of Japan copper is 9,000; that of Swedish copper, 9,324.
It melts at 275° Wedgwood; according to the calculation of the Dijon academicians, at 1449° Fahrenheit. When allowed to cool slowly, it assumes a crystalline form. The Abbé Mongez, to whom we owe many valuable experiments on the crystallization of metals, informs us, that these crystals are quadrangular pyramids, frequently interlaced into one another.
When copper is heated red hot in contact with air, brown is soon covered with a brown earthy crust, which may be easily separated by hammering or by plunging the metal into water. If the heat be continued, another scale of the same kind soon forms; and by continuing the process the whole metal may be converted into an earthy-like crust, which is merely a combination of copper and oxygen, and is therefore called brown oxyd of copper. It is composed of about 8 1/2 parts of copper and 16 of oxygen.
When copper is dissolved in sulphuric acid, and precipitated by means of lime, it falls in the form of a blue, coloured powder, which is the blue oxyd of copper. If this oxyd of copper be dried in the open air, it assumes a green colour, and is then called the green oxyd of copper. This last oxyd may also be produced by distilling a sufficient quantity of nitric acid off copper. Little satisfactory is yet known with respect to these oxyds; it has not even been ascertained whether the blue and green be really two different oxyds, or whether the difference in colour be owing to some other cause. It is probable, however, that the green oxyd contains more oxygen than the blue; because the blue oxyd affirms a green colour when exposed for some time to the open air, during which it may be supposed to absorb oxygen. An experiment of Fourcroy proves incontrovertibly, that the brown oxyd contains less oxygen than the green. He converted the green oxyd into the brown by applying heat; and during the distillation obtained oxygen gas.
The affinities of the oxyds of copper, according to Bergman, are as follows:
- Pyro-mucous acid, - Oxalic, - Tartarous,
(o) Ammonia is an alkali hereafter to be described. It is often called, in English, hartshorn.
(r) We shall have occasion to consider these celebrated experiments afterwards.
(a) These two are added from Bergman. Bergman places lead before tin, and zinc before bismuth. When copper is long exposed to the air, its surface becomes covered over with a green crust, which is green oxid of copper. This oxidation never penetrates beyond the surface.
Copper is not attacked by water at the boiling temperature; but if cold water be allowed to remain long on its surface, the metal becomes partly oxidated.
Sulphur mixes readily with copper. The combination may be formed by mixing the ingredients together and applying a pretty strong heat. Sulphuret of copper is brittle, softer than copper, of a black colour externally, and within of a leaden grey. It is composed, according to Kirwan's experiments, of 81 parts of copper and 19 of sulphur.
Mr Pelletier formed phosphuret of copper by melting together one ounce of copper, one ounce of phosphoric glass, and one dram of charcoal. It was of a white colour. On exposure to the air, it lost its lustre and became blackish. Margraf was the first person that formed this phosphuret. His method was to dilute phosphorus and brown oxid of copper together. It is formed most easily by projecting phosphorus into red hot copper. According to Pelletier, it contains 20 parts of phosphorus and 80 of copper. This phosphuret is harder than iron: it is not ductile, and yet cannot easily be pulverized. Its specific gravity is 7.1220. It crystallizes in tetrahedral prisms.
1. Copper combines readily with gold when the two metals are melted together. The compound is of a reddish colour, more fusible than gold, but less ductile. The proportions of the ingredients which form this alloy are not known; nor would it be easy to ascertain them, as the two metals are almost equally fusible. The current gold of this country is composed of 11 parts of gold and one part of copper.
2. The alloy of copper and silver is made as easily as that of gold, and the properties are equally unknown. It is harder and more sonorous than silver. The current silver coin of Britain is composed of 15 parts of silver and one of copper.
3. Platinum combines readily with copper. The alloy is much more fusible than platinum; it is ductile, hard, takes a fine polish, and is not liable to tarnish. This alloy has been employed with advantage for composing the mirrors of reflecting telescopes.
4. The amalgam of copper cannot be formed by simply mixing that metal with mercury, nor even by the application of heat; because the heat necessary to melt copper sublimes mercury. Dr Lewis has given several processes for forming this amalgam. One of the simplest is to triturate mercury with a quantity of common salt and verdigris; a substance composed of oxid of copper and vinegar. The theory of this process is not very obvious.
The affinities of copper are, according to Bergman, as follows:
- Gold - Silver - Arsenic - Iron - Manganese - Zinc - Antimony - Platinum - Tin - Lead - Nickel - Bismuth - Cobalt - Mercury - Sulphuret of alkali - Sulphur - Phosphorus
**Sect. VI. Of Iron.**
Iron, the most abundant and most useful of all the discovery metals, was neither known so early, nor wrought so easily, as gold, silver, and copper. For its discovery we must have recourse to the nations of the east, among whom, indeed, almost all the arts and sciences first sprung up. The writings of Moses (who was born about 1635 years before Christ) furnish us with the amplest proof at how early a period it was known in Egypt and Phoenicia. He mentions furnaces for working iron, ores from which it was extracted; and tells us, that swords, knives, axes, and tools for cutting stones, were then made of that metal. How many ages before the birth of Moses iron must have been discovered in these countries, we may perhaps conceive, if we reflect, that the knowledge of iron was brought over from Phrygia to Greece by the Dactyls, who settled in Crete during the reign of Minos I., about 1431 years before Christ; yet during the Trojan war, which happened 200 years after that period, iron was in such high estimation, that Achilles proposed a ball quoted by him as one of his prizes during the games which he celebrated in honour of Patroclus (x). At that period none of their weapons were formed of iron. Now if the Greeks in 100 years had made so little progress in an art which they learned from others, how long must it... Iron unites readily with sulphur. Sulphuret of iron, Sulphuret; formerly called pyrites, is found ready formed in many parts of the world. It is not easy to determine the proportions of its ingredients, because it is capable of combining both with iron and sulphur, and consequently, if there happens to be any excess of either during its formation, it takes it up. Perhaps the proportions are not far from equal parts of sulphur and of iron. It is of a pale yellow or brownish colour, and is capable of assuming a crystalline form. Its specific gravity is about 4,000. When placed upon the fire, it precipitates; and at a red heat loses its yellow colour, and becomes of an iron grey, excepting its surface, which is of a bright red. It melts at 120° Wedgwood in a covered crucible into a bluish flag, somewhat porous internally. When exposed to air and moisture, the native sulphur, as happens in all sulphures, gradually absorbs oxygen, and is converted into an acid.
If iron filings and sulphur be mixed together, and formed into a paste with water, the sulphur decomposes the water, and absorbs oxygen so rapidly that the mixture takes fire, even though it be buried under ground. This phenomenon was first discovered by Homberg; and it is considered as affording an explanation of the origin of volcanoes. The native sulphuret of iron has been observed more than once to take fire on being suddenly moistened with water.
Iron combines readily with phosphorus, and forms phosphuret of iron; to which Bergman, who first discovered it, gave the name of siderum.
There is a particular kind of iron, known by the name of cold short iron, because it is brittle when cold, though it be malleable when hot. Bergman was employed at Upsal in examining the cause of this property, while Meyer was occupied at Stetin with the same investigation; and both of them discovered, nearly at the same time, that, by means of sulphuric acid, a white powder could be separated from this kind of iron, which by the usual process they converted into a metal of a dark steel grey, exceedingly brittle, and not very soluble in acids. Its specific gravity was 6,700; it was not so fusible as copper; and when combined with iron rendered it cold short. Both of them concluded that this substance was a new metal; and Bergman gave it the name of siderum. But Klaproth soon after recollected that the salt composed of phosphoric acid and iron bore a great resemblance to the white powder obtained from cold short iron, suspected the presence of phosphoric acid. phosphoric acid in this new metal. To decide the point, he combined phosphoric acid and iron, and obtained, by heating it in a crucible along with charcoal powder (s), a substance exactly resembling the new metal. Meyer, when Klaproth communicated to him this discovery, informed him that he had already satisfied himself, by a more accurate examination, that siderum contained phosphoric acid. Soon after this, Scheele actually decomposed the white powder obtained from cold hot iron, and thereby demonstrated, that it was composed of phosphoric acid and iron. The siderum of Bergman, however, is composed of phosphorus and iron, the phosphoric acid being deprived of its oxygen during the reduction; or it is phosphuret of iron. It may be formed by fusing in a crucible an ounce of phosphoric glass, an ounce of iron, and half a dram of charcoal powder. It is very brittle, and appears white when broken. When exposed to a strong heat, it melts, and the phosphorus is dissipated. It may be formed also by melting together equal parts of phosphoric glass and iron-filings. Part of the iron combines with the oxygen of the phosphoric glass, and is vitrified; the rest forms the phosphuret, which sticks to the bottom of the crucible. It may be formed also by dropping small bits of phosphorus into iron-filings heated red hot. The proportions of the ingredients of this phosphuret have not yet been determined.
Iron likewise combines with carbon, and forms a carburet. Carburet of iron has been long known and used in the arts under the names of plumbago and black lead. It is of a dark iron grey or blue colour, and has something of a metallic lustre. It has a greasy feel, and blackens the fingers, or any other substance to which it is applied. It is found in many parts of the world, especially in England, where it is manufactured into pencils. It is not affected by the most violent heat as long as air is excluded, nor is it in the least altered by simple exposure to the air, or to water. Its nature was first investigated by Scheele; who proved, by a very ingenious analysis, that it could be converted almost wholly into carbonic acid gas, and that the small residuum was iron. It follows from this analysis, that it is composed of carbon and iron; for the carbon during its combination had been converted into carbonic acid gas. By the subsequent experiments of Pelletier and other French chemists, it has been shown to consist nearly of nine parts of carbon to one of iron.
There are a great many varieties of iron, which are distinguished by particular names; but all of them may be reduced under one or other of the three following states: Wrought iron (or simply iron), steel, and cast or new iron.
Wrought Iron is the substance which we have hitherto described. As it has never yet been decomposed, we consider it when pure as a simple body; but it has seldom or never been found without some small mixture of foreign substances. These substances are either some of the other metals, or oxygen, carbon, or phosphorus.
Steel is distinguished from iron by the following properties.
It is so hard as to be unworkable while cold, or at least it acquires this property by being immersed while ignited into a cold liquid; for this immersion, though it has no effect upon iron, adds greatly to the hardness of steel.
It is brittle, resists the file, cuts glass, affords sparks with flint, and retains the magnetic virtue for any length of time.
It loses this hardness by being ignited and cooled very slowly.
It melts at above 130° Wedgwood. It is malleable when red hot, but scarcely so when raised to a white heat.
It may be hammered out into much thinner plates than iron. It is more sonorous; and its specific gravity, when hammered, is greater than that of iron.
By being repeatedly ignited in an open vessel, and hammered, it becomes wrought iron.
Cast Iron is distinguished by the following properties:
It is scarcely malleable at any temperature. It is generally so hard as to resist the file. It can neither be cast iron hardened nor softened as steel can by ignition and cooling. It is exceedingly brittle. It melts at 130° Wedgwood. It is more sonorous than steel.
Cast iron is converted into wrought iron by exposing it for a considerable time in a furnace to a heat sufficiently strong to melt it. During the process it is constantly stirred by a workman, that every part of it may be equally exposed to the air. In about an hour the hottest part of the mass begins to heave and swell, and to emit a lambeat blue flame. This continues nearly an hour; and by that time the conversion is completed. The heaving is evidently produced by the emission of an elastic fluid.
Wrought iron may be converted into steel by being kept for some hours in a strong red heat, surrounded with charcoal powder in a covered crucible. By this process, which is called cementation, the iron gains some weight.
These different kinds of iron have been long known, and the converting of them into each other has been practised in very remote ages. Many attempts have been made to explain the manner in which this conversion is accomplished. According to Pliny, steel owes its peculiar properties chiefly to the water to which it is plunged in order to be cooled. Becher supposed that fire was the only agent; that it entered into the iron, and converted it into steel. Reaumur was the first who attended accurately to the process; and his numerous experiments have certainly contributed to elucidate the subject. He supposed that iron was converted into steel by combining with saline and oily or sulphurous particles, and that these were introduced by the fire. But it was the analysis of Bergman, published in 1781, that first paved the way to the explanation of the nature of these different species of iron.
By dissolving in diluted sulphuric acid 100 parts of cast iron, he obtained 40 ounces measures of hydrogen; from 100 parts of steel he obtained 48 ounces measures; and from 100 parts of wrought iron, 10 ounces measures. Now as the hydrogen is produced by the property which iron has of decomposing water and uniting with its oxygen, it is evident that the greater the quantity of hydrogen obtained,
(s) This process in chemistry is called reduction. tained; with the more oxygen does the iron combine. But the quantities of iron were equal; they ought therefore to have combined with equal quantities of oxygen. But it is evident, from the quantities of hydrogen obtained, that the cast iron received less oxygen than either of the other two: cast iron therefore must contain already some oxygen, since it requires less than the other two species in order to be saturated. Here then is one difference between cast iron and the other two kinds; it contains oxygen. Steel, on the contrary, does not appear to contain any oxygen. The difference between the quantity of hydrogen produced during its solution and that of wrought iron, which contains no oxygen, is exceedingly small, and it has been found to diminish in proportion to the purity of the steel.
From 100 parts of cast iron Bergman obtained 2.2 parts of plumbago, or \( \frac{1}{47} \); from 100 parts of steel, 0.5, or \( \frac{1}{200} \); and from 100 parts of wrought iron, 0.12, or \( \frac{3}{250} \). Now plumbago is composed of \( \frac{3}{8} \)ths of carbon; cast iron therefore contains a considerable quantity of carbon, steel a smaller quantity, and wrought iron a very minute portion, which diminishes according to its purity, and would vanish altogether if iron could be obtained perfectly pure. Mr Grignon, in his notes on this analysis, endeavoured to prove, that plumbago was not essentially a part of cast iron and steel, but that it was merely accidentally present. But Bergman, after considering his objections, wrote to Morveau on the 18th November 1783, "I will acknowledge my mistake whenever Mr Grignon finds me a single bit of cast iron or steel which does not contain plumbago; and I beg of you, my dear friend, to endeavour to discover some such, and to send them to me; for if I am wrong, I wish to be undeceived as soon as possible." This was almost the last action of the illustrious Bergman. He died a few months after at the age of 49, leaving behind him a most brilliant reputation, which no man ever more deservedly acquired. His industry, his indefatigable, his astonishing ingenuity, would alone have contributed much to establish his name; his extensive knowledge would alone have attracted the attention of philosophers; his ingenuity, penetration, and accurate judgment, would alone have secured the applause; and his candour and love of truth procured him the confidence and the esteem of the world—But all these qualities were united in Bergman, and conspired to form one of the greatest men and noblest characters that ever adorned human nature.
The experiments of Bergman were fully confirmed by those of Morveau, Vandermonde, Monge, and Berthollet, who have likewise thrown a great deal of additional light on the subject. From all these experiments the following deductions may be made.
Wrought iron is a simple substance, and if perfectly pure would contain nothing but iron.
Steel is iron combined with carbon. The proportion of this last ingredient has not yet been ascertained; Dr Pearson fixes it at \( \frac{1}{200} \)th part at a medium. Steel, in consequence of its composition, has been called by some chemists carburet of iron; but before affixing it that name, which has been also given to plumbago, it ought to be determined what are the proportions of carbon and iron which saturate each other. Is it the proportion in which these two substances exist in steel, or that which forms plumbago? In the first case, plumbago is carburet of iron combined with carbon; in the second, steel is carburet combined with iron. Or is it some intermediate proportion? Till these points be determined, perhaps it would be better to continue the old names than to risk the imposition of false ones.
Cast iron is iron contaminated with various foreign substances, the proportions of which vary according to circumstances. These substances are chiefly oxyd of iron and carbon, and sometimes silica (†).
Bergman found a quantity of manganese in the iron and steel which he examined; but it appears from the experiments of Vauquelin, that his method of determining the presence of that metal was not accurate.
Mr Vauquelin* has lately analysed four kinds of steel with great care, and contrived his processes with much ingenuity. The result of his analysis is as follows:
| First steel, composed of | Carbon | 0.00789 | |-------------------------|--------|---------| | | Silica | 0.00315 | | | Phosphorus | 0.00345 | | | Iron | 0.98551 |
| Second steel, composed of | Carbon | 0.00683 | |---------------------------|--------|---------| | | Silica | 0.00273 | | | Phosphorus | 0.00827 | | | Iron | 0.98217 |
| Third steel, composed of | Carbon | 0.00789 | |--------------------------|--------|---------| | | Silica | 0.00315 | | | Phosphorus | 0.00791 | | | Iron | 0.98105 |
| Fourth steel, composed of | Carbon | 0.00631 | |---------------------------|--------|---------| | | Silica | 0.00252 | | | Phosphorus | 0.01520 | | | Iron | 0.97597 |
It cannot be concluded from these experiments, that all steel contains phosphorus and silica; far less that these substances enter necessarily into the composition of steel. This may be the case, and former analyses may not have been nice enough to detect it; but before it can be admitted, it must be shewn that these substances are always present in steel, and that it loses its essential properties when deprived of them.
Iron combines with most metals.
1. The alloy of gold and iron is very hard, and might, according to Dr Lewis who examined it, be employed with advantage in forming cutting instruments.
2. That iron combines with silver is certain, but hardly anything is known about the nature of the compound.
3. Platinum is usually found alloyed with iron. Dr Lewis did not succeed in his attempts to unite these metals.
† An earth which shall be described in the next chapter. metals by fusion, but he melted together cast iron and platinum. The alloy was excessively hard, and possessed ductility.
4. There is very little affinity between iron and mercury; they cannot therefore be amalgamated by simple mixture, even with the affluence of heat. Vogel affirms that he has produced an amalgam of iron by the following process: Pound one part of iron filings and two parts of alum in a mortar to a fine powder; then pour in two or three parts of mercury, and triturate till the substances be thoroughly mixed. Pour on a little water, and continue the trituration for about an hour. If then no particles of iron can be distinguished, pour on a little more water to wash out the alum, and then dry the amalgam. If particles of iron be perceptible, the trituration must be continued till they disappear.
5. Iron may be united to copper by fusion, but not without considerable difficulty. The alloy has been applied to no use.
The affinities of iron, according to Bergman, are as follows:
- Nickel, - Cobalt, - Manganese, - Arsenic, - Copper, - Gold, - Silver, - Tin, - Antimony, - Platinum, - Bismuth, - Lead, - Mercury, - Sulphur of alkali, - Carbon? - Phosphorus? - Sulphur?
Sect. VII. Of Tin.
The Phenicians were the first of those nations which make a figure in ancient history that were acquainted with tin. They procured it from Spain* and from Britain, with which nations they carried on a very lucrative commerce. At how early a period they imported this metal we may easily conceive, if we recollect that it was in common use in the time of Moses†.
Tin is of a greyish white colour; it has a strong disagreeable taste, and emits a peculiar smell when rubbed.
It is very malleable: tin leaf, or tinfoil as it is called, is about 1/200th part of an inch thick, and it might be beat out into leaves as thin again if such were wanted for the purposes of art. Its ductility, however, is exceedingly imperfect; for a tin wire 1/8th of an inch in diameter, is capable of supporting only 49 pounds without breaking†. It is very flexible, and produces a cracking noise when bended.
Its hardness is 6‡. Its specific gravity is 7.291; after hammering, 7.299§.
It melts at the temperature 410°, according to Dr Lewis; according to the Dijon academicians, at 419°.
When heated red hot in close vessels it sublimes. It crystallizes in the form of a rhombooidal prism.
Tin unites very readily with oxygen. When heated in contact with air, its surface soon becomes covered with a grey pellicle; when this is taken off, another appears soon after; and in this manner the whole metal may be converted into a dirty grey powder, which is the grey oxyd of tin. It is composed, according to Fourcroy, of 90 parts of tin and 10 of oxygen.
When tin is heated red hot in contact with air, it takes fire‡, and burns with a very lively white flame, and Geffre gradually sublimed. If the sublimate be examined, it is found to consist of a white powder; it is the white oxyd of tin. The white oxyd is perhaps never obtained quite pure by this process; it seems always to contain a mixture of grey oxyd; but it may be obtained pure by pouring nitric acid upon tin, and then drying it. That metal having a much stronger attraction for oxygen than azot has, decomposes the acid with the greatest rapidity, and affumes the appearance of a white powder, which is the white oxyd. This oxyd possesses many of the properties of an acid, and is therefore often called flamic acid. It seems to consist of about 77 parts of tin and 23 of oxygen‡.
The affinities of the grey oxyd of tin, according to Bergman, are as follows:
- Pyromucous acid, - Sebacic acid, - Tartaric, - Muratic, - Sulphuric, - Oxalic, - Aetic, - Phosphoric, - Nitric, - Succinic, - Fluoric, - Saccharoactic, - Citric, - Formic, - Lactic, - Acetous, - Boracic, - Prussic.
Tin combines readily with sulphur. This sulphuret may be formed by fusing the two ingredients together. It is brittle, heavier than tin, and not so fusible. It is of a bluish colour and lamellated structure, and is capable of crystallizing. According to Bergman, it is composed of 80 parts of tin and 20 of sulphur; according to Pelletier, of 85 parts of tin and 15 of sulphur*. See his Dictionary.
Koroway's Miner. ii.
It is a mass consisting of beautiful gold coloured flakes, and is used as a paint. It is composed of about 40 parts of sulphur and 60 of white oxyd of tin†. The process for making this substance was formerly very complicated. Pelletier first demonstrated its real composition, and was hence enabled to make many important improvements in the manner of manufacturing it.
Phosphorus is easily combined with tin, by melting in a crucible equal parts of filings of tin and phosphoric glass. Tin has a greater affinity for oxygen than phosphorus has. Part of the metal therefore combines with the ret, the oxygen of the glass during the fusion, and flies off in the state of an oxyd, and the rest of the tin combines with the phosphorus. The phosphuret of tin may be cut with a knife; it extends under the hammer, but separates in laminae. When newly cut it has the colour of silver; its filings resemble those of lead. When these filings are thrown on burning coals, the phosphorus takes fire. This phosphuret may likewise be formed by dropping phosphorus gradually into melted tin. According to Pelletier, to whose experiments we are indebted for the knowledge of all the phosphurets, it is composed of about 85 parts of tin and 15 of phosphorus*. Margnat also formed this phosphuret; but he was ignorant of its composition.
Tin does not seem capable of combining with carbon. It is capable of combining with most of the metals.
1. It mixes readily with gold by fusion; but the proportions in which these metals combine chemically are still unknown. When one part of tin and twelve of gold are melted together, the alloy is brittle, hard, and bad coloured. Twenty-four parts of gold and one of tin produce a pale coloured alloy, harder than gold, but possessed of considerable ductility. Gold alloyed with no more than 1/9th of tin is scarcely altered in its properties, according to Mr Alchornet; but Mr Tillet, who has lately examined this alloy, found, that whenever it was heated it broke into a number of pieces.
2. The alloy of silver and tin is hardly known. According to Gellert and succeeding chemists, it is exceedingly brittle.
3. The alloy of platinum and tin is very fusible and brittle, at least when these metals are mixed in equal proportions.
4. Mercury dissolves tin very readily, by being poured on it when melted. This amalgam crystallizes in the form of cubes, according to Daubenton; but, according to Sage, in grey brilliant square plates, thin towards the edges, and attached to each other so that the cavities between them are polygonal. It is composed of three parts of mercury and one of tin. The amalgam of tin is used to silver the backs of glass mirrors.
5. Tin unites very readily with copper, and forms alloys known by the names of bronze and bell-metal. The proportions of the ingredients cannot easily be assigned, perhaps because the alloy has an affinity both for copper and tin. The specific gravity of the alloy in all proportions is greater than the mean specific gravity of the two metals separately. When the quantity of tin is small compared to that of the copper, 1/6th for instance, the alloy is called bronze; it is brittle, yellow, and much heavier than copper; much more fusible, and less liable to be altered by exposure to the air. It was this alloy which the ancients used for sharp edged instruments before the method of working iron was brought to perfection. The bronze of the Greeks, and perhaps the as of the Romans, was nothing else. Even their copper coins contain a mixture of tin*.
6. Tin seems capable of being united to iron by fusion. That there is an affinity between these metals is evident from their adhesion when iron is dipped into melted tin. This is the method of making temple. The affinities of tin, according to Bergman, are as follows:
Zinc, Mercury, Copper, Antimony, Gold, Silver, Lead, Iron, Manganese, Nickel, Arsenic, Platinum, Bismuth, Cobalt, Sulphuret of alkali, Oxygen? Sulphur? Phosphorus?
Sect. VIII. Of Lead.
Lead appears to have been very early known. It is mentioned several times by Moses. The ancients seem to have considered it as nearly related to tin.
Lead is of a bluish white colour, somewhat darker than tin. When newly melted it is very bright, but of lead soon becomes tarnished by exposure to the air. It has scarcely any taste, but emits on friction a peculiar smell.
It is very malleable, and may be reduced to thin plates by the hammer; but its ductility is very imperfect: a wire of lead 1/9th of an inch in diameter is only capable of supporting a weight of 20½ pounds*. Its hardness is 5½; its specific gravity is 11.3323†. Kirwan's Dictionary. Its specific gravity is not increased by hammering, neither does it become harder, as is the case with other metals; a proof that the hardness which metals acquire under the hammer is in consequence of an increase of density.
It melts, according to Dr Lewis, at 540° Fahrenheit; according to the Dijon academicians, at 549°. When exposed to a violent heat it evaporates completely.
When cooled slowly, after being fused, it crystallizes. The Abbé Mongez obtained it in quadrangular pyramids, lying on one of their sides. Each pyramid was composed as it were of three layers. Pajot obtained it in the form of a polyhedron with 32 faces, formed by the concourse of six quadrangular pyramids†.
Lead stains paper or the fingers of a bluish black colour.
There is a strong affinity between this metal and oxygen. When nitric acid is poured upon it, an effervescence ensues, owing to the decomposition of the acid; the lead seizes oxygen from it, and is converted into a white powder, which may be obtained pure by evaporating it to dryness, and then washing it in pure water. This is the cobalt oxyd of lead. It is composed of about 95 parts of lead and five of oxygen†. The affinities of this oxyd are, according to Bergman, as follows:
Sulphuric acid, Sebacic, Saccharoelastic, Oxalic, Arsenic, Tartarous, Phosphoric, Muriatic, G g 2 Benzoic, When lead is exposed to heat in contact with air, its surface is soon covered with a grey pellicle; when this is taken off, another soon forms; and in this manner the whole lead may soon be converted into a dirty grey powder, which seems to be the white oxyd mixed with a little lead. When this powder is heated red hot, it assumes a deep yellow colour. This is the yellow oxyd of lead, formerly called mafficot. If the heat be continued, the colour is gradually changed to a beautiful red. This is the red oxyd of lead, formerly called minium. It is composed, as Lavoisier has shewn, of 88 parts of lead and 12 of oxygen.
The manner in which these changes are brought about is evident; the metal gradually absorbs oxygen from the atmosphere. This has been actually proved by experiment. These oxyds (if they really differ in the proportion of oxygen) resemble acids in several of their properties. They are very easily converted into glaigs by fusion. Scheele has shewn that there is also a brown oxyd of lead, which contains more oxygen than any of the others.
Sulphuret unites easily to lead by fusion. The sulphuret of lead is brittle, of a deep grey colour, and much less fusible than lead. These two substances are often found naturally combined; the compound is then called galena. Sulphuret of lead is composed, according to the experiments of Wenzel, of 868 parts of lead and 132 of sulphur.
Phosphuret of lead may be formed by mixing together equal parts of filings of lead and phosphoric glaigs, and fusing them in a crucible. It may be cut with a knife, but separates into plates when hammered. It is of a silver white colour with a tinge of blue, but it soon tarnishes when exposed to the air. This phosphuret may also be formed by dropping phosphorus into melted lead. It is composed of about 12 parts of phosphorus and 88 of lead.
Lead combines with most of the other metals.
1. Little is known concerning the alloy of lead and gold. It is said to be brittle.
(v) Benzoat of lead is decomposed by muriatic acid. Trommsdorf, Ann. de Chim. xi. 317.
(v) Suberic acid decomposes nitrat of lead. See Jameson's Mineralogy, p. 166. Zoonic acid produces the same effect, as Berthollet has observed.
(v) Schrickel places it after the three mineral acids.
(w) Contra Celsum, lib. vi. 22.—"Cellus de quibusdam Perarum mysteriis sermonem facit. Harum rerum, inquit, aliquod reperitur in Perarum doctrina Mithracisque corum mysteriis vestigium. In illis enim duae celebres conversiones, alia stellarum fixarum, errantium alia, et animae per cas transitus quodam symbolo representantur, quod hujusmodi est. Scala altas portas habens, in summa autem octava porta. Prima portarum plumbosa, altera flanen," As to the characters by which these metals were expressed, astrologers seem to have considered 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 Ω is supposed to represent the scythe of Saturn; Υ the thunderbolts of Jupiter; Ξ the lance of Mars, together with his shield; Ψ the looking-glass of Venus; and Φ the caduceus or wand of Mercury.
The alchemists, however, give a very different account of these symbols. Gold was the most perfect metal, and was therefore denoted by a circle. Silver approached nearest it; but as it was inferior, it was denoted only by a semicircle. In the character Ω the adepts discovered gold with a silver colour. The cross at the bottom expressed the presence of a mysterious something, without which mercury would be silver or gold. This something is combined also with copper; the possible change of which into gold is expressed by the character Ψ. The character Ξ 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 the top, or the upright line ought only to touch the horizontal, and not to intersect it. Philosophical gold is concealed in steel; and on this account it produces such valuable medicines. Of tin, one half is silver, and the other consists of the unknown something; for this reason the cross with the half moon appears in Υ. In lead this something is predominant; and a similitude is observed in it to silver. Hence in its character Ψ the cross stands at the top, and the silver character is only suspended on the right hand behind it.
The fact, however, according to Professor Beckmann, from whom most of the above remarks have been taken, seems to be, that these characters are mere abbreviations of the old names of the planets. "The character of Mars (he observes), according to the oldest mode of representing it, is evidently an abbreviation of the word Θορρόπης, under which the Greek mathematicians understood that deity; or, in other words, the first letter Θ with the last letter ρ placed above it. The character of Jupiter was originally the initial letter of Ζωτική and in the oldest manuscripts of the mathematical and astrological works of Julius Firmicus, the capital Ζ only is used, to which the last letter ρ 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 Θορρόπης, which was the name of that goddess. The imaginary scythe of Saturn has been gradually formed from the two first letters of his name Σατυρός, 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 Μερκούριος, one needs only look at the abbreviations in the oldest manuscripts, where they will find that the Σ was once written as Σ; they will remark also that transcribers, to distinguish this abbreviation from the rest still more, placed the Ο thus Ο, and added under it the next letter ρ. 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 Ψ from the C and ρ 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."
Sect. IX. Of Zinc.
The ancients were acquainted with a mineral to which they gave the name of Cadmea, from Cadmus, who first taught the Greeks to use it. They knew that when melted with copper it formed brals; and that when burnt, a white spongy kind of ashes was volatilised, which they used in medicine*. This mineral contained a good deal of zinc; and yet there is no proof remaining that the ancients were acquainted with that metal (x). It is first mentioned in the writings of Albertus Magnus, who died in 1280; but whether he had seen it is not so clear, as he gives it the name of marcasite of gold, which implies, one would think, that it had a yellow colour (y).
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(x) Grignon indeed says, that something like it was discovered in the ruins of an ancient Roman city in Champagne; but the substance which he took for it was not examined with any accuracy. It is impossible therefore to draw any inference whatever from his assertion. Bulletin des fouilles d'une ville Romaine, p. 11.
(y) The passages in which he mentions it are as follows:—De Mineral. lib. ii. cap. 11. "Marchafita, five marchafida..." The word zinc occurs first in the writings of Paracelsus, who died in 1541. He informs us very gravely, that it is a metal, and not a metal, and that it consists chiefly of the ashes of copper. This metal has also been called spelter.
Zinc has never been found in Europe in a state of purity, and it was long before a method was discovered of extracting it from its ore (z). Henkel pointed out one in 1721, and Von Swab obtained it by distillation in 1742, and Margraf published a process in the Berlin Memoirs in 1746.
It is of a bluish white colour, somewhat lighter than lead. It has neither taste nor smell.
It has some degree of malleability; for by compression it may be reduced into thin plates; but it cannot be drawn out into wire. It is more brittle when hot than when cold.
Its hardness is 6. Its specific gravity, when compressed, is 7.198; in its usual state, 6.862. It melts at about 609° Fahrenheit.
When allowed to cool slowly, it crystallizes in small bundles of quadrangular prisms, disposed in all directions. If they are exposed to the air while hot, they assume a blue changeable colour.
When zinc is kept melted in contact with air, it becomes covered with a grey pellicle, which gradually assumes a yellowish tint. By removing this pellicle from time to time, the whole of the metal may be reduced into a grey powder. This is the grey oxyd of zinc.
This oxyd is probably composed of about 8 parts of zinc and 15 of oxygen. When zinc is violently heated, it burns with a bright white flame, and at the same time a quantity of very light white flakes are sublimed. These flakes are the white oxyd of zinc, which contains a good deal more oxygen than the grey oxyd.
Zinc may also be oxidated by solution in acids, particularly the nitric acid. Whether the oxyd obtained by precipitating zinc from its solution in that acid, or by distilling that acid off zinc, be really different from the white oxyd, has not yet been properly ascertained; but one would be apt to suspect, from the experiments mentioned by Mr Kirwan, that it contained a good deal more oxygen.
The affinities of the oxyds, or rather of the white oxyd of zinc, are, according to Bergman, as follows:
- Oxalic acid, - Sulphuric, - Pyromelous, - Muriatic, - Saccharoactic, - Nitric, - Sebacic, - Tartaric, - Phosphoric, - Citric, - Succinic, - Fluoric, - Arsenic, - Formic, - Lactic, - Acetous, - Boracic, - Prussic, - Carbonic, - Ammonia.
There is an affinity between sulphur and zinc, as is evident from these two substances being often found united; but it is very difficult to form the sulphuret of zinc artificially, on account of the rapid oxidation and consequent volatilization of the zinc. Morveau, however, succeeded in forming it.
Zinc may be combined with phosphorus, by dropping small bits of phosphorus into it while in a state of fusion. Pelletier, to whom we are indebted for the experiment, added also a little resin, to prevent the oxidation of the zinc. Phosphuret of zinc is of a white colour, a metallic splendor, but resembles lead more than zinc. It is somewhat malleable. When hammered or filed, it emits the odour of phosphorus. When exposed to a strong heat, it burns like zinc.
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Marchafida ut quidam dicunt, est lapis in substantia, et habet multas species, quare colorum accipit ejuilibet metalli, et sic dicitur marchafida argentea et aurea, et sic dicitur albis. Metallum tamen quod colorat cum non distillat ab iugo, sed evaporat in ignem, et sic relinquitur cenis inutilis, et hic lapis notus est apud alchimicos, et in multa locis veniantur.
Lib. iii. cap. 10. "Æs autem inventur in venis lapidis, et quod est apud locum qui dicitur Gosclaria est purissimum et optimum, et toti substantiae lapidis incorporatum, ita quod totus lapsis est ficat marchafida aurea, et profundatum est melius ex eo quod purius.
Lib. v. cap. 5. "Dicimus igitur quod marchafida duplicem habet in sui creatione substantiam, argentii vivi scilicet mortificati, et ad fixationem approximantis, et sulphuris aduentis. Ipsum habere sulphuretatem comprehensam manifesta experientia. Nam cum sublimetur, ex illa emanat substantia sulphurea manifesta comburens. Et sine sublimatione similiter perpenditur illus sulphureitas.
"Nam si ponatur ad ignitionem, non fulcitur illam pruinosam inflammatione sulphuris inflammetur, et ardeat. Ipsum vero argentii vivi substantiam manifestat habere sensibiliter. Nam albedinem praestat Veneri meri argentii, quemadmodum et ipsum argentum vivum, et colorum in ipsius sublimatione caelestium praefere, et luciditatem manifestam metallicam habere videmus, quae certum reddunt artificem Alchimiae, illam habet substantias continere in radice iusa."
(z) The real discoverer of this method appears to have been Dr Isaac Lawson. See Pett, III. diff. 7. and Watson's Chemical Essays.
(a) Pott observed, that it was 1/10th heavier than the zinc from which it was obtained; and Mr Boyle had long before ascertained the same fact.—Shaw's Boyle, II. 391, 394.
This oxyd of zinc was well known to the ancients. Dioscorides describes the method of preparing it. The ancients called it pompheya, the early chemists gave it the name of lana philosophica. Dioscorides compares it to wool, Phosphorus combines also with the oxyd of zinc, a compound which Margraf had obtained during his experiments on phosphorus. When 12 parts of oxyd of zinc, 12 parts of phosphoric glaas, and two parts of charcoal powder, are distilled in an earthen ware retort, and a strong heat applied, a metallic substance sublimes of a silver-white colour, which when broken has a viscous appearance. This, according to Pelletier, is phosphuret of oxyd of zinc. When heated by the blowpipe, the phosphorus burns, and leaves behind a glass transparent while in fusion, but opaque after cooling.
Zinc also combines with carbon, and forms carburet of zinc. The French chemists have shewn that zinc generally contains some carbon.
Zinc combines with most of the metals:
1. It mixes with gold in any proportion. The alloy is the whiter and the more brittle the greater quantity of zinc it contains. An alloy, consisting of equal parts of these metals, is very hard and white, receives a fine polish, and does not tarnish readily. It has therefore been proposed by Mr Malouin as very proper for the specula of telephones. One part of zinc is laid to destroy the ductility of 100 parts of gold.
2. The alloy of silver and zinc is easily produced by fusion. It is brittle.
3. Platinum combines very readily with zinc. The alloy is brittle, pretty hard, very fusible, of a bluish white colour, not so clear as that of zinc.
4. Zinc may be combined with mercury by fusion. The amalgam is solid. It crystallizes when melted and cooled slowly into lamellated hexagonal figures, with cavities between them. They are composed of one part of zinc and two and a half of mercury. It is used to rub on electrical machines, in order to excite electricity.
5. Zinc combines very readily with copper. This alloy, which is called brafs, was known to the ancients. They used an ore of zinc to form it, which they called cadmia. This alloy was very much valued by the ancients. Dr Watson has proved that it was to brafs which they gave the name of orichalcum. Their ore was copper or rather bronze (a). Brafs is composed of about three parts of copper and one of zinc. It is of a beautiful yellow colour, more fusible than copper, and not so apt to tarnish. It is malleable, and so ductile that it may be drawn out into wire. When the alloy contains three parts of zinc and four of copper, it assumes a colour nearly the same with gold, but it is not so malleable as brafs. It is then called pinchbeck, prince's metal, or Prince Rupert's metal.
6. The alloy of iron and zinc has scarcely been examined; but Malouin has shewn that zinc may be used instead of tin to cover iron plates; a proof that there is antimony, an affinity between the two metals.
7. Tin and zinc combine easily. The alloy is harder than tin. This alloy is often the principal ingredient in the compound called pewter.
8. Mr Gmelin has succeeded in forming an alloy of zinc and lead by fusion. He put some dust into the mixture, and covered the crucible, in order to prevent the evaporation of the zinc. When the zinc exceeded the lead very much, the alloy was malleable, and much harder than lead. A mixture of two parts of zinc and one of lead formed an alloy more ductile and harder than the last. A mixture of equal parts of zinc and lead formed an alloy differing little in ductility and colour from lead; but it was harder, and more susceptible of polish, and much more sonorous. When the mixture contained a smaller quantity of zinc, it still approached nearer the ductility and colour of lead, but it continued harder, more sonorous, and susceptible of polish, till the proportions approached to one of zinc and 16 of lead, when the alloy differed from the last metal only in being somewhat harder.
The affinities of zinc, according to Bergman, are as follows:
| Copper | Antimony | |--------|----------| | Tin | Mercury | | Silver | Gold | | Cobalt | Arsenic | | Platinum | Bismuth | | Lead | Nickel | | Iron | |
Sect. X. Of Antimony.
The ancients were acquainted with an oxyd of antimony to which they gave the names of σιλβανος and σιλβιον. Pliny informs us, that it was found in silver ore; and *Pliny, I., we know that at present there are silver ores † in which xxiii. c. 6, it is contained. It was used as an external application Miner. ii. to sore eyes; and Pliny gives us the method of preparing it ‡. Galen supposes that the τελεγραφος of Hippocrates *Pliny, Hist. was a preparation of antimony; but this wants proof. It does not appear, however, that the ancients considered this substance as a metal, or that they knew antimony in a state of purity (c). Who first extracted it from its ore we do not know; but Basil Valentine, a chemist of the 16th century, is the first who describes the process.
(b) The ancients do not seem to have known accurately the difference between copper, brafs, and bronze. Hence the confusion observable in their names. They considered brafs as only a more valuable kind of copper, and therefore often used the word as indifferently to denote either. It was not till a late period that mineralogists began to make the distinction. They called copper as cyprium, and afterwards only cyprum, which in processes of war was converted into cyprum. When these changes took place is not known accurately. Pliny uses cyprum, lib. xxxvi. c. 26. The word cyprum occurs first in Spartan, who lived about the year 290. He says in his life of Caracalla, cancelli ex ore vel cupro.
(c) Mr Roux indeed, who at the request of Count Caylus analysed an ancient mirror, found it composed of copper, lead, and antimony. This would go far to convince us that the ancients knew this metal, provided it could be proved that the mirror was really an ancient one; but this point appears to be extremely doubtful. Antimony. Sulphuret of antimony is easily melted by a moderate heat; if the heat be continued, the sulphur sublimes, and at the same time the antimony absorbs oxygen, and is converted into a grey oxyd. This sulphuret is composed of 74 parts of antimony and 26 of sulphur.
The grey oxyd of antimony is also capable of combining with about $\frac{3}{10}$ of sulphur. This compound, by fusion, may be converted into glass. It was formerly used in medicine under the name of glass of antimony.
When equal parts of antimony and phosphoric glass are mixed together with a little charcoal powder, and then melted in a crucible, phosphuret of antimony is produced. It is of a white colour, brittle, appears laminated when broken, and at the fracture there appear a number of small cubic facettes. When melted it emits a green flame, and then sublimes in the form of a white powder. Phosphuret of antimony may likewise be prepared by fusing equal parts of antimony and phosphoric glass, or by dropping phosphorus into melted antimony.
Antimony is capable of combining with most of the metals.
1. Gold may be alloyed with antimony by fusing them together. The antimony is afterwards separable by an intense heat. This alloy is little known, and has never been applied to any use.
2. The alloy of silver and antimony is brittle, and its specific gravity, as Gellert has observed, is greater than intermediate between the specific gravities of the two metals which enter into it.
3. Platinum easily combines with antimony. The alloy is brittle, and much lighter than platinum. The antimony cannot afterwards be completely separated by heat.
4. Mercury does not easily combine with antimony. Mr Gellert succeeded in amalgamating this metal by putting it into hot mercury, and covering the whole with water.
5. Copper combines readily with antimony by fusion. The alloy is of a beautiful violet colour, and its specific gravity is greater than intermediate.
6. Iron combines with antimony, and forms a brittle hard alloy, the specific gravity of which is less than intermediate. The magnetic quality of iron is much more diminished by being alloyed with antimony than with any other metal.
7. The alloy of tin and antimony is white and brittle; its specific gravity is less than intermediate.
8. When equal quantities of lead and antimony are fused, the alloy is porous and brittle: three parts of lead and one of antimony form a compact alloy, malleable, and much harder than lead: 12 parts of lead and one of antimony form an alloy very malleable, and a good deal harder than lead: 16 parts of lead and one of antimony form an alloy which does not differ from lead except in hardness. This alloy forms printers types.
9. Zinc and antimony form a brittle alloy, the specific gravity of which is less than intermediate. The alloys of antimony are little known. Gellert is almost the only person who has examined them. It would require a great number of experiments to be able to fix the proportions of their ingredients.
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(d) Muriatic acid decomposes benzoate of antimony. Trommsdorff, Ann. de Chim. xi. 317. The affinities of antimony are, according to Bergman, as follows:
Iron, Copper, Tin, Lead, Nickel, Silver, Bismuth, Zinc, Gold, Platinum, Mercury, Arsenic, Cobalt, Sulphuret of arsenic, Sulphur, Phosphorus?
Sect. XI. Of Bismuth.
The ancients appear to have known nothing of bismuth, nor do we know who discovered it; but it is first mentioned by George Agricola, who was born about the end of the 15th century.
Bismuth is of a yellowish or reddish white colour, and almost deliquescent both of taste and smell.
It is brittle. Its hardness is 6*. Its specific gravity is 9.8227†. It melts at 460° Fahrenheit ‡.
When heated in close vessels, it sublimes. When allowed to cool slowly after fusion, it crystallizes.
Bismuth is not altered by water. When exposed to the air it soon tarnishes.
When bismuth is kept fused in contact with air, it is gradually oxidized. When heated red hot, it emits a very faint blue flame, and its oxyd evaporates in the form of a yellowish smoke. When this smoke is collected, it is found to consist of a brown-coloured powder.
This is the brown oxyd of bismuth. It is composed of about 9 parts of bismuth and 6 of oxygen*.
Bismuth decomposes nitric acid with great rapidity, by attracting its oxygen. If the quantity of acid be considerable, it dissolves the oxyd as it forms; but the greater part of it may be precipitated by diluting the acid with water. This precipitate, which is a white powder, is white oxyd of bismuth. It is composed of about 84 parts bismuth and 16 of oxygen†.
The affinities of the oxyds of bismuth are, according to Bergman, as follows:
Oxalic acid, Arsenic, Tartarous, Phosphoric, Sulphuric, Schabic, Muriatic, Benzoic (z)‡, Nitric, Fluoric, Saccharolic, Succinic, Citric,
Formic, Lactic, Acetous, Prussic, Carbonic, Ammonia.
Salphur combines readily with bismuth by fusion. Sulphuret of bismuth is of a bluish grey colour, and crystallizes into beautiful tetrahedral needles. It is composed of 85 parts of bismuth and 15 of sulphur‡.
There appears to be little affinity between bismuth and phosphorus. Mr. Pelletier attempted to produce the phosphuret of bismuth by various methods without success. When he dropped phosphorus, however, into bismuth in fusion, he obtained a substance which did not appear to differ from bismuth, but which, when exposed to the blow-pipe, gave evident signs of containing phosphorus. Phosphuret of bismuth, according to Pelletier, is composed of about 96 parts of bismuth and four of phosphorus*.
Bismuth combines readily with most of the metals.
1. Equal parts of bismuth and gold form a brittle alloy, nearly of the same colour with bismuth†.
2. Equal parts of bismuth and silver form also a brittle alloy, but less so than the last. The specific gravity of both these is greater than intermediate‡.
3. The alloy of bismuth and platinum is also very brittle. When exposed to the air it assumes a purple, violet, or blue colour. The bismuth may be separated by heat§.
4. Mercury dissolves bismuth very easily. The amalgam is more fluid than pure mercury, and has the property of dissolving lead and rendering it also fluid‖. It is capable, however, of crystallizing. The crystals are either octahedrons, lamellated triangles, or hexagons. They are composed of one part of bismuth and two of mercury‖.
5. The alloy of copper and bismuth is not so red as copper.
6. Nothing is known concerning the alloy of iron and bismuth.
7. Bismuth and tin unite readily. A small portion of bismuth increases the brightness, hardness, and toughness of tin; it often therefore enters into the composition of the compound called pewter. Equal parts of tin and bismuth form an alloy that melts at 280°; eight parts of tin and one of bismuth, melt at 390°; two parts of tin and one of bismuth, at 330°†.
8. The alloy of lead and bismuth is of a dark grey colour, a close grain, but very brittle.
9. Bismuth does not combine with zinc.
10. The alloy of antimony and bismuth is unknown. Bismuth likewise enters into triple compounds with metals: Two parts of lead, three of tin, and five of bismuth, form an alloy which melts at the heat of boiling water, which is 212°.
The affinities of bismuth, according to Bergman, are as follows:
Lead, Silver, Gold, H h
Mercury,
(z) Muriatic acid decomposes benzoat of bismuth.—Trommsdorf, Ann. de Chim. xi. 317. Sect. XII. Of Arsenic.
The word arsenic (arsenic) occurs first in the works of Dioscorides, and of some other authors who wrote about the beginning of the Christian era. It denotes in their works the same substance which Aristotle had called arsenicum (r), and his disciple Theophrastus arsenicum, which is a reddish coloured mineral, composed of arsenic and sulphur, used by the ancients in painting, and as a medicine.
The white oxyd of arsenic, or what is known in commerce by the name of arsenic, is mentioned by Avicenna in the 11th century; but at what period the metal called arsenic was first extracted from that oxyd is unknown. Paracelsus seems to have known it. It is mentioned by Schroeder in his Pharmacopoeia published in 1649.
Arsenic, when pure, is of a bluish white colour. It is exceedingly brittle. Its hardness is 7. Its specific gravity is 5.102.
When exposed to the temperature of 354° in close vessels it sublimes, and crystallizes in regular tetrahedrons.
It is not much altered by water. Boiling water, however, is capable of dissolving, and retaining the strength of arsenic; but that part of the metal is no doubt reduced to the state of an oxyd.
When arsenic is exposed to the open air, it very soon loses its lustre, and is gradually converted into a greyish black substance by combining with oxygen. This is called the grey oxyd of arsenic.
When exposed to a moderate heat in contact with air, it sublimes in the form of a white powder, and at the same time emits a smell resembling garlic. If the heat be increased, it burns with an obscure bluish flame. This sublimate is called the white oxyd of arsenic, which is composed of 93 parts of arsenic and 7 of oxygen.
It is of a sharp acid taste, which at last leaves an impression of sweetness, and is one of the most virulent poisons known. It has an allacious smell. It is soluble in 80 parts of water at the temperature of 65°, and in 15 parts of boiling water. When this solution is evaporated, the oxyd crystallizes. When heated to 283°, it sublimes; if heat be applied in close vessels, it becomes pellucid like glass, but when exposed to the air it soon recovers its former appearance. The specific gravity of this glass is 5.000; that of the white oxyd, 3.706. This oxyd is capable of combining with most of the metals, and in general renders them brittle. Its affinities, according to Bergman, are as follows:
1. Muriatic acid, 2. Oxalic acid, 3. Sulphuric acid, 4. Nitric acid, 5. Sulfuric acid, 6. Tartaric acid, 7. Phosphoric acid, 8. Fluoric acid, 9. Saccharic acid, 10. Succinic acid, 11. Citric acid, 12. Formic acid, 13. Lactic acid, 14. Arsenic acid, 15. Acetic acid, 16. Prussic acid, 17. Ammonia, 18. Water, 19. Alcohol.
Arsenic, or rather the white oxyd of arsenic, is capable of combining with an additional dose of oxygen. The compound produced is arsenic acid, first discovered by Scheele, which contains 91 parts of arsenic and 9 of oxygen.
Arsenic combines readily with sulphur. When heat is applied to a mixture of white oxyd of arsenic and pure sulphur, the oxyd is decomposed, part of the sulphur combines with its oxygen, and the remainder unites with sulphur, the reduced metal. The sulphuret of arsenic produced by this process is of a yellow colour, and was formerly called orpiment. It is composed, according to Wellrum, of 20 parts of arsenic and 80 of sulphur. It is often found native. If a stronger heat be applied, so as to melt the sulphuret, it sublimes a scarlet colour, and is much less volatile than formerly. This new compound was formerly called realgar. It is composed, according to Wellrum, of 80 parts of arsenic and 20 of sulphur. The difference therefore between it and orpiment is evident. During the fusion part of the sulphur without doubt sublimes. It might be called red sulphuret of arsenic.
Arsenic combines readily with phosphorus. The phosphuret of arsenic may be formed by distilling equal parts of its ingredients over a moderate fire. It is black and brilliant, and ought to be preserved in water. It may be formed likewise by putting equal parts of phosphorus and arsenic into a sufficient quantity of water, and keeping the mixture moderately hot for some time.
Arsenic unites with most metals, and in general renders them more brittle and more fusible.
1. Melted gold takes up 1/8th of arsenic. The alloy is brittle and pale. 2. Melted silver takes up 1/4th of arsenic. The alloy is brittle. 3. The alloy of platinum and arsenic is brittle and very fusible. It was first formed by Scheffer. The arsenic may be separated by heat. 4. The amalgam of arsenic is composed of five parts of mercury and one of arsenic. 5. Copper takes up 1/8th of arsenic. This alloy is white;
(f) Pliny seems to make a distinction between sandaracha and arsenic. See Lib. xxxiv. c. 18. white; and when the quantity of arsenic contained in it is small, both ductile and malleable. It is called white tombac.
6. Iron is capable of combining with more than its own weight of arsenic. This alloy is white, brittle, and capable of crystallizing. It is found native.
7. The alloy of tin and arsenic is harder and more porous than tin, and has much resemblance externally to zinc. Tin often contains a small quantity of arsenic.
8. Lead takes up \( \frac{1}{3} \)th of arsenic. The alloy is brittle and dark coloured.
9. Zinc takes up \( \frac{1}{4} \)th of arsenic, antimony \( \frac{1}{4} \)th, and bismuth \( \frac{1}{4} \)th.
The affinities of arsenic, according to Bergman, are as follows:
- Nickel, - Cobalt, - Copper, - Iron, - Silver, - Tin, - Gold, - Platinum, - Zinc, - Antimony, - Sulphuret of alkali, - Sulphur, - Phosphorus.
Sect. XIII. Of Cobalt.
A mineral called cobalt (c), of a grey colour, and very heavy, has been used in different parts of Europe since the 15th century to tinge glas's of a blue colour. From this mineral Brandt obtained in 1733 a new metal, to which he gave the name of cobalt.
Cobalt is of a white colour, inclining to a bluish or steel grey. When pure, it is somewhat malleable while red hot. Its hardness is 8. Its specific gravity is 8.15 (it). It requires for fusion a heat at least as great as that required for iron, which melts at 1300° Wedgewood. No heat has been produced great enough to volatilize it.
Cobalt, when pure, does not seem to be affected by air or water.
It is attracted by the magnet.
It is not oxidated by heat without very great difficulty; but it has the property of decomposing nitric acid, and of attracting oxygen by that means with great rapidity.
The oxyd of cobalt is of so deep a blue as to appear black. The oxyd procured by heat is composed of 88 parts of cobalt and 12 of oxygen; that by nitric acid contains about 77 parts of cobalt and 23 of oxygen.
Its affinities, according to Bergman, are as follows:
- Oxalic acid, - Muriatic, - Sulphoric, - Tartarous, - Nitric, - Sebacic, - Phosphoric, - Fluoric, - Saccharoactic, - Succinic, - Citric, - Formic, - Lactic, - Acetous, - Arsenic, - Boracic, - Prussic, - Carbonic, - Ammonia.
The sulphuret of cobalt is not formed without difficulty. It is scarcely known.
Phosphuret of cobalt may be formed by heating the phosphorus metal red hot, and then gradually dropping in small bits of phosphorus. It contains about \( \frac{1}{3} \)th of phosphorus. It is white and brittle, and when exposed to the air soon loses its metallic lustre. The phosphorus is separated by heat, and the cobalt is at the same time oxidated. This phosphuret is much more fusible than pure cobalt.
The combinations of cobalt with other metals have been very little examined into.
1. The alloy of gold and cobalt is not known.
2. Cobalt does not combine with silver by fusion; but, according to Gellert, the alloy of silver and cobalt may be formed: it is brittle and of a grey colour.
3. The alloy of platinum and cobalt is unknown.
---
(c) The word cobalt seems to be derived from cobaltus, which was the name of a spirit that, according to the superstitious notions of the times, haunted mines, destroyed the labours of the miners, and often gave them a great deal of unnecessary trouble. The miners probably 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; for as it was not known at first to what use the mineral could be applied, it was thrown aside as useless. It was once customary in Germany to introduce into the church-service a prayer that God would preserve miners and their works from kobolds and spirits. See Beckmann's History of Inventions, II. 362.
Matheius, in his tenth sermon, where he speaks of cadmia fulgida (probably cobalt ore), says, "Ye miners call it kobolt; the Germans call the black devil and the old devil's whores and flags, old and black kobol, which by their witchcraft do injury to people and to their cattle."
Lehmann, Paw, Delaval, and several other philosophers, have supposed that fulgida (oxyd of cobalt melted with glass and pounded) was known to the ancients, and used to tinge the beautiful blue glass still visible in some of their works; but we learn from Gmelin, who analysed some of these pieces of glass, that they owed their blue colour, not to the presence of cobalt but of iron.
According to Lehmann, cobalt ore was first used to tinge glass blue by Christopher Schurter, a glass-maker at Platten, about the year 1540.
(ii) Berg. II. 231. According to Briffon, 78119. Nickel.
4. Mercury does not appear to amalgamate with cobalt.
5. The alloy of copper and cobalt is scarcely known.
6. The alloy of iron and cobalt is very hard, and not easily broken. Cobalt generally contains some iron, from which it is with great difficulty separated.
7. The alloy of tin and cobalt is of a light violet colour.
8. Cobalt does not combine with lead by fusion.
9. The alloy of zinc and cobalt is not formed without difficulty.
10. The alloy of antimony and cobalt is unknown.
11. Cobalt does not combine with bismuth by fusion.
12. Arsenic combines very readily with cobalt. The alloy is brittle, much more fusible, and more easily oxidized than pure cobalt.
The affinities of cobalt are as follows:
- Iron, - Nickel, - Arsenic, - Copper, - Gold, - Platinum, - Tin, - Antimony, - Zinc, - Sulphuret of alkali, - Sulphur, - Phosphorus?
Sect. XIV. Of Nickel.
A heavy mineral of a red colour is met with in several parts of Germany, which bears a strong resemblance to an ore of copper; but none of that metal can be extracted from it; for this reason the Germans called it kupfer nickel (devil's copper). Hieron mentioned it in 1694. Cronstedt was the first chemist who examined it with accuracy. He concluded from his experiments, which were published in the Stockholm Transactions for 1751 and 1754, that it contained a new metal, to which he gave the name of nickel.
Some chemists, particularly Mr Sage, affirmed, that it contained no new metal, but merely a compound of various known metals, which could be separated from each other by the usual processes. These affections induced Bergman to undertake a very laborious course of experiments, in order if possible to obtain nickel in a state of purity; for Cronstedt had not been able to separate a quantity of arsenic, cobalt, and iron, which adhered to it with much obstinacy. These experiments have been very fully detailed in the article Chemistry in the Encyclopaedia, to which we beg leave to refer. Bergman has shewn, that nickel possesses peculiar properties, and that it can neither be reduced to any other metal, nor formed artificially by any combination of metals. It must therefore be considered as a peculiar metal. It may possibly be a compound, and so likewise many other metals; but we must admit every thing to be a peculiar body which has peculiar properties, and we must admit every body to be simple till some proof be actually produced that it is a compound; otherwise we forfeit the road of science, and get into the regions of fancy and romance.
Nickel is of a greyish white colour, and when less pure inclines a little to red.
It is both ductile and malleable. Its hardness is 8. Its specific gravity 9,000. It requires for fusion a temperature at least equal to 150° Wedgwood.
It is powerfully attracted by the magnet, and is even possessed of the property of attracting iron. This induced Bergman to suppose that nickel, when purest, was still contaminated with about one third of iron; but as this is the only proof of its containing iron, Klaproth, with reason, deems it an insufficient one, and considers attraction by the magnet as a property of nickel.
When exposed to a strong heat, nickel is oxidated slowly. Its oxyd is of a brown colour; if impure, it is greenish. The oxyd of nickel, according to Klaproth, is composed of 77 parts of nickel and 33 of oxygen.
Its affinities, according to Bergman, are as follows:
- Oxalic acid, - Muriatic, - Sulphuric, - Tartarous, - Nitric, - Sebatic, - Phosphoric, - Fluoric, - Saccharolactic, - Succinic, - Citric, - Formic, - Lactic, - Acetous, - Arsenic, - Boracic, - Prufic, - Carbonic, - Ammonia, - Potash, - Soda?
Cronstedt found that nickel combined readily with sulphur by fusion. The sulphuret which he obtained was yellow and hard, with small sparkling facets; but the nickel which he employed was impure.
Nickel combines very readily with phosphorus, either by fusing it along with phosphoric glass, or by dripping phosphorus into it while red hot. The phosphuret of nickel is of a white colour, and when broke exhibits the appearance of very slender prisms collected together. When heated, the phosphorus burns, and the metal is oxidated. It is composed of 83 parts of nickel and 17 of phosphorus. The nickel, however, on which this experiment was made, was not pure.
Little is known concerning the alloys of nickel with other metals. Equal parts of silver and nickel form a white ductile alloy. Equal parts of copper and nickel form a red ductile alloy. The compounds which this metal forms with tin and zinc are brittle. It does not combine with mercury. It has a very strong affinity for iron, cobalt, and arsenic, and is scarcely ever found except combined with some of them.
Its affinities, according to Bergman, are as follows:
- Iron, - Cobalt, - Arsenic, - Copper, Copper, Gold, Tin, Antimony, Platinum, Bismuth, Lead, Silver, Zinc, Sulphuret of alkali, Sulphur, Phosphorus?
Sect. XV. Of Manganese.
The dark grey mineral called manganese, in Latin magnesia (according to Boyle, from its resemblance to the magnet), has been long known and used in making pigs. A mine of it was discovered in England by Mr. Boyle. It was long supposed to be an ore of iron; but Pott and Cronstedt having demonstrated that it contained very little of that metal, the latter referred it in his Mineralogy to a distinct order of earths, which he called terre magnetica. Bergman, from its specific gravity, and several other qualities, suspected that it was a metallic oxyd; he accordingly made several attempts to reduce it, but without success; the whole mass either assuming the form of ferric, or yielding only small separate globules attracted by the magnet. This difficulty of fusion led him to suspect that the metal he was in quest of bore a strong analogy to platinum. In the mean time, Dr. Gahn, who was making experiments on the same mineral, actually succeeded in reducing it by the following process: He lined a crucible with charcoal powder moistened with water, put into it some of the mineral formed into a ball by means of oil, then filled up the crucible with charcoal powder, fitted another crucible over it, and exposed the whole for about an hour to a very intense heat. At the bottom of the crucible was found a metallic button, or rather a number of small metallic globules, equal in weight to one third of the mineral employed*. It is easy to see by what means this reduction was accomplished. The charcoal attracted the oxygen from the oxyd, and the metal remained behind. This metal is called manganese.
Manganese is of a greyish white colour. It is not malleable, and yet not so brittle as to be easily broken. Its hardness is 8†. Its specific gravity is 7,000‡. Its fusion requires so great a heat, that it has been very seldom accomplished.
When reduced to powder, it is attracted by the magnet.
When exposed to the air, it very soon tarnishes, and assumes a darker colour, till at last it becomes black and friable. This change is produced by the absorption of oxygen. It takes place much more rapidly if heat be applied to the metal. The substance thus obtained is the black oxyd of manganese. This oxyd is found in great abundance in nature, though scarcely ever in a state of purity. It is composed of 75 parts of manganese and 25 of oxygen*.
If a quantity of muriatic acid be poured upon this manganese oxyd, and heat applied, part of the acid combines with some of the oxygen of the oxyd, and flies off in yellow fumes. The oxyd is dissolved in the ret. If potash be added to this solution, a white powder is precipitated. This is the white oxyd of manganese. It contains, according to Bergman, about 80 parts of manganese and 20 of oxygen. It soon attracts more oxygen when exposed to the air, and is converted into black oxyd.
The affinities of the white oxyd, according to Bergman, are as follows:
- Oxalic acid, - Citric, - Phosphoric, - Tartarous, - Fluoric, - Muriatic, - Sulphuric, - Nitric, - Saccharinic, - Succinic, - Sebacic, - Tartaric, - Formic, - Lactic, - Acetous, - Prussic, - Carbonic.
The sulphuret of manganese is unknown.
Phosphorus may be combined with manganese by phosphorus gliss; or by dropping phosphorus upon red hot manganese. The phosphuret of manganese is of a white colour, brittle, granulated, disposed to crystallize, not altered by exposure to the air, and more fusible than manganese. When heated, the phosphorus burns and the metal becomes oxydated ‡.
Manganese combines readily with carbon by fusion (1).
Little is known concerning the alloys of manganese. It combines readily with copper. The compound, according to Bergman, is very malleable, its colour is red, and it sometimes becomes green by age. Gmelin made a number of experiments to see whether this alloy could be formed by fusing the black oxyd of manganese along with copper. He partly succeeded, and proposed to substitute this alloy instead of the alloy of copper and arsenic, which is used in the arts †. We believe, however, that upon trial the new alloy has been found not to answer.
Manganese combines readily with iron; indeed it has scarcely ever been found quite free from some mixture of that metal. It combines also very easily with arsenic and tin, not easily with zinc, and not at all with mercury §.
The affinities of manganese, according to Bergman, are as follows:
- Copper, - Iron, - Gold,
Silver,
(1) Bergman, III. 379.—Sometimes manganese is very speedily oxydated by exposure to the air; sometimes scarcely altered by it, as Klaproth and Pelletier have observed. Mr Kirwan supposes, that the manganese which is soon altered contains carbon, and that this is the cause of the difference. See Miner. II. 288. Silver, Tin, Sulphuret of alkali, Phosphorus? Carbon?
The three metals, cobalt, nickel, and manganese, resemble iron in several particulars: Like it, they are magnetic, very hard, and very difficult to fuse; but they differ from it in specific gravity, malleability, and in the properties of all their combinations with other substances; the oxyds, for instance, of iron, cobalt, nickel, and manganese, possess very different qualities.
**Sect. XVI. Of Tungsten.**
There is a mineral found in Sweden of an opaque white colour and great weight; from which last circumstance it got the name of tungsten, or ponderous stone. Some mineralogists considered it as an ore of tin, others supposed that it contained iron. Scheele analysed it in 1781, and found that it was composed of lime and a peculiar earthy-like substance, which he called from its properties tungstic acid. Bergman conjectured that the basis of this acid was a metal; and this conjecture was soon after fully confirmed by the experiments of Messrs D'Elhuyart, who obtained the same substance from a mineral of a brownish black colour, called by the Germans wolfram, which is sometimes found in tin mines. This mineral they found to contain 65% of tungstic acid; the rest of it consisted of manganese, iron, and tin. This acid substance they mixed with charcoal powder, and heated violently in a crucible. On opening the crucible after it had cooled, they found in it a button of metal, of a dark brown colour, which crumbled to powder between the fingers. On viewing it with a glas, they found it to consist of a congeries of metallic globules, some of which were as large as a pin head. The metal thus obtained is called tungsten. The manner in which it was produced is evident; tungstic acid is composed of oxygen and tungsten; the oxygen combined with the carbon, and left the metal in a state of purity.
Tungsten is externally of a brown colour, internally of a fleck grey. Its specific gravity is 17,600. It is more fusible than manganese.
When heat is applied to tungsten it is converted into a yellow powder, composed of 80 parts of tungsten and 20 of oxygen. This is the yellow oxyd of tungsten or tungstic acid.
The sulphuret of tungsten is of a bluish black colour, hard, and capable of crystallizing.
Phosphorus is capable of combining with tungsten.
Of the alloys of tungsten we know nothing, except from the experiments of Elhuyarts, which have been transcribed into the article chemistry in the Encyclopaedia; to which, therefore, we beg leave to refer.
**Sect. XVII. Of Molybdenum.**
The Greek word molybdenea, and its Latin translation plumbea, seem to have been employed by the ancients to denote various oxyds of lead; but by the moderns they were applied indiscriminately to all substances possessed of the following properties: Light, friable, and soft, of a dark colour and greasy feel, and which leave a film upon the fingers. Scheele first examined these minerals with attention. He found, that two very different substances had been confounded together. To one of these, which is composed of carbon and iron, and which has been already described, he appropriated the word plumbea; the other he called molybdenea.
Molybdenea is composed of fealy particles adhering slightly to each other. Its colour is bluish, very much resembling that of lead. Scheele analysed it, and obtained sulphur and a whitish powder, which possessed the properties of an acid, and which, therefore, he called acid of molybdenea. Bergman first suspected that the basis of this acid was a metal. It was at the request of Bergman and Scheele that Mr Hielm began the laborious course of experiments by which he succeeded in obtaining a metal from this acid. His method was to form it into a paste with linseed oil, and then to apply a very strong heat. This process he repeated several times successively. Kluproth and Pelletier also attempted to reduce it, and with equal success. The metal is molybdenum (K).
Molybdenum is externally of a whitish yellow colour, but its fracture is a whitish grey.
Hitherto it has only been procured in small grains, agglomerated together in brittle masses.
Its specific gravity is 7,500. It is almost fusible in our fires.
When exposed to a strong heat, it is gradually converted into a whitish-coloured oxyd. When nitric acid is poured upon it, molybdenum attracts oxygen, and is converted into a white oxyd, which possesses the properties of an acid. This is the molybdic acid.
Molybdenum combines readily with sulphur; and the compound has exactly the properties of molybdenea, the substance which Scheele decomposed. Molybdenea is therefore sulphuret of molybdenum. The reason that Scheele obtained from it molybdic acid was, that the metal combined with oxygen during his process.
Molybdenum is also capable of combining with phosphorus.
Few of the alloys of this metal have been hitherto examined.
It seems capable of uniting with gold. The alloy is probably of a white colour.
It combines readily with platinum while in the state of an oxyd. The compound is fusible. Its specific gravity is 20,000.
The alloys of molybdenum with silver, iron, and copper, are metallic and friable; those with lead and tin are powders which cannot be fitted.
**Sect. XVIII. Of Uranium.**
There is a mineral found in the George Wagfort mine at Johann Georgenthal in Saxony, partly in a pure or unmixed state, and partly stratified with other kinds of stones and carths. The first variety is of a blackish colour inclining to a dark iron grey, of moderate splendour, a close texture, and when broken presents a somewhat uneven, and, in the smallest particles, a conchoidal surface. It is quite opaque, tolerably hard, and on being pounded yields a black powder. Its specific gravity is about 7,500. The second sort is distinguished
(x) This name was given it by Hielm. This fossil was called pebblestone; and mineralogists, misled by the name (i.), had taken it for an ore of zinc, till the celebrated Werner, convinced from its texture, hardness, and specific gravity, that it was not a blend, placed it among the ores of iron. Afterwards he suspected that it contained tungsten; and this conjecture was seemingly confirmed by the experiments of some German mineralogists, published in the Miners Journal. But Klaproth, whose analyses always display the most consummate skill, joined with the most rigid accuracy, examined this mineral about the year 1789, and found that it consisted chiefly of sulphur combined with a peculiar metal, to which he gave the name of uranium (m).
Uranium is of a dark grey colour; internally it is somewhat inclined to brown. Its malleability is unknown. Its hardness is about 6. It requires a stronger heat for fusion than manganite. Indeed Klaproth only obtained it in very small conglutinated metallic grains, forming altogether a porous and foamy mass—its specific gravity is 6.440.
When exposed for some time to a red heat, it suffers no change. By means of nitric acid, however, it may be converted into a yellow powder. This is the yellow oxyd of uranium. This oxyd is found native mixed with the mineral above described. Its affinities have not yet been determined.
Uranium is capable of combining with sulphur. The mineral from which Mr Klaproth first obtained it is a native sulphuret of uranium.
Nothing is known concerning the alloys or affinities of uranium.
Sect. XIX. Of Titanium.
There is a mineral found in Hungary which, from its external appearance, has been called red lead; but Klaproth, who examined it about the year 1795, discovered that it consisted chiefly of a peculiar metal, to which he gave the name of titanium.
Titanium is of a brownish red colour, and considerable lustre. It is brittle. Its hardness is 9; its specific gravity 4.18.
When exposed to a strong heat in a clay crucible, it suffered no alteration, except that its colour became browner; but in a coal crucible it lost its lustre and broke to pieces.
It is found naturally crystallized in right-angled quadrangular prisms, longitudinally furrowed, and about 1 inch in length.
No acid had any effect in oxidizing it; but when mixed with five times its weight of potash, and heated in a porcelain furnace, it melted, and formed when cold a dense greyish mass, the surface of which was crystal-lized. When dissolved in boiling water, it soon let fall a white powder, weighing about one third more than the titanium employed. This is the oxyd of titanium. Fifty grains of it were reduced by ignition to 38. While hot it was yellowish, but, like oxyd of zinc, became white as it cooled. When heated on charcoal, it affirms first a rosy red, and afterwards a flake blue colour, and at last melts into an imperfect bead with a finely striated surface. Mr Klaproth did not succeed in reducing it to the metallic state.
Titanium does not seem to have any affinity for sulphur.
There was a substance discovered by Mr McGregor in the valley of Menachan in Cornwall, and hence called menachanite. Upon this substance Mr McGregor made a very interesting set of experiments, which were published in the Journal de Physique for 1791. He suspected it to contain a new metal. From its properties, Mr Kirwan conjectured that it was the same with titanium; and this conjecture has been very lately confirmed by Mr Klaproth, who analysed menachanite, and found it to be an ore of that metal.
Sect. XX. Of Tellurium.
In the mountains of Fatzbay, near Zaletna in Transylvania, there is a mine called Mariabill; the ore of tellurium, which is wrought for the gold that it contains. Mr Muller of Reichenstein examined it in 1792, and suspected that it contained a new metal; and Bergman, to whom he had sent some of the ore, was of the same opinion; but the quantity of the mineral which these chemists had examined was too inconsiderable to enable them to decide with certainty. Klaproth analyzed a larger quantity of it about the year 1797, and found that 1000 parts of it consisted of 72 parts of iron, 25 of gold, and 925 of a new metal, to which he has given the name of tellurium (n).
Tellurium is of a white colour like tin, approaching somewhat to the grey colour of lead. It is very brittle and friable. Its fracture is laminated. Its specific gravity is 6.115.
It is as easily melted as lead. When suffered to cool quietly and gradually, it readily assumes a crystallized surface.
When heated by the blowpipe upon charcoal, it burns with a very lively flame of a blue colour, inclining at the edges to green. It is so volatile as to rise entirely in a whitish grey smoke; at the same time it exhales a disagreeable odour like that of radishes. This smoke is the white oxyd of tellurium, which may be formed also by dissolving the metal in nitro-muriatic acid, and pouring into the saturated solution a quantity of water: a white powder precipitates, which is the oxyd.
When this oxyd is heated for some time in a retort, it melts, and appears, after cooling, of a yellow straw colour, having acquired a sort of radiated texture. When formed... Tellurium, formed into a paste with any fat oil, and distilled in a red heat, brilliant metallic drops are observed to cover the upper part of the retort, which at intervals fall to the bottom of the vessel, and are immediately replaced by others. After cooling, metallic fixed drops are found adhering to the sides and at the bottom of the vessel; the remainder of the metal is reduced. Its surface is brilliant and almost always crystallized. When this oxyd is exposed to heat on charcoal, it is reduced with a rapidity that resembles detonation.
Tellurium combines with sulphur. The sulphuret of this metal is of a grey colour and radiated structure.
When placed on red hot charcoal, the metal burns as well as the sulphur with a blue flame.
Tellurium amalgamates with mercury by simple trituration. — The other properties of this metal are unknown.
A new metal has lately been discovered by Vauquelin in the red lead ore of Siberia. It is grey, very hard, brittle, and easily crystallizes in small needles. He has given it the name of chromium (o).
We have now described all the metals at present known. The following table will exhibit in one view their principal properties.
| Metal | Colour | Hardness | Specific Gravity | Melting Point | Malleability | Ductility | |-------|--------|----------|-----------------|---------------|--------------|-----------| | Gold | Yellow | 6 | 19,300 | 32 W. (r) | 282000 | 500 | | Silver| White | 6½ | 10,510 | 28 W. | 160000 | 270 | | Platinum | White | 7½ | 23,000 | 150 W. | above | 500 | | Mercury| White | | 13,568 | -39 F. | | | | Copper| Red | 8 | 8,870 | 27 W. | 1449 F. | 299½ | | Iron | Blue-grey | 9 | 7,788 | 150 W. | 20577 F. | Magnetic | | Tin | White | 6 | 7,299 | 410 F. | 2000 | 49 | | Lead | Blue-white | 5 | 11,352 | 540 F. | | 29½ | | Zinc | White | 6 | 7,190 | 700 F. | | | | Antimony| Grey | 6½ | 6,860 | 700 F. | | | | Bismuth| Yellow-white | 6 | 9,822 | 460 F. | | | | Arsenic| White | 7 | 8,310 | 400 F. | | | | Cobalt| White | 8 | 8,150 | 130 W. | 17977 F. | Magnetic | | Nickel| White | 8 | 9,000 | 150 W. | 20577 F. | Magnetic | | Manganese| White | 8 | 7,000 | 150 W. | 20577 F. | Magnetic | | Tungsten| Brown | 6 | 17,600 | | | | | Molybdenum| Grey | | 7,500 | | | | | Uranium| Grey | 6 | 6,440 | | | | | Titanium| Red | 9 | 4,180 | | | | | Tellurium| White | | 6,115 | 540 F. | | | | Chromium| Grey | | | | | |
(o) From xenus, because it possesses the property of giving colour to other bodies in a remarkable degree.
(r) W. Wedgwood's pyrometer. F. Fahrenheit's thermometer. We have seen that all the metals are capable of combining with oxygen; that almost every one forms various oxyds, containing different quantities of oxygen, and varying in colour and other properties according to the proportion of oxygen which they contain. No part of chemistry has more engaged the attention of philosophers than the metallic oxyds; and yet such is the difficulty of the subject, that scarcely any part of chemistry is more imperfectly understood.
We neither know how many oxyds every particular metal is capable of forming, nor the manner in which they are formed: neither have the differences between oxyds of the same metallic base been enquired into; though there cannot be a doubt that they differ, not only in their affinities, but in many of their other properties. The white oxyd of manganese, for instance, combines readily with acids, but the black is incapable of uniting with any.
Mr Proult, in a very valuable paper which he lately published concerning the oxyds of iron*, hints that metals are only capable of two degrees of oxidation, or, which is the same thing, that only two different oxyds can be produced from the same metal. We think he has proved this completely as far as iron is concerned; and probably the observation holds good with respect to many other metals. Arsenic, copper, tin, molybdenum, and perhaps even mercury, seem to be capable of only two degrees of oxidation; but it would require a very numerous and accurate set of experiments to be able to determine the matter, or even to form a probable conjecture. Analogy is certainly against the supposition; for it has been demonstrated that some substances at least are capable of combining with three different doses of oxygen (q.), and why may not this be the case also with the metals?
There is one observation, however, which we owe to Mr Proult, the truth of which cannot be doubted, and which is certainly of the highest importance—that metals are not capable of indefinite degrees of oxidation, but only of a certain number; and that every particular oxyd consists of a determinate quantity of the metal and of oxygen chemically combined. Iron, for instance, is not capable, as has been supposed, of uniting with oxygen in all the intermediate degrees between $\frac{1}{2}$ and $\frac{3}{4}$, and consequently of forming 20 or 30 different oxyds; it can only combine with precisely $\frac{1}{2}$ parts, or $\frac{3}{4}$ parts, and with no other proportions; and therefore is only capable of forming two oxyds, the green and the brown. In like manner, every other metal combines with certain proportions of oxygen, and forms either two oxyds or more according to its nature. To talk therefore of oxidating a metal indefinitely is not accurate, except it be intended to signify the combining of part of it with oxygen, while the rest remains in its natural state. If iron be oxidated at all, it must be combined with $\frac{1}{2}$ of oxygen; if it be oxidated more than this, it must be combined with $\frac{3}{4}$ of oxygen.
We beg leave to add another observation, which we consider as of no less importance, and which will serve in some measure to modify and explain what has been just now said. Oxygen is capable of uniting with metals, or with any other substance for which it has an affinity, only in one determinate proportion. Iron, for instance, and oxygen can only combine in the proportion of 73 parts of iron and 27 of oxygen. These two quantities saturate each other, and form a compound which is incapable of receiving into it any more oxygen or iron: this compound is the green oxyd of iron. How comes it then, it will be asked, that there is another oxyd of iron, the brown oxyd, which contains 52 parts of iron and 48 of oxygen, proportions certainly very different from 73 and 27? We answer, there is an affinity between the green oxyd of iron and oxygen; they are capable of combining together, and of saturating each other in the proportion of about 71.5 parts of green oxyd and 28.5 of oxygen; and the compound which they form is the brown oxyd, which of course contains 52 parts of iron and 48 of oxygen: But then it is not formed by the combination of these two substances directly, but by the combination of the green oxyd and oxygen. In like manner, the arsenic acid is not composed of arsenic and oxygen combined directly, but of white oxyd of arsenic combined with oxygen. The very same thing takes place in all the other metals. We cannot at present prove the truth of this observation in a satisfactory manner, because it would be necessary to draw our proofs from combinations which are yet unclassified; but we will have occasion to consider it afterwards.
We have seen, that all the metals hitherto tried are capable of combining with sulphur, except gold and titanium; that all of them on which the experiments have been made can be united with phosphorus; and that three of them, iron, zinc, and manganese, united with carbon; and perhaps many more of them may hereafter be found capable of assuming the form of carburets.
We have seen, too, that they are capable of uniting with one another and forming alloys. This was long reckoned peculiar to metals, and it is at present one of the best criterions for determining the metallic nature of any substance. Much is wanting to render the chemistry of alloys complete. Many of them have never been examined; and the proportions of almost all of them are unknown. Neither has any accurate method been yet discovered of determining the affinities of metals for each other. The order of affinities which we have given for each metal was determined by Bergman; but he acknowledged himself that he wanted the proper data to ensure accuracy.
**Chap. IV. Of Earths.**
The word earth, in common language, has two meanings; it sometimes signifies the globe which we inhabit, and sometimes the mould on which vegetables grow. Chemists have examined this mould, and have found that it consists of a variety of substances mixed together without order or regularity. The greatest part of it, however, as well as of the stones, which form apparently so large a proportion of the globe, consists of a small number of bodies, which have a variety of common pro-
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(q.) We shall see afterwards that azot is one of these. These bodies chemists have agreed to class together, and to denominate earths.
Every body which possesses the following properties is an earth:
1. Insoluble in water, or nearly so; or at least becoming insoluble when combined with carbonic acid. 2. Little or no taste or smell; at least when combined with carbonic acid. 3. Incombustible, and incapable while pure of being altered by the fire. 4. A specific gravity not exceeding 4.9. 5. When pure, capable of assuming the form of a white powder.
The earths at present known amount to nine; the names of which are, lime, magnesia, barytes, fluorites, alumina, silica, jargonia, adamantia, glaucia.
Every one of the above characteristics is not perhaps rigorously applicable to each of these bodies; but all of them possess a sufficient number of common properties to render it useful to arrange them under one class.
Sect. I. Of Lime.
Lime has been known from the earliest ages. The ancients employed it in medicine; it was the chief ingredient in their mortar; and they used it as a manure to fertilize their fields.
It abounds in many parts of the world, or perhaps we should rather say, that there is no part of the world where it does not exist. It is found purest in limestones, and marbles and chalk. None of these substances, however, is strictly speaking, lime; but they are all capable of becoming lime by a well-known process, by keeping them some time in a white heat; this process is called the burning of lime; the product is denominated quicklime. This last substance is what we call lime.
Pure lime is of a white colour, moderately hard, but easily reduced to a powder.
It has a hot burning taste, and in some measure corrodes and destroys the texture of those animal bodies to which it is applied. It has no smell. Its specific gravity is 2.3.
If water be poured on newly burnt lime, it swells and falls to pieces, and is soon reduced to a very fine powder. In the mean time, so much heat is produced, that part of the water flies off in vapour. If the quantity of lime flacked (as this process is termed) be great, the heat produced is sufficient to set fire to combustibles. In this manner, vessels loaded with lime have sometimes been burnt. When great quantities of lime are flacked in a dark place, not only heat, but light also is emitted, as Mr Pelletier has observed. When flacked lime is weighed, it is found to be heavier than it was before. This additional weight is owing to the combination of part of the water with the lime; which water may be separated again by the application of a red heat; and by this process the lime becomes just what it was before being flacked.
Six hundred parts of water, at the temperature of 60°, dissolve about one part of lime; boiling hot water dissolves about double that quantity. This solution is called lime-water. It is limpid, has an aerid taste, and changes vegetable blue colours to green. One ounce troy of lime-water contains about one grain of lime.
One thousand parts of lime are capable of absorbing, and retaining, at a heat of 600°, 228 parts of water.
Lime has never yet been obtained in the state of crystals.
It is incapable of being fused by the most violent heat that can be produced in furnaces, or even by the most powerful burning-glasses.
Lime unites readily with sulphur, and forms sulphuret of lime. This compound may be obtained by mixing and flacking lime and flowers of sulphur together, and adding a little water. The heat produced by the flacking of the lime is sufficient to make the sulphur and the lime unite. This sulphuret is of a red colour. When water is poured on it, sulphurated hydrogen gas is emitted. The sulphur is gradually converted into sulphuric acid by uniting with the oxygen of the water, the hydrogen of which flies off in the form of gas, diffusing at the same time a part of the sulphur.
It is capable also of combining with phosphorus.—Phosphuret of lime decomposes water by the assistance of lime, of a moderate heat, and gives out phosphuretted hydrogen gas.
Limestone and chalk, though they are capable of being converted into lime by burning, possess hardly any of the properties of that active substance. They are neither soluble, scarcely soluble in water, and do not perceptibly act on animal bodies. Now, to what are the new lime properties of lime owing? What alteration does it undergo in the fire?
It had been long known, that limestone loses a good deal of weight by being burned or calcined. It was natural to suppose, therefore, that something was separated from it during calcination. Accordingly, Van Helmont, Ludovicus, and Macquer, made experiments in succession, in order to discover what that something was; and they concluded from them that it was pure water, which the lime recovered again when exposed to the atmosphere. As the new properties of lime could hardly be ascribed to this loss, but to some other cause, Stahl's opinion, like all the other chemical theories of Stahl, that wonderful man, was generally acceded to. He supposed that the new properties which lime acquired by calcination, were owing entirely to the more minute division of its particles by the action of the fire. Boyle indeed had endeavoured to prove, that these properties were owing to the fixation of fire in the lime; a theory which was embraced by Newton and illustrated by Hales, and which Meyer new modelled, and explained with so much ingenuity and acuteness as to draw the attention of the most distinguished chemists. But while Meyer was thus employed in Germany, Dr Black of Edinburgh published those celebrated experiments which form to brilliant an era in the history of chemistry.
He first ascertained that the quantity of water separated from limestone during its calcination was not nearly equal to the weight which it lost. He concluded in consequence, that it must have lost something else than mere water. What this could be, he was at first at a loss to conceive; but recollecting that Dr Hales had proved, that limestone, during its solution in acids, emitted a great quantity of air, he conjectured that this might probably be what it lost during calcination. He calcined it accordingly, and applied a pneumatic apparatus to receive the product. He found his conjecture verified; verified; and that the air and the water which separated from the lime, were together precisely equal to the loss of weight which it had sustained. Lime therefore owes its new properties to the loss of air; and limestone differs from lime merely in being combined with a certain quantity of air: for he found that, by restoring again the same quantity of air to lime, it was converted into limestone. This air, because it existed in lime in a fixed state, he called fixed air. It was afterwards examined by Dr Priestley and other philosophers, found to possess peculiar properties, and to be that species of gas now known by the name of carbonic acid gas. Lime then is a simple substance, that is to say, it has never yet been decomposed; and limestone is composed of carbonic acid and lime. Heat separates the carbonic acid, and leaves the lime in a state of purity.
The affinities of lime, according to Bergman, are as follows:
- Oxalic acid, - Suberio (x)? - Sulphuric, - Tartarous, - Succinic, - Phosphoric, - Saccharoactic, - Nitric, - Muriatic, - Schabic, - Fluoric, - Arsenic, - Formic, - Lactic, - Citric, - Benzoic, - Sulphurous, - Acetous, - Boracic, - Nitrous, - Carbonic, - Prussic, - Sulphur, - Phosphorus, - Water, - Fixed oil.
Sect. II. Of Magnesia.
About the beginning of the eighteenth century, a Roman canon exposed a white powder to sale at Rome as a cure for all diseases. This powder he called magnesia alba. He kept the manner of preparing it a profound secret; but in 1727 Valentini informed the public that it might be obtained by calcining the lixivium which remains after the preparation of nitre; and two years after, Slevogt discovered that it might be precipitated by potash from the mother ley (s) of common salt. This powder was generally supposed to be lime, till Frederic Hoffman observed that it formed very different combinations with other bodies. But little was known concerning its nature till Dr Black published his celebrated experiments in 1755. Margraf published a dissertation on it in 1759, and Bergman another in 1773, in which he collected the observations of these two philosophers, and which he enriched also with many additions of his own.
As magnesia has never yet been found native in a state of purity, it may be prepared in the following procuring manner: Sulphat of magnesia, a salt composed of this earth and sulphuric acid, exists in sea water, and in many springs, particularly some about Epson, from which circumstance it was formerly called Epson salt. This salt is to be dissolved in water, and half its weight of potash added. The magnesia is immediately precipitated, because potash has a stronger affinity for sulphuric acid. It is then to be washed with a sufficient quantity of water, and dried.
Magnesia thus obtained is a very soft white powder, which has very little taste, and is totally destitute of smell.—Its specific gravity is about 2.35.
It is soluble in about 7900 times its own weight of water at the temperature of 60°.
Even when combined with carbonic acid (for which it has a strong affinity) it is capable of absorbing and retaining 1½ times its own weight of water, without letting go a drop; but on exposure to the air, this water evaporates, though more slowly than it would from lime.
Magnesia has never yet been obtained in a crystallized form.
It tinges vegetable blues of an exceedingly slight green.
It is not melted by the strongest heat which it has been possible to apply; but Mr D'Arcey observed that, in a very high temperature, it became somewhat agglomerated.
When magnesia and sulphur are put into a vessel of water, and kept for some time exposed to a moderate heat, they combine, and form sulphuret of magnesia; which, according to Fourcroy, is capable of crystallizing.
The phosphuret of magnesia has never been examined. Effect of Equal parts of lime and magnesia mixed together, heat on and exposed by Lavosier to a very violent heat, did not mixtures melt; neither did they melt when Mr Kirwan placed them in the temperature of 150° Wedgwood.—The following table, drawn up by Mr Kirwan from his own experiments, shews the effect of heat on these two earths mixed together in different proportions.
| Proportions | |------------| | 1 : 2 |
(x) The affinity of this acid for lime is inferior to the oxalic, which decomposes the suberat of lime. [J. Macdonald's Mineral. of Shetland and Arran, p. 168.]
(s) The mother ley is the liquid that remains after as much as possible of any salt has been obtained from it. Common salt, for instance, is obtained by evaporating sea water. After as much salt has been extracted from a quantity of sea water as will crystallize, there is still a portion of liquid remaining. This portion is the mother ley. The affinities of magnesia, according to Bergman, are as follows:
- Oxalic acid, - Phosphoric, - Sulphuric, - Fluoric, - Sebacic, - Arsenic, - Saccharoactic, - Succinic, - Nitric, - Muriatic, - Tartarous, - Citric, - Formic, - Lactic, - Benzoinic, - Acetous, - Boracic, - Sulphurous, - Nitrous, - Carbonic, - Prussic, - Sulphur, - Phosphorus?
Water.
Sect. III. Of Barytes.
A very heavy mineral is found in Sweden, Germany, and Britain, which Margraf considered as a compound of sulphuric acid and lime. But Scheele and Gahn analyzed it in 1774, and found that it consisted of sulphuric acid combined with a peculiar species of earth. This analysis was soon after confirmed and extended by Bergman. The earth was at first called terra ponderosa; heavy earth, on account of the great specific gravity of the substance from which it was obtained. Morveau called it barote (from baros, heavy), which Bergman changed into barytes; and this last term is now universally adopted.
Barytes is generally found combined either with sulphuric or carbonic acid. From the first of these compounds, which is by far the most common, it may be obtained by the following process:
Reduce the mineral to a powder, and mix it with 2½ its weight of carbonat of soda (r), previously deprived of all its water. Expose the mixture to a red heat for an hour and a half, avoiding fusion, and a double decomposition takes place; the sulphuric acid unites with the soda, while the carbonic acid combines with the barytes. Wash it in a sufficient quantity of water to dissolve the compound of sulphuric acid and soda, the carbonat of barytes, which is almost insoluble, remains behind. Leave it should be mixed with some other earths, which is generally the case, boil it for three hours in ten times its weight of distilled vinegar, the specific gravity of which is 1.033; by which the barytes will be dissolved, and likewise the lime and magnesia, if there happen to be any; but every other earth (v) remains untouched. Pour off the solution, and add to it sulphuric acid as long as any precipitate is formed. This precipitate consists of the whole barytes and the lime (if there be any) combined with sulphuric acid. Wash it in 50 times its weight of water, and all the lime will be dissolved. There will now remain nothing but barytes combined with sulphuric acid, which may be decomposed as before by carbonat of soda (s). The carbonic acid may then be separated by applying a very violent heat (t); or, what is better, nitric acid may be poured upon it, which will separate the carbonic acid and combine with the barytes; and then the nitric acid may be driven off by a moderate heat (u).
Barytes thus obtained is a light, spongy, porous, body, which may be very easily reduced to powder. It has a harsh and more caustic taste than lime; and when taken into the stomach, proves a most violent poison. It has no perceptible smell.
Its specific gravity has not yet been ascertained.
It imbibes water with a hissing noise, but, according to Dr Hope, without swelling or splitting as lime does (v). However, when exposed to the air, as Fourcroy and Vauquelin inform us, it effloresces, cracks, bursts, swells up, heats, and becomes white, by absorbing moisture (w).
Cold water dissolves about ¼ part of its weight of barytes, and boiling water more than half its weight. As the water cools, the barytes is deposited in crystals, the shape of which varies according to the rapidity with which they have been formed. When most regular, they are flat hexagonal prisms, having two broad sides, with two intervening narrow ones, and terminated at each end by a four-sided pyramid, which in some instances constitutes the larger part of the crystal. When formed slowly, they are distinct and large; but when the water is saturated with barytes, they are deposited rapidly, and are generally more slender and delicate. Then, too, they are attached to one another in such a manner as to assume a beautiful foliaceous appearance, not unlike the leaf of a fern (x).
These crystals are transparent and colourless, and appear to be composed of about 53 parts of water and 47 of
(t) Soda is an alkali; which shall be afterwards described. Carbonat of soda is soda combined with carbonic acid, the common state in which it is obtained; potash might also be used.
(v) Except stromites, which Pelletier has detected in this mineral. of barytes. When exposed to the heat of boiling water, they undergo the watery fusion, or, which is the same thing, they melt without losing any of the water which they contain. A stronger heat makes the water fly off. When exposed to the air, they attract carbonic acid, and crumble into dust. They are soluble in 17 parts of water at the temperature of 60°; but boiling water dissolves any quantity whatever; the reason of which is evident; at that temperature their own water of crystallization is sufficient to keep them in solution.
Water saturated with barytes is called barytic water. It has the property of converting vegetable blues to a green.
When barytes is exposed to the blow-pipe on a piece of charcoal, it fuses, bubbles up, and runs into globules, which quickly penetrate the charcoal. This is probably in consequence of containing water; for Lavoisier found barytes not affected by the strongest heat which he could produce.
Barytes combines readily with sulphur. The easiest way of forming sulphuret of barytes is to mix eight parts of sulphuret of barytes with one part of pounded charcoal, and apply a strong heat. The charcoal combines with the oxygen of the sulphuric acid, and the compound flies off in the form of carbonic acid gas. There remains behind sulphur combined with barytes. Sulphuret of barytes is soluble in water; it is of a yellow colour. It is capable of crystallizing; and then assumes a yellowish white colour.
The phosphuret of barytes has not been examined. No mixture of barytes and lime, nor of barytes and magnesia, is fusible in the strongest heat which it has been possible to apply.
The affinities of barytes, according to Bergman, are as follows:
- Sulphuric acid, - Oxalic, - Succinic, - Fluoric, - Phosphoric, - Saccharoactic, - Suberic (v)? - Nitric, - Muriatic, - Sebacic, - Citric, - Tartarous, - Arsenic, - Fluoric, - Lactic, - Benzoic, - Acetous, - Boracic, - Sulphurous, - Nitrous, - Carbonic, - Prussic, - Sulphur, - Phosphorus, - Water, - Fixed oils.
(v) Suberic acid decomposes muriat and nitrat of barytes. Jamison's Mineral of Shetland and Arran.
About the year 1787, a mineral was brought to Edinburgh, by a dealer in fossils, from the lead mine of Strontian in Argyleshire, where it is found imbedded in the ore, mixed with several other substances. It is sometimes transparent and colourless, but generally has a tinge of yellow or green. Its hardness is 5. Its specific gravity varies from 3.4 to 3.726. Its texture is generally fibrous; and sometimes it is found crystalized in slender prismatic columns of various lengths.
This mineral was generally considered as a carbonat of barytes; but Dr Crawford having observed some difference between its solution in muriatic acid and that of barytes, mentioned in his treatise on muriat of barytes, published in 1790, that it probably contained a new earth, and sent a specimen to Mr Kirwan that he might examine its properties. Dr Hope had also suspected that its basis differed from barytes; and accordingly he made a set of experiments on it in 1791, which were read to the Royal Society of Edinburgh in 1792. These experiments fully proved that it contained a peculiar earth. Mr Kirwan likewise analysed the strontian mineral, and drew precisely the same conclusions. It has been analysed also by Mr Klaproth of Berlin, and Mr Pelletier of Paris. It consists of carbonic acid combined with a peculiar earth, to which Dr Hope gave the name of strontites. This appellation we shall adopt.
The carbonic acid may be separated by a heat of 140° Wedgwood, and then the strontites remains behind.
Strontites has been found in Argyleshire in Scotland, near Bristol in England, and in Pennsylvania. It has been found also in France and in Sicily. It is of a white colour. It has a pungent acrid taste. When pounded in a mortar, the powder that rises is offensive to the nostrils and lungs. It is not poisonous.
One hundred and sixty-two parts of water, at the temperature of 60°, dissolve nearly one part of it. The solution is clear and transparent, and converts vegetable blues to a green. Hot water dissolves it in much larger quantities; and as it cools the strontites is deposited in colourless transparent crystals. These are in the form of thin quadrangular plates, generally parallelograms, the largest of which seldom exceeds one-fourth of an inch in length. Sometimes their edges are plain, but they often consist of two facets, meeting together and forming an angle like the roof of a house. These crystals generally adhere to each other in such a manner as to form a thin plate of an inch or more in length and half an inch in breadth. Sometimes they assume a cubic form. They contain about 68 parts in 100 of water. They are soluble in 51.4 parts of water, at the temperature of 60°. Boiling water dissolves nearly half its weight of them. When exposed to the air, they lose their water, attract carbonic acid, and fall into powder.
When strontites is thrown into water, it attracts it with a hissing noise, much heat is produced, and it falls into powder much more rapidly than lime.
It combines with sulphur either by fusion in a crucible, or by being boiled with it in water. The sul-
*Hope, ibid. †Hope, ibid. ‡Hope, ibid. §Hope, ibid. ||Hope, ibid. ****Hope, ibid. phuret is of a dark yellowish brown colour. It is soluble in water.
The affinities of fluorites, as ascertained by Dr Hope, are as follows:
- Sulphuric acid, - Oxalic, - Tartarous, - Fluoric, - Nitric, - Muriatic, - Succinic, - Phosphoric, - Acetous, - Arsenic, - Boracic, - Carbonic.
Sect. V. Of Silica.
If one part of powdered flints or sand, mixed with three parts of potash, be put into a crucible, and kept in a state of fusion for half an hour, a brittle mass will be formed almost as transparent as glass, which quickly attracts moisture from the atmosphere, and is entirely soluble in water. This solution is called liquor silicum, or liquor of flints. It was first accurately described by Glauber, a chemist who lived about the middle of the 17th century.
If an acid be poured into this liquor, a white spongy substance is precipitated, which may be purified from every accidental mixture by washing it in acids, muriatic acid for instance. This substance is called siliceous earth or silica. It was first distinguished as a peculiar earth by Pott in 1746, though it had been known long before; and Cartheuer, Scheele, and Bergman proved in succession that it could not, as some chemists had supposed, be reduced to any other earth.
Silica, when dried, is a soft white powder, without either taste or smell.
Its specific gravity is 2.66.
It is insoluble in water except when newly precipitated from the liquor silicum, and then one part of it is soluble in 1000 parts of water. It has no effect on vegetable colours.
It is capable of absorbing about one-fourth of its weight of water, without letting any drop from it; but on exposure to the air, the water evaporates very readily.
Silica may be formed into a paste with a small quantity of water; this paste has not the smallest ductility, and when dried forms a loose, friable, and incoherent mass.
Silica is capable of assuming a crystalline form. Crystals of it are found in many parts of the world. They are known by the name of rock crystal. When pure they are transparent and colourless like glass; they assume various forms; the most usual is a hexagonal prism, surrounded with hexagonal pyramids on one or both ends, the angles of the prism corresponding with those of the pyramids. Their hardness is very great, amounting to eleven. Their specific gravity is 2.653.
There are two methods of imitating these crystals by art. The first method was discovered by Bergman. He dissolved silica in fluoric acid, the only acid in which it is soluble, and allowed the solution to remain undisturbed for two years. A number of crystals were then found at the bottom of the vessel, mostly of irregular figures, but some of them cubes with their angles truncated. They were hard, but not to be compared in this respect with rock crystal.
The other method was discovered by accident. Professor Seigling of Erfurt had prepared a liquor silicum, which was more than usually diluted with water, and contained a superabundance of alkali. It lay undisturbed for eight years in a glass vessel, the mouth of which was only covered with paper. Happening to look at it by accident, he observed it to contain a number of crystals; on which he sent it to Mr Trommldorff, professor of chemistry at Erfurt, who examined it. The liquor remaining amounted to about two ounces. Its surface was covered by a transparent crust, so strong that the vessel might be inverted without spilling any of the liquid. At the bottom of the vessel were a number of crystals, which proved on examination to be a plat of potash and carbonat of potash (w). The crust on the top consisted partly of carbonat of potash, partly of crystallized silica. These last crystals had assumed the form of tetrahedral pyramids in groups; they were perfectly transparent, and so hard that they struck fire with steel.
Silica endures the most violent heat without alteration.
It seems incapable of combining with sulphur or phosphorus.
1. The effect of heat upon lime and silica, mixed in various proportions, will appear from the following experiments of Mr Kirwan.
| Proportions | Heat | Effect | |------------|------|--------| | 50 Lime | 150° Wedg. | Melted into a mass of a white colour, semitransparent at the edges, and striking fire, tho' feebly, with steel; it was somewhat between porcelain and enamel. | | 80 Lime | 156 | A yellowish white loose powder. | | 20 Lime | 156 | Not melted, formed a brittle mass. |
2. Equal parts of magnesia and silica melt with great difficulty into a white enamel when exposed to the most violent heat which can be produced. They are infusible in interior heats in whatever proportion they are mixed.
3. The effect of heat on various mixtures of barites and silica will appear from the following experiments of Baron Mr Kirwan.
Proportions. With a small quantity of water it forms a very tough ductile paste, and does not readily mix with more.
In its usual state of dryness it is capable of absorbing 24 times its weight of water, without suffering any to drop out. It retains this water more obstinately than any of the earths hitherto described. In a freezing cold it contracts more, and parts with more of its water than any other earth; a circumstance which is of some importance in agriculture.
Alumina has never yet been obtained in a crystallized form. It has no effect whatever on vegetable colours.
The most intense heat does not fuse it, but it has the singular property of diminishing in bulk in proportion to the intensity of the fire to which it is exposed. It becomes at the same time exceedingly hard: Mr Laugier rendered it capable of cutting glass; and Mr Boyle had long before done the same thing.
Wedgwood took advantage of this property of alumina, and by means of it constructed an instrument for measuring high degrees of heat. It consists of pieces wedged of clay of a determinate size, and an apparatus for measuring their bulk with accuracy: One of these pieces is thrown into the fire, and the temperature is estimated by metering the contraction of the piece. For a more complete description of this important instrument, we refer to the article Thermometer in the Encyclopaedia Britannica.
Alumina is hardly susceptible of combining with sulphur or phosphorus; but from the experiments of La Grange, it appears to have an affinity for carbon.
1. The effect of heat on various mixtures of lime and alumina will appear from the following table:
| Proportion | Heat | Effect | |------------|------|--------| | 75 Lime | 150° Wedg. | Not melted. | | 66 Lime | 150° Wedg. | Remained a powder. | | 33 Lime | (x) | Melted. | | 25 Lime | (x) | Melted. |
2. Magnesia and alumina have no action whatever on each other, even when exposed to a heat of 150° Wedgewood.
3. The effect of heat on different mixtures of barytes and alumina will appear from the following experiments of Mr Kirwan:
Proportions:
(x) These three experiments were made by Ehrman: The heat was produced by directing a stream of oxygen gas on burning charcoal, and is the most intense which it has been hitherto possible to produce. 4. Nothing is known concerning the effect of heat on mixtures of stonites and alumina.
5. Equal parts of alumina and silica harden in the temperature of 160° Wedgwood, but do not fuse*. Kirwan's Min. i. 58. Achard found them fusible in all proportions in a heat probably little inferior to 150° Wedgwood. Mixtures of these two earths in various proportions form clays, but these are seldom uncontaminated with some other ingredients.
6. From the experiments of Achard, it appears that no mixture of lime, magnesia, and alumina, in which the lime predominates, is vitrifiable, except they be nearly in the proportions of three lime, two magnesia, one alumina; that no mixture in which magnesia predominates will melt in a heat below 166°; that mixtures in which the alumina exceeds are generally fusible, as will appear from the following table†:
| Proportions | Heat | Effect | |-------------|------|--------| | 80 Alumina 20 Barytes | 150° Wedg. | Scarcely hardened. | | 75 Alumina 25 Barytes | 156 | No sign of fusion, a loose powder. | | 66 Alumina 33 Barytes | 152 | As the former. | | 50 Alumina 50 Barytes | 150 | As the former. | | 20 Alumina 80 Barytes | 148 | Somewhat harder, but no sign of fusion. | | 25 Alumina 75 Barytes | 150 | Harder, but no sign of fusion. |
7. From the same experiments, and those of Kirwan, we learn, that, in mixtures of lime, silica, and alumina, when the lime exceeds, the mixture is generally fusible either into a glass or a porcelain, according to the proportions. The only infusible proportions were,
| Proportions | Effect | |-------------|--------| | 2 Lime 3 Silica | | | 1 Lime 1 Silica | | | 2 Alumina 2 Silica | |
That if the silica exceeds, the mixture is frequently fusible into an enamel or porcelain, and perhaps a glass; and that when the alumina exceeds, a porcelain may often be attained, but not a glass‡.
8. As to mixtures of magnesia, silica, and alumina, when the magnesia exceeds, no fusion takes place at 150°. When the silica exceeds, a porcelain may often be attained; and three parts silica, two magnesia, and one alumina, formed a glass. When the alumina exceeds, nothing more than a porcelain can be produced*.
9. Achard found that equal parts of lime, magnesia, silica, and alumina, melted into a glass. They fused also in various other proportions, especially when the silica predominated.
The affinities of alumina are as follows:
- Sulphuric acid, - Nitric, - Muriatic, - Oxalic, - Tartaric, - Floric, - Sebacic, - Tartarous, - Succinic, - Saccharolactic, - Citric, - Phosphoric, - Formic, - Lactic, - Benzoic, - Acetous, - Boracic, - Sulphurous, - Nitrous, - Carbonic, - Prussic.
Sect. VII. Of Jargon.
Among the precious stones which come from the island of Ceylon, there is one called jargon, which is of several of the following properties.
Its colour is various, grey, greenish white, yellowish, reddish brown, and violet. It is often crystallized, either in right angular quadrangular prisms surmounted with pyramids, or octahedrals consisting of double quadrangular pyramids. It has generally a good deal of lustre, at least internally. It is mostly semitransparent. Its hardness is from 10 to 16: Its specific gravity from 4.16 to 4.7*.
It loses scarcely any of its weight in a melting heat; for Klaproth found that 300 grams, after remaining in it for an hour and a half, were only one-fourth of a grain lighter than at first†. Neither was it attacked either by muriatic or sulphuric acid, even when afflicted by heat. At last, by calcining it with a large quantity of soda, he dissolved it in muriatic acid, and found that 100 parts of it contained 31.5 of silica, five of a mixture of nickel, etc. Jargonia has a strong resemblance to alumina. It is of a white colour. Its specific gravity probably exceeds 4,000.
It differs from alumina in the compounds which it forms with other bodies, in being insoluble in a boiling solution of pure potash or soda, and in being insoluble by heat when mixed with these substances in a state of dryness.
No more of its properties are yet known.
**Sect. VIII. Of Adamantia.**
There is a stone found in China and in the East Indies near Bombay, which from its hardness has been called adamantine spar. Mr Greville first received some specimens of it, and made it known to several French and English naturalists.
The variety which comes from China is crystallized in hexagonal prisms. It is of a grey colour. The entire pieces are opaque, but thin plates of it are transparent. It is so hard, that it not only cuts glass as easily as the diamond, but even scratches rock crystal and many other very hard stones. Its specific gravity is 3,710.
The variety which comes from Bombay, and which is whiter than the other, is called corundum.*
Mr Greville sent some specimens of this stone to Mr Klaproth, that he might analyse it; a task which he found very difficult to perform, for the common processes had no effect upon it. At last he succeeded by fusing it 12 times in a silver crucible with 15 parts of soda, and exposing it each time for five hours to the strongest heat which the crucible could endure. After each fusion he softened the mass with boiling water, precipitating by acids the earth which the soda had dissolved. He digested also different times the undecomposed part in boiling acids. By this process he decomposed it, and found that it was composed of two parts of alumina, and one of a peculiar earth which has been called adamantia.
This earth he at first took for silica; but it differs from it in not being insoluble when mixed with potash or soda. Its specific gravity probably exceeds 3,000†.
Nothing more is known concerning its properties.
A new earth has lately been discovered by Mr Vauquelin in the beryl, to which he has given the name of glaucina. His account of its properties we have not hitherto been able to procure; we must therefore reserve our description of it till we come in the order of the alphabet to the word GLUCINA.
These are all the simple earths hitherto discovered; for Sidnaea (v), which was announced by Mr Wedgewood as a peculiar earth, has lately been proved by Mr Hatchet* to be merely a mixture of several earths which have been long known.
The first four earths have a great many common properties: they tinge vegetable blues green, they have a strong affinity for carbonic acid, and combine readily with all acids. They have sometimes been called alka lime earths.
There is a strong resemblance between silica and adamantia, and between alumina and jargonia.
None of the earths have been hitherto decompounded, nor has the smallest proof ever been brought that they are compounds. We must therefore, in the present state of chemistry, consider them as simple bodies. Many attempts, indeed, have been made to show that there was but one earth in nature, and that all others were derived from it. The earth generally made choice of as the simplest was silica (z). But none of these attempts, notwithstanding the ingenuity of several of the authors, has been attended with the smallest shadow of success.
We have mentioned formerly, that it was almost the universal opinion of chemists that metals were composed of some of the earths united to phlogiston; but of late an attempt has been made to prove that all the earths are metallic oxys, and that they can actually be reduced to the state of metals.
Baron had long ago suspected that alumina had somewhat of a metallic nature; and Bergman had been induced, by its great weight and several other appearances, to conjecture that barytes was a metallic oxyd:
But the first chemist who ventured to hint that all earths might be metallic oxys was Mr Lavoisier*. * Chemistry.
About the year 1792, soon after the publication of Mr. Lavoisier's book, Mr Tondi and Professor Ruprecht, both of Schemnitz, announced, that they had obtained from barytes, by the application of a strong heat, a metal of the colour of iron, and attracted by the magnet, which they called borbonium; from magnesia another, which they called aquilum; a third from lime, also called aquilum; and a fourth from alumina, which they denominated apalum. Their method of proceeding was to apply a violent heat to the earths, which were surrounded with charcoal in a Hessian crucible, and covered with calcined bones in powder.
But their experiments were soon after repeated by Klaproth, Savorelli, and Thaukli; and these accurate chemists soon proved, that the pretended metals were all of them phosphurets of iron. The iron, by the violence of the heat, had been extracted from the crucible, and the phosphorus from the bones. The earths therefore must still continue a distinct class of bodies: and, as Klaproth has observed, their properties are so exceedingly different from those of metallic oxys, that the supposition of their being composed of the same ingredients is contrary to every fact, and to every analogy with which we are acquainted.
**Chap. V. Of Caloric.**
Nothing is more familiar to us than heat; to attempt to define it therefore would be unnecessary. When we say that a person feels heat, that a stone is hot, the expressions
(y) This substance was contained in a mineral brought from Sidney Cove in New Holland. Wedgewood's analysis was published in 1790. Klaproth afterwards analysed it without finding the new earth which it had been supposed to contain; but doubts were entertained concerning the identity of the minerals examined by these two philosophers. These doubts have been removed by Mr Hatchet.
(z) Mr Sage, however, pitched upon lime. expressions cause no difficulty; every one understands them perfectly; yet in each of these propositions the word heat has a distinct meaning. In the one, it signifies the sensation of heat; in the other, the cause of that sensation. This ambiguity, though of little consequence in common life, leads unavoidably in philosophical discussions to confusion and perplexity. It was to prevent this that the French chemists made choice of the word caloric, to signify the cause of heat. When I put my hand on a hot stone, I experience a certain sensation, which I call the sensation of heat; the cause of this sensation is caloric.
Concerning the nature of caloric, there are two opinions which have divided philosophers ever since they turned their attention to the subject. Some suppose that caloric, like gravity, is merely a property of matter, and that it consists, some how or other, in a peculiar vibration of its particles; others, on the contrary, think that it is a distinct substance. Each of these opinions has been supported by the greatest philosophers; and the obscurity of the subject is such, that both sides have been able to produce exceedingly plausible and forcible arguments. The recent discoveries, however, in this branch of chemistry, have rendered the latter opinion much more probable than the former. Indeed we do not see how it is possible to account for many of the phenomena of nature, unless caloric be considered as a substance, as we trust shall appear from the investigation into which we are about to enter. We mean, then, with the generality of modern chemists, to take it for granted, that caloric is a substance, without pretending to be able to demonstrate the truth of our opinion, but merely because we consider it as infinitely more plausible than the other. If the receiver of an air-pump, while it contains a thermometer, be suddenly exhausted of air, the thermometer sinks several degrees, and then gradually rises again to its former height. Now if heat be owing to vibration, how comes it that the small quantity of matter remaining in the receiver is first insufficient, and afterwards sufficient to maintain the temperature? Is it not more probable that part of the caloric was carried off with the air, and that it gradually returned through the glass, which it is capable of pervading, though with difficulty? When air is let into an exhausted receiver, the thermometer, as Lambert first observed, rises several degrees. Is not this owing to an additional quantity of caloric introduced by the air? The thermometer then sinks slowly. Is not this because the superabundant caloric gradually pervades the glass and flies off? Taking it for granted then, that caloric is a substance, we proceed to examine its properties.
1. When bodies become hot, or, which is the same thing, when caloric enters into them, they expand in all directions; and this expansion is proportional to the accumulation of caloric. The first and most obvious property of caloric then is the power of expanding bodies. It does not, however, expand all substances equally, and we are still ignorant of the law which it follows. All that can be done therefore is to collect facts till this law be discovered. A number of these may be seen in the following table:
| Temperature | Water | Mercury | Linseed oil | Alcohol | |-------------|-------|---------|-------------|---------| | 30 | | | | | | 32 | | | | | | 35 | | | | | | 40 | | | | | | 45 | | | | | | 50 | | | | | | 55 | | | | | | 60 | | | | | | 65 | | | | | | 70 | | | | | | 75 | | | | | | 80 | | | | | | 85 | | | | | | 90 | | | | | | 95 | | | | |
Table of the Expansion of various Bodies at different Temperatures. ### Table of the Expansion of various Bodies at different Temperatures continued.
| Temperature | Sulphuric acid | Nitric acid | Glass | Air | Oxygen gas | Azotic gas | Hydrogen gas | Nitrous gas | Carb. acid gas | Ammonia cal gas | |-------------|----------------|-------------|-------|-----|------------|------------|--------------|-------------|---------------|----------------| | 32° | | | | | | | | | | | | 40 | | | | | | | | | | | | 45 | | | | | | | | | | | | 50 | | | | | | | | | | | | 55 | | | | | | | | | | | | 60 | | | | | | | | | | | | 65 | | | | | | | | | | | | 70 | | | | | | | | | | | | 75 | | | | | | | | | | | | 80 | | | | | | | | | | | | 90 | | | | | | | | | | | | 100 | | | | | | | | | | | | 110 | | | | | | | | | | | | 122 | | | | | | | | | | | | 130 | | | | | | | | | | | | 150 | | | | | | | | | | | | 167 | | | | | | | | | | | | 170 | | | | | | | | | | | | 190 | | | | | | | | | | | | 212 | | | | | | | | | | |
### Table of the Expansion of Metals from 32° to 212°†.
| Temperature | Antimony | Steel | Iron | Soft Iron | Bismuth | Copper | Brass | Brass Wire | |-------------|----------|-------|------|-----------|---------|--------|-------|------------| | 32° | 120000 | 120000| 120000| 120000 | 120000 | 120000 | 120000| 120000 | | 212 | 120130 | 120147| 120151| 120167 | 120204 | 120225 | 120232| | | White heat | 123428* | 121500*| 122571*| | | | | |
| Tin | Lead | Zinc | Hammered Zinc | Zinc 8 Tin | Lead 1 Tin | Brass 2 Zinc | Pewter | Copper 3 Tin (a) | |-----|------|------|---------------|------------|------------|---------------|--------|-----------------| | 32° | 120000| 120000| 120000 | 120000 | 120000 | 120000 | 120000 | 120000 | | 212 | 120298| 120344| 120355 | 120373 | 120323 | 120301 | 120247 | 120274 |
(A) This mark † implies that, owing to some inaccuracy in making the experiments, the numbers to which it is attached are not to be depended on.
(n) The metal whose expansion is here given was an alloy composed of three parts of copper and one of tin. The figures in some of the preceding columns are to be understood in the same manner. Thus in the last column but two, the metal consisted of two parts of brass alloyed with one of zinc. From this table, it appears that the gases are more expanded by caloric than fluids, and fluids more than solids; and that the expansion of all bodies hitherto examined, mercury alone excepted, goes on in an increasing series. To the expanding power of caloric there is one singular exception: From 30° to 40° Fahrenheit, water, instead of being expanded, suffers a remarkable contraction, as is evident from the following table of its bulk for every degree between 30° and 40°.
| Bulk | |------| | 30° - | 100074 | | 31° - | 100070 | | 32° - | 100066 | | 33° - | 100063 | | 34° - | 100060 | | 35° - | 100058 | | 36° - | 100056 | | 37° - | 100055 | | 38° - | 100054 | | 39° - | 100054 | | 40° - | 100054 |
From 40° it expands like other substances on being heated (n).
The expansion of bodies by caloric has furnished us with an instrument for measuring the various degrees of it in different substances, we mean the thermometer; and as mercury is the only fluid which expands equably, it is obviously the only proper one for thermometers. The thermometer uniformly used in this article is that of Fahrenheit, except when some other is particularly mentioned.
2. By means of the thermometer, we learn that there is no body which does not contain caloric, because there is none so cold that it cannot be made colder; and cooling a body is nothing else but abstracting a part of the caloric which it contains.
3. Caloric cannot be confined in any body while those in its neighbourhood are colder, but continues to rush out till everything is reduced to the same temperature. This does not proceed from the attraction of the colder bodies, but from the tendency of caloric to exist everywhere in an equal degree of tension: For when hot bodies are placed in the exhausted receiver of an air-pump, as we learn from Mr Picquet†, or in the Torricellian vacuum, as Count Rumford has shown us‡, the caloric leaves them in the same manner, tho' more slowly, and they are equally reduced to the temperature of the surrounding bodies. This property has been called the equilibrium of caloric. The only way therefore to confine or accumulate this substance in a body, is to surround it with bodies which are hotter than itself.
4. The equilibrium of caloric seems evidently to prove that its particles repel each other. This repulsion will cause them when accumulated in any place to fly off in every direction, and to continue to separate till they are opposed by caloric in other bodies of the same relative density with themselves, which, by repelling them in its turn, compels them to continue where they are. The caloric in bodies therefore is in what has been called by Mr Picquet a state of tension (c). Its particles are actuated by a force which would make them separate to an indefinite distance, were they not confined by the opposite force of the caloric which surrounds them. The equilibrium therefore depends on the balancing of two opposite forces; the repulsion between the particles of caloric in the body, which tends to diminish the temperature; and the repulsion between the caloric of the body and the surrounding caloric, which tends to raise the temperature. When the first force is greater than the second, as is the case when the temperature of a body is higher than that of the surrounding bodies, the caloric flies off, and the body becomes colder. When the last force is stronger than the first, as is the case when a body is colder than those which are around it, the particles of its caloric are obliged to approach nearer each other, new caloric enters to occupy the space which they had left, and the body becomes hotter. When the two forces are equal, the bodies are said to be of the same temperature, and no change takes place*.
It is the action of these opposite forces which makes the thermometer a measure of temperature. When applied to any body, it continues to rise or fall till the caloric in it and in the body to which it is applied are of the same tension, and then it remains stationary. The thermometer therefore merely indicates that the temperature of the body to which it is applied is equal to its own. It is obvious that, in order to obtain the real temperature of bodies, the thermometer should be so small that the quantity of caloric, which enters or leaves it, may not materially affect the result.
This property of caloric seems to be the cause of the elasticity of the gases, in which, as we shall shew afterwards, it exists in great quantities. Perhaps it is the cause of elasticity in general; for we have no demonstrative evidence that the particles of elastic bodies repel each other (v), and we are certain that all of them contain caloric. Perhaps also it is owing to this repulsive property of caloric that the particles of no body actually touch each other; for the less caloric we leave in a body, the nearer its particles approach to one another. The expansion of bodies by caloric seems also to depend on the same property. The particles of caloric uniting with those of the body, endeavour to drag them along when they recede from each other. The expansion
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(n) There was a curious fact concerning dilatation observed by Mr de Luc. A brass rod which he used as a thermometer became in summer habitually longer; that is to say, that after being for some time lengthened by heat, it did not contract by the application of cold to its old length, but continued somewhat longer. In winter the contrary phenomenon took place. After being contracted for some time by cold, it did not return to its old length on the application of heat, but kept somewhat shorter. A leaden rod showed these effects in a greater degree. Glass has not this quality. De Luc supposes that this property is inversely as the elasticity of bodies. Glass is perfectly elastic, and lead is less elastic than brass.—Journ. de Phys. xviii. 369.
(c) The phrase was first used by Mr Volta.
(d) We acknowledge that several philosophers of the first rank, Epicurus for instance, and Boscovich, have supposed, that the particles of all bodies both attract and repel each other; but we cannot help thinking it rather improbable (if it be possible) that two such opposite properties should exist together. son of bodies therefore ought to be inversely as their cohesion, and directly as the tension of the caloric which they contain. This property of caloric seems likewise to afford an explanation of a very curious fact, which was first, we believe, mentioned by Dr. Lavoisier in his Treatise on the Modifications of the Atmosphere, and afterwards ascertained by Dr. George Fordyce, that bodies become absolutely lighter by being heated. He took a glass globe three inches in diameter, with a short neck, and weighing 451 grains; poured into it 1700 grains of water from the New River, London, and then sealed it hermetically. The whole weighed 2150½ grains at the temperature of 32°. It was put for twenty minutes into a freezing mixture of snow and salt till some of it was frozen; it was then, after being wiped dry with a dry linen cloth, next with clean washed dry leather, immediately weighed, and found to be ½ th of a grain heavier than before. This was repeated exactly in the same manner five different times. At each, more of the water was frozen and more weight gained. When the whole water was frozen, it was ⅛ ths of a grain heavier than it had been when fluid. A thermometer applied to the globe stood at 10°. When allowed to remain till the thermometer rose to 32°, it weighed ⅛ ths of a grain more than it did at the same temperature when fluid. We shall shew afterwards that ice contains less caloric than water of the same temperature with it. The balance used was nice enough to mark ⅛ th part of a grain. Morveau too found, much about the same time, that water put into vessels hermetically sealed weighed more when frozen than when fluid; and Mr. Chauffier found, that two pounds of sulphuric acid were three grains heavier when frozen than after they had recovered their fluidity. Now if the particles of caloric repel each other, bodies which contain it in great quantities must be somewhat repelled by each other. The more replete therefore that any body is with caloric, the more it will be repelled by the earth, which always contains a great quantity; and this repulsion must in some degree counteract its gravitation. This explanation was first suggested, we believe, by Dr. Black.
The same property explains another curious fact discovered by Mr. Piélet of Geneva, that caloric moves more readily vertically upwards than downwards. He took a tube of tinplate, two inches in diameter and 44 inches in length, and inclosed in it a bar of copper four lines in diameter and 33 inches in length, which was placed and fixed exactly in its axis. This tube was exhausted of air, by means of an air-pump, till the manometer stood at the height of four lines. It was inclosed in another tube of plate-wood, except about two inches, exactly in the middle, to which place the sun's rays were directed for half an hour by means of a concave mirror. The ends of the copper bar were scooped out into concave hemispheres; and into each of these the bulb of a very sensible thermometer was fixed. The tube was placed vertically. The highest thermometer, which we shall call A, rose to 95°, a hundred and one seconds before the lowest B. The thermometer B rose no higher than 95°; but the thermometer A reached 101.75°. Caloric To see whether this difference was owing to the thermometers, the tube was inverted, and consequently the highest thermometer in the former experiment was lowest in this. The thermometer B now rose from 49° to 97.25° in 281°; the thermometer A in 2763°, or 47° sooner than B. It was evident from this result, that the thermometer A was more sensible than the thermometer B by 47°. If this be subtracted from 101°, the former difference, it will leave 54°, as the difference resulting from position. These experiments were repeated with only this difference, that round the ends of the bar and the bulbs of the thermometers (but without touching the bulbs) some folds of oiled paper were wrapped to confine the caloric. The superior thermometer A rose from 30° to 106.25° in 34 minutes, which was 93° sooner than the inferior B; it rose to 110.75°, the thermometer B only to 106.25°. The tube being reversed, the thermometer A, which was now lowest, rose from 46° to 115.25° in 40° 30°, or forty seconds sooner than the thermometer B. This subtracted from 93°, as formerly, leaves 53° for the difference of situation. The superior thermometer mounted after the burning glass was removed, 0.15°, remained stationary for 80°, and after five minutes had only descended 0.45°; the other did not ascend at all; in one minute it descended 0.225°, and in 6° 8° it descended 2.47°. In 22° 50° the inferior descended 63.725°, the superior 61.475°. From these experiments, it is obvious that the particles of caloric move somewhat faster, and in somewhat greater quantity, upwards than downwards; owing, doubtless, to the repulsive power of the caloric in the earth. The small quantity of air that remained in the tube, may perhaps be supposed sufficient to account for the difference, without allowing any such tendency upwards in caloric. But it is evident from the experiments of the Florentine academicians on the same subject, with tubes full of air, that even when in great abundance, that fluid hardly affected the rising of the superior thermometer; surely then its effect must be altogether imperceptible when so little of it remained; and in the third and fourth experiments the oiled paper prevented any of the heated air from approaching the thermometer.
5. If we take a bar of iron and a piece of stone of equal dimensions, and putting one end of each into the fire, apply either thermometers or our hands to the other, we shall find the extremity of the iron sensibly hot long before that of the stone. Caloric therefore does not pass through all bodies with the same celerity and ease. The power that bodies have to allow it a passage through them is called their conducting power; those that allow it to pass with facility, are called good conductors; those through which it passes with difficulty, are called bad conductors; and those which do not allow it to pass at all, non conductors.
It is probable that all solids conduct heat in some degree, at least this is the case with every one at present known. Wood and charcoal are exceeding bad conductors of caloric (1). Count Rumford informs us, that a piece of wood of green oak plank was employed to stir the melted metal of which cannons were founding at Munich, and it was often allowed to remain a considerable time in the furnace; yet the caloric had penetrated to so inconsiderable a depth, that at the distance of 3/8th of an inch below the surface, the wood did not seem to have been the least affected by it; the colour remained unchanged, and it did not appear to have lost even its moisture.
Glass is also a very bad conductor; and this is the reason that it is so apt to crack on being heated or cooled suddenly; one part of it receiving or parting with its caloric before the rest, expands or contracts, and destroys the cohesion.
Metals are the best conductors of caloric of all the solids hitherto examined. The conducting powers of all, however, are not equal. Dr. Ingenhousz procured cylinders of several metals exactly of the same size, and having coated them with wax, he plunged their ends into hot water, and judged of the conducting power of each by the length of wax-coating melted. From these experiments he concluded, that the conducting powers of the metals which he examined were in the following order:
- Silver, - Gold, - Copper, nearly equal, - Tin, - Platinum, - Iron, - Steel, - Lead, much inferior to the others.
Next to metals alone seems to be the best conductors; but this property varies considerably in different stones. Bricks are much worse conductors than most stones. All solids capable of being melted become non conductors the moment they are heated to the melting point; the caloric enters them easily enough, but it remains in them.
All fluids hitherto examined are non conductors of caloric. They can receive it indeed from other substances, and they can give it out to other substances; but one particle can neither receive it nor give it out to another particle. Before a fluid therefore can either be heated or cooled, every particle must go individually to the substance from which it receives or to which it gives out caloric. For this very important discovery the world is indebted to Count Rumford. Before the publication of his essays it had not even been suspected; so far from it, that fluids had been ranked among the best conductors of caloric.
In a set of experiments on the communication of heat, he made use of thermometers of an uncommon size. Having exposed one of these (the bulb of which was near four inches in diameter) filled with alcohol to as great a heat as it could support, he placed it in a window to cool where the sun happened to be shining. Some particles of dust had by accident been mixed with the alcohol; these being illuminated by the sun, became perfectly visible, and discovered that the whole liquid in the tube of the thermometer was in a most rapid motion, running swiftly in opposite directions upwards and downwards at the same time. The ascending current occupied the axis, the descending current the sides of the tube. When the sides of the tube were cooled by means of ice, the velocity of both currents was accelerated. It diminished as the liquid cooled; and when it had acquired the temperature of the room, the motion ceased altogether. This experiment was repeated with linseed oil, and the result was precisely the same. These currents were evidently produced by the particles of the liquid going individually to the sides of the tube, and giving out their caloric. The moment they did so, their specific gravity being increased, they fell to the bottom, and of course pushed up the warmer part of the fluid, which was thus forced to ascend along the axis of the tube. Having reached the top of the tube, the particles gave out part of their caloric, because specifically heavier, and tumbled in their turn to the bottom.
As these internal motions of fluids can only be discovered by mixing with them bodies of the same specific gravity with themselves, and as there is hardly any substance of the same specific gravity with water which is not soluble in it, Count Rumford had recourse to the following ingenious method of ascertaining whether that fluid also followed the same law. The specific gravity of water is increased considerably by dissolving any salt in it; he added, therefore, potash to water till its specific gravity was exactly equal to that of amber, a substance but very little heavier than pure water. A number of small pieces of amber were then mixed with this solution, and the whole put into a glass globe with a long neck, which, on being heated and exposed to cool, exhibited exactly the same phenomena with the other fluids. A change of temperature, amounting only to a very few degrees, was sufficient to set the currents a-flowing; and a motion might at any time be produced by applying a hot or a cold body to any part of the vessel. When a hot body was applied, that part of the fluid nearest it ascended; but it descended on the application of a cold body.
If caloric passes through water only by the internal motion of its particles, as this experiment seems to prove, it is evident that every thing which embarrasses these motions must retard its transmission; and accordingly Count Rumford found this to be the case. He took a large linseed-oil thermometer with a copper bulb and glass tube; the bulb was placed exactly in the centre of a brass cylinder, so that there was a void space between them all around 0.2515 of an inch thick. The thermometer was kept in its place by means of four wooden pins projecting from the sides and bottom of the cylinder, and by the tube of it passing through the cork stopper of the cylinder. This cylinder was filled with pure water, then held in melting snow till the thermometer fell to 32°, and immediately plunged into a vessel of boiling water. The thermometer rose from 32° to 200° in 597". It is obvious that all the caloric which served to raise the thermometer must have made its way through the water in the cylinder. The experiment was repeated exactly in the same manner, but the water in the cylinder, which amounted to 2276 gr., had 192 gr. of starch boiled in it, which rendered it much less fluid. The thermometer now took 1109" to rise from 32° to 200°. The same experiment was again repeated with the same quantity of pure water, having 192 gr. of cider-down mixed with it, which would merely tend to embarrass the motion of the particles. A quantity of stewed apples were also in another experiment put into the cylinder. The following tables exhibit the result of all these experiments.
**Time the Caloric was in passing into the Thermometer.**
| Temperature | Through the Water and Starch | Thro' the Water and Eiderdown | Through stewed Apples | Through pure Water | |-------------|------------------------------|-------------------------------|-----------------------|-------------------| | Seconds | Seconds | Seconds | Seconds | Seconds | | Therm. rose from 32° to 200° in | 119 | 949 | 1096 | 597 | | Therm. rose 80°, viz. from 80° to 160°, in | 341 | 269 | 335 | 172 |
**Time the Caloric was in passing out of the Thermometer.**
| Temperature | Through the Water and Starch | Thro' the Water and Eiderdown | Through stewed Apples | Through pure Water | |-------------|------------------------------|-------------------------------|-----------------------|-------------------| | Seconds | Seconds | Seconds | Seconds | Seconds | | Therm. fell from 100° to 40° in | 1548 | 1541 | 1749 | 1032 | | Therm. fell 80°, viz. from 160° to 80°, in | 468 | 460 | 520 | 277 |
Now, neither the starch nor the eiderdown could produce any alteration in the water except impeding its internal motions; consequently whatever impedes these motions diminishes the conducting power of water. But this could not happen unless every individual particle actually went from the cylinder to the thermometer.
Only one proof more was wanting to remove every doubt; and this proof also Count Rumford has given us. If water be a non-conductor, it is evident that no caloric can pass downwards when the heat is applied to the surface; for as the particles of water become specifically lighter by being heated, they cannot sink to the bottom. Accordingly Count Rumford found, that water might be made actually to boil near the top of a glass tube, while that at the bottom was not sensibly warmed. Owing to the law already mentioned, indeed, that water, after being cooled down to 40°, expands instead of contracting when its temperature is lowered, a mass of water may be raised to 40° by applying the heat to its upper surface; because water at 40° is heavier than at any degree below it, and will therefore sink to the bottom; but its temperature cannot be raised any higher. This Count Rumford proved, by showing that water of the temperature of 40°, placed above ice, will melt as much of it in the same time as water at any higher temperature whatever, even boiling hot.
Into a cylindrical glass jar 4½ inches in diameter and 13½ inches high, he put 43.87 cubic inches, or 1 lb. 11½ oz. troy of water, and placing the jar in a freezing mixture composed of pounded ice and common sea salt, he froze the water into one compact mass. The jar was then put into a mixture of pounded ice and pure water, reaching exactly to the top of the ice in it, and suffered to remain there four hours, that the ice might come to the temperature of 32°; then boiling water was cautiously poured on it, and the jar still allowed to stand in the ice and water. He soon found that a considerable quantity of ice was melted at the very beginning of the experiment, owing to the agitation into which the water was thrown by the act of pouring it into the vessel. To prevent this as much as possible, he covered the ice with a small quantity of ice cold water, upon which he placed a flat shallow dish of light wood 4½ inches in diameter, and about one-fourth of an inch thick at the bottom. This vessel was perforated by several hundred very small holes. The hot water was poured into this dish through a long wooden tube, the bottom of which was stopped up, and the water made to issue through small holes in the side at the lower end. As this dish always floated on the surface of the water, and as the fluid pouring through it by a number of small holes was not projected with force, it is evident that a considerable part of these violent motions was prevented. The following is the result of three experiments made in this manner.
| Number of Experiments | Time the hot Water was on the Ice | Temperature of the hot Water one inch below its Surface | Quantity of Ice melted | |-----------------------|----------------------------------|--------------------------------------------------------|----------------------| | 1 | 10 minutes | At the beginning: 192° | 580 gr. | | 2 | 30 minutes | At the end: 165° | 914 gr. | | 3 | 180 minutes | At the end: 95° | 3200 gr. |
From these experiments he determined the quantity of ice melted in the act of pouring the water into the jar, supposing equal quantities to be melted in equal times. If 3200 grains were melted in 180', subtracting 580, the quantity melted in 10', there remains 2620 gr.; for the quantity melted in 170', in every ten of which 154 gr. must have been melted; for 170 : 10 : 1 : 2620 : 154 nearly. Subtracting 154 from 580, the quantity melted in the first ten minutes, there remains 426 gr., for the quantity melted in pouring the water into the jar. From the second experiment it follows, by a similar calculation, that 159 gr. were melted every 10 minutes; which shows that the motions produced by pouring in the water had not ceased in 30 minutes. It will be nearer the truth, therefore, if we endeavour to discover the quantity melted every ten minutes by comparing the second and third experiments. By a similar calculation to the above, it comes out to be 152 gr. The following table exhibits the results of several experiments, made exactly in the same manner, but with water at a much lower temperature. From these experiments it appears that the quantity of ice melted in 10° by water at the temperature of 41° was 222 gr., while boiling water melted only 152 gr. in the same time. To discover whether any of this was melted in the act of pouring in the water; from a mean of the two last experiments it appears, that 601 grains were melted in 30°; if from this 222 grains (the mean of the four first) be deducted, there will remain 379 grams for the quantity melted in 20°, consequently 189½ grains is what must have been melted in the ordinary course of the process; a quantity considerably above 152 grams. Therefore water at 41° melts more ice in the same time than boiling water. This Count Rumford accounts for by supposing, that in the hot water the descending current from the top of the vessel, and ascending one from the ice, meeting one another in that part of the vessel where the temperature is 40°, retard each other's motions, and thus prevent the melting process from going on so rapidly as when there is no descending current. And he found accordingly, that when the cooling of the water above was retarded by wrapping up the jar in a warm covering, the ice melted faster; and when the cooling above was accelerated, it melted slower. It is evident, that in the one case the velocity of the descending current was diminished, in the other accelerated.
Thus it has been completely proved, that water is a non-conductor of caloric. But is this the case also with other liquids?
When water was frozen in a glass jar by means of a freezing mixture, Count Rumford observed, that the ice first began to be formed at the sides, and gradually increased in thickness; and that the water on the axis of the vessel, which retained its fluidity longest, being compressed by the expansion of the ice, was forced upwards, and when completely frozen formed a pointed projection or nipple, which was sometimes half an inch higher than the rest of the ice. Upon ice frozen in this manner, he poured olive oil, previously cooled down to 32°, till it stood at the height of three inches above the ice. The vessel was surrounded as high as the ice with a mixture of pounded ice and water. A solid cylinder of wrought iron, 13th inch in diameter and 12 inches long, provided with a hollow cylindrical sheath of thick paper, was heated to the temperature of 210° in boiling water; and being suddenly introduced into its sheath, was suspended from the ceiling of the room, and very gradually let down into the oil, until the middle of the flat surface of the hot iron, which was directly above the point of conical projection of the ice, was distant from it only 1/10th of an inch. The end of the sheath descended 1/10th of an inch lower than the end of the hot metallic cylinder. Now it is evident, that if olive oil was a conductor, caloric would pass down through it from the iron and melt the ice. None of the ice, however, was melted; and when mercury was substituted for oil, the result was just the same; consequently it follows, that neither oil nor mercury is a conductor of heat. We may conclude, therefore, with Count Rumford, that this is the case with liquids in general.
Senebier observed some time ago, that air was a very bad conductor of caloric, and that it resisted every change of temperature very much. But it was referred for Count Rumford to prove, that it conducted its power at all only by the internal motions of its particles, or that it was in fact a non-conductor, exactly in the sense that liquids are non-conductors. This he established by shewing, that whatever tended to obstruct or impede the internal motions of its particles, diminished its conducting power. By mixing with a quantity of air 1/10th of its bulk of cider-down, he diminished its conducting power more than one half. The warmth of furs and feathers and silk depends on a very strong attraction between them and air, which is therefore confined in their interstices, and thus the caloric prevented from passing out of the body. A single metallic cover to a boiler in a short time grew so hot that it could not be touched, while another of exactly the same form, but double, with a quantity of air confined in the middle, scarcely felt hot. There can be no doubt that all the gates are also non-conductors; and Count Rumford has proved the same thing of steam by the following experiment, which we shall relate in his own words:
"A large globular bottle being provided, of very thin and very transparent glass, with a narrow neck, and its bottom drawn inward so as to form a hollow hemisphere about 6 inches in diameter; this bottle, which was about 8 inches in diameter externally, being filled with cold water, was placed in a shallow dish, or rather plate, about 10 inches in diameter, with a flat bottom formed of very thin sheet brass, and raised upon a tripod, and which contained a small quantity (about 1/10th of an inch in depth) of water; a spirit lamp being then placed under the middle of this plate, in a very few minutes the water in the plate began to boil, and the hollow formed by the bottom of the bottle was filled with clouds of steam, which, after circulating in it with surprising rapidity 4 or 5 minutes, and after forcing out a good deal of air from under the bottle, began gradually to clear up. At the end of 8 or 10 minutes (when, as I supposed, the air remaining with the steam in the hollow cavity formed by the bottom of the bottle had acquired nearly the same temperature as that of the steam) these clouds totally disappeared; and though the water continued to boil with the utmost violence, the contents of this hollow cavity became to perfectly invisible, and so little appearance was there of steam, that, had it not been for the streams of water which were continually running down its sides, I should almost have been tempted to doubt whether any steam was actually generated."
Upon Upon lifting up for an instant one side of the bottle, and letting in a smaller quantity of cold air, the clouds instantly returned, and continued circulating several minutes with great rapidity; and then gradually disappeared as before. This experiment was repeated several times, and always with the same result; the steam always becoming visible when cold air was mixed with it, and afterwards recovering its transparency when, part of this air being expelled, that which remained had acquired the temperature of the steam.
Finding that cold air introduced under the bottle caused the steam to be partially condensed, and clouds to be formed, I was desirous of seeing what visible effects would be produced by introducing a cold solid body under the bottle. I imagined that if steam was a conductor of heat, some part of the heat in the steam passing out of it into the cold body, clouds would of course be formed; but I thought if steam was a non-conductor of heat, that is to say, if one particle of steam could not communicate any part of its heat to its neighbouring particles, in that case, as the cold body could only affect the particles of steam actually in contact with it, no cloud would appear; and the result of the experiment showed that steam is in fact a non-conductor of heat; for, notwithstanding the cold body used in this experiment was very large and very cold, being a solid lump of ice nearly as large as an hen's egg, placed in the middle of the hollow cavity under the bottle, upon a small tripod or stand made of iron wire; yet as soon as the clouds, which were formed in consequence of the unavoidable introduction of cold air in lifting up the bottle to introduce the ice, were dissipated, which soon happened, the steam became so perfectly transparent and invisible, that not the smallest appearance of cloudiness was to be seen anywhere, not even about the ice, which, as it went on to melt, appeared as clear and as transparent as a piece of the finest rock crystal." Thus, then, it appears, that all elastic fluids are non-conductors as well as liquids.
6. If equal quantities of water and of mercury be placed at the same distance from a fire, the mercury will become hot much sooner than the water. After a sufficient interval, however, both of them acquire the same temperature. Now caloric flows into all bodies while they continue of a lower temperature than those around them, and it flows with equal rapidity into all bodies of the same conducting powers, as is the case with these two fluids: But if equal quantities of caloric were constantly flowing into the mercury and the water, and yet the water took a longer time to become hot than the mercury, it must require a greater quantity of caloric to raise water to a given temperature than it does to raise mercury. Bodies that require a greater quantity of caloric to raise them to a particular temperature than other bodies require, are said to have a greater capacity for caloric. That the capacity for caloric is different in different bodies, was first observed by Dr Black. Dr Irvine afterwards investigated the subject, and Dr Crawford published a great number of experiments on it in his Treatise on Heat. Professor Wilcke of Stockholm also discovered the same property of bodies. He called the quantity of caloric necessary to raise the temperature of substances a given number of degrees, their specific caloric; a term which we shall also employ, because the phrase capacity for caloric is liable to a great deal of ambiguity, and has introduced confusion into this subject (v). If two substances of unequal temperatures, as water at 100° and alcohol at 50°, be mixed together, the mixture will be of a temperature different both from that of the water and the alcohol, the water will become colder and the alcohol hotter; the water will give out caloric to the alcohol till both are reduced to the same temperature. Now if it requires just as much caloric to raise alcohol a certain number of degrees as it does to raise water the same number, that is, if these two fluids are of the same specific caloric, it is evident that the temperature of the mixture will be just 75°; for as soon as the water has given out 25° of caloric, the alcohol has acquired 25°, consequently both will be reduced to the same temperature, and will remain stationary; but if the specific caloric of the water be greater than that of the alcohol, the temperature of the mixture will be higher than 75°; for 25° of caloric in that case would raise alcohol more than 25°. If the specific caloric of water be so much greater than that of alcohol, that what raises water 20° will raise alcohol 30°; then the temperature after mixture will be 80°, because when the water has given out 20°, the alcohol will have risen 30°, and of course both will be of the same temperature. On the contrary, if the specific caloric of alcohol were greater than that of water, the temperature of the mixture would be under 75°. If the same quantity of caloric that raised alcohol 20°, raised water 30°, then the temperature of the mixture would be 70°. Thus the ratios of the specific caloric of bodies may be discovered by mixing them together at different temperatures.
The first set of experiments on this subject, in point of time, were probably those of Mr Wilcke. They were first published in the Stockholm Transactions for specific calorics by 1781, but had been made long before. The manner in which they were conducted is exceedingly ingenious, and they furnish us with the specific caloric of many of the metals. The metal on which the experiment was to be made was first weighed accurately (generally one pound was taken), and then being suspended by a thread, was plunged into a large vessel of tinplate, filled with boiling water, and kept there till it acquired a certain temperature, which was ascertained by a thermometer. Into another small box of tinplate exactly as much water at 32° was put as equaled the weight of the metal. Into this vessel the metal was plunged, and suspended in it so as not to touch its sides or bottom; and the degree of heat, the moment the metal and water were reduced to the same temperature, was marked by a very accurate thermometer. He then calculated what the temperature would have been if a quantity of water equal in weight to the metal, and of the same temperature with it, had been added to the ice-cold water instead of the metal.
(f) The term specific caloric has been used in a different sense by Seguin. He used it for the whole caloric which a body contains. Let $M$ be a quantity of water at the temperature $C$, 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, $s =$ specific gravity of water; then $m : M :: 1 : gs$ hence $m = \frac{M}{g} = (M$ being made $= 1) \frac{1}{g}$. Substituting this value of $m$ in the formula, $\frac{MC + mc}{M + m} = x$, in which $M = 1$ and $C = 32$, $x$ will be $= \frac{32 + c}{2 + 1}$.
Therefore if the specific gravity of the metal be multiplied by $32$, and the temperature of the metal be added, and the sum be divided by the specific gravity of the metal $+ 1$, 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 $\frac{MC + mc}{M + m} = x$, $x$ be made $= N$, $M = 1$, $C = 32$, $m$ will be $= \frac{N - 32}{c - N}$. Therefore if from the temperature to which the ice-cold water was raised by the metal $32$ be subtracted, and if from the temperature of the metal be subtracted the temperature to which it raised
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 give out the same quantity of caloric; which, being divided equally among their particles, gives to each particle a quantity of caloric inversely as the bulks of the metal and water; that is, the specific caloric of the water is to that of the metal as $1$ to $\frac{N - 32}{c - N}$.
We shall now give a specimen or two of his experiments, and the calculations founded on them, as above described.
| Number of experiments | Temperature of the metal | Temperature to which it would have been raised by a quantity of water equal in weight and heat to the metal | Temperature to which it would have been raised by water equal in bulk and temperature to the metal | Denominator of the fraction $N - 32$ | |-----------------------|-------------------------|-------------------------------------------------|-------------------------------------------------|----------------------------------| | 1 | 163.4 | 38.3° | 97.7° | 38.55° | | 2 | 144.5 | 37.4° | 88.25° | 37.58° | | 3 | 127.4 | 36.5° | 79.7° | 36.68° | | 4 | 118.4 | 36.05° | 75.2° | 36.25° | | 5 | 103.1 | 35.6° | 65.75° | 35.42° | | 6 | 95 | 34.45° | 63.5° | 35.06° |
Mean $19,712$
Lead.
(a) We have altered all these formulas 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 Willeke did. In it the freezing point is zero; and consequently instead of $32$ in the formula, $0$ is always substituted. 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
\[ \frac{1}{19712} \]
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. He ascertained at the same time, that the specific caloric of a body did not vary with the temperature, but continued always the same. This will appear evident from the experiments on gold and lead above exhibited.
Next, in point of time, and not inferior in ingenious contrivances to ensure accuracy, were the experiments of Dr Crawford, made by mixing together bodies of different temperatures. These were published in his Treatise on Heat.
Several experiments on the specific caloric of bodies were made also by Lavoisier and De la Place, which, from the well-known accuracy of these philosophers, cannot but be very valuable.
Their method was exceedingly simple and ingenious; it was first suggested by De la Place. An instrument was contrived, to which Lavoisier gave the name of calorimeter. It consists of three circular vessels nearly inscribed into each other, so as to form three different apartments, one within the other. These three we shall call the interior, middle, and external cavities. The interior cavity \( ffff \) (see section of the instrument fig. 4.), Calorific, 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, which is composed of the same materials. The middle cavity \( bbb \) is filled with ice. This ice is supported by the grate mm, and under the grate is placed a sieve. The external cavity \( sasa \) is also filled with ice. We have mentioned already, that no caloric can pass through ice. It can enter ice, indeed, but it remains in it, and is employed in melting it. The quantity of ice melted, then, is a measure of the caloric which has entered into the ice. The exterior and middle cavities being filled with ice, all the water is allowed to drain away, and the temperature of the interior cavity to come down to 32°. Then the substance, the specific caloric of which is to be ascertained, is heated a certain number of degrees, suppose to 212°, and then put into the interior cavity inclosed in a thin vessel. As it cools, it melts the ice in the middle cavity. In proportion as it melts, the water runs through the grate and sieve, and falls through the conical funnel \( ced \) and the tube \( xz \) into a vessel placed below to receive it. The external cavity is filled with ice, in order to prevent the external air from approaching the ice in the middle cavity and melting part of it. The water produced from it is carried off through the pipe ST. The external air ought never to be below 32°, nor above 41°. In the first case, the ice in the middle cavity might be cooled too low; in the last, a current of air flows through the machine and carries off some of the caloric. By putting various substances at the same temperature into this machine, and observing how much ice each of them melted in cooling down to 32°, it was easy to ascertain the specific caloric of each. Thus, if water, in cooling from 212 to 32°, melted one pound of ice; and mercury, .029 of a pound; the specific caloric of water was one, and that of mercury .029. This appears by far the simplest method of making experiments on this subject; and must also be the most accurate, provided we can be certain that all the melted snow flows into the receiver. But from an experiment of Mr Wedgwood, one would be apt to conclude that this does not happen. He found that the melted ice, so far from flowing out, actually froze again, and choked up the passage.
A table of the specific caloric of various bodies was And Kirkeville drawn up by Mr Kirwan, and published by Macgallan in his Treatise on Heat.
From all these sources we have drawn up the following table, which exhibits at one view the specific caloric of those bodies on which experiments have hitherto been made.
We have added to it a column, expressing the specific caloric of equal bulks of the same bodies; which seems to be a more accurate way of considering this subject, and indeed the only way in which the phrase capacity for caloric is intelligible. This column was formed by multiplying the specific caloric of equal weights of the various substances into their respective specific gravities. ### Table of the Specific Calorie of Various Bodies, that of Water being = 1,0000 (h).
#### I. Gases.
| Bodies | Specific Gravity | Specific Calorie of equal Weight | Specific Calorie of equal Volume | |-------------------------|------------------|----------------------------------|----------------------------------| | Hydrogen gas | 0.00094 | 21,4000 | 0.00214 | | Oxygen gas | 0.0034 | 47,490 | 0.006411 | | Common air | 0.00122 | 1,7900 | 0.002183 | | Carbonic acid gas | 0.00183 | 1,2459 | 0.001930 | | Steam | | 1,5500 | | | Azotic gas | 0.00120 | 0,7036 | 0.000952 |
#### II. Liquids.
| Bodies | Specific Gravity | Specific Calorie of equal Weight | Specific Calorie of equal Volume | |-------------------------|------------------|----------------------------------|----------------------------------| | Water | 1,000 | 1,0000 | 1,0000 | | Carbonat of ammonia | | 1,851 | | | Arterial blood | | 1,030 | | | Cows milk | 1,0324 | 0,9999 | 1,0322 | | Sulphuret of ammonia | 0.818 | 0,9940 | 2,8130 | | Venous blood | | 0,8028 | | | Solution of brown sugar | | 0,8600 | | | Nitric acid | | 0,844 | | | Sulphate of magnesia | | 0,844 | | | Water | | 0,844 | | | Common salt | | 0,832 | | | Water | | 0,8167 | | | Muriat of ammonia | | 0,779 | | | Water | | 0,765 | | | Tartar | | 0,734 | | | Solution of potas | 1,346 | 0,759 | 1,2216 | | Sulphate of iron | | 0,734 | | | Water | | 0,728 | | | Oil of olives | | 0,9153 | 0,710 | 0,6498 | | Ammonia | | 0,997 | 0,7080 | 0,7041 | | Muriatic acid | | 1,122 | 0,6800 | 0,763 | | Sulphuric acid | | 0,6631 | | | Water | | 0,649 | | | Alum | | 0,649 | | | Lime | | 0,6181 | | | Nitre | | 0,646 | | | Water | | 0,6371 | 0,6021 | 0,4993 | | Alcohol | | 0,840 | 0,5998 | 1,120 | | Nitrous acid | | 1,355 | 0,576 | 0,780 | | Linseed oil | | 0,9403 | 0,528 | 0,4964 | | Spermaceti oil | | 0,5000 | | | Oil of turpentine | | 0,9910 | 0,472 | 0,4132 | | Vinegar | | 0,3870 | 0,3966 | | | Lime | | 0,3346 | | | Water | | 0,3100 | 0,4123 | | Mercury | | 0,1030 | 0,1039 |
#### III. Solids.
| Bodies | Specific Gravity | Specific Calorie of equal Weight | Specific Calorie of equal Volume | |-------------------------|------------------|----------------------------------|----------------------------------| | Ice | | 0,9000 | | | Ox-hide with the hair | | 0,787 | | | Lungs of a sheep | | 0,769 | | | Lean of ox-beef | | 0,7400 | | | Rice | | 0,5030 | | | Horse beans | | 0,5020 | | | Duft of the pine tree | | 0,5000 | | | Peafe | | 0,4920 | | | Wheat | | 0,4770 | | | Barley | | 0,4210 | | | Oats | | 0,4160 | | | Pitcoal | | 0,2777 | | | Charcoal | | 0,2631 | | | Chalk | | 0,2509 | | | Kult of iron | | 0,2500 | | | White oxyd of antimony | | 0,2270 | | | wafted | | | | | Oxyd of copper nearly | | 0,2272 | | | freed from air | | 0,2199 | | | Quicklime | | 0,195 | | | Stone-ware | | 0,195 | | | Agate | | 2,648 | 0,195 | 0,517 | | Crystal | | 3,189 | 0,1929 | 0,6152 | | Cinders | | 0,1923 | | | Swedish glas | | 2,1386 | 0,187 | 0,448 | | Ashes of cinders | | 0,185 | | | Sulphur | | 1,99 | 0,183 | 0,3680 | | Flint glas | | 3,3293 | 0,174 | 0,5792 | | Rult of iron nearly freed| | | | | from air | | | | | White oxyd of antimony | | 0,1666 | | | ditto | | | | | Ashes of the elm | | | | | Oxyd of zinc nearly free| | | | | from air | | | | | Iron (d) | | 7,876 | 0,1264 | 0,993 | | Brass (d) | | 8,358 | 0,1141 | 0,971 | | Copper (d) | | 8,784 | 0,1121 | 1,027 | | Sheet iron | | | 0,1099 | | | Oxyd of lead and tin | | | 0,102 | | | Gun-metal | | | 0,1100 | | | White oxyd of tin nearly free from air | | | | | | Zinc (d) | | 7,154 | 0,0981 | 0,735 | | Ashes of charcoal | | | 0,0929 | | | Silver | | 0,0901 | 0,082 | 0,833 | | Yellow oxyd of lead nearly free from air | | | | | | Tin (e) | | 7,380 | 0,0661 | 0,444 | | Antimony (d) | | 6,167 | 0,0637 | 0,390 | | Gold | | 19,040 | 0,050 | 0,966 | | Lead (e) | | 11,450 | 0,0424 | 0,487 | | Bismuth | | 9,861 | 0,043 | 0,427 |
(h) The specific calorie of the substances marked * was ascertained by Dr Crawford, those marked † by Mr Kirwan, ‡ by Lavoisier and La Place, ** by Wilcke, || by Count Rumford. § Is the mean of Crawford, Kirwan, and Lavoisier; ¶ mean of Lavoisier and Kirwan; (c) mean of Crawford and Lavoisier; (d) mean of Wilcke and Crawford; (e) mean of Wilcke, Crawford, and Kirwan. If a quantity of ice, at a low temperature, sup- posed at 2°, be suspended in a warm room, it will be- come gradually less cold, as may be discovered by means of a thermometer, till it reaches the temperature of 32°; but there it stops. The ice, however, diffuses slowly; and at the end of several hours, when it is all just melted, the thermometer still stands at 32°. Af- ter this it begins to rise, and soon reaches the tempera- ture of the room. Here the ice continues for several hours colder than the air around it. Caloric must then be continually flowing into it; yet it does not become hotter; it is changed, however, into water. Ice there- fore is converted into water by a quantity of caloric uniting with it. This caloric has been called latent ca- loric, because its presence is not indicated by the ther- mometer. It might, perhaps, with more propriety, as Professor Pictet observes, be called caloric of fluidity; for there are other cases in which caloric exists in bo- dies without raising their temperature. This very im- portant discovery was made by Dr Black as early as 1757, and seems to have led the way to all the subse- quent discoveries in this part of chemistry, which have almost completely changed the appearance of the science: for the discovery that caloric may exist in bodies while the thermometer cannot indicate its presence, is one of the strongest links in the chain of facts by which the nature of combustion was ascertained.
The caloric which unites with ice, and renders it fluid, appears again during the act of freezing. If a quantity of water be carried into a room where the temperature is below the freezing point, suppose at 20°, it cools gradually down to 32°; but it becomes no colder till it is all frozen, which takes up some time. The moment it is all converted into ice, it begins again to cool, and soon reaches the temperature of the room. In this case, the water is surrounded by a colder atmosphere; it must therefore be giving out ca- loric constantly; yet it does not become colder till it is all frozen, that is to say, till it has lost all its ca- loric of fluidity.
Dr Black proved, by a very accurate experiment, that the quantity of caloric of fluidity is sufficient to raise the same quantity of water 140°.
All solids become fluid by absorbing a quantity of caloric. Landriani proved, that this is the case with sulphur, alum, nitre, and several of the metals; and it has been found to be the case with every substance hitherto examined. Fluidity, therefore, is owing to a union between the solid and a certain quantity of ca- loric.
The late Dr Irvine of Glasgow advanced a theory on this subject different from that of Dr Black. The spe- cific caloric of water being greater than that of ice, it requires a greater quantity of caloric to raise it to a given temperature than it does to raise ice. The calo- ric does not therefore become latent; it only seems to do so from the greater specific caloric of water. This theory was zealously adopted by Dr Crawford. Dr Black observed very justly, that it did not account for the production of fluidity at all. The specific caloric of water is indeed greater than that of ice; but how is the ice converted into water? This is an objection which the advocates for Dr Irvine's, or Dr Crawford's, theory (as it has been improperly called) will not easily answer. Let us now examine whether this theory ac- counts for the apparent loss of caloric. It follows from Mr Kirwan's experiments, that the specific caloric of water is to that of ice as 10 to 9 (i). Dr Black proved, that as much caloric entered the ice as would have raised it; had it been water, 140°. Let us sup- pose that it would only have raised the ice 140°; in that case the melted ice ought to have been of the tem- perature of 158°, for 10 : 9 :: 140 : 126; but it was only 12°. Therefore 126° of caloric have disappar- eared, and cannot be accounted for by the change of spe- cific caloric. Nor can the accuracy of Dr Black's ex- periment be suspected: it has been repeated in every part of the world, and varied in every possible way. We cannot doubt, therefore, that caloric unites with substances, and causes them to become fluid, or that there is in fact a caloric of fluidity different from specific caloric.
Water also is converted into steam by uniting with Caloric of caloric. Dr Black put an iron vessel, containing four evaporation ounces of water at the temperature of 53°, upon a cal- iron table which was red hot. The water rose to the boiling point in three minutes; but it did not after- wards become any hotter. It evaporated, however, in 18 minutes; and the steam was precisely at the tempe- rature of 212°. During the first three minutes, it re- ceived 150° of caloric, and as much must have been en- tering it during every three minutes while the evapo- ration continued, as the temperature was always much lower than that of the table. This caloric, instead of raising the temperature of the water, was employed in converting it into steam. There is also, therefore, a quantity of latent caloric in steam. It might, as Mr Pictet observes, be called, with propriety, caloric of eva- poration. This caloric appears again if the steam be condensed. If it be made to pass, for instance, through a pipe surrounded with cold water, it is condensed in the pipe, and drops out from it in the form of water. The caloric of the steam enters into the water around the pipe, and the quantity of it in degrees may be dis- covered by the number of degrees which it raises that water. By an experiment of this kind, it was proved, that the caloric of evaporation would be sufficient to heat water red hot, were it employed only in raising its temperature, instead of converting it into steam. It is therefore at least equal to 800°. Mr Watt showed af- terwards that it was 920°.
Even spontaneous evaporation, as Dr Black first ob- served, is owing to the same cause: and this explains why bodies cool when water is evaporated from their surface;
(1) We do not know how this was ascertained: Not by mixing water and ice surely; because that would be taking for granted the thing to be proved; because it would give a very different result; and what is still worse, the specific caloric in that case would differ according to the temperature and the quantity of water. To give an instance: Mr Gadolin concludes, from 180 experiments made by mixing hot water and ice, that the specific caloric of ice is to that of water only as 1 to 2°; and had he varied the quantities and the temperatures, he might have obtained several other ratios.
Surface; a fact which has been long known, and which has been employed in warm countries to diminish the temperature of liquids, and even to convert them into ice (x). That water is evaporated by uniting with caloric, and not by solution in air, has been proved very completely by De Luc in his Treatise on Meteorology.
The evaporation of alcohol, ether, and every other substance on which experiments have been made, has been found owing to the same cause. Bodies, therefore, are converted into vapour by uniting with caloric.
8. If caloric, as has been shown, exists in bodies at the lowest temperature which we are able to procure, and if it exists in them while the thermometer cannot discover its presence—there is any method of ascertaining its absolute quantity in bodies? At what degree would a thermometer stand (supposing the thermometer capable of measuring so low) were the body to which it is applied totally deprived of caloric? or what degree of the thermometer corresponds to the real zero?
The first person (as far as we know), at least since men began to think accurately on the subject, who conceived the possibility of determining this question, was Dr Irvine of Glasgow. He invented a theorem, in order to ascertain the real zero, which has, we know not for what reason, been ascribed by several writers to Mr Kirwan. He took it for granted (and the fact is proved by all the experiments hitherto made) that the specific caloric of bodies continued the same in every degree of temperature, as long as they remained in the same state, that is to say, as long as they continued either solid or fluid or in a state of vapour; but that the specific caloric of the same body while solid was less than while fluid, and less while fluid than while in a state of vapour. He took it for granted, too, that the 340 degrees of caloric which entered ice during its solution without raising its temperature, entered merely in consequence of the increased specific caloric of the water, and that they were exactly proportional to this increased specific caloric. He took it for granted, likewise, that the specific caloric of bodies was proportional
(x) Galen informs us, that the ancient Egyptians were accustomed to put water previously boiled into earthen jars, and expose them all night on the upper part of their houses to the air. Before sunrise these vessels were put into the ground, moistened on the outside with water, and then surrounded with fresh plants; by which means the water was preserved cool during the whole day. Comment. in lib. vi. Hippoc. de morbis vulgar. 4. 10. p. 396.
By a similar process, water, in the East Indies, is converted into ice.
The following singular passage, which has been pointed out to us by the ingenious Dr Barclay, lecturer on anatomy in Edinburgh, furnishes a striking proof that the ancients were led, by a very different method of reasoning, to deduce, from their philosophical theory of the four elements, conclusions concerning the nature of heat not very different from those of the moderns.
"Si enim res se habet, ut omnia, quae alantur et quae crescunt, continant in se vim caloris; sine qua neque ali possint nec crescere. Nam omne, quod est calidum et igneum, cietur et agitur motu suo: quod autem altius et crescit, motu quoddam utitur certo et equilibri; qui quadam remanet in nobis, tamen feniens et vita remanet: refrigero autem et extinso calore, occidimus ipsi et exsiliimus. Quod quidem Cleantes his etiam argumentis docet, quanta vis infit calor in omni corpore: negat enim ullum effe eibum tam graven, quem in nocte et die concequatur; cujus etiam in reliquis ineft calor his quas natura reliquit. Jam vero venae et arteriae mincare non definitur, quasi quoddam igneum motum; animadversumque facit eip, cum cor animantis aliquo evoluit ita mobiliter palpitaret, ut imitaretur igneum celebritatem. Omne igitur quod vivit, vivit animal vive terra editum, id vivit propter includum in eo calorem. Ex quo intelligi debet, eas caloris naturam, vim habere in se vitalem per omnem mundum pertinentem. Atque id faciliter cernemus, tota genere hoc igneum, quod tranat omnia, subtillis explicato. Omnes igitur partes mundi (tangam antem maxunas) calore fuita suffumantur. Quod primum in terrae natura perspicit potest. Nam et lapidum conficitur aque tritus elici ignem videmus; et recutis foilione terram sumare calentem;
atque etiam ex puteis jugibus aquam calidam trahi, et id maxime fieri temporibus hibernis, quod magna vis caloris, terre continetur cavernis; eaque hieme fit denbor; ob quamque caufam, calorem infitum in terris continerat arctius.
"Longa est oratio, multaeque rationes, quibus doceri posset, omnia, quae terra concepiat, semina, quaeque ipsa ex fe generata stirpibus infixa continetur, ea temperazione caloris et oriri et augefere. Atque aquae etiam admixtae esse calorem, primum ipse liquor, tum aquae declarat effusio: quae neque conglaciaret frigoribus, neque nive pruinaque concreceret, nisi eadem fe admixto calore liquefacta et dilatae diffundaret. Itaque et aquilonibus reliquisque frigoribus defecit humus: et idem vicissim mollitur tepescet et tabescet calore. Atque etiam maria agitata ventis ita tepefcent, ut intelligi facile posset, in tantis illis humoribus effe includum calorem. Nec enim ille externus et adventivus habendus est tepor, sed ex intimis maris partibus agitacione excitatus: quod nostris quoque corporibus contingit, cum moto atque exercitatio recalcet. Ipse vero aer, qui natura est maxime frigidus, maiusque est expers caloris. Ille vero et multo quidem calore admixtus est: ipse enim oritur ex respiratione aquae: cum enim enim quasi vapor quidam aer habendus est. Is autem exsilit motu ejus caloris, qui aquis continetur. Quam similitudinem cernere possimus in his aquis, quae efferefcent subtilis igneum. Jam vero reliqua quarta pars mundi, ea et ipsa tota natura servida est, et ceteris natris omnis salutarem impertit et vitae calorem. Ex quo concluditur, cum omnes mundi partes fulmineantur calore, mundum etiam ipsum similis parique natura in tanta diurnitate fervari: eoque magis, quod intelligi debet, calidum illud atque igneum ita in omni fusum effe natura, ut in eo init procreandi vis et caufa gignendi, a quo et animantia omnia, et ea quorum flirpes terra continentur, et nati fit necesse et augefere. Cicero de natura Deorum, lib. ii. c. 9, et 10. their absolute calorific, or to all the caloric which existed in each.
On these data he reasoned in the following manner: Let A be a body in a state of fluidity; B the same body in a state of solidity. If the specific calorific of A and B be known, and if it be known how many degrees the caloric, disengaged during the change of B into A, would raise the temperature of A, it may be found by an easy process how many degrees all the caloric contained in B would raise the temperature of A; and the sum of these two numbers will represent in degrees the whole quantity of caloric in A: for the quantity of caloric in A must be just equal to the caloric in B, together with what entered into it in passing from the state of B to that of A. Let the specific calorific of A be 6, that of B 1; and let the quantity of caloric disengaged during the change of A into B be sufficient to raise the temperature of A 50°. If the specific calorific be proportional to the absolute calorific, it must contain exactly 6 times as much caloric as B. The 50° which entered into A when it changed its state, must be just 5 times as great as all the caloric of B; because when added to the caloric of B, it formed the caloric in A, which is just 6 times as great as the caloric in B. Therefore to discover the caloric in B, we have only to divide 50° by 5, or, which is the same thing, to state this proportion 6 : 1 = 50° : : 1 : 100. The caloric in B, therefore, in this case is just as much as would raise the temperature of A 100°. Therefore, if to 100°, the caloric of B, be added 50°, = caloric disengaged in the passage of A to B, this will give 60° = to all the caloric in A. Therefore, in all cases, the difference between the numbers expressing the specific calorific of the solid and fluid, is to the number expressing the specific calorific of the solid, as the quantity of caloric disengaged during the passage of the fluid into a solid is to the quantity of caloric in the fluid.
Dr Crawford embraced this theorem; and concluded, from a number of experiments made on purpose to ascertain the fact, that the real zero was 1268° below 0, or 1300° below the freezing point.
This subject deserves to be considered with attention. If this theorem in fact furnishes us with the real zero, it is one of the most important discoveries which has ever been made in chemistry; but if it proceeds on erroneous principles, it will only involve us in endless mazes of error and absurdity.
In the first place, if the real zero has any meaning at all, it must signify the degree to which the thermometer (supposing it could be used) would sink on being applied to a body which contained no heat. It must therefore be a fixed point; and were the theorem which we are examining well founded, experiments upon every different substance, if conducted with accuracy, would lead to the same result. Let us see whether this be the case.
From Dr Crawford's experiments, it follows, as we have seen, that the real zero is 1268° below 0.
Mr Kirwan, from comparing the specific calorific of water and ice, fixed the real zero at 1048° below 0.
From the experiments of Lavolier and La Place on a mixture of water and quicklime, in the proportion of 9 to 16, it follows, that the real zero is 2736° below 0.
From their experiments on a mixture of 4 parts of sulphuric acid and 3 parts of water, it follows, that the real zero is 5803° below 0.
Their experiments on a mixture of 4 parts of sulphuric acid and 5 of water, place it at 2073° below 0.
Their experiments on 9½ parts of nitric acid and 1 of lime, place it at 1889° below 32°.
These results differ from one another so enormously, and the last of them, which makes the real zero a negative quantity, is so absurd, that they are alone sufficient to convince us that the data on which they are founded are not true. Should it be said that their difference is not owing to any defect in the theorem, but to inaccuracies in making the experiments—we answer, that the theorem itself is founded on similar experiments; and if experiments of this nature, even in the hands of the most accurate chemists, cannot be freed from such enormous errors, how can we depend on any consequences deduced from them? and where, then, is our evidence for the truth of the theorem?
But, farther, there is no proof whatever that the specific calorific of bodies is proportional to their absolute calorific. The specific calorific of iron is greater than that of water, or even azotic gas; yet surely it is very improbable that iron contains more absolute calorific than either of these substances.
If the specific calorific of bodies has any meaning at all, it can only be, that the same quantity of caloric raises the temperature of one body a greater number of degrees than it does another. When we say that the specific calorific of A is = 6, and that of B = 1, what do we mean, unless that the quantity of caloric which raises B 6° raises A only 1°, or that what raises B 6° or 60°, raises A only 1° or 10°? When we say that the specific calorific of water is 10, and that of ice 9, do we not mean, that the quantity of caloric which raises the ice 10° or 100°, raises water only 9° or 90°? Yet during the change of ice into water, 140° of caloric enter it without raising its temperature; a quantity greater than what can be accounted for by the difference of specific calorific by 120°. The quantity that disappears, therefore, is not proportional to the difference of specific calorific; and therefore any theory which depends on that supposition cannot be well founded. When water is converted into steam, 80° of caloric disappear; yet the specific calorific of steam is to that of water, according to Dr Crawford's own experiments, only as 155 to 100: so that no less than 283° disappear, which cannot be accounted for according to this theory.
Dr Irvine's theorem, therefore, is insufficient for ascertaining the real zero; and hitherto no method has been discovered which can solve this problem.
9. If there be no body without calorific, if it exists in different quantities in different bodies, even when their differences are the same; and while the thermometer cannot indicate its presence—in what state does it exist in them? We cannot surely suppose that it is contained by them just as water is contained by a vessel of wood or metal, or that they are filled with it in the same manner that a hollow globe of tin-plate perforated with holes is filled with water when it is plunged into a quantity of that liquid; or that bodies are filled with calorific merely because they are immersed in an ocean of calorific. Were that the case, the specific and absolute calorific of bodies would always be proportional; and they would of necessity be inversely as the specific gravity of the respective bodies; because the less the specific gravity, the more room would be left for the particles. ticles of caloric. But this is by no means the case: the specific gravity of iron, for instance, is greater than that of tin; yet the specific caloric of iron is more than double that of tin: the specific gravity of oxygen gas is greater than that of common air; yet the specific caloric of the first of these substances is more than three times as great as that of the other. There must be something, therefore, in bodies themselves quite different from, and unconnected with the vacuities between their particles, which dispose some to admit more caloric than others. And what can that be but a disposition in different bodies to unite with a greater or a smaller quantity of caloric, and to retain it with more or less firmness according to their affinity for it? Dr Black pointed out, long ago, by discovering latent heat, that caloric unites with bodies; and this seems to be the only real key for unfolding the actions of this extraordinary substance. If caloric be matter, can it be destitute of that property which all other matter possesses, we mean attraction? And if it possesses attraction, must it not combine with those bodies that attract it just as other bodies combine with each other? Must there not be formed a chemical union between caloric and other substances, which can only be broken by chemical means, by presenting a third body which has a greater affinity either for the caloric or the body to which it is united, than they have for each other?
That it unites chemically with some bodies, at least, cannot be doubted; as we have shown already, that whenever a solid is converted into a liquid, a quantity of caloric enters, and remains in it; and that both the solid and the caloric lose their characteristic properties. This is precisely what takes place in every chemical union. All liquids, therefore, consist of solids combined with caloric. We have seen, too, that liquids are converted into vapors by the very same process. There are therefore, at least, two very large classes of bodies—liquids and vapors—in which we are certain that caloric exists in a state of chemical combination.
And gases: There is another class of bodies which resembles vapors in almost all their properties: these are the gases. Like them, they are invisible and elastic, and capable of indefinite expansion. Is it not probable, then, that the gases also, as well as the vapors, owe their properties to caloric? That they also consist of their respective bases combined with that subtle substance? This probability has been reduced to certainty by an experiment of Lavoisier. By adding two tubes to the calorimeter formerly described, he contrived to make known quantities of air to pass through the interior cavity, and to support combustion. He found, that when a pound of oxygen gas was made to combine in this manner with phosphorus, as much caloric was disengaged as melted 87½ pounds of ice*. Now every pound of ice absorbs as much caloric in the act of melting as is sufficient to raise a pound of water 140°. Therefore the whole caloric disengaged was sufficient to raise a pound of water 122½°. All this could not have come from the phosphorus, because it had been converted into a liquid, and must therefore have absorbed instead of parted with caloric, and because the quantity of caloric disengaged in all cases of combustion is proportional, not to the combustible, but to the oxygen absorbed. Oxygen gas, then, is composed of oxygen and caloric: and if this be the case with one gas, why not with all?
We may conclude, therefore, that the gases, as well as liquids and vapors, owe their form to the caloric which they contain. The only difference between them and vapors is, that the latter return to their liquid state by the mere action of cold; whereas most of the gases resist the lowest temperature which it has been possible to apply. It was natural to expect, that if caloric combined chemically with bodies, its affinity would be different for different substances, and that its affinity for some bodies would be so great that it would not leave them to combine with any other. It was natural to expect this, because it is the case with every other substance with which we are acquainted. The difference, then, between the gases and vapors is not surprising. The affinity of the former for caloric is not only much greater than that of the latter, but much greater than that of any other substance.
It is owing to this strong affinity between oxygen and hydrogen, and azot and caloric, that they cannot be obtained except in a gaseous form: and we shall describe several other substances afterwards exactly in the same circumstances. Had we any substance possessed of a greater affinity for caloric than they have, we should be able, by presenting it, to deprive them of their gaseous form. Doubtless there is a difference in the affinity between these bodies themselves and caloric; but as all of them are already saturated, this difference cannot be discovered. If we could obtain them uncombined with caloric, that is to say, in a concrete state, it would be easy to ascertain this point. Suppose, for instance, that hydrogen had the strongest affinity for caloric, and that we possessed it in a concrete state—it would be easy, by presenting it to the other gases, to deprive their bases of the caloric with which they are united, and thus to obtain them also uncombined with any other substance.
But though we are acquainted with no substance that has a greater affinity for caloric than the bases of the gases, there are many substances which have a greater affinity for these bases than caloric has. When any such substance is presented, the base combines with it, and the caloric is left at liberty. Thus, when phosphorus is presented to oxygen gas, the phosphorus and oxygen unite together, and the caloric flies off. We are now, therefore, able to answer one of the questions proposed at the end of the second chapter. Whence comes the caloric which appears during combustion? It is separated from the oxygen, which leaves it in order to enter into a new combination.
The caloric also, which sometimes appears when two bodies combine together, is set at liberty exactly in the same manner. When sulphuric acid and water, for instance, are mixed together, a very considerable heat is produced; a good deal of caloric, therefore, becomes sensible. In this case, the water combines with the acid, and at the same time lets go the caloric with which it was formerly combined, and becomes denser. In the same manner, to give another instance, when water is poured upon quicklime, a very great quantity of caloric becomes manifest. The water in this case combines with the quicklime, and assumes a concrete form, and of course lets go the caloric with which it was previously united.
It is no uncommon thing in nature to observe why two bodies, after combining together, manifesting a much stronger affinity for a third body than either of them does. them had while separate. Thus, silver has no perceptible affinity for sulphuric acid, neither has oxygen; but unite them together, and they combine with that acid very readily. A great many instances of the same kind might be produced. Were there substances, then, which, after combining together, have a greater affinity for caloric than any of them had while separate, this ought not to surprise us, because the same phenomenon is often observed in other bodies. Now this is actually the case with regard to caloric. Mix together, for instance, common salt and snow, the mixture instantly becomes liquid, and so cold, that it sinks the thermometer down to zero. In this case, the snow and salt united have a much stronger affinity for caloric than either of them had while separate; they attract it therefore from other bodies with which they happen to be in contact, till they have obtained a dose sufficient for their satiation; and by this satiation they manifest by becoming liquid. It is for this reason that all salts produce cold during their solution in water, when the freezing point of the solution formed is below that of water. All such solutions have a strong affinity for caloric; they therefore attract it till they are saturated, which appears by their becoming fluid. A number of experiments have been lately made in order to procure artificial cold by means of such combinations. The most complete set of experiments of that nature with which we are acquainted, is those of Mr Walker, published in the Philosophical Transactions for 1795. We shall present the result of his experiments in the following table:
**Table of Freezing Mixtures.**
| Mixtures | Thermometer sinks | |---------------------------|-------------------| | Muriat of ammonia | 5 parts | | Nitre | 5 | | Water | 16 | | From 50° to 10° | | | Sulphate of soda | 8 | | Water | 16 | | From 50 to 4 | | | Nitrat of ammonia | 1 | | Water | 1 | | From 50 to 4 | | | Nitrat of ammonia | 1 | | Carbonate of soda | 1 | | Water | 1 | | From 50 to 7 | | | Sulphate of soda | 3 | | Diluted nitric acid | 2 | | From 50 to 3 | | | Sulphate of soda | 6 | | Muriat of ammonia | 4 | | Nitre | 2 | | Diluted nitric acid | 4 | | From 50 to 10 | | | Sulphate of soda | 6 | | Nitrat of ammonia | 5 | | Diluted nitric acid | 4 | | From 50 to 14 | | | Phosphat of soda | 9 | | Diluted nitric acid | 4 | | From 50 to 12 | |
In order to produce these effects, the salts employed must be fresh crystallized, and newly reduced to a very fine powder. The vessels in which the freezing mixture is made should be very thin, and just large enough to hold it, and the materials should be mixed together as quickly as possible. The materials to be employed in order to produce great cold ought to be first reduced to the temperature marked in the table, by placing them in some of the other freezing mixtures; and then they are to be mixed together in a similar freezing mixture. If, for instance, we wish to produce a cold of — 46°, the snow and diluted nitric acid ought to be cooled down to 0°, by putting the vessel which contains each of them into the 12th freezing mixture in the above table, before they are mixed together. If a still greater cold is required, the materials to produce it are to be brought to the proper temperature by being previously placed in the second freezing mixture. This process is to be continued till the required degree of cold has been procured.
From the facts already known, we may conclude, that the particles of caloric have two properties, that of repelling each other, and of attracting and being attracted by other substances. As there is no body in which composition which does not contain caloric, we may safely conclude, that there is no body in nature which has not an affinity for it. When it unites with bodies, though the repulsion of its particles may be overcome by their attraction for the particles of the body, and by the attraction... traction of these particles for each other—we cannot suppose it annihilated: It must therefore be the more powerful the greater the quantity of caloric combined in any body is. Probably, then, there is more caloric combined with gases, less with fluids, and least with solids. It does not follow, however, from this that the quantity of caloric combined with any body is proportional to the distance between its particles, because that may depend on other causes. Thus, though hydrogen gas is much rarer than oxygen gas, it does not follow that hydrogen is combined with more caloric than oxygen, because the rarity may be owing to the smaller cohesive force of the particles of hydrogen allowing a smaller quantity of caloric to produce a greater effect.
If caloric unites only chemically with bodies, there ought to be a certain point of saturation between it and the substances with which it combines, because this takes place in all other chemical combinations. Oxygen gas, for instance, consists of a certain quantity of oxygen united with caloric. Now if this gas be a chemical compound, the two ingredients ought to saturate each other in such a manner, that no more of either could be admitted. But it cannot be denied, that more caloric can still be added to oxygen gas, for its temperature may be raised at pleasure as high as we think proper. This, at first sight, seems to be an insuperable objection to the theory that caloric only combines chemically with bodies. It ought to be remembered, however, that caloric is not singular in this respect. There are other bodies in nature, and bodies too which certainly combine with other substances only by affinity, which exhibit the very same phenomenon. Water is capable of combining with sulphuric acid and many other salts almost in any proportion, at least no limits have hitherto been observed. Oxygen, too, combines with almost every body in various proportions: We have seen, that with almost every metal it forms at least two different oxyds. Why then may not caloric be capable of uniting in the same manner? Allowing, therefore, that it were impossible to explain why bodies are capable of combining with caloric after saturation, this could be no objection to the theory that it only unites chemically with bodies, because the same phenomenon is exhibited by other bodies which it cannot be doubted combine only by means of affinity.
The manner in which these other combinations are formed has been already hinted, and shall be considered more fully afterwards; at present we shall only attempt to explain the action of caloric. Let us suppose, then, that caloric is presented to oxygen; that they combine together in a certain proportion, and saturate each other. The product of this combination is oxygen gas; a substance possessed of properties very different from those of caloric or oxygen in a concrete state; it is incapable of being decomposed by any merely mechanical method, and exhibits all the appearances of a simple substance. Let us therefore consider this compound for a moment as a simple substance. May it not still have an affinity for caloric? and will it not, in that case, unite with it? Oxygen gas and caloric have an affinity for each other; accordingly, when presented to one another they combine in a certain proportion, and form a new compound, differing from oxygen gas, properly so called, in elasticity, specific gravity, and several other particulars. The affinity, however, between oxygen gas and caloric is much feebler than that between oxygen and caloric; for the new compound is easily broken, and the caloric absorbed by many other substances. We can even conceive this new compound still to have an affinity for caloric, to unite with it, and to form another compound, the affinity between the ingredients of which is still feebler. And in this manner may the indefinite increase of temperature be accounted for.
Substances may be conceived to be conductors of caloric inversely as their affinity for it. Good conductors may have very little affinity for caloric; and for that reason it may be easily forced through them by the repulsion of its own particles. But those substances which have a great affinity for caloric, combine with it the moment it is presented to them; and consequently it cannot pass through them. Thus, when it is presented to ice, the affinity between the two substances is so great, that the caloric unites with the very first particles of ice which it meets with. The particles behind these cannot receive any caloric, except by attracting it from the particles with which it has already combined. But the affinity of one particle of ice for caloric cannot be greater than that of another particle of ice; and the union of two bodies cannot be broken by a force not greater than that which unites them; therefore the caloric cannot pass from one particle to another. Consequently, supposing all the particles to keep their places, no new caloric could enter. Just as when a piece of marble is put into sulphuric acid, the crust of sulphate of lime which very soon covers it prevents the acid from getting to the particles of marble within. But as soon as a particle of ice unites with caloric, water, the new compound, leaves its station, and allows the caloric a passage to the other particles.
In the same manner, when caloric is presented to water, it combines with the outermost stratum of particles, and forms with them a compound which cannot be decomposed by the other particles of the water, because their affinity for caloric is no greater than that of the particles already united with it. No more caloric, then, could gain admission, were it not that (the specific gravity of the new compound being inferior to that of the uncombined water) it immediately changes its place, and allows another stratum of particles to occupy its room. These unite with caloric, and are displaced in their turn. And in this manner the process goes on, till all the particles have combined with caloric; or, which is the same thing, till the whole of the water is heated.
But supposing the first stratum of particles to remain in their place after their union with caloric, we can conceive an affinity still to subsist between the new compound, thus formed, and caloric. In that case the new compound, which we shall call A, would combine with an additional dose of caloric, and form a second compound B, differing in several respects from the first. We can conceive also the affinity between the first compound A and caloric to be inferior to that between water and caloric. In that case, the second stratum of particles of water would separate the additional dose with which the first stratum had united. In this manner would two strataums of particles combine with caloric. The first stratum of particles would combine with another dose of caloric, and form a second compound B as before. But this compound could not now be decomposed by the second stratum of particles, because because they had already united with a dose of caloric; and therefore their affinity for a new dose could be no greater than that of the first stratum of particles. The process of heating could go on no farther. But we can conceive the second compound B, into which the first stratum has entered, still to have an affinity for caloric, to combine with a dose of it, and to form with it a third compound C. We can conceive, at the same time, the affinity between the second compound B and caloric to be less than that between the first compound A and caloric. In that case, the second stratum of particles would take this last dose from the first stratum, and form with it a second compound B. The third stratum of particles, which is still uncombined with caloric, would now attract this new dose from the second stratum, and combine with it. And, supposing the caloric still flowing towards the water, the first stratum would again form the third compound C, by uniting with a fresh dose; this new dose would be again attracted by the second stratum, and the first stratum would again form the third compound C, by uniting with another dose of caloric. Thus three strata of particles would be combined with caloric; the first stratum would contain three doses, the second stratum two, and the third one. The process of heating would again stop; because now the affinity of the second stratum is no greater than that of the first, nor the affinity of the third stratum greater than that of the second, nor that of the fourth than that of the third. But we can conceive an affinity still to subsist between caloric and the third compound C, into which the first stratum has entered, and this affinity, at the same time weaker than that between the second compound B and caloric. In that case they would combine and form a fourth compound D. This new dose would be attracted by the second stratum of particles, which would combine with it and form the third compound C; the third stratum would attract it from the second, and form with it the second compound B; and the fourth stratum would attract it from the third, and enter into the first compound A. The first stratum would again enter into the fourth compound D; which would be again decomposed by the second stratum; and the compound formed by the second stratum, by the third stratum. The fourth compound D would be again formed by the first stratum, and again decomposed by the second stratum. It would be formed a third time, and could not now be decomposed. Four strata of particles would now have combined with caloric; the first stratum with four doses; the second, with three doses; the third, with two; and the fourth, with one. We can conceive this process to go on exactly in the same manner, till all the particles of water have combined with a dose of caloric. In that case, the quantity of caloric combined with every stratum of particles would form a regular decreasing series from that part of the water at which the caloric enters to that part which is farthest distant from it. The process of heating would go on very slowly; and the heat of that part of the water, which is farthest distant from the source of caloric, could never be nearly equal to that of the part which is nearest to that source. This seems in fact to be the manner in which all those solids are heated which are bad conductors of caloric; in all probability it is the way in which all solids are heated.
That caloric combines with bodies merely by means of affinity, seems at first sight contrary to fact; for there is no substance whatever which may not be cooled indefinitely merely by surrounding it with other bodies which are colder than itself. Place a piece of hot iron, reciprocal for instance, in cold water, it is very soon cooled down to the temperature of that liquid. This seems plain enough; the attraction of water for caloric is greater than that of iron; but reverse the experiment; put hot water within cold iron, and the water is cooled in its turn down to the temperature of the iron; so that the iron also has a greater affinity for caloric, as well as the water; which is absurd.
But it ought to be remembered, that caloric not only possesses affinity, but that it has another property also, of which every other species of matter, except perhaps light, seems to be destitute, a repulsion between its own particles. It is necessary for all organized bodies, and probably for all bodies, that they should possess a certain quantity of caloric; and on this account the greatest care has been taken to secure its equal distribution. This seems to be one use at least of its repulsive power; a power which is never destroyed, however closely caloric is united with other bodies. We have shewn already, that this power is increased by diminishing the quantity of surrounding caloric; and when thus increased to a certain degree, it may at last equal, and even exceed, the affinity between the caloric and the bodies to which it is united; and in that case part of the caloric would necessarily fly off. It seems to be in this manner that bodies reciprocally cool each other, and that they have always a tendency to an equilibrium of temperature. Thus steam by cold is converted into water, and water into ice. And the affinity between bodies and that caloric which is employed in regulating the temperature seems to be so weak, that the repulsion between the particles of caloric easily overcomes it, and restores the equilibrium. But the affinity between some substances and caloric is so great, that no diminution of temperature has been found sufficient to overcome it. This is the case, as we have already seen, with oxygen gas.
The specific caloric of bodies seems to depend on two things; their affinity for caloric, and the distance between their particles. For what is temperature but difference in the disposition of a body to part with caloric? The more caloric a body is disposed to part with, we call its bodies' temperature the higher; the less it parts with when a colder body is applied, its temperature is said to be the lower. If oxygen gas parts with no caloric to a thermometer which stands at —10°, we say its temperature is —10°; yet we know that even then it contains, in all probability, much more caloric than the mercury in the thermometer does. Now the stronger the affinity between any substance and caloric, the greater quantity of caloric will be required before the repulsion between its particles is sufficient to overcome this attraction; consequently the more caloric is necessary to raise it a given number of degrees. And the farther distant the particles of bodies are, the farther from one another must the particles of caloric be to which they are united; and consequently the weaker must be the repulsion between them.
We cannot deny how new this theory of the action of caloric will appear to those who have been accustomed ed to look upon Dr Crawford's opinions on this subject as fully proved; nor do we pretend that it can be reconciled with these opinions. But this, we hope, is no proof of its falsehood. We think it can be fairly deduced from Dr Black's doctrine of latent heat: we know, too, that Bergman believed caloric capable of combining chemically with bodies: and Morveau has not only embraced the same opinion, but seems to affirm, that all the combinations into which caloric enters are chemical*. And were this question to be decided by authority, we appeal to all the world, whether other three men could be produced to whose decisions one would more willingly submit (1). We do not, however, mean to rely its evidence on authority; let it be compared with facts, and put to the test of experiment; and by its correspondence with these let it stand or fall.
12. Caloric both hastens the solution of salts in water, and increases the solvent power of the water; for water dissolves a much greater quantity of almost every salt when hot than when cold. The reason that caloric produces these effects is obvious from those properties of it which have been described. It hastens solution by putting the particles of the fluid in motion, and thus bringing all of them into contact with the salt: for only those particles can act as solvents which are in contact with the salt. It increases the solvent power of the fluid by combining with it, and forming a compound which has a greater affinity for the salt, and which therefore dissolves more of it than the fluid alone would have done. This new compound is destroyed by cooling; and then the additional dose of the salt which had been dissolved is precipitated.
13. We should come now to the consideration of the two remaining questions proposed at the end of the second chapter, Why do bodies combine with oxygen at one temperature and not at another? And why is caloric necessary to produce this union? But as the difficulty of these questions is not inferior to their importance, we shall delay any attempt to answer them till we come to treat of affinity.
14. It now only remains to consider the methods by which caloric may be obtained in a sensible state. These methods may be reduced to four: combustion, percussion, friction, and light: the last of which shall be considered afterwards.
We have seen already, that the combustion of simple combustibles and metals is merely their combination with oxygen, during which the oxygen parts with the caloric with which it was formerly united. Now the very same thing takes place in other combustions. The combustible unites with oxygen, which at the same time gives out its caloric. The change then which the combustible body suffers is not owing to the action of caloric on it, but to its combining with oxygen. The very same change can be brought about without any of the usual phenomena which attend combustion, simply by presenting the oxygen combined with some other body instead of caloric. Nitric acid, for instance, is a body which contains in it a good deal of oxygen: If phosphorus be mixed with this acid, it attracts part of the oxygen, and, without any of the usual phenomena which attend combustion, is converted into phosphoric acid. Strictly speaking, then, combustion is nothing else but the combination of oxygen with the burning body, and the term might therefore be used in every case where such an union takes place; and in this sense indeed it is now employed by several writers. But the term combustion is in common language confined to those cases where the oxygen was previously combined with caloric, and where a quantity of heat and light become sensible; and perhaps it would be better, in order to prevent ambiguity, never to employ it in any other sense.
We are not yet absolutely certain that caloric and light may not become sensible in other combinations besides those into which oxygen enters. There are other substances besides oxygen capable of combining with caloric; for instance, hydrogen and azote: and unless their affinity for caloric be greater than for any other substance, they may be capable of combining with other substances, and separating from caloric, at least the impossibility of this has never yet been demonstrated. It is improper, therefore, to appropriate the word combustion to the combinations of oxygen, till it can be shown that the phenomena usually denoted by that name are never owing to any other cause. There is even one case in which these phenomena present themselves, in which we are next to certain that oxygen has no share. There is an affinity between sulphur and iron, and a high temperature promotes their union. When these substances are mixed together, and heated till they just begin to appear red hot, they combine together, and at the same time, as the Dutch chemists first observed, a good deal of caloric and light is evolved. The very same phenomenon appears in a vacuum, or in any kind of air whatever. The explanation of them is very simple and obvious. The sulphur or the iron, or perhaps both, had previously been combined with a quantity of caloric; and when they united together, this caloric of course separated from them.
The theory of combustion adopted by the earlier chemists was very different from the preceding. Stahl, or some as has been already explained, considered combustion in every instance as owing to the separation of phlogiston; and this opinion soon became universal. He considered phlogiston as the same thing with the element of fire; which was capable both of becoming fixed in bodies, and of existing in a state of liberty. Two of its properties in this last state were heat and light. The heat and the light, then, which became sensible during combustion, were nothing else, according to Stahl, but two properties of phlogiston or the element of fire. Macquer, to whose illustrious labours several of the most important branches of chemistry owe their existence, by Macquer, we believe, the first person who perceived a striking defect in this theory of Stahl. Sir Isaac Newton had proved that light is a body; it was absurd, therefore, to make it a mere property of phlogiston or the element of fire. Macquer accordingly considered phlogiston as nothing else but light fixed in bodies. This opinion was embraced by a great number of the most distinguished philosophers.
(1) The same opinion has been embraced by Seguin, Pictet, Gadolin, and several other philosophers. We did not mention them, because the theory given above differs in a few particulars from theirs. But we have derived much instruction from their ingenious writings; and many of the facts, which we have given, were obtained from them. distinguished chemists; and many ingenious arguments were brought forward to prove its truth. But if phlogiston be only light fixed in bodies, whence comes the heat that manifests itself during combustion? Is this heat merely a property of light? Dr Black proved that heat is capable of combining with, or becoming fixed in bodies which are not combustible, as in ice and water; and concluded of course, that it is not a property but a body. From that time heat or caloric was considered by the greatest number of chemists as a distinct substance from phlogiston.
Soon after this, a phenomenon, which had been observed from the earliest ages, and which probably, for that very reason, had been neglected, began to be attended to; that combustibles would not burn except in contact with air. Dr Priestley observed, that the air in which combustibles had been suffered to burn till they were extinguished, had undergone a very remarkable change; for no combustible would afterwards burn in it, and no animal could breathe it without suffocation (k). He concluded, as Dr Rutherford had done before him, that this change was owing to phlogiston; that the air had combined with that substance; and that air was necessary to combustion, by attracting the phlogiston, for which it had a strong affinity. If so, phlogiston could not be light any more than caloric; for if it separated from the combustible merely by combining with air, it could not surely display itself in the form of light. The question then recurred with double force, What is phlogiston? Dr Crawford, of whose ingenious experiments on the specific caloric of bodies we have already given an account, without attempting to answer this question, made a considerable improvement in the theory of combustion, by supposing that the phlogiston of the combustible combined with the air, and at the same time separated the caloric and light with which that fluid had been previously united. The heat and the light, then, which appeared during combustion, existed previously in the air. This theory was very different from Stahl's, and certainly a great deal more satisfactory. But still the question, What is phlogiston? remained to be answered. Mr Kirwan, who had already raised himself to the first rank among chemical philosophers by many important discoveries, and many ingenious investigations of some of the most difficult parts of chemistry, attempted to answer this question, and to prove that phlogiston was the same with hydrogen*. The subject was now brought to a state capable of the most complete decision. Does hydrogen actually exist in all combustible substances? and is it separated from them during every combustion? The French chemists who answered his treatise, showed that this is by no means the case; and that therefore there was no proof whatever of the identity of phlogiston and hydrogen. And Mr Kirwan in consequence, with that candour which distinguished superior minds, gave up his opinion as untenable.
Mr Lavoisier had already put the question, What evidence is there of the existence of phlogiston at all? of phlogiston? There is only this single proof, that substances after decomposition are different from what they formerly were. That this difference takes place is certainly true; but it is owing, not to the separation of any substance, but to the combination of one. It follows, therefore, that there is no proof whatever of the existence of any such substance as phlogiston in nature; and of course we must conclude, that no such substance exists (v).
15. It is well known, that heat is produced by the percussion of hard bodies against each other. When a piece of iron is smartly and quickly struck with a hammer, it becomes red hot; and the production of sparks by the collision of flint and steel is too familiar a fact to require being mentioned. No heat, however, has ever been observed to follow the percussion of liquids, nor of soft bodies which easily yield to the stroke.
It has long been known, that hammering increases the density of metals. The specific gravity of iron before hammering is 7.988; after being hammered, 7.840; that of platinum before hammering is 19.504; after it, 23.00. Now condensation diminishes the specific caloric of bodies. After one of the clay pieces used in Wedgwood's thermometer has been heated to 120°, it is reduced to one half of its former bulk, though it has lost only two grains of its weight, and its specific caloric is at the same time diminished one third*. But we cannot conceive the specific caloric of a body to be diminished without its giving out at the same time a quantity
(k) These very observations had been made almost a century before by Mayow; but chemistry was then in its infancy; little attention was paid to them, and they had been forgotten.
(l) Mr Lavoisier was therefore the author of what is called the antiphlogistic theory in chemistry, or the theory which accounts for the phenomena of chemistry without the assistance of phlogiston. It has been so called in opposition to the theory of Stahl, which explained everything by means of phlogiston, and which is therefore called the phlogistic theory.
Some chemists have affected to omit Lavoisier's name altogether, when they spoke of the antiphlogistic theory. According to them, that theory was founded upon the experiments and discoveries of other chemists, and Lavoisier had no other merit but that of bringing it into public notice.
That Mr Lavoisier virtually at least claimed several of the discoveries of others, we are forced to be under the necessity of acknowledging; and that many of the experiments, brought forward to disprove the existence of phlogiston, were first made by others, is known to all the world; but it is equally evident, that the first person who actually formed the theory was Lavoisier; and surely the merit lies in that. It is not those who collect the stones, and the timber, and the mortar, but he who lays the plan, and shows how to put the materials together, that is in reality the builder of the house. Who did not know, as well as Newton, that a stone fell to the ground, and that the planets revolved round the sun? and yet, who but Newton could have formed the theory of gravitation? We would not be understood to detract any thing from the merit of the other illustrious philosophers who have adorned the present age, many of whom are at least equal, and some of them superior to Lavoisier; but we are afraid that envy, or some worse motive, guided the pen of one at least of the most active and violent antagonists of that illustrious and unfortunate philosopher. quantity of caloric; and we know for certain that caloric is evolved during condensation. A thermometer placed within a condenser rises several degrees every time air is thrown in. We can even see a reason for this. When the particles of a body are forced nearer each other, the repulsive power of the caloric combined with them is increased, and consequently a part of it will be apt to fly off. Now, after a bar of iron has been heated by the hammer, it is much harder and brittle than before. It must then have become denser, and consequently must have parted with caloric. It is an additional confirmation of this, that the same bar cannot be heated a second time by percussion until it has been exposed for some time to a red heat. It is too brittle, and flies to pieces under the hammer. Now brittleness seems in most cases owing to the absence of the usual quantity of caloric. Glass unannealed, or, which is the same thing, that has been cooled very quickly, is always extremely brittle. When glass is in a state of fusion, there is a vast quantity of caloric accumulated in it, the repulsion between the particles of which must of course be very great; so great indeed, that they would be disposed to fly off in every direction with inconceivable velocity, were they not confined by an unusually great quantity of caloric in the surrounding bodies; consequently if this surrounding caloric be removed, the caloric of the glass flies off at once, and more caloric will leave the glass than otherwise would leave it, because the velocity of the particles must be greatly increased. Probably then the brittleness of glass is owing to the deficiency of caloric; and we can scarcely doubt that the brittleness of iron is owing to the same cause, if we recollect that it is removed by the application of new caloric. Part therefore of the caloric which appears in consequence of percussion seems to proceed from the body struck; and this is doubtless the reason why those bodies, the density of which is not increased by percussion, as liquids and soft substances, are not heated at all.
We say part of the caloric; because, often at least, part of it is probably owing to another cause. By condensation, as much caloric is evolved as is sufficient to raise the temperature of some of the particles of the body high enough to enable it to combine with the oxygen of the atmosphere. The combination actually takes place, and a great quantity of additional caloric is separated by the decomposition of the gas. That this happens during the collision of flint and steel cannot be doubted; for the sparks produced are merely small pieces of iron heated red hot by uniting with oxygen during their passage through the air, as any one may convince himself by actually examining them. Mr. Lane has shown that iron produces no sparks in the vacuum of an air-pump; but Mr. Kirwan has observed that they are produced under common spring water; and we know that iron at a certain temperature is capable of decomposing water.
When quartz, rock crystal (m), or other very hard stones, are struck against one another, they emit sparks, if they be often made to emit sparks above a sheet of white paper, there are found upon it a number of small black bodies, not very unlike the eggs of flies. These bodies are hard but friable, and when rubbed on the paper leave a black flake. When viewed with a microscope, they seem to have been melted. Muriatic acid changes their colour to a green, as it does that of limes. These substances evidently produced the sparks by being heated red hot. Lamanon (s) supposes that they are particles of quartz combined with oxygen. Were that the case, the phenomenon would be precisely similar to that which is produced by the collision of flint and steel. That they are particles of quartz cannot be doubted; but to suppose them combined with oxygen is contrary to all experience: for these stones never show any disposition to combine with oxygen even when exposed to the most violent heat. La Mettrie made experiments on purpose to see whether Lamanon's opinion was well founded; but they all turned out unfavourable to it. And Monge ascertained, that the particles described by Lamanon were pure crystal unaltered, with a quantity of black powder adhering to them. He concludes accordingly, that these fragments had been raised to so high a temperature during their passage through the air, that they set fire to all the minute bodies that came in their way. We must therefore either suppose that all the caloric was produced by mere condensation, which is not probable, or acknowledge that we cannot explain the phenomenon.
16. Caloric is not only produced by percussion, but also by friction. Fires are often kindled by rubbing pieces of dry wood smartly against one another. It is well known that heavy loaded carts sometimes take fire by the friction between the axle-tree and the wheel. Now in what manner is the caloric evolved or accumulated by friction? Not by increasing the density of the bodies rubbed against each other, as happens in cases of percussion; for heat is produced by rubbing soft bodies against each other, the density of which therefore cannot be increased by that means, as any one may convince himself by rubbing his hand smartly against his coat. It is true, indeed, that heat is not produced by the friction of liquids, but then they are too yielding
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(m) These stones are composed of almost pure silica. (s) This ingenious and unfortunate young man, to whom we are indebted for these facts, fell a victim to his ardour for knowledge. He accompanied La Perouse in his last voyage, and was murdered with the most savage cruelty, together with La Langlois and several others, by the natives of the island of Maoua. When a man of genius, anxious to acquire honest fame, and a man too nobly disinterested as Lamanon, thus falls prematurely before he has attained the object of his wishes,
"Cut off from nature's and from glory's course! Which never mortal was so fond to run,"
—who can withhold the tribute of regret and admiration, when they
—conjecture what he might have proved, "And think life only wanting to his fame." to be subjected to strong friction. It is not owing to the specific caloric of the rubbed bodies decreasing; for Count Rumford found, that there was no sensible decrease†, nor, if there were a decrease, would it be sufficient to account for the vast quantity of heat which is sometimes produced by friction.
Count Rumford took a cannon cast solid and rough as it came from the foundry; he caused its extremity to be cut off, and formed, in that part, a solid cylinder attached to the cannon 7½ inches in diameter and 9½ inches long. It remained joined to the rest of the metal by a small cylindrical neck. In this cylinder a hole was bored 3½ inches in diameter and 7½ inches in length. Into this hole was put a blunt steel borer, which by means of horses was made to rub against its bottom; at the same time a small hole was made in the cylinder perpendicular to the bore, and ending in the solid part a little beyond the end of the bore. This was for introducing a thermometer to measure the heat of the cylinder. The cylinder was wrapped round with flannel to keep in the heat. The borer pressed against the bottom of the hole with a force equal to about 10,000 lbs. avoirdupois, and the cylinder was turned round at the rate of 32 times in a minute. At the beginning of the experiment the temperature of the cylinder was 65°; at the end of 30 minutes, when it had made 960 revolutions, its temperature was 130°. The quantity of metallic dust or scales produced by this friction amounted to 837 grains. Now, if we were to suppose that all the caloric was evolved from these scales, as they amounted to just 3/4 part of the cylinder, they must have given out 94° to raise the cylinder 1°, and consequently 6616° to raise it 70° or to 130°, which is certainly incredible†.
Neither is the caloric evolved during friction, owing to the combination of oxygen with the bodies themselves or any part of them. By means of a piece of clock-work, Mr. Picquet made small cups (fixed on the axis of one of the wheels) to move round with considerable rapidity, and he made various substances rub against the outsides of these cups, while the bulb of a very delicate thermometer placed within them marked the heat produced. The whole machine was of a size sufficiently small to be introduced into the receiver of an air pump. By means of this machine a piece of adamantine spar was made to rub against a steel cup in air; sparks were produced in great abundance during the whole time, but the thermometer did not rise. The same experiment was repeated in the exhausted receiver of an air pump (the manometer standing at four lines); no sparks were produced, but a kind of phosphoric light was visible in the dark. The thermometer did not rise. A piece of brass being made to rub in the same manner against a much smaller brass cup in air, the thermometer (which almost filled the cup) rose 0.3°, but did not begin to rise till the friction was over. This shows us that the motion produced in the air carried off the caloric as it was evolved. In the exhausted receiver it began to rise the moment the friction began, and rose in all 1.2°. When a bit of wood was made to rub against the brass cup in the air, the thermometer rose 0.7°, and on substituting also a wooden cup it rose 2.1°, and in the exhausted receiver 2.4°, and in air condensed to 1½ atmospheres it rose 0.5°†.
If these experiments be not thought conclusive, we have others to relate, which will not leave a doubt that the heat produced by friction is not connected with the decomposition of oxygen gas. Count Rumford contrived, with his usual ingenuity, to inclose the cylinder above described in a wooden box filled with water, which effectually excluded all air, as the cylinder itself and the borer were surrounded with water, and at the same time did not impede the motion of the instrument. The quantity of water amounted to 18,77 lbs. avoirdupois, and at the beginning of the experiment was at the temperature of 60°. After the cylinder had revolved for an hour at the rate of 32 times in a minute, the temperature of the water was 107°; in 30 minutes more it was 178°; and in 2 hours and 30 minutes after the experiment began, the water actually boiled. According to the computation of Count Rumford, the caloric produced would have been sufficient to heat 26,58 lbs. avoirdupois of ice-cold water boiling hot; and it would have required 9 wax candles of moderate size, burning with a clear flame all the time the experiment lasted, to have produced as much heat. In this experiment all access of water into the hole in the cylinder where the friction took place was prevented. But in another experiment, the result of which was precisely the same, the water was allowed free access†.
The caloric, then, which appears in consequence of friction, is neither produced by an increase of the density, nor by an alteration in the specific caloric of the substances exposed to friction, nor is it owing to the dearth present composition of the oxygen of the atmosphere—Whence is explicable, then is it derived? This question we are altogether unable to answer. We cannot, however, think, that the conclusion which Count Rumford is disposed to draw from his experiments is warranted by the premises. He supposes that because we cannot explain the manner that proof that caloric is accumulated by friction, there is no such substance as caloric at all, but that it is merely a peculiar kind of motion. We would beg leave to ask, how the facts mentioned in the former part of this chapter, many of which were furnished by this ingenious philosopher himself, and all of which combine to render the existence of caloric as a substance probable, can be destroyed and set aside, merely because there are other phenomena in nature connected with caloric which cannot be accounted for? Were it possible to prove that the accumulation of caloric by friction is incompatible with its being a substance, in that case Count Rumford's conclusion would be a fair one; but this surely has not been done. We are certainly not yet sufficiently acquainted with the laws of the motion of caloric (allowing it to be a substance) to be able to affirm with certainty that friction could not cause it to accumulate in the bodies rubbed. This we know at least to be the case with electricity. Nobody has been hitherto able to demonstrate, in what manner it is accumulated by friction; and yet this has not been thought a sufficient reason to deny its existence.
Indeed there seems to be a very close analogy between caloric and electric matter. Both of them tend to diffuse themselves equally, both of them dilate bodies, both of them fuse metals, and both of them kindle combustible substances. Mr. Achard has proved, that electricity can be substituted for caloric even in those cases where its agency seems peculiarly necessary; for he found that, by constantly supplying a certain quantity of the electric fluid, eggs could be hatched just as when they are kept... kept at the temperature of 103°. An accident indeed prevented the chickens from actually coming out; but they were formed and living, and within two days of bursting their shell. Electricity has also a great deal of influence on the heating and cooling of bodies. Mr Pilet exhausts a glass globe, the capacity of which was 1220 cubic inches, till the manometer within it stood at 175 lines. In the middle of this globe was suspended a thermometer which hung from the top of a glass rod fixed at the bottom of the globe, and going almost to its top. Opposite to the bulb of this thermometer two lighted candles were placed, the rays of which, by means of two concave mirrors, were concentrated on the bulb. The candles and the globe were placed on the same board, which was supported by a non-conductor of electricity. Two feet and a half from the globe there was an electrifying machine, which communicated with a brass ring at the mouth of the globe by means of a metallic conductor. This machine was kept working during the whole time of the experiment; and consequently a quantity of electric matter was constantly passing into the globe, which formed an atmosphere not only within it, but at some distance round, as was evident from the imperfect manner in which the candles burned. When the experiment began the thermometer stood at 49.8°. It rose to 70.2° in 73 minutes. The same experiment was repeated, but no electric matter thrown in; the thermometer rose from 49.8° to 70.2° in 105°; so that the electricity halved the heating almost a third. In the first experiment the thermometer rose only to 71.3°, but in the second it rose to 77°. This difference was doubtless owing to the candles burning better in the second than the first experiment; for in other two experiments made exactly in the same manner, the maximum was equal both when there was and was not electric matter present.
These experiments were repeated with this difference, that the candles were now inflated, by placing their candlesticks in dishes of varnished glass. The thermometer rose in the electrical vacuum from 52.2° to 74.7° in 105°; in the simple vacuum in 96°. In the electrical vacuum the thermometer rose to 77°; in the simple vacuum to 86°. It follows from these experiments, that when the globe and the candles communicated with each other, electricity halved the heating of the thermometer; but that when they were inflated separately, it retarded it. One would be apt to suspect the agency of electricity in the following experiment of Mr Pilet: Into one of the brass cups formerly described, a small quantity of cotton was put to prevent the bulb of the thermometer from being broken. As the cup turned round, two or three fibres of the cotton rubbed against the bulb, and without any other friction the thermometer rose five or six degrees. A greater quantity of cotton being made to rub against the bulb, the thermometer rose 15 degrees.
We do not mean to draw any other conclusion from these facts, than that electricity is very often concerned in the heating of bodies, and that probably some such agent is employed in accumulating the heat produced by friction. Supposing that electricity is actually a substance, and taking it for granted that it is different from caloric, does it not in all probability contain caloric as well as all other bodies? Has it not a tendency to accumulate in all bodies on friction, whether conductors or non-conductors? May it not then be accumulated in those bodies which are rubbed against one another? or, if they are good conductors, may it not pass through them during the friction in great quantities? May it not part with some of its caloric to these bodies, either on account of their greater affinity or some other cause? and may not this be the source of the caloric which appears during friction?
CHAP. VI. Of Light.
By means of light bodies are rendered visible. Light has been considered as a substance composed of minute particles moving in straight lines from luminous bodies with inconceivable rapidity. The discoveries of Newton established this opinion on the firm basis of mathematical demonstration; and since his time it has been generally embraced. Huyghens, indeed, and Euler, advanced another (o). They considered light as a subtle fluid, filling all space, which rendered bodies visible by its undulations. But they supported their hypotheses rather by flinging objections to the theory of Newton, than by bringing forward direct proofs. Their objections, even if valid, instead of establishing their own opinions, would prove only that the phenomena of light are not completely understood; a truth which no man will refuse to acknowledge, whatever side of the question he adopts. Newton and his disciples, on the contrary, have shown, that the known phenomena of light are insufficient with the undulations of a fluid, and have brought forward a great number of direct arguments, which it has been impossible to answer, in support of their theory. It can hardly be doubted, therefore, that the Newtonian theory of light is the true one.
Dr Bradley, who, by a number of very accurate experiments, and a process of reasoning peculiarly ingenious, discovered the aberration of light of the fixed stars, has shown from it that the velocity of light is to that of the earth in its orbit as 10313 to 1. Light therefore moves at the rate of 195218 miles in a second.
Light, by means of a prism, may be separated into seven rays, differing from each other in colour; red, orange, yellow, green, blue, indigo, violet. None of these are capable of farther decomposition. Marat, indeed, pretended that he had reduced them to three; but his experiments are now known to have been merely philosophical frauds.
When light passes obliquely into a denser medium, it differs refracted towards the perpendicular; when into a rarer, from the perpendicular. Sir Isaac Newton discovered that the rays differed in their refrangibility in the order in which they have been named, the red being the least, the violet the most refrangible. Mr Blair has observed, that the ratios of the refrangibility of the different rays, though not their order, vary somewhat in different mediums.
(o) Dr Franklin did the same, without taking any notice of these philosophers, of whose opinions perhaps he was ignorant. See Trans. Philad. III. 5. When light passes within a certain distance of a body, parallel to which it is moving, it is bent towards it; when it passes at a greater distance, it is bent from it.
The first of these properties is called refraction, the second deflection. Now the rays differ in these properties in the order in which they were named; the red being softest, the violet least inflexible and deflectable. This was suspected by David Rittenhouse *, but was first demonstrated by the ingenious experiments of Mr Brougham †.
When light falls upon a visible body, some of it is reflected back; and the more polished or the whiter any surface is, the more light it reflects. The rays of light differ also in reflectivity (see Reflexity, Suppl.), the red being the most, the violet the least reflexible. This discovery we owe to the same ingenious gentleman ‡.
These properties of light constitute the subject of Optics; to which we refer those who wish to see them investigated. We mention them here because they prove that light is acted on by other bodies, that it is subjected to the laws of attraction, and, consequently, that it possesses gravity.
2. The particles of light seem also, like those of caloric, to possess the property of repelling one another; at least their rapid motion, in all directions, from luminous bodies, seems to be owing to some such property.
3. Light is capable of entering into bodies, and remaining in them, and of being afterwards extricated without any alteration. Father Beccaria, and several other philosophers, have shown us by their experiments, that there are a great many substances which become luminous after being exposed to the light. This property was discovered by carrying them instantly from the light into a dark place, or by darkening the chamber in which they were exposed. Most of these substances, indeed, lose this property in a very short time, but they recover it again on being exposed to the light; and this may be repeated as often as we please. We are indebted to Mr Canton for some very interesting experiments on this subject, and for discovering a composition which possesses this property in a remarkable degree. He calcined some common oyster shells in a good coal fire for half an hour, and then pounded and fitted the purest part of them. Three parts of this powder were mixed with one part of the flowers of sulphur, and rammed into a crucible which was kept red hot for an hour. The brightest parts of the mixture were then scraped off, and kept for use in a dry phial well stoppered. When this composition is exposed for a few seconds to the light, it becomes sufficiently luminous to enable a person to distinguish the hour on a watch by it. After some time it ceases to shine, but recovers this property on being again exposed to the light. Light then is not only acted upon by other bodies, but it is capable of uniting with them, and afterwards leaving them without any change.
It is well known that light is emitted during combustion; and it has been objected to this conclusion, that these bodies are luminous only from a slow and imperceptible combustion. But surely combustion cannot be suspected in many of Father Beccaria's experiments; when we reflect that one of the bodies on which they were made was his own hand, and that many of the others were altogether incombustible; and the phenomena observed by Mr Canton are also incompatible with the notion of combustion. His pyrophorus shone only in consequence of being exposed to light, and lost that property by being kept in the dark. It is not exposure to light which causes substances capable of combustion at the temperature of the atmosphere to become luminous, but exposure to air. If the same temperature continues, they do not cease to shine till they are consumed; and if they cease, it is not the application of light, but of caloric, which renders them again luminous; but Canton's pyrophorus, on the contrary, when it had lost its property of shining, did not recover it by the application of heat, except it was accompanied by light. The only effect which heat had was to increase the separation of light from the pyrophorus, and of course to shorten the duration of its luminosity. Two glass globes, hermetically sealed, containing each some of this pyrophorus, were exposed to the light and carried into a dark room. One of them, on being immersed in a bath of boiling water, became much brighter than the other, but in ten minutes it ceased to give out light; the other remained visible for more than two hours. After having been kept in the dark for two days, they were both plunged into a bath of hot water; the pyrophorus which had been in the water formerly did not shine, but the other became luminous, and continued to give out light for a considerable time. Neither of them afterwards shone by the application of hot water; but when brought near to an iron heated to as scarcely to be visible in the dark, they suddenly gave out their remaining light, and never shone more by the same treatment; but when exposed a second time to the light, they exhibited over again precisely the same phenomena; even a lighted candle and electricity communicated some light to them. Surely these facts are altogether incompatible with combustion, and fully sufficient to convince us that light alone was the agent, and that it had actually entered into the luminous bodies.
It has been questioned, indeed, whether the light emitted by pyrophori be the same with that to which they are exposed. Mr Wilson has proved, that in many cases at least it is different, and in particular that on many pyrophori the blue rays have a greater effect than any other, and that they cause an extraction of red light. Mr de Groffler has thrown the same thing with regard to the diamond, which is a natural pyrophorus ‡. Still, however, it cannot be questioned that the luminousness of these bodies is owing to exposure to light, and that the phenomenon is not connected with combustion.
But light appears capable, not only of entering into bodies, but of combining with them chemically. The combined phenomena of the phosphor seem to be instances of this, and a great many facts concur to prove that light enters into the composition of oxygen gas. When vegetables grow in the light, they give out oxygen gas; but no oxygen is extracted in the dark, even though heat be applied †. From this it is evident, that the formation of this gas from plants, or perhaps the decomposition of the water which they contain, depends upon the action of light; and that as this decomposition is chemical, the light to produce it must either combine with the oxygen or the hydrogen, or at least contribute to the combination of some other substance with one or other of them. When the oxyds of gold or silver are exposed... exposed to light, they are reduced to the metallic state*, and at the same time a quantity of oxygen gas is extracted†. In this case, it is evident that the light must either combine with the oxygen or the metals. If a quantity of nitric acid be exposed for some time to the light, it becomes yellow, as is well known, and a quantity of oxygen gas is found floating on its top. If it be now carried to a dark place, the oxygen is gradually absorbed, and the acid becomes colourless. In this case, nitric acid is decomposed by means of light, and reformed into nitrous acid and oxygen gas. The light must therefore have combined either with the nitrous acid or the oxygen. But no change whatever appears to have been produced in the nitrous acid; for if it be obtained in the dark by any other process, it has precisely the same properties. The oxygen, on the contrary, is converted into a gas. It is more probable, then, that the light has combined with the oxygen than with the acid. Hence there is reason to suspect that light makes one of the ingredients of oxygen gas. Caloric has already been shown to make another ingredient.
During combustion, a quantity of light as well as caloric is almost always evolved. We must conclude, therefore, that light makes a part of the composition either of the combustibles themselves, or of the oxygen gas with which they unite. We have already shown, that oxygen gas probably contains light; and this probability is confirmed by another fact. Substances may be combined with oxygen without the emission of any light, provided the oxygen be not in the state of a gas. If phosphorus, for instance, be put into nitric acid, it attracts oxygen, and is converted into phosphoric acid without the emission of any light. Now if the light which appears during combustion had been combined with the combustible, it ought to appear in all cases when that combustible is united with oxygen, whether the oxygen has previously been in the state of a gas or not. But as this is not the case, we may certainly infer, that the light which appears during combustion is extricated, not from the combustible, but from the oxygen gas. And this seems at present to be the opinion of the greater number of philosophers.
But we must acknowledge, that this conclusion is not without its difficulties, and difficulties, too, which, in the present state of chemistry, it does not seem possible to surmount.
In the first place, it is evident, that light may be produced during combustion, though the oxygen be not in the state of a gas: For if nitric acid be poured upon oil of turpentine, the oil takes fire, and burns with the greatest rapidity, and a great deal of light is emitted. This combustion is occasioned by the oxygen of the acid combining with the ingredients of the oil. It follows, therefore, if the light emitted was previously combined with the oxygen, that oxygen must contain light when not in the state of a gas. Mr Proult has shown that a great variety of similar combustions may be produced. But what is very remarkable, by proper caution the very same combinations may be made to take place without the visible-emission of any light. In that case they take place very slowly, as happens also when phosphorus decomposes nitric acid; so that the emission or non-emission of light seems to depend not upon the state of the oxygen, so much as upon the rapidity or slowness of the combination. It is true, indeed, as
the late Dr Hutton of Edinburgh observed, that light may be emitted in these slow combinations though it be not visible; and this is very probably the case: but then the proof is destroyed that light exists in oxygen gas, from its not appearing during combinations in which the oxygen did not exist previously in a gaseous state.
In the second place, the colour of the light emitted during combustion differs almost always accordinging to the combustible. During the combustion of phosphorus, tin, and zinc, the light emitted is white; during that of sulphur and bitumen, blue. Now if this light were united with the oxygen, why does it not appear always of the same colour, whatever be the combustible?
In the last place, the phenomena of phosphorescence show that light is capable of entering into other bodies as well as oxygen gas; and the emission of light on the collision of two flint stones, when no oxygen gas can be decomposed, is a proof of the same kind, which cannot be got over.
In the present state of chemistry, therefore, it cannot be concluded, that the light emitted during combustion does not exist in the combustibles as well as in the oxygen.
4. Light has the property of heating bodies. All light bodies, however, are not heated by it. Those which bodies are perfectly transparent, or which allow all the light to pass through them, suffer no alteration in their temperature. Thus light may be concentrated upon water or glass without producing any effect. Neither does it produce much change upon those bodies (mirrors, for instance) that reflect all or nearly all the light which falls upon them. And the insensibility of the alteration of temperature is always proportional to the fineness of the polish, or which is the same thing, to the quantity of light which is reflected. So that we have reason to conclude, that if a substance could be procured which reflected all the light that fell upon it, the temperature of such a substance would not be at all affected by light falling upon it. Dr Franklin exposed upon snow pieces of cloth of different colours (white, red, blue, black,) to the light of the sun, and found that they sunk deeper, and consequently acquired heat, in proportion to the darkness of their colour. Now it is well known that dark-coloured bodies, even when equally exposed to the light, reflect less of it than those which are light-coloured. But since the same quantity falls upon each, it is evident that dark-coloured bodies must absorb and retain more of it than those which are light-coloured. That such an absorption actually takes place is evident from the following experiment. Mr Thomas Wedgwood placed two lumps of luminous or phosphorescent marble on a piece of iron heated just under redness. One of the lumps of marble which was blackened over gave out no light; the other gave out a great deal. On being exposed a second time in the same manner, a faint light was seen to proceed from the clean marble, but none at all could be perceived to come from the other. The black was now wiped off, and both the lumps of marble were again placed on the hot iron: The one that had been blackened gave out just as little light as the other. In this case, the light which ought to have proceeded from the luminous marble disappeared; it must therefore have been stopped. stopped in its passage out, and retained by the black paint. Now black substances are those which absorb the most light, and they are the bodies which are most heated by exposure to light. Cavalli observed, that a thermometer with its bulb blackened stands higher than one which has its bulb clean, when exposed to the light of the sun, the light of day, or the light of a lamp.
Mr. Pieter made the same observation; and took care to ascertain, that when the two thermometers were allowed to remain for some time in a dark place, they acquired precisely the same height. He observed, too, that when both thermometers had been raised a certain number of degrees, the clean one fell a good deal faster than the other. But it is not a small degree of heat alone which can be produced by means of light. When its rays are concentrated by a burning glass, they are capable of setting fire to combustibles with ease, and even of producing a temperature at least as great, if not greater, than what can be procured by the most violent and best conducted fires. In order to produce this effect, however, they must be directed upon some body capable of absorbing and retaining them; for when they are concentrated upon transparent bodies, or upon fluids, mere air for instance, they produce little or no effect whatever. We may conclude, therefore, in general, that in all cases when light produces heat it is absorbed.
5. All bodies become luminous when their temperature is raised a certain number of degrees. No fact is more familiar than this; so well known indeed is it, that little attention has been paid to it. When a body becomes luminous by being heated in a fire, it is said in common language to be red hot. It follows from all the experiments hitherto made, that the temperature at which they become red hot is nearly the same in all bodies.—It seems to be pretty near 800°. A red hot body continues to shine for some time after it has been taken from the fire and put into a dark place. The constant accretion, then, either of light or heat is not necessary for the shining of bodies; but if a red hot body be blown upon by a strong current of air, it ceases to shine immediately. Consequently the moment the temperature of a body is diminished by a certain number of degrees, it ceases to be luminous.
Whenever a body reaches the proper temperature, it becomes luminous, independent of any contact of air; for a piece of iron wire becomes red hot while immersed in melted lead.
To this general law there is one remarkable exception. It does not appear that the gases become luminous even at a much higher temperature. The following ingenious experiment of Mr. T. Wedgwood seems to set the truth of this exception in a very clear point of view. He took an earthen ware tube B (fig. 5.), bent so in the middle that it could be sunk, and make several turns in the large crucible C, which was filled with sand. To one end of this tube was fixed the pair of bellows A; at the other end was the globular vessel D, in which was the passage F, furnished with a valve to allow air to pass out, but none to enter. There was another opening in this globular vessel filled with glass, that one might see what was going on within. The crucible was put into a fire; and after the sand had become red hot, air was blown through the earthen tube by means of the bellows. This air, after passing through the red-hot sand, came into the globular vessel. It did not shine; but when a piece of gold wire E was hung at that part of the vessel where the earthen ware tube entered, it became faintly luminous. A proof, that though the air was not luminous, it had been hot enough to raise other bodies to the shining temperature.
6. Thus it appears that light and heat reciprocally influence each other; that the fixation of light in bodies is the cause always produces heat, and that the application of sufficient strongly heat always occasions the extrication of light. Are heat and light, then, owing to the same cause? Does light become calorific merely by being fixed in bodies? and does calorific assume the appearance of light whenever it is extricated from them? In short, are calorific and light merely names for the same substance, called calorific when it is fixed in bodies, and light when in a state of liberty?
To these questions it may be answered, That if calorific and light were one and the same substance, they ought to produce precisely the same effects. Now this is not the case: a black body is not heated sooner by mere calorific than any other, though the contrary takes place when both are exposed to the light. Heat cannot make growing vegetables exhale oxygen gas, though light does it almost instantaneously. When oxy-muriatic acid (a compound of oxygen and muriatic acid) is exposed to the light, a quantity of oxygen gas flies off, and nothing remains but common muriatic acid. Light then decomposes this acid; for if you wrap up a bottle in black cloth, so as to exclude light, and then expose it equally to the sun, no such decomposition takes place. Now this decomposition cannot be produced by mere calorific. If the acid be heated, it simply evaporates without being altered. Chaptal has proved (p.), that the rays of light directed on certain parts of glasses, containing solutions of salts, cause them to crystallize in that part in preference to any other. These observations have been confirmed and extended by Mr. Dorthes. Now calorific produces no such effects, nor has the temperature any influence on the phenomenon.
These facts are sufficient to show that light and calorific, even when they have entered into bodies, produce different effects, and that therefore they have different properties (q.). But if the only difference between them were, that the one is in a state of liberty, the other in
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(p) Petit made the same observations in 1722. See Memoirs of the Academy of Sciences for that year, p. 95, and 331.
(q) We must acknowledge, however, that the following ingenious experiments of Professor Petit might be adduced, to prove that light and calorific possess at least one property in common, that of moving in straight lines.
He placed two concave mirrors of tin, of nine inches focus, at the distance of twelve feet two inches from one another. In the focus of one of them he placed a ball of iron two inches in diameter, heated so as not to be visible. that of combination; the moment light entered a body it ought to be no longer light but caloric, and consequently ought to produce precisely the same effects with caloric. And since this is not the case, we are warranted surely to conclude that light and caloric are not the same, but different substances. How then does caloric occasion the appearance of light, and light that of caloric?
We have seen already, that there is no body in nature which does not contain caloric; and light has such an influence upon every thing, it produces such important changes upon the animal and vegetable kingdoms, it can be extricated from such a vast number of bodies, that in all probability we may conclude, with regard to it also, that it exists in all, or in almost all, the bodies in nature. We have no means of ascertaining either the quantity of light or of caloric that exists in bodies; but if we were to judge from the quantity which appears during combustion, we must reckon it very considerable. Now, may there not exist a repulsion between the particles of caloric and light? It is not easy, at least, to see why light flies off during combustion with such rapidity, if this be not the case. If such a repulsion actually exists, it will follow that caloric and light cannot be accumulated in the same body beyond a certain proportion. If the caloric exceed, it will tend to drive off the light; if the light, on the contrary, happens to prevail, it will displace the caloric.
If caloric and light actually exist in all bodies, there must be an affinity between them and all other bodies; and this affinity must be so great, as to render ineffective the repulsion which exists between light and caloric. Let us suppose now, that these two substances exist in all bodies in certain proportions, it will follow, that the more either of caloric or light is added to any body, the stronger must the repulsion between their particles become; and if the accumulation be still going on, this repulsion will soon become great enough to balance their affinity for the body in which they exist, and consequently will dispose them to fly off. If caloric, for instance, be added to a body, whenever the body arrives at a certain temperature it becomes luminous, because part of the light which was formerly combined with it is driven off. This temperature must depend partly upon the affinity between the body and caloric, and partly upon its affinity for light. Pyrophori, for instance, the affinity between which and light does not seem to be very great, become luminous at a very moderate temperature. This is the case with the pyrophorus of Canton. A great many hard bodies become luminous when they are exposed to a moderate heat; fluor, for instance, carbonat of barytes, spar, tea shell, and a great many others, which are enumerated by Mr Thomas Wedgwood.
The same ingenious gentleman has observed, that gold, silver, copper, and iron, become luminous when heated visible in the dark; in the other was placed the bulb of a thermometer. In five minutes the thermometer rose from 4° to 14° (Reaumur). A lighted candle, which was substituted for the ball of iron, made the thermometer rise in one experiment from 4.6° to 14°; in another, from 4.2° to 14.3°. In this case both light and heat appeared to act. In order to separate them, he interposed between the two mirrors a plate of clear glass. Before the interposition of the glass, the thermometer had risen from 2° to 12°, where it was stationary. After the interposition of the glass it sunk in nine minutes to 5.7°; and when the glass was again removed it rose in seven minutes to 11.1°; yet the light which fell on the thermometer did not seem at all diminished by the glass. Mr Pictet therefore concluded, that the caloric had been reflected by the mirror, and that it had been the cause of the rise of the thermometer. In another experiment, a glass matrafs was substituted for the iron ball, nearly of the same diameter with it, and containing 2044 grains of boiling water. Two minutes after a thick screen of silk, which had been interposed between the two mirrors, was removed, a Fahrenheit's thermometer, which was in the other focus, rose from 47° to 50.5°; and the moment the matrafs was removed from the focus the thermometer again descended. On repeating the experiment, with this variation, that the bulb of the thermometer was blackened, it rose from 51.5° to 53.5°.
The mirrors of tin were now placed at the distance of 90 inches from each other; the matrafs with the boiling water in one of the foci, and a very sensible air thermometer in the other, every degree of which was equal to 1/36th of a degree of Reaumur. Exactly in the middle space between the two mirrors there was placed a very thin common glass mirror, suspended in such a manner that either side could be turned towards the matrafs. When the polished side of this mirror was turned to the matrafs, the thermometer rose only 0.5°; but when the side covered with tinfoil, and which had been blackened with ink and smoke, was turned toward the matrafs, the thermometer rose 3.5°. In another experiment, when the polished side of the mirror was turned to the matrafs, the thermometer rose 3°, when the other side 9.2°. On rubbing off the tinfoil, and repeating the experiment, the thermometer rose 18°. On substituting for the glass mirror a piece of thin white pasteboard of the same dimensions with it, the thermometer rose 10°. On putting a matrafs full of snow into one of the foci (the mirrors in this experiment were 10 feet distant from each other), the air thermometer sunk several degrees, and rose again when the matrafs was removed. When nitric acid was poured on the snow, the thermometer sunk 5° or 6° lower.
Taking it for granted that these experiments proved the motion of caloric in straight lines like light, Mr Pictet endeavoured to discover the velocity of its motion. For this purpose he placed two concave mirrors at the distance of 69 feet from each other; the one of tin as before, the other of platter gilt, and 18 inches in diameter. Into the focus of this last mirror he put the air thermometer, and the bullet of iron heated as before into that of the other. A few inches from the face of the tin mirror there was placed a thick screen, which was removed as soon as the bullet reached the focus. The thermometer rose the instant the screen was removed without any perceptible interval; hence he concluded, that the time caloric takes in moving 69 feet is too short to be measured. See Pictet sur le Feu, chap. iii. heated in times inversely proportional to their specific calories. Now the specific calories of these metals are in the following order:
Iron, Copper, Silver, Gold.
They become luminous, therefore, when exposed to the same degree of heat, in the following order:
Gold, Silver, Copper, Iron.
Now the smaller the specific calorie of any body is, the less must be the quantity of calorie necessary to raise it a given number of degrees; the sooner therefore must it arrive at the temperature at which it gives out light. It was natural to expect, then, if the emission of light from a body by the application of heat be owing to the repulsion between calorie and light, that those bodies should become luminous soonest in which that repulsion increases with the greatest rapidity; and this we see is precisely the case. The only question to be determined before drawing this conclusion is, Whether the same quantity of calorie entered all of them? That depends upon their conducting power, which, according to Ingenhouz, is in the following order:
Silver, Gold, Copper, Iron.
We see, then, that this conducting power is nearly in the order in which these metals become luminous; so that the greatest quantity of calorie would enter those which become soonest luminous. Now this is just what ought to happen, provided the expulsion of light from a luminous body, by the application of heat, be owing to the repulsion between the particles of calorie and light.
The repulsion between the different rays of light and calorie does not seem to be equal; the repulsion between the blue rays and calorie seems to be greater than that between the red rays and calorie; and the repulsion between all the rays and calorie seems to be directly as their refrangibility: accordingly, when heat is applied to a body, the blue rays escape sooner, and at a lower temperature, than the red rays and others which are most refrangible. When sulphur, for instance, is burnt at a low temperature, the colour of the flame is blue; and when examined by the prism it is found to consist of the violet, indigo, blue, and sometimes of a small quantity of the green rays; but when this substance is burnt at a high temperature the colour of the flame is white, all the rays separating together. When
We must observe, with regard to these experiments, that the idea that calorie can be reflected, and that it can move in straight lines like light, or that there is such a thing as radiant heat, to use the phrase of Lambert and Scheele, is directly contrary to the experiments of Count Rumford, formerly described; by which he showed the incapacity of various bodies to conduct heat; for if calorie could move in straight lines through transparent mediums, it would be absurd to say that either air, or water, or oil, was a non-conductor of it. But these bodies have in fact been found to be non-conductors; and therefore it must follow unavoidably, that there is no such thing as radiant calorie. Consequently, if the experiments of Mr Picquet can be explained, on the supposition that light and not calorie was the agent, that alone will be sufficient to exclude them from ranking as proofs of the identity of heat and light. Now this has been done with a great deal of ingenuity by the late Dr James Hutton of Edinburgh, in his treatise on the Philosophy of Light, Heat, and Fire.
He had previously convinced himself, by a number of experiments, that the different species of light possessed very different degrees of intensity when measured by the eye and the thermometer. He rendered light of different colours equally intense to the eye, by varying the distance from the luminous body till he could just read by the light of it. In this way he compared the red light from a fire of coals with the white light of flame, and found, that when they were equally powerful in affording vision, the red was by far the most powerful in producing heat. When a body is heated to incandescence, it emits first the white or compound light; but as it cools, the light which it emits becomes of the red species, and this is the last which disappears. As the body cools, therefore, the power of its light to produce heat does not diminish so fast as its power to produce vision; consequently, when this last ceases entirely, the other may still in a certain degree remain. We may suppose, therefore, that the iron ball in Mr Picquet's experiments, after it had lost all light to the eye, continued still to emit rays, which, though they made no impression on that organ, had power to produce heat, and that it was these rays collected by the mirrors that raised the thermometer. What confirms this is, that when the bulb of the thermometer was blackened it rose higher than at other times; for calorie, as has been already mentioned, would have produced no such effect. As to the effect of the matrix of water, it is explained, by supposing that all bodies, raised to a certain temperature, emit rays of light, whether they have been heated red hot or not.
As to the effect of the snow in lowering the thermometer, which was certainly a very singular and unlooked-for effect, Dr Hutton explains it, by supposing that all bodies emit rays of light, whatever their temperature is, and that this irradiation diminishes as their temperature diminishes. On that supposition, it is evident that the temperature of the thermometer, like that of all other bodies, is maintained partly by the irradiation of invisible light from the surrounding bodies—it must therefore, since it is placed in the focus of one of the mirrors, be affected by whatever body is placed in the focus of the other. If that body be colder than the surrounding bodies, less light will be irradiated from it and thrown upon the thermometer; consequently the thermometer will be deprived till the deficiency is supplied by some other channel.
Such is the ingenious hypothesis by which Dr Hutton has explained the experiments of Mr Picquet; and the explanation, though it is not without very considerable difficulties, must be allowed at least to be the most plausible which has hitherto been given, and to be highly deserving of being put to the test of experiment. bodies have continued to burn for some time, they may be supposed to have lost the greater part of the most refrangible rays; hence the red appearance of bodies, charcoal for instance, that have burnt for some time, the only rays which remain to separate being the orange, yellow, and red.
The blue rays seem not only to repel caloric with greater force, but likewise to have a greater affinity for other bodies than the red rays have; for they decompose the oxyd of silver (or rather the muriate of silver) much sooner, and to a greater extent, than the red rays; hence we see the reason why the application of the blue rays to Mr. Wilson's pyrophorin and to the diamond causes an extrication of red rays.
We have seen already, that the gases are not heated red hot by the application of heat. It would follow from this, that the gases do not contain light; but the contrary is certain; for light is actually extricated during the combustion of hydrogen, and must therefore have existed either in the oxygen or hydrogen gas, or in both. Probably therefore the reason that heat does not extricate light from the gases is, that the affinity between their bases and light is exceedingly strong; it would therefore require a more than usual temperature to produce its extrication; and on account of the great dilatability of these gases, which always tends to diminish the repulsion between the caloric and light, this temperature cannot be applied. It is easy to see, upon the supposition that there exists a repulsion between caloric and light, why the accumulation of light should produce heat, and why light only occasions heat in those bodies that absorb it.
Such is the theory of the cause of the reciprocal extrication of light and caloric by the application of these substances respectively to bodies, which has been proposed by several ingenious chemists (x); and we acknowledge frankly, that it appears to us by far the most plausible of all the explanations of this phenomenon with which we are acquainted.
It is not, however, beyond the reach of objections, and objections too, we are afraid, altogether incompatible with its truth. Were the repulsion between caloric and light the only cause of the luminous effects of hot bodies, the continual application of heat would surely in time separate the whole of the light which was combined with the body, and then it would cease to be luminous altogether; but we have no reason to suppose
(x) Particularly by Dr. Parr, who is said to be the author of a paper on this subject, published in the Exeter Memoirs.
(s) A gentleman, to whom we mentioned this objection, observed, that in the case of bodies long exposed to heat, the light, which appears to proceed from them, might, in fact, be extricated from the atmosphere by the caloric communicated to it from the heated body. This thought is new and ingenious, and might easily be put to the test of experiment. Some of the facts mentioned in the text are rather hostile to it; but should it prove well founded, it would go far to remove most of the difficulties in which the theory of light is at present involved.
(t) This Newton of chemistry died in 1786, at the age of 44. His moral character, according to Mr. Erhart and others, who were the companions of his youth, and Mefrs. Gaclon, Espling, and those who knew him in his latter days, was irreproachable and praiseworthy. His outward appearance was not expressive of the great mind which lay concealed as it were under a veil. He seldom joined in the usual conversations and amusements of society, having as little leisure as inclination to do so; for what little time he had to spare from the hurry of his profession (an apothecary), was constantly filled up in the prosecution of experiments. It was only when he received visits from his friends, with whom he could converse upon his favourite science, that he indulged himself in a little relaxation. For such friends he had a sincere affection, as he had also for those that lived at a distance, and even for such as were not personally known to him. He kept up a regular correspondence with Mefrs. Erhart, Meyer, Kirwan, Crell, and several other chemists. See Crell's Life of Scheele. have meant hydrogen. It is needless therefore to examine his theory, as it is now known that the combination of hydrogen and oxygen forms not caloric but water (v). The whole fabric therefore has tumbled to the ground; but the importance of the materials will always be admired, and the ruins of the structure shall remain eternal monuments of the genius of the builder.
Mr de Lune, so well known for his important meteorological labours, has advanced another theory*. According to him, light is a body which moves constantly in straight lines, with such rapidity that its gravitation towards other substances bears no sensible proportion to its motion. Light has the property of combining with another unknown substance, and the compound formed is caloric, which possesses very different properties from light. Caloric is constantly describing helicoidal curves round an axis, which accounts for the flowness of its apparent motion. Light produces or increases heat, partly by increasing the expansive power of caloric, and partly by combining with the unknown fulgurance, and forming new caloric; caloric, on the other hand, is always decomposed when bodies become luminous. This theory is certainly ingenious, and would remove many of the difficulties which we at present labour under in attempting to explain the phenomena of caloric and light. It is, however, liable to other difficulties, which could not be easily surmounted. But it is needless to examine these, as the theory itself is supported by no evidence whatever, and cannot therefore be admitted.
Another theory has been advanced by the late Dr Hutton of Edinburgh (v); a man of undoubted genius, but of rather too speculative a turn of mind, and who sometimes involved himself in difficulties from his very ingenuity. All his writings display evident marks of the profound philosopher: they contain much instruction; and even his mistakes are not without their use; but unfortunately his manner is so peculiar, that it is scarcely more difficult to procure the secrets of science from Nature herself, than to dig them from the writings of this philosopher. He supposes that there are two kinds of matter, gravitating matter and light; the last of which wants gravity, and consequently neither possesses magnitude (w) nor momentum. Light has the power of being fixed in bodies; and then it becomes either caloric or phlogiston, which differs in some particulars from caloric, but in what, the Doctor does not specify tell us.
Part of this theory we have examined already when we attempted to prove that light and caloric were different substances. The other part of the theory seems to involve a contradiction; for how could light become fixed in a body, unless it were attracted by it? and if light possesses attraction, it surely cannot be destitute of gravity; for what is gravity but attraction (x)?
Thus, notwithstanding the ingenuity of the philosophers who have attempted to investigate this part of chemistry, the connection between light and caloric is still unknown. We must content ourselves, therefore, with considering them at present as distinct substances, and leave the solution of the many difficulties which at present perplex us to the more happy labours of future enquirers.
PART II. OF COMPOUND BODIES.
To those bodies, which are composed of two simple substances combined together, for want of a better name we have given the appellation of compound bodies. They may be reduced under five classes:
1. Water; 2. Alcohol; 3. Oils; 4. Alkalies; 5. Acids.
These shall be the subject of the five following chapters; and we shall finish this part of the article with some observations on Affinity.
CHAP. I. Of Water.
Water is a well-known liquid, found in abundance in every part of the world, and absolutely necessary for the existence of animals and vegetables.
When pure, in which state it can be obtained only by distillation, it is transparent, and destitute of colour, taste, and smell.
A cubic foot of water, at the temperature of 55°, weighs, according to the experiments of Professor Roebison of Edinburgh (see Specific Gravity, Encyc.), 998½ avoirdupois ounces, or 437½ grams troy each; or only 1¼ ounces less than 1000 avoirdupois ounces; so that rain water, at the same temperature, will weigh pretty nearly 1000 ounces. The specific gravity of water is always supposed = 1,000, and it is made the measure of the specific gravity of every other body.
When water is cooled down to 32°, it assumes the form of ice. If this process goes on very slowly, the ice assumes the form of crystalline needles, crossing each other at angles either of 60° or 120°, as Mr de Mairan has remarked; and it has been often observed in large crystals of determinate figures. Ice, while kept at a temperature considerably below 32°, is very hard, and may be pounded into the finest dust. It is elastic. Its specific gravity is less than that of water.
(v) This candid philosopher afterwards acknowledged, that the proofs for the composition of water were complete; but we do not know exactly how he attempted to reconcile his theory of heat with the belief that water was composed of oxygen and hydrogen; two opinions which are certainly incompatible.
(w) See his dissertations on different subjects of natural philosophy.
(x) Indeed Dr Hutton refused this property to gravitating matter also; following, in this particular, the theory of the celebrated Bofcovich.
(x) We hope not to be accused of disputing merely about the meaning of a word, till what is said on this subject in the chapter of the present article, which treats of Affinity, has been examined. When water is heated to the temperature of 212°, it boils, and is gradually converted into steam. Steam is an invisible fluid like air, but of a less specific gravity. It occupies about 1200 times the space that water does. Its elasticity is so great, that it produces the most violent explosions when confined. It is upon this principle that the steam-engine has been constructed. See Steam and Steam-Engine, Encycl.
The phenomena of boiling are owing entirely to the rapid formation of steam at the bottom of the vessel. The boiling point of water varies according to the pressure of the atmosphere. In a vacuum water boils at 90°; and when water is confined in Papin's digester, it may be almost heated red hot without boiling. The mixture of various salts with water affects its boiling point considerably. Mr. Achard made a number of experiments on that subject; the result of which may be seen in the following tables:
**Class I. Salts which do not affect the Boiling Point.**
- Sulphate of copper.
**Class II. Salts which raise the Boiling Point.**
| Salt | Boiling Point | |-----------------------|---------------| | Muriate of soda | 1035° | | Sulphate of soda | 56 | | Sulphate of potash | 09 | | Nitrate of potash | 35 | | Boracic acid | 212 | | Carbonate of soda | 235 |
This augmentation varies with the quantity of salt dissolved. In general, it is the greater the nearer the solution approaches to saturation.
**Class III. Salts which lower the Boiling Point.**
| Salt | Boiling Point | |-----------------------|---------------| | Borax | 1350° | | Saturated solution of | | | Sulphate of magnesia | 247 | | A very small quantity | | | Alum | | | A greater quantity | | | A saturated solution | | | Sulphate of lime | 202 | | Sulphate of zinc | | | Sulphate of iron | | | Acetite of lead | |
**Class IV.**
| Salt | Boiling Point | |-----------------------|---------------| | Muriate of ammonia | 945 | | Saturated solution of | | | Carbonate of potash | 979 | | Small quantity of | | | Saturated solution of | |
Water was once supposed to be incompressible; but the contrary has been demonstrated by Mr. Canton. The Abbé Mongez made a number of experiments, long after that philosopher, on the same subject, and obtained similar results.
Water was believed by the ancients to be one of the four elements of which every other body is composed; and, according to Hippocrates, it was the substance which nourishes and supports plants and animals. That water was an unchangeable element continued to be believed till the time of Van Helmont, who made plants grow for a long time in pure water. From which experiment it was concluded, that water was convertible into all the substances found in vegetables. Mr. Boyle having digested pure water in a glass vessel hermetically sealed for above a year, obtained a quantity of earthy scales; and concluded, in consequence, that he had converted it partly into earth. He also obtained the same earth by distilling water in a tall glass vessel over a slow fire. Margraf repeated the experiment with the same result, and accordingly drew the same conclusion. But the opinion of these philosophers was never very generally received. The last person who embraced it was probably Mr. Wafelson, who published his experiments on the subject in the Journal de Physique for 1780. Mr. Lavoisier had proved, as early as 1773, that the glass vessels in which the distillation was performed lost a weight exactly equal to the earth obtained. Hence it follows irresistibly, that the appearance of the earth, which was silica, proceeded from the decomposition of the vessels; for glass contains a large proportion of silica. It has been since shown by Dr. Priestley, that water always decomposes glass when applied to its surface for a long time in a high temperature.
We have formerly mentioned, that water is composed of oxygen and hydrogen. This great discovery has contributed more perhaps than any other to the advancement of the science of chemistry, by furnishing a key for the explanation of a prodigious number of phenomena. The evidence, therefore, on which it rests, and the objections which have been made to it, deserve to be examined with peculiar attention.
The first person probably who attempted to discover what was produced by burning hydrogen gas was Scheele. He concluded, that during the combustion oxygen and hydrogen combined, and that the product was caloric.
In 1776 Macquer, assisted by Sigaud de la Fond, set fire to a bottle full of hydrogen gas, and placed a saucer above the flame, in order to see whether any fuliginous smoke would be produced. The saucer remained perfectly clean; but it was moistened with drops of a clear liquid, which they found to be pure water.
Next year Bucquet and Lavoisier exploded oxygen and hydrogen gas, and made an attempt to discover what was the product; about the nature of which they had formed different conjectures. Bucquet had supposed that it would be carbonic acid gas; Lavoisier, on the contrary, suspected that it would be sulphuric or sulphurous acid. What the product was they did not discover; but they proved that no carbonic acid gas was formed, and consequently that Mr. Bucquet's hypothesis was ill founded.
In the beginning of the year 1781, Mr. Warltire, at the request of Dr. Priestley, fired a mixture of these two gases contained in a copper vessel; and observed, that after the experiment the weight of the whole was diminished. Dr. Priestley had previously, in the presence of Mr. Warltire, performed the same experiment in a glass vessel. This vessel became moist in the inside, and was covered with a foamy substance, which Dr. Priestley afterwards supposed to be a part of the mercury used in filling the vessel.
In the summer of 1781, Mr. Henry Cavendish, who had been informed of the experiments of Priestley and Warltire, Water. Warltire, set fire to 500,000 grain measures of hydrogen gas, mixed with about 24 times that quantity of common air. By this process he obtained 135 grains of pure water. He also exploded 19,500 grain mixtures of oxygen gas with 37,000 of hydrogen gas, and obtained 30 grains of water containing in it a little nitric acid. From these experiments he concluded that water was a compound.—Mr Cavendish must therefore be considered as the real discoverer of the composition of water. He was the first who ascertained that water was produced by firing oxygen and hydrogen gas, and the first that drew the proper conclusion from that fact. Mr Watt, indeed, had also drawn the proper conclusion from the experiments of Dr Priestley and Mr Warltire, and had even performed a number of experiments himself to ascertain the fact, before Mr Cavendish had communicated his; but he had been deterred from publishing his theory by former experiments of Dr Priestley, which appeared contrary to it. He has therefore a claim to the merit of the discovery; a claim, however, which does not affect Mr Cavendish, who knew nothing of the theory and experiments of that ingenious philosopher.
Meanwhile, in the winter 1781-2, Mr Lavoisier, who had suspected, that when oxygen and hydrogen gas were exploded, sulphuric or sulphurous acid was produced, made an experiment in order to ascertain the fact, at which Mr Gingembre affixed. They filled a bottle, capable of holding five pints (French), with hydrogen gas, to which they set fire, and then corked the bottle, after pouring into it 2 oz. (French) of lime water. Through the cork there passed a copper tube, by means of which a stream of oxygen gas was introduced to support the flame. Though this experiment was repeated three times, and instead of lime water a weak solution of alkali and pure water were substituted, they could not observe any product whatever. This result astonished Mr Lavoisier exceedingly; he resolved, therefore, to repeat the experiment on a larger scale, and if possible with more accuracy. By means of pipes furnished with stop-cocks, he put it in his power to supply both gases as they should be wanted, that he might be enabled to continue the burning as long as he thought proper.
The experiment was made by Lavoisier and la Place on the 24th of June 1783, in the presence of Mefris le Roi, Vandermonde, several other academicians, and Sir Charles Blagden, who informed them that Mr Cavendish had already performed it, and that he had obtained water. They continued the inflammation till all their stock of gases was wasted, and obtained about 295 grains of water, which, after the most rigid examination, appeared to be perfectly pure. From this experiment Lavoisier concluded, that water was composed of oxygen and hydrogen. Mr Monge soon after performed the same experiment, and obtained a similar result; and it was soon after repeated again by Lavoisier and Meusnier on a scale sufficiently large to put the fact beyond doubt.
Suppl. Vol. I. Part I.
(v) A variety of instruments have been invented by which they have denominated Gasometers.
(z) This gas shall be afterwards described. It has the property of absorbing almost instantaneously the oxygen gas with which it comes into contact. It is therefore often used, in order to discover how much oxygen gas exists in any mixture.
The proofs that water is a compound are of two kinds; it has been actually composed, and it has been decomposed.
With regard to the composition of water, we shall relate the celebrated experiment made by Lavoisier and Meusnier in the month of February 1785, in the presence of a numerous deputation from the academy of sciences, and so many other spectators, that it may be considered as having been performed in public. Every precaution was taken to ensure success. The gases had been prepared with care, and held for some time over a solution of potash, in order to deprive them of any acidity which they might accidentally contain; and before entering into the glass globe where they were to be burnt, they were made to pass over newly calcined potash, to deprive them of the water which they might happen to retain in solution. The hydrogen gas had been obtained by passing steam through iron at a white heat; the oxygen gas was procured from the red oxide of mercury. The combustion took place in a large glass globe, into which the gases were admitted by means of tubes furnished with stop-cocks; and the most ingenious contrivances were employed to ascertain exactly the quantities of each which were consumed. The whole machine is described at large by Mr Meusnier in the Memoirs of the Academy of Sciences for 1782.
The quantities of gas employed, after deducting the 432 grains of residuum which were not consumed, were 2794.76 grains of oxygen gas, and 471.125 of hydrogen gas. After taking from these 32.25 grains, = the humidity of which the oxygen gas was deprived by the calcined potash, and 44.25 grains, = the weight which the hydrogen lost by the same process, there remains altogether 3188.4 grams of gas.
The quantity of water obtained amounted to 3219 grams; the specific gravity of which was to distilled water as 1.0051 to 1. This quantity was 30 grams more than the gas employed. The difference, no doubt, was owing to a small error in estimating the weight of the gases; which indeed it is extremely difficult to avoid, as the weight is altered by the smallest difference of temperature. This water had a slight smell, and a taste feebly acid; it reddened slightly blue paper, and effervesced with the carbonat of potash. 11.52 grams of that water being saturated with potash, and evaporated to dryness, left 20 grams of a salt which melted on the fire like nitre. It follows from this experiment, that the quantity of acid contained in the whole water would not have been quite sufficient to have formed 56 grams of nitre.
The residuum weighed, as has been already observed, 432 grams; its volume was equal to 444 grams of oxygen gas; it was diminished by nitrous gas (z) precisely as gas would be which contained 0.24 parts of oxygen; it rendered lime water somewhat turbid, which indicated the presence of carbonic acid gas.
From the comparison of the weights, and volumes of the gases consumed, it was concluded that water contains... Water, fills of 0.85 parts, by weight, of oxygen, and 0.15 of hydrogen.
Experiment. This experiment was soon after repeated by Mr le de Gineau upon a still larger scale, and in the presence of a great number of spectators. It continued for no less than 12 days, and was performed with the most rigorous exactness of which experiments of that nature will admit.
The oxygen gas employed, which had been procured from the black oxide of manganese, occupied the space of 35085 cubic inches, and weighed 18208.5 grains.
The hydrogen gas was obtained by dissolving iron in diluted sulphuric acid. Its volume was 7496.7 cubic inches, and its weight 4735.3 grains.
The two gases, therefore, amounted to 23054.8 cubic inches. From which taking the residuum after combustion, which amounted to 2831.0 cubic inches, there remains for the quantity consumed 20223.8 cubic inches.
The water found in the glass globe after the combustion amounted to 20139.0 cubic inches.
And there were carried off by the residuum, 540 cubic inches.
In all, 20183.0 cubic inches.
Which is just 30 grains less than the weight of the gases which disappeared, or 1/3 part of their weight.
This difference arose from the same difficulties which attended the experiment of Lavoisier. As the errors are on different sides, we are warranted to conclude that this was the case, and that it was not owing to any real difference between the gases and the product.
The water was examined in the presence of Messrs Lavoisier, le Roi, Monge, Berthollet, Bayen, and Pelletier. Its specific gravity was to that of distilled water as 1.001025 to 1. It contained no sulphuric nor muriatic acids; yet it had an acid taste, and converted vegetable blues to a red. 6666 grams of it required for saturation 36 grams of carbonat of potash, and furnished by evaporation 26.5 grams of crystals of nitre.
The whole water, therefore, would have required 109.7 grams of carbonat of potash for saturation.
This water affected lime water a little; and it was found, that the residuum of the gas contained some carbonic acid gas. This residuum formed a nineteenth part of the volume of the two gases employed, and an eighth of their weight. It contained 462 grams of carbonic acid gas, or about 1/2 part; the rest was azotic gas, with about 1/4 part of oxygen.
This experiment gave the proportions of oxygen and hydrogen in water as follows:
Oxygen, 1.848 Hydrogen, 1.152
1.000
This is so near the determination of Mr Lavoisier, that it must be considered as a very strong confirmation of it.
In the year 1790, another similar experiment was performed by Seguin, Fourcroy, and Vauquelin, in the presence of a number of commissioners appointed by the academy of sciences. Every precaution was taken to ascertain the quantity of gas employed with the utmost exactness, and to exclude all atmospheric air as completely as possible.
The hydrogen gas was procured by dissolving zinc in sulphuric acid diluted with 7 parts of water. The oxygen gas was obtained by distilling oxy-muriatic acid of potash (a).
The quantity of hydrogen gas employed amounted to 862.178 grams troy. The quantity of oxygen gas amounted to 1347.5198 cubic inches (French). Its purity was such, that it contained three cubic inches of azotic gas in the 100. The whole gas, therefore, contained 404.256 cubic inches. There were likewise in the glass vessel in which the combustion took place 15 cubic inches (French) of atmospheric air, which consisted of 11 cubic inches of azotic and four of oxygen gas. So that the whole oxygen gas employed amounted to 13274.942 cubic inches; and it contained besides 415.256 cubic inches of azotic gas. They ascertained by experiment, that a cubic inch of this oxygen gas, thus diluted with 1/10 of azotic, weighed 4040 of a grain troy. Now, according to the experiments of Lavoisier, a cubic inch (French) of azotic gas weighs only 3646 of a grain troy. Consequently the weight of pure oxygen gas is greater than 14040; and by calculation they showed it to amount to 14051 of a grain troy. The weight of the whole oxygen gas employed, therefore, was 5206.659 grams troy; and that of the azotic gas mixed with it 1514.02 grams troy.
The combustion continued 183 hours; and during all that time our philosophers never quitted the laboratory. The flame was exceedingly small, and the heat produced by no means great. This was owing to the very small stream of hydrogen, which was constantly flowing into the vessel.
The water obtained amounted to 5943.798 grams troy, or 12 oz. 7 dwts. and 15.798 grams. It exhibited no mark of acidity, and appeared in every respect to be pure water. Its specific gravity was to that of distilled water as 18671 to 18672; or nearly as 1.000053 to 1.
The residuum of gas in the vessel after combustion amounted to 987 cubic inches (French); and on being examined, was found to consist of the following quantities of gases:
Azotic gas, 467 cubic inches. Carbonic acid gas, 39 cubic inches. Oxygen gas, 465 cubic inches. Hydrogen gas, 16 cubic inches.
Total, 987 cubic inches.
The Weight of which is as follows:
Azotic gas, 170.288 gr. troy. Carbonic acid gas, 23.306 gr. troy. Oxygen gas, 188.371 gr. troy. Hydrogen gas, 9.530 gr. troy.
Total, 382.465 gr. troy.
Now the weight of the whole gases employed was 6310.239 gr. troy. That of the water obtained, and of the residuum, 6326.263 gr. troy.
Or, 16.024 grams more than had been employed. This small quantity must have been lost.
(a) A salt composed of oxy-muriatic acid and potash. must have been owing to common air remaining in the tubes, and other parts of the apparatus, in spite of all the precautions that were taken to prevent it; if it did not rather proceed from unavoidable errors in their valuations.
The quantity of azotic gas introduced was 151,178 The quantity found in the residuum was 170,258
There was therefore a surplus of - - - 19,080 gr.
As sufficient precautions had been taken to prevent the introduction of carbolic acid gas, the quantity found in the residuum must have been formed during the process. There must therefore have been a small quantity of carbon introduced. Now zinc often contains carbon, and hydrogen has the property of dissolving carbon; probably, then, the carbon was introduced in this manner. The carbolic acid found in the residuum amounted to 23,356 grains, which, according to Lavoisier's calculation, is composed of 8,958 grams of carbon, and 14,398 grams of oxygen.
Subtracting these 8,958 grams of carbon, and the 532 grams of hydrogen, which remained in the vessel, from the total of hydrogen introduced, there will remain 852,690 grams for the hydrogen that disappeared.
Subtracting the 14,398 grams of oxygen which entered into the composition of the carbolic acid, and the residuum of oxygen, which amounted to 188,371 grams, the quantity of oxygen that disappeared will amount to 593,940 grams.
Hydrogen that disappeared, - - - 852,690 gr. troy. Oxygen, - - - - - - - - - 593,940
Total, - - - - - - - - - 594,630
Quantity of water obtained, - - - - - - - 594,379
Which is less than the gases consumed by - - - - - - - 2,832 grams.*
Such are the principal experiments upon which the opinion is founded that water is a compound. Let us examine them, and see whether they are sufficient to establish that opinion. The circumstances which chiefly claim our attention, and which have been chiefly insisted on, are these:
1. The whole of the gases was not consumed. 2. In the residuum were found several substances which were not introduced, and which must therefore have been formed during the combustion. 3. The water obtained was seldom perfectly pure. It generally contained some nitric acid. 4. As only part of the gases were consumed, and as all gases contain water in them, might not the gas which disappeared have been employed in forming the other substances found in the residuum? and might not the water obtained have been merely what was formerly dissolved in the gases, and which had been precipitated during the experiment?
That the whole of the gases was not consumed will not surprise us, if we recollect that it is impossible for that to take place, allowing them to be perfectly pure, except they be mixed in precisely the proper proportions; and not even then, except every particle of them could be raised to the proper temperature. Now how can this be done in experiments of that nature?
But how is it possible to procure a large quantity of gas completely pure? And supposing it were possible, how can every particle of atmospheric air be excluded? In the last experiment, notwithstanding every precaution, 15 cubic inches (French) were admitted; and there is reason to believe from the results, that the quantity was even considerably greater than this; but if any atmospheric air be admitted, there must be a residuum of azotic gas.
In the first experiment, it had been previously ascertained that the oxygen gas employed contained 1/4th of azotic, or about 233,05 grams; and the residuum contained at most 329,1 grams, or 96,05 grams more than what had for certain pre-existed in the gases.
In the second experiment, the azot in the residuum amounted at most to 1/4th of the oxygen gas employed. But the oxygen was procured from the black oxyd of manganese, which always yields a quantity of azot as well as of carbolic acid. It has been ascertained, that the azot, mixed with oxygen gas procured in that manner, often exceeds 1/4th.
In the third experiment, the azotic gas found in the residuum amounted to 170,258 grams; and the quantity contained in the gases before combustion amounted to 151,178 grams: the surplus, therefore, amounted to 19,080 grams.
Now, is it not much more probable that these considerable quantities of azot, which in the last experiment amounted to no more than 1/4th part by weight of the whole gas employed, pre-existed in the gases before the combustion began, though their extreme minuteness prevented them from being discovered, than that they were formed during the experiment? A supposition which is directly contradicted by a great number of well ascertained facts.
As to the carbolic acid gas, which in the second experiment amounted to 1/4th of the gases employed, it was evidently derived from the manganese, which almost constantly contains it. And when carbolic acid is once mixed with oxygen, it is difficult to separate it by means of lime water, except a large quantity be used, as Mr Cavendish has well observed. The reason is, that oxygen gas has the property of dissolving carbolic acid, as Mr Welter has remarked. Mr le Fevre de Guéneau ascertained by experiment, that 1870 cubic inches of oxygen gas, which did not affect lime water, lost between 1/4th and 1/2th of its weight when washed in milk of lime (b).
In a second experiment, he previously washed the two gases in milk of lime, and the residuum after combustion contained no carbolic acid gas. In a third experiment he washed only the oxygen, and obtained products equally free from carbolic acid. It is certain, then, that the carbolic acid is but an accidental mixture. As to the carbolic acid of the third experiment above related, which amounted only to 1/4th part of the gases employed, the source of it has been already pointed out.
---
* Lime mixed with water till it is of the thickness of milk, or rather of cream. As to the nitric acid, the quantity of nitre obtained in Mr Lavoisier's experiment was 56 grains; which, according to Mr Kirwan's calculation, contain 30,156 grains of nitric acid; a quantity considerably less than \( \frac{1}{2} \) part of the gases which disappeared. In the second experiment, the nitre obtained amounted to 807 grains; which, according to Kirwan, contain 43,456 grains of nitric acid, or less than \( \frac{1}{2} \) part of the gases consumed. Now, as nitric acid is composed of oxygen and azot, both of which were present in the vessel, it is easy to see how it was produced. And that its production is merely accidental, and not necessary, is evident from the last experiment, in which no nitric acid was formed. It has been ascertained, indeed, that the formation of this acid during these experiments is quite arbitrary. It never is formed when the combustion goes on so slowly as to produce but little heat, as Seguin has ascertained*; because oxygen and azot do not combine except at a high temperature. Nor is it formed even at a high temperature, as Mr Cavendish has proved†, except there be a deficiency of hydrogen; because hydrogen has a stronger affinity for oxygen than azot has.
The quantity of water obtained in the first experiment was just 30 grains more than the weight of the gases which had disappeared; the water obtained in the second was precisely 30 grains less than the gases consumed; and in the third experiment, the difference was only 16 grains. The quantities of gas operated upon were large; in all of the experiments several thousand grains, and in one of them above 20 thousand. Now, how is it possible that the water produced should correspond exactly with the gases consumed (for the differences are so small as not to merit any attention), unless the water had been formed by the combination of these gases?
Dr Priestley, however, who made a great many experiments on this subject, drew from them a very different conclusion; and thought he had proved, that during the combustion the two gases combined, and that the combination was nitric acid. This theory was adopted, or rather it was suggested, by Mr Keir, who has supported it with a great deal of ingenuity‡.
Let us examine these experiments of Dr Priestley*, and see whether they warrant the conclusions he has drawn from them. The gases were exploded in vessels of copper. He found that the quantity of water obtained was always less than that of the gases which he had used. He obtained also a considerable quantity of nitric acid. In the experiment made on the largest quantity of the gases, and from which he draws his conclusions, the quantity of liquid obtained amounted to 442 grains. This liquid was examined by Mr Keir.
It was of a green colour, 72 grains of brown oxyd of copper were deposited in it, and it contained a solution of nitrat of copper (copper combined with nitric acid). Mr Keir analysed this liquor: it consisted of pure water and nitrat of copper; and Mr Keir concluded that the nitric acid formed amounted to \( \frac{1}{2} \) of the oxygen gas employed. Mr Berthollet, however, has shown that it could not have amounted to more than \( \frac{1}{2} \) part. Let us suppose, however, that it amounted to \( \frac{1}{2} \).
What has become of them? They have combined, says Dr Priestley, and formed nitric acid. This nitric acid is only \( \frac{1}{2} \) of their weight: Dr Priestley supposes, however, that it contains the whole oxygen and hydrogen that existed in these gases, and that all the rest of the weight of these gases was owing to a quantity of water which they had held in solution. Oxygen gas, then, (for we shall neglect the hydrogen, which Dr Priestley was not able to bring into view at all) is composed of one part of oxygen and 19 of water. Where is the proof of this? Dr Priestley informs us, that he ascertained by experiment that half the weight of carbonic acid gas was pure water. Supposing the experiment accurate (c), what can be concluded from it? Surely to bring it forward in proof, that oxygen gas consists of \( \frac{1}{2} \) parts, or almost wholly of water, is downright trifling. It is impossible, therefore, from Dr Priestley's experiments, allowing his suppositions and conjectures their utmost force, to account for the disappearing of the two gases, or the appearance of the water, without admitting that this liquid was actually composed of oxygen and hydrogen. It we add to this, that no oxygen gas has hitherto (as far as we know at least) been procured absolutely free from some admixture of azot, and that his oxygen was always procured either from red oxyd of lead, or from black oxyd of manganese, or red oxyd of mercury, all of which substances yield a considerable proportion of azot; that in one experiment, in which he observes that his oxygen was very pure, as it had been obtained from red oxyd of mercury, Mr Berthollet (d) ascertained, by actually making the experiment, that part of the very same oxyd which Dr Priestley had employed yielded a gas, \( \frac{1}{2} \) of which was azot*; if we add, that it has been proved beyond all possibility of doubt, and to Dr Priestley's own satisfaction, that nitric acid is composed of oxygen and azot—we shall find it no difficult matter to explain the origin of that acid in Dr Priestley's experiments: and if we recollect that in Seguin's experiment, upon a much larger scale indeed than Dr Priestley's, no nitric acid at all was formed, it will be impossible for us to believe for a moment that the compound formed by oxygen and hydrogen is nitric acid. Thus Dr Priestley's
(c) He informs us, that the carbonat of barytes does not yield its carbonic acid by means of heat (this Dr Hope has shewn to be a mistake); but that, when the vapours of water are passed over it, the gas is disengaged: and he determines, by the water missing, how much has combined with the gas. According to him, 60 grains of water enter into the composition of 147 grains of gas. But, besides affixing too small a weight to the gas, he forgot that its temperature was high, and that therefore it was capable of combining with much more water than in its usual state: nor did he ascertain whether more of this water was deposited on the vessels; and yet, by neglecting this precaution, Moreau has shewn, that Mr Kirwan, in a similar experiment, obtained a result nine times greater than it ought to have been. Encycl. Method. Chim. art. Air.
(d) Mr Berthollet had supplied Dr Priestley with the oxyd. He had received two ounces of it from Mr Le Blanc, one of which he sent to Dr Priestley, and the other he referred. ley's experiments rather confirm than destroy the theory of the composition of water. We obtain from them, however, one curious piece of information, that the presence of copper increases the quantity of nitric acid formed. This curious fact, with a variety of others of a similar nature, will perhaps afterwards claim our attention; but at present we must consider another theory which this phenomenon suggested, and which was first proposed, we believe, by Mr de la Metherie (x).
Had the French chemists, it has been said, employed copper vessels in their experiments, they would have obtained three times the quantity of nitric acid. This acid, therefore, must in their experiments have been decomposed, after having been formed, for want of a base to combine with; and the azot which appeared in the residuum was owing to this decomposition. Hydrogen and oxygen, therefore, do not form water, but azot (r). Let us examine the experiment of Mr Le Fevre by this theory, as the quantity of azot was accurately ascertained. The nitric acid obtained amounted to 43456 grams; three times that quantity is 130368 grams, into which 23054 grams of gas were converted; which is impossible. Or even supposing that the decomposition had been going on during the whole experiment, which is directly contrary to Dr Priestley's experiments, and which there is no reason whatever to suppose, but every reason against—fill the whole azot amounted only to 1/4th of the quantity of gas employed, allowing this gas to have contained no azot, which was evidently not the case. It appears, then, that this hypothesis, even if it could be admitted, would be totally inadequate to account for the phenomena. But if we were to examine it by Mr Seguin's experiment, its absurdity would be still more glaring. In that experiment the azotic gas amounted to only 19 grams, and the quantity of gas which disappeared was 5946 grams: so that were the hypothesis true, oxygen and hydrogen gas would consist of one part of oxygen and hydrogen and 312 parts of water; a supposition so enormously absurd, that it is impossible for any person even to advance it.
It is impossible, therefore, for the phenomena which attend the combustion of oxygen and hydrogen gas to be accounted for in any way consistent with common sense, except we suppose that water is formed.
But the experiments above related, conclusive as they appear, are not the only ones by which this important fact has been ascertained. M. Van Troostwyk and Dieman, assisted by Mr Cuthbertson, filled a small glass tube, 1/4th of an inch in diameter and 12 inches long, with distilled water. One end of this tube was sealed hermetically; but, at the same time, a small gold wire had been passed through it. Another wire passed through the open end of the tube, and could be fixed at greater or smaller distances from the first wire. By means of these wires, they made a great number of electrical explosions pass through the water. Bubbles of air appeared at every explosion, and collected at the top of the tube. When electric sparks were passed through this air, it exploded and disappeared almost completely. It must therefore have consisted of a mixture of oxygen and hydrogen gas, and this gas must have been formed by the decomposition of the water; for they had taken care to deprive the water before hand of all its air, and they used every precaution to prevent the access of atmospheric air; and, besides, the quantity of gas produced did not diminish, but rather increased, by continuing to operate a number of times upon the same water, which could not have been the case had it been merely air dissolved in water; nor would atmospheric air have exploded and left only a very small residuum, not more than 1/5th part. They had taken care also to prove that the electric spark did not contribute to form hydrogen gas; for on passing it through sulphuric and nitric acids, the product was not hydrogen, but oxygen gas.
These experiments have been since repeated by Dr Pearson, assisted by Mr Cuthbertson. He produced, by means of electricity, quantities of gas from water, amounting to 365488 cubes of 1/5th of an inch each; on nitrous gas being added to which, it suffered a diminution of bulk, and nitrous acid appeared to have been formed: It must therefore have contained oxygen gas. When oxygen gas was added to the remainder, and an electric spark passed through it, a diminution took place precisely as when oxygen and hydrogen gas are mixed: It must therefore have contained hydrogen. When an electric spark was passed through the gas thus produced from water, the gas disappeared, being no doubt converted into water.
Such are the proofs by which the compound nature of water is ascertained; and we do not believe that any physical fact whatever can be produced which is supported by more complete evidence.
But what becomes of the caloric which was previously combined with these gases? It passes through the vessel and is lost, and its weight is too inconsiderable to make any sensible variation in the quantity of the product. If we were to judge from analogy, we would conclude, that the oxygen and hydrogen, while in the state of gas, are probably somewhat lighter than after they are condensed into water; but the difference, if it exists, can scarcely be sensible.
Water is capable of combining with a vast number of substances: all bodies, indeed, which are soluble in water form a chemical union with it.
Its affinity for other bodies is doubtless various, though we have no method of ascertaining this difference, except
(x) Another favourite theory of La Metherie was, that gases themselves are destitute of gravity, and that they owe their whole weight to the water with which they are combined: that during combustion the water of the two gases is depolished; and that the gases themselves escape through the vessel and are lost. He complains bitterly that this theory had never been noticed by his antagonists; as if it were necessary to refute a hypothesis which is not supported by any proof whatever, and as if it had not been proved that oxygen increases the weight of metals, and consequently possesses gravity.
(r) This, as has been formerly explained, was the original opinion of Dr Priestley; to which, though he does not explain himself fully, he evidently still adheres. There is then no difference between his theory and this, except what relates to the decomposition of the nitric acid. except in those bodies which have no affinity, or but a very small affinity, for each other; and it is only in a few even of these that this difference can be ascertained. If nitrat of barytes be poured into lime water, the lime is precipitated, owing, no doubt, to the superior affinity of the nitrat for water. Several very curious instances of the affinity of different salts for water have been mentioned by Mr Quatremere Dijonval. When the solutions of nitrat of lime and nitrat of magnesia in water are mixed together, the nitrat of magnesia is precipitated. Nitrat of magnesia is also precipitated by nitrat of lime, and sulphate of magnesia by sulphate of lime; so that it would seem that the salts which have magnesia for their basis, have a less affinity for water than those whose basis is lime.
Water has the property of dissolving oxygen gas. If a quantity of common air be confined for some time above water, the whole of the oxygen is absorbed, and nothing but the azotic gas remains. This fact was first observed by Mr Scheele.
**Chap. II. Of Alcohol.**
Wine has been known from the earliest ages. The Scriptures inform us, that Noah planted a vineyard and drank wine; and the heathen writers are unanimous in ascribing the invention of this liquor to their earliest kings and heroes. Beer, too, seems to have been discovered at a very remote period. It was in common use in Egypt in the time of Herodotus. Tacitus informs us, that it was the drink of the Germans. Whether the ancients had any method of procuring ardent spirits from these or any other liquors, does not appear. The Greeks and Romans seem to have been ignorant of ardent spirits altogether, at least we can discover no traces of any such liquor in their writings. But among the northern nations of Europe, intoxicating liquors were in use from the earliest ages. Whether these liquors resembled the beer of the Germans, we do not know. It is certain, at least, that the method of procuring ardent spirits by distillation was known in the dark ages; and it is more than probable that it was practised in the north of Europe much earlier. They are mentioned expressly by Thaddaeus Villanovanus, and Lully.
Ardent spirits, such as brandy, for instance, rum, and whisky, consist almost entirely of three ingredients, water, alcohol or spirit of wine, to which they owe their strength, and a small quantity of a peculiar oil, to which they owe their flavour.
The alcohol may be separated from the water by the following process. Into the whisky or other ardent spirit a quantity of potash is to be put, which has just immediately before been exposed for about half an hour in a crucible to a red heat, in order to deprive it of moisture. Potash in this state has a strong attraction for water; it accordingly combines with the water of the spirit, and the solution of potash thus formed sinks to the bottom of the vessel, and the alcohol, which is lighter, floats over it, and may easily be decanted off; or, what is perhaps better, the solution of potash may be drawn off from below it by means of a stop cock placed at the bottom of the vessel. It is impossible to fix the quantity of potash which ought to be used, because that must depend entirely on the strength of the spirit; but it is of no consequence though the potash employed be a little more than enough. The alcohol thus obtained contains a little potash dissolved, which may be separated by distilling it in a water bath with a very small heat. The alcohol passes over, and leaves the potash behind. It is proper not to distil to dryness. This process is first mentioned by Lally. Alcohol may be obtained in the same manner from wine and from beer; which liquids owe their strength entirely to the quantity of that substance which they contain.
Alcohol is a transparent liquor, colourless like water, free of a pleasant smell, and a strong penetrating agreeable taste. It is exceedingly fluid, and has never been frozen, though it has been exposed to a cold so great that the thermometer stood at -60°.
Its specific gravity when pure is about 0.800.
It is exceedingly volatile boiling at the temperature of 170°; in which heat it assumes the form of an elastic fluid, capable of resisting the pressure of the atmosphere, but which condenses again into alcohol when that temperature is reduced. In a vacuum it boils at 56°, and exhibits the same phenomena: so that were it not for the pressure of the atmosphere, alcohol would always exist in the form of an elastic fluid, as transparent and invisible as common air. This subject was first examined with attention by Mr Lavoisier. The fact, however, had been known long before.
Alcohol has a strong affinity for water, and is miscible with it in all proportions. The specific gravity of all the different mixtures, in every proportion, and in all the different degrees of temperature, from 3° to 100°, has been lately ascertained with great accuracy by Sir Charles Blagden and Mr Gilpin. But as a very full account of these interesting experiments has been given in the Encyclopaedia in the article SPIRITOUS LIQUORS, we do not think ourselves at liberty to repeat it here.
If alcohol be set on fire, it burns all away with a blue flame, without leaving any residuum. Boerhaave observed, that when the vapour which escapes during this combustion is collected in proper vessels, it is found to consist of nothing but water. Junker had made the same remark; and Dr Black suspected, from his own observations, that the quantity of water obtained, if properly collected, exceeded the weight of the alcohol consumed. This observation was confirmed by Lavoisier; who found that the water produced during the combustion of alcohol exceeded the alcohol consumed by about 4th part.
Different opinions were entertained by chemists about the nature of alcohol. Stahl thought that it was composed of a very light oil, united by means of an acid to a quantity of water. According to Junker, it was composed of phlogiston, combined with water by means of an acid. Cartheuer, on the other hand, affirmed, that it contained no acid, and that it was nothing else than pure phlogiston and water. But these hypotheses were mere assertions supported by no proof whatever. Lavoisier was the first who attempted to analyse it.
He set fire to a quantity of alcohol in close vessels, by means of the following apparatus: BCDE (fig. 6) is a vessel of marble filled with mercury. A is a strong glass vessel placed over it, filled with common air, and capable of containing about 15 pints (French). Into this vessel is put the lamp R filled with alcohol, the weight of which has been exactly determined. On the wick of the lamp is put a small particle of phosphorus. The mercury is drawn up by suction to the height JH. This glass communicates by means of the pipe LK with another glass vessel S filled with oxygen gas, and placed over a vessel of water T. This communication may be shut up at pleasure by means of the stop-cock M.
Things being thus disposed, a crooked red hot iron wire is thrust up through the mercury, and made to touch the phosphorus. This instantly kindles the wick, and the alcohol burns. As soon as the flame begins to grow dim, the stop-cock is turned, and a communication opened between the vessels S and A; a quantity of oxygen gas rushes in, and restores the brightness of the flame. By repeating this occasionally, the alcohol may be kept burning for some time. It goes out, however, at last, notwithstanding the admixture of oxygen gas.
The result of this experiment, which Mr Lavoirier repeated a great number of times, was as follows:
The quantity of alcohol consumed amounted to 76,7083 grains troy.
The oxygen gas consumed amounted to 266,82 cubic inches, and weighed 90,506 grains troy.
The whole weight of the substances consumed, therefore, amounted to 167,2143 grains.
After the combustion, there were found in the glass vessel 115,41 cubic inches of carbonic acid gas, the weight of which was 78,1102 grains troy. There was likewise found a considerable quantity of water in the vessel, but it was not possible to collect and weigh it. Mr Lavoirier, however, estimated its weight at 89,0951 grains; as he concluded, with reason, that the whole of the substances employed were still in the vessel. Now the whole contents of the vessel consisted of carbonic acid gas and water; therefore the carbonic acid gas and water together must be equal to the oxygen gas and alcohol which had been consumed.
But 78,1102 grains of carbonic acid gas contain, according to Mr Lavoirier's calculation, 55,279 grains of oxygen; 92,506 grains, however, of oxygen gas had disappeared; therefore 15,227 grains must have been employed in forming water.
35,227 grains of oxygen gas require, in order to form water, 6,238 grains of hydrogen gas; and the quantity of water formed by this combination is 41,265 grains. But there were found 89,095 grains of water in the glass vessel; therefore 47,83 grains of water must have existed ready formed in the alcohol.
It follows from all these data, that the 76,7083 grains of alcohol, consumed during the combustion, were composed of
\[ \begin{align*} 22,840 & \text{ Carbon,} \\ 6,038 & \text{ Hydrogen,} \\ 47,830 & \text{ Water.} \end{align*} \]
Such were the consequences which Mr Lavoirier drew from his analysis. He acknowledged, however, that there were two sources of uncertainty, which rendered his conclusions not altogether to be depended upon. The first was, that he had no method of determining the quantity of alcohol consumed, except by the difference of weight in the lamp before and after combustion; and that therefore a quantity might have evaporated without combustion, which, however, would be taken into the sum of the alcohol consumed. But this error could not have been great; for if a considerable quantity of alcohol had existed in the state of vapour in the vessel, an explosion would certainly have taken place. The other source of error was, that the quantity of water was not known by actual weight, but by calculation.
To this we may add, that Mr Lavoirier was not warranted to conclude from his experiment, that the water of alcohol found in the vessel, which had not been formed by the oxygen gas used, had existed in the alcohol in the state of water; he was intitled to conclude from his data, that the ingredients of that water existed in the alcohol before combustion; but not that they were actually combined in the state of water, because that combination might have taken place, and in all probability did partly take place, during the combustion. It follows, therefore, from Mr Lavoirier's experiments, that alcohol, supposing he used it perfectly pure, which is not probable, is composed of
\[ \begin{align*} 0.2988 & \text{ parts carbon,} \\ 0.1840 & \text{ parts hydrogen,} \\ 0.5172 & \text{ parts oxygen.} \end{align*} \]
But it gives us no information whatever of the manner in which these ingredients are combined. That alcohol contains oxygen, has been proved by a very ingenious set of experiments performed by Mefis Fourcroy and Vauquelin. When equal parts of alcohol and sulphuric acid are mixed together, a quantity of caloric is disengaged, sufficient to elevate the temperature of the mixture to 190°. Bubbles of air are emitted, the liquor becomes turbid, assumes an opal colour, and at the end of a few days a deep red. When examined, the sulphuric acid is found to have suffered no change; but the alcohol is decomposed, partly converted into water and partly into ether, a substance which we shall describe immediately. Now, it is evident that the alcohol could not have been converted into water unless it had contained oxygen.
When equal parts of sulphuric acid and alcohol are mixed together and heat applied, the mixture boils at 205°, and a liquid equal to half the weight of the alcohol comes over into the receiver. This liquid is ether.
Ether is obscurely hinted at in some of the older chemical authors, but little attention was paid to it till a paper appeared in the Philosophical Transactions for 1730, written by a German, who called himself Froedelius (a), containing a number of experiments on it. In this paper it first received the name of ether.
Ether is limpid and colourless, of a very fragrant proper smell, and a hot pungent taste. Its specific gravity is 0.7394. It is exceedingly volatile, boiling in the open air at 98°, and in a vacuum at —20°. Were it not therefore for the pressure of the atmosphere, it would always exist in a gaseous state. Ether unites with water in the proportion of ten parts of the latter to one of the former.
(a) The name was supposed to have been feigned. It is exceedingly inflammable, and when kindled in the state of vapour burns with rapidity, or rather explodes, if it be mixed with oxygen gas.
Chemists entertained various opinions respecting the nature of ether. Macquer supposed, that it was merely alcohol deprived by the acid of all its water. But it was generally believed that the acid entered partly into its composition. Since the nature of acids has become better known, a great number of philosophers have supposed that ether is merely alcohol combined with a quantity of oxygen furnished by the acid. The real composition of this singular substance has been lately ascertained by the experiments of Fourcroy and Vauquelin.
"A combination (say they) of two parts of sulphuric acid and one part of alcohol elevates the temperature to 20°, becomes immediately of a deep red colour, which changes to black a few days afterwards, and emits a smell perceptibly ethereal.
"When we carefully observe what happens in the combination of equal parts of alcohol and concentrated sulphuric acid exposed to the action of caloric in a proper apparatus, the following phenomena are seen:
"1. When the temperature is elevated to 208°, the fluid boils, and emits a vapour which becomes condensed by cold into a colourless, light, and odorant liquor, which from its properties has received the name of ether. If the operation be properly conducted, no permanent gas is disengaged until about half the alcohol has passed over in the form of ether. Until this period there passes absolutely nothing but ether and a small portion of water, without mixture of sulphurous or of carbonic acid.
"2. If the receiver be changed as soon as the sulphurous acid manifests itself, it is observed that no more ether is formed, but the sweet oil of wine, water, and acetic acid, without the disengagement hitherto of a single bubble of carbonic acid gas. When the sulphuric acid constitutes about four-fifths of the mass which remains in the retort, an inflammable gas is disengaged, which has the smell of ether, and burns with a white oily flame. This is what the Dutch chemists have called carbonated hydrogen gas, or elephant gas, because when mixed with the oxy-muriatic acid it forms oil. At this period the temperature of the fluid contained in the retort is elevated to 230° or 234°.
"3. When the sweet oil of wine ceases to flow, if the receiver be again changed, it is found that nothing more passes but sulphurous acid, water, carbonic acid gas; and that the residuum in the retort is a black mass, consisting for the most part of sulphuric acid thickened by carbon.
"The series of phenomena here exposed will justify the following general inductions:
"1. A small quantity of ether is formed spontaneously, and without the affluence of heat, by the combination of two parts of concentrated sulphuric acid and one part of alcohol.
"2. As soon as ether is formed, there is a production of water at the same time; and while the first of these compositions takes place, the sulphuric acid undergoes no change in its intimate nature.
"3. As soon as the sulphurous acid appears, no more ether is formed, or at least very little; but then there passes the sweet oil of wine, together with water and acetic acid.
"4. The sweet oil of wine having ceased to come over, nothing further is obtained but the sulphurous and carbonic acids, and at last sulphur, if the distillation be carried to dryness.
"The operation of ether is therefore naturally divided into three periods: the first, in which a small quantity of ether and water are formed without the affluence of heat; the second, in which the whole of the ether which can be obtained is disengaged without the accompaniment of sulphurous acid; and the third, in which the sweet oil of wine, the acetic acid, the sulphurous acid, and the carbonic acid, are afforded. The three stages have no circumstance common to all, but the continual formation of water, which takes place during the whole of the operation.
"The ether which is formed without the affluence of caloric, and the carbon which is separated without decomposition of the sulphuric acid, prove that this acid acts on alcohol in a manner totally different from what has hitherto been supposed. It cannot, in fact, be affirmed, that the acid is altered by the carbon, because daily experience shews that no sensible attraction takes place between these two bodies in the cold; neither can it be affected by the hydrogen; for in that case sulphurous acid would have been formed, of which it is known that no trace is exhibited during this first period. We must therefore have recourse to another species of action, namely, the powerful attraction exercised by the sulphuric acid upon water. It is this which determines the union of the principles which exist in the alcohol, and with which the concentrated acid is in contact; but this action is very limited if the acid be small in quantity; for an equation of affinity is soon established, the effect of which is to maintain the mixture in a state of repose.
"Since it is proved that ether is formed in the cold by the mixture of any quantities of alcohol and sulphuric acid, it is evident that a mass of alcohol might be completely changed into ether and vegetable acid by using a sufficient abundance of sulphuric acid. It is equally evident that the sulphuric acid would not by this means undergo any other change than that of being diluted with a certain quantity of water. This observation proves, that alcohol contains oxygen, because water cannot exist without this principle, which must be afforded by the alcohol only, since the sulphuric acid suffers no decomposition.
"We must not, however, imagine, from these facts, that ether is alcohol minus oxygen and hydrogen. Its properties alone would contradict this; for a quantity of carbon proportionally greater than that of the hydrogen is at the same time separated. It may, in fact, be conceived, that the oxygen, which in this case combines with the hydrogen to form water, not only saturated that hydrogen in the alcohol, but likewise the carbon. So that, instead of considering ether as alcohol minus hydrogen and oxygen, we must, by keeping an account of the precipitated carbon and the small quantity of hydrogen contained in the water which is formed, regard it as alcohol plus hydrogen and oxygen.
"The foregoing are the effects produced by a combination of alcohol and sulphuric acid, spontaneously produced without foreign heat. Let us, in the next place, observe how this combination is effected when caloric is added. The phenomena are then very different, though some of the results are the same." In the first place, we must observe, that a combination of sulphuric acid and alcohol in equal parts does not boil at less than 207 degrees of temperature, while that of alcohol alone boils at 75°. Now since ebullition does not take place till the higher temperature, it is clear that the alcohol is retained by the affinity of the sulphuric acid, which fixes it more considerably. Let us also consider that organic bodies, or their immediate products, exposed to a lively brisk heat, without the possibility of escaping speedily enough from its action, suffer a partial or total decomposition, according to the degree of temperature. Alcohol undergoes this last alteration when passed through an ignited tube of porcelain. By this sudden decomposition it is converted into water, carbonic acid, and carbon. The reason, therefore, why alcohol is not decomposed when it is submitted alone to heat in the ordinary apparatus for distillation, is, that the temperature at which it rises in vapours is not capable of effecting the separation of its principles; but when it is fixed by the sulphuric acid or any other body, the elevated temperature it undergoes, without the possibility of disengagement from its combination, is sufficient to effect a commencement of decomposition, in which ether and water are formed, and carbon is deposited. Nothing more therefore happens to the alcohol in these circumstances than what takes place in the distillation of every other vegetable matter in which water, oil, acid, and coal, are afforded.
Hence it may be conceived that the nature of the products of the decomposition of alcohol must vary according to the different degrees of heat; and this explains why at a certain period no more ether is formed but the sweet oil of wine and acetic acid. In fact, when the greatest quantity of the alcohol has been changed into ether, the mixture becomes more dense, and the heat which it acquires previous to ebullition is more considerable. The affinity of the acid for alcohol being increased, the principles of this acid become separated; so that, on the one hand, its oxygen seizes the hydrogen, and forms much water, which is gradually volatilized; while, on the other, the ether retaining a greater quantity of carbon, with which at that temperature it can rise, affords the sweet oil of wine. This last ought therefore to be considered as an ether containing an extraordinary portion of carbon, which gives it more density, less volatility, and a lemon yellow colour.
During the formation of the sweet oil of wine, the quantity of carbon which is precipitated is no longer in the same proportion as during the formation of ether.
What we have here stated concerning the manner in which ether is formed by the simultaneous action of the sulphuric acid and heat, appears so conformable to truth, that nearly the same effects may be produced by a caustic fixed alkali. In this case also a kind of ether and a sweet oil of wine are volatilized, and coal is precipitated. It is therefore only by fixing the alcohol that the sulphuric acid permits the caloric to operate a sort of decomposition. It may also be urged as a proof of this assertion, that the sulphuric acid, which has served to make ether as far as the period at which the sweet oil of wine begins to appear, is capable of saturating the same quantity of alkali as before its mixture with the alcohol.
Ether may also be obtained by means of several other acids. The different liquids thus formed are distinguished by prefixing the name of the acid used in the process. Thus the ether above described is called sulphuric ether; that obtained by means of nitric acid, nitric ether, and so on. There are several minute shades of difference between these various ethers, which have not yet been properly enquired into.
Alcohol is capable of dissolving a great many bodies. A considerable number of these, with the quantities soluble, is exhibited in the following tables.
### I. Substances dissolved in large Quantities
| Names of the Substances | Temperature | 240 parts of alcohol diffused | |-------------------------|-------------|-----------------------------| | Nitrat of cobalt | 54° | 240 parts | | copper | 54° | 240 | | alumina | 54° | 240 | | magnesia | 180° | 694 | | Muriat of zinc | 54° | 240 | | alumina | 54° | 240 | | magnesia | 180° | 1313 | | iron | 180° | 240 | | copper | 180° | 240 | | Acetite of lead | 113° | | | copper | 135° | | | Benzoic acid | | | | Sulphat of magnesia | | | | Nitrat of zinc decomposed | | | | iron decomposed | | | | bismuth decomposed | | |
### II. Substances dissolved in small Quantities
| Names of the substances | 240 parts of alcohol at the boiling temperature dissolve | |-------------------------|--------------------------------------------------------| | Muriat of lime | 240 parts | | Nitrat of ammonia | 214 | | Oxy-muriat of mercury | 212 | | Succinic acid | 177 | | Acetite of soda | 112 | | Nitrat of silver | 100 | | Refined sugar | 59 | | Boracic acid | 48 | | Nitrat of soda | 23 | | Acetite of copper | 18 | | Muriat of ammonia | 17 | | Arseniat of potash | 9 | | Acidulated oxalat of potash | 7 | | Nitrat of potash | 5 | | Muriat of potash | 5 | | Arseniat of soda | 4 | | Barytes | | | Strontites | | | White oxyd of arsenic | 3 | | Tartrat of potash | 1 | | Phosphorus | | | Nitrat of lead | | | Carbonat of ammonia | |
*Withering, Phil. Trans. lxxiii. 330.*
*Id. ibid.* III. Substances insoluble with Alcohol.
| Sugar of milk, Borax, Tartar, Alum, Sulphat of ammonia, lime, barytes*, iron (green), copper, silver, mercury, zinc, potash, | Sulphat of soda, magnesia, Sulphite of soda, Tartrite of soda and potash, Phosphoric acid, Nitrat of lead, mercury, Muriat of lead, silver ‡, Common salt, Carbonat of potash, soda. |
These have been chiefly borrowed from tables which Mr de Morveau published in the Journal de Physique July 1785, and which were drawn up for the most part from the experiments described in Wenzel's Treatise on Affinities.
The affinities of alcohol are very imperfectly known. Those stated by Bergman are as follows:
- Water, - Ether, - Volatile oil, - Sulphurets of alkalica.
**CHAP. III. Of Oils.**
Oil, which is of such extensive utility in the arts, was known at a very remote period. It is mentioned in Genesis, and during the time of Abraham was even used in lamps*. The olive was very early cultivated, and oil extracted from it in Egypt. Cecrops brought it from Sais, a town in Lower Egypt, where it had been cultivated from time immemorial, and taught the Athenians to extract oil from it. In this manner the use of oil became known in Europe†. But the Greeks seem to have been ignorant of the method of procuring light by means of lamps till after the siege of Troy; at least Homer never mentions them, and constantly describes his heroes as lighted by torches of wood.
Oils are divided into two classes, Fixed and Volatile; each of which is distinguished by peculiar properties.
I. The fixed oils, called also fat or expressed oils, are numerous, and are obtained partly from animals and partly from vegetables, by simple expression. As instances, we shall mention whale oil or train oil, obtained from the blubber of the whale; olive oil, obtained from the fruit of the olive; linseed oil and almond oil, obtained from linseed and almond kernels. Fixed oils may also be obtained from poppy seeds, hemp seeds, beech mast, and many other vegetable substances.
All these oils differ from each other in several particulars, but they also possess many particulars in common. Whether the oily principle in all the fixed oils is the same, and whether they owe their differences to accidental ingredients, is not yet completely ascertained, as no proper analysis has hitherto been made; but it is exceedingly probable, as all the oils hitherto tried have been found to yield the same products. In the present state of our knowledge, it would be useless to give a particular description of all the fixed oils, as the differences between them have not even been accurately ascertained. We shall content ourselves, therefore, with giving the characters which distinguish fixed oils in general, and an analysis of one oil, by way of specimen.
Fixed oils are insoluble in alcohol, which distinguishes them from volatile oils. They are also insoluble in water, etc.
They have an unctuous feel, are transparent while fluid, are destitute of smell, and have a mild insipid kind of taste.
They are all susceptible of becoming solid by exposure to a sufficient degree of cold. Olive oil and almond oil freeze at 10° degrees ‡.
They are capable of being converted into vapour by heat; but require for that purpose a temperature considerably superior to that of boiling water. Olive oil boils at 600°, and most of the fixed oils hitherto tried require nearly the same degree of heat.
When in the state of vapour they take fire on the approach of an ignited body, and burn with a yellowish white flame. It is upon this principle that candles and lamps burn. The wick or oil is first converted into the state of vapour in the wick; it then takes fire, and supplies a sufficient quantity of heat to convert more oil into vapour; and this process goes on while any oil remains. The wick is necessary to prevent a sufficiently small quantity of oil at once for the heat to act upon. If the heat were sufficiently great to keep the whole oil at the temperature of 600°, no wick would be necessary, as is obvious from oil catching fire spontaneously when it has been raised to that temperature.
Mr Lavoisier analysed olive oil by burning it in precisely the same apparatus as that which he employed for analysing alcohol.
The quantity of oil consumed amounted to 15.79 grains troy.
The quantity of oxygen gas amounted to 50.86 gr. troy. The whole amount therefore of the substances consumed during the combustion is 66.65 grains troy.
The carbonic acid obtained amounted to 44.30 gr. There was also a considerable quantity of water, the weight of which could not be accurately ascertained; but as the whole of the substances consumed were converted into carbonic acid gas and water, it is evident, that if the weight of the carbonic acid be subtracted from the weight of these substances, there must remain precisely the weight of the water. Mr Lavoisier accordingly concluded, by calculation, that the weight of the water was 22.15 grains. Now the quantity of oxygen in 44.30 grains of carbonic acid gas is 32.04 grains, and the oxygen in 22.15 grains of water is 18.82 grains; both of which taken together amount to 50.86 grams, precisely the weight of the oxygen gas employed.
There does not appear therefore to be any oxygen in olive oil.
The quantity of carbon in 44.30 grains of carbonic acid gas is 12.47 grams; and the quantity of hydrogen in 22.15 grams of water is 3.32 grams; both of which, when taken together, amount to 15.79 grams, which is the weight of the oil consumed.
It follows, therefore, from this analysis, that 15.79 grams of olive oil are composed of
- 12.47 Carbon, - 3.32 Hydrogen.
Olive Olive oil therefore is composed of about
79 Carbon, 21 Hydrogen.
In what manner these substances are combined, cannot be learned from this analysis. Whether they combine directly, and saturate each other in that proportion, as is most probable—or whether the hydrogen is combined previously with a part of the carbon, and that compound combining with a certain quantity of carbon, forms oil, is altogether uncertain. Yet these questions are of the utmost importance; and till the method of solving them be discovered, we never can acquire any precise ideas about the constituent parts of a great number of substances, which, though formed ultimately of the same ingredients, differ very much in their properties from one another; as wax and oil; alcohol, sugar, and ether.
When fixed oils are exposed to the atmosphere, they become thick, acquire a brown colour, and a peculiarly unpleasant smell; they are then said to be rancid. When oil is poured upon water, so as to form a thin layer on its surface, and is in that manner exposed to the atmosphere, these changes are produced much sooner, the oil becomes thicker, and assumes an appearance very much resembling wax. Berthollet, who first examined these phenomena with attention, ascribed them to the action of light; but Sennegier observed, that no such change was produced on the oil though ever so long exposed to the light, provided atmospherical air was excluded; but that it took place on the admission of oxygen gas, whether the oil was exposed to the light or not. It cannot be doubted, then, that it is owing to the combination of oxygen. All substances that are capable of supplying that principle, the metallic oxyds, for instance, and several of the acids, produce the same effect upon oils; and it is a known fact, that oil is capable of reducing many of the metallic oxyds to the metallic state, and consequently that it has a stronger affinity for oxygen.
Mr. Chaptal has supposed that oils become rancid merely because they contain a quantity of mucilage, with which the oxygen combines, and that when oxygen combines with fixed oils, it produces a different effect, converting them into what is called drying oils.
It is certain that oils contain a quantity of mucilage; but some change is evidently produced on the oils themselves by rancidity; for no agitation in water is capable of restoring them to their former state, although water deprives them of their mucilage. Drying oils, so called because they are capable of drying completely when spread out, a property which renders them useful in painting, seem, as Sennegier observes, to be completely deprived of mucilage; for, in order to render an oil drying, it must be boiled, which evaporates or decomposes all the mucilage; they seem also to lose part of their hydro-
Fixed oils are capable of dissolving sulphur at their boiling temperature. The solution is very fetid, owing fixed oils to a partial decomposition of the oil. Hydrogen gas dissolves off, having a quantity of sulphur dissolved in it. When the solution cools, the sulphur crystallizes.
Fixed oils dissolve phosphorus. The solution is lu. And phosphorous, from the slow combustion of the phosphorus.
Fixed oils are capable of combining with many of the metallic oxyds. The compounds are called metallic soaps. Several of the oxyds are decomposed by being boiled in oils.
Fixed oils combine also with the alkaline earths and with alumina. The compounds are called earthy soaps.
The affinities of the oils are as follows:
| Lime | Nitric acid | |------|------------| | Barytes | Muriatic acid | | Fixed alkalies | Sulphurous acid | | Magnesia | Sulphuric acid | | Ammonia | Acetous acid | | Oxid of mercury | Sulphur | | Other metallic oxyds (H) | Phosphorus (I) |
Alumina.
II. Volatile oils, called also essential oils, are all volatile obtained from vegetables. They have a strong aromatic smell, and a pungent acid taste. They are so volatile, that they may be distilled by the heat of boiling water. They are soluble in alcohol, but not in water. They evaporate on the application of heat, without leaving any stain behind them, which is not the case with the fixed oils. By this test, accordingly, it is easy to discover whether they have been adulterated with any of the fixed oils. Let a drop of the volatile oil fall upon a sheet of writing paper, and then apply a gentle heat to it. If it evaporates without leaving any stain upon the paper, the oil is pure; but if it leaves a stain, it has been contaminated with some fixed oil or other.
Volatile oils are very numerous, and differ from one another, in fluidity and weight, in their freezing point, and in several other particulars. Little attention has been paid to the greatest part of them, because few of them have been found of any use. The principal quality for which they are valued is their odour. Some of them are obtained by expression, as oil of bergamot, lemons, oranges; others by distillation, as oil of peppermint, thyme, lavender, &c. It would be useless, even if it were possible, to give a particular description of all the volatile oils.
They are more inflammable than the fixed oils; a quality which they owe to their volatility. As far as experiments have hitherto been made, they seem to consist of carbon and hydrogen; but nothing is known concerning the proportions of these ingredients. They thicken when exposed to the air, probably by combining with oxygen, and form resins (K).
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(u) Their order not well ascertained.
(i) The first column was ascertained by Berthollet. The last is to be considered as unconnected with the first.
On account of the affinity of these two classes of bodies for each other, it has not been possible to discover which of them has the greatest affinity for oil.
(k) Resins are concrete vegetable juices; the distinguishing property of which is insolubility in water and solubility in alcohol. Common resin, or rosin, from which they derive their name, is one of them; and sealing wax consists almost entirely of another. When exposed to cold, or when kept for a long time, some of them deposit crystals resembling the acid of benzoic (l).
They dissolve sulphur, and form what have been called balsams of sulphur.
They are capable of combining with most of the substances that unite with fixed oils. Their affinities, which certainly differ from those of fixed oils, have not yet been properly ascertained.
**CHAP. IV. Of Alkalies.**
Substances possessed of the following properties are called alkalies:
1. Incombustible. 2. Capable of converting vegetable blues to a green. 3. A hot caustic taste. 4. Very soluble in water, even when combined with carbonic acid.
There are three alkalies, potash, soda, and ammonia. The two first are called fixed alkalies, because a very violent heat is necessary to volatilize them; the last is called volatile alkali, because it very easily assumes a gaseous form, and is consequently diffused by a very moderate degree of heat.
**Sect. I. Of Potash.**
If a sufficient quantity of wood be burnt to ashes, and these ashes be afterwards washed repeatedly with water till it comes off free from any taste, and if this liquid be filtrated and evaporated to dryness, the substance which remains behind is potash; not, however, in a state of purity, for it is contaminated with several other substances; but sufficiently pure to exhibit many of its properties. In this state, it occurs in commerce under the name of potash. It may be purified considerably, by putting it in a crucible, keeping it red hot for some time; then dissolving it in water, filtrating it, and evaporating it again to dryness. By the following method it may be obtained nearly pure: Mix together equal quantities of nitre and carbon, and put them by little and little into a red hot crucible. They burn with a vivid flame, and leave behind them a quantity of potash. This is to be dissolved in water, filtrated, and evaporated to dryness. Or potash may be obtained by burning tartar wrapped up in brown paper and placed in a crucible (m).
The potash procured by these last processes is exceedingly white; it is not, however, quite pure; for it is combined with a substance which blunts all its properties considerably. This substance is carbonic acid gas; from which it may be separated by dissolving it, and mixing with it an equal quantity of lime made into a paste with water. The lime has a greater affinity for carbonic acid gas, and therefore combines with it; and the pure potash remains dissolved in the water, and may be separated from the lime by filtrating the mixture. This process, however, must be performed in close vessels; for there is a little carbonic acid gas in the atmosphere, which would again combine with the potash if it were allowed to stand exposed to the air.
It is then to be evaporated till a thick pellicle appears on its surface, and afterwards allowed to cool; and all the crystals which have formed are to be separated, for they consist of foreign salts. The evaporation is then to be continued in an iron pot; and, during the process, the pellicle which forms on the surface is to be carefully taken off with an iron skimmer. When no more pellicle appears, and when the matter ceases to boil, it is to be taken off the fire, and must be constantly agitated while cooling with an iron spatula. It is then to be dissolved in double its own weight of cold water. This solution is to be filtered and evaporated in a glass retort till it begins to deposit regular crystals. If the mass consolidates ever so little by cooling, a small quantity of water is to be added, and it must be heated again. When a sufficient number of crystals have been formed, the liquor which swims over them, and which has assumed a very brown colour, must be decanted off, and kept in a well-closed bottle till the brown matter has subsided, and then it may be evaporated as before, and more crystals obtained. The crystals may then be dissolved in pure water. By this process, which was invented by Mr Lowitz of Petersburgh*, potash may be obtained in a state of the greatest purity. The shape of its crystals is very different, according to the way in which they have been produced. When allowed to form in the cold, they are octahedrons in groups, and contain 0.13 of water: When formed by evaporation on the fire, they assume the figure of very thin transparent blades of extraordinary magnitude, which, by an assemblage of lines crossing each other in prodigious numbers, present an aggregate of cells or cavities, commonly so very close, that the vessel may be inverted without losing one drop of the liquid which it contains†.
Pure potash is so exceedingly corrosive, that when applied to any part of the body, it destroys it almost instantaneously. On account of this property, it has been called caustic, and is often used by surgeons under the name of the potential cautery, to open abscesses, and destroy useless or hurtful excrescences.
As potash is never obtained at first in a state of purity, but always combined with carbonic acid, it was long before chemists understood to what the changes the cause produced upon it by lime were owing. According to cauli- fome, it was deprived of a quantity of mucilage, in which it had formerly been enveloped; while, according to others, it was rendered more active by being more comminuted. At last, in 1766, Dr Black published the celebrated experiments which we have so often mentioned; in which he proved, by the most ingenious and satisfactory analysis, that the potash which the world had considered as a simple substance, was really a compound,
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(l) See a paper by Margueron on this subject, Ann. de Chim. xxi. 174. (m) That potash was known to the ancient Gauls and Germans, cannot be doubted, as they were the inventors of soap, which, Pliny informs us, they composed of ashes and tallow. These ashes (for he mentions the ashes of the beech tree particularly) were nothing else but potash; not, however, in a state of purity. Plinius, lib. xviii. c. 51. The same, too, mentioned by Aristophanes and Plato, appears to have been a ley made of the same kind of ashes. compound, consisting of potas and carbonic acid; that lime deprived it of this acid; and that it became more active by becoming more simple.
While Dr Black was thus occupied in Scotland, Mr Meyer was employed in Germany in the same researches; from which, however, he drew very different conclusions. His Essays on Lime appeared in 1764. Pouring into lime water a solution of potas (carbonate of potash), he obtained a precipitate, which he found not to differ from lime-stone. The alkali had therefore deprived the lime of its causticity and its active properties; and these very properties it had itself acquired. From which he concluded, that the causticity of lime was owing to a particular acid with which it had combined during its calcination. The alkali deprived the lime of this acid, and therefore had a stronger affinity for it. To this acid he gave the name of oxidum pingue or causticum. It was, according to him, a subtile elastic mixt, analogous to sulphur, approaching very nearly to the nature of fire, and actually composed of an acid principle and fire. It was expandible, compressible, volatile, astringent, capable of penetrating all vessels, and was the cause of causticity in lime, alkalies, and metals.
This theory was exceedingly ingenious, and it was supported by a vast number of new and important facts. But notwithstanding the reputation and acknowledged genius and merit of its author, it never gained many followers; because the true theory of causticity, which had been already published by Dr Black, soon became known on the continent; and, notwithstanding some opposition at first, soon carried conviction into every unprejudiced mind. Even Mr Meyer himself readily acknowledged its truth and importance, though he did not at first, on that account, give up his own theory.
When potas is exposed to the action of fire, it first becomes soft, and melts into a transparent liquid at the commencement of ignition.
When exposed to the air, it attracts moisture very fast, and is soon converted into a liquid. It attracts, at the same time, carbonic acid gas, for which it has a very strong affinity. It is impossible, then, to keep potas in a state of purity, except in very close vessels.
It unites readily with sulphur, and forms sulphuret of potas. This compound may be formed two ways; either by melting the ingredients together, or by boiling them in water, and then filtrating the solution. Sulphuret of potas when dry, in which state it is obtained by the first process, is of a brown colour. It is soluble in water, and very soon attracts moisture.
While dry it produces no change upon the air of the atmosphere, as Messrs Dieman, Van Troortwyck, Nieuwland, and Bondt, ascertained by experiment. But when moistened with water, it very soon absorbs all the oxygen gas which happens to be in the vessel in which it is included, and leaves nothing but azotic gas. This fact was first observed by Scheele, and induced him to use sulphuret of potas for an endometer, or instrument to measure the quantity of oxygen contained in any given portion of atmospheric air.
If sulphuret of potas be allowed to remain moist, and in contact with the atmosphere, it is gradually converted into sulphat of potas by the sulphur combining with oxygen, and forming sulphuric acid. At the same time the sulphuret emits a fetid smell, which is known to be the odour of sulphurated hydrogen gas.
The sulphuret then decomposes the water with which it is mixed. Very little sulphurated hydrogen gas, however, is emitted, except an acid (the sulphuric, for instance) be poured upon the mixture, and then it is given out very copiously. The reason of this is, that there is an affinity between the potas and this gas. Accordingly it is retained by the potas after it is formed. But as the acids have a much stronger affinity for potas, as soon as any of them is poured in the gas is obliged to separate.
If liquid sulphuret of potas be kept in close vessels, it is not decomposed except in part; because as soon as the alkali is saturated with the sulphurated hydrogen gas, the action of the sulphur on the water is at an end.
The explanation of the action of this sulphuret on the atmosphere, which the Dutch chemists above-mentioned give from these data, is as follows:
Sulphuret of potas decomposes water; sulphurated hydrogen gas is formed, and absorbed by the alkali. This gas has a strong affinity for oxygen, which it absorbs from the atmosphere; the hydrogen combines with this oxygen, and forms water; and the sulphur is again precipitated, or rather left combined with the potas. Water is again decomposed by the attraction of the sulphur for oxygen; new sulphurated hydrogen gas is again formed; again absorbed; again attracts oxygen gas; and is again decomposed. And this process goes on till the whole of the sulphur has combined with oxygen, and consequently till the sulphuret is converted into a sulphat. — The only part of this theory which requires confirmation is the action of sulphurated hydrogen gas on oxygen gas, and the consequent formation of water. And thus they have rendered not improbable, by shewing that sulphurated hydrogen gas combined with alkali has the property of absorbing oxygen gas from the atmosphere.
Potas unites with phosphorus by fusion, and forms a phosphauret of potas. Little is known concerning phosphauret's properties, except that it produces phosphauret of hydrogen gas.
Potas seems also capable of combining with carbon.
Potas does not combine with the metals; but it unites with many of their oxys.
When a solution of potas is boiled upon silica recently procured, it dissolves part of it. As the solution cools, it assumes the appearance of a jelly, even though previously diluted with 17 times its own weight of water.
When equal parts of silica and potas are melted together, they combine and form glass. A substance which, whether we consider its hardness, beauty, and transparency, its amazing ductility while hot, or the difficulty of decomposing it, must be allowed to be one of the most useful compounds ever invented by man.
When the quantity of potas is double or triple that of the silica, the glass is soluble in water, and forms what is called liquor silicum.
Potas seems also capable of combining in the same manner with barytes, lime, magnesia, and alumina; but these combinations have never been examined with attention. Lime, however, is often added to the materials for making glass, and is supposed to increase its hardness and solidity.
The metallic oxys have the property of rendering glass more fusible, and of communicating various co... Alkalis. hours to it; they accordingly very often make a part of its composition. The colours communicated by these oxyds will appear from the following table:
| Metallic Oxyds | Colour communicated to Glass | |----------------|-----------------------------| | Oxyd of gold and tin | Purple | | Silver | Yellow or golden | | Iron | Pale green | | Lead | Colourless | | Zinc | White | | Antimony | Green (s) | | Arsenic | White | | Cobalt | Blue | | Nickel | Blue (o) | | Manganese | Red | | Tungsten | Colourless | | Molybdenum | Colourless | | Uranium | Grey (opaque) | | Titanium | White (opaque) | | Tellurium | White | | Chromium | Green |
Potash combines readily with fixed oils, and forms the compound known by the name of soap.
Potash has never yet been decomposed. Several chemists, indeed, have conjectured, that it was a compound of lime and azot; and some persons have even endeavoured to prove this by experiment; but none of their proofs are at all satisfactory. We ought, therefore, in strict propriety, to have assigned it a place in the first part of this article: but this would have separated the alkalies from each other, and would have introduced a confusion into the article, which would have more than counterbalanced the logical exactness of the arrangement. Besides, we are certain, from a variety of facts, that all the alkalies are compounds: One of them has actually been decomposed; and the other two have been detected in the act of formation, though the ingredients which compose them have not hitherto been discovered.
Whether potash contains lime is a different question. Were we to judge from analogy, we should suppose, that the four alkaline earths, and the three alkalies, possess one common principle. They have a great number of common properties, and perhaps ought to be clasped altogether under the name of alkalies.
That azot enters into the composition of all these bodies, as Fourcroy has conjectured, is far from improbable. One alkali, as we shall soon see, actually contains azot. But no conclusion can be drawn till future discoveries have lifted off the veil which at present obstructs our view.
The affinities of potash are as follows:
- Sulphuric acid, - Nitric, - Muriatic, - Sebastic, - Fluoric, - Phosphoric,
Oxalic, Tartarous, Arsenic, Sucinic, Citric, Formic, Lactic, Benzoic, Sulphurous, Acetous, Saccharalactic, Boracic, Nitrous, Carbonic, Prussic, Oil, Sulphur, Phosphorus, Water.
The place of the metallic oxyds has not yet been ascertained.
Sect. II. Of Soda.
Soda, called mineral alkali, because it is found in the earth, was known to the ancients under the names of nigra and nitrum (r). It was long confounded with potash; and perhaps was never properly distinguished from it till Du Hamel published a paper on the subject in 1736.
Its properties, while pure, are precisely the same as those of potash, excepting only that its affinity for other bodies is not so strong; it does not, therefore, require any particular description. We ought to mention, however, that it differs from potash in one particular: potash attracts moisture in the air, but soda parts with it, and when exposed to the atmosphere, soon crumbles down into a dry powder.
It is capable of combining with all the substances with which potash unites; but it forms compounds possessed, in general, of very different properties from those of the compounds into which potash enters.
It is reckoned more proper than potash for forming glaiss and soap.
Some chemists have supposed that it is composed of magnesia and azot; but their proofs are insufficient.
The order of its affinities is the same with that of potash.
Sect. III. Of Ammonia.
Ammonia (q), volatile alkali, or hartshorn, as it is called in commerce, is mentioned as early as the 16th century. Both Basil Valentine and Raymond Lully described the methods of procuring it. Dr Black was the first who distinguished pure ammonia from the carburet of ammonia, or ammonia combined with carbonic acid; and Dr Priestley first discovered the method of obtaining it in a state of complete purity.
To obtain pure ammonia, mix common sal ammoniac with three parts of flaked lime; apply heat; and receive
(x) If the glass be made with soda. (o) But reddish if the glass be formed of soda. Klaperoth. (r) The nigra of the Athenians was evidently the same substance; and so was the nigra of the Hebrews. (q) We have adopted this word, which is Dr Black's, because we think it preferable to ammoniac or ammias; the words proposed and used by the French chemists. receive the product in a vessel filled with mercury standing in a basin of mercury. A gas comes over, which is pure ammonia*. This gas is transparent like common air, and is not condensed by cold.
Its specific gravity is \( \frac{1}{8} \). It is to common air as 600 to 1000†.
It has a very strong, but not unpleasant smell. Animals cannot breathe it without death. When a lighted candle is let down into this gas, it goes out three or four times successively; but at each time the flame is considerably enlarged by the addition of another flame of a pale yellow colour, and at last this flame descends from the top of the vessel to the bottom‡.
Water absorbs this gas with avidity. It disappears almost instantly on the introduction of a little water. From an experiment of Dr Priestley, it appears that water saturated with this gas is of the specific gravity \( \frac{1}{1435} \).
This water acquires the smell of ammonia. It has a very strong disagreeable taste, and converts vegetable colours to a green.
Ammonia in the state of gas has no effect upon sulphur or phosphorus. Carbon absorbs it; probably because it contains water. Neither hydrogen nor azot produce any alteration on it.
Alcohol and ether absorb it in considerable quantity§.
Dr Priestley discovered, that when electric explosions were made to pass through this gas, its bulk was gradually augmented to thrice the space which it formerly occupied. It was then mostly converted into hydrogen gas. He discovered, too, that heat produced the very same effect†. These experiments prove that hydrogen enters as an ingredient into the composition of ammonia.
Mr Scheele observed, that when ammonia was treated with the oxys of manganese, gold, or mercury, the oxys were reduced; the ammonia disappeared; and nothing remained but a quantity of azotic gas. These facts induced Bergman to conjecture, that ammonia was composed of hydrogen and azot; a conjecture which has been fully confirmed by the experiments of Berthollet.
This ingenious chemist observed, that if oxy-muriatic acid and ammonia be mixed, an effervescence takes place; azot is set free, a quantity of water formed, and the oxy-muriatic acid is converted into common muriatic acid. Now the substances mixed were ammonia and oxy-muriatic acid, which is composed of oxygen and muriatic acid; the products were, muriatic acid, azot, and water, which is composed of oxygen and hydrogen. The oxygen of the water was furnished by the acid; the other products must have been furnished by the ammonia, which has disappeared. Ammonia, therefore, must be composed of azot and hydrogen. Mr Berthollet proved, that ammonia was composed of these ingredients by a number of other experiments. For instance, if the oxyd of copper be heated in contact with ammoniacal gas, it is restored to the metallic state; the ammonia disappears, a quantity of water is formed, and azotic gas is disengaged. It follows from Mr Berthollet's experiments, that ammonia is composed of 121 parts of azot and 19 of hydrogen‡. According to Dr Austin, it is composed of 12 parts of azot, and 32 of hydrogen§.
After the composition of ammonia had been thus ascertained, it became a question of some consequence, whether it could be formed artificially? Dr Austin accordingly mixed hydrogen and azotic gas together in the proper proportions, and endeavoured to make them combine by the application of heat, by electricity, by ammonia and by cold; but he found, that while these two substances were in a gaseous state, they could not be combined by any method which he could devise. It could not be doubted, however, that the combination often takes place when these bodies are presented to each other in a different form. Dr Priestley‡ and Mr Kavan† had actually produced it, even before its composition was known. Accordingly he found, that when tin is moistened with nitric acid, and after being allowed to digest for a minute or two, a little potash or lime is added, ammonia is immediately exhaled*. In that case, the nitric acid and the water which it contains are decomposed; the oxygen of each unites with the tin, and reduces it to the state of an oxyd; and at the same time the hydrogen of the water combines with the azot of the acid, and forms ammonia, which is driven off by the stronger affinity of the potash or lime. Dr Austin succeeded also in forming ammonia by several other methods. He introduced into a glass tube filled with mercury a little azotic gas, and then put into the gas some iron-alloys moistened with water. The iron decomposes the water and combines with its oxygen; and the hydrogen meeting with azot at the moment of its admission, combines with it, and forms ammonia. This experiment shows, that the gaseous state of the azot does not prevent its combination with hydrogen.
Ammonia may be combined with sulphur by mixing together two parts of nitric acid (ammonia combined with muriatic acid), two parts of lime, and one part of sulphur, and distilling; a yellow liquor is obtained, which contains sulphuret of ammonia. It is capable of crystallizing.
The phosphuret of ammonia is unknown.
Ammonia is capable of combining with several of the metallic oxys, particularly copper.
It combines with fixed oils, and forms soap.
The order of its affinities is precisely the same with that of the fixed alkalies.
**CHAP. V. Of Acids.**
Substances possessed of the following properties are denominated acids.
1. When applied to the tongue they excite that sensation which is called sour or acid.
2. They change the blue colours of vegetables to a red. The vegetable blues employed for this purpose are generally tincture of litmus and syrup of violets or of radishes, which have obtained the name of reagents or tests. If these colours have been previously converted to a green by alkalies, the acids restore them again.
3. They unite with water in almost any proportion.
4. They combine with all the alkalies, and most of the metallic oxys and earths, and form with them those compounds which are called neutral salts.
It must be remarked, however, that every acid does not possess all these properties; but all of them possess a sufficient number of them to distinguish them from other substances. And this is the only purpose which artificial definition is meant to answer.
Paracelsus believed that there was only one acid principle. The acids at present known amount to about 39, most of which have been examined within these 30 years. Their names are as follows:
1. Sulphuric acid, 2. Sulphurous, 3. Nitric, 4. Nitrous, 5. Muriatic, 6. Oxy-muriatic, 7. Phosphoric, 8. Boracic, 9. Fluoric, 10. Carbonic, 11. Acetic, 12. Oxalic,
This theory has been carried so far by some chemists, that they have considered it as a conclusive proof, that oxygen did not enter into the composition of a body, if they could show that the body was not an acid. Thus, according to them, water cannot contain oxygen, because water is not an acid.—But surely no theory, however ingenious and satisfactory, can for a moment be put in competition with experiment. The ways of Nature are not as our ways, nor her thoughts as our thoughts.
Sect. I. Of Sulphuric Acid.
Sulphur combines with two different quantities of oxygen: with the smaller quantity it forms sulphurous acid; with the larger, sulphuric acid. The last of these is the subject of the present section.
The ancients were acquainted with some of the compounds into which sulphuric acid enters; alum, for instance, and green vitriol; but they appear to have been ignorant of the acid itself. It is first mentioned in the works of Basil Valentine, which were published about the end of the 15th century.
It was for a long time obtained by distilling green vitriol, a salt composed of sulphuric acid and green oxide of iron; hence it was called oil of vitriol, and afterwards vitriolic acid. Another method of obtaining it was by burning sulphur under a glass bell; hence it was called also oleum sulphuris per campanam. The French chemists in 1787, when they formed a new chemical nomenclature, gave it the name of sulphuric acid.
At present it is generally procured by burning a mixture of sulphur and nitre in chambers lined with porous lead. The theory of this process requires no explanation. The nitre supplies a quantity of oxygen to the sulphur, and the air of the atmosphere furnishes the rest. The acid thus obtained is not quite pure, containing a little potash, some lead, and perhaps also nitric and sulphurous acids. These acids may be driven off by applying for some time a gentle heat, and afterwards the sulphuric acid itself may be distilled over pure.
It appears from an experiment of Mr Berthollet, that sulphuric acid contains 63.2 parts of sulphur, and 36.8 of oxygen. He ascertained, in the first place, that nitre is totally decomposed by being heated with ¼ th of sulphur. He then mixed together 288 grains of nitre and 72 of sulphur; and after exposing them to a sufficient heat, he found 12 grains of sulphur sublimed, and 228 grains of sulphur of potash. But the sum of the ingredients was 360 grams; consequently 120 grams had been dissipated. All this loss must have been suffered by the acid of the nitre, for the heat was too small to separate any of the alkali. According to Mr Kirwan, 288 grams of nitre contain 132.96 of alkali. Sulphuric acid is a liquid, somewhat of an oily consistence, transparent and colourless as water, without any smell, and of a very strong acid taste. When applied to animal or vegetable substances, it very soon destroys their texture.
It always contains a quantity of water; part of which, however, may be driven off by the application of a moderate heat. This is called concentrating the acid. When as much concentrated as possible, its specific gravity is 2,000.
It changes all vegetable blues to a red, except indigo.
According to Erxleben, it boils at 54°6; according to Bertram, at 57°2.
When exposed to a sufficient degree of cold, it crystallizes or freezes; and after this has once taken place, it freezes again by the application of a much inferior cold. Morveau froze it at — 4°; it assumed the appearance of frozen snow. After the process began it went on in a cold not nearly so intense. The acid melted slowly at 27°8; but it froze again at the same temperature, and took five days to melt in the temperature of 43°1.
Chaptal, who manufactured this acid, once observed a large glass vessel full of it crystallized at the temperature of 48°. These crystals were in groups, and consisted of flat hexahedral prisms, terminated by a six-sided pyramid. They felt hotter than the surrounding bodies, and melted on being handled.
Chaptal has observed, that sulphuric acid, in order to crystallize, must not be too concentrated. This observation has been extended a good deal further by Mr Keir. He found, that sulphuric acid, of the specific gravity of 1.780, froze at 45°; but if it was either much more or much less concentrated, it required a much greater cold for congelation.
Sulphuric acid has a very strong attraction for water. Neumann found, that when exposed to the atmosphere it attracted 6.25 times its own weight. Mr Gould found, that 180 grains of acid, when exposed to the atmosphere, attracted 68 grains of water the first day, 58 the second, 39 the third, 23 the fourth, 18 the fifth, and at last only 5, 4, 3, 4, 3, &c. The 28th day the augmentation was only half a grain.
The Suppl. Vol. I. Part I.
(s) Mr Poujet undertook the examination of the specific gravity of alcohol mixed with different quantities of water. He took for his standard alcohol whose specific gravity was 0.8199, at the temperature of 65°75. He then formed 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 till the last contained only one measure of alcohol and nine of water. He took care that each of these measures should contain equal bulks, which he ascertained by weight, observing that a measure of water was to a measure of alcohol as 1 to 0.8199. Thus 10000 grains of water and 8199 of alcohol formed a mixture containing equal bulks of each. From the specific gravity of each of these mixtures he discovered how much they had diminished in bulk in consequence of mixture, by the following method.
Calling A the real specific gravity of any of the mixtures; B its specific gravity found by calculation, supposing no diminution of bulk; n the number of measures composing the whole mass; n - x the number to which it is reduced in consequence of mutual penetration—it is evident, since the increase of density does not diminish the weight of the whole mass, that \( nB = n - x \times A \). Therefore \( x = \frac{A - B}{A} \times n \), or (making \( n = 1 \)) \( \frac{A - B}{A} \times A \) is therefore the diminution of volume produced by the mixture. The first 50 numbers of the following table were formed by adding these augmentations to the specific gravity of the above mixture found by calculation, and taking the arithmetical mean for the intermediate quantities. The remaining numbers were formed from actual observation. He found by the first part of the table, that 100 parts of acid, of the specific gravity 1.8472, contained 88.5 parts standard, consequently 400 grains of this acid contain 35.4 grains standard. He took six portions of this acid, each containing 400 grains, and added to them as much water as made them contain respectively 48, 46, 44, 42, 40, 38 grains standard. The quantity of water to be added in order to produce this effect, he found by the following method. Suppose \( x \) = the quantity of water to be added to 400 parts of acid, that the mixture may contain 48 per cent. of standard acid. Then \( 400 + x : 354 :: 100 : 48 \), and consequently \( x = 337.5 \). After finding the specific gravity of these, the half of each was taken out, and as much water added; and thus the specific gravities, corresponding to 24, 23, 22, 21, 20, 19, were found. Then fix more portions, of 400 grains each, were taken, of the specific gravity 1.8393, and the proper quantity of water added to make them contain 36, 35, 34, 33, 32, 31, 30, 29, 28, 27 per cent. of standard. Their specific gravities were found, the half of them taken out, and as much water added; and thus the specific gravity of 18, 17, 16, 15, 14, and 13 found. Care was taken, after every addition of water, to allow the ingredient sufficient time to unite.
The last 11 numbers were only found by analogy; observing the series of decrement of the four last numbers before them.
The following table contains the result of Mr Poujet's experiments, calculated according to that formula; the whole volume or \( n \) being = 1.
| Measures of Water | Alcohol | Diminution of the whole volume = 1 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 |
It is evident, from this table, that the diminution of the bulk of the mixture follows a regular progression. It is greatest when the measures of water and alcohol are equal, and diminishes as it approaches both ends of the series. Mr Poujet accounts for this by conceiving the alcohol to be dissolved in the water, which retains a part of it in its pores, or absorbs it. The quantity absorbed ought to be in the ratio of that of the solvent and of the body dissolved, and each measure of water will retain a quantity of alcohol proportional to the number of measures of alcohol in the mixture. Thus in a mixture formed of nine measures of alcohol and one of water, the water will contain a quantity of alcohol = 9; in one of eight measures of alcohol and two of water, the water will contain a quantity of alcohol = 8. Therefore the diminution of bulk in each mixture is in a ratio compounded of the measures of alcohol and water which form it; in the above table, as \( 1 \times 9, 2 \times 8, 3 \times 7, 4 \times 6, \ldots \). And in general, taking the diminution of bulk when the measures of both liquids are equal for a constant quantity, and calling it \( e \), calling the number of measures \( n \), the number of measures of alcohol \( x \), the increase of density... density or diminution of bulk $z$; we shall have $c = \frac{n}{2} \times \frac{n}{2} : n - x \times x$, and $z = \frac{4c}{n^2} \times n - x^2$, or (making $n = 1$) $= 4c - 4c^2$.
The diminution of bulk, calculated according to this formula, make the last column of the above table. They correspond very well with experiment, while the measures of alcohol are more than those of water, but not when the reverse is the case. This Mr Poujet thinks is owing to the attraction which exists between the particles of water, and which, when the water is considerable compared with the alcohol, retards the union of the water with the alcohol.
By the formula $z = \frac{4c}{n^2}$, the quantity of alcohol of the standard may be determined in any mixture where the alcohol exceeds the water.
Let the number of measures, or the whole mass $= 1$
The measures of alcohol $= n$
The diminution of bulk at equal measures $= c$
The diminution of bulk of a mixture containing $x$ measures of alcohol $= 4c - 4c^2$
The specific gravity of water $= a$
The specific gravity of the alcohol $= b$
The specific gravity of the unknown mixture $= y$
Then Then since the increase of density does not change the weight of the whole, \(1 - x \times a + b \times = 1 - 4c \times + 4c \times^2 \times y\).
Hence \(x = 0.5 - \frac{a - b}{8c} + \sqrt{\frac{a - y}{4c} + \left(\frac{a - b}{8c} - 0.5\right)}\)
\[y = \frac{a - ax + bx}{1 - 4c \times + 4c \times^2}\]
And making \(a = 1, b = 0.8199, c = 0.0288\)
\[x = 0.5 - \frac{0.1801}{0.2304y} + \sqrt{\frac{1 - y}{0.1152y} + \left(0.1801 - 0.2304y - 0.5\right)}\]
\[y = \frac{1 - 0.1801x}{1 - 0.1152x + 0.1152x^2}\]
See Irish Trans. III. Oxyd of antimony, — arsenic, — mercury, — silver, — gold, — platinum,
Oil, Water.
Sect. II. Of Sulphurous Acid.
Sulphurous acid is composed of sulphur and oxygen combined; the proportions have not been ascertained; but the fact itself, and that the quantity of oxygen is less than what enters into sulphuric acid, has been proved beyond the possibility of doubt. Neither can it be doubted, though the fact has not been attended to, that in this acid the sulphur and oxygen mutually saturate each other; and that sulphuric acid is not composed of sulphur and oxygen, but of sulphurous acid and oxygen. Phosphorus is capable of decomposing sulphuric acid by the influence of heat, of seizing a quantity of its oxygen, and converting it into sulphurous acid; but upon sulphurous acid it has no effect whatever. The affinity of phosphorus, therefore, for oxygen is less than that of sulphur; yet it is capable of taking oxygen from sulphuric acid. Is it not evident from this, that sulphuric acid is composed of sulphurous acid and oxygen? and that sulphur has a stronger affinity for oxygen than sulphurous acid has?
For if both the acids were composed directly of sulphur and oxygen, it would follow from experiment, that the affinity of phosphorus for oxygen was both stronger and weaker than that of sulphur; which would be absurd.
Sulphurous acid has been known since the time of Stahl. Scheele first discovered the method of obtaining it in quantities; and Dr Priestley first procured it in a state of purity; for Scheele's acid was dissolved in water.
Stahl's method of procuring sulphurous acid was to burn sulphur at a low temperature, and expose it to its flames cloth dipped in a solution of potash. By this method he obtained a combination of potash and sulphurous acid; for at a low temperature sulphur forms by combustion only sulphurous acid. On this salt Scheele poured a quantity of tartaric acid, and then applied a gentle heat. The sulphurous acid is in this manner displaced, because its affinity for potash is not so strong as that of tartaric acid; and it comes over into the receiver dissolved in water. It is now commonly procured by mixing with sulphuric acid oil, grease, metals, or any other substance that has a stronger affinity for oxygen than sulphurous acid, and applying a heat sufficient to distil over the sulphurous acid as it forms. Mr Berthollet has found, that sugar is the best substance to employ for this purpose.
Dr Priestley poured a little oil on sulphuric acid, applied heat, and received the product in a glass jar filled with mercury. It was sulphurous acid free from all superfluous water, and in a gaseous form.
In this state it is colourless and invisible like common air. It is incapable of maintaining combustion; nor can animals breathe it without death. It has a strong and suffocating odour. It is this odour which burning sulphur exhales. Its specific gravity, according to Bergman, is 1.0246; according to Lavoisier, sulphurous acid is 1.0251. Cloutet and Monge found, that by the application of extreme cold it is converted into a liquid.
Dr Priestley discovered, that when a strong heat is applied to this acid in close vessels, a quantity of sulphur is precipitated, and the acid is converted into sulphuric acid. Berthollet obtained the same result; but Fourcroy and Vauquelin could not succeed.
Water absorbs this acid with avidity. According to Dr Priestley, 1000 grains of water, at the temperature of 54°, absorb 39.6 grains of this acid. The specific gravity of water saturated with sulphurous acid is 1.040. Water in the state of ice absorbs it very rapidly, and is instantly melted. Water saturated with this acid can be frozen without parting with any of it.
When water, which has been saturated with this acid at the freezing temperature, is exposed to the heat of 65°, it is filled with a vast number of bubbles, which continually increase, and rise to the surface. These bubbles are a part of the acid separating from it. It freezes a few degrees below 32°.
Sulphuric acid absorbs it at zero; but allows great part of it to escape at 32°.
It reddens tincture of turmeric; but destroys the colour of syrup of violets.
It is decomposed by hydrogen and carbon, and sulphurated hydrogen gas, when assisted by heat.
Oxygen gas gradually converts it into sulphuric acid; but this change does not take place unless water be present.
It does not seem capable of oxidising any of the metals except iron, zinc, and manganese.
When in the state of gas it is absorbed by oils and ether.
When glass tubes, filled with sulphurous acid in the state of gas, are exposed to a strong heat, a quantity of sulphur precipitates, and the rest of the acid is converted into the sulphuric.
It combines with the alkalies, alkaline earths, and alumina, and many of the metallic oxides, and forms neutral salts, known by the name of fulgurites.
Its affinities, as far as they have been investigated, are as follows:
Barter, Lime, Potash, Soda, Magnesia, Ammonia, Alumina, Jargonite, Metallic oxides, Water,
Sect. III. Of Nitric Acid.
There are three different substances composed of azot and oxygen, nitric acid, nitrous acid, and nitrous gas. The first contains most oxygen; the last contains least.
Nitric acid seems to have been first obtained in a separate state by Raymond Lully, who was born at Majorca in 1235. He procured it by distilling a mixture of nitre and clay. Basil Valentine, who lived in the 15th century, describes the process minutely, and calls the acid water of nitre. It was afterwards denominated Nitric acid is generally obtained in large manufactories by distilling a mixture of nitre (n) and clay; but the acid procured by this process is weak and impure. Chemists generally prepare it by distilling three parts of nitre and one of sulphuric acid in a glass retort. This method was first used by Glauber. When obtained in this manner it contains some nitrous acid, which may be expelled by the application of a very gentle heat.
Nitric acid is one of the most important instruments of analysis which the chemist possesses; nor is it of inferior consequence when considered in a political or commercial view, as it forms one of the most essential ingredients of gunpowder. Its nature and composition accordingly have long occupied the attention of philosophers. We shall endeavour to trace the various steps by which its component parts were discovered.
As nitre is often produced upon the surface of the earth, and never except in places which have a communication with atmospheric air, it was natural to suppose that air, or some part of the air, entered into the composition of nitric acid. Mayow having observed, that nitre and atmospheric air were both possessed of the property of giving a red colour to the blood, and that air was deprived of this property by combustion and respiration—concluded, that nitre contained that part of the air which supported combustion, and was necessary for respiration.
Dr Hales, by applying heat to nitric acid, and what he called Walton mineral, obtained a quantity of air possessed of singular properties. When atmospheric air was let into the jar which contained it, a reddish turbid fume appeared, a quantity of air was absorbed, and the remainder became transparent again. Dr Priestley discovered, that this air could only be obtained from nitric (u) acid; and therefore called it nitrous air. He found, that when this gas was mixed with oxygen gas, nitrous acid was reproduced. Here, then, we find, that oxygen is a part of the nitric acid, and consequently that Mayow's affirmation is verified.
Dr Priestley, however, explained this fact in a different manner. According to him, nitrous gas is composed of nitrous acid and phlogiston. When oxygen is added, it separates this phlogiston, and the acid of course is precipitated. This hypothesis was adopted by Macquer and Fontana; and these three philosophers endeavoured to support it with their usual ingenuity. But there was one difficulty which they were unable to surmount. When the two gases are mixed in proper proportions, almost the whole assumes the form of nitric acid; and the small residuum (1/37th part), in all probability, or rather certainly, depends on some accidental impurity in the oxygen gas. What then becomes of the oxygen and phlogiston? Dr Priestley supposed that they formed carbonic acid gas; but Mr Cavendish proved, that when proper precautions are taken, no such acid appears.
Dr Priestley had procured his nitrous gas by dissolving metals in nitric acid; during the solution of which a great deal of nitrous gas escapes. He supposed that nitrous gas contained phlogiston, because the metal was oxidated (and consequently, according to the then received theory, must have lost phlogiston) during its formation. Mr Lavoisier proved, that this supposition was ill-founded, by the following celebrated experiment. To 945 grains of nitric acid (specific gr. 1.316) he added 1124 grains of mercury. During the solution 273.234 cubic inches of nitrous gas were produced. He then distilled the salt (oxyd of mercury), which had been formed to dryness. As soon as it became red hot it emitted oxygen gas, and continued to do so till almost the whole of the mercury was revived; The quantity of oxygen emitted was 287.742 cubic inches. All that had happened, therefore, during the solution of the mercury, was the separation of the acid into two parts; nitrous gas, which flew off, and oxygen, which united with the metal (x).
Mr Lavoisier concluded, therefore, that the whole of the nitrous gas was derived from the nitric acid; that nitric acid is composed of oxygen and nitrous gas; and that the proportions are nearly 64 parts by weight of nitrous gas, and 36 of oxygen gas.
But there was one difficulty which Mr Lavoisier acknowledged he could not remove. The quantity of oxygen obtained by decomposing nitric acid was often much greater than what was necessary to saturate the nitrous gas. Mr De Morveau attempted to account for this; but without success. Nitrous gas itself was evidently a compound; but the difficulty was to discover the ingredients. Mr Lavoisier concluded, from an experiment made by decomposing nitre by means of charcoal, that it contained azot; and several of Dr. Priestley's experiments led to the same result. But what was the other ingredient?
Mr Cavendish had observed, while he was making experiments on the composition of water, that some nitric acid was formed during the combustion of oxygen and hydrogen gas, and that its quantity was increased by adding a little azot to the two gases before the explosion. Hence he concluded, that the formation of the acid was owing to the accidental presence of azotic gas. To verify this conjecture, he passed an electrical shock through a quantity of common air enclosed in a glass tube; the air was diminished, and some nitric acid formed. He repeated the experiment, by mixing together oxygen and azotic gas; and found, that when they bore a certain proportion to each other they were totally convertible into nitric acid. In one experiment, the proportion of azot to oxygen (in bulk) was as 416 to 914; in another, as 1920 to 4860.
These experiments were immediately repeated by Messrs Van Marum and Van Troolwyk, and with nearly the same result.
The most convenient method of performing them is the following: Take a glass tube, the diameter of
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(1) Nitre is composed of nitric acid and potash. (2) Or nitrous acid; for at the period of Dr Priestley's discovery (1772) they were not accurately distinguished. (3) We have already mentioned, in a preceding note, that this experiment was first made by Mr Bayen. See Part I. chap. iii. of this Article. which is about the sixth part of an inch, through the cork that shuts one end of which let a small metallic conductor pass with a ball at each end. Fill this tube with mercury, and plunge its open end into a basin of mercury; then put into it a mixture of 0.13 of azotic and 0.87 of oxygen gas, till it occupies three inches of the tube; and introduce a solution of potash till it fill half an inch more. Then, by means of the conductor, make electrical explosions (from a very powerful machine) to pass through the tube till the air is as much diminished as possible. Part of the potash will be found converted into nitre. Mr Cavendish actually saturated the potash with this acid. Mr Van Marum did not, though a good deal more gas had disappeared than in the experiments of Mr Cavendish. This difference evidently depends on the quantity of potash contained in a given weight of the solution. The solution which Mr Van Marum used was no doubt stronger than that which Mr Cavendish employed.
Dr Priestley had observed several years before these experiments were made, that atmospheric air was diminished by the electric spark, and that during the diminution the infusion of turpentine became red; but he concluded merely, that he had precipitated the acid of the air. Landriani, who thought, on the contrary, that carbonic acid gas was formed, denounced the alteration of lime-water by it as a proof of his opinion. It was to refute this notion that Mr Cavendish undertook his experiments. He has since that time repeated them with the same success.
It cannot be doubted, then, that nitric acid is composed of azot and oxygen; for the objections of Dr Priestley have been considered while we were treating of water. Consequently nitrous gas must also be composed of the same ingredients. According to Lavoisier, nitric acid is composed of four parts, by weight, of oxygen and one part of azot.
Nitric acid is liquid, colourless, and transparent; but the affinity between its component parts is so weak, that the action of light is sufficient to drive off a part of its oxygen in the form of gas; and thus, by converting it partly into nitrous acid, to make it assume a yellow colour. Its taste is exceedingly acid and peculiar. It is very corrosive, and tinges the skin of a yellow colour, which does not disappear till the epidermis comes off.
It has a strong affinity for water, and has never yet been obtained except mixed with that liquid. When concentrated, it attracts moisture from the atmosphere, but not so powerfully as sulphuric acid. It also produces heat when mixed with water, owing evidently to the concentration of the water.
The specific gravity of the strongest nitric acid that can be procured is, according to Rouelle, 1.583; but at the temperature of 65°, Mr Kirwan could not procure it stronger than 1.5543.
Taking this acid for the standard, Mr Kirwan has calculated how much of it exists in nitric acid of inferior density. His determination may be seen in the following table, which was formed precisely in the same manner as that formerly given of the strength of sulphuric acid.
| Parts | Specific Gravity | |-------|-----------------| | 1 | 1.5543 | | 2 | 1.5295 | | 3 | 1.5183 | | 4 | 1.5070 | | 5 | 1.4957 | | 6 | 1.4844 | | 7 | 1.4731 | | 8 | 1.4719 | | 9 | 1.4707 | | 10 | 1.4695 | | 11 | 1.4683 | | 12 | 1.4671 | | 13 | 1.4640 | | 14 | 1.4611 | | 15 | 1.4582 | | 16 | 1.4553 | | 17 | 1.4524 | | 18 | 1.4471 | | 19 | 1.4422 | | 20 | 1.4373 | | 21 | 1.4324 | | 22 | 1.4275 | | 23 | 1.4222 | | 24 | 1.4171 | | 25 | 1.4120 | | 26 | 1.4069 |
Now, how much water does nitric acid contain, the density of which is 1.5543?
Mr Kirwan dried a quantity of crystallized carbonat Quantity of soda in a red heat, and dissolved it in water, in such a proportion, that 367 grains of the solution contained 50.05 of alkali. He saturated 367 grains of this solution with 147 grains of nitric acid, the specific gravity of which was 1.5754, and which therefore, by the preceding table, contained 45.7 per cent. of acid standard. The carbonic acid driven off amounted to 14 grains. On adding 939 grains of water, the specific gravity of the solution, at the temperature of 38.5°, was 1.401. By comparing this with a solution of nitrat of soda, of the same density, precisely in the manner described formerly under sulphuric acid, he found, that the salt contained in it amounted to $\frac{1}{16}$ of the whole. There was an excess of acid of about two grains. The weight of the whole was 1439 grains; the quantity of salt consequently, was $\frac{1439}{16} = 85.142$ grains. The quantity of alkali was $50.05 - 14 = 36.05$. The quantity of standard acid employed was 66.7. The whole of which amounted to 102.75 grains; but as only 85.142 grains entered into the composition of the salt, the remaining 17.608 must have been pure water mixed with the nitric acid. But if 66.7 of standard acid contain 17.608 of water, 100 parts of the same acid must contain 26.18.
One hundred parts of standard nitric acid, therefore, is composed of 73.62 parts of pure nitric acid and 26.38 of water. But as Mr Kirwan has not proved that nitrat of soda contains no water, perhaps the proportion of Nitric Acid.
Its action on other bodies.
Nitric acid is decomposed by a great variety of substances. When poured upon oils, it sets them on fire. This is occasioned by a decomposition both of the acid and oil. The oxygen of the acid combines with the carbon and with the hydrogen of the oils, and at the same time lets go a quantity of caloric. Hence we see that the oxygen which enters into the composition of the nitric acid, still contains a great deal of caloric; a fact which is confirmed by a great number of other phenomena. The combustion of oils by this acid was first taken notice of by Borrichius and Slare; but it is probable that Homberg communicated it to Slare. In order to set fire to the fixed oils, it must be mixed with some sulphuric acid; the reason of which seems to be, that these oils contain water, which must be previously removed. The sulphuric acid combines with this water, and allows the nitric acid, or rather the oil and nitric acid together, to act. The drying oils do not require any sulphuric acid; they have been boiled, and consequently deprived of all moisture. It sets fire also to charcoal, provided it be perfectly dry. This fact was first observed by Proust, and afterwards confirmed by the Dijon academicians. It sets fire also to zinc, bismuth, and tin, if it be poured on them in fusion, and to filings of iron, if they be perfectly dry. In all these cases, the acid is decomposed. Sulphurated hydrogen gas also takes fire, and burns with a strong flame by means of this acid.
It is capable of oxidizing all the metals except gold, platinum (x), and titanium. It appears, from the experiments of Scheffer, Bergman, Sage, and Tillet, that nitric acid is capable of dissolving (and consequently of oxidizing) a very minute quantity even of gold.
Nitric acid combines with alkalies, alkaline earths, alumina, and argonias, and with the oxyds of metals, and forms compounds which are called nitrates. It does not act upon silica nor adamantia.
The order of its affinities is as follows:
- Barytes, - Potash, - Soda, - Strontiates *, - Lime, - Magnesia, - Ammonia, - Alumina, - Argonia †, - Metallic oxyds, in the same order as for sulphuric acid. - Water.
(x) Nitre, however, acts upon platinum, as Mr Tennant has proved. Phil. Trans. 1797. Morveau had made the same observation in the Éléments de Chimie de l'Académie de Dijon.
(y) Bernhardt, however, relates, in 1765, that once, when he was distilling a mixture of ten pounds of nitre with an equal quantity of calcined vitriol, which he had put into a retort, to which was fitted an adapter between the retort and the receiver, which contained a quantity of water—he observed a considerable quantity of a white crystalline salt formed in the adapter, while the liquid acid passed as usual into the receiver. This salt was very volatile, smoked strongly when it was exposed to the air, and exhaled a red vapour; it burnt, to a black coal, wood, feathers, or linen, as sulphuric acid does; and where a piece of it fell, it evaporated in form of a blood-red vapour, till the whole of it disappeared. Half an ounce of these crystals dissolved in water with spouting and hissing, like that of a red hot iron dipped in water, and formed a green nitrous acid. Some of this salt being put into a bottle, which was not well stopped, entirely vanished. These crystals were evidently the same with Dr Priestley's. See Keir's Dictionary.
Sect. IV. Of Nitrous Acid.
If oxygen gas be mixed with nitrous gas, a quantity of red fumes appear, which are readily absorbed by water. These red fumes are nitrous acid.
If a glass vessel containing nitric acid be inverted into another vessel containing the same acid, and exposed to the light, the inverted glass will become partly full of oxygen gas, and at the same time part of the nitric acid is converted into nitrous acid *. It follows, from this experiment, that nitrous acid contains less oxygen than nitric acid. Lavoisier has calculated, that it contains somewhat less than three parts of oxygen to one of azot.
Nitrous acid is of a brown or red colour, exceedingly volatile, and emitting a very suffocating and scarcely tolerable odour. When to this acid concentrated, a fourth part by weight of water is added, the colour is changed from red to a fine green; and when equal parts of water are added, it becomes blue †. Dr Priestley observed, that water impregnated with this acid in the state of vapour became first blue, then green, and lastly yellow. A green nitrous acid became orange-coloured while hot, and retained a yellow tinge when cold. A blue acid became yellow on being heated in a tube hermetically sealed. An orange-coloured acid, by long keeping, became green, and afterwards of a deep blue; and when exposed to air, resumed its original colour. These colours seem to depend upon the concentration of the acid.
Dr Priestley found that water absorbed great quantities of this acid in the state of vapour; and that when saturated, its bulk was increased one-third.
In the state of vapour, it is absorbed rapidly by oils. Whale oil, by absorbing it, became green, thick, and heavier. It gradually decomposed the acid, retained the oxygen, and emitted the azot in the state of gas ‡.
It is absorbed by sulphuric acid, but seemingly without producing any change; for when water is poured into the mixture, the heat produced expels it in the usual form of red fumes §. The only singular circumstance attending this impregnation is, that it disposes the sulphuric acid to crystallize *. This fact, first observed by Dr Priestley in 1777 (y), was afterwards confirmed by Mr Cornette.
Nitrous acid appears capable of combining with most of the bodies with which nitric acid unites. The salts which it forms are called nitrates.
Its affinities have never been accurately examined. Bergman supposes them the same with those of nitric acid. Nitrous gas was first obtained by Dr Hales, but its properties were discovered by Dr Priestley. It may be procured by dissolving metals in nitric or nitrous acid, and catching the product by means of a pneumatic apparatus.
As nitrous acid is formed by combining nitrous gas and oxygen, it is evident that nitrous gas contains less oxygen than nitrous acid. According to Lavoisier, it is composed of two parts of oxygen and one of azot.
Nitrous gas is elastic, and invisible like common air. It extinguishes light, and instantly kills all those animals that are obliged to breathe it. Its specific gravity, according to Mr Kirwan, is 0.601458.
Dr Priestley found that water was capable of absorbing about one-tenth of nitrous gas, and that by the absorption it acquired an agreeable taste. Water parts with all the nitrous gas it has imbibed on being frozen.
Neither phosphorus nor sulphur seem capable of decomposing nitrous gas.
Mr Linck, professor at Rostoc, found that three parts of nitrous gas and two of hydrogen gas, obtained by sulphuric acid and iron, are scarcely, or not at all, diminished when exposed to daylight over water. Common air is not more diminished by this admixture kept a long time; but the mixture itself of these two gases is diminished by the addition of new portions of nitrous gas.
Mr Linck concludes, from this observation, that part of the oxygen of the nitrous gas combined with the hydrogen and formed water, and that the remaining oxygen and azot formed a mixture similar to the air of the atmosphere. Mr Vanquelin had previously made the same observation. The affinity of hydrogen, therefore, for oxygen is greater than that of azot.
Oils imbibe nitrous gas with avidity, and decompose it.
Nitric acid absorbs a vast quantity of it, and is by that means converted into nitrous acid. Sulphuric acid also absorbs it.
The most important property of nitrous gas is that of combining instantly with oxygen gas, and forming nitrous acid, which is instantly absorbed by water. This property induced Dr Priestley to use nitrous gas as a test of the purity of common air. He mixed together equal bulk of these substances, and judged of the purity of the air by the diminution of bulk. The apparatus used for this purpose, which consists of a graduated tube, has been called an eudiometer. This eudiometer has been greatly improved by Fontana, but it is still liable to uncertainty in its application. Perhaps the best eudiometer is fulphuret of potash, which, as Morveau has discovered, absorbs, on the application of heat, the whole oxygen in a given bulk of air almost instantaneously.
Dr Priestley found that nitrous gas was decomposed by passing electric explosions through it.
Let us now consider in what manner oxygen and azot are combined in the three substances which have been just described.
It can hardly be conceived that azot is capable of combining with three different proportions of oxygen, and of being saturated with each; it is surely much more probable, that in nitrous gas the oxygen and azot saturate each other directly and completely; that nitrous acid is composed of nitrous gas and oxygen, and nitric acid of nitrous acid and oxygen. And this supposition is confirmed by considering that the strength of affinity by which the oxygen is retained in each of these substances is very different. Some substances, as light, are capable of decomposing nitric acid, by seizing some of its oxygen, and of converting it into nitrous acid; but they have no effect whatever upon nitrous acid or nitrous gas. Others, as bismuth, copper, phosphorus, and sulphur, are capable of decomposing both nitric and nitrous acids, but are incapable of altering nitrous gas; and others, again, as carbon, zinc, and iron, are capable of decomposing all the three. Every body which is capable of decomposing nitrous acid is capable also of decomposing nitric acid; and every body that decomposes nitrous gas is capable also of decomposing the other two. But the reverse of this is not true. The affinity of oxygen, then, for azot, nitrous gas, and nitrous acid, is different: oxygen has a stronger affinity for azot than it has for nitrous gas, and a stronger affinity for nitrous gas than for nitrous acid. But if all these bodies were direct combinations of azot and oxygen, how could this difference of affinity take place? Is it reasonable to suppose, that a substance has a stronger affinity for one proportion of any other body than for another proportion? or that, if such a difference existed, the strongest affinity should not always prevail?
Mix together nitric acid and nitrous gas in proper proportions, and the whole mixture is converted into nitrous acid; but mix nitrous and nitric acids together, and no change whatever is produced. In the first case, is it not evident that the affinity of nitrous gas for oxygen is greater than that of nitrous acid; that therefore it decomposes the nitric acid, deprives it of oxygen, and leaves it in the state of nitrous acid? But, in the second case, no change can take place, because nitric acid is composed of nitrous acid and oxygen; and it would be absurd to suppose, that nitrous acid has a stronger affinity for oxygen than nitrous acid has. But were azot and oxygen capable of uniting in various proportions, why should not a mixture of nitric and nitrous acids, or of nitrous gas and nitrous acid, form new substances? And why are the only substances which appear in decompositions nitrous acid and nitrous gas? Surely these reasons are sufficient to show us, that these bodies are combined in the following manner:
- Azot and Oxygen form nitrous gas; - Nitrous gas and oxygen form nitrous acid; - Nitrous acid and oxygen form nitric acid.
Perhaps there may be even more links in the chain than we are aware of. The dephlogisticated nitrous air of Dr Priestley, which Dieman and Van Troostwyck have lately proved to be composed of 37 parts of oxygen and 63 of azot, and of which little more is known than that it supports flame, is noxious to animals, absorbed by water, and only obtained by means of substances capable of decomposing nitrous gas—perhaps this air is composed directly of oxygen and azot, nitrous gas of this air and oxygen, and so on. There may be even links still farther back than that.
Sect. V. Of Muriatic Acid.
Muriatic acid appears to have been known to Basil of Muriatic Valentine; but Glauber was the first who extracted it acid. Muriatic Acid.
Common salt by means of sulphuric acid. Common salt is composed of muriatic acid and soda, for which last substance sulphuric acid has a stronger affinity. This acid was first called spirit of salt, afterwards marine acid, and now, pretty generally, muriatic acid.
It is sometimes prepared by mixing one part of common salt with seven or eight parts of clay, and distilling the mixture. The clay, in this instance, is supposed to act chiefly by means of the sulphuric acid which it always contains (z). But this subject still requires further elucidation. By these processes, muriatic acid is obtained dissolved in water. Dr Priestley discovered, that by applying heat to this solution, and receiving the product in vessels filled with mercury, a gas was procured; which gas is muriatic acid in a state of purity.
Muriatic acid gas is invisible and elastic, like common air. It destroys life and extinguishes flame. A candle, just before it goes out in it, burns with a beautiful green, or rather light blue flame; and the same flame appears when it is first lighted again.
The specific gravity of muriatic acid in the state of gas is, according to Mr Kirwan, \( \frac{6}{10} \times 2315 \), which is nearly double that of common air.
Water absorbs this gas with avidity. Ten grains of water are capable of absorbing ten grains of the gas. The solution thus obtained occupies the space of 13.3 grains of water nearly. Hence its specific gravity is \( \frac{1}{150} \), and the density of the pure muriatic acid in it is \( \frac{3}{10} \) (a).
As muriatic acid can only be used conveniently when dissolved in water, it is of much consequence to know how much pure acid is contained in a given quantity of liquid muriatic acid of any particular density.
Now the specific gravity of the purest muriatic acid that can easily be procured and preserved, is \( \frac{1}{196} \); it would be needless, therefore, to examine the purity of any muriatic acid of superior density. Mr Kirwan calculated that muriatic acid, of the density \( \frac{1}{196} \), contains \( \frac{4}{25} \) parts of acid of the density \( \frac{1}{150} \), which he took for the standard; then, by means of experiments, he formed the following table:
| Specific Gravity | Parts of Muriatic Acid | |------------------|-----------------------| | \( \frac{1}{196} \) | 49 | | \( \frac{1}{191} \) | 48 | | \( \frac{1}{187} \) | 47 | | \( \frac{1}{183} \) | 46 | | \( \frac{1}{179} \) | 45 | | \( \frac{1}{175} \) | 44 | | \( \frac{1}{171} \) | 43 | | \( \frac{1}{167} \) | 42 | | \( \frac{1}{163} \) | 41 | | \( \frac{1}{159} \) | 40 | | \( \frac{1}{155} \) | 39 | | \( \frac{1}{151} \) | 38 |
Muriatic acid (for this solution of the acid in water
(z) Morveau has shown, that even alumina contains sulphuric acid, provided a precipitation, on adding muriat of barytes, be a sufficient test.
(a) For let \( D = \) the density of a mixture; \( m \) the weight of the denser ingredient; \( d \) its density; \( l \) the weight of an into the vessel; and apply a small receiver, with a little water in it, fitted to the retort merely by a fillet of brown paper. In about a quarter of an hour the receiver will appear filled with a yellow-coloured gas; it is then to be removed, and others applied successively till the operation be finished.
This gas is oxy-muriatic acid, first discovered by Scheele, while he was making experiments on manganese, and called by him dephlogisticated muriatic acid, because he thought it muriatic acid deprived of phlogiston. The French chemists called it oxygenated muriatic acid, which Dr Pearson contracted into oxy-muriatic acid; and this last name we have adopted, because it is shorter and equally distinct.
The true theory of the formation and composition of this acid, which was first given by Berthollet, will appear from the following facts: The black oxyd of manganese is, during the process, converted into white oxyd, and must therefore have given out a quantity of oxygen. When oxy-muriatic acid dissolved in water is presented to the light in a vessel half empty, oxygen gas is disengaged and floats above, and the acid is converted into common muriatic acid: Consequently oxy-muriatic acid is composed of muriatic acid and oxygen. Black oxyd of manganese is composed of white oxyd and oxygen; muriatic acid has a stronger affinity for oxygen than the white oxyd; during the distillation the black oxyd is decomposed, the oxygen combines with muriatic acid, and the product is oxy-muriatic acid gas.
Oxy-muriatic acid gas is of a yellow colour. It supports flame, but cannot be breathed without proving noxious. The death of the ingenious and industrious Pelletier, to whom we have so often referred, was occasioned by his attempting to respire it. A consumption was the consequence of this attempt, which, in a short time, proved fatal.
It does not unite readily with water. Scheele found, that after standing 12 hours over water, 4/5ths of the gas were absorbed; the remainder was common air, which no doubt had been contained in the vessel before the operation. Berthollet surrounded several bottles containing it with ice: as soon as the water in these bottles was saturated, the gas became concrete, and sunk to the bottom of the vessels; but the smallest heat made it rise in bubbles, and endeavour to escape in the form of gas*. Weitrum observed that it became solid when exposed in large vessels to the temperature of 40°; and that then it exhibited a kind of crystallization†. The specific gravity of water saturated with this gas at the temperature of 43°, is 1.003‡. Water impregnated with it has not an acid, but an aulere taste §, unlike that of other acids.
It renders vegetable colours white, and not red, as other acids do; and the colour thus destroyed can neither be restored by acids nor alkalies. It has the same effects on yellow wax. If the quantity of vegetable colours to which it is applied be sufficiently great, it is found reduced, to the state of common muriatic acid. Hence it is evident, that it destroys these colours by communicating oxygen. This property has rendered oxy-muriatic acid a very important article in bleaching.
Nitrous gas, hydrogen, sulphur, sulphurous acid, and phosphorus, decompose this acid, by depriving it of its oxygen, and leaving the muriatic acid in a separate state. Phosphorus, however, does not produce this effect readily, except when assisted by heat*.
When muriatic acid is mixed with nitric acid, the compound has precisely the smell and the qualities of oxy-muriatic. It can scarcely be doubted, therefore, that as far as it acts as an acid, different from the muriatic and the nitric, it is nothing else but oxy-muriatic acid.
This mixture of the two acids was formerly called aqua regia; but at present it is called by the French chemists nitro-muriatic acid. It is first mentioned by Isaac the Hollander, and seems to have been known before the muriatic acid itself. It was prepared by pouring nitric acid on common salt. The nitric acid decomposes the salt, and part of it unites with the muriatic acid thus set at liberty.
Oxy-muriatic acid oxidizes all the metals (except perhaps, titanium) without the affluence of heat.
It decomposes red sulphuret of mercury, or cinnabar, bodies, which neither sulphuric nor nitric acid is able to accomplish†.
All the substances placed before muriatic acid in the table of the affinities of oxygen, are capable of decomposing this acid. Many of them, when plunged into it while in the state of gas, actually take fire. Weitrum observed, for instance, that when pieces of wood were plunged into this gas, they took fire; that arsenic burned with a blue and green flame; bismuth, with a lively bluish flame; nickel, with a white flame, bordering on yellow; cobalt, with a white flame, approaching to blue; zinc, with a lively white flame; tin, with a feeble bluish flame; lead, with a sparkling white flame; copper and iron, with a red flame; that powdered charcoal took fire in it at the temperature of 90°, and that ammonia produced with it a loud detonation‡.
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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 \( l = \frac{m + m' - kD}{D} = \frac{5}{1.5} = 3.3 \); and \( d = \frac{m}{l} = \frac{10}{3.3} = 3.03 \). See Irish Transactions, vol. iv.
This calculation, however, is formed upon the supposition that the water suffers no condensation at all—a supposition certainly contradicted by every analogy, and which, as Mr Kirwan has shown, the experiments mentioned in Mr Kirwan's first paper are insufficient to prove. With alkalis, earths, and metallic oxyds, it is capable of combining and forming neutral salts, which have been called oxy-muriats.
The affinities of this acid, according to Lavoisier, are as follows:
- Alumina, - Jargonia * - Ammonia, - Oxyd of antimony, - Silver, - Arsenic, - Barytes, - Strontites ? - Oxyd of bismuth, - Lime, - Oxyd of cobalt, - Copper, - Tin, - Iron, - Magnesia (a), - Oxyd of manganese, - Mercury, - Molybdenum, - Nickel, - Gold, - Platinum, - Lead, - Potas, - Soda, - Oxyd of tungsten, - Zinc (c).
The component parts of muriatic acid are still imperfectly known. Dr Girtaner pretended, about the year 1790, that he had decomposed it; and that it consisted of hydrogen combined with a greater proportion of oxygen than enters into the composition of water. He passed electrical explosions through muriatic acid, and obtained a quantity of oxygen and hydrogen gas. But a repetition of these experiments showed, that the gases were owing, not to the decomposition of the acid, but to that of the water with which the acid was combined.
The experiments of Mr Lambe (d) have lately opened a new and unexpected path, which seems to lead directly to the discovery of the component parts of this acid. He found, that when iron was acted upon by sulphurated hydrogen gas, a substance was produced which possessed all the properties of oxy muriat of iron (oxy-muriatic acid combined with iron). The sulphurated hydrogen gas which he used was obtained from sulphuret of iron, formed by fusing equal parts of iron and flowers of sulphur; and it was extracted by diluted sulphuric acid. In a solution of this gas in distilled water, he digested iron-slings, previously purified by repeated washings with distilled water. The bottle was filled with the solution, and corked. The iron was plentifully acted upon; numerous bubbles arose, which drove the cork out of the bottle; they were strongly inflammable, and probably, therefore, pure hydrogen gas. The liquor gradually lost its odour of sulphurated hydrogen gas, and after some days smelled very much like stagnant rain-water. As the bubbles ceased to be produced, it recovered its transparency. On evaporating a small quantity of this solution in a watch-glass to dryness, a bitter deliquescent salt was left behind. On this salt a little sulphuric acid was dropped, and paper moistened with ammonia was held over the glass; white vapours were immediately formed over the glass; and consequently some volatile acid was separated by the sulphuric acid. Mr Lambe evaporated about eight ounce-measures of the same liquor; and, as before, dropped a little sulphuric acid on the residue; a strong effervescence was excited, very pungent acid fumes arose, which, from their smell, were readily known to be muriatic. The same truth was established beyond a doubt, by holding a bit of paper moistened with water, which made the vapours visible in the form of a grey smoke; a distinguishing characteristic, as Bergman has observed, of the muriatic acid.—When manganese and mercury were dissolved in sulphurated hydrogen gas, the salts formed gave the same unequivocal marks of the presence of muriatic acid.
Shall we conclude from these facts, that the basis of muriatic acid is sulphurated hydrogen; that muriatic acid is sulphurated hydrogen combined with oxygen; that this combination takes place during the solution of the iron; and that the escape of hydrogen is owing to the decomposition of the water?
**Sect. VII. Phosphoric Acid.**
Phosphorus is capable of forming combinations with two different quantities of oxygen; with the larger it forms phosphoric; and with the smaller phosphorous acid.
Phosphoric acid was unknown till after the discovery of phosphorus. Boyle is perhaps the first person who mentions it: he discovered it by allowing phosphorus to burn slowly in common air. But Margraff was the first person who examined its properties, and discovered it to be a peculiar acid.
It may be procured by exposing phosphorus to a moderate heat: the phosphorus takes fire, combines with oxygen, and is converted into an acid.
It may also be prepared by exposing phosphorus during five weeks to the ordinary temperature of the atmosphere, even in winter; when the phosphorus undergoes a slow combustion, and is gradually changed into a liquid acid. For this purpose, it is usual to put small pieces of phosphorus on the inclined side of a glass funnel, through which the liquor which is formed drops into the bottle placed to receive it. From one ounce of phosphorus about three ounces of acid liquor may be thus prepared, called phosphoric acid by deliquescence.
Schelle has contrived another mode of obtaining the phosphoric
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(b) According to Tromsdorf, oxy-muriatic acid is incapable of combining with magnesia. *Ann. de Chim.* xxii. 218.
(c) This is the order of the affinities of nitro-muriatic acid. Many facts (some of which shall appear afterwards) concur to prove that the affinities of the oxy-muriatic acid are the same, and indeed that they are the same acids.
(d) Analysis of the waters of two mineral springs at Lemington Priors. *Manchester Memoirs,* vol. V. part iii. phosphoric acid from phosphorus without combustion, by the mere action of the nitric acid on phosphorus. Mr Lavoisier has repeated and described this process. He put two pounds of nitric acid, the specific gravity of which was 1.29895, into a retort, the contents of which were equal to six or seven French pints, and to which a balloon was fitted. Having placed this retort in a sand-bath, and brought the heat of the acid contained in it to 134° deg., he added successively small quantities of phosphorus, about ten or twelve grains at a time, until he had dissolved 24th oz. At first the effervescence was great, but at last he was obliged to apply heat to effect the solution. The operation lasted 17 or 18 hours. A good deal of nitrous acid had passed into the receiver. He then poured the contents of the retort into a smaller retort, and evaporated by means of a stronger heat, until the phosphoric acid began to distil in white vapours. The remaining acid was so thick, that he could not pour it out of the retort, and therefore could not ascertain its quantity; but he supposes it might be eight or nine ounces, in which he thinks there were about 2½ ounces of phosphorus; the remaining ¼ ounce being supposed to have evaporated. The quantity of oxygen imbibed he reckons at 3½ ounces, and the quantity of water at about 2 ounces.
Lavoisier computes, that phosphoric acid contains 100 parts of phosphorus and 154 of oxygen.
The colour of this acid is white; it has no smell, has an acid taste; but is not corrosive (x).
It is exceedingly fixed. When exposed to the fire in a matrix with a long neck, it loses at first the greater part of its water; then an odour of garlic is felt, owing to some phosphorus, from which it is exceedingly difficult to clear it entirely; there is likewise a small quantity of the acid volatilized along with the water. The liquor then becomes thick and milky; small luminous depositions take place from time to time, and they continue for some time after the vessel is taken from the fire. If the matter be then put into a crucible, and placed among burning coals, it first boils violently, and gives out a vapour which tinges flame green, and is at last converted to a white transparent glass, insoluble in water.
The specific gravity of this acid in a state of dryness is 2.687 +, that of phosphoric acid by deliquescence 1.417 *. It is capable of crystallizing; its crystals are quadrangular prisms terminated by quadrangular pyramids.
Phosphoric acid obtained by deliquescence, when mixed with an equal quantity of distilled water, acquired so little heat as to raise the thermometer only one degree, as Mr Sage observed.
Mr Lavoisier raised Réaumur's thermometer from 8° to 14° or 15° by mixing phosphoric acid boiled to the consistence of a syrup, with an equal quantity of water; and from 8° to 32° or 33° when the acid was as thick as turpentine.
Phosphoric acid is capable of oxidizing iron, tin, lead, zinc, antimony, bismuth, manganese. When fused with several of these metals, as tin, lead, iron, and zinc, it is converted into phosphorus; a proof that they have a stronger affinity for oxygen.
It does not act upon gold, platinum, silver, copper, mercury, arsenic, cobalt, nickel. It appears, however, to have some action on gold in the dry way, as it is called; for when fused with gold-leaf it affines a purple colour; a proof that the gold has been oxidized.
It is capable of combining with alkalies, alkaline earths, alumina, and metallic oxyds; and of forming salts, known by the name of phosphates.
Phosphoric acid, by the affluence of heat, is capable of decomposing glass.
Its affinities are as follows:
| Lime, | Its affinities | |-------------|---------------| | Barytes, | | | Strontites | | | Magnesia, | | | Potas, | | | Soda, | | | Ammonia, | | | Alumina, | | | Jargoma*, | | | Metallic oxyds, as in sulphuric acid, | | | Water. | |
The Phosphorous Acid is formed when phosphorus is exposed to a flow spontaneous combustion at the phosphorous temperature of the atmosphere; but it gradually absorbs more oxygen, and is converted into phosphoric acid.
Concerning phosphorous acid nothing of any consequence is at present known, except that it contains less oxygen than phosphoric acid.
Sect. VIII. Boracic Acid.
The word borax first occurs in the works of Geber, an Arabian chemist of the tenth century. It is a name given to a species of white salt much used by various artists. Its use in fiddling metals appears to have been known to Agricola.
Borax is found mixed with other substances in Thibet. It seems to exist in some lands adjacent to lakes, from which it is extracted by water, and deposited in those lakes; whence in summer, when the water is shallow, it is extracted and carried off in large lumps. Sometimes the water in these lakes is admitted into reservoirs, at the bottom of which, when the water is exhausted by the summer's heat, this salt is found. Hence it is carried to the East Indies, where it is in some measure purified and crystallized; in this state it comes to Europe, and is called tincal. In other parts of Thibet, it seems, by accounts received from China, they dig it out of the ground at the depth of about two yards, where they find it in small crystalline masses, called by the Chinese mu poun, hou poun, and pin poun; and the earth or ore is called pounsa *.
Though borax has been in common use for nearly three centuries, it was only in 1702 that Homberg, by distilling a mixture of borax and green vitriol, discovered the boracic acid. He called it auristic or sedative salt, of boracic acid.
(x) We have observed, however, that when very much concentrated it destroyed the texture of vegetable substances, paper, for instance, very completely. that borax contained soda; and at last Baron proved, by a number of experiments, that borax was composed of boracic acid and soda; that it might be reproduced by combining these two substances—and that therefore the boracic acid was not formed during the decomposition of borax, as former chemists had imagined, but was a peculiar substance which pre-existed in that salt.
This conclusion has been called in question by Mr. Cadet*, who affirmed, that it was composed of soda, the vitrifiable earth of copper, another unknown metal, and muriatic acid. But this assertion has never been confirmed by a single proof; Mr. Cadet has only proved, that boracic acid sometimes contains copper; and Beaumé's experiments are sufficient to convince us, that this metal is merely accidentally present, and that it is probably derived from the vessels employed in crystallizing borax: That boracic acid generally contains a little of the acid employed to separate it from the soda, with which it is combined in borax: And that crude borax contains a quantity of earth imperfectly saturated with boracic acid.—All which may be very true; but they are altogether insufficient to prove that boracic acid is not a peculiar substance, since it displays properties different from every other body.
Meflins Exchaquet and Struve have endeavoured, on the other hand, to prove, that the phosphoric and boracic acids are the same. But their experiments merely shew, that these acids resemble one another in several particulars; and though they add considerably to our knowledge of the properties of the phosphoric acid, they are quite inadequate to establish the principle which these chemists had in view; since it is not sufficient to prove the identity of the two acids, to shew us a resemblance in a few particulars, while they differ in many others. Boracic acid must therefore be considered as a distinct substance, the component parts of which are entirely unknown.
The easiest method of procuring boracic acid is the following one: Dissolve borax in hot water, and filter the solution; then add sulphuric acid, by little and little, till the liquor be rather more than saturated. Lay it aside to cool, and a great number of small, shining, laminated crystals will form. These are the boracic acid. They are to be washed with cold water, and drained upon brown paper.
This acid has a sourish taste at first, then makes a bitterish cooling impression, and at last leaves an agreeable sweetness. Its crystals have some resemblance to spermaceti, and it has the same kind of feel.
It changes vegetable blues to red; it has no smell; but when sulphuric acid is poured on it, a transient odour of musk is produced*. The air produces no change on it.
According to Reuss, it is soluble in 20 parts of cold water, eight parts of warm water, and 2½ of boiling water. According to Wenzel, 960 grains of boiling water dissolve 434 of this acid. According to Moreau, one pound of boiling water dissolves only 183 grains.
It is exceedingly fixed when not combined with water. When exposed to a violent fire it is converted into a white transparent glass; which, however, is soluble in water, and produces the acid again by evaporation.
Boracic acid is also soluble in alcohol; and alcohol containing it burns with a green flame.
Its specific gravity is 1.479†.
Paper dipped into a solution of boracic acid burns with a green flame.
Though mixed with fine powder of charcoal, it is nevertheless capable of vitrification; and with heat it melts into a black bitumen-like mass, which is, however, soluble in water, and cannot be easily calcined to ashes, but sublimes in part‡.
With the affluence of a distilling heat it dissolves in oils, especially in mineral oils; and with these it yields fluid and solid products, which give a green colour to spirit of wine.
When boracic acid is rubbed with phosphorus, it does not prevent its inflammation; but an earthly yellow matter is left behind†.
It is hardly capable of oxidising, or dissolving any of the metals except iron and zinc, and perhaps copper.
Boracic acid combines with alkalies, alkaline earths, and alumina, and most of the metallic oxyds, and forms compounds, which are called borats.
Its affinities are as follows:
| Lime, | |-------------| | Barytes, | | Strontites ‡,| | Magnesia, | | Potassa, | | Soda, | | Ammonia, | | Oxide of zinc,| | iron, | | lead, | | tin, | | cobalt, | | copper, | | nickel, | | mercury, | | Alumina, | | Jargonia §, | | Water, | | Alcohol, |
Sect. IX. Fluoric Acid.
The mineral called fluor or fusible spar, was not properly distinguished from other spars till Margraf published a dissertation on it in the Berlin Transactions for acid 1768. He first proved, that it contained no sulphuric acid, as had been formerly supposed; he then attempted to decompose it, by mixing together equal quantities of this mineral and sulphuric acid, and distilling them. By this method he obtained a white sublimate, which he supposed to be the fluor itself volatilized by the acid. He observed, with astonishment, that the glass retort was corroded, and even pierced with holes. Nothing more was known concerning fluor till Scheele published his experiments three years after; by which he proved, that it was composed chiefly of lime and a particular acid, which has been called fluoric acid.
To obtain it, put eight ounces of finely powdered fluor into a retort, and pour on it an equal quantity of sulphuric acid, and lute to the retort, as exactly as possible, a receiver containing eight ounces of water. Vapours immediately appear and darken the inside of the vessel. These are the acid in the state of gas. The distillation is to be conducted with a very moderate heat, not only to allow the gas to condense, but also to prevent the fluor itself from subliming. After the pro- Scheele supposed, that the silica produced was formed of fluoric acid and water; and Bergman adopted the same opinion. But Wiegbleb and Buccholz showed, that the quantity of silica was exactly equal to what the retort lost in weight; and Meyer completed the proof that it was derived from the glass, by the following experiment: He put into each of three equal cylindrical tin vessels a mixture of three oz. of sulphuric acid and one oz. of fluor, which had been pulverized in a mortar of metal. Into the first he put one oz. of pounded glass; into the second, the same quantity of quartz in powder; and into the third, nothing. Above each of the vessels he hung a sponge moistened with water; and having covered them, he exposed them to a moderate heat. The sponge in the first cylinder was covered with the crust in half an hour; the sponge in the second in two hours; but no crust was formed in the third, though it was exposed several days. In consequence of this decisive experiment, Bergman gave up his opinion, and wrote an account of Meyer's experiment to Morveau, who was employed in translating his works, to enable him to correct the mistake in his notes.
Soon after the discovery of this acid, difficulties and doubts concerning its existence as a peculiar acid were started by some French chemists, disguised under the name of Boulangier, and afterwards by Mr Achard and Mr Monnet. To remove these objections, Mr Scheele instituted and published a new set of experiments; which not only completely established the peculiar nature of the fluoric acid, but once more displayed the unrivalled abilities of the illustrious discoverer. These important particulars we pass over thus lightly, because they have been partly treated of already in the article Chemistry (Encyc.).
One experiment, however, we cannot omit, because it is sufficient of itself to destroy almost all the objections of his antagonists, which consisted in attempting to prove, that the fluoric acid was merely a modification of the acid employed to extract it. We shall give it in Mr Scheele's own words:
"I melted together (says he) in a crucible two ounces of finely pulverized fluor spar with four ounces of potash. As soon as they were melted, I poured out the mass, rubbed it, when it became cold, to a powder, and extracted the alkali from it again by lixiviation with water. I evaporated the lixivium to dryness; and threw away the remaining undissolved powder (which was only one of the component parts of the fluor, and which dissolved readily, and with effervescence, in acids) from its solution (in which it may be precipitated by sulphuric acid in the form of felsite (fulphat of lime). Upon a little of the dried alkali, put into a small retort, I poured some sulphuric acid, fitted to it a receiver containing some water; and even before the retort was become hot, I observed this water to be covered over with a pellicle of siliceous earth: a certain proof that the alkali had extracted the acid from the fluor during its exposure to the fire with it. Should Mr Achard, agreeably to the opinion which he has adopted, conclude from this experiment, that the alkali separated the volatile earth from the fluor (f); still he must certainly allow this earth of his to be of an acid nature, since the alkali is capable of disengaging it from the calcareous earth.—The remaining portion of the dried alkali I dissolved again in water, and saturated the superfluous alkali with pure nitric acid. After expelling from this saturated solution, by means of heat, the carbonic acid gas, which in such cases is always retained in the liquor, I dropped some of it into lime-water; whereupon I obtained a white precipitate, which was a regenerated fluor. I now dissolved some oxyd of lead in vinegar, and continued to add to the ley, which had been saturated with nitric acid, as much of this solution as was requisite, till all precipitation ceased. Thus I transferred the fluor acid from the alkali to the oxyd of lead. After washing the precipitate in cold water, and drying it, I dropped upon a small quantity of it a few drops of sulphuric acid: a frothing up immediately ensued, accompanied with an extrication of fluor acid vapours. But perhaps, in this case, the volatile earth of fluor unites with the fulphuric acid, and converts this fixed, or almost fixed acid into acid gas. I can easily make allowance to Dr Priestley for being inclined to draw such a conclusion, since this celebrated philosopher does not pretend to be a chemist (g). Being desirous of seeing whether heat alone was capable of expelling this acid from the oxyd of lead, I put a little of this fluorated oxyd into a small retort, the receiver to which contained some water. The oxyd was melted; but I could not perceive any acid. The bottom of the retort was moreover quite corroded and dissolved, so that the whole ran into the fire. Thus the oxyd of lead retains this acid in the fire, and will not part with it, unless the oxyd is combined with some other substance. I therefore rubbed the remainder of my fluorated oxyd of lead with an equal quantity of charcoal powder, and distilled the mixture in an open fire in a small glass retort, to which was adapted a receiver containing some water. As soon as the reduction of the oxyd of lead took place, the neck of the retort became incrusted with a white sublimate, and a siliceous pellicle appeared upon the water. The sublimate had a sour taste, because the siliceous earth of which it consists is penetrated with fluoric acid; and the acid water in the receiver fell down, on the addition of volatile alkali, a siliceous earth."
Sorry are we to add, that since the death of this admirable man, to use the words of Mr Kirwan, a man as eminent in the chemical as Newton in the mathematical branch of natural philosophy, Mr Monnet has thought proper to renew his attacks in a style of harshness and acrimony that inspires infinite disgust. The falsity of his reasoning is sufficiently exposed by Mr Lavoisier, in the 6th volume of his late learned edition of Macquer's Dictionary.
Fluoric acid may be obtained in the form of gas, by applying a moderate heat to sulphuric acid and fluor spar, and receiving the product over mercury.
This gas is the acid in a state of purity. It is invisible and elastic like air; it does not maintain combustion,
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(f) Mr Achard affirmed, that fluor was composed of a peculiar volatile earth. (g) Dr Priestley at first advanced this hypothesis; but he afterwards gave it up. Carbolic Acid.
It is heavier than common air. It corrodes the skin almost instantly. It combines rapidly with water; and if it has been obtained by means of glass vessels, it deposits at the same time a quantity of silica.
Water impregnated with this gas does not freeze at a higher temperature than \(23^\circ\).
In the state of gas this acid does not act upon nitrous gas nor sulphur. Alcohol and ether absorb it, but it does not alter their qualities.
It is capable of oxidizing iron, zinc, copper, and arsenic.
It does not act upon gold, platinum, silver, mercury, lead, tin, antimony, cobalt.
It combines with alkalies, alkaline earths, and alumina, and metallic oxides, and forms compounds denominated fluors.
It is capable, as we have seen, of dissolving silica, which is insoluble in every other acid; accordingly it corrodes glass. This property has induced several ingenious men to attempt, by means of it, to engrave, or rather etch, upon glass.
The affinities of fluoric acid are as follows:
- Lime, - Barytes, - Strontites, - Magnesia, - Potash, - Soda, - Ammonia, - Oxyd of zinc, - Manganese, - Iron, - Lead, - Tin, - Cobalt, - Copper, - Nickel, - Arsenic, - Bismuth, - Mercury, - Silver, - Gold, - Platinum, - Alumina, - Jargonite, - Water, - Silica, - Alcohol.
Sect. X. Of Carbonic Acid.
Carbonic acid is composed of carbon and oxygen. According to Lavoisier's experiments, the proportions are 28 parts of carbon and 72 of oxygen. Mr Proult informs us, that there is also a carbonous acid (\(n\)); but with this acid we are not at present acquainted, and cannot therefore describe it.
Paracelsus and Van Helmont were acquainted with the fact, that air is extricated from solid bodies during certain processes, and the latter gave to air thus produced the name of gas. Boyle called these kinds of air artificial airs, and suspected that they might be different from the air of the atmosphere. Hales ascertained the quantity of air that could be extricated from a great variety of bodies, and showed that it formed an essential part of their composition. Dr Black proved, that the substances then called lime, magnesia, and alkalies, are compounds, consisting of a peculiar species of air, and pure lime, magnesia, and alkali. To this species of air he gave the name of fixed air, because it existed in these bodies in a fixed state. This air or gas was afterwards investigated by Dr Priestley, and a great number of its properties ascertained. From these properties Mr Keir first concluded that it was an acid; and this opinion was soon confirmed by the experiments of Bergman, Fontana, &c. Dr Priestley at first suspected that this acid entered as an element into the composition of atmospheric air; and Bergman adopting the same opinion, gave it the name of aerial acid. Mr Beaudry called it mephitic acid, because it could not be respired without occasioning death; and this name was also adopted by Moreau. Mr Keir called it calcareous acid; and at last Mr Lavoisier, after discovering its composition, gave it the name of carbonic acid gas.
The opinions of chemists concerning the composition of carbonic acid have undergone as many revolutions as its name. Dr Priestley and Bergman seem at first to have considered it as an element; and several celebrated chemists maintained that it was the acidifying principle. Afterwards it was discovered that it was a compound, and that oxygen gas was one of its component parts. Upon this discovery the prevalent opinion of chemists was, that it consisted of oxygen and phlogiston; and when hydrogen and phlogiston came (according to Mr Kirwan's theory) to signify the same thing, it was of course maintained that carbonic acid was composed of oxygen and hydrogen: though Mr Lavoisier demonstrated, that it was formed by the combination of carbon and oxygen, this did not prevent the old theory from being maintained; because carbon was itself considered as a compound, into which a very great quantity of hydrogen entered. But after Mr Lavoisier had demonstrated, that the weight of the carbonic acid produced was precisely equal to the carbon and oxygen employed; after Mr Cavendish had discovered that oxygen and hydrogen when combined did not form carbonic acid, but water—it was no longer possible to hesitate that this acid was composed of carbon and oxygen. Accordingly all farther dispute about it seems now at an end. At any rate, as we have already examined the objections that have been made to this conclusion, it would be improper to enter upon them here.
If anything was still wanting to put this conclusion beyond the reach of doubt, it was to decompose carbonic acid, and thus to exhibit its component parts by analysis as well as synthesis. This has been actually done by the ingenious Mr Tennant. Into a tube of glass he introduced a bit of phosphorus and some
(n) When there are two acids having the same base, but containing different quantities of oxygen, they are distinguished by their termination. The name of that which contains most oxygen ends in \(i\), the other in \(o\). Thus sulphuric and sulphurous acids, nitric and nitrous, phosphoric and phosphorous, carbonic and carbonous. It is absorbed by red hot charcoal, as Morozzo and La Metherie have shown.
It is capable of combining with alkalies, alkaline earths, and alumina, and several metallic oxyds, and of forming compounds known by the name of carbonates. It pounds, has no affinity for jargonia, according to Klaproth; but, according to Vauquelin, it has.
Its affinities, as arranged by Bergman, are as follows:
- Barytes, - Lime, - Strontites, - Potas, - Soda, - Magnesia, - Alumina, - Metallic oxyds, as in sulphuric acid,
Oxygen gas,
Water,
Alcohol,
Sect. XI. Of Acetous Acid.
Acetous acid or vinegar was known many ages before the discovery of any other acid, those only excepted which exist ready formed in vegetables. It is mentioned by Moses, and indeed seems to have been in common use among the Israelites and other eastern nations at a very early period.
The methods of procuring, purifying, and concentrating this acid, have been already given in the articles Chemistry, Fermentation, and Vinegar (Encyc.) and cannot therefore be repeated in this place.
It has been ascertained beyond a doubt, that this acid is composed of carbon, hydrogen, and oxygen; but neither the manner in which these substances are combined, nor their proportions, have been accurately ascertained.
Acetous acid, as commonly prepared, is very fluid, Lowitz's has a pleasant smell, and an acid taste. It reddens vegetable colours. In this state it is mixed with a great proportion of water; but Mr Lowitz of Petersburg has discovered, that it may be obtained in a solid crystallized form. Of this curious and instructive process we shall transcribe his own account.
"I have long been accustomed (says he) to prepare concentrated vinegar by congelation in the following manner: I freeze a whole barrel of vinegar as much as possible; then distil the remaining unfrozen vinegar in a water-bath; by which means I at first especially collect the spirituous etherial part; the vinegar, which next comes over, I freeze again as much as possible, and afterwards purify it, by distilling it again with three or four pounds of charcoal powder. Thus I never fail to get a very pure, sweet-smelling, highly concentrated vinegar; the agreeable odour of which, however, may be still further improved."
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(1) Count Muffin-Puschin having boiled a solution of carbonat of potas on purified phosphorus, obtained carbon. This he considered as an instance of the decomposition of carbonic acid, and as a confirmation of the experiments related in the text. See Ann. de Chim. xxv. 105.
(2) At least near the surface of the earth. Lamanon, Mongez, and the other unfortunate philosophers who accompanied La Perouse in his last voyage, have rendered it not improbable that at great heights the quantity of this gas is much smaller. They could detect none in the atmosphere at the summit of the Peak of Teneriffe. See Lamanon's Memoir at the end of La Perouse's Voyage. improved by the addition of a proper quantity of the etherial liquor collected at the beginning of the first distillation, but which must be previously dephlegmated by two or three rectifications.
"After the distillation in the water-bath was over, that no vinegar might be lost, I used to move the retort, with the charcoal powder which remained in it, to a sand-bath; and thus I obtained, by means of a strong fire, a few ounces more of a remarkably concentrated vinegar, which was of a yellow colour.
"Having collected about ten ounces of this concentrated vinegar, I exposed it last winter in the month of December to a cold equal to —22°; in which situation it shot into crystals from every part. I let what remained fluid drop away from the crystals into a basin placed underneath, first in the cold air, and afterwards at the window within doors. There remained in the bottle snow-white finely foliated crystals, closely accumulated one upon the other, and which I at first took to be nothing but ice: on placing them upon the warm stove, they dissolved into a fluid which was perfectly as limpid as water, had an uncommonly strong, highly pungent, and almost suffocating acetic smell, and in the temperature of —37° immediately congealed into a solid white crystallized mass, resembling camphor.
"After I had observed that vinegar in this state is of such an extraordinary strength and purity as to be in its highest degree of perfection, I took all possible pains to find out a method of obtaining all the acetic acid in the state of glacial vinegar.
"To avoid circumlocution, I shall denote the strength of each sort of vinegar, which it was necessary for me to know in my experiments, by degrees, which I ascertain in the following manner: viz., to one drachm of vinegar I add, drop by drop, a clear solution of equal parts of carbonat of potash and water, till all at once a cloudiness or precipitation appears. Although, on the appearance of this sign, the acid is already supersaturated with the alkali, yet it seems to me to be a more accurate test for ascertaining its strength than the cessation of effervescence; for, as the point of saturation approaches, the effervescence becomes so imperceptible, that it is almost impossible to determine with precision when it is really at an end. Now, every five drops of the alkaline solution, which I find it necessary to add to the vinegar till the precipitation takes place, I reckon as one degree. Thus, for example, if a determinate quantity of vinegar requires 25 drops for that effect, I denote its strength by five degrees. This is about the strength of good distilled vinegar.
"I call that vinegar which, in consequence of its concentration, is capable of crystallizing in a great degree of cold, crystallizable vinegar; the crystals of vinegar, separated after the crystallization is completed from the remaining fluid portion, I call glacial vinegar; and, lastly, to the fluid residuum I give the name of mother-ley of vinegar.
"From a great number of experiments, I have found that vinegar must have at least 14 degrees of concentration before it can be brought to crystallize by exposure to the most intense cold. Vinegar must be of the strength of 42 degrees at least, in order to become glacial vinegar; viz., in this state of concentration it has the property of crystallizing in a degree of cold not exceeding that in which water begins to freeze.
"I have found that charcoal, on being distilled with vinegar in a water-bath, possesses the singular and hitherto unknown property of imbuing a certain quantity of the acetic acid in a very concentrated state, and of retaining it so strongly, that the acid cannot be separated from it again but by the application of a considerably greater degree of heat than that of boiling water. Upon this circumstance is founded the new method which I have discovered of concentrating vinegar, so as to obtain all its acid in the purest state, viz., that of a glacial vinegar.
"Let a barrel of vinegar be concentrated by freezing in the manner above described, and let the concentrated vinegar thus obtained, free from all inflammable or spirituous parts, be put into two retorts: Add to each of them five pounds of good charcoal reduced to a fine powder, and subject them to distillation in a water-bath. When no more drops of vinegar come over, put the distilled liquor into two fresh retorts; and after adding five pounds of charcoal powder to each, proceed as before to the distillation in a water-bath. In the mean while, the two first retorts are to be placed in a sand-bath, that, by means of a brisk fire, the crystallizable vinegar, which is retained in the apparently dry charcoal powder, may be expelled from it. The heat must be strong enough to make the drops follow one another every two seconds; and when, in this degree of heat, 20 seconds intervene between each drop, the vinegar which has been collected must be removed; for what follows is hardly anything else but mere water. In this manner about six ounces and a half of crystallizable vinegar, which is generally of the strength of between 36 and 40 degrees, may be collected from each retort. As soon as the distillation by the water-bath in the two retorts is over, the distilled liquor is to be poured back again into the first retorts upon the charcoal powder, which remains in them, and which has been already used; and from each of these retorts the remaining crystallizable vinegar (which generally amounts to as much as the first quantity) is to be abstracted by distillation in a sand-bath. These operations may be alternately repeated till all the acid of the vinegar which had been concentrated by freezing is converted into crystallizable vinegar; or until the distilled liquor, constantly becoming weaker and weaker at every repetition of the distillation, comes over at length in the state of mere water, which, with the above mentioned quantity of charcoal powder, generally happens at the fourth or fifth distillation. Now, in order to obtain the greatest part of the pure acid contained in the crystallizable vinegar in the form of glacial vinegar, it must be set to crystallize in a great degree of cold; and the mother-ley must be afterwards thoroughly drained from the glacial vinegar, by letting it drop from the crystals, first in the cold, and then in the room before the window. The mother-ley may be rendered further crystallizable, by distilling it with a little charcoal powder; the weaker part, which comes over first, being put aside. But if a person wishes to keep the crystallizable vinegar for other purposes, and without separating any glacial vinegar from it, he must distil the whole of it again with charcoal powder in a sand-bath.
"I have found by accurate experiments, that, by means of this curious process, ten pounds of vinegar concentrated by freezing to the 90th degree, may be made..." made to yield 38 ounces of crystallizable vinegar, from which 20 ounces of glacial vinegar may be obtained.
"What constitutes the excellence of this method is, that the concentration and purification are effected by one and the same medium, viz., the charcoal powder; in consequence of which, both intentions are fulfilled at the same time.
Last year, after much reflection, I was so happy as to find out another very effectual method of separating the acetous acid from the other substances combined with it, so as to obtain it at once in the state of a glacial vinegar of the greatest possible strength. The separating medium which I thought of is sulphate of potash supersaturated with sulphuric acid; a salt in which, conformably to my purpose, the sulphuric acid exists in a perfectly dry and dephlegmated state.
By means of this salt a highly concentrated glacial vinegar may be obtained in the following manner:
Let three parts of acetated soda, prepared with vinegar distilled over charcoal, and evaporated to perfect dryness, be melted in a strong heat; then pour it out, and rub it to a very fine powder. Mix this powder very accurately with eight parts of supersaturated sulphate of potash that has been previously well dried, and in like manner reduced to a fine powder; put the whole into a retort, and distil with a gentle heat, in such manner, that along with the drops some vapours also may be perceived to come out of the neck of the retort; but by no means so that the receiver shall be filled with these vapours. Notwithstanding the moderate heat, the vinegar comes over very fast, and the quantity of glacial vinegar, of the strength of 14 degrees, which is thus obtained, amounts to nearly two parts."
Acetous acid is capable of oxidizing iron, zinc, lead, nickel, tin, copper.
It does not act upon gold, silver, platinum, mercury, bismuth, cobalt, antimony, arsenic.
It combines with alkalies, alkaline earths, and alumina, and metallic oxys, and forms compounds known by the name of acetics.
Its affinities are as follows:
- Barytes, - Potas, - Soda, - Strontites? - Lime, - Magnesia, - Ammonia, - Oxide of zinc, - Manganese, - Iron, - Lead, - Tin, - Cobalt, - Copper, - Nickel, - Arsenic, - Bismuth, - Mercury, - Antimony, - Silver, - Gold, - Platinum, - Alumina, - Jargonia?
Water, Alcohol, Acetic Acid.
Sect. XII. Of Acetic Acid.
If acetite of copper be distilled, an acid comes over of a more pungent smell than acetous acid, capable of crystallizing, and having a stronger affinity for other bodies than acetous acid. It is called acetic acid, and is supposed to contain a larger proportion of oxygen than acetous acid. This additional dose it is supposed to receive from the oxyd of copper, which during the process is reduced to the metallic state. It can hardly be doubted that the glacial vinegar of Lowitz, described in the preceding section, is really acetic acid, though it would perhaps be difficult to explain its formation. Its affinities are the same with those of the acetous acid.
Sect. XIII. Of Oxalic Acid.
Sugar, a well-known substance extracted from the sugar-cane, appears to have been used in the East at a very early period; but it made its way westward very slowly. As a medicine, it is mentioned by Dioscorides; but it was not in common use in Europe till after the 14th century.
It has been proved that sugar is composed of oxygen, compound carbon, and hydrogen. Lavoisier concluded, from a long series of delicate experiments, that it consists of 8 parts sugar of hydrogen, 64 of oxygen, and 28 of carbon.
From sugar, by a particular process, an acid has been discovered obtained called oxalic acid, because it exists ready form of oxalic acid, as Scheele has proved, in the oxalic acetoforma, or acid wood forrel. At first, however, it was called the acid of sugar, or the saccharine acid.
As the earliest and best account of the oxalic acid was published by Bergman, he was for a long time reckoned the discoverer of it; but Mr. Elharta, one of Scheele's intimate friends, informs us, that the world is indebted for its knowledge of this acid to that illustrious chemist*, and Hermitadt and Wollram assign the discovery to the same author†. The assertions of these gentlemen, who had the best opportunity of obtaining accurate information, are certainly sufficient to establish part i. the fact, that Scheele was the real discoverer of oxalic acid.
Bergman gives us the following process for obtaining this acid. "Put one ounce of white sugar powdered Method of into a tubulated retort, with three ounces of strong nitric acid, the specific gravity of which is to that of water as 1:567. When the solution is over, during which many fumes of the nitrous acid escape, let a receiver be fitted, and the liquor made to boil, by which abundance of nitrous gas is expelled. When the liquor in the retort acquires a reddish brown colour, add three ounces more of nitric acid, and continue the boiling till the fumes cease, and the colour of the liquor vanishes. Then let the contents of the retort be emptied into a wide vessel; and, upon cooling, a crystallization will take place of slender quadrilateral prisms, which are often affixed to each other at an angle of 45°. These crystals, collected and dried on blotting paper, will be found to weigh 1½ dr. 19 gr. By boiling the remaining lixivium with two ounces of nitric acid in the retort, till the red fumes almost disappear, and by repeating the crystallization as before, ½ dr. 13 gr. of solid acid will be obtained. If the process be repeated once once more upon the residuum, which has now a glutinous consistence, with the successive additions of small quantities of nitric acid, amounting in all to two ounces, a saline brown deliquescent mass will be formed, weighing half a dram, of which about a half will be lost by a farther purification. The crystals obtained thus at different times may be purified by solution and crystallization, and by digesting the last lixivium with some nitric acid, and evaporation with the heat of the sun.
By the same process Bergman obtained it from gum arabic, alcohol, and honey; Scheele, Hermstedt, Wetterström, Hoffman, &c. from a great variety of other vegetable productions; and Berthollet from a great number of animal substances.
It is of great consequence not to use too much nitric acid, otherwise the quantity of oxalic acid will be diminished; and if a very great quantity of nitric acid be used, no oxalic acid will be obtained at all*. On the contrary, if too small a quantity of nitric acid be used, the acid obtained will not be the oxalic, but the tartarous†. We think we have observed, that a considerably larger proportion of oxalic acid may be obtained by pouring nitric acid on sugar, and allowing these substances to act upon each other while cold. When the process is conducted in that manner, hardly anything separates but nitrous gas.
Oxalic acid is capable of crystallization, or rather it is generally obtained in that state. Its crystals are quadrilateral prisms, the ends of which often terminate in ridges†.
They are soluble in their own weight of boiling water; water at the temperature of 65° dissolves half its weight of them. The specific gravity of the solution is 1.0593. One hundred parts of boiling alcohol dissolve 36 parts of these crystals; but at a mean temperature only 40 parts§. They are not easily soluble in ether. Fixed and volatile oils dissolve them, and they may be again obtained by gentle evaporation. Too violent a heat would sublime the acid itself.
Oxalic acid has a very acid taste when it is concentrated, but a very agreeable acid taste when sufficiently diluted with water¶.
It changes all vegetable blues except indigo to a red. One grain of crystallized acid, dissolved in 1920 grains of water, reddens the blue paper with which sugar loaves are wrapped; one grain of it, dissolved in 3600 grains of water, reddens paper stained with turmeric*. According to Morveau, one part of the crystallized acid is sufficient to communicate a sensible acidity to 2633 parts of water†.
Its fixity is such, that none of it is sublimed when water containing it in solution is raised to the boiling temperature.
When this crystallized acid is exposed to heat in an open vessel, there arises a smoke from it, which affects disagreeably the nose and lungs. The residuum is a powder of a much whiter colour than the acid had been. By this process it loses \( \frac{1}{3} \) ths of its weight; but soon recovers them again on exposure to the air. When distilled, it first loses its water of crystallization, then liquefies and becomes brown; a little phlegm passes over, a white saline crust sublimes, some part of which passes into the receiver; but the greatest part of the acid is destroyed, leaving in the retort a mass \( \frac{1}{3} \) th of the whole, which has an empyreumatic smell, blackens sulphuric acid, renders nitric acid yellow, and dissolves in muriatic acid without alteration. That part of the acid which sublimes is unaltered. When this acid is distilled a second time, it gives out a white smoke, which, condensing in the receiver, produces a colourless uncrystallizable acid, and a dark coloured matter remains behind*. During all this distillation a vast quantity of elastic vapour makes its escape. From 279 grams of oxalic acid, Bergman obtained 129 cubic inches of gas, half of which was carbonic acid and half hydrogen. Fontana from an ounce of it obtained 430 cubic inches of gas, one-third of which was carbonic acid, the rest hydrogen. From these facts, it is evident that oxalic acid is composed of oxygen, hydrogen, and carbon; but the proportions are still unknown.
When nitric acid is frequently distilled off oxalic acid, acetic acid is produced*. The sulphuric acid, when concentrated, seems to produce the same effect. Muriatic and acetic acids dissolve oxalic acid, but without altering it†.
Oxalic acid is capable of oxidizing lead, copper, iron, tin, bismuth, nickel, cobalt, zinc, manganese, arsenic. It does not act upon gold, silver, platinum, mercury, bodies.
Oxalic acid combines with alkalies, alkaline earths, and alumina, and metallic oxyds, and forms salts known by the name of oxalates.
Its affinities, according to Bergman, are as follows:
| Substance | Oxalic Acid | |-----------|-------------| | Lime | | | Barytes | | | Strontites† | | | Magnesia | | | Potash | | | Soda | | | Ammonia | | | Alumina | | | Jargonite | | | Metallic oxyds as in sulphuric acid. |
Sect. XIV. Of Tartarous Acid.
Tartar, or cream of tartar as it is commonly called when pure, has occupied the attention of chemists for several centuries. Duhamel and Groffe, and after them Margraf and Rouelle the Younger, proved, that it was composed of an acid united to potash; but Scheele was the first who obtained this acid in a separate state. He communicated his process for obtaining it to Retzius, who published it in the Stockholm Transactions for 1770. It consisted in boiling tartar with lime, and in decomposing the tartrate of lime thus formed by means of sulphuric acid.
This acid, by a gentle evaporation, yields crystals irregular in their figure, that every chemist who has treated of this subject has given a different description*.
According to Bergman, they generally consist of lamellae†; according to Van Pack‡, De Saene, they assume oftentimes the form of long pointed prisms†; Spielman and Corvinus‡ obtained them in needle-like groups, some of them lance-shaped, others needle-formed, others pyramidal. Moreau obtained them needle-like form§. They do not experience any change in the air; heat 323. heat decomposes them. In the open fire they burn without leaving any other residuum than a coal, which generally contains a little lime. In close vessefs, the product is carbonic acid and hydrogen gas. If the proper quantity of nitric acid be distilled off the crystals, they are converted into oxalic acid, and the nitric acid, as usual, passes into the nitrous acid. Hence it is evident that tartarous acid also, like the four former, is composed of oxygen, hydrogen, and carbon; but the proportions are equally uncertain.
This acid, when in crystals, dissolves readily in water. Bergman obtained a solution, the specific gravity of which was 1.230. Moreau observed, however, that crystals formed spontaneously in a solution, the specific gravity of which was 1.084.
It has a very sharp acid taste, and reddens vegetable blues.
Tartarous acid does not oxidize gold, silver, platinum, lead, bismuth, nor tin, and hardly antimony and nickel.
It combines with alkalies, alkaline earths, and alumina, and metallic oxides, and forms salts known by the name of tartrites.
The order of its affinities is the same as that given for oxalic acid; except that, according to Lavoisier, the oxide of silver comes before that of mercury.
Sect. XV. Of Citric Acid.
Chemists have always considered the juice of oranges and lemons as a peculiar acid. This juice contains a quantity of mucilage and water, which render the acid impure, and subject to spontaneous decomposition. Mr Georgius took the following method to separate the mucilage. He filled a bottle entirely with lemon-juice, corked it, and placed it in a cellar; in four years the liquid was become as limpid as water, a quantity of mucilage had fallen to the bottom in the form of flakes, and a thick crust had formed under the cork. He exposed this acid to a cold of 23°, which froze a great part of the water, and left behind a strong and pretty pure acid. It was Scheele, however, that first pointed out a method of obtaining this acid perfectly pure. He saturated lemon-juice with lime, educated the precipitate, which consisted of citric acid and lime, separated the lime from it by diluted sulphuric acid, cleared it from the fulphat of lime by repeated filtrations and evaporation; then evaporated it to the consistence of a syrup, and let it by in a cool place; a quantity of crystals formed, which were pure citric acid. It exists ready formed also in the juices of the following berries: Vaccinium octicoccos, Vaccinium vitis idaea, prunus padus, folium dulcamara, rosa canina, cherries.
Scheele advises the use of an excess of sulphuric acid, in order to insure the separation of all the lime; but, according to Dizé, this excess is necessary for another purpose. A quantity of mucilage still adheres to the citric acid in its combination with lime, and sulphuric acid is necessary to decompose this mucilage, which, as Fourcroy and Vauquelin have proved, it is capable of doing. His proof of the presence of mucilage is, that when the solution of citric acid in water, which he had obtained, was sufficiently concentrated by evaporation, it assumed a brown colour, and even became black towards the end of the evaporation. The crystals also were black. By repeated solutions and evaporations, this black matter was separated, and found to be carbon. Hence he concluded that mucilage had been present; for mucilage is composed of carbon, hydrogen, and oxygen; sulphuric acid causes the hydrogen and oxygen to combine and form water, and the carbon remains behind. It is not certain, however, as Mr Nicholson remarks very justly, that the sulphuric acid may not act upon the citric acid itself, and that the carbon may not proceed from the decomposition of it; at least the experiments of Mr Dizé are insufficient to prove the contrary. In that case, the smaller the excess of sulphuric acid used the better.
The crystals of citric acid are rhombooidal prisms, the faces of which are inclined to each other in angles of about 120 and 60 degrees, terminated at each end by four trapezoidal faces, which include the solid angles. They are not altered by exposure to the air.
An ounce of distilled water, at the temperature of the atmosphere, dissolves one ounce and two drams of crystallized citric acid; and during the solution the temperature is lowered 29.75°. Boiling water dissolves twice its weight of this acid.
Citric acid has a very acid taste; it turns vegetable blues to a red.
It is capable of oxidizing iron, zinc, tin. It does not act upon gold, silver, platinum, mercury, bismuth, antimony, arsenic.
It combines with alkalies, alkaline earths, and aluminas, and metallic oxides, and forms salts known by the name of citrates.
Fire decomposes this acid, converting it into an acridulous phlegm, carbonic acid gas, and carbonated hydrogen gas. Its solution in water is also gradually decomposed, if access of air be permitted. It is evident, therefore, that this acid is also composed of oxygen, hydrogen, and carbon.
Scheele said that he could not convert it into oxalic acid by means of nitric acid, as he had done several other acids; but Welthum affirms, that this conversion may be effected; and thinks that Scheele had probably failed from having used too large a quantity of nitric acid, by which he had proceeded beyond the conversion into oxalic acid, and had changed the citric acid into vinegar; and in support of his opinion, he quotes his own experiments: from which it appeared that, by treating sixty grains of citron acid with different quantities of nitric acid, his products were very different. Thus with 200 grains of nitric acid he got 30 grains of oxalic acid; with 300 grains of nitric acid he obtained only 15 grains of the oxalic acid; and with 600 grains of nitric acid no vestige appeared of the oxalic acid. On distilling the products of these experiments, especially of the last, he obtained vinegar mixed with nitric acid.
The affinities of this acid are as follows:
| Lime (L), | Barytes, | Strontites, | Magnesia, | Potash, | Soda, | |-----------|----------|------------|-----------|--------|------|
(1) Mr De Brefrey places barytes before lime. Sect. XVI. Of Malic Acid.
Schelle discovered a peculiar acid in the juices of several fruits, which, because it is found most abundantly in apples, has been called malic acid.
He obtained it by the following process: Saturate the juice of apples with potash, and add to the solution acetite of lead till no more precipitation ensues. Wash the precipitate carefully with a sufficient quantity of water; then pour upon it diluted sulphuric acid till the mixture has a perfectly acid taste, without any of that sweetness which is perceptible as long as any lead remains dissolved in it; then separate the sulphate of lead, which has precipitated, by filtration, and there remains behind pure malic acid.
This acid is contained in the berries of the barberry vulgaris, the sambucus nigra, the prunus spinosa, the ferbus cuneiparia, and the prunus domestica.
If nitric acid be distilled with an equal quantity of sugar, till the mixture assumes a brown colour (which is a sign that all the nitric acid has been abstracted from it), this substance will be found of an acid taste; and after all the oxalic acid which may have been formed is separated by lime-water, there remains another acid, which may be obtained by the following process: Saturate it with lime, and filter the solution; then pour upon it a quantity of alcohol, and a coagulation takes place. This coagulum is the acid combined with lime. Separate it by filtration, and edulcorate it with fresh alcohol; then dissolve it in distilled water, and pour in acetite of lead till no more precipitation ensues. The precipitate is the acid combined with lead, from which it may be separated by diluted sulphuric acid. It possesses all the properties of malic acid. This acid, therefore, may be obtained from sugar; and it may be converted into oxalic acid, by distilling off it the proper quantity of nitric acid.
This acid bears a strong resemblance to the citric, but differs from it in the following particulars:
1. The citric acid shoots into fine crystals, but this acid does not crystallize. 2. The salt formed from the citric acid with lime is almost insoluble in boiling water; whereas the salt made with malic acid and the same bains is readily soluble by boiling water. 3. Malic acid precipitates mercury, lead, and silver, from the nitrous acid, and also the solution of gold when diluted with water; whereas citric acid does not alter any of these solutions.
Malic acid seems to have a less affinity than citric acid for lime; for when a solution of lime in the former acid is boiled one minute with a salt formed from volatile alkali and citric acid, a decomposition takes place, and the latter acid combines with the lime and is precipitated.
The malic acid combines with alkalies, alkaline earths, lime and alumina, and metallic oxyds, and forms salts known under the name of malats.
Its affinities have not yet been ascertained.
Sect. XVII. Of Lactic Acid.
If milk be kept for some time it becomes sour. The acid which then appears in it was first examined by Scheele, and found by him to have peculiar properties. It is called lactic acid. In the whey of milk this acid is mixed with a little curd, some phosphat of lime, sugar of milk, and mucilage. All these must be separated before the acid can be examined. Scheele accomplished this by the following process:
Evaporate a quantity of sour whey to an eighth part, and then filtrate it; this separates the cheesy part. Saturate the liquid with lime-water, and the phosphat of lime precipitates. Filtrate again, and dilute the liquid with three times its own bulk of water; then let fall into it oxalic acid, drop by drop, to precipitate the lime which it has dissolved from the lime-water; then add a very small quantity of lime-water, to see whether too much oxalic acid has been added. If there has, oxalate of lime immediately precipitates. Evaporate the solution to the consistence of honey, pour in a sufficient quantity of alcohol, and filtrate again; the acid passes through dissolved in the alcohol, but the sugar of milk and every other substance remains behind. Add to the solution a small quantity of water, and distil with a small heat; the alcohol passes over, and leaves behind the lactic acid dissolved in water.
This acid is incapable of crystallizing; when evaporated to dryness, it deliquesces again in the air.
When distilled, water comes over first, then a weak acid resembling the tartarous, then an empyreumatic oil mixed with more of the same acid, and lastly carbonic acid and hydrogen gas—there remains behind a small quantity of coal.
The combinations which this acid forms with alkalies, earths, and metallic oxyds, are called lactats.
Its affinities, according to Bergman, are as follows:
- Barytes - Potash - Soda - Ammonia - Lime - Magnesia - Alumina - Jargonia - Metallic oxyds as in sulphuric acid - Water - Alcohol
Sect. XVIII. Of Succinolactic Acid.
Is a quantity of fresh whey of milk be filtrated, and sugar of then evaporated by a gentle fire till it is of the consistence of honey, and afterwards allowed to cool, a solid mass If this be dissolved in water, clarified with the white of eggs, filtrated, and evaporated to the consistence of a syrup, it deposits on cooling a number of brilliant, white, cubic crystals, which have a sweet taste, and for that reason have been called sugar of milk. Fabricius Bartholet, an Italian, was the first European who mentioned this sugar. He described it in his Encyclopedia Hermetico dogmatica, published at Boulogna in 1693; but it seems to have been known in India long before that period.
After Mr Scheele had obtained oxalic acid from sugar, he wished to examine whether the sugar of milk would furnish the same product. Upon four ounces of pure sugar of milk, finely powdered, he poured 12 ounces of diluted nitric acid, and put the mixture in a large glass retort, which he placed in a sand bath. A violent effervescence ensuing, he was obliged to remove the retort from the sand-bath till the commotion ceased. He then continued the distillation till the mixture became yellow. As no crystals appeared in the liquor remaining in the retort, after standing two days he repeated the distillation as before, with the addition of eight ounces of nitric acid, and continued the operation till the yellow colour, which had disappeared on addition of the nitrous acid, returned. The liquor in the retort contained a white powder, and when cold was observed to be thick. Eight ounces of water were added to dilute this liquor, which was then filtrated, by which the white powder was separated; which being edulcorated and dried weighed 7½ dr. The filtrated solution was evaporated to the consistence of a syrup, and again subjected to distillation, with four ounces of nitric acid as before; after which, the liquor, when cold, was observed to contain many small, oblong, four crystals, together with some white powder. This powder being separated, the liquor was again distilled with more nitric acid as before; by which means the liquor was rendered capable of yielding crystals again; and by one distillation more, with more nitrous acid, the whole of the liquor was converted into crystals. These crystals, added together, weighed five drams; and were found, upon trial, to have the properties of the oxalic acid.
Mr Scheele next examined the properties of the white powder, and found it to be an acid of a peculiar nature; he therefore called it the acid of sugar of milk. It is now called the succinolactic acid.
According to Scheele, it is soluble in 60 parts of its weight of boiling water; but Meffris Hermiladt* and Morveau† found, that boiling water only dissolved ¼ th part: it deposited about ¼ th part on cooling in the form of crystals.
The solution has an acid taste, and reddens the infusion of turnsole. Its specific gravity, at the temperature of 53°, is 1.0015.
When distilled, it melts very readily, becomes black, and frothes; a brown salt sublimes into the neck of the retort, which has the odour of a mixture of amber and benzoin, having an acid taste, easily soluble in alcohol, with greater difficulty in water, and burning in the fire with a flame. There passes into the receiver a brown liquid, having some of this salt dissolved in it: There remains behind a coal, which Hermiladt found to contain a small quantity of lime. Concentrated sulphuric acid distilled on this salt becomes black, frothes, and decomposes it.
Mr Hermiladt of Berlin had made similar experiments on sugar of milk at the same time with Scheele, and with similar results; but he concluded, that the white powder which he obtained was nothing else than oxalate of lime with excess of acid, as indeed Scheele himself did at first. After he became acquainted with Scheele's conclusions, he published a paper in defence of his own opinion; but his proofs are very far from establishing it, or even rendering its truth probable. He acknowledges himself, that he has not been able to decompose this supposed salt: he allows that it possesses properties distinct from the oxalic acid; but he attributes this difference to the lime which it contains; yet all the lime which he could discover in 240 grains of this salt was only 20 grains; and if the alkali which he employed was a carbonate (as it probably was), these 20 must be reduced to 11.
Now Morveau has shown, that oxalic acid, containing the same quantity of lime, exhibits very different properties. Besides, this acid, whatever it is when united with lime, is separated by the oxalic, and must therefore be different from it, as it would be absurd to suppose that an acid could displace itself. The fact that oxalic acid must therefore be considered as a distinct acid, as it possesses peculiar properties.
Its compounds with alkalies, earths, and metallic oxyds, are denominated succinolactate.
Its affinities, according to Bergman, are as follows:
- Lime, - Barites, - Magnesia, - Potash, - Soda, - Ammonia, - Alumina, - Jargonia†,
Metallic oxyds as in sulphuric acid,
Water,
Alcohol.
Sect. XIX. Of Gallic Acid.
There is an excretion, known by the name of nut-galls, which grows on some species of oaks. This substance contains a peculiar acid, called from that circumstance gallic acid, the properties of which were first examined with attention by the commissioners of the academy of Dijon; and the result of their experiments was published in 1777, in the third volume of their Elements of Chemistry. In these experiments, however, they employed the infusion of galls, in which the acid is combined with the tanning principle (m). It was reserved for Scheele to obtain it in a state of purity.
(m) A substance lately discovered by French chemists, which exists also in oak-bark, and every other body which may be substituted for that bark in the operation of tanning. It resembles the resin in many properties; but its distinguishing property is that of forming with glue a compound insoluble in water. When a little of the decoction of glue is dropped into an infusion of nut-galls, a white curdy precipitate is instantly seen: This is the tanning principle combined with glue. The name tanning principle has been applied to it, because tanning consists in combining this principle with skin, by which they are converted into leather. He observed, in an infusion of galls made with cold water, a sediment, which proved on examination to have a crystalline form and an acid taste. By letting an infusion of galls remain a long time exposed to the air, and removing now and then the mouldy skin which formed on its surface, a large quantity of this sediment was obtained; which being edulcorated with cold water, redissolved in hot water, filtrated and evaporated very slowly, yielded an acid salt in crystals as fine as sand.
There is a shorter method of obtaining this acid in a still purer state than Scheele obtained it.
Pour sulphuric ether on a quantity of powdered galls, and allow it to remain a few hours; by which time it becomes coloured. Put this tincture into a retort, and distil off the ether with a small heat. The residuum possesses the colour and brittleness of a resin, and has all the characters of Rouelle's resinous extract; it does not attract moisture from the atmosphere. Dissolve it in its own weight of water, and add sulphuric acid, drop by drop, till the liquor has become of a manifestly acid taste. It causes a white precipitate, which becomes coloured, and is immediately redissolved. At the end of some hours a resinous matter will have precipitated. Decant off the fluid, dilute it with half its weight of water, filtrate and evaporate it to 1/3 in a moderate heat; add pure barytes till the liquor is no longer capable of decomposing muriat of barytes; then filtrate it again; and on evaporation in a moderate heat small white prismatic crystals of gallic acid are formed on the sides of the vessel.
It appears from the experiments of Deyeux, that the fulbitance extracted from nut-galls by ether does not differ much from the extract by water. Probably, then, the only reason for employing ether is the small heat necessary for evaporating it.
There is still another method of obtaining this acid. Distil nut-galls in a strong heat, a white substance sublimes, which crystallizes in the form of needles: This is gallic acid. If the crystals are impure, they may be purified by a second sublimation: but the heat must not be too violent, otherwise the crystals will melt into a brown mass. This process was discovered by Scheele.
But the most elegant method of obtaining gallic acid is that of Mr Prout. When a solution of muriat of tin is poured into an infusion of nut-galls, a copious yellow precipitate is instantly formed, consisting of the tanning principle, combined with the oxyd of tin. After diluting the liquid with a sufficient quantity of water to separate any portion of this precipitate which the acids might hold in solution, the precipitate is to be separated by filtration. The liquid contains gallic acid, muriatic acid and muriat of tin. To separate the tin, a quantity of sulphurated hydrogen gas is to be mixed with the liquid. Sulphuret of oxyd of tin is precipitated under the form of a brown powder. The liquid is then to be exposed for some days to the light, covered with paper, till the superfluous sulphurated hydrogen gas exhales. After this, it is to be evaporated to the proper degree of concentration, and put by to cool. Crystals of gallic acid are deposited. These are to be separated by filtration, and washed with a little cold water. The evaporation of the rest of the liquid is to be repeated till all the gallic acid is obtained from it.
The gallic acid thus obtained has a very acid taste, and reddens vegetable colours. It is soluble in 14 parts of boiling water, and in 12 parts of water at the temperature of the atmosphere. Alcohol dissolves one-fourth of its weight of this acid at the temperature of the atmosphere. When boiling hot, it dissolves a quantity equal to its own weight.
When placed upon burning coals, gallic acid takes fire, and at the same time diffuses a very strong odour, which has something aromatic in it. When strongly heated, it melts, boils, becomes black, is distipated, and leaves a quantity of charcoal behind it. When distilled, a quantity of oxygen gas is disengaged, an acid liquor is found in the receiver, with some gallic acid not decomposed, and there remains in the retort a quantity of carbon. If what has passed into the receiver be again distilled, more oxygen gas is obtained, some gallic acid still sublimes, and a quantity of carbon remains in the retort. By repeated distillations the whole of the acid may be decomposed. This decomposition may be more easily accomplished by distilling repeatedly a solution of gallic acid in water. The products are oxygen gas, charcoal, and an acid liquor.
From these experiments, Mr Deyeux, who performed them, has concluded, that gallic acid is composed of five oxygen, and a much larger proportion of carbon than enters into the composition of carbonic acid. But this conclusion is not warranted by the analysis; for Mr Deyeux did not find that the quantity of oxygen gas and carbon obtained was equal to that of the gallic acid decomposed: and in the acid liquor which came over, there evidently existed a quantity of water, which doubtless was formed during the distillation. Scheele, by treating gallic acid with nitric acid in the usual manner, converted it into oxalic acid. Now it is certain, that oxalic acid contains hydrogen as well as carbon. It cannot be doubted, then, that gallic acid is composed of oxygen, hydrogen, and carbon, in proportions not yet ascertained. But Mr Deyeux has proved, that the quantity of carbon is very great, compared with that of the hydrogen.
Gallic acid combines with alkalies, earths, and metallic oxyds, and forms compounds, known by the name of gallats.
Its affinities have not yet been determined; but oxyd of iron seems to have a stronger affinity for it than for any other substance; for gallic acid is capable of taking it from every other acid. In consequence of this property, the infusion of galls is employed to detect the presence of iron in any liquid. As soon as it is poured in, if iron be present, a black or purple colour is produced.
Sect. XX. Of Benzoin acid.
Benzoin or benjamin (as it is sometimes called) is a kind of resin brought from the East Indies; obtained, according to Dr Dryander, from the flyrax benzoe, a tree which grows in the island of Sumatra. This substance consists partly of a peculiar acid, described as long ago as 1658 by Blaise de Vigenere, in his Treatise on Fire and Salt, under the name of flowers of benzoin, because it was obtained by sublimation. This acid, which is now called the benzoin acid, may be sublimed from benzoin by heat; or it may be obtained by Scheele's Benzoin acid has little or none of the peculiar odour which distinguishes benzoin. Its taste is not acid, but sweetish and very pungent. It hardly affects the infusion of violets; but it reddens that of turpentine, especially if that infusion be hot. Heat volatilizes this acid, and makes it give out a strong odour, which excites coughing. When exposed to the heat of the blow-pipe in a silver spoon, it melts, becomes as fluid as water, and evaporates without taking fire. It only burns when in contact with flame, and then it leaves no residuum behind. When thrown upon burning coals, it rises in a white smoke. When allowed to cool after being melted, it hardens, and a radiated crust forms on its surface.
It suffers no other alteration in the air than losing the little of the odour of benzoin which remained to it.
Cold water dissolves no sensible quantity of it; but it is soluble enough in hot water: 480 grains of boiling water dissolve 20 grains of it; 19 of these are deposited, when the water cools, in long, slender, flat, feather-like crystals.
Concentrated sulphuric acid dissolves it without heat or any other change, except becoming somewhat brown: when water is poured into the solution, the benzoic acid separates and coagulates on the surface without any alteration. Nitric acid presents precisely the same phenomena, and also the sulphurous and nitrous acids. Neither the muriatic, the oxy-muriatic, nor the phosphoric acids dissolve it. The acetous, formic, and fumaric acids, when hot, dissolve it precisely as water does; but it crystallizes again when these acids cool.
Alcohol dissolves it copiously, and lets it fall on the addition of water.
Little is known respecting its base.
It combines with alkalies, earths, and metallic oxides, and forms salts, known by the name of benzoinates.
Its affinities, from the experiments of Trommelfor, appear to be as follows:
- White oxide of arsenic, - Potash, - Soda, - Ammonia, - Barytes, - Lime, - Magnesia, - Alumina, - Jargonia, - Water, - Alcohol,
Sect. XXI. Of Succinic Acid.
Amber is a well-known brown, transparent, inflammable body, pretty hard, and susceptible of polish, found at some depth in the earth, and on the sea-coast of several countries. It was in high estimation among the ancients both as an ornament and a medicine. When this substance is distilled, a volatile salt is obtained, which is mentioned by Agricola under the name of salt of amber; but its nature was long unknown. Boyle was the first who discovered that it was an acid. From succinum, the Latin name of amber, this acid has received the appellation of succinic acid.
Suppl. Vol. I. Part I.
It is obtained by the following process: Fill a retort half way with powdered amber, and cover the powder with a quantity of dry sand; place on a receiver, and distill in a sand-bath without employing too much heat. There passes over first an insipid phlegm; then obtaining a weak acid, which, according to Scheele, is the acetic acid; then the succinic acid attaches itself to the neck of the retort; and if the distillation be continued, there comes over at last a thick brown oil, which has an acid taste.
The succinic acid is at first mixed with a quantity of oil. Perhaps the best method of purifying it is that recommended by Pott, to dissolve it in hot water, and to put upon the filter a little cotton, previously moistened with oil of amber; this substance retains most of the oil, and allows the solution to pass clear. The acid is then to be crystallized by a gentle evaporation. And this process is to be repeated till the acid is quite pure. The crystals are white, shining, and of a foliated triangular prismatic form; they have an acid taste, but are not corrosive; they redden tincture of turpentine, but have little effect on that of violets.
They sublime when exposed to a considerable heat, but not at the heat of a water-bath. In a sand bath they melt, and then sublime and condense in the upper part of the vessel; but the coal which remains shows that they are partly decomposed.
One part of this acid dissolves in 96 parts of water at the temperature of 50°, according to Spiegelman; in 24 parts at the temperature of 52°, and in 2 parts of water at the temperature of 212°, according to Stockar de Neuforn; but the greatest part crystallizes as the water cools. According to Roux, however, it still retains more of the acid than cold water is capable of dissolving.
240 grains of boiling alcohol dissolve 177 of this acid; but crystals again shoot as the solution cools.
The combinations of this acid are called succinates. Its component parts are still unknown.
Its affinities, according to Morveau, are as follows:
- Barytes, - Lime, - Potash, - Soda, - Ammonia, - Magnesia, - Alumina, - Jargonia, - Metallic oxides, as in sulphuric acid, - Water, - Alcohol.
Sect. XXII. Of Camphoric Acid.
Camphor is a well-known white crystalline substance, of a strong taste and smell, obtained from a species of laurel in the East Indies; and Mr. Proust has shown that several volatile oils contain a considerable quantity of it. It is so volatile, that it cannot be melted in open vessels, and so inflammable, that it burns even on the surface of water.
When camphor is set on fire in contact with oxygen gas, it burns with a very brilliant flame; much caloric is disengaged; water is formed, the inner surface of the vessel is covered with a black matter, which is undoubtedly carbon; and a quantity of carbonic acid gas is also produced. Camphoric Acid.
Hence it follows, that it is composed of hydrogen and carbon, at least principally.
If one part of camphor and six parts of pulverized clay be mixed together, by means of alcohol, in a mortar, the mixture made up into balls, and when dry put into a retort, and distilled by a moderate heat—a quantity of oil comes over, and there remains in the retort a black substance, which consists of the clay intimately mixed with a quantity of carbon. If the fire be not cautiously managed, a quantity of camphor also sublimes. By this process, camphor is decomposed, and separated into oil and carbon.
122,284 parts of camphor produced 45,856 parts of oil and 30,571 of carbon.
Total 76,427
Lots 45,821
Carbonated hydrogen gas and carbonic acid were also formed.
The oil obtained has the following properties:
It has a sharp caustic taste, and leaves upon the tongue a sense of coldness. It has an aromatic odour, approaching to that of thyme or rosemary. Its colour is a golden yellow.
When exposed to the air, it partly evaporates, and there remains a thick brown matter with a sharp bitterish taste, which at last also evaporates.
With alkalies, it forms a soap, which possesses all the characters of soaps made with volatile oils.
Alcohol dissolves it entirely; and when water is added to the solution it becomes milky, but no precipitate is produced.
These properties show that this is a volatile oil, and consequently it is probable that camphor is composed of volatile oil and carbon.
Mr Kofegarten, by distilling nitric acid off camphor eight times successively, obtained an acid in crystals*, to which the name of camphoric acid has been given.
His experiments have been repeated by Mr Bouillon La Grange. He mixed together 122,284 parts of camphor with 489,136 parts of nitric acid of the specific gravity 1.33, and distilled them. Much nitrous and carbonic acid gas were disengaged, and part of the camphor was sublimed; but part was converted into an acid. He returned the sublimed camphor into the retort, poured on it the same quantity of nitric acid as at first, and distilled again. This process he repeated till the whole camphor was acidified†. The quantity of camphoric acid obtained amounted to 53,498. The quantity of nitric acid was 2114,538.
Camphoric acid thus obtained is in snow-white crystals, of the form of parallelopipeds*.
These crystals effloresce in the air†.
Camphoric acid has a slightly acid bitter taste, and a smell like that of saffron.
It reddens vegetable colours.
It is soluble in 200 parts of cold water, according to Kofegarten; in 96 parts of water at the temperature of 60°, according to La Grange. Boiling water dissolves ¼ th of its weight §.
According to Kofegarten, it is insoluble in alcohol; according to La Grange, alcohol dissolves it, and when the solution is left in contact with the air of the atmosphere, the acid crystallizes. It is not precipitated from its solution in alcohol by the addition of water*.
When this acid is placed on ignited coals, it emits a dense aromatic fume, and is entirely dissipated. By a gentler heat, it melts, and is sublimed. If it be put into a heated porcelain tube, and oxygen gas be passed through it, the acid does not undergo any change, but is sublimed.
By mere distillation, it first melts and then sublimes; by which process its properties are in some respect changed. It no longer reddens the tincture of turpentine, but acquires a brisk aromatic smell; its taste becomes less penetrating, and it is no longer soluble either in water or the sulphuric and muriatic acids. Heated nitric acid turns it yellow and dissolves it. Alcohol likewise dissolves it; and if this solution be left in contact with the air of the atmosphere, it crystallizes.
Camphoric acid does not produce any change in sulphur; alcohol and the mineral acids totally dissolve it; and so likewise do the volatile and the fat oils.
Camphoric acid does not precipitate lime from lime-water. It produces no change on the solution of indigo in sulphuric acid.
It forms combinations with the alkalies, earths, and metallic oxides, which are called camphorates.
Its affinities, as far as ascertained by La Grange, are as follows*.
Lime, Potash, Soda, Barytes, Ammonia, Alumina, Magnesia,
Sect. XXIII. Of Suberic Acid.
Cork, a substance too well known to require any description, is the bark of a tree which bears the same of its name. By means of nitric acid, Brugnatelli converted it into an acid†, which has been called the suberic acid‡, from Suber, the Latin name of the cork tree. Several chemists affirmed that this acid was the oxalic, because it possessed several properties in common with it. These affections induced Bouillon La Grange to undertake a set of experiments on suberic acid. These experiments, which have been published in the 23rd volume of the Annales de Chimie, completely establish the peculiar nature of suberic acid, by showing that it possesses properties different from those of every other acid.
To prepare it, a quantity of found cork grated down small is to be put into a retort, five times its weight of pure nitric acid of the specific gravity 1.261 poured upon it, and the mixture distilled by means of a gentle heat. Red vapours are immediately discharged; the cork swells up and becomes yellow, and as the distillation advances, it sinks to the bottom, and its surface remains frothy. If that froth does not form properly, it is a proof that some part of the cork has escaped the action of the acid. In that case, after the distillation is pretty far advanced, the acid which has passed into the receiver is to be poured back into the retort, and the distillation continued till no more red vapours can be perceived; and then the retort is to be immediately taken out of the sand-bath, otherwise its contents would become black and adhere to it. While the matter contained in the retort is hot, it is to be poured into a glass vessel, placed upon a sand-bath, over a gentle fire, and constantly stirred with a glass rod. By this means it becomes gradually gradually thick. As soon as white vapours, exciting a tickling in the throat, begin to disengage themselves, the vessel is removed from the bath, and the mass continuously stirred till it is almost cold.
By this means an orange-coloured mass is obtained of the consistence of honey, of a strong and sharp odour while hot, but having a peculiar aromatic smell when cold.
On this mass twice its weight of boiling water is to be poured, and heat applied till it becomes liquid; and then that part of it which is insoluble in water is to be separated by filtration (n). The filtered liquor becomes muddy; on cooling it deposits a powdery sediment, and a thin pellicle forms on its surface. The sediment is to be separated by filtration, and the liquor reduced to a dry mass by evaporating in a gentle heat. This mass is suberic acid. It is still a little coloured, owing to some accidental mixture, from which it may be purified either by saturating it with potash and precipitating it by means of an acid, or by boiling it along with charcoal powder.
Suberic acid thus obtained is not crystallizable, but when precipitated from potash by an acid it assumes the form of a powder; when obtained by evaporation it forms thin irregular pellets.
Its taste is acid and slightly bitter; and when dissolved in a small quantity of boiling water it acts upon the throat, and excites coughing.
It reddens vegetable blues; and when dropped into a solution of indigo in sulphuric acid (liquid blue, as it is called in this country), it changes the colour of the solution, and renders it green.
Water at the temperature of 60° or even 70° dissolves only $\frac{1}{57}$th part of its weight of suberic acid, and if the acid be very pure, only $\frac{1}{42}$th part: boiling water, on the contrary, dissolves half its weight of it.
When exposed to the air, it attracts moisture, especially if it be impure.
When exposed to the light of day, it becomes at last brown; and this effect is produced much sooner by the direct rays of the sun.
When heated in a matras, the acid sublimes, and the inside of the glass is surrounded with zones of different colours. If the sublimation be stopped at the proper 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 blow-pipe on a spoon of platinum, it first melts, then becomes pulverulent, and at last sublimes entirely with a smell resembling that of sebacic acid (o).
It is not altered by oxygen gas;—the other acids do not dissolve it completely. Alcohol develops an aromatic odour, and an ether may be obtained by means of this acid.
It converts the blue colour of nitrate of copper to a green; the sulphate of copper also to a green; green sulphate of iron to a deep yellow; and sulphate of zinc to a golden yellow (r).
It has no action either on platinum, gold, or nickel; its action but it oxidizes silver, mercury, copper, lead, tin, iron, or other bismuth, arsenic, cobalt, zinc, antimony, manganese, and bodies molybdenum.
With alkalies, earths, and metallic oxyds, it forms compounds known by the name of suberats.
Its affinities are as follows (q):
| Potass. | Soda. | |---------|-------| | Sulphuric acid, Nitric, Muriatic, Suberic. |
| Alumina. | |----------| | Sulphuric acid. Oxalic, Suberic. |
| Oxyd of Tin. | |--------------| | Muriatic, Suberic. |
| Oxyd of Mercury. | |------------------| | Sebacic acid, Nitric, Suberic. |
| Barytes. | |----------| | Sulphuric acid, Oxalic, Muriatic, Suberic. |
| Lime. | |-------| | Oxalic acid, Sulphuric, Muriatic, Suberic. |
| Oxyd of Silver. | |-----------------| | Muriatic, Sulphuric, Suberic. |
| Oxyd of Molybdenum. | |---------------------| | Suberic acid. |
| Oxyd of Antimony. | |--------------------| | Muriatic, Suberic, Manganese the same. |
(s) When this substance is put into a matras, water poured on it, and heat applied, it melts; and when the vessel is taken from the fire and allowed to cool, one part of it, which is of the consistence of wax, swims on the surface of the water, and another part precipitates to the bottom of the vessel, and assumes the appearance of a whitish magma. When this magma is separated by filtration, and washed and dried, a white talc-like powder is obtained, mixed with lignous threads, soluble in acids and alkalies.
(o) An acid which shall be afterwards described.
(r) Owing perhaps to the presence of a little iron in the sulphate.
(q) The place which the suberic acid occupies in the affinities of the alkalies, earths, and metallic oxyds, as far as this subject has been investigated by Bouillon La Grange, will appear by the following tables:
| Potass. | Soda. | |---------|-------| | Sulphuric acid, Nitric, Muriatic, Suberic. |
| Alumina. | |----------| | Sulphuric acid. Oxalic, Suberic. |
| Oxyd of Tin. | |--------------| | Muriatic, Suberic. |
| Oxyd of Mercury. | |------------------| | Sebacic acid, Nitric, Suberic. |
| Barytes. | |----------| | Sulphuric acid, Oxalic, Muriatic, Suberic. |
| Lime. | |-------| | Oxalic acid, Sulphuric, Muriatic, Suberic. |
| Oxyd of Silver. | |-----------------| | Muriatic, Sulphuric, Suberic. |
| Oxyd of Molybdenum. | |---------------------| | Suberic acid. |
| Oxyd of Antimony. | |--------------------| | Muriatic, Suberic, Manganese the same. |
| Oxyd of Copper. | |-----------------| | Sulphuric, Suberic. | Mr Buillon La Grange, to whom we are indebted for all the facts relative to this acid, supposes that it is composed of oxygen, hydrogen, and carbon; but Mr Jameson, in consequence of the result of a series of experiments which he made on charcoal, has been led to suspect that it consists entirely of carbon and oxygen. He found that, by the action of nitric acid upon charcoal, a brown, bitter, deliquescent mass was formed, soluble in water, alcohol, and alkalies, and which emitted, particularly when heated, a very fragrant odour. This matter was more or less soluble in water according to the time that it had been exposed to the action of the acid. When the nitric acid used was concentrated, and considerable in quantity, part of the charcoal was converted into an acid, which possessed the characters of the suberic acid.
These facts are curious, and may extend our knowledge of the nature of vegetable acids, but they are insufficient to prove the absence of hydrogen in suberic acid, because charcoal cannot easily be procured perfectly free from hydrogen, and because several of the properties of suberic acid indicate the presence of hydrogen in it, its becoming brown, for instance, when exposed to the light. Mr Jameson has observed, that the acid which exists ready formed in peat possesses the properties of suberic acid.
**Sect. XXIV. Of Lactic Acid.**
About the year 1786, Dr Anderson of Madras mentioned, in a letter to the governor and council of that place, that nests of insects, resembling small earthy shells, had been brought to him from the woods by the natives, who eat them with avidity. These supposed nests he soon afterwards discovered to be the coverings of the females of an undescribed species of coccus, which he shortly found means to propagate with great facility on several of the trees and shrubs growing in his neighbourhood (r).
On examining this substance, which he called white lac, he observed in it a very considerable resemblance to bees wax; he noticed also, 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; and in one of his letters he complains, that the children whom he employed to gather it were tempted by its sweetness to eat so much of it as materially to reduce the produce of his crop. Small quantities of this matter were sent into Europe in 1789, both in its natural state and melted into cakes; and in 1793 Dr Pearson, at the request of Sir Joseph Banks, undertook a chemical examination of its qualities, and his experiments were published in the Philosophical Transactions for 1794.
A piece of white lac, from 3 to 15 grains in weight, is probably produced by each insect. These pieces are of a grey colour, opaque, rough, and roundish. When white lac was purified by being strained through muslin, it was of a brown colour, brittle, hard, and had a bitterish taste. It melted in alcohol, and in water of the temperature of 145°. In many of its properties it resembles bees wax, though it differs in others; and Dr Pearson supposes that both substances are composed of the same ingredients, but in different proportions.
Two thousand grains of white lac were exposed in such a degree of heat as was just sufficient to melt them. As they grew soft and fluid, there oozed out 550 grains of a reddish watery liquid, which smelled like newly baked bread (s). To this liquid, Dr Pearson has given the name of lactic acid (t).
It possesses the following properties:
- It turns paper stained with turpentine to a red colour. - After being filtered, it has a slightly fetid taste with a bitterness, but is not at all sour. - When heated, it smells precisely like newly baked hot bread.
On standing, it grows somewhat turbid, and deposits a small quantity of sediment.
Its specific gravity at the temperature of 60° is 1.025.
A little of it having been evaporated till it grew very turbid, afforded on standing small needle-shaped crystals in mucilaginous matter.
Two hundred and fifty grains of it were poured into a very small retort and distilled. As the liquor grew warm, mucilage-like clouds appeared; but as the heat increased they disappeared again. At the temperature of 200°, the liquor distilled over very fast: A small quantity of extractive matter remained behind. The distilled liquor while hot smelled like newly baked bread, and was perfectly transparent and yellowish. A shred of paper stained with turpentine, which had been put into the receiver, was not reddened; nor did another which had been immersed in a solution of sulphate of iron, and also placed in the receiver, turn to a blue colour upon being moistened with the solution of potash (r).
---
(r) The Chinese collect a kind of wax, which they call pe-la, from a coccus, deposited for the purpose of breeding on several shrubs, and manage it exactly as the Mexicans manage the cochineal insect. It was the knowledge of this that induced Dr Anderson to attempt to propagate his insect.
(s) The same liquid appears on pressing the crude lac between the fingers; and we are told, that when newly gathered it is replete with juice.
(t) A proof that the acid was not the prussic. About one hundred grains of this distilled liquid being evaporated till it grew turbid, after being set by for a night, afforded acicular crystals, which under a lens appeared in a group not unlike the umbel of parsley. The whole of them did not amount to the quarter of a grain. They tasted only bitterish.
Another 100 grains being evaporated to dryness in a very low temperature, a blackish matter was left behind, which did not entirely disappear on heating the spoon containing it very hot in the naked fire; but on heating oxalic acid to a much less degree, it evaporated and left not a trace behind.
Carbonat of lime distilled in this distilled liquid with effervescence. The solution tasted bitterish, did not turn paper stained with turpentine red, and on adding to it carbonat of potas a copious precipitation ensued. A little of this solution of lime and of alkali being evaporated to dryness, and the residuum made red hot, nothing remained but carbonat of lime and carbonat of potas.
This liquid did not render nitrat of lime turbid, but it produced turbidness in nitrat and marit of barites.
To five hundred grains of the reddish-coloured liquor obtained by melting white lac, carbonat of soda was added till the effervescence ceased, and the mixture was neutralised; for which purpose three grains of the carbonat were necessary. During this combination a quantity of mucilaginous matter, with a little carbonat of lime, was precipitated. The saturated solution being filtrated and evaporated to the due degree, afforded on standing deliquescent crystals, which on exposure to fire left only a residuum of carbonat of soda.
Lime-water being added to this reddish-coloured liquor produced a light purple turbid appearance; and on standing there were clouds just perceptible.
Sulphuret of lime occasioned a white precipitation, but no sulphurated hydrogen gas was perceptible by the smell.
Tincture of galls produced a green precipitation.
Sulphat of iron produced a purplish colour, but no precipitation; nor was any precipitate formed by the addition first of a little vinegar, and then of a little potas, to the mixture.
Acetite of lead occasioned a reddish precipitation, which redissolved on adding a little nitric acid.
Nitrat of mercury produced a whitish turbid liquor.
Oxalic acid produced immediately the precipitation of white acicular crystals, owing probably to the presence of a little lime in the liquid.
Tartrite of potas produced a precipitation not unlike what takes place on adding tartarous acid to tartrite of potas (v); but it did not dissolve again on adding potas.
Such were the properties of this acid discovered by Dr Pearson. Its destructibility by fire, and its affording carbon, distinguish it from all the acids described in this article before the acetous; and its peculiar smell when heated, its precipitating tartrite of potas without forming tartar, its bitterish taste, and its being converted into vapour at the temperature of 200°, distinguish it from all the acids hitherto examined.
**Sect. XXV. Of Pyromucous Acid.**
Pyromucous (v) acid is procured by distilling sugar or any of the fruit juices. As they foam very much, the retort should be large, and seven eighths of it empty obtaining a prodigious quantity of carbuncle acid and carbonated pyromucous acid. Hydrogen gas is disengaged; a very thin light coal remains behind in the retort. Morveau found the glass of the retort attacked. The quantity of sugar distilled was 2304 grains; the coal weighed 982 grains. There were 428 grains of a brown liquor in the receiver, consisting mostly of an acid phlegm. This redistilled gave 313 grains of a liquor almost limpid, the specific gravity of which was 1.0155 at the temperature of 77°. It reddened blue paper. This acid may be concentrated by freezing, or by combining it with some base, potas, for instance, and decomposing the compound by a stronger acid, as, for example, the sulphuric.
It has a very sharp taste. When exploded to heat in proper open vessels, it evaporates, leaving a brown spot. Difficult, filled in close vessels, it leaves charcoal behind it.
It does not dissolve gold as Schreickel and Lemery and several other chemists affirmed.
It does not attack silver nor mercury, nor even their oxyds. It corrodes lead, and forms hydric and long crystals. Copper forms with it a green solution; With iron it forms green crystals; with antimony and zinc greenish solutions.
The compounds which it forms are called pyromucites. Its affinities, according to Morveau, are as follows:
- Potas, - Soda, - Barites, - Lime, - Magnesia, - Ammonia, - Alumina, - Jargonite, - Metallic oxyds as in sulph. acid, - Water, - Alcohol.
**Sect. XXVI. Of Pyro-lignous Acid.**
It is well known that the smoke of burning wood is exceedingly offensive to the eyes: And chemists have obtained long ago observed, that an acid might be obtained by pyro-lignous acid.
It is to Mr Goettling, however, and to the Dijon academicians, who repeated his experiment, that we are indebted for what knowledge we possess of the peculiar properties of this acid, which, because it is obtained from wood by means of fire, has been called the pyro-lignous acid (w). It appears to be the same from whatever kind of wood it is obtained.
Mr Goettling filled an iron retort with pieces of birch tree bark, and obtained by distillation a thick, brown, very empyreumatic acid liquor. This liquor he allowed
(v) On this addition, tartar, or acidulated tartrite of potas, is formed, which precipitates, because it is very little soluble in water. The addition of potas dissolves it again.
(v) Morveau called this acid syrupous acid.
(w) Goettling called it ligneous acid. allowed to remain at rest for three months, and then separated from it a quantity of oil which had risen to the top. By distilling this liquor again, and then saturating it with potash, and evaporating to dryness, he obtained a brown saline mass; which, by being redissolved in water, and evaporated, yielded greyish white crystals: These crystals were composed of pyro-lignous acid and potash. He poured upon them, by little and little, a quantity of sulphuric acid; and by applying a gentle heat, the pyro-lignous acid came over in considerable purity.
The Dijon academicians obtained this acid from beech wood: by distilling 55 ounces, they procured 17 ounces of acid; which, when rectified by a second distillation, was of the specific gravity 1.02083.
It reddens vegetable colours: when exposed to a strong heat, it takes fire, and is destroyed. It unites very well with alcohol.
Its compounds are called pyro-lignites.
Its affinities, as fixed by Mr Eloy Bourfier de Clervaux and Mr de Morveau, are as follows:
- Lime, - Barytes, - Potash, - Soda, - Magnesia, - Ammonia, - Oxide of zinc, - Manganese, - Iron, - Lead, - Tin, - Cobalt, - Copper, - Nickel, - Arsenic, - Bismuth, - Mercury, - Antimony, - Silver, - Gold, - Platinum, - Aluminium, - Jargonite.
Sect. XXVII. Of Pyro-tartarous Acid.
An acid may also be obtained by distilling tartar; it is called pyro-tartarous acid.
It has an empyreumatic taste and odour; reddens the pyro-tartaric tincture of turpentine; but has no effect on that of violets.
Little is known concerning this acid, except that many of its properties are the same with those of the pyro-lignous; and Morveau conjectures, that, if properly purified, it would probably be discovered to be the same with it.
The compounds which it forms are called pyro-tartarites.
Its affinities are unknown. Morveau supposes that they are the same with those of the pyro-lignous acid.
The 18 preceding acids are all (except the lactic and saccharic) denominated vegetable acids, because they are obtained from vegetable substances. We have placed the lactic and saccharic acids in the same class; because they bear a strong resemblance to vegetable acids, and because they are evidently composed of the same ingredients with them.
Vegetable acids are distinguished from all the acids described in the beginning of this chapter, by their de-structibility by fire.
There is no circumstance in chemistry which has attracted greater attention than the possibility of converting the various vegetable acids into each other by means of different processes. To explain what passes during these processes, it would be necessary to know exactly the component parts of every vegetable acid, the manner in which these acids are combined, and the affinities which exist between each of their ingredients. This, however, is very far from being the case at present. Though a vast number of experiments have been made on purpose to throw light on this very point, the difficulties which were to be encountered have been so great, that no accurate results have yet been obtained.
It follows from these experiments, that all the vegetable acids are composed chiefly, at least, of oxygen, hydrogen, and carbon; but that the proportions differ in every individual acid. We say chiefly, because it has been suspected from some phenomena, that one or two of these acids contain besides a little azot. Let us take a view of what is at present known of the composition of these acids in their order.
1. As to carbonic acid, its composition has been ascertained with tolerable accuracy; it consists of about 28 parts of carbon and 72 of oxygen.
2. By distilling 7680 grains of acetite of potash, Dr Higgins obtained the following products:
- Potash, 3862.994 grains. - Carbonic acid gas, 1473.564. - Carbonated hydrogen gas, 1047.6018. - Refluxum consisting of carbon, 78.0000. - Oil, 180.0000. - Water, 340.0000. - Deficiency (x), 726.9102.
This deficiency Dr Higgins found to be owing to a quantity of water and oil which is carried off by the elastic fluids, and afterwards deposited by them. He calculated it, in the present case, at 700 grams of water and 26,9402 grams of oil. Now, since acetite of potash is composed of acetic acid and potash, and since the whole of the potash remained unaltered, it follows, that the acetic acid was converted into carbonic acid gas, carbonated hydrogen gas, carbon, oil, and water; all of which are composed of oxygen, hydrogen, and carbon.
Now 1473.564 gr. of carbonic acid gas are composed of 1060.966 gr. of oxygen, and 415.598 gr. of carbon.
1047.6018 grams of carbonated hydrogen gas, from a comparison of the experiments of Dr Higgins and Lavoisier, may be supposed to consist of about 714.6008 grams of carbon, and 333.0010 of hydrogen.
200,9402 grams of oil contain 163,4828 grams of carbon and 43,4574 grams of hydrogen.
1040 grams of water contain 884 grams of oxygen and 156 grams of hydrogen.
Therefore
(x) For 29.1 grams of oxygen gas had also disappeared from the air of the vessels. Therefore 3817,006 grains of acetic acid are composed of 1944,966 - 29,1 = 1915,866 grains of oxygen, 532,458.4 grains of hydrogen, and 1368,6816 grains of carbon. Consequently 100 parts of acetic acid are composed of
\[ \begin{align*} &50.19 \text{ oxygen}, \\ &13.94 \text{ hydrogen}, \\ &35.87 \text{ carbon}. \end{align*} \]
These numbers can only be considered as approximations to the truth; for the object of Dr Higgins was not to ascertain the proportions of the ingredients which compose acetic acid; and therefore his experiments were not conducted with that rigid accuracy which would have been necessary for that purpose.
It is extremely probable, that during the acetic fermentation, or the conversion of alcohol into acetic acid, a quantity of water is formed; and it is certain that oxygen is absorbed. It follows from this, that acetic acid contains more carbon and less hydrogen than alcohol. Now we have reason, from Lavoisier's experiments, to believe, that alcohol is formed of
\[ \begin{align*} &51.72 \text{ oxygen}, \\ &18.40 \text{ hydrogen}, \\ &29.88 \text{ carbon}. \end{align*} \]
Lavoisier supposes that this acid contains also azot.
3. Acetic acid is supposed to consist of the same base with acetic acid, combined with a larger proportion of oxygen; we would rather say, that it is acetic acid combined with oxygen.
4. When oxalic acid is distilled with six times its weight of sulphuric acid, the products are acetic acid, sulphurous acid, carbonic acid gas, and sulphuric acid remains in the retort. Hence it follows, that oxalic acid contains more carbon than acetic acid; but that it is composed of the same ingredients. It has been supposed, that oxalic acid is composed of sugar and oxygen. Now sugar, according to Lavoisier, is composed of
\[ \begin{align*} &\text{Hydrogen} & &8 \\ &\text{Oxygen} & &64 \\ &\text{Carbon} & &28 \end{align*} \]
These proportions are rather unfavourable to that notion; at least if any dependence can be put in the composition of acetic acid as deduced from the experiments of Dr Higgins.
5. Hermann dissolved four ounces of tartaric acid in 16 ounces of water, and kept the solution in a vessel covered with paper in a warm place. In three months the taste of the solution was changed, and the air in the upper part of the vessel was found to be carbonic acid. In six months the solution was converted into acetic acid. It follows from this experiment, that tartaric acid contains more carbon than acetic acid, and that their ingredients are the same. If any doubts should remain, the following experiment is sufficient to remove them. Weilnau mixed strong sulphuric acid with tartaric acid, and added manganese; acetic acid was produced, and a great quantity of carbonic acid gas was disengaged. When nitric acid is distilled off tartaric acid, it is converted into oxalic acid, as Scheele first proved. Hence it has been supposed by some, that oxalic acid differs from tartaric merely in containing more oxygen; but this is very far indeed from being proved. According to Hassenfratz, tartaric acid contains a considerable quantity of azot.
6. When citric acid is allowed to remain in a bottle slightly corked along with a little alcohol, the citric acid is gradually converted into acetic acid. Weilnau converted it into oxalic acid by means of nitric acid.
7. Malic acid was converted into oxalic by means of nitric acid by Scheele. It has been supposed to contain more oxygen than oxalic acid. Some of it is always formed during the common process of converting sugar into oxalic acid. Were we to judge from an experiment, which, however, was not performed with sufficient accuracy, we would conclude that the base of malic acid is gum; for by distilling two parts of weak nitric acid off one part of gum in a very small heat, we obtained a quantity of acid more in weight than the gum, which exhibited several of the distinguishing properties of malic acid. It was exceedingly light, white, and spongy, and attracted water very quickly from the atmosphere, and could not afterwards be brought by evaporation to its former state.
8. Scheele converted lactic acid into acetic by mere exposure to the atmosphere, and found that a quantity of carbonic acid was disengaged. Hence this acid is merely the acetic with a smaller proportion of carbon.
9. The gallic acid, we have seen, contains more carbon than any of the others.
10. Nothing is known concerning the composition of the benzoic and succinic acids. Hermann says he converted benzoic acid to oxalic by means of nitric acid; but Morveau did not observe that any change was produced.
11. The base of camphoric is probably camphor.
Though these eighteen are the only acids which have hitherto been examined with attention, it cannot be doubted that the number of vegetable acids, either existing naturally, or at least capable of being formed by art, is considerably greater. Morveau has lately ascertained, that the red colours of flowers are owing to acids: This had already been conjectured by Linnæus.
Sect. XXVIII. Of Prussian Acid.
About the beginning of the present century, Dieffenbach, a chemist of Berlin, wishing to precipitate a solution of cochineal mixed with a little alum and sulphate of iron, borrowed from Dippel some potash, from which that chemist had distilled several times his animal oil. On pouring in the potash, Dieffenbach was surprised to see, instead of the red precipitate which he had expected, a beautiful blue powder falling to the bottom of the vessel. By reflecting on the materials which he had employed, he easily discovered the method of procuring the blue powder at pleasure. This powder was called Prussian blue, from the place where it was discovered. It was announced in the Berlin Memoirs for 1710; but the process was concealed, because it had become a lucrative article of commerce. A method of preparing it, however, was published by Woodward in the Philosophical Transactions for 1724, which he said he had got from one of his friends in Germany. This method was as follows: Detonate together 4 ounces of nitre and as much tartar, in order to procure an extemporaneous alkali; then add 4 ounces of dried bullock's blood, mix the the ingredients well together, and put them into a crucible covered with a lid, in which there is a small hole; calcine with a moderate fire till the blood emits no more smoke or flame capable of blackening any white body exposed to it; increase the fire towards the end, so that the whole matter contained in the crucible shall be moderately but feebly red. In this state throw it into two pints of water, and boil it for half an hour. Decant off this water, and continue to pour on more till it come off insipid. Add all these liquids together, and boil them down to two pints. Dissolve two ounces of sulphate of iron and eight ounces of alum in two pints of boiling water; mix this with the former liquor while both are hot. An effervescence takes place, and a powder is precipitated of a green colour mixed with blue. Separate this precipitate by filtration, and pour muriatic acid upon it till it becomes of a beautiful blue; then wash it with water and dry it.
Different explanations were given of the nature of this precipitate by different chemists. All of them acknowledged that it contained iron, but to account for the colour was the difficult point. Brown, and Geoffroy, and Neumann, discovered in succession, that a great many other animal substances besides blood communicated to alkali the property of forming Prussian blue. Macquer undertook an examination of this substance, and published the result of his experiments in the Memoirs of the French Academy for 1752.
He observed, that when alkali is added to a solution of iron in any acid, the iron is precipitated of a yellow colour, and soluble in acids; but if iron be precipitated from an acid by an alkali prepared as above described, by calcination with blood (which has been called a Prussian alkali), it is of a green colour. Acids dissolve only a part of this precipitate, and leave behind an insoluble powder which is of an intense blue colour. The green precipitate therefore is composed of two different substances, one of which is Prussian blue; the other, as he ascertained by experiment, is the brown or yellow oxyd of iron; and the green colour is owing to the mixture of the blue and yellow substances. When heat is applied to the insoluble precipitate, its blue colour is destroyed, and it becomes exactly similar to common oxyd of iron. It is composed therefore of iron and some other substance, which heat has the property of driving off. If this insoluble precipitate be boiled with a very pure alkali, it loses its blue colour also, and at the same time the alkali acquires the property of precipitating of a blue colour solutions of iron in acids, or it has become precisely the same with the Prussian alkali. Prussian blue, therefore, is composed of iron and something which a pure alkali can separate from it, something which has a greater affinity for alkali than for iron. By boiling a quantity of alkali with Prussian blue, it may be completely saturated with this something, which we shall call colouring matter, and then it has lost all its alkaline properties. No acid can separate this colouring matter from iron after it is once united with it. When iron dissolved in an acid is mixed with an alkali saturated with the colouring matter, a double decomposition takes place, the acid unites with the alkali, and the colouring matter with the iron, and forms Prussian blue. The reason that, in the common method of preparing Prussian blue, a quantity of yellow oxyd is precipitated, is, that there is not a sufficient quantity of colouring matter (for the alkali is never saturated with it) to saturate all the iron displaced by the alkali; a part of it therefore is mixed with Prussian blue. Muriatic acid dissolves this oxyd, carries it off, and leaves the blue in a state of purity. Such were the conclusions which Macquer drew from his experiments; experiments which not only discovered the composition of Prussian blue, but threw a ray of light on the nature of affinities, which has contributed much towards the advancement of that important branch of chemistry.
The nature of the colouring matter, however, was still unknown. Macquer himself supposed, that it was pure phlogiston; but the opinion was untenable. He had shewn that it possessed the property of forming neutral salts, and therefore Bergman and Morveau suspected that it was an acid.
Scheele undertook the task of examining its nature, and published the result of his experiments in the Stockholm Transactions for 1782.
He observed, that the Prussian alkali, after being exposed for some time to the air, lost the property of forming Prussian blue; the colouring matter must therefore have left it.
He put a small quantity of it into a large glass globe, corked it up, and kept it some time; but no change by was produced either in the air or the Prussian alkali. Something must therefore displace the colouring matter when the alkali is exposed to the open air, which is not present in a glass vessel. Was it carbonic acid gas? To ascertain this, he put a quantity of Prussian alkali into a glass globe filled with that gas, and in 24 hours the alkali was incapable of producing Prussian blue. It is therefore carbonic acid gas which displaces the colouring matter. He repeated this experiment with this difference, that he hung in the globe a bit of paper which had been previously dipped into a solution of sulphate of iron, and on which he had let fall two drops of an alkaline lixivium, in order to precipitate the iron. This paper was taken out in two hours, and became covered with a fine blue on adding a little muriatic acid. Carbonic acid, then, has the property of separating the colouring matter from alkali without decomposing it.
He found also that other acids produced the same effect. The colouring matter then may be obtained per ingemnhaps in a separate state. He accordingly made a number of attempts to procure it, and at last discovered the following process: He boiled together for some minutes two ounces of Prussian blue in powder, one ounce of the red oxyd of mercury, and six ounces of water; then palled the whole through a filter, and washed the residue with two ounces of boiling water. The oxyd of mercury has a greater affinity for the colouring matter than the oxyd of iron; it therefore unites with it, and forms with it a salt soluble in water. The iron remains behind upon the filter, and the liquid is a solution of the colouring matter combined with mercury. He poured this solution upon half an ounce of pure iron-filings, and added at the same time three grains of sulphuric acid. The iron separates the oxygen from the mercury, in order to combine with the sulphuric acid; the mercury is precipitated in its metallic state, and leaves behind it a quantity of sulphate of iron and of colouring matter dissolved in water, but not combined, as the colouring matter is unable to separate the iron from the acid.
He then distilled in a gentle heat; the colouring mat- The colouring matter, then, which we shall henceforth call the Prussian acid, is composed of azot, hydrogen, and carbon; but the proportions of these ingredients have not yet been determined. It is considered as an acid, though the presence of oxygen has not been proved, because it has the property of forming neutral salts with the same bases as other acids.
The Prussian acid is exceedingly volatile, and evidently capable of existing in a gaseous state. It has a peculiar odour, not disagreeable, and which has been compared to the flowers of the peach. It has a sweetish and somewhat hot taste, and excites cough.
It has no affinity for alumina nor for alcohol.
This substance differs exceedingly in its action from all other acids.
It is capable of combining, like them, with earths, alkalies, and metallic oxyds, and of forming compounds which have been denominated Prussiates. But it enters much more readily into triple compounds with alkalies or earths, and metallic oxyds, than into combinations with earths or alkalies separately; and though its affinity appears to be greater for alkalies and earths than for metallic oxyds, yet when in a free or gaseous state it does not enter into combinations with earths or alkalies without difficulty, and it is separated from them much more easily than from metallic oxyds. Mere exposure to the light of the sun, or to a heat of 110°, is sufficient for that purpose.
Its affinities are supposed to be as follows:
| Potash | Soda | |--------|------| | Ammonia | Lime | | Barytes | Magnesia | | Oxyd of zinc | iron | | manganese | cobalt | | nickel | lead | | tin | copper | | bismuth | antimony | | arsenic | silver | | mercury | gold | | platinum (v). |
Sect. XXIX. Of Formic Acid.
In the 15th century several botanists observed with discovery astonishment, that the flower of succory, when thrown into an ant-hill, became as red as blood: But it was Mr S. Fether who first discovered that ants possessed a peculiar acid, which he obtained by distilling these animals. His experiments were published in the Philosophical Transactions.
(v) We suspect that this is not the real order of the affinities of this acid; the metallic oxyds ought probably to be placed before the alkalies and earths, and the metallic Prussiates ought to occupy the place which is at present filled by the metallic oxyds. The reasons for this conjecture will appear afterwards. See Part III. chap. ii. sect. 23, of this article. cal Transactions for 1670. Though Hoffman afterwards repeated his process, little was known concerning the nature of this acid till Margraf undertook its examination, and published his experiments in the Berlin Memoirs for 1749.
The species of ants from which the formic acid is obtained is the *formica rufa*, which reside most commonly in woods, or at least in elevated and dry places. They have been found to contain the greatest quantity of acid in the months of June and July. If at that season one of these animals be pressed upon paper tinged with turpentine, it changes the colour of it to a most lively red; they even sometimes stain it merely by crawling over it.
There are two methods of obtaining the formic acid, distillation and lixiviation.
When the first method is to be employed, the ants are to be washed clean, dried with a gentle heat, put into a retort, and distilled with a moderate heat, gradually increased till all the acid has come over. It is mixed with an empyreumatic oil, from which it is separated by passing it through a strainer previously moistened with water. By this process Messrs Arduvson and Ochm obtained from a pound of ants 7½ ounces of acid, the specific gravity of which, at the temperature of 60°, was 1.0075*. Morveau obtained from 29 ounces of ants 23 ounces of pretty strong acid†. Margraf added a quantity of water, but it is evident that this serves merely to weaken the acid.
When the other method is preferred, the ants are to be washed in cold water, put upon a clean linen cloth, and boiling water poured on them repeatedly till it can extract no more acid. The linen is then to be squeezed, and the several liquors mixed and filtrated. This method was first used by Arduvson and Ochm: they obtained from a pound of ants an acid liquor which had more specific gravity than common vinegar. It is to be purified from the oil which adheres to it by repeated distillations. After four distillations the empyreumatic oil still manifests its presence by its smell, but this smell vanishes if the acid be exposed for some time to the air; a quantity of essential oil, however, still remains, which cannot be separated. The specific gravity of the acid thus rectified is 1.0011‡.
Hermitadt employed a third method. He expressed the juice of dry ants, and by this means obtained from 2 lbs. of these animals 21 oz. 2 dr. of juice, which on distillation yielded a clear pure acid, equal in strength to very concentrated vinegar.
This acid seems to be capable of assuming a gaseous form; at least Hermitadt observed, that when he put some of it into a bottle with a glass stopper, the stopper was frequently raised by an elastic fluid making its escape, and that after some days it had lost its smell†. When this acid is boiled with nitric acid, a gas is extracted, which renders lime water turbid, and has a very pungent odour‡.
This acid has a strong but not unpleasant smell, a caustic taste, and when much diluted a pleasant acidity. When most concentrated, its specific gravity is 1.0453†.
One part of this acid, mixed with 7.5 parts of water, gives a faint red to syrup of violets; mixed with 430 parts of water, it reddens paper coloured with turpentine; mixed with 1300 parts of water, it produces no effect on the infusion of turpentine‡. It mixes readily with alcohol.
It unites readily with the other acids. When boiled with sulphuric acid, it becomes black. White acid vapours rise when the mixture becomes hot; and when it boils, a gas rises which unites with difficulty to water and lime-water; the formic acid is again obtained, but its quantity is diminished§.
Nitric acid decomposes it altogether, and is itself converted into nitrous acid. Muriatic acid does not alter it. Oxy-muriatic acts like nitric acid*.
Its compounds are called formiates.
Its affinities are the same with those given above for phosphoric acid.
**Sect. XXX. Of Sebacic Acid.**
Chemists had long suspected that an acid could be obtained from tallow, on account of the acid nature of the fumes which it emitted at a high temperature; but it was M. Grutzmacher who first demonstrated this acid in a dissertation *De Officio Medulla*, published in 1748†. Leenh. M. Rhodes mentioned it in 1753, and Segner published a dissertation on it in 1754, and Crell examined its properties very fully in two dissertations published in the Phil. Trans. for 1780 and 1781. It was called at first acid of fat, and afterwards sebacic acid.
It may be procured by heating together a mixture of suet and lime. Sebat of lime is formed, which may be purified by solution in water. It is then to be put into a retort, and sulphuric acid poured on it. Sebacic acid passes over on the application of heat.
Sebacic acid has an acid, sharp, bitterish taste, and a very pungent smell. It reddens tincture of litmus. Heat causes it to assume a yellow colour.
It oxidizes silver, mercury, copper, iron, lead, tin, zinc, antimony, manganese.
It does not act upon bismuth, cobalt, nickel. When mixed with nitric acid it dissolves gold.
Its compounds are called sebats.
Its affinities, according to Morveau, are as follows:
- Barytes, - Potash, - Soda, - Lime, - Magnesia, - Ammonia, - Alumina, - Jargon†, - Oxid of zinc, - Manganese, - Iron, - Lead, - Tin, - Cobalt, - Copper, - Nickel, - Arsenic, - Bismuth, - Mercury, - Antimony, - Silver.
**Sect. XXX. Of Bombyc Acid.**
Mr Boissier de Sauvages observed, that the juice of the silkworm, in the disease called in France *mauca*†, was acid; and Chauffier remarked, that the silkworm, after being converted into a butterfly, gives out a liquor which turns vegetable blues to a red. He found, that during the time that the animal was forming its cocoon, the acid was deposited in a reservoir near the anus. By means of a pair of scissors he collected some which reddened blue paper, united with alkalies with effervescence, and even attacked the scissors. He afterwards collected it by infusing the chrysalids in alcohol, which dissolved the acid, but left the impurities untouched.
This acid has never been examined with attention; so that almost all its properties are unknown.
Sect. XXXI. Of Zoonic Acid.
Mr Berthollet has obtained a peculiar acid by distilling vegetable and animal substances, to which he has given the name of the zoonic acid†. He procured it by distilling the gluten of wheat, the yeast of beer, bones, and woollen rags; and concludes, therefore, that it may be produced by the distillation of all animal substances.
To obtain this acid pure, he mixed lime with the distilled liquid, after having separated the oil, which it always contains (for the product of the distillation of animal substances is chiefly oil and carbonat of ammonia). He boiled this mixture till the carbonat of ammonia was exhausted; he then filtered it, added a little more lime, and boiled it again till the smell of the ammonia had gone off entirely. The liquor, which now contained only zoonat of lime, he filtered again, and then added a little water impregnated with carbolic acid, in order to precipitate any lime which might happen to be dissolved in the liquid without being combined with the zoonic acid.
After concentrating the zoonat of lime, he mixed it with phosphoric acid, and distilled it in a retort. At a heat nearly equal to that of boiling water, the zoonic acid passes over in a state of purity.
The zoonic acid has an odour like that of meat when frying, and it is actually formed during that process. It has an astringent taste.
It gives a red colour to paper tinged with turpentine.
With alkalies and earths it produces salts, which do not appear capable of crystallizing.
It forms a white precipitate in the solutions of acetate of lead and nitrat of mercury.
Part of the zoonic acid seems to be destroyed by the action of heat during the distillation of the zoonat of lime with phosphoric acid; for the liquor, which is in ebullition, becomes brown, and grows black at the end of the operation; hence Mr Berthollet concludes that the zoonic acid contains carbon. The zoonat of silver, when kept, becomes gradually brown; hence he concludes that the acid contains hydrogen. These conclusions he draws from a very ingenious theory of his, which has been already described in the article BLEACHING in this Supplement.
The five preceding acids have obtained the name of animal acids, because they are all obtained from the animal kingdom. It can scarcely be doubted that a more accurate examination of animal substances will add considerably to the number of these acids.
Sect. XXXII. Of Arsenic Acid.
Arsenic acid, which was first discovered by Scheele, may be produced by simply mixing the white oxyd of arsenic with oxy-muriatic acid, and applying a heat sufficient to sublime the muriatic acid. The theory of this operation is evident: the white oxyd has a greater affinity for oxygen than muriatic acid has; of course, if it combines with it, and is thus converted into arsenic acid, and the muriatic acid is easily sublimed by applying heat.
Landriani has informed us, that this acid may be so formed by subliming several times successively the white oxyd of arsenic, and taking care every time to renew the air. This process is equally simple; the oxyd combines at a high temperature with the oxygen of the atmosphere.
This acid is exceedingly fixed. When exposed to the air it attracts humidity, and at last becomes liquid. At the temperature of 65° it dissolves in two-thirds of its weight of water. Its solution may be evaporated to dryness, and even converted into a glass, which attracts moisture from the air, and acts powerfully on the crucible.
It is poisonous as well as the white oxyd of arsenic.
When exposed to a red heat, it is partly decomposed and converted into white oxyd of arsenic†.
It does not act upon gold, platinum, silver, mercury.
It oxidizes copper, iron, lead, tin, zinc, bismuth, antimony, cobalt, nickel, manganese, and arsenic, and in a very strong heat mercury and silver.
According to Berthollet's experiments, arsenic acid is composed of eight parts of white oxyd of arsenic and one part of oxygen.
Its compounds are called arseniates.
Its affinities are as follows:
- Lime, - Barytes, - Magnesia, - Potash, - Soda, - Ammonia, - Oxyd of zinc, - Manganese, - Iron, - Lead, - Tin, - Cobalt, - Copper, - Nickel, - Bismuth, - Mercury, - Antimony, - Silver, - Gold, - Platinum, - Alumina, - Jargonia†, - Water.
Sect. XXXIII. Of Tungstic Acid.
Tungstic acid, or oxyd of tungsten, was first discovered by Scheele; but the acid which he examined of tungstic was not pure, being composed, as Mr Luyart has shown, acid of nitric acid, ammonia, and tungstic acid. The real acid is insoluble in water, taffeta, and incapable of turning vegetable blues red till it has been first rendered soluble. Molybdic Acid.
Soluble by being partly combined with ammonia. It is of a beautiful yellow colour, which becomes blue when exposed to the light, or heated violently in close vessels. It does not recover its yellow colour except by calcination in the open air, and then increases in weight. When put into muriatic acid along with tin, zinc, or iron, the liquor becomes blue*. Treated with acetic acid, it becomes blue. When reduced to a glass with phosphat of soda, the blue colour appears and disappears according as the blue or yellow part of the flame is directed to it, as happens to manganese. Probably this blue substance is an oxyd of tungsten with a smaller quantity of oxygen.
Its compounds are called tungstates. Its affinities are as follows*:
- Lime, - Barytes, - Magnesia, - Potash, - Soda, - Ammonia, - Alumina, - Jargonia†?
Sect. XXXIV. Of Molybdic Acid.
Concrete molybdic acid, first discovered by Scheele, is white, and has an acid but metallic taste. Its specific gravity is 3.75*. It is not altered in the air. When heated in a crucible till it is beginning to melt, it experiences no alteration. It remains fixed even in a great fire as long as the crucible is covered; but the moment it is uncovered the acid rises unaltered in a white smoke. It dissolves in 570 parts of water. The solution reddens turnsole; nitric acid does not affect it, but sulphuric and muriatic acids dissolve it by the affluence of heat.
It may be prepared by treating the ore of molybdenum with nitric acid, and washing the acid when formed in water.
When combined with potash, it forms a colourless salt.
Mixed with filings of tin and muriatic acid, it immediately becomes blue, and precipitates flakes of the same colour, which disappear after some time, if an excess of muriatic acid has been added, and the liquor assumes a brownish colour.
With the solution of nitrat of lead it forms a white precipitate, soluble in nitric acid.
When mixed with a little alcohol and nitric acid, it does not change its colour.
With a solution of nitrat of mercury, or of nitrat of silver, it gives a white flaky precipitate.
With the nitrat of copper it forms a greenish precipitate.
With solutions of sulphat of zinc, muriat of bismuth, muriat of antimony, nitrat of nickel, muriats of gold and platinum, it produces white precipitates when these solutions do not contain an excess of acid.
When melted with borax, it gives it a bluish colour.
Paper dight in this acid becomes in the sun of a beautiful blue colour*.
Sulphur is capable of partly decomposing it by heat. Its compounds are called molybdates. Its affinities are unknown.
Sect. XXXV. Of Chromic Acid.
In the year 1779, Mr Pallas discovered, in the gold mine of Berefof, near Ekaterinbourg in Siberia, a mineral of a red colour, with a shade of yellow, crystallized in small acute angled quadrangular prisms, sometimes smooth, sometimes longitudinally streaked, and often hollow. Mr Macquart, professor of medicine at Paris, who in 1783 had been sent to the north by the French government in order to collect mineralogical information, brought with him a quantity of this mineral, which has been distinguished by the name of red lead ore of Siberia, and in 1786 analysed four ounces of it along with Mr Vauquelin. They found it to contain,
| Lead | 36½ | | Oxygen | 37½ | | Iron | 24½ | | Alumina | 2 |
and a little silver*.
Mr Bindheim of Moscow analysed it soon after, and found it to contain,
| Lead | 00 | | Molybdic acid | 11.66 | | Nickel | 5.66 | | Oxid of iron | 1 | | Air and water | 5 | | Silica | 4.5 |
and a little copper and cobalt†.
Vauquelin examined it again in 1797, and found that all the former analyses were inaccurate.
A hundred parts of this mineral, reduced to a fine powder, were mixed with 300 parts of the saturated carbonat of potash, and about 4000 parts of water; and this mixture was exposed for an hour to a boiling heat. He observed, 1st, that when these matters began to act upon each other there was produced a strong effervescence, which continued a long time; 2nd, that the orange colour of the lead became a brick red; 3rd, that at a certain period the whole matter seemed to dissolve; 4th, that in proportion as the effervescence advanced the matter reappeared under the form of a granulated powder, of a dirty yellow colour; 5th, that the liquor assumed a beautiful golden yellow colour. When the effervescence had entirely subsided, and appeared to have no longer any action on the substances, the liquor was filtered, and the metallic dust collected on the paper. After being washed and dried, it weighed no more than 78 parts; the potash, therefore, had taken from it 22 parts.
He poured upon the 78 parts just mentioned some of the nitric acid, diluted in 12 parts of water, which produced a brisk effervescence. The greater part of the matter was dissolved; the liquor assumed no colour, and there remained only a small quantity of powder of an orange-yellow colour. The liquor of the residuum was separated by the help of a syphon, the matter washed several times, and the washings united with the first liquor. This residuum, dried, weighed no more than 14 parts; from which it follows, that the nitric acid had dissolved 64.
He again mixed these 14 parts with 42 parts of the carbonat of potash and the necessary quantity of water, and and then treated them as before, and the phenomena were the same. The liquor, after being filtered, was united to the former; and the residuum, washed and dried, weighed no more than two parts, which were still red lead, and therefore thrown away.
The two nitric solutions, united and evaporated, produced 92 parts of nitrat of lead, crystallized in octahedra, perfectly white and transparent. These 92 parts of nitrat of lead, dissolved in water, were precipitated by a solution of the sulphat of soda. This produced 84 parts of the sulphat of lead, which were equivalent to 56,68 of metallic lead.
The alkaline liquors were found to contain a salt composed of potash combined with a peculiar acid, which Mr Vauquelin afterwards called chromic acid.
These liquors, subjected to evaporation until a saline pellicle was formed on their surface, produced, on cooling, yellow crystals; among which there was carbonat of potash, not decomposed. These crystals dissolved in water, and the solution united with the mother water, the whole was mixed with weak nitric acid until the carbonat of potash was saturated. The liquor then had a very dark orange-red colour. Being united with a solution of the muriat of tin, newly made, it first assumed a brown colour, which afterwards became greenish. Mixed with a solution of the nitrat of lead, it immediately produced the red lead. Lastly, evaporated spontaneously, it produced ruby-red crystals, mixed with crystals of the nitrat of potash. Ninety-eight parts of this mineral, decomposed as above mentioned, having produced 81 parts of the sulphat of lead, 100 parts would have given 87,65, which are equivalent to 37,1 of metallic lead. But admitting, as experiment proves (says Mr Vauquelin), that 100 parts of lead absorb, in combining with acids, 12 parts of oxygen, the 57,1 of metallic lead ought to contain in the red lead 6,86 of this principle, and we ought to have for the mineralizing acid 36,4.
Chromic acid crystallizes in the form of elongated prisms of a ruby colour.
When mixed with filings of tin and the muriatic acid, it becomes at first yellowish brown, and afterwards assumes a beautiful green colour.
When mixed with a little alcohol and nitric acid, it immediately assumes a bluish green colour, which preserves the same shade even after deliquescence. Ether alone gives it the same colour.
With a solution of nitrat of mercury, it gives a precipitate of a dark cinnamon colour.
With a solution of nitrat of silver, it gives a precipitate, which, the moment it is formed, appears of a beautiful carmine colour, but becomes purple by exposure to the light. This combination, exposed to the heat of the blow-pipe, melts before the charcoal is inflamed. It assumes a blackish and metallic appearance. If it be then pulverised, the powder is still purple; but after the blue flame of the lamp is brought in contact with this matter, it assumes a green colour, and the silver appears in globules disseminated throughout its substance.
With nitrat of copper, it gives a chestnut red precipitate.
With the solutions of sulphat of zinc, muriat of bismuth, muriat of antimony, nitrat of nickel, and muriat of platinum, it produces yellowish precipitates when these solutions do not contain excess of acid. With Chromic Acid, muriat of gold, it produces a greenish precipitate.
When melted with borax or glaas, it communicates to them a beautiful emerald green colour.
Paper impregnated with chromic acid affumes in the light a greenish colour.
When mixed with muriatic acid, the mixture was capable of dissolving gold like aqua regia; when this mixture of the two acids is distilled, oxy-muriatic acid is disengaged, and the liquor affumes a very beautiful green colour.
Sulphuric acid, while cold, produces no effect upon it; but when warmed, it makes it affume a bluish green colour, probably by favouring the disengagement of oxygen.
When this acid is heated along with charcoal, it is reduced to the metal called chromium. It is therefore composed of this metal and oxygen. From Vauquelin's experiments, it appears to contain one part of chromium and two parts of oxygen.
Such are the properties of this acid, as far as they have hitherto been discovered. Vauquelin is the only chemist who has examined it; and from his memoir the above account has been taken.
The four last described acids are called metallic acids, because they are composed of metals and oxygen.
It is believed, that most of the metals, we would rather say of the metallic oxys, are capable of being converted into acids by being combined with oxygen. It is certain that this is the case with platinum; and Hermann, by distilling nitric acid off tin, converted it into a white mass, soluble in three parts of water, which has been called flamic acid. Several more of the metallic oxys act the part of acids. But no complete set of experiments on this important subject has yet appeared.
**CHAP. VI. Of Affinity.**
The meaning of the word affinity has been already explained; and it must appear evident, from the use of affinity, which has been made of it in this article, that the consideration of the nature of affinity is the most important part of chemistry. While its laws are unknown, chemistry is not a science, but a wilderness of facts without beauty or regularity; every thing is equally perplexing and incomprehensible. The chemist, instead of being able to trace the operations of Nature, is lost in an endless maze of uncertainty, without a guide to conduct him, or a ray of light to illuminate his steps. It is the knowledge of affinity which dispels the darkness, removes the confusion, shows us the order which subsists in all the phenomena of nature, points out their dependence on one another, and enables us to direct them as we think proper, to make them subservient to the improvement of the arts, and thus to render them the ministers of our comforts and enjoyments.
1. When two bodies are united together by affinity, it unites bodies particle to particle.
By particles we do not mean what philosophers have called atoms, or the smallest parts into which it is possible to divide matter; but the smallest parts which make make an integrant of any substance. Water, for instance, consists of oxygen and hydrogen; but when we speak of a particle of water, we do not mean the oxygen or the hydrogen separately, but the smallest possible quantity of these combined in such a manner as to form water. It is the integrant particles of bodies which are united by affinity. Thus sulphuric acid is composed of sulphur and oxygen combined together; and ammonia, of hydrogen and azot combined in the same manner. Now when sulphuric acid and ammonia combine, it is not their elements, sulphur, oxygen azot, and hydrogen, which unite together, particle with particle, but the particles of the acid and the alkali as integrants. This is evident; because if these substances be separated from each other by means of a stronger affinity, they are found precisely in the same state as before they entered into combination.—When the substances which combine are simple, the ultimate and integrant particles are the same: But we are not certain that any of the bodies with which we are acquainted is simple, in the strict and proper sense of the word.
2. What is this affinity which unites bodies together? The older chemists thought that all solvents, or substances capable of dissolving others, were composed of particles which had the form of wedges or hooks; that solution consisted in the immersion of these wedges or hooks between the particles of the bodies to be dissolved; and that chemical combination was merely the linking of the different particles together by means of holes in one set of particles, into which the hooks or the wedges of the other set were thrust. Such explanations, absurd as they may appear, were fashionable among chemical philosophers till the days of Sir Isaac Newton, who first ascribed the chemical union of bodies to an attraction between the particles themselves. This explanation, after a violent struggle on the part of the chemists, has been at last unanimously adopted.
Affinity, then, is an attraction between the particles of different bodies, by which they are drawn towards one another, and kept united. This we take for granted, and consider as a fact, without pretending to explain how they come to be possessed of this power, or how they exert it; both of which are evidently beyond the reach of the human understanding.
But though we cannot discover the manner in which affinity acts, we can see, at least, that it follows certain laws, and that they are inviolable; for similar phenomena always occur when the circumstances are the same. Now what are the laws which affinity follows? There is a species of attraction which matter possesses, called gravitation, the laws of which were investigated by Sir Isaac Newton. Is affinity the same with gravitation, or does it follow different laws?
Upon a slight view of these two attractions, their phenomena appear very different. Gravitation acts at very great distances; affinity not until the bodies are mixed together; Gravitation acts on the whole mass; affinity only on the particles; Bodies gravitate to one another directly as their masses, and inversely as the squares of their distances. But how can affinity follow these laws, when it does not act till the bodies are apparently in contact? or supposing that it does act, how can they account for the phenomena of affinity? If barytes be presented to a compound of sulphuric acid and potash, the acid immediately leaves the alkali and combines with the earth: But had gravitation been the only power acting, ought not the barytes to have united with the sulphate of potash without producing any decomposition?
These striking differences have convinced many philosophers, as they seem to have done Newton himself, that gravitation and affinity are different species of attraction. Let us not, however, embrace this conclusion vaguely, or without affixing a precise meaning to our words.
Gravitation and chemical affinity are said to be different species of attraction. But what is attraction? It is proved merely a general fact, or that tendency which is observed among all the portions of matter towards each other, but which exhibits very different appearances under different circumstances. The tendency of matter towards matter at sensible distances is called gravitation, and its laws have been completely investigated; but neither that tendency, nor those laws, have been, or can be, shewn to be essential to the existence of matter. Chemical affinity is the tendency of particles towards each other at insensible distances, or when these particles are mixed together; and this tendency appears to be regulated by laws different from those of gravitation. Like gravitation, it is merely an observed fact; and however different these facts may appear to be, they are probably both brought about by the same forces. It is indeed true, that gravitation is directly as the masses of matter, and inversely as the squares of the distances of these masses; while the attraction, which is called chemical affinity, seems to observe very different rules. But we have shewn elsewhere (see Origs. p. 62—68, Encyc.; and Boscovich in this Suppl.), that the same forces repel at one distance and attract at another; and that they may produce all the various phenomena of chemical affinity.
The difficulties to be accounted for in chemical affinities are their intensity, their different degrees of strength, and their being elective, or, which is the same thing, the capacity which one body has of displacing another.
How come affinities, it may be asked, to differ in intensity? Perhaps we might with propriety refer this querit to the study of Boscovich's curve; but as our modern chemists are not generally versant in such studies, we beg leave to observe, in this place, that we have no proof whatever of absolute contact between bodies. On the contrary, it is highly probable, we had almost said demonstrable, that particles are in every instance at some distance from one another. For, on the supposition that two bodies were in actual contact, their attraction for each other would not only be as great as possible, but as great as the attraction of any other body for either of them could possibly be: Consequently, it necessarily follows, that since bodies chemically combined can be separated, they are not in actual contact (a); but if they are not in contact, their distance from one another
(a) Perhaps the following demonstration, which we borrow from the ingenious Mr Brougham, will render this more evident. In fig. 7, let the body A have for P an attraction which at the distance of AP is proportional... Another may vary in different cases, and the force of affinity will vary with the distance. Here then is a reason why the affinity of different bodies varies in strength. Sulphuric acid, for instance, has a stronger affinity for barytes than for lime; because when the combinations are formed, the distance between the acid and barytes is not so great as that between the acid and lime.
But why do the distances differ? If affinity be the same with gravitation, it must tend to bring the particles nearer one another. And what then prevents the lime from approaching as near the acid as the barytes does? We reply, the figure of its particles. This answer was first given to the question by Buffon, and it is fully adequate to solve the difficulty. The particles of bodies, indeed, are a great deal too minute for us to discover their figure by actual inspection; but the phenomena of crystallization show us that this difference actually exists.
The crystals of every body assume a peculiar figure. Now as these crystals are all formed in the same manner, and by the same law, it is impossible to conceive any other reason for their variety but the difference in the form of the particles which compose them.
But why does one body displace another? When a particle of barytes is brought within a certain distance of a particle of sulphuric acid and lime combined together, affinity acts, and draws them nearer to one another; and the barytes, from its figure, approaches nearer the acid than the lime could, and forms with it a compound, the figure of which is such, relatively to that of the lime, that they cannot approach within a small enough distance of each other to counteract the attraction of the earth. Accordingly no compound is formed; for all that is meant by two particles having formed a compound is, that their attraction for each other is greater than the attraction of the surrounding bodies for either.
Having thus seen that none of the phenomena of affinity are inconsistent with their resulting from the forces which bring about the phenomena of gravitation, we have a right to conclude, that it is at least highly probable, that all the motions of the corporeal world are produced by the same power which, though not essential to matter, was impressed upon every atom of it by the Great Creator when he formed this universe; and that as the effects of this power are modified according to the situation of the bodies on which it acts, they are known by the different names of gravity, adhesion, cohesion, and affinity.
Gravity is the attraction between bodies so distant, that the masses alone influence the result, and that the power may be considered as placed in the centre of the attracting bodies.
Adhesion supposes a distance too small for our senses. It has been demonstrated to be proportional to the number of touching points, which depends upon the figure of the particles that form the bodies.
Cohesion takes place only between particles of the same nature. These, instead of touching only in one superficiality, as in adhesion, touch in every point where their figure will allow contact; consequently the force of cohesion also must depend upon the figure of the particles.
Affinity unites bodies of a different nature, not merely by one superficiality, as adhesion does, but particle to particle, like cohesion; and the most perfect contact is formed that the figure of the particles will admit. Therefore, in this case also, the intensity depends upon the figure of the particles.
3. If we make the attempt, we shall find that water will not dissolve any quantity of common salt that we please. Water which refuses to take up any more is said to be saturated with salt. Neither can we combine any quantity of potash with a given portion of sulphuric acid: we may add as much of it as we please, indeed; but if we evaporate the liquid, in order to obtain the salt in crystals, we shall find that only part of the potash has united with the acid, and that the rest has crystallized separately. From these examples, it must appear evident, that bodies combine with one another by affinity only in certain proportions; or, which is the same thing, that a determinate number of particles of each of the ingredients goes to the formation of an integrant particle of the compound, and that into this integrant no additional particles of either ingredient can be admitted. Let us suppose, for instance, that the particles of sulphuric acid are tetrahedrons, and that the particles of potash are of such a form, that one of them can attach itself to each of the sides of the acid particle: In that case, an integrant particle of sulphate of potash would be composed of five particles, one of acid and four of alkali; for it is evident, that just four particles of potash would combine with every particle of acid, and that the acid would then be saturated, or, which is the same thing, would be incapable of receiving any more alkaline particles into combination with it. Let us suppose now, that there is just as much potash as saturates the acid; if more acid be poured in, it cannot enter into combination with the potash, because all the potash is already combined with acid.
Thus it appears evident, from the nature of affinity, that the ingredients in every combination must mutually saturate each other, and that no more of either can be
tional to PM; then let P move towards A, so as to come to the situation P', and let the attraction here be P'M'; as it is continual during the motion of P' to P', MM' is a curve line. Now in the case of the attraction of bodies for one another, PM is less than P'M'; and consequently MM' does not ever return into itself, and therefore it must go ad infinitum, having its arc between AB and AC, to which it approaches as asymptotes, the abscissa always representing the distance, and the ordinate the attraction at that distance. Let P' now continue its motion to P", and M' will move M"; and if P" meets A, or the bodies come into perfect contact, P'M" will be infinite; so that the attraction being changed into cohesion will be infinite, and the bodies inseparable, contrary to universal experience; so that P can never come nearer to A than a given distance. Nicholson's Journal, I. 555. be admitted into the compound than what is necessary to produce this saturation. It follows equally, that there can be no union without saturation, except there be a deficiency in some one of the ingredients: For supposing that there is a sufficient number of particles of potash, and that every particle of sulphuric acid requires four of them, as before, for saturation, the very same cause that produces the union of one, two, or three particles of potash with a particle of acid, must produce the union of all the four.
Even when there is a deficiency of one of the ingredients, saturation must equally take place; for those particles of acid that happen to be nearest the alkali must still be saturated; because the affinity of all the acid particles for alkali was originally equal, and the difference of the distance must give the superiority to those that are nearest; and those particles of acid that are once saturated with potash cannot be deprived of it by any of the other particles, otherwise the affinity of some particles of sulphuric acid for potash would be greater than that of others; which is absurd.
It will no doubt be objected to all this, that there are innumerable instances of additional portions of some one of the ingredients being received into a compound after saturation, and that some substances seem to be equally well saturated with different doses of another. Oxygen, for instance, combines with azot in three different proportions, and forms nitrous gas, nitrous acid, and nitric acid. The metals, too, form, in the same manner, different oxyds; and a great many instances of the same kind occur among the neutral salts.
But it ought to be remembered, that the conclusions against which these objections are urged, are consequences deduced, we think fairly, from a proposition which we consider as demonstrated, that affinity is a species of attraction (n). These phenomena cannot therefore be admitted as valid objections, except it can be shewn that they are really incompatible with these conclusions. Now that this is not the case, has been shown, in the most satisfactory manner, by Morveau†. These apparent exceptions are owing to an affinity which exists between the compound as an integrant and one of its ingredients, and are not instances of various degrees of saturation, but of the formation of new compounds. According to this very ingenious idea, which, we believe, first originated with Bergman, and was first seen in its full extent by Morveau, we have formerly explained in what manner the various metallic oxyds are formed: the first oxyd is a compound of the metal and oxygen; the second, of the first oxyd and oxygen; the third, of the second oxyd and oxygen; and so on. In the same manner we have explained the various combinations of azot and oxygen; and the explanation may easily be extended to every other case. These apparent objections, then, are not incompatible with the above conclusions, but perfectly consistent with them; and consequently they cannot be admitted as of any force.
There is one phenomenon, indeed, which proves, independent of these conclusions, that these combinations are actually formed in the manner we have supposed, and which therefore merits particular attention. The phenomenon is, that the affinity between the two simple substances is almost always greater than that between the compound and any of its ingredients. The affinity, for instance, between azot and oxygen is greater than that between nitrous gas and oxygen; and the affinity between nitrous gas and oxygen greater than that between nitrous acid and oxygen: For if nitrous gas be mixed with nitric acid, the whole is converted into nitrous acid; but no change whatever is produced when nitric and nitrous acids, or nitrous gas and nitrous acid, are mixed; and every substance which is capable of decomposing nitrous gas is capable also of decomposing nitrous and nitric acids; but many substances are capable of decomposing nitrous and nitric acids which have no effect upon nitrous gas. In the same manner, the affinity between sulphur and oxygen is greater than that between sulphurous acid and oxygen: for when sulphur is mixed with sulphuric acid, the whole is converted into sulphurous acid; but no change takes place when sulphur and sulphurous acid, or sulphurous and sulphuric acids are mixed together. A great many instances of the same kind might easily be produced, if these were not sufficient to establish the point. This curious fact affords a very strong proof that the bases, as well as the quantity of oxygen, is different in almost all the vegetable acids. Did the tartaric, oxalic, and acetic acids, for instance, consist of the same base with various doses of oxygen; were the tartaric composed of the base and oxygen; the oxalic, of tartaric acid and oxygen; the acetic, of oxalic acid and oxygen—in that case, a mixture of acetic and tartaric acids ought to form oxalic acid; but that this does not happen, any one may convince himself by actual experiment.
We do not mean to affirm, that this fact, though it is certainly very often true, holds in all cases; in some, perhaps, the reverse may be true, though we do not recollect at present any instance of that kind.
4. Since the affinity of almost every two bodies for each other differs in strength from that between every other two, it becomes an important problem to determine the strength of every affinity in numbers. The solution of this problem would give a clearness and precision to chemistry equal to that of any other branch of natural philosophy whatever, and enable it to advance with a degree of rapidity hitherto thought unattainable. No wonder, then, that this problem has occupied the attention of some of the most eminent philosophers who have dedicated their time to chemistry.
If the observations formerly made, in order to shew Attempts that to show
(n) Were any farther proof of this proposition required, we would observe, that cohesion acts as an antagonist to affinity, and may be often rendered so strong as to prevent affinity from acting with efficacy. Thus alumina and jargonia, when sufficiently heated, become insoluble in acids, without undergoing any other alteration than that of an increase of cohesion by their particles being brought nearer each other; for destroy this cohesion, and they become as soluble as ever. Now it follows from this, that if cohesion be attraction, so must affinity. The experiments of Morveau, to be afterwards mentioned, demonstrate, that adhesion and affinity are produced by the same cause: Consequently, if adhesion be attraction, so must affinity. that the difference in the strength of affinities depends upon the different forms of the particles which have an affinity for each other; be conclusive, it is evident, that the certain method of learning the strength of affinities would be to discover the forms of the particles of all bodies. But no method has hitherto been discovered by which it is possible of becoming acquainted with the figure of the particles of bodies. The experiments indeed of the Abbé Haüy (afterwards to be described) point out a method by which the primary figure of crystals may be investigated with a good deal of plausibility; but this leaves the knowledge of the figure of the particles which compose these crystals still uncertain.
As nobody, therefore, has attempted to take this road, in order to calculate the strength of affinities, let us at present consider the different methods which have been proposed for that purpose, that we may see whether any of them will answer the end intended.
Wenzel supposed, that the time taken by one body to dissolve another is a measure of the affinity which subsists between them. But the hypothesis of that ingenious philosopher will not bear the test of examination; for the time of solution evidently depends upon circumstances unconnected with affinity. The cohesion of the body to be dissolved, and the nature of the compound formed, must occasion very great differences in the time of solution of different bodies, even on the supposition that their affinities were all the same.
Fourcroy proposed to measure the affinity of bodies by the difficulty of separating them after they are combined; but we have no method for measuring this difficulty. Lavoisier and De la Place, indeed, proposed calorific for this purpose; but there are many compounds which calorific cannot separate, and it never produces a separation except by means of its affinity for one or other of the ingredients of the compound. Before calorific, therefore, could be employed as a measure, it would be necessary to know exactly the strength of its own affinity for every other substance; which is just a case of the problem to be resolved.
Macquer supposed, that the affinity of bodies for one another was in the compound ratio of the facility of their union, and the difficulty of their separation: But as we are in possession of no method of ascertaining either of these, it is evident that this theory, even allowing it to be just (which it certainly is not), could be of no use for afflicting us to calculate the force of affinities.
Another method has been proposed by the distinguished philosophical chemist Mr de Morveau (c).
In 1713, Dr Brook Taylor made some experiments on the adhesion of surfaces; and concluded from them, that the force of adhesion might be determined by the weight necessary to produce a separation. But in 1772, Mefris La Grange and Cigna, observing that the surfaces of water and oil adhere together, and taking it for granted that these two liquids repel each other, concluded, in consequence, that their adhesion was not owing to attraction; and hence inferred, that adhesion, in general, is always owing to the pressure of the atmosphere. This conclusion induced Morveau to examine the subject; he found, that adhesion was not affected by the pressure of the atmosphere; for it required the same weight to separate a disk of glass (30 lines in diameter) from the surface of mercury in the open air, and under an exhausted receiver. He observed, that the same disk adhered to water with a force of 258 grains, and to the solution of potash, though denser, only with a force of 210. This result not only proved that adhesion was owing to attraction, but made him conceive the possibility of applying this method to the calculation of affinities: For the force of adhesion being necessarily proportional to the points of contact, and this being the case also with affinity, it is evident, that the adhesion and the affinity between the same substances are proportional, and that therefore the knowledge of the one would furnish us with the ratio of the other.
Struck with this idea, he constructed cylinders of different metals, perfectly round, an inch in diameter and the same in thickness, and having a small ring in their upper surface, by which they might be hung exactly in equilibrium. He suspended these cylinders, one after another, to the beam of a balance; and after counterpoising them exactly, applied them to a quantity of mercury placed about two lines below them, making them slide along its surface, to prevent any air from lodging between them and the mercury. He then marked exactly the weight necessary to overcome their adhesion, taking care to change the mercury after every experiment. The table of the results is as follows:
| Metal | Force of Adhesion | |-------------|------------------| | Gold | 446 gr. | | Silver | 429 | | Tin | 418 | | Lead | 397 | | Bismuth | 372 | | Platinum | 282 | | Zinc | 204 | | Copper | 142 | | Antimony | 126 | | Iron | 115 | | Cobalt | 8 |
The differences of these results cannot be owing to the pressure of the air, which was the same in all; nor do they correspond to the densities of the metals; nor can they be owing to accidental differences in the polish of the cylinders, for a plate of rough iron adheres more strongly to mercury than one of the same diameter explicitly polished;—but they follow precisely the order of affinity, and therefore may be considered as the measure of the strength of the affinity between these different metals and mercury. They furnish us also with a convincing proof, that affinity is attraction, and the same species of attraction with adhesion; and that therefore, if the one be reducible to gravitation, so must the other.
Mr Achard, convinced of the importance of Mr Morveau's observations, made a great many experiments on adhesion, and published the result of them in 1780. He
(c) Now Mr Guyton: we have used the old name all along in the text to avoid ambiguity. proved, that the force of adhesion was not affected by alterations in the height of the barometer, but that its force became weaker as the heat of the fluid increased (p); and that the temperature remaining the same, the force of adhesion increased in the same ratio with the surfaces of the adhering bodies. He made about 620 experiments on the adhesion of different solids and fluids, proved that the force of adhesion did not depend on the densities of the adhering bodies, nor on the different cohesive force of the fluids; and, after a laborious calculation, concluded, that it depended on the figure of the particles of the adhering fluid and solid.
These experiments and calculations of Mr Achard are certainly of importance; and we would have given them here, had not the objects of them been substances which can furnish but few data for calculating the force of affinities.
This method of measuring the force of affinities seems to be an accurate one, and if it could be applied to every case of affinity, would, in all probability, enable us to solve the problem which we are now considering: But unfortunately, its application is very limited, being confined to those cases alone in which one of the bodies can be presented in a fluid, and the other in a solid state. Nor can it be applied indiscriminately to all those cases; for whenever the cohesion of any liquid is much inferior to the force of its adhesion to any solid, the separation takes place in the particles of the liquid itself, and consequently we do not obtain the measure of its adhesion to the solid, but of its own cohesion, and that, too, imperfectly. Thus, for instance, Mr Achard found, that sealing-wax adhered to water with a force of 92 grains, and to alcohol only with a force of 53½; yet we know that sealing-wax has a greater affinity for alcohol than for water; because alcohol dissolves it, which water is incapable of doing.
The difference in the result in this instance was evidently owing to the smaller cohesion of alcohol. Mr Morveau's method must therefore be confined to those cases in which the cohesion of the liquid is stronger than its adhesion to the solid, which may be known by the surface of the solid not being moistened; and to those in which the cohesion is not much inferior to the adhesion; for then, it is evident, that the force of cohesion will be increased as the force of adhesion.
Let us suppose, for instance, that two solids, A and B, are made to adhere to the surface of a liquid, and that A can only form an adhesion with 50 particles of the liquid, whilst B adheres to 100; it is evident, that a much smaller force will destroy the cohesion of the 50 particles to which A adheres with the rest of the liquid, than what will be required to destroy the cohesion of the 100 particles united to B with the same liquid.
The method of Mr Morveau, then, may be applied with accuracy in both cases; and when they occur can only be determined by experiment. It cannot, however, be applied indiscriminately even then; for unless the solid and the fluid be presented in such a state that no gas is extricated when the adhesion takes place, an accurate judgment cannot be formed of the force of adhesion. When marble (carbonate of lime), for instance, is applied to the surface of sulphuric acid, there is an extrication of gas, which very soon destroys the adhesion, and prevents an accurate result. Were it possible to employ quicklime instead of marble, this would be prevented; or if this cannot be accomplished, why might not lime be employed, united with some acid that would not assume a gelatinous form, and at the same time has a weaker affinity than sulphuric acid for lime? Why might not the phosphate of lime, for instance, be used, which may be reduced to a state of hardness sufficiently great for the purpose? The extrication of gas, during the application of metals to the surfaces of acids, might be prevented by oxidizing their surfaces. It is true, indeed, this could not be done with all the metals, on account of the nature of the oxides, but it might with several; copper, for instance, and silver. It cannot be doubted, that by these methods, and other contrivances that might be fallen upon, a sufficient number of results might be obtained to render this method of the greatest importance. It is rather surprising, therefore, that it has never been prosecuted.
Mr Kirwan has proposed another method of solving the problem. While he was engaged in his experiments on the strength of acids, he observed that the quantity of real acid necessary to saturate a given quantity of each of the bases was inversely as the affinity between the respective bases and the acid; and that the quantity of each of the bases necessary to saturate a given quantity of acid was directly as the affinity between the base and the acid. Thus 100 grams of each of the acids require more alkali for saturation than lime, and more lime than magnesia, as may be seen in the following table:
| 100 grams of | Potash, Soda, Lime, Ammon, Mag., Alum. | |--------------|----------------------------------------| | Sulphuric acid | 215 165 110 90 80 75 | | Nitric acid | 215 165 95 87 75 65 | | Muriatic acid | 215 158 89 79 71 55 |
He concluded, therefore, that the affinity between acids and their bases may be estimated by the quantity of bases necessary for saturation. Thus the affinity between potash and sulphuric acid is 215, and that between nitric acid and lime 96.
We have mentioned formerly, that the principle on which Mr Kirwan calculated the strength of the acids was founded on a mistake. It must follow of course, therefore, that the numbers which result from it must also be wrong. This Mr Kirwan has acknowledged, and seems to have given up all thoughts of ascertaining the strength of affinities by this method. But before it be abandoned altogether, we wish the following observations were considered.
Bergman long ago established as a principle, under the name of a chemical paradox, that the stronger any remedy fails was, the less of any other it required for saturation. Thus, according to him,
(b) Strictly speaking, this is owing not so much to a decrease of the force of adhesion, as of that of the cohesion of the fluid itself. 100 parts of potas require 78.5 Sulphuric acid, 64 Nitric; 51.5 Muriatic; 42 Carbonic.
100 parts of soda - 177 Sulphuric, 135.5 Nitric, 125 Muriatic, 80 Carbonic.
This proposition, which has been admirably illus-
| Parts of | Bergman | Wenzel | Kirwan | |----------|---------|--------|--------| | Barytes | 15.4 | 30.8 | | | Potas | 78.6 | 64 | 51.5 | | Soda | 175 | 135.5 | 125 | | Lime | 143.7 | 134.4 | 70.45 | | Magnesia | 173.67 | 159.25 | 82.92 | | Ammonia | | | | | Alumina | 211.11 | 220.2 | 77.7 |
It is evident at first sight, that Bergman's experiments correspond exactly with the proposition. To saturate, according to him, 100 parts of potas, requires 78.6 of sulphuric acid, 64 of nitric, and 51.5 of muriatic acid. There is only one deviation from the proposition in the whole table, and this regards barytes, which, according to him, is saturated with 15.4 of sulphuric and 30.8 of muriatic acid. But Mr Morveau has shewn, by several accurate experiments, that barytes requires much more sulphuric acid for saturation than Bergman supposed §. And Klapproth has shewn, that 100 parts of barytes require 49.2 of strong sulphuric acid for saturation *. And Dr Withering's calculation† agrees almost exactly with this; nor does that of Fourcroy differ much from it ‡. Instead of 15.4 of sulphuric acid, therefore, which, according to Bergman, are necessary to saturate 100 of barytes, it should be 42.3.
The first and last columns of Wenzel and Kirwan's experiments agree equally well with the proposition, but the second deviates from it completely. Wenzel probably might have been misled by the manner of performing his experiments; but the same objection does not seem to lie against those of Kirwan.
It can scarcely be doubted, however, to whatever cause the error is to be imputed, that the numbers in the second column of Mr Kirwan's table are too large. The following experiment of Morveau is sufficient to show this.
According to Mr Kirwan's experiments, the proportions of acid and alkali in the four following farts are as under:
Sulphat of potas { Acid 100 Potas 108.7
Now when sulphat of potas and nitrat of lime are mixed together, a double decomposition takes place, and sulphat of lime and nitrat of potas are formed. Let these two farts be mixed together; let the quantity of sulphat of potas be such, that the acid contained in it amounts to 100; and let a more than sufficient quantity of nitrat of lime be added, to saturate the sulphuric acid with lime. It is evident that for that purpose 80.6 of lime must be present; and the quantity of nitric acid combined with these 80.6 must be 234.4. This quantity would require for saturation 195.32 of potas, but there are only 108.7 in the mixture; consequently there ought to exist in the mixture, after the mutual decomposition of the farts, 64.87 of nitric acid in a state of liberty. Such would be the result, provided Mr Kirwan's numbers were accurate; but the fact is, that no such excess of acid exists in the mixture *; and consequently the quantity of nitric acid contained in nitrat of lime is stated too high by Mr Kirwan. Although therefore Mr Kirwan's tables do not coincide with the proposition which we are considering, this is not to be considered as a proof of its falsehood; as there is reason, from the experiment above described, to suspect some error in the data from which Mr Kirwan calculated the strength of the acids.
The truth of the second proposition may be judged of by the following tables: It appears that all the table of Bergman agrees with the proposition except the numbers which correspond to sulphat of soda, sulphat of alumina, nitrat of lime, and muriat of soda, which the late experiments of Mr Kirwan have sufficiently shown to be inaccurate.
Wenzel's table corresponds exactly, except the columns under ammonia and alumina, which Moreau has proved to be inaccurate.
Kirwan's table corresponds exactly, except with regard to the quantity of ammonia necessary to saturate muriatic acid, which does not appear to have been accurately determined by experiment.
Let us therefore take the truth of these two propositions for granted, and let us consider every deviation from them as an error; and let us see whether they will enable us to discover the absolute affinity of sulphuric, nitric, and muriatic acids, for their respective bases.
Table I. Quantity of Base necessary to Saturate 100 Parts of the three Acids.
| Sulph. acid | Nitric acid | Muriat. acid | |-------------|-------------|--------------| | 333.3 | 258.4 | 324.7 | | 123.3 | 148.4 | 188.8 | | 78.7 | 95.6 | 126.1 | | 68.3 | 74.4 | 116.7 | | 56.8 | 62.8 | 97.3 | | 49.3 | 54.8 | 78.5 |
Table II. Quantity of Acid necessary to Saturate 100 Parts of the six Bases.
| Sulph. acid | Nitric acid | Mur. acid | |-------------|-------------|-----------| | 42 | 42 | 42 | | 75 | 75 | 75 | | 65 | 65 | 65 | | 69.5 | 69.5 | 69.5 | | 57.8 | 57.8 | 57.8 | | 42 | 42 | 42 | | 47.3 | 47.3 | 47.3 |
The first of these tables represents the affinity between the same acid and its various bases; and the second that of the bases for the different acids. If it were required to know the ratios of the affinity which different bases have for any particular acid, the first table, supposing it accurate, would give it exactly. In like manner, if it were required to know the ratios of the affinity of the acids for the various bases, we would find them in the second table.
But if we wished to know what was the affinity between one acid and base, compared with that between another acid and a different base; or if we wanted to have not the relative but the absolute affinity between two bodies—it is plain that we could not find it in either of the tables; for the absolute affinity must consist of two things, the affinity which the acid has for the base, and the affinity which the base has for the acid. Now the first table gives us the one of these, and the second the other; so that in order to represent affinity in absolute numbers, the two tables must be multiplied into one another. This was the mistake into which Mr Kirwan fell. His method consisted merely in constructing a table like our first, which (supposing the numbers accurate) gave only the affinity between the bases and the same acid, but left out the affinity between the different acids and the same base; consequently the different columns could not be compared with each other.
It is evident, however, that, if the tables were multiplied together in their present state, they could not possibly give an accurate table of affinities. For that purpose, it is necessary to put the same number in the first column of each table, and then to substitute other numbers in the remaining columns, having the same ratio to one another with the numbers in the original columns. This is done in the following tables.
Table I. Ratios of the Affinity of six Bases for three Acids.
| Sulph. acid | Nitric acid | Mur. acid | |-------------|-------------|-----------| | 100,00 | 52.8 | 33.73 | | 100,00 | 57.43 | 36.98 | | 100,00 | 58.11 | 38.84 | | 29.27 | 28.77 | 35.70 | | 24.34 | 24.28 | 29.94 | | 11.12 | 19.59 | 24.15 | TABLE II. Ratios of the Affinity of three Acids for six Bases.
| | Sulph. acid | Nitric acid | Mur. acid | |--------|-------------|-------------|-----------| | Barytes| 100.00 | 90.42 | 74.54 | | Potas | 100.00 | 79.01 | 65.32 | | Soda | 100.00 | 80.03 | 62.35 | | Lime | 100.00 | 92.24 | 60.05 | | Magnesia| 100.00 | 90.34 | 59.68 | | Ammonia| 100.00 | 90.02 | 62.77 |
TABLE III. Affinity between three Acids and six Bases in Absolute Numbers.
| | Sulph. acid | Nitric acid | Mur. acid | |--------|-------------|-------------|-----------| | Barytes| 10000 | 9042 | 7454 | | Potas | 528 | 4537 | 3794 | | Soda | 3373 | 2969 | 2419 | | Lime | 2927 | 2653 | 2143 | | Magnesia| 2434 | 2193 | 1786 | | Ammonia| 2112 | 1763 | 1515 |
On the supposition that the two propositions mentioned above were strictly true, and that the numbers which we fixed upon were precisely the quantities of acid and base necessary to saturate each other reciprocally, this last table would represent accurately in numbers the strength of the affinities of the three acids for each of the six bases respectively.
We must acknowledge, however, that the truth of these propositions has not hitherto by any means been sufficiently proved; but a great number of facts concur to render them exceedingly probable, and highly worthy of the attention of chemical philosophers. And we hope that the method proposed by Morveau, and which had been previously practised by Richter, of verifying theoretical calculations of the composition of the salts, by mixing together two salts which mutually decompose each other, and ascertaining whether the result corresponds with calculation, will be followed out, and that it will be the means of ensuring more accuracy than it has hitherto been possible to obtain.
No one will suspect that anything which has here been said is meant as a reflection on the ingenious chemists who have attempted to solve this most difficult of all chemical problems, the proportion of the ingredients which enter into the composition of the salts. Mr Kirwan, in particular, is entitled to the greatest praise for the persevering industry with which he has prosecuted the subject, for the candour which he has displayed, and for the new route which he has opened to the chemical philosopher. Though this problem has not hitherto been solved, and though the difficulties which surround it are almost insurmountable, we may hope much from the general sense which is at present entertained of its importance, and from the zeal and abilities of those philosophers who have particularly turned their attention to it.
In the mean time, the following table of the strength of affinities by Morveau, though the numbers be arbitrary, will be found of very great use.
| | Sulph. acid | Nitric acid | Mur. acid | |--------|-------------|-------------|-----------| | Barytes| 66 | 62 | 36 | | Potas | 62 | 58 | 32 | | Soda | 58 | 50 | 31 | | Lime | 54 | 44 | 24 | | Ammonia| 46 | 38 | 21 | | Magnesia| 50 | 40 | 22 | | Alumina| 40 | 36 | 18 |
Although every chemical combination is produced by the same general law, yet as their phenomena vary somewhat according to circumstances, affinities have, for the sake of greater perspicuity, been divided into three classes. These classes may be reduced to three—simple affinity, compound, and dissolving affinities.
The first class comprehends all those cases in which only two bodies combine together; as, for instance, fulphoric acid and potash, oxygen and carbon. The affinities which belong to this class are known by the name of simple or single affinities. Although one of the substances to be combined happens to be already united with another body, the combination is still reckoned a case of single affinity. Thus suppose the sulphuric acid previously combined with magnesia, and forming with it the salt called fulphat of magnesia, as soon as potash is presented, the acid leaves the earth (which is precipitated), and unites with the alkali. Even when three bodies combine, it often happens that the union is produced merely by single affinity. Thus, when some potash is dropped into tartarous acid, part of the acid unites with the alkali, and forms tartrite of potash; after this the remainder of the acid combines with the tartrite just formed, and composes a new salt known by the name of acidulous tartrite of potash, or tartar. This is evidently nothing else than two instances of simple affinity immediately following each other.
When more than three bodies are mixed, decompositions and new combinations often take place, which affinity could
(n) This table, however, does not correspond quite accurately to all the phenomena. For instance, according to it, fulphat of barytes is not decomposed by carbonat of soda, although the contrary takes place in fact. could not have been produced had the bodies been presented in a different state. If, for instance, into a solution of sulphate of potash there be poured nitric acid, no decomposition is produced, because the sulphuric acid has a stronger affinity for potash than nitric acid has. For the very same reason, ammonia may be poured into the solution without producing any change. But if nitrate of ammonia be poured in, a decomposition instantly takes place, and two new bodies, sulphate of ammonia and nitrate of potash, are formed. Such cases of decomposition form the second class of affinities. They were called by Bergman cases of double elective attraction; a name which is exceedingly proper when there are only four bodies concerned. But as there are often more than four, it is necessary, as Mr Morveau has observed, to employ some more comprehensive term. We shall therefore call the affinities belonging to this class compound affinities (x); and comprehend under the term all cases where more than three bodies are present, and produce combinations which would not have been formed without their united action. In these cases the affinity of all the various bodies for each other acts, and the resulting combination is produced by the action of those affinities which are strongest. The manner in which these combinations and decompositions take place, was first clearly explained by Dr Black. Let the affinity between potash and sulphuric acid be = 62; that between nitric acid and ammonia = 38; that between the same acid and potash = 58; and that between the sulphuric acid and ammonia = 46. Now, let us suppose that all these forces are placed so as to draw the ends of two cylinders crossing one another, and fixed in the middle in this manner:
\[ \begin{array}{ccc} \text{Potash} & \text{Nitric acid} \\ 62 & 38 \\ \end{array} \]
\[ \begin{array}{ccc} \text{Sulph. acid} & \text{Ammonia} \\ 58 & 46 \\ \end{array} \]
It is evident, that as 58 and 46 = 104, are greater than 62 + 38 = 100, they would overcome the other forces and shut the cylinders. Just so the affinity between potash and nitric acid, together with that between sulphuric acid and ammonia, overcomes the affinity between potash and sulphuric acid, and that between nitric acid and ammonia, and produces new combinations.
In all cases of compound affinity, there are two kinds of affinities to be considered; i.e., those affinities which tend to preserve the old compound, these Mr Kirwan has called quiescent affinities; and those which tend to destroy them, which he has called divalent affinities.
Thus, in the instance above given, the affinity between potash and sulphuric acid, and that between nitric acid and ammonia, are quiescent affinities, which endeavour to preserve the old compound; and if they are strongest, it is evident that no new compound can take place. On the contrary, the affinity between potash and nitric acid, and that between sulphuric acid and ammonia, are divalent affinities; and as they are in this case strongest, they actually destroy the former combinations and form new ones.
Bergman, who published a great many cases of compound affinities, employed to explain them a method somewhat different from this. He would have represented the above case in the following manner:
\[ \begin{array}{ccc} \text{Potash} & \text{Nitric acid} \\ \text{Sulphate of Potash} & \text{Nitrat of Ammonia} \\ \text{Sulph. acid} & \text{Ammonia} \\ \text{Sulphate of Ammonia} \\ \end{array} \]
At the four corners of an imaginary square are placed the four substances, so that one acid shall be diagonally opposite to another. On the right and left side of the square are placed the old compounds, each on the side of its own ingredients, and above and below are placed the new compounds.
Mr Elliot improved this method of Bergman, by adding numbers expressive of the affinity of the various substances. It is in cases of compound affinity that the ratios of affinities, if we were possessed of them, would be peculiarly useful. For it is evident, that if we knew the strength of affinities in absolute numbers, we would be able to determine beforehand all the cases of compound affinity.
If we knew, for instance, that the affinity between the muriatic acid and barytes were = 36; that between the same acid and potash = 32; the affinity between potash and carbonic acid = 9; and that between the same acid and barytes = 14—we would be certain, previous even to experiment, that when muriat of barytes and carbonat of potash are mixed, a double decomposition would take place; which we know from experiment to be actually the case.
Another instance of decomposition by compound affinities.
\[ \begin{array}{ccc} \text{Muriat of Potash} & \text{Carbonat of Potash} \\ \text{Muriatic acid} & \text{Potash} \\ \text{Muriat of Barytes} & \text{Carbonic acid} \\ \text{Barytes} & \text{Carbonat of Barytes} \\ \end{array} \]
(s) Morveau called them affinités par concours. Supposing Morveau's numbers exact, it follows also, even prior to experiment, that no decomposition takes place when sulphate of lime and muriate of potash are mixed;
for the quiescent affinities are 86, and the divalent only 82.
Nor when acetite of lime and muriate of soda are mixed;
because the quiescent affinities are 47, and the divalent only 45. These cases where no decomposition takes place have been called by Morveau cases of inverse compound affinity.
Morveau has proposed the following improvements in representing these cases of compound affinities:
When decomposition does not take place, nothing is to be written above and below the square, as in the two last examples. When a new compound remains dissolved, a straight line is to be placed between it and the square, as in the following scheme:
When a new compound is precipitated, a line bent downwards in the middle is to be placed between it and the square, as in the following scheme:
When a new compound is sublimed, the line between it and the square is to be pointed upwards in the middle; thus
When a new compound is partly dissolved and partly precipitated, the line placed between it and the square is to assume the following shape:
When it is partly dissolved and partly sublimed, the following is the line to be used:
The third class of affinities has been called by Mr Morveau disposing affinities, because they dispose substances to combine that would not otherwise have done so. Suppose, for instance, that sulphur is presented to oxygen gas, it does not manifest any affinity for it; but combine it previously with potash, and it unites with oxygen with avidity. Its previous union with potash, in this case, disposed it to unite with oxygen. The cause of this curious affinity is not yet well understood. If we consider what it was that prevented the sulphur and oxygen from combining, we shall find, that it can only be its own attraction of cohesion, and the affinity between the oxygen and caloric which are combined. Whatever then diminishes this attraction of cohesion, or of aggregation as it has been called, must facilitate the union of of the sulphur with oxygen. This is done in some measure by the potash. Besides, if affinity depends upon the figure of particles, it is evident, that there must be an affinity between the new compound and oxygen; but the moment the oxygen approaches within a certain distance of the sulphur, it unites with it, as its affinity is much greater for that substance than for the compound.
The following is another instance of this curious affinity: Sugar, as Lavoisier has proved, is composed of oxygen, hydrogen, and carbon. Now if concentrated sulphuric acid be poured upon sugar, the oxygen and hydrogen combine, and form water, which unites with the acid, and the carbon is precipitated. In this case, the presence of the acid disposes the oxygen and hydrogen to combine. In what manner this new combination is produced, it would not be easy to explain: not by weakening the attraction of cohesion; for we do not see how the acid could produce that effect. The only explanation that can be given, is to suppose that the sulphuric acid, when it approaches within a certain distance of the oxygen and hydrogen, attracts them; and that this attraction, together with the affinity between the oxygen and hydrogen, is greater than that which produces the combination between the ingredients of the sugar themselves: the consequence of which must be decomposition.
6. We come now to one of the most difficult questions in chemistry—Why do bodies require different temperatures in order to unite? and why does the presence of caloric in many cases favour or rather produce union, while it prevents or destroys it in others?
These questions were proposed at the end of the second chapter of this article; and we referred them for this place, not because we hoped to be able to answer them in a satisfactory manner, but because no intelligible answer could be given till the nature of affinity had been previously considered. Some substances, phosphorus, for instance, combine with oxygen at the common temperature of the atmosphere; others, as carbon, require a higher temperature; and others, as hydrogen and azotic gas, do not combine except at a very high temperature. To what are these differences owing?
In answer to this question, we observe, that the attraction of cohesion evidently opposes that of affinity. Those bodies which we prefer to combine together are generally aggregates, or, which is the same thing, consist of many similar particles united by cohesion: for we have no method of separating bodies into their integrant particles, except affinity. Now we can conceive the attraction of cohesion between the particles of a body to be so great as to prevent them altogether from obeying the impulse of affinity. That this actually happens in some cases cannot be doubted: for if pure alumina be formed into a paste, and heated sufficiently, it becomes so hard that no acid can act upon it; yet its nature is not in the least changed: by proper treatment it may be again rendered soluble; and when precipitated from this new solution it has recovered all its original properties. The effect of the fire, then, was merely to increase the cohesion, by separating all the water, and allowing the particles to approach nearer each other.
It is evident, that whatever diminishes the cohesion which exists between the particles of any body, must tend to facilitate their chemical union with the particles of other bodies: this is the reason that bodies combine more easily when held in solution by water, or when they have been previously reduced to a fine powder. Now caloric possesses the property of diminishing cohesion. And one reason why some bodies require a high temperature to cause them to combine is, that at a low temperature the attraction of cohesion is in them superior to that of affinity; accordingly, it becomes necessary to weaken that attraction by caloric till it becomes inferior to that of affinity. The quantity of caloric necessary for this purpose must vary according to the strength of the cohesion and of the affinity; it must be inversely as the affinity, and directly as the cohesion. Therefore, if we knew precisely the force of the cohesion between the particles of any body, and of the affinity between the particles of that body and of any other, we could easily reduce the temperature necessary to calculation.
That caloric or temperature acts in this manner cannot be doubted, if we consider, that other methods of diminishing the attraction of cohesion may be substituted for it with success. A large lump of charcoal, for instance, will not unite with oxygen at so low a temperature as the same charcoal will do when reduced to a very fine powder; and charcoal will combine with oxygen at a still lower temperature, if it be reduced to its integrant particles, by precipitating it from alcohol, as Dr Priestley did by passing the alcohol through red hot copper. And to show that there is nothing in the nature of oxygen and carbon which renders a high temperature necessary for their union, if they be presented to each other in different circumstances, they combine at the common temperature of the atmosphere; for if nitric acid, at the temperature of 60°, be poured upon charcoal powder, well dried in a close crucible, the charcoal takes fire, owing to its combining with the oxygen of the acid. And in some other situations, carbon is so completely divided that it is capable of combining with the oxygen of the atmosphere, or, which is the same thing, of catching fire at the common temperature: this seems to be the case with it in those pyrophorists that are formed by distilling to dryness several of the neutral salts which contain acetic acid. These observations are sufficient to show, that caloric is in many cases necessary in order to diminish the attraction of cohesion.
But there is a difficulty still remaining, How comes it that certain bodies will combine with oxygen without the assistance of any foreign heat, provided the combination be once begun, though a quantity of caloric is necessary to begin the combination? and that other bodies require to be surrounded by a great quantity of caloric during the whole time of their combining with oxygen? Alcohol, for instance, if once kindled, burns till it is quite consumed; and this is the case with oils also, provided they be furnished with a wick.
We must observe, in the first place, that we would err very much, were we to suppose that a high temperature is not as necessary to these substances during the whole of their combustion as at the commencement of it; for Mr Monge found, on making the trial, that a candle would not burn after the temperature of the air around it was reduced below a certain point.
All substances which continue to burn after being once kindled are volatile, and they burn the easier in proportion proportion to that volatility. The application of a certain quantity of caloric to alcohol volatilizes part of it; that is to say, diminishes the attraction of its cohesion so much that it combines with oxygen. The oxygen which enters into this combination gives out as much heat as volatilizes another portion of the alcohol; which combines with oxygen in its turn; more heat is given out; and thus the process goes on. Oils and tallow exhibit the very same phenomena; only as they are less volatile, it is necessary to assist the process by means of the capillary attraction of the wick, which confines the action of the caloric evolved to a small quantity of oil, and thus enables it to produce the proper effect. In short, then, every substance which is capable of continuing to burn after being once kindled is volatile, or capable of being converted into vapour by the degree of heat at first applied. The reason that a live coal will not burn when suspended insulated in the air, is not, as Dr Hutton supposed, because its light is diffused; but because the coal cannot be converted into vapour by the degree of heat which it contains, and because the cohesion of its particles is too great to allow it to combine with oxygen without some such change. There are some coals, however, which contain such a quantity of bitumen that they will burn even in the situation supposed by Dr Hutton, and continue to burn, provided they be furnished with any thing to act as a wick. It is needless to add, that bitumen, like oil, is easily converted into vapour.
But this explanation, instead of removing our difficulties, has only served to increase them. For if caloric only acts by diminishing the attraction of cohesion, and converting these substances into vapour, why do not all elastic fluids combine at once without any additional caloric? why do not oxygen and hydrogen, when mixed together in the state of gas, unite at once and form water? and why do not oxygen and azot, which are constantly in contact in the atmosphere, unite also and form nitrous gas? Surely it cannot be the attraction of cohesion that prevents this union. And if it be ascribed to their being already combined with caloric, how comes it that an additional dose of one of the ingredients of a compound decomposes it? Surely, as Mr Monge has observed, this is contrary to all the other operations in chemistry.
That the particles of fluids are not destitute of an attraction for each other, is evident from numberless facts. The particles of water draw one another after them in cases of capillary attraction; which is probably owing to the attraction of cohesion. It is owing to the attraction of cohesion, too, that small quantities of water form themselves into spheres: Nor is this attraction so weak as not to be perceptible. If a small plate of glass be laid upon a globule of mercury, the globule, notwithstanding the pressure, continues to preserve its round figure. If the plate be gradually charged with weights one after another, the mercury becomes thinner and thinner, and extends itself in the form of a plate; but as soon as the weights are removed, it recovers its globular figure again, and pushes up the glass before it. Here we see the attraction of cohesion, not only superior to gravitation, but actually overcoming an external force.
And if the workman, after charging his plate of glass, glas with weights, when he is forming mirrors, happens to remove these weights, the mercury which had been forced from under the glass, and was going to separate, is drawn back to its place, and the glass again pushed up. Nor is the attraction of cohesion confined to solids and liquids; it cannot be doubted, that it exists also in gases; at least it is evident, that there subsists an attraction between gases of a different kind; for although oxygen and azotic gas are of different gravities, and ought therefore to occupy different parts of the atmosphere, we find them always mixed together; and this can only be ascribed to an attraction.
And were we to allow, with Humboldt and several other chemists, that these two gases are chemically combined in atmospherical air, an opinion contradicted by a late experiment in France (v); still the existence of carbonic acid gas in every part of the atmosphere can only be ascribed (if the inaccuracy of the expression may be tolerated) to a kind of cohesion. And whoever has been accustomed to pneumatic experiments must have observed, that small portions of air, as well as water, form themselves into spheres, and that the attraction of cohesion is so strong in gases, that large globules of them often adhere by a single point to the bottom of vessels filled with heavy fluids; whereas, had there been no attraction of cohesion, every part of the globule ought to have ascended to the surface of the fluid, except the particles immediately in contact with the vessel. Allowing, then, that there is an attraction of cohesion between the particles of gases, let us see whether that will not assist us in removing the difficulty.
It seems evident, in the first place, that the affinity between the bases of the gases under consideration and oxygen is greater than their affinity for that dose of caloric which produces their elastic form; for when they are combined with oxygen, the same dose will not separate them again. Let us take hydrogen for an instance: The affinity of hydrogen is greater for oxygen than for the caloric which gives it its gaseous form; but the oxygen is also combined with caloric, and there exists an attraction of cohesion between the particles of the hydrogen gas; the same attraction subsists between those of oxygen gas. Now the sum of all these affinities, namely, the affinity between hydrogen and caloric, the affinity between oxygen and caloric, the cohesion of the particles of the hydrogen, and the cohesion of the particles of oxygen—is greater than the affinity between the hydrogen and oxygen; and therefore no decomposition can take place. Let the affinity between Oxygen and caloric be - - - - 50 Hydrogen and caloric - - - - 50 Cohesion of oxygen - - - - 4 Cohesion of hydrogen - - - - 2
Sum of quiescent affinities, - - - - 106 The affinity of oxygen and hydrogen, - - - - 105 The quiescent affinities being greater than the divellent affinities, no decomposition can take place.
(v) Air brought by means of a balloon from a great height in the atmosphere was found to contain less oxygen gas than the same quantity of air near the ground. Let now a quantity of caloric be added to the oxygen and hydrogen gas; it has the property of expanding them, and of course of diminishing their cohesion; while its affinity for them is so small that it may be neglected. Let us suppose that it diminishes the cohesion of the oxygen 1, and of the hydrogen also 1, their cohesion will now be 3 and 3; and the quiescent affinities being only 104, while the divalent are 105, decomposition would of course take place, and a quantity of caloric would thus be let at liberty to produce the same effects upon the neighbouring particles.
Thus, then, caloric acts only by diminishing cohesion: And the reason that it is required so much in gaseous substances, and in those combinations into which oxygen enters, is the strong affinity of oxygen and the other bases of the gases for caloric; for, owing to the repulsion which exists between the particles of that subtle substance, an effect is produced by adding large doses of it, contrary to what happens in other cases. The more of it is accumulated, the stronger is the repulsion between its particles; and therefore the more powerful is its tendency to fly off; and as this tendency is opposed by its affinity for the body and the cohesion of its particles, it must diminish both these attractions.
Though we have thus attempted to explain what has been always considered as one of the most difficult problems in chemistry, we are far from supposing that we have removed every difficulty. Much still remains to be done before the action of light and caloric can be fully understood; and there may be other agents, of whose existence we have not yet even conceived the idea.
One difficulty still remains to be examined. Heat not only produces the combination of some bodies, but also occasions the decomposition of others. How does it act in these cases?
That many of these decompositions are produced by chemical affinity, will be evident from the following examples.
When sulphur and arsenic acid are exposed to heat, sulphuret of arsenic is formed evidently by a kind of compound affinity.
In the same manner, when nitrat of potash and boracic acid are exposed to heat, the nitric acid is volatilized, and borat of potash is left behind.
In the same manner, it would be easy to explain how all the decompositions by the dry way, as it is called, are produced.
But how comes caloric to decompose water after having produced the union of oxygen and hydrogen? The union, we have seen, was probably brought about by the play of opposite affinities; but in the separation, caloric seems to act by its peculiar power, or the repulsion which exists between its particles. When caloric combines with an integrant particle of water, this repulsion must separate the component parts somewhat from one another; consequently it must weaken their affinity; for every increase of distance produces that effect. Now let us suppose that the affinity between oxygen and hydrogen is 105, and that the affinity between caloric and each of these bodies is 50; as soon as the particles of oxygen and hydrogen are so far separated from each other that their affinity is less than 100, they will unite with caloric in preference, because the sum of their affinities for caloric is equal to 100; consequently, whenever that takes place water will be decomposed. Hence we see the reason why more heat is always necessary to produce the decomposition of bodies than what produced their union.
Caloric possesses another singular property, that of changing the compound affinities of bodies, even when it Part III. Of doubly compound bodies.
The bodies which consist of combinations of those substances that have been denominated compound, and which, for that reason, we have ventured to call doubly compound bodies, may be reduced to three classes:
1. Soaps, 2. Neutral salts, 3. Hydrophilic substances.
These shall form the subject of the three following chapters; and we shall finish this part of the article with some observations on crystallization.
Chap. I. Of Soaps.
The compounds into which oils enter without decomposition have been denominated soaps.
Oils are capable of combining with alkalies, earths, and metallic oxides; they are capable also of combining with several of the acids. There are therefore two classes of soaps: 1. Alkaline, earthy, and metallic soaps, which for the sake of brevity we shall call alkaline soaps; and,
2. Acid soaps. These two classes form the subject of the two following sections.
Sect. I. Of Alkaline Soaps.
As there are a great number of oils, all or most of which are capable of combining with alkalies, earths, and oxydes, it is natural to suppose that there are as many genera of alkaline soaps as there are oils. That there are differences in the nature of soaps corresponding to the oil which enters into their composition, is certain; but these differences are not of sufficient importance to require very particular description. We shall therefore describe all the alkaline soaps together, and notice, as we go along, some of the most important differences resulting from the oily ingredients.
1. Soap of soda, or common soap. The word soap (SOAP, SOAP) first occurs in the works of Pliny and Galen, and is evidently derived from the old German word SOAP (SOAP). Pliny informs us, that soap was first discovered by the Gauls; that it was composed of tallow and... Soap may be prepared by the following process. A quantity of the soda of commerce, which is a carbonate of soda, and which is often called barilla from the name of a plant, by burning which it is procured in great quantities in Spain, is pounded and mixed in a wooden vessel, with about a fifth part of its weight of lime, flaked and passed through a sieve immediately before. Upon this mixture a quantity of water is poured, considerably more than what is sufficient to cover it, and allowed to remain on it for several hours. The lime attracts the carbonic acid from the soda, and the water becomes strongly impregnated with the pure alkali. This water is then drawn off by means of a stop cock, and called the first ley. Its specific gravity should be about 1.200.
Another quantity of water is then to be poured upon the soda, which, after standing two or three hours, is also to be drawn off by means of the stop cock, and called the second ley.
Another portion of water is poured on; and after standing a sufficient time, is drawn off like the other two, and called the third ley.
Another portion of water may still be poured on, in order to be certain that the whole of the soda is dissolved; and this weak ley may be put aside, and employed afterwards in forming the first ley in subsequent operations.
A quantity of oil, equal to six times the weight of the soda used, is then to be put into the boiler, together with a portion of the third or weakest ley, and the mixture must be kept boiling and agitated constantly by means of a wooden instrument. The whole of the third ley is to be added at intervals to the mixture; and after it is consumed, the second ley must be added in the same manner. The oil becomes milky, combines with the alkali, and after some hours it begins to acquire consistence. A little of the first ley is then to be added, not forgetting to agitate the mixture constantly. Portions of the first ley are to be added at intervals; the soapy substance acquires gradually greater consistence, and at last it begins to separate from the watery part of the mixture. A quantity of common salt is then to be added, which renders the separation much more complete. The boiling is to be continued still for two hours, and then the fire must be withdrawn, and the liquor must be no longer agitated. After some hours repose the soap separates completely from the watery part, and swims upon the surface of the liquor. The watery part is then to be drawn off; and as it contains a quantity of carbonate of soda, it ought to be reserved for future use.
The fire is then to be kindled again; and, in order to facilitate the melting of the soap, a little water, or rather weak ley, is to be added to it. As soon as it boils, the remainder of the first ley is to be added to it at intervals. When the soap has been brought to the proper consistence, which is judged of by taking out small portions of it and allowing it to cool, it is to be withdrawn from the fire, and the watery part separated from it as before. It is then to be heated again, and a little water mixed with it, that it may form a proper pate. It is then to be poured into the vessels proper for cooling it; in the bottom of which there ought to be a little chalk in powder, to prevent the soap from attaching itself to it. In a few days the soap will have acquired sufficient consistence to be taken out, and formed into proper cakes (ii).
The use of the common salt in the above process is to separate the water from the soap; for common salt has a stronger affinity for water than soap has.
Olive oil has been found to answer best for making soap, and next to it perhaps tallow may be placed; but a great variety of other oils may be employed for that purpose, as appears from the experiments of the French chemists above quoted. They found, however, that linseed oil and whale oil were not proper for making hard soaps, though they might be employed with advantage in the manufacture of soft soaps. Whale oil has been long used by the Dutch for this last purpose.
Soap may also be made without the assistance of heat; but in that case a much longer time and a larger proportion of alkali is necessary.
Manufacturers have contrived various methods of softening or phosphating soap, or of adding ingredients which increase its weight without increasing its value. The most common substance used for that purpose is water; which may be added in considerable quantities, especially to soap made with tallow (the ingredient used in this country), without diminishing its consistence. This fraud may be easily detected, by allowing the soap to lie for some time exposed to the air. The water will evaporate from it, and its quantity will be discovered by the diminution of the weight of the soap. As soap phosphated in this manner would lose its water by being kept, manufacturers, in order to prevent that, keep their soap in saturated solutions of common salt; which do not dissolve the soap, and at the same time, by preventing all evaporation, preserve, or rather increase, the weight of the soap. Messrs Darcey, Lelievre, and Pelletier, took two pieces equal in weight of soap phosphated in this manner, and placed the one in a dry place in the open air, and the other in a saturated solution of common salt. After a month, the first had lost 7/85 of its weight, the other had gained about 1/85 parts. Various other methods have been tried upon to phosphatize soap; but as they are not, we hope, generally known, it would be doing an injury to the public to describe them here.
Different chemists have analysed soap, in order to ascertain the proportions of its ingredients; but the result of their experiments is various, because they used soap containing various quantities of water. From the experiments of Darcey, Lelievre, and Pelletier, it appears that soap newly made and exposed to false contains:
- 917.5 Oil, - 137 Alkali, - 487 Water.
Soap is soluble both in water and in alcohol. Its properties as a detergent are too well known to require any description.
(ii) See the Memoir of Darcey, Lelievre, and Pelletier, in the Ann. de Chim. XIX. 253. It is decomposed by lime, and by compound affinity (1) by sulphate of lime, nitrate of lime, muriate of lime, and probably all the salts which contain lime.
2. Soap of potash. Potash may be substituted for soda in making soap, and in that case precisely the same process is to be followed. It is remarkable, that when potash is used, the soap does not assume a solid form; its consistence is never greater than that of hog's lard. This is what in this country is called soft soap. Its properties as a detergent do not differ materially from those of hard soap, but it is not nearly so convenient for use. The alkali employed by the ancient Gauls and Germans in the formation of soap was potash; hence we see the reason that it is described by the Romans as an unguent.
Some persons have affirmed that they knew a method of making hard soap with potash. Their method is this: After forming the soap in the manner above described, they add to it a large quantity of common salt, boil it for some time, and the soap becomes solid when cooled in the usual way. That this method may be practised with success has been ascertained by Messrs Darcey, Lefebvre, and Pelletier; but then the hard soap thus formed does not contain potash but soda; for when the common salt (muriate of soda) is added, the potash of the soap decomposes it, and combines with its muriatic acid, while at the same time the soda of the salt combines with the oil, and forms hard soap; and the muriate of potash formed by this double decomposition is dissolved in the water and drawn off along with it.
Chaptal has lately proposed to substitute wool in place of oil in the making of soap. The ley is formed in the usual manner, and made boiling hot, and threads of woollen cloth of any kind are gradually thrown into it; they are soon dissolved. New portions are to be added sparingly, and the mixture is to be constantly agitated. When no more cloth can be dissolved, the soap is made. This soap is said to have been tried with success. It might doubtless be substituted for soap with advantage in several manufactures, provided it can be obtained at a cheaper rate than the soaps at present employed.
Fifth, too, have been lately substituted for oil with equal success. The only disadvantage which soap made in this manner is liable to, is a disagreeable smell, from which it cannot easily be freed.
3. Soap of ammonia. This soap was first particularly attended to by Mr Berthollet. It may be formed by pouring carbonat of ammonia on soap of lime. A double decomposition takes place, and the soap of ammonia swims upon the surface of the liquor in the form of an oil; or it may be formed with still greater ease by pouring a solution of muriate of ammonia into common soap dissolved in water. We have formed it often by mixing caustic ammonia and oil.
It has a more pungent taste than common soap. Water dissolves a very small quantity of it; but it is easily dissolved in alcohol. When exposed to the air, it is gradually decomposed.
4. Soap of lime. This soap may be formed by pouring lime-water into a solution of common soap. It is insoluble both in water and alcohol. Carbonat of fixed alkali decomposes it by compound affinity. It melts with difficulty, and requires a strong heat.
5. Soap of magnesia. This soap may be formed by mixing together solutions of common soap and fulphate of magnesia. It is exceedingly white. It is unctuous, dries with difficulty, and preserves its whiteness after desiccation. It is insoluble in boiling water. Alcohol and fixed oil dissolve it in considerable quantity. Water renders its solution in alcohol milky. A moderate heat melts it; a transparent mass is formed, slightly yellow, and very brittle.
6. Soap of alumina. This soap may be formed by mixing together solutions of alum and of common soap. Of alumina. It is a flexible soft substance, which retains its suppleness and tenacity when dry. It is insoluble in alcohol, water, and oil. Heat easily melts it, and reduces it to a beautiful transparent yellowish mass.
7. Soap of barytes resembles almost exactly the soap of lime.
8. Soap of mercury. This soap may be formed by mixing together a solution of common soap and of corrosive muriate of mercury. The liquor becomes milky, and the soap of mercury is gradually precipitated. This soap is viscous, not easily dried, loses its white colour when exposed to the air, and acquires a slate colour, which gradually becomes deeper, especially if exposed to the sun or to heat. It dissolves very well in oil, but sparingly in alcohol. It readily becomes soft and fluid when heated.
9. Soap of zinc. This soap may be formed by mixing together a solution of sulphate of zinc and of soap. It is of a white colour, inclining to yellow. It dries speedily, and becomes triable.
10. Soap of cobalt. This soap, made by mixing nitrate of cobalt and common soap, is of a dull leaden colour, and dries with difficulty, though its parts are not connected.
Mr Berthollet observed, that towards the end of the precipitation there fell down some green coagula, much more consistent than soap of cobalt. These he supposed to be a soap of nickel, which is generally mixed with cobalt.
11. Soap of tin. It may be formed by mixing common soap with a solution of tin in nitro-muriatic acid. It is white. Heat does not fuse it like other metallic soaps, but decomposes it.
12. Soap of iron. Formed by means of sulphate of iron. It is of a reddish brown colour, tenacious, and easily fusible. When spread upon wood, it sticks in and dries. It is easily soluble in oil, especially of turpentine. Berthollet proposes it as a varnish.
13. Soap of copper. Formed by means of sulphate of copper. It is of a green colour, has the feel of a resin, and becomes dry and brittle. Hot alcohol renders its colour deeper, but scarcely dissolves it. Ether dissolves it, liquefies it, and renders its colour deeper and more beautiful. It is very soluble in oils, and gives them a pleasant green colour.
14. Soap of lead. It may be formed by means of acetate of lead.
(1) In this and the following chapter, compound affinity is not taken always in its strict and proper sense, but is applied to all those decompositions in which the affinities of more than three bodies act. Chemistry.
15. Soap of silver.—It may be formed by means of nitrat of silver. It is at first white, but becomes redish by exposure to the air. When fused, its surface becomes covered with a very brilliant iridescence; beneath the surface it is black.
16. Soap of gold.—It is at first white, and of the consistence of cream. It gradually assumes a dirty purple colour, and adheres to the skin so that it is difficult to efface the impression.
17. Soap of manganese.—It is at first white, but it assumes in the air a reddish colour, owing evidently to the absorption of oxygen. It speedily dries to a hard brittle substance, and by liquefaction assumes a brown blackish colour.
We owe the following refinements to Mr Mezaize.
18. Soap of turpentine and potash.—576 grains of turpentine and potash were dissolved in 9216 grains of alcohol, and then 576 grains of potash were added. The alcohol was distilled off at a boiling water heat. There remained in the retort 648 grains of a brownish foamy matter, which when spread on glass appeared transparent. There remained also nearly the same quantity of potash dissolved in water. This soap was put in a vessel for six weeks; during which time 72 grains of solution of potash separated from it. It had assumed the consistence of honey. Its colour was browner. It was completely soluble in water; the solution was milky. It dissolved also in alcohol. It had no disagreeable taste. Vinegar decomposed it.
19. Soap of benzoin and potash.—By treating 9216 grains of alcohol, 1728 grains of benzoin, and 576 grains of potash, as above, 1728 grains of a soap were obtained, browner than that of turpentine, of an odour a little aromatic. When left in a cellar for six weeks, it became solid. Its solution in water was yellowish. Vinegar decomposed it. This compound is the same with Starkey's soap.
20. Soap of balm of Peru and potash.—1152 grains of balm, 2304 grains of potash, and 9216 grains of alcohol, produced a soap of a reddish colour, and pretty consistent.
21. Soap of guaiac and potash.—1728 gr. of guaiac was dissolved in 18648 grains of alcohol and the solution filtered, and to this 1728 grains of potash were added, and the soap obtained as above. It was solid, of a brown colour at first, which afterwards became green on the surface, but remained unaltered within. Its solution in water was greenish. It had no disagreeable taste. It dissolved in alcohol, and formed a green tincture. Vinegar decomposed it.
22. Soap of scammony and potash.—By the above process a soap was obtained with scammony pretty consistent, of a brown colour, soluble in water, and not decomposed by the water of pits from which scammony is obtained. It has no disagreeable taste. Its solution in alcohol is of a deep amber colour.
Sect. II. Of Acid Soaps.
Method of forming acid soaps.
Sulphuric acid may be combined with oils in the following manner: Put two ounces of it into a glass mortar, and add, by little and little, three ounces of the oil nearly boiling hot, triturating it constantly. A mixture is obtained of the consistence of turpentine. Dissolve it in about six ounces of boiling water, and the soap will unite into a mass as the water cools. If it still contain an excess of acid, dissolve it again in boiling water, and continue this process till the soap is perfectly neutralised.
1. Soap of sulphuric acid and linseed oil.—It dissolves entirely in water. The solution is opaque, of a bluish white colour, viscid, and frothless when agitated. Alcohol dissolves it. The solution is transparent and brown. Potash decomposes it, forming sulphate of potash. The oil floats on the top, of the consistence of wax. Ammonia decomposes it; and if too much be added it forms soap of ammonia. Magnesia, lime, nitric acid, and muriatic acid, also decompose it. Distilled, it yielded a few drops of water and an oil, which coagulated, and was of the consistence of wax.
2. Soap of sulphuric acid and oil of almonds.—Soluble in water; solution milky.—Frothless.—Soluble in alcohol; solution brown and transparent. Potash, lime, nitric acid, muriatic acid, sulphuric acid (the oil separated assumed the consistence of turpentine), tartar, acidulous oxalat of potash, sal ammoniac, muriat of lead and zinc decompose it. It is not decomposed by vinegar, boracic acid, acetate of ammonia, borax, copper, tin, nor lead. When distilled, there passed over a little water and an oil, which coagulated and melted very readily; there remained behind a coat.
3. Soap of sulphuric acid and olive oil.—It is brown, and of the consistence of wax. Solution in hot water is white, opague, viscid; frothless. Solution in alcohol transparent and brown. Potash, ammonia, magnesia, nitric acid, muriatic acid, vinegar, nitre, sal ammoniac, acetate of lead and white oxyd of lead decompose it.
4. Soap of sulphuric acid and butter of cocoa.—It is of a hard, and marbled like Venice soap. Solution in water is grey, opague, viscid; frothless. Solution in alcohol yellow and transparent. Potash, ammonia, nitric, muriatic acids, tartar, sal ammoniac, tartrate of potash, acetate of lead, and zinc in powder, decompose it. When distilled, there came over water, an oil that coagulated, and a few drops of a black oil, which also congealed; both were inacid.
5. Soap of sulphuric acid and wax.—It is white, and becomes very hard. Its solution in water is white, and opague, and frothless. Its solution in alcohol is yellow and transparent. Potash, ammonia, nitric and muriatic acids decompose it.
6. Soap of sulphuric acid and spermaceti.—It is of a brown. It dissolves in water; the solution is milky, viscid, and frothless on agitation. It dissolves in alcohol; the solution is transparent and yellow. It is decomposed by as much alkali as saturates the acid; if more be added, it unites with the oil and forms a new soap. Lime and magnesia decompose it. The oil is also separated, and appears in the form of a coagulum on adding to the solution nitric acid, muriatic acid, tartar, nitre, nitrat of soda, common salt, and zinc in powder; but not on adding vinegar, tin, lead.
7. Soap of sulphuric acid and oil of eggs.—Its solution in water is white, opague, viscid; frothless; that in alcohol yellow and transparent. Alkalis decompose it; but if too much be added a new soap is formed. Nitric and muriatic acids separate the oil of the consistence of wax, wax, the first yellow, the last a deep brown. Nitre, sal ammoniac, acetite of lead, iron filings, zinc powder, decompose it; vinegar, borax, filings of lead do not.
To unite this acid with the essential oils, three ounces were put into a glass mortar, and four ounces of the oil were added, drop by drop, and care taken to prevent its becoming hot; equal parts of water were then poured on, and the whole heated slowly nearly to the temperature of boiling water; on cooling, the soap united into a brown mass.
8. Soap of sulphuric acid and turpentine. It is brown, and of the confluence of soft wax. Its solution in water is grey, opaque, viscid; frothless; its solution in alcohol is brown and transparent. Alkalies decompose it; with too much it forms at the boiling heat a new soap.
Nitric and muriatic acids separated the oil thickened, as did also white oxyd of lead, nitric of lead, nitric of soda, and iron filings; but acetic acid, boric acid, tartarite of potash, and tin filings, produced no such effect.
9. Soap of sulphuric acid and amber oil.—Its solution in water and alcohol as in the last soap. Alkalies, magnesia, and lime, decomposed it. Nitric and muriatic acids separated the oil of the confluence of wax. Tartar, sal ammoniac, nitric of antimony, acetite of lead, iron filings, decomposed it; vinegar, acetite of ammonia, and lead did not.
Mr Achard, to whom we owe these soaps, could not succeed in his attempts to form soaps with nitric and muriatic acids.
**Chap. II. Of Neutral Salts.**
The word salt has been used in chemistry in a very extensive, and not very definite sense. Every body which is fapidly melted, soluble in water, and not combustible, has been called a salt.
Salts were considered by the older chemists as a class of bodies intermediate between earths and water. Many disputes arose about what bodies ought to be comprehended under this class, and what ought to be excluded from it. Acids and alkalies were allowed by all to be salts; but the difficulty was to determine concerning earths and metals. Several of the earths possess all the properties which have been ascribed to salts; and the metals are capable of entering into combinations which possess saline properties. It is needless for us to enter into this dispute at present, as we have taken the liberty, in imitation of some of the best modern chemists, to expunge the class of salts altogether, and to arrange those subordinate classes, which are usually referred to it, under distinct heads.
The word neutral salt was originally applied exclusively to combinations of acids and alkalies, which were considered as substances possessing neither the properties of acids nor alkalies, but properties intermediate between the two. But the word is now always taken in a more extensive sense, and signifies all compounds formed by the combination of acids with alkalies, earths, or metallic oxides. In these compounds, the earth, alkali, or oxide, is denominated the base. Each order of salts is denominated after the acid which enters into its composition; and every individual salt is distinguished by subjoining the name of its base. Thus all the salts into which sulphuric acid enters are called sulphates, and the salt formed by the combination of sulphuric acid and potash is called sulphate of potash.
It is evident, then, that there must be as many orders of neutral salts as there are acids; and as many salts in each order as there are alkalies, earths, and metallic oxides, supposing every acid capable of combining with every one of these substances. But besides these simple combinations of one acid and one base, there are others more complex, composed of two acids combined with one base, or two bases combined with one acid, or a neutral salt combined with an acid or a base. These combinations have been called triple salts; and they increase the number of neutral salts very considerably.
In the following sections we shall take a short view of the properties of the principal neutral salts at present known; for this wide and important region of chemistry is still very far from being completely explored.
**Sect. I. Of Sulphates.**
Sulphuric acid is capable of combining with all the alkalies, with alkaline earths, alumina, jargonica, and the greater number of the metallic oxides. The principal neutral salts which it forms are as follows:
1. Sulphate of potash.—This salt may be formed by saturating dilute potash with sulphuric acid, and then evaporating the solution gently till crystals are formed. It seems to have been known at a very early period by chemists, and a great variety of names were given to it, according to the manner of forming it, or the fancy of the operator. Some of these names were: *specificum purgans*, *nitrum fixum*, *arcuatum duplicatum*, *panacea balatifica*, *sal de dubius*, *sal falsi brevis glafer*, &c.; but it was commonly known by the name of vitriolated tartar till the French chemists called it *sulfate of potash*, when they formed their new nomenclature in 1787 (x).
When the solution of sulphate of potash is sufficiently diluted, it affords by evaporation hexahedral pyramids, or short hexagonal prisms, terminated by one or more hexangular pyramids. But these crystals vary much in their figure, according to the care with which they are prepared.
It has a very disagreeable bitter taste. Its specific gravity is 2.293 (y).
It is soluble in the temperature of 60° in 16 times its weight of water; in a boiling heat, it is soluble in 5 times its weight.
According to Bergman, it is composed of 40 parts of acid, 52 parts of alkali, and 8 of water; but according to Kirwan, whose experiment has been already described, it is composed of 45 parts of acid and 55 of alkali.
It suffers no alteration in the air.
When placed upon burning coals, it breaks into pieces with a noise resembling a number of small explosions succeeding each other at short intervals (z), but suffers no other alteration. In a red heat it melts.
It has hitherto been applied to little use. It is a purgative.
(x) Bergman called it *alkali vegetabile vitriolatum*, and Morveau *vitriol of potash*.
(y) This is called *decrepitation*. purgative, but its disagreeable taste prevents it from being much employed for that purpose.
It often has an excess of acid, owing, as Mr Bergman and Morveau have very ingeniously explained, to an affinity which exists between this salt and sulphuric acid.
It is decomposed by compound affinity by the following salts:
Nitrat of soda (m), Nitrat of silver, lime, lead, barytes*, acetite of barytes, florites†, muriat of lime †, ammonia, lead ‡, magnesia, magnesia? mercury, soda §.
It is sometimes luminous in the dark, as Mr Glauber has observed*.
2. Sulphat of soda.—This salt was first discovered by Glauber a German chemist, and for that reason was long known by the name of Glauber's salt. He himself called it sal mirabile. It may be prepared by saturating soda with sulphuric acid, but is more usually obtained by decomposing common salt in order to procure muriatic acid.
Its crystals are transparent, and when formed by slow evaporation, are six-sided prisms terminated by dihedral summits.
Its taste at first has some resemblance to that of common salt, but soon becomes very disagreeably bitter.
It is soluble in twice its own weight of water at the temperature of 60°, and in its own weight of boiling water.
It is composed, according to Bergman, of 27 parts of acid, 15 of alkali, and 58 of water; but, according to the experiments of Kirwan, of 22 parts of acid, 17 of alkali, and 61 of water.
When exposed to the air, it loses great part of its water, and falls into a white powder (n).
When exposed to heat, it first undergoes the watery fusion (o), then its water is evaporated, it is reduced to a white powder, and at last in a red heat it melts.
Mr Kirwan has observed, that part of the acid, as well as the water, is driven off by the application of a strong heat †.
This salt is used as a purgative.
It often combines with an excess of acid.
It is decomposed by compound affinity by the following substances.
Nitrat of lime, Acetite of barytes, magnesia, potas, muriat of potas, lime, soda, carbonat of barytes, magnesia, potas, lime ‡.
3. Sulphat of ammonia.—This salt was discovered by Glauber, and called by him secret sal ammoniac. It was also called vitriolated ammoniac. It may be prepared by saturating ammonia with sulphuric acid.
Its crystals are generally small six-sided prisms, whose planes are unequal, terminated by six-sided pyramids.
It has a sharp bitter taste.
It is soluble in twice its own weight of water at the temperature of 60°, and in its own weight of boiling water.
According to Mr Kirwan, it is composed of 29.7 of alkali, 55.7 of sulphuric acid, and 14.6 of water ||.
When exposed to the air, it slowly attracts moisture.
When heated, it first decrepitates, then melts, and in close vessels sublimes, but with some loss of its alkali †.
It has not hitherto been applied to any use.
It is apt to contain an excess of acid.
It is decomposed by compound affinity by the following salts:
Nitrat of lime, Acetite of soda, magnesia, barytes, mercury?, lime, muriat of potas, magnesia, soda, carbonat of potas, barytes, soda, lime, barytes, magnesia, lime, mercury*, magnesia, acetite of potas, phosphat of lime ‡.
4. Sulphat of barytes. This substance was first discovered by Scheele. It abounds in nature. It is generally in the form of a hard very heavy stone.
It is sometimes found crystallized; but the variety of sulphat forms is so great that they baffle all description.
It is soluble in 43,000 times its weight of water at the temperature of the atmosphere *.
Sulphuric acid dissolves it when concentrated and boiling, but it is precipitated by the addition of water.
When exposed to heat it melts, and, if the heat be very strong, gradually dissolves.
After being heated red hot, it has the property of being luminous in the dark. This was first observed in a variety of this substance known by the name of Bologna stone. Lemery informs us, that this property was first discovered by an Italian shoemaker named Vincenzo Caffiarolo. This man found a Bologna stone at the foot of Mount Paterno, and its brightness and gravity made him suppose that it contained silver. Having exposed it to the fire, doubtless in order to extract from it the precious metal, he observed that it was luminous in the dark. Struck with the discovery, he repeated the experiment, and it constantly succeeded with him.
From an experiment of Mr Klaproth, it appears to be composed of 33 parts of acid and 77 of barytes.
It is decomposed by compound affinity by the following salts:
Nitrat of soda, Nitrat of magnesia, lime, carbonat of potas, ammonia, soda ‡.
5. Sulphat of lime. This substance was well known to the ancients under the name of gypsum; but the composition of gypsum was not known till Margraf and Macquer analyzed it, and proved that it was composed of sulphuric acid and lime. The artificial compound
(m) Most of these double decompositions in this and the following sections are inserted on the authority of Morveau. See his table of Affinity, page 360 of this article.
(n) This is called efflorescing.
(o) When substances melt by means of the water they contain on the application of heat, they are said to undergo the watery fusion. It is found crystallized in various forms, sometimes transparent and sometimes opaque; and when pure it is of a white colour.
It has a slightly nauseous taste, scarcely perceptible except by drinking a glass of water impregnated with it.
It is soluble in 500 parts of water at the temperature of 60°, but much more soluble in boiling water.
It is composed, according to Bergman, of 46 parts of acid, 32 of earth, and 22 of water; according to the late experiments of Mr Kirwan, when far dried as still to retain its glassy appearance, it contains 48 of acid, 34 of earth, and 18 of water; which differs very little from the determination of Bergman.
It is not affected by exposure to the air.
It is soluble in sulphuric acid.
When exposed to heat, it undergoes a kind of watery fusion, but afterwards it cannot be melted by the strongest heat. In a clay crucible indeed it fuses at 130° Wedgwood, owing evidently to the presence of the clay.
When heated red hot and cooled, it is called plaster of Paris; a substance so useful for casting moulds, &c., on account of its property of becoming solid almost immediately when reduced into a paste with water.
By compound affinity it is decomposed by the following substances:
- Acetite of barytes, - Carbonat of potas, - Potas, - Foda, - Carbonat of barytes, - Magnesia, - Alumina.
6. Sulphate of strontites. This salt, first formed by Dr Hope, is a white powder destitute of taste. It is soluble in 384 parts of boiling water. Sulphuric acid dissolves it readily when assisted by heat, but it is precipitated by the addition of water to the solution.
7. Sulphate of magnesia. This salt was first observed in the springs at Epsom in England by Grew in 1675; but Dr Black was the first who accurately ascertained its composition. It has been called Epsom salts, salt carbonatic amarus, and Seyller salt.
It crystallizes in quadrangular prisms, whose plains are equal, surmounted by quadrangular pyramids.
It has an excessively bitter taste.
At the temperature of 60° it is soluble in its own weight of water, and in 4ths of its weight of boiling water. The volume of water is increased 4th by adding the salt.
It is insoluble in alcohol.
It is composed, according to Bergman, of 19 parts of earth, 33 of acid, and 48 of water; according to Mr Kirwan, of 17 parts of earth, 29.46 of acid, and 53.54 of water.
When exposed to the air it effloresces, and is reduced to powder.
When exposed to heat it undergoes the watery fusion, and by increasing the temperature its water is evaporated, but it cannot be decomposed by means of sulphuric heat.
It is sometimes employed as a cathartic, but its chief use is to furnish magnesia by its decomposition.
It is decomposed by compound affinity by the following farts:
- Murat of potas, - Acetite of lime, - Foda (r), - Carbonat of barytes, - Lime, - Potas, - Acetite of barytes, - Foda (r), - Potas, - Ammonia (q).
8. Sulphate of ammonia and magnesia. This triple sulphate of salt was discovered by Mr Fourcroy. Into the solution ammonia of 100 parts of sulphate of magnesia in 500 parts of water, 12 parts of ammonia being poured, a very small quantity of magnesia was precipitated; and a considerable quantity more on the addition of another dose of ammonia; but farther additions had no effect. From the magnesia precipitated, it appeared that 38 parts of the sulphate had been decomposed. There remained, therefore, 62 parts in solution, mixed with a large quantity of ammonia. By evaporation, 92 parts of a white transparent rhombohedral salt were obtained, evidently composed of sulphuric acid, ammonia, and magnesia, in the proportions that would have formed 62 parts of sulphate of magnesia and 30 of sulphate of ammonia, and probably consisting of a combination of these two sulphates.
9. Sulphate of alumina. This salt may be formed by dissolving alumina in sulphuric acid. It has an attrac-
(1) Only below the temperature of 32°. (2) Only below the temperature of 212°.
Scheele, Gren, Ann. de Chim., xxiii. Fourcroy, Ann. de Chim., ii. 291. It has been long known, indeed, that one of its ingredients is sulphuric acid (r); and the experiments of Geoffroy, Hellot, Pott, Margraf, and Macquer, proved incontrovertibly that alumina is another ingredient. But sulphuric acid and alumina are incapable of forming alum: Manufacturers knew, that the addition of a quantity of potash, or of ammonia, or of some substance containing these alkalies, is almost always necessary; and it was proved, that in every case in which such additions are unnecessary, the earth from which the alum is obtained contained already a quantity of potash. Various conjectures were made about the part which potash acts in this case; but Chaptal and Vauquelin appear to have been the first chemists that ascertained by decisive experiments that alum was a triple salt, composed of sulphate of alumina and of potash united together (s).
Alum crystallizes in large octahedrons, composed of two tetrahedral pyramids, applied to each other at their bases.
It has a sweetish and astringent taste, and always reddens the tincture of turpentine.
It is soluble at the temperature of 60°, in from 10 to 15 times its own weight of water, according to its purity; pure alum being most insoluble. Seventy-five parts of boiling water dissolve 100 of alum.
A hundred parts of alum contain, according to Kirwan, 17.62 parts of acid, 18 of earth (and alkali), and 64.78 of water.
When exposed to the air it effloresces slightly.
When exposed to a gentle heat it undergoes the watery fusion. A strong heat causes it to swell and foam, and to lose about 44 per cent. of its weight, consisting chiefly of water of crystallization. What remains is called calcined or burnt alum, and is sometimes used as a corrosive.
Alum is of great importance as a mordant in dyeing, and is used also in several other arts.
By compound affinity it is decomposed by the following salts:
| Nitrate of soda, | Acetate of potash, | |-----------------|--------------------| | lime | soda | | ammonia | lime | | magnesia | ammonia | | Muriate of barytes, | Carbonate of barytes, | | potash | potash | | soda | soda | | lime | lime | | ammonia | ammonia | | magnesia | magnesia |
If three parts of alum and one of flour or sugar be melted together in an iron ladle, and the mixture dried so till it becomes blackish and ceases to swell; if it be then pounded small, put into a glass phial, and placed in a sand-bath till a blue flame issues from the mouth of the phial, and after burning for a minute or two be allowed to cool (t), a substance is obtained known by the name of Homberg's pyrophorus, which has the property of catching fire whenever it is exposed to the open air, especially if the air be moist.
This substance was accidentally discovered by Homberg about the beginning of the 18th century, while he was engaged in his experiments on the human faeces. He had distilled a mixture of human faeces and alum till he could obtain nothing more from it by means of heat; and four or five days after, while he was taking the residue out of the retort, he was surprised to see it take fire spontaneously. Soon after Lemeroy the Younger discovered that honey, sugar, flour, or almost any animal or vegetable matter, could be substituted for human faeces; and afterwards Mr Lejou de Suvigny showed that several other fats containing sulphuric acid might be substituted for alum.
Scheele proved, that an alum deprived of potash was incapable of forming pyrophorus, and that sulphate of potash might be substituted for alum. And Mr Proult has shown, that a number of neutral salts, composed of vegetable acids and alkalies, or earths, when distilled by a strong fire in a retort, left a residue which took fire spontaneously on exposure to the air.
These facts have thrown a great deal of light on the nature of Homberg's pyrophorus, and enabled us in some measure to account for its spontaneous inflammation. It has been ascertained, that part of the sulphuric acid is decomposed during the formation of the pyrophorus, and of course a part of the alkaline base becomes uncombined with acid, and the carbon, which gives it its black colour, is evidently divided into very minute particles. It has been ascertained, that during the combustion of the pyrophorus a quantity of oxygen is absorbed. The inflammation seems to be owing to a disengaging affinity. Part of the carbon and of the sulphur attract oxygen from the atmosphere, in order to combine with the potash, and the caloric disengaged produces a temperature sufficiently high to kindle the rest of the carbon.
Alum is capable of combining with alumina, and of forming what has been called alum saturated with its earth, which is an insoluble, tallow-like, earthy-like substance.
It is capable also, as Chaptal informs us, of combining with several other bases, and of forming many triple salts, which have never yet been examined with attention.
(r) Some chemists have thought proper to call the sulphuric acid, obtained by distilling alum, spirit of alum.
(s) This they did in the two memoirs above quoted, and which were first published in the 2nd volume of the Annales de Chimie. An account of Vauquelin's memoir has been already given under the article Alum in this Supplement. Chaptal's memoir is no less interesting. This celebrated chemist appears, from the facts stated in the 2nd volume of the Annales, p. 222, to have made his discovery before Vauquelin; who, however, was ignorant of what Chaptal had done, as he informs us in the Ann. de Chim. xxv. 107, that his paper was read to the Institute a fortnight before that of Chaptal's came to Paris. He informs us, too, that Decroixelles had long before made the same discovery, and that he had published it in Berthollet's Art de la Teinture.
(t) Care must be taken not to keep it too long exposed to the heat. 11. Sulphate of jargonia (v). In order to combine jargonia with acids, they should be poured upon it while it is yet moist, after being precipitated from some of its solvents; for after it is dry, acids do not act upon it without difficulty. By this method sulphate of jargonia is easily formed. It is white, and without sensible taste. Heat expels the acid from it, and the jargonia remains in a state of purity. At a high temperature charcoal converts it into a sulphuret, which is soluble in water, and which, by evaporation, furnishes crystals of hydro-sulphuret (v) of jargonia.
Klaproth informs us, that with excess of acid sulphate of jargonia forms transparent stelliform crystals, soluble in water, and having an astringent taste.
12. Sulphate of iron. There are two sulphates of iron, which were first accurately distinguished by Mr. Proult. The one contains the green oxyd, the other the red oxyd of iron. We shall, in imitation of Mr. Proult, designate them from their colours.
The green sulphate of iron.—This salt, which is composed of sulphuric acid and green oxyd of iron, is found native, and was known to the ancients. It is mentioned by Pliny under the names of molybdites, calchium. It was formerly called green vitriol.
It is generally prepared by exposing native sulphuret of iron, a very abundant mineral, to air and moisture. Its crystals are of a light green colour, and in the form of rhombohedral parallelepipeds.
It has a sharp astringent taste.
It is soluble in five times its weight of water at the temperature of 60°, and in 4ths of its weight of boiling water.
It is insoluble in alcohol.
According to Bergman, it is composed of 39 parts of acid, 23 of oxyd, and 38 of water; but according to Mr. Kirwan, of 26 parts of acid, 28 (u) of oxyd, and 46 of water.
When exposed to the air, it effloresces; but if it be moistened, it is gradually converted into red sulphate of iron.
When heated, it first assumes a yellow colour, loses its water and its acid; if the heat be increased, nothing remains but a yellow powder.
The Prussian alkali precipitates from the solution of this salt a white powder, which gradually becomes blue by attracting oxygen.
It is used in dyeing, and in making ink, &c.
It is decomposed by compound affinity, by
Nitrat of silver,
Muriat of soda.
The red sulphate of iron may be formed by exposing a solution of green sulphate to the air, or by treating it with nitric acid. It was formerly called mother water of vitriol.
Little is known of its properties, except that it is deliquescent, incrustable, and soluble in alcohol.
It was first accurately examined by Mr. Proult.
The green sulphate of iron generally contains some of it, which may be separated by means of alcohol.
It is alone capable of forming Prussian blue with the Prussian acid, and of striking a black colour with the gallic acid.
We have observed, that when it is diluted with water, and an excess of sulphuric acid is poured in, it is again slowly converted into green sulphate.
13. Sulphate of zinc.—This salt, according to the best accounts, was discovered at Rammelfangen in Germany, about the middle of the 16th century.
Jargonia, or, as the French chemists call it, zirconia, has been discovered in great abundance in France by Morveau, who found that the hyacinths of Expilly contained more than half their weight of it. From Vauquelin's analysis they appear to be composed of
| Parts | |-------| | 32 | parts of silica, | | 64 | jargonia, | | 2 | oxyd of iron. |
Jargonia has been examined with great care by these two philosophers, the experiments of Klaproth have been confirmed, and several new properties of it have been discovered. Perhaps a more detailed account than we have hitherto given of this new earth may not be unacceptable to our readers.
Jargonia is a white powder, its specific gravity is considerable, it has a feel resembling that of silica, it has no taste, and is insoluble in water. When separated from its solutions by pure alkalies, it retains, when exposed to the air to dry, a pretty considerable quantity of water, which renders it transparent, and gives it a resemblance to gum arabic both in its colour and fracture.
When exposed to the heat of the blow-pipe it does not melt; but Vauquelin melted it by exposing it surrounded with charcoal in a porcelain crucible to an intense heat for an hour and a half. Its specific gravity was then 4.35; its colour was grey, and its hardness such that it was capable of scratching glass. It melts with borax, and forms a transparent and colourless glass; but phosphat of soda and the fixed alkalies do not attack it.
It is insoluble in the fixed alkalies, has very little affinity for carbonic acid, and is precipitated from its solutions together with iron by the Prussian alkali.
Its affinities, as far as they have been ascertained by Vauquelin, are as follows:
- Vegetable acids, order unknown, - Sulphuric acid, - Muriatic, - Nitric.
See upon this subject the Memoirs of Morveau and Vauquelin, Ann. de Chim., xxii. 72, and xxii. 179.
These curious salts form the subject of the next chapter.
Perhaps the quantity of oxyd is somewhat over-rated here; for before it was examined by Mr. Kirwan, it had assumed a red colour; it must therefore have been converted into the brown or red oxyd by attracting oxygen from the atmosphere. It is of a white colour, and its crystals are rhombohedral prisms, terminated by quadrangular pyramids; there is generally a slight defect in two of the opposite angles of the prism, which produces a quadrangular section. Its specific gravity is 2,000.
It has a sharp acetylic taste.
It is soluble in 2,28 parts of water at the temperature of 60°; but in a much smaller quantity of boiling water.
It is composed, according to Bergman, of 40 (v) parts of acid, 20 of oxyd, and 40 of water: Kirwan supposes, that it is composed of 12 parts of acid, 26.4 of zinc, 20 of oxyd, 41.6 of water (w).
According to Bergman, this salt is not altered in the air; others affirm that it effloresces. This, no doubt, depends upon the place where it is kept.
Heat decomposes this salt.
14. Sulphat of manganese.—This salt was first obtained by Scheele (x): It is composed of sulphuric acid and white oxyd of manganese.
Its crystals are oblique parallelopipeds; they are of a white colour, and very bitter.
These crystals are decomposed by a strong red heat, and the sulphuric is converted into sulphurous acid by the oxyd attracting its oxygen, and being changed into black oxyd.
15. Sulphat of nickel.—This salt, which is composed of sulphuric acid and oxyd of nickel, was first described by Bergman. Its crystals are in the form of decahedrons, composed of two quadrangular truncated pyramids; they are of a green colour.
16. Sulphat of cobalt.—This salt was first mentioned by Mr Brandt. Its crystals are of a reddish colour; but if any nickel be present, they are green.
17. Sulphat of lead.—This salt has been long known: it is composed of sulphuric acid and white oxyd of lead. The crystals are white, small, and most commonly needle-shaped: according to Sage, they are tetrahedral prisms.
It is soluble in 18 parts of water.
Heat decomposes it.—It is very caustic.
18. Sulphat of tin.—Nothing is known concerning this salt, except that it crystallizes in fine needles interlaced with one another.
19. Sulphat of copper.—This salt appears to have been known to the ancients. It is generally obtained by evaporating those waters which naturally contain it. It is called also blue vitriol.
Its crystals are of a deep blue colour; they are in the form of oblong rhomboids. Its specific gravity is 2,230.
It has a very strong acetylic taste; and indeed is employed as a caustic.
It is soluble in four parts of water at the temperature of 60°; but in a much smaller quantity of boiling water.
It is composed, according to Bergman, of 46 parts of acid, 26 of oxyd of copper, and 28 of water. Kirwan supposes it to contain 27,68 of acid, 35 of oxyd, and 37,32 of water.
When exposed to the air, it effloresces, and is covered with a yellowish grey powder.
It requires a very strong heat to decompose it.
It has the property of communicating a green colour to flame.
It is used in the preparation of several paints, and for a variety of other purposes.
It is decomposed by compound affinity, by acetite of lead.
20. Sulphat of bismuth.—Little is known of this salt, except that it is with difficulty crystallized, and is highly deliquescent.
21. Sulphat of antimony.—This salt does not crystallize. It is easily decomposed by heat.
22. Sulphat of arsenic.—This salt is scarcely known. It does not appear to be crystallizable. It is decomposed by water.
23. White sulphat of mercury.—This salt may be formed by boiling together two parts of mercury and three of concentrated sulphuric acid, and stopping the process whenever the mercury is converted into a white mass. This mass, in order to remove the excess of acid, is to be washed repeatedly with small portions of water, till it ceases to redden turnsole. The sulphat of mercury, thus obtained, is very white. Its crystals are either small plates or prisms. Its taste is not very caustic. It is soluble in 500 parts of water at the temperature of 55°, and in 287 parts of boiling water. It is composed of 83 parts of white oxyd of mercury, 12 of sulphuric acid, and 5 of water. It is not altered by exposure to the air. Heat decomposes it.
This sulphat is capable of combining with a new portion of acid: It was in that state before it was washed with water. This salt, which may be called acridulous white sulphat of mercury, has a very caustic taste, and is corrosive. It reddens vegetable blues. It is soluble in 157 parts of water at the temperature of 55°, and in 33 parts of boiling water.
24. Yellow sulphat of mercury.—This salt may be obtained by continuing to boil the preceding mixture of mercury and sulphuric acid till the mercury assumes a yellow colour. It appears to be composed of yellow oxyd of mercury and a small portion of sulphuric acid. It is soluble in 2000 parts of water at the temperature of 55°, and in 600 parts of boiling water. The solution is colourless. It was formerly called turbit mineral.
25. Sulphat of ammonia and mercury.—This triple salt may be formed by pouring ammonia into a solution of sulphat of mercury. If only a small quantity of ammonia be used, a copious blackish precipitate takes place, part of which is converted into running mercury by exposure to light; and consequently is black oxyd of mercury; the remaining part is the triple salt. If a large quantity of ammonia be used, only the black oxyd... When exposed to the air, it effloresces, becomes sulphite, opaque and hard, and is gradually converted into sulphate of potash by absorbing oxygen.
When exposed to a sudden heat, it decrepitates, loses its water; at a red heat some sulphurous vapours are emitted; at last a portion of sulphur separates, and the residuum is sulphate of potash, with a slight excess of alkali.
Nitric and oxy-muriatic acids convert it into sulphate of potash by imparting oxygen.
It decomposes the oxys of gold, silver, mercury, the red oxys of lead, the black oxys of manganese, and the brown oxys of iron. When the green oxys of iron and the white oxys of iron are boiled with it in water, and an acid added, a precipitate takes place of these bodies united to some sulphur, and the salt is converted into a sulphate; at the same time sulphurated hydrogen gas is emitted.
By compound affinity it is decomposed by:
All salts with base of soda, except the borat and carbonat;
All metallic salts except carbonat;
All neutral salts whose acid has a stronger affinity for potash than sulphurous acid has.
2. Sulphate of soda.—This salt was first accurately described by Fourcroy and Vauquelin.
It is white and perfectly transparent. Its crystals are four-sided prisms, with two very broad sides and two very narrow ones, terminated by dihedral pyramids.
Its taste is cool and sulphurous.
It is soluble in four times its weight of cold water, but it is more soluble in hot water.
It is composed of 18.8 parts of soda, 31.2 of acid, and 50 of water.
By exposure to air, it effloresces, and is slowly converted into a sulphate.
When exposed to heat, it undergoes the watery fusion, and afterwards exhibits precisely the same phenomena as the sulphate of potash.
Metallic oxys and salts affect it precisely as they do sulphate of potash.
It is decomposed by compound affinity by carbonat of potash, and the other salts which decompose sulphate of potash.
3. Sulphate of ammonia.—This salt was first described by Fourcroy and Vauquelin.
It crystallizes in six-sided prisms terminated by five-sided pyramids.
Its taste is cool and penetrating like that of the other ammoniacal salts, but it leaves a sulphurous impression in the mouth.
It is soluble in its own weight of cold water. Its solubility is increased by heat.
It is composed of 29.07 parts of ammonia, 60.93 of acid, and 10.87 of water.
When exposed to the air, it attracts moisture, and is soon converted into a sulphate.
Heat volatilizes it without decomposition.
Its habitudes with metallic oxys and salts are nearly the same with those of the above described sulphites, sulphate of potash only it is capable of forming with several of them triple barter salts.
4. Sulphate of barytes.—This salt was first described by Berthollet.
It is very insoluble; it has no perceptible taste; and is perfectly insoluble in water.
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Sect. II. Of Sulphites.
Salts composed of sulphurous acid united respectively with alkalies, earths, or oxys, are called sulphites.
Those hitherto examined are the following:
1. Sulphite of potash.—This salt was first formed by Stahl; but was first accurately described by Berthollet, Fourcroy, and Vauquelin.
It may be formed by passing sulphurous acid into a saturated solution of carbonat of potash till all effervescence ceases. The solution becomes hot, and crystallizes by cooling.
Its crystals are white and transparent; their figure that of rhomboidal plates. Its crystallization often presents small needles diverging from a common centre.
Its taste is penetrating and sulphurous. At the common temperature of the atmosphere, it is soluble in its own weight of water, but much more soluble in boiling water.
When exposed to the air, it effloresces, becomes sulphite, opaque and hard, and is gradually converted into sulphate of potash by absorbing oxygen.
When exposed to a sudden heat, it decrepitates, loses its water; at a red heat some sulphurous vapours are emitted; at last a portion of sulphur separates, and the residuum is sulphate of potash, with a slight excess of alkali.
Nitric and oxy-muriatic acids convert it into sulphate of potash by imparting oxygen.
It decomposes the oxys of gold, silver, mercury, the red oxys of lead, the black oxys of manganese, and the brown oxys of iron. When the green oxys of iron and the white oxys of iron are boiled with it in water, and an acid added, a precipitate takes place of these bodies united to some sulphur, and the salt is converted into a sulphate; at the same time sulphurated hydrogen gas is emitted.
By compound affinity it is decomposed by:
All salts with base of soda, except the borat and carbonat;
All metallic salts except carbonat;
All neutral salts whose acid has a stronger affinity for potash than sulphurous acid has.
2. Sulphite of soda.—This salt was first accurately described by Fourcroy and Vauquelin.
It is white and perfectly transparent. Its crystals are four-sided prisms, with two very broad sides and two very narrow ones, terminated by dihedral pyramids.
Its taste is cool and sulphurous.
It is soluble in four times its weight of cold water, but it is more soluble in hot water.
It is composed of 18.8 parts of soda, 31.2 of acid, and 50 of water.
By exposure to air, it effloresces, and is slowly converted into a sulphate.
When exposed to heat, it undergoes the watery fusion, and afterwards exhibits precisely the same phenomena as the sulphate of potash.
Metallic oxys and salts affect it precisely as they do sulphate of potash.
It is decomposed by compound affinity by carbonat of potash, and the other salts which decompose sulphate of potash.
3. Sulphite of ammonia.—This salt was first described by Fourcroy and Vauquelin.
It crystallizes in six-sided prisms terminated by five-sided pyramids.
Its taste is cool and penetrating like that of the other ammoniacal salts, but it leaves a sulphurous impression in the mouth.
It is soluble in its own weight of cold water. Its solubility is increased by heat.
It is composed of 29.07 parts of ammonia, 60.93 of acid, and 10.87 of water.
When exposed to the air, it attracts moisture, and is soon converted into a sulphate.
Heat volatilizes it without decomposition.
Its habitudes with metallic oxys and salts are nearly the same with those of the above described sulphites, sulphate of potash only it is capable of forming with several of them triple barter salts.
4. Sulphate of barytes.—This salt was first described by Berthollet.
It is very insoluble; it has no perceptible taste; and is perfectly insoluble in water. It is composed of 59 parts of barytes, 39 parts of acid, and 2 of water.
It does not easily change into a sulphate by exposure to air; but heat produces this effect.
5. Sulphite of lime.—This salt was first described by Berthollet.
Its crystals are six-sided prisms, terminated each by a very long pyramid.
It has scarcely any taste; however, when kept long in the mouth, it communicates to the tongue a taste which is manifestly sulphurous.
It is very sparingly soluble in water, except with excess of acid.
It is composed of 47 parts of lime, 48 of sulphurous acid, and 5 of water.
By contact of air it is converted into a sulphate, but very slowly.
Heat converts it into a sulphate by depriving it of a portion of sulphur.
It is decomposed by compound affinity by:
1. Carbonates of alkalies. 2. Phosphates of alkalies. 3. Most metallic salts.
6. Sulphite of magnesia.—This salt was first described by Fourcroy and Vauquelin.
Its crystals are white and transparent, and in the form of deformed tetrahedrons.
Its taste is mild and earthy at first, and afterwards sulphurous.
It is sparingly soluble in water, except when there is an excess of acid.
It is composed of 16 parts of magnesia, 39 of acid, and 45 of water.
It becomes opaque when exposed to the air; is very slowly converted into a sulphate.
By exposure to heat, it softens, swells up, and becomes ductile like gum; a strong heat decomposes it altogether.
It is decomposed by:
Alkaline salts, Earthy salts, except those of alumina.
7. Sulphite of alumina.—First formed by Berthollet.
It does not crystallize, but is converted into a soft mass. It is not soluble in water, but becomes abundantly so when there is an excess of acid.
It is composed of 44 parts of alumina, 32 of acid, and 24 of water.
Heat decomposes it.
8. Sulphite of iron.—It was first formed by Berthollet.
Its crystals are white, and have but very little of the acrid taste of iron salts.
Berthollet also formed the sulphites of zinc and tin, but he has not described them.
Sect. III. Of Nitrates.
Those salts, in the composition of which the nitric acid forms one ingredient, are called nitrates.
1. Nitrat of potash, nitre, or saltpetre.—As this salt is produced naturally in considerable quantities, particularly in Egypt, it is highly probable that the ancients were acquainted with it; but scarcely anything certain can be collected from their writings. If Pliny mentions it at all, he confounds it with soda, which was known by the names of nitron and nitrum. It is certain, however, that it has been known in the east from time immemorial. Roger Bacon mentions this salt in the 13th century under the name of nitre.
It crystallizes in slender oblong hexagonal prisms, often striated, terminated by hexagonal pyramids obliquely truncated. Its specific gravity is 1.920.
Its taste is sharp, bitterish, and cooling.
It is soluble in seven times its weight of water at the temperature of 60°, and in nearly its own weight of boiling water.
According to Bergman, it is composed of 31 parts of acid, 61 of potash, and 8 of water; but this proportion of acid is undoubtedly too small. According to Mr Kirwan, it is composed of 41.2 of acid, 46.15 of alkali, and 12.65 of water.
It is not altered by exposure to the air.
When exposed to a strong heat, it melts; and congeals by cooling into an opake mass, which has been called mineral crystal. If the heat be continued, the acid is gradually decomposed and driven off. When the solution of nitre is exposed to a boiling heat, part of the salt is evaporated along with the water, as Wallerius, Kirwan, and Lavoisier, observed lucidly. When nitre is exposed to heat along with many combustible substances, its acid is decomposed; the combustible feizes the oxygen, and at the same time a lively white flame appears, attended with a decrepitation; this is called the detonation of nitre.
Nitre mixed with charcoal and sulphur in proper proportions forms gunpowder.
Nitre is decomposed by compound affinities by Acetite of barytes.
No phenomenon has excited the attention of chemical philosophers more than the continual reproduction of nitre in certain places after it had been extracted from them. Prodigious quantities of this salt are necessary for the purposes of war; and as Nature has not laid up great magazines of it as she has of some other salts, this annual reproduction is the only source from which it can be procured. It became, therefore, of the utmost consequence, if possible, to discover the means which Nature employed in forming it, in order to enable us to imitate her processes by art, or at least to accelerate and facilitate them at pleasure. Numerous attempts accordingly have been made to explain and to imitate these processes.
Stahl, setting out on the principle that there is only one acid in nature, supposed that nitric acid is merely sulphuric acid combined with phlogiston; and that this combination is produced by putrefaction; he affirmed accordingly, that nitre is composed by uniting together potash, sulphuric acid, and phlogiston. But this opinion, which was merely supported by very far-fetched analogies, could not stand the test of a rigorous examination.
Lemery the Younger accordingly advanced another; affirming, that all the nitre obtained existed previously in animals and vegetables, and that it is formed in these substances by the processes of vegetation and animalization. But it was soon discovered that nitre exists, and is actually formed, in many places where no animal nor vegetable substance had been decomposed; and consequently, this theory was as untenable as the former. So far indeed is it from being true that nitre is formed alone by these processes, that the quantity of nitre in plants has been found to depend entirely on the soil in which they grow. At last by the numerous experiments of several French philosophers, particularly by those of Thouvenel, it was discovered that nothing else is necessary for the production of nitre but a basis of lime, heat, and an open, but not too free communication with dry atmospheric air. When these circumstances combine, the acid is first formed, and afterwards the alkali makes its appearance.
How the air furnishes materials for this production is easily explained, now that the component parts of the nitric acid are known to be oxygen and azot. But how lime contributes to their union it is not so easy to see. It is a disposing affinity, which, like most others referred to thatingular clas, our present knowledge of the nature of affinity does not enable us to explain. The appearance of the potas is equally extraordinary. If any thing can give countenance to the hypothesis, that potas is composed of lime and azot, it is this singular fact.
2. Nitrat of soda. This salt was called formerly cubic nitre.
It forms rhomboidal crystals. Its specific gravity is 1.870.
It has a cool sharp taste, and is somewhat more bitter than nitre.
It is soluble in about three parts of water at the temperature of 60°, and is scarcely more soluble in boiling water.
It is composed, according to Bergman, of 43 parts of acid, 32 of soda, and 25 of water. From an experiment formerly described, Mr Kirwan concludes, that it contains 57.6% of acid, and 42.3% of alkali; but perhaps the proportion of acid may be somewhat over-rated, as no direct proof has been brought that the salt contains no water.
When exposed to the air it rather attracts moisture.
Its phenomena in the fire are the same with those of nitre, only it does not melt so easily.
It is decomposed by compound affinity by the following salts:
- Sulphat of barytes, Muriat of ammonia, - potas, Acetite of barytes, - alumina, potas, - Muriat of barytes, Carbonat of barytes, - potas, potas, - lime,
3. Nitrat of ammonia. This salt crystallizes with difficulty into regular needles. It was formerly called nitrum fennovatile, and nitrum flammeum.
It has a sharp, acid, somewhat urinous taste.
It is soluble in about half its weight of boiling water.
It is composed of 58 parts of acid, about 26 of alkali, and 16 of water.
When exposed to the air it deliquesces.
When exposed to heat, it first undergoes the watery fusion, afterwards detonates, and is completely decomposed. Berthollet has shown, that this phenomenon is owing to the hydrogen of the alkali entering into combination with the oxygen of the acid, and forming water, while the acid flies off in a gaseous form.
By compound affinity it is decomposed by the following substances:
- Sulphat of barytes, Acetite of barytes, - potas, potas, - alumina, soda,
Acetite of lime, Muriat of lime, magnesia, magnesia, alumina, alumina, Muriat of barytes, Carbonat of barytes, potas, potas, foda, foda,
4. Nitrat of barytes. This salt may be formed into Nitrat of hexagonal crystals, but it requires great address to produce them.
It attracts moisture from the atmosphere.
Heat decomposes it, and leaves pure barytes. The decomposition of this salt by heat is the most convenient method of procuring pure barytes yet known. It was first proposed by Mr Vauquelin.
By compound affinity it is decomposed by
Alkaline carbonats, Oxalat of ammonia *.
5. Nitrat of lime. This salt forms by crystallization of six-sided prisms, terminated by decahedral pyramids, but more commonly small regular octahedral needles.
It has a sharp bitterish taste.
It is soluble in two parts of cold water, and in its own weight of boiling water.
Boiling alcohol dissolves its own weight of it †.
According to Bergman, it is composed of 43 parts of acid, 32 of lime, and 25 of water. Kirwan has found, that 100 parts of lime require for saturation 180 parts of acid ‡.
Nitrat of lime deliquesces when exposed to the air.
Heat decomposes it like all other nitrates.
By compound affinity it is decomposed by
Sulphat of barytes, Acetite of potas, potas, Carbonat of barytes, foda, potas, ammonia, foda, alumina, ammonia, Muriat of barytes, alumina, potas, magnesia,
Acetite of barytes, Tungstat of ammonia §.
6. Nitrat of strontites. This salt, first formed by Dr Hope, crystallizes readily, but the crystals are very irregular in their shape; sometimes they are hexagonal truncated pyramids; sometimes octahedrons, consisting of two four-sided pyramids united at their bases.
It is soluble in its own weight of water at the temperature of 60°, and in little more than half its weight of boiling water. It has a strong pungent taste.
In a dry air it effloresces, but in a moist air it deliquesces.
It deflagrates on hot coals. Subjected to heat in a crucible, it decrepitates gently, and then melts. In a red heat it boils, and the acid is dissipated. If a combustible substance be at this time brought into contact with it, a deflagration with a very vivid red flame is produced *.
7. Nitrat of magnesia. The composition of this salt was first ascertained by Dr Black.
Its crystals are quadrangular prisms. It has a very bitter taste. It is very soluble in water. Alcohol dissolves ¼ of its own weight of it †.
One hundred parts of magnesia require 255 of nitric acid for saturation ‡.
It deliquesces in the air, according to Bergman; but Dijonval affirms, that he has procured it in crystals which rather effloresce. It is decomposed by heat.
By compound affinity it is decomposed by
Sulphat of barytes, Murat of lime, potas, Acetite of barytes, foda, potas, ammonia, foda, alumina, lime, Murat of barytes, Carbonat of barytes, potas, potas, foda, lime.
8. Nitrat of ammonia and magnesia. This triple salt was discovered by Mr Fourcroy. Into a saturated solution of nitrat of magnesia, containing 73 grains of magnesia, he poured ammonia as long as any precipitate could be obtained. Twenty-one grains of magnesia were precipitated; 52 grains remained combined with the acid and the ammonia. He found that 52 grains of magnesia produced, when saturated with nitric acid, 288 grains of nitrat; and that the quantity of nitric acid necessary to saturate 21 grains of magnesia, when saturated with ammonia, produced 84 grams of nitrat of ammonia. He concludes, therefore, though the data are not quite satisfactory, that the triple salt is composed of 288 grams of nitrat of magnesia, and 84 of nitrat of ammonia.
9. Nitrat of alumina. This seems to have been first attended to by Baume. Its crystals are pyramidal. It has a very astringent taste. It is soluble in water, and deliquesces in the air.
10. Nitrat of jargonia. This salt may be easily formed by pouring nitric acid on newly precipitated jargonia.
It always contains an excess of acid. By evaporation a yellowish transparent matter is obtained, exceedingly tenacious and viscid, and which dries with difficulty. It has an astringent taste, and leaves on the tongue a viscid matter, owing to its being decomposed by the saliva. It is only very sparingly soluble in water; the greatest part remains under the form of gelatinous and transparent flakes. Like all the other salts into which jargonia enters, it is decomposed by heat. It is decomposed also by sulphuric acid, which occasions a white precipitate, soluble in excess of acid; by carbonat of ammonia, which produces a precipitate soluble by adding more carbonat; and by an infusion of nut galls in alcohol, which produces a white precipitate, soluble in an excess of the infusion; unless the jargonia contains iron; in which case the precipitate is a greyish blue, and part of it remains insoluble, giving the liquor a blue colour. This liquor, mixed with carbonat of ammonia, produces a matter purple by transmitted light, but violet by reflected light. Gallic acid also precipitates nitrat of jargonia of a greyish blue, but the colour is not so fine. Most of the other vegetable acids decompose this salt, and form combinations insoluble in water.
11. Nitrat of iron. The green oxyd of iron decomposes, but does not combine with nitric acid. The brown oxyd forms with it a red or brown solution, which by evaporation may be reduced to a jelly, but will not crystallize.
12. Nitrat of zinc. The oxyd of zinc combines with nitric acid, and forms with it a salt which crystallizes in compressed and flatted tetrahedral prisms, terminated by four edged pyramids.
Its solution is exceedingly caustic. When placed on burning coals it melts and detonates as it dries. It can scarcely be dried without being in some measure decomposed.
It deliquesces in the air.
13. Nitrat of manganese. This salt, composed of oxyd of manganese and nitric acid, was first examined by Scheele. Its crystals are small and shining, of a very bitter taste, and soluble in water.
14. Nitrat of cobalt. It is of a pale red colour, and crystallizes in needles. It deliquesces when exposed to the air. Heat decomposes it. When nickel is present, cobalt this salt affords a green colour.
15. Nitrat of nickel. Its crystals are of a green colour, and in the form of rhomboidal cubes. They are deliquescent, and are gradually decomposed when exposed to the air, the acid leaving them.
16. Nitrat of lead. Nitric acid combines with the white oxyd of lead. The crystals of this salt are of a lead, white colour; their form an irregular octagon, or rather truncated hexahedral pyramid. When exposed to heat it decrepitates, and melts with a yellowish flame.
By compound affinity it is decomposed by
Murat of potas, foda, ammonia, Carbonat of foda.
17. Nitrat of tin. Tin is converted into an acid by nitric acid; it is not probable, therefore, that any permanent nitrat of tin can be formed.
18. Nitrat of copper. This salt appears to have been first obtained by Macquer.
Its form, when properly crystallized, is an oblong parallelogram. It is of a fine blue colour. It is exceedingly caustic. It melts at 77°.
It is deliquescent in a moist air, but in a dry place is covered with a green efflorescence. It is very soluble in water. Heat decomposes it.
19. Nitrat of bitumeth. This salt crystallizes in various forms. Fourcroy obtained it in flattened rhomboids. It effloresces in the air. Water decomposes it. It detonates in the fire.
20. Nitrat of antimony. Little is known concerning this salt, except that it is very deliquescent, and is decomposed by heat.
21. Nitrat of arsenic. With white oxyd of arsenic nitric acid forms a salt which crystallizes. It is very deliquescent. It does not detonate.
22. Nitrat of mercury. This salt may be formed by dissolving mercury in nitric acid. It crystallizes in cold in regular flat 4-sided figures; but their form differs according to the manner in which the crystallization has been performed.
It is soluble in water.
This salt is exceedingly caustic. It detonates on coals. When heated in a crucible it melts, and is decomposed. The oxyd attracts oxygen from the acid, which flies off in the form of nitrous gas, and red oxyd of mercury remains behind.
It is slowly decomposed also in the air. It is decomposed by compound affinity by
Sulphat of copper, and a great many other sulphates, Phosphat of foda, Borax.
23. Nitrat of ammonia and mercury. This triple salt may be formed by pouring ammonia into a solution of mercury. of nitrat of mercury. If only enough of ammonia to saturate the acid be used, the triple salt precipitates in the form of a white powder; but with an excess of ammonia it remains dissolved, and forms by evaporation very bright polyhedral crystals.
It has a very sharp taste. It is soluble in 1200 parts of water at the temperature of 55°. Hot water separates a little ammonia, which renders it still more insoluble. It turns vegetable blues green. Muriatic acid dissolves it.
According to Fourcroy's analysis, it is composed of 68.20 parts of oxyd of mercury, 16 of ammonia, and 15.30 of nitric acid and water.
When distilled it yields ammonia, azotic gas, oxygen gas, yellow oxyd of mercury, and pure mercury.
24. Nitrat of silver. This salt may be formed by dissolving silver in nitric acid.
It forms flat transparent crystals composed of needles. It is exceedingly caustic. When melted it forms a grey mass called lapath informis, from its great corrosiveness.
It is very soluble in water. It is not altered by exposure to the air. Light decomposes it.
By compound affinity it is decomposed by
The sulphates, The muriats,
25. Nitrat of uranium. This salt was first formed by Klaproth. Its crystals are hexagonal plates of a greenish yellow colour. The largest were 1/3rd of an inch in length and 1/4th in breadth.
26. Nitrat of titanium. It is capable of crystallizing.
27. Nitrat of tellurium. The solution of tellurium in nitric acid is transparent and colourless. When concentrated, it produces in time small white light crystals in the form of needles, which exhibit a dendritic aggregation.
Sect. IV. Of Nitrates.
The salts which the nitrous acid forms with alkalies, earths, and metallic oxys, are denominated nitrates. Very few of them have been examined; we shall not therefore attempt a description of them.
Sect. V. Of Muriats.
Salts into which the muriatic acid enters are called muriats.
1. Muriat of potash. This salt was formerly called febrifuge or digestive salt of Sylvius, and regenerated sea salt. Its crystals are cubes, but rather irregular. It has a disagreeable bitter taste. Its specific gravity is 1.836.
It is soluble in three times its weight of water at the temperature of 60°, and in double its weight of boiling water.
It is composed, according to Bergman, of 34 parts of acid, 61 of potash, and 8 of water. Kirwan has found it to contain 36 of acid, 46 of alkali, and 18 of water.
It suffers little alteration from exposure to the air. When exposed to heat, it first decrepitates, then melts, and at last is volatilized, but without decomposition.
The following salts decompose it by compound affinity:
- Sulphat of soda, Nitrat of ammonia, - ammonia, magnetia, - alumina, alumina, - lime, lead.
2. Muriat of soda, common or sea salt. This salt has been known, and in common use, from the earliest ages. It is sometimes called also fulgum. Its crystals are cubes, but they often assume other forms. Its specific gravity is 2.120.
Its taste is universally known, and is what is strictly speaking denominated salt.
It is soluble in 2 1/4 times its weight of water at the temperature of 60°, and in 2 1/4 its weight of boiling water.
According to Bergman, it is composed of 52 parts of acid, 42 of alkali, and 6 of water. According to the late experiments of Mr Kirwan, of 40 parts of acid, 35 of alkali, and 25 of water.
It is not affected by exposure to the air. It ought to be observed, however, that the muriat of soda in common use contains, besides other impurities, a quantity of muriat of magnesia, which renders it deliquescent.
When heated it decrepitates. Heat volatilizes, but does not decompose it.
The following salts decompose it by compound affinity:
- Sulphat of ammonia, Nitrat of silver, - alumina, Acetite of barites, - potash, Pyrolignite of barites, - iron, lead, - Nitrat of ammonia, Carbonat of potash (a), - magnetia, Alum (b), - alumina, Red oxyd of lead (c).
That the red oxyd of lead decomposes this salt is a well-known fact, and it has been considered as contrary to the laws of affinity. Mr Haffefratz endeavoured to account for it by supposing that the oxyd is combined with carbonic acid, and that therefore it is a case of compound affinity. Mr Curaudan has proved that carbonic acid, instead of promoting, impedes the decomposition; and that, in fact, carbonat of lead is incapable of decomposing muriat of soda. He concludes, therefore, that the phenomenon cannot be accounted for by the commonly received laws of affinity. We cannot, however, think, that the phenomenon is to be unaccountable as Mr Curaudan supposes; for muriatic acid is capable of decomposing the red oxyd of lead, of combining with part of its oxygen, and of being converted into oxy-muriatic acid. Now if oxy-muriatic and nitro-muriatic acids be merely the same substance in a different form, as there is the strongest reason for supposing, the white oxyd of lead has a stronger affinity for it than soda has, and ought therefore to decompose it.
3. Muriat of ammonia, or sal ammoniac. This salt was known to the ancients, and was called by them sal ammoniac, because it was found in great quantities near the temple of Jupiter Ammon in Africa.
It assumes the form of plumose crystals. The individual crystals are long hexahedral pyramids. Its specific gravity is 1.120.
It has an acrid, poignant, urinous taste.
It dissolves in about three times its weight of water at the temperature of 60°, and in a much smaller quantity of boiling water.
It is composed, according to Kirwan, of 35 parts of acid, 30 of alkali, and 45 of water.
In its common form (which is an opaque mass) it is not affected by the air, but its crystals are liable to deliquesce. Heat volatilizes without decomposing it.
The following salts decompose it by compound affinity:
- Sulphate of alumina, - Nitrate of soda, - Acetate of magnesia, - Lead, - Carbonate of barytes, - Potash, - Soda, - Lime,
When this salt is sublimed with gold leaf, there is found in the neck of the retort an amethyst coloured matter, bordering on purple, soluble in water, and forming a purple solution. When filtered there remains behind a purple powder. This salt seems from this to be capable of oxidizing gold.
4. Muriate of barytes. This salt was first described by Bergman, but it has been most particularly attended to by Dr Crawford.
It affords oblong square crystals.
It has an unpleasant astringent taste.
It is not very soluble in water. It is soluble in alcohol.
It is not altered by exposure to the air, nor does heat in all probability decompose it.
Dr Crawford wrote a treatise on it in 1790, in which he recommended its use internally for scrofulous complaints. Care ought to be taken not to give it in too large quantities, as, like the other compounds of barytes, it is poisonous.
The following salts decompose it by compound affinity (z):
- Sulphate of soda, - Nitrate of lime, - Ammonia, - Magnesia, - Alumina,
Nitrate of soda,
5. Muriate of ammonia and barytes. This triple salt was first discovered by Fourcroy. It may be formed by pouring a carbonate of ammonia into a solution of muriate of barytes. It is easily decomposed by heat, but none of the alkalies nor their carbonates are capable of altering it.
6. Muriate of lime. This salt was formerly called fixed ammonia, because it was commonly obtained by decomposing sal ammoniac by means of lime.
Its crystals are four sided flattened prisms, terminated by a very sharp pyramid; but it is not easily crystallized.
Its taste is very bitter.
It is soluble in about 1 part of cold water, and less than its own weight of boiling water. Alcohol dissolves its own weight of it.
According to Bergman, it is composed of 3 parts of acid, 44 of lime, and 25 of water. According to Kirwan, 100 parts of lime require for saturation 86 parts of muriatic acid.
(v) Only at the common temperature. At a high temperature carbonat of ammonia decomposes muriate of magnesia. See Weferm, Ann. de Chim. ii. 118.
(z) Bergman affirmed, that this salt decomposed all the sulphates, and proposed it therefore as a certain means of discovering the presence of sulphuric acid, however combined in any solution; for the sulphate of barytes is almost entirely insoluble in water. But Mr Puffis has observed, that it does not decompose sulphate of lime nor of potash. See Ann. de Chim. xv. 317.
It very speedily deliquesces when exposed to the air.
By heat it melts into a very hard vitreform substance.
The following salts decompose it by compound affinity:
- Sulphate of soda, - Ammonia, - Magnesia, - Alumina, - Nitrate of soda, - Ammonia, - Magnesia, - Alumina,
7. Muriate of strontites. This salt was first formed by Dr Hope. Its crystals are very long, slender, hexagonal prisms. It has a peculiar, sharp, penetrating taste.
Three parts of these crystals are soluble in two parts of water at the temperature of 60°. Boiling water dissolves any quantity of them whatever.
They contain 42 per cent. of water of crystallization.
They suffer no change when exposed to the air except it be very moist; in which case they deliquesce.
When heated, they first undergo the watery fusion, and are then reduced to a white powder. A very violent heat decomposes this salt.
Muriatic acid precipitates this salt from its solution in water. That acid, therefore, has a stronger affinity for water than the salt has.
8. Muriate of magnesia. This salt abounds in sea water.
It is not easily crystallized. Bergman's method was to evaporate it by a considerable heat to the proper degree of concentration, and then to expose it to a sudden cold. By this method he obtained it in small needles.
It has a very bitter taste. It is soluble in its own weight of water, and in five parts of alcohol.
A saturated solution of it quickly forms a jelly; on which if hot water be poured, spongy masses are formed not even soluble in muriatic acid.
It is composed, according to Bergman, of 34 parts of acid, 41 of earth, and 25 of water. According to Kirwan, 100 parts of magnesia require for saturation 104.275 of acid.
It deliquesces very speedily when exposed to the air.
A strong heat decomposes it. When dried in a high temperature, it is very caustic.
The following substances decompose it by compound affinity:
- Sulphate of soda, - Ammonia, - Alumina, - Nitrate of ammonia,
Acetate of potash,
Carbonat Carbonat of barytes, Carbonat of soda, potas, ammonia (y)
9. Muriat of ammonia and magnesia. This triple salt was first mentioned, we believe, by Bergman. It may be formed by pouring ammonia into a solution of muriat of magnesia. Part of the magnesia is precipitated, but great part of it remains dissolved, and combined with the acid and the ammonia. This triple salt is composed, according to Forneroy, of 73 parts of muriat of magnesia and 27 of muriat of ammonia.
10. Muriat of alumina. This salt crystallizes with difficulty. It has an astringent taste. Its solution is gelatinous, and cannot be filtrated without much dilution in water. It is deliquescent. When evaporated to dryness, it forms a gummy mass; in a strong heat it is decomposed.
The following salts decompose it by compound affinity:
Nitrat of ammonia, Acetite of magnesia, Acetite of barytes, Carbonat of barytes, potas, potas, soda, soda, lime, ammonia.
11. Muriat of jargonia. This salt is easily formed by pouring muriatic acid on newly precipitated jargonia. It is colourless; its taste is very astringent; by evaporation it furnishes small transparent crystals in needles, which lose their transparency in the air. Muriat of jargonia is very soluble in water and in alcohol; to the flame of which it does not communicate any particular colour. Heat decomposes it; and it is decomposed likewise by the saliva when taken into the mouth.
When muriat of jargonia contains a little silica, it forms cubic crystals without concretion, and resembling a jelly. These crystals, when exposed to the air, gradually lose their transparency, and diminish in volume, and there are formed in the middle of the salt white silky needle-shaped crystals.
Muriat of jargonia is decomposed by sulphuric acid; part of the sulphat precipitates, and part remains dissolved in the muriatic acid. When this acid is driven off by heat, the remainder of the sulphat is gradually deposited; if the evaporation be stopped before the mass be reduced to dryness, it forms a kind of jelly when cold. It is also decomposed by the phosphoric, citric, tartaric, oxalic and succinic acids, which form with jargonia insoluble compounds that precipitate in white flakes.
The gallic acid poured into muriat of jargonia produces a white precipitate; but a green, bordering on grey, if the jargonia contain iron; and this last precipitate becomes, when dry, of a bright black colour, and resembles China ink. The liquid preserves a greenish colour; new portions of gallic acid produce no further precipitation; but carbonat of ammonia separates in great abundance a flaky matter of a purplish colour, not unlike that of the leys of wine. From these experiments it follows, that gallic acid has a greater affinity for jargonia than muriatic acid has; and that the gallic acids of jargonia and iron are soluble in muriatic acid.
Carbonat of potas decomposes muriat of jargonia, and part of the carbonic acid combines with the earth, and renders it easily soluble in acids though dried.
Carbonat of ammonia occasions a precipitate, which is mostly dissolved by adding more carbonat.
Prufat of mercury produces an abundant precipitate, which is soluble in muriatic acid; and which consequently is not muriat of mercury.
A plate of zinc, introduced into a solution of muriat of jargonia, occasions a slight effervescence; the liquor becomes milky, and in a few days becomes a white ferrimtransparent jelly.
Alumina decomposes muriat of jargonia with the assistance of a slight heat; the alumina dissolves, the liquor becomes milky, and assumes the form of a jelly. When the muriat contains iron, it remains in the solution, and the precipitated jargonia is quite pure. Here, then, is a method of freeing jargonia from iron.
12. Muriat of iron. Muriatic acid forms with the green oxyd of iron a salt which crystallizes in flat needles. When exposed to the air, they deliquesce, and the green oxyd attracts oxygen, and is gradually converted into a brown oxyd. Heat decomposes this salt.
13. Muriat of zinc. This salt, procured by dissolving zinc or its oxyd in muriatic acid, does not crystallize. Its solution is colourless. When heated, it becomes of a blackish brown. By distillation, a part of the acid is separated, and muriat of zinc remains behind of a milk white colour, solid, and formed of small radiated needles. It attracts moisture in the air.
14. Muriat of manganese. Muriatic acid dissolves the white oxyd of manganese. Its solution affords by evaporation angular shining crystals: They are deliquescent and soluble in alcohol.
15. Muriat of cobalt. The solution of oxyd of cobalt in muriatic acid is of a pale red, except it be contaminated with nickel or iron, when it is greenish. It crystallizes in small needles, which are very deliquescent. Heat decomposes it.
16. Muriat of nickel. This salt is deliquescent, and loses its acid when exposed to the air.
17. Muriat of lead. Muriatic acid combines with the oxyd of lead easily enough; but this salt is more readily procured by pouring muriatic acid into a solution of nitrat of lead; the muriat immediately precipitates in the form of a white powder. It is soluble in 30 times its weight of boiling water; and the solution yields by evaporation small, slender, brilliant needles in bundles. It is somewhat deliquescent. When exposed to heat, it melts into a brown mass, formerly called cornaceous lead.
It is decomposed by compound affinity by Sulphat of silver*, Carbonat of soda.
18. Muriat of tin. This salt may be formed by dissolving tin in hot muriatic acid. By evaporation, it affords needle shaped crystals, which are deliquescent. This salt has a strong affinity for oxygen. It decomposes oxy-muriatic, nitric, sulphurous, arsenic, molybdic and tungstic acids, the red oxyd of mercury, black oxyd of manganese, oxyd of antimony, zinc, fil-
(y) Only at a high temperature. See Muriat of Ammonia. ver, and gold; and by that means is converted into oxy- muriat of tin. It even absorbs oxygen when exposed to the air*. These compositions are doubtless produc- ed by diffusing affinity.
19. Muriat of copper. This salt may be formed by diffusing copper or its oxyd in muriatic acid.
Its crystals are prismatic. It is of a beautiful grass green colour. It has a very affligring and caustic taste. It deliquesces when exposed to the air. A moderate heat is sufficient to melt it; and when cooled it congeals into a mass. It requires a strong heat to volatilize it.
It is decomposed by nitrat of silver †.
20. Muriat of bismuth. This salt crystallizes with difficulty. By sublimation it forms a soft fusible sub- stance, formerly called butter of bismuth.
21. Muriat of antimony. This salt is found native. It crystallizes in prisms. When heated, it evaporates.
22. Muriat of arsenic. This salt crystallizes; it is very volatile, and not very soluble, in water §.
23. Muriat of mercury. This salt may be prepared by pouring diluted muriatic acid into a diluted solu- tion of nitrat of mercury; the muriat of mercury is immediately precipitated in the form of a white pow- der. Common salt may be used instead of muriatic acid. This salt was formerly called white mercurial precipitate and calomel.
It crystallizes; but the form of the crystals, which are very small, has not been determined.
It has little taste. It is almost insoluble in water. It is used as a medicine.
It is decomposed by sulphat of ammonia *.
24. Muriat of ammonia and mercury. This triple salt was first discovered by Fourcroy. It may be form- ed by pouring ammonia into a solution of corrosive mu- riat of mercury. It has the appearance of a white powder. Its taste is at first earthy, afterwards metallic. It is nearly insoluble in water. According to Fourcroy's analysis, it is composed of 81 parts of oxyd of mercury, 16 of muriatic acid, and 3 of ammonia.
Heat decomposes it; producing ammonia, azotic gas, and muriat of mercury.
Sulphuric, nitric, and muriatic acids decompose it †.
25. Muriat of silver. This salt may be formed by diffusing oxyd of silver in muriatic acid, or, which is better, by pouring muriatic acid into nitrat of silver; muriat of silver immediately precipitates. It is very little soluble in water; according to Monnet, one part of it requires 3072 parts of water.
When exposed to a small heat, it melts into a grey semi- transparent mass, not unlike horn; hence it was formerly called lapis cornua. A long continued heat decomposes it. This salt is very caustic; it is employed as an ef- fervescing under the name of lunar caustic.
26. Muriat of titanium has been formed by Mr Kla- proth.
Sect. VI. Of Oxy-muriats.
Those salts, into which the oxy-muriatic acid enters as an ingredient, are called oxy-muriats. As we con- sider the nitro-muriatic acid to be precisely the same with the oxy-muriatic, its combinations of course must receive the same name.
(z) We have been informed, that this salt had been used by bleachers in Scotland some years before Mr Ten- nant proposed it.
1. Oxy-muriat of potash. This singular salt was dis- covered by Mr Berthollet in 1786. It may be formed by saturating a solution of potash with oxy muriatic acid gas. By evaporating this solution in the dark, the common muriat of potash is first obtained; when it is thus separated, and the liquor allowed to cool, oxy-muriat of potash crystallizes.
Its crystals are rhomboids, of a silvery brilliancy. It has an infipid cooling taste, resembling that of nitre. It is soluble in 17 parts of water at the temperature of 65°, and in 2½ parts of boiling water q. It does not deliquesce in the air; but light converts it into com- mon muriat by separating oxygen. When heated, it melts, and gives out oxygen gas; and this is the best method hitherto discovered of obtaining that gas in a state of purity. According to Mr Hoyle, it contains about half its weight of concrete oxygen.
When mixed with charcoal, iron, and many other combustibles, and heated, it detonates with astonishing violence. This property induced the French chemists to propose it as a substitute for nitre in the preparation of gunpowder. The attempt was made at Effons in 1788; but no sooner had the workmen begun to triturate the mixture of charcoal, sulphur and oxy muriat, than it exploded with violence, and proved fatal to Mr Letors and Mademoiselle Chevrard. The force of this gunpowder when it is prepared is much greater than that of the common sort of powder; but the danger of pre- paring it, and even of using it after it is prepared, is so great, that it can hardly ever be substituted with advan- tage for common gunpowder.
Fourcroy and Vauquelin ascertained by experiment, that this salt exploded when triturated with sulphur, charcoal, antimony, arsenic, cinnamon, sugar, gums, oils, alcohol, ether, and sulphuret of iron. When these sub- stances were mixed, and struck with a hammer, the ex- plosion took place. The theory of these explosions was first pointed out by Mr Berthollet. The oxygen of the oxy-muriatic acid combines with the combustible, and at the same time lets go a quantity of calo- rie; and trituration or percussion acts merely by bring- ing the particles which combine within the sphere of each other attraction.
2. Oxy-muriat of soda. This salt was discovered at the same time by Mr Berthollet. Its properties are re- lated the same with the last, except that it is too deliques- cent to be used.
3. Oxy-muriat of ammonia. This combination is impossible. The oxy-muriatic acid and ammonia de- compose each other.
4. Oxy-muriat of barytes. These salts were dis- covered by Berthollet also. They all possess the property of detonating with combustibles, and of being reduced by that means to the state of common muriats. Mr Tennant has lately proposed the oxy- muriat of lime as a substitute for the other substances formerly used in the new mode of bleaching; particu- larly for bleaching printed cottons: And, as far as we can learn, it answers the purpose remarkably well (z).
7. Oxy-muriat of mercury. This salt was formerly called corrosive sublimate, and afterwards corrosive muriat of cury, Berthollet first pointed out the nature of its composition.
This salt was mentioned by Rhazes in the 10th century; and it seems to have been known in the east at an earlier period (a). The methods of preparing it used by the older chemists were numerous, complicated, and generally concealed as secrets. We shall not attempt, therefore, to give any account of them; and the methods used by later chemists have been described at considerable length in the article Chemistry (Encyc. n° 815).
It may be prepared by dissolving mercury in a sufficient quantity of oxy-muriatic acid, or by dissolving red oxyd of mercury in common muriatic acid.
When carefully crystallized, this salt assumes the form of cubes or oblique parallelopipeds, or rather quadrangular prisms, with sides alternately narrower, and terminated by two inclined planes meeting together.
It has an exceedingly disagreeable metallic taste.
It is soluble in 19 times its weight of water at the temperature of 30°. Boiling water, according to Macquer, dissolves half its weight of it. Alcohol, at the temperature of 70°, dissolves 4ths of its weight of this salt.
It does not attract moisture from the air.
It is soluble in sulphuric, nitric, and muriatic acids.
When triturated with 4ths of its weight of mercury and a little water, and then sublimed, it forms a white insipid salt, called formerly calomel or feces mercury. This, as Scheele has proved, is precisely the same with common muriat of mercury.
The theory of these two preparations is now pretty obvious. The experiments of Adet and Pelletier have shown, that oxy-muriatic acid may be obtained from corrosive muriat of mercury (b). We may conclude, therefore, with confidence, that the salt is an oxy-muriat. It cannot be prepared by means of common muriatic acid, except with red oxyd of mercury, or some other substance from which it may absorb oxygen.
When pure mercury is added to oxy-muriat, it seizes the oxygen from the oxy-muriat, and the whole is converted into common muriat.
It is decomposed by:
Tartar, Mold metals.
8. Oxy-muriat of tin. When an amalgam of tin is triturated with its own weight of corrosive muriat of mercury, and the mixture is distilled in a glass retort by means of a very gentle heat, there passes over a thick white smoke, which condenses into a colourless liquor that emits copious fumes, and has been called, in consequence, smoking liquor of Libavius. This liquor was examined by Mr Adet. He found, that when about 4d part of water was added to this liquor, it ceased to fume, and assumed a crystalline form; that then it might be even made red hot without subliming. It therefore owes its volatility to want of water, or rather to a strong attraction for water. He found that this substance was capable of dissolving, and therefore of oxidizing more tin, without the emission of any hydrogen, and consequently without the decomposition of water; he concluded from this, that it was composed of oxy-muriatic acid and tin (c). This has been completely proved by Mr Pelletier, who found, that when oxyd of tin was combined with oxy-muriatic acid, it formed a compound precisely the same with the smoking liquor of Libavius.
This salt may be prepared, as Pelletier has proved, by dissolving tin in muriatic acid, and then saturating it with oxy muriatic acid gas.
It is used in dyeing.
9. Oxy-muriat of iron. This salt is deliquescent; oxy muriat colours it; of a pure bitter taste, without any of the tart of iron; sweet agreeableness of the common salts of iron.
Few of the other oxy-muriats have been hitherto examined with attention: Many of the metals, indeed, have been dissolved in aqua regia; but in most of these solutions the salt produced is a common muriat. The nitric acid supplies oxygen, and the muriatic acid dissolves the oxyd.
Sect. VII. Of Phosphates.
Those salts, into which phosphoric acid enters as an ingredient, are called phosphates. This class of salts was first discovered by Margraf.
1. Phosphate of potash. This salt crystallizes in short phosphate tetrahedral prisms, terminated by quadrangular pyramids.
It is very soluble in cold water, and still more so in hot water.
It decrepitates on ignited coals like common salt.
When a very strong heat is applied, it melts into an opaque vitreous mass, still soluble in water.
The following salts decompose it by compound affinity:
- Sulphate of lime, - Muriat of mercury, - Nitrat of mercury, - Acetate of lead.
2. Phosphate of soda.—Dr Pearson, who first formed phosphate this salt, gives the following process for preparing it:
Dissolve in a long-necked matrix 1450 grams of crystallized carbonat of soda in 1200 grams of water at the temperature of 150°. Add gradually 100 grams of phosphoric acid of the specific gravity 1.85. Boil the liquor for some minutes; and while it is boiling hot, filter it, and pour it into a shallow vessel. Let it remain in a cool place, and crystals will continue to form for several days. From the above quantities of materials he has obtained from 1450 to 1550 grams of crystals.
Its crystals are rhomboidal prisms, of which the acute angles are 60°, and the obtuse angles 120°, terminated by a three-sided pyramid.
Its taste is almost the same with that of common salt.
It is soluble in water. When exposed to the air it effloresces.
This salt has been introduced into medicine as a purgative, and on account of its pleasant taste has of late been much used. It is usually taken in broth, which it is employed to season instead of common salt.
Heliot remarked a particular salt in urine, different from those that had usually been observed, in 1737. Haupt described it in 1740 under the name of sal mirabile.
(a) If we listen to Junker, the ancients applied the name mercurium to this salt; mercury they called argentum creum. Phosphat of arsenic.—It crystallizes in small grains hardly soluble in water.
14. Phosphat of uranium.—First formed by Klaproth. It does not crystallize, but assumes the appearance of yellowish white flakes, difficultly soluble in water.
15. Phosphat of antimony and lime.—Dr Pearson has discovered, that the well-known medicine called Farnet's powder is a triple salt, composed of phosphoric acid, oxyd of antimony, and lime. It is very insoluble in water.
The remaining phosphats are scarcely known.
Sect. VIII. Of Borats.
The compounds into which the boracic acid enters are called borate.
1. Borat of potash.—This salt, formed by combining boracic acid and potash, is very little known. Baron first formed it. Borat of potash crystallizes, is soluble in water, and may be melted into a vitreous mass, soluble in water.
2. Borat of soda or borax.—This salt is brought from the East Indies in an impure state under the name of tinkal. When purified in Europe, it takes the name of borax.
Its crystals are hexangular prisms, of which two sides are much broader than the remainder, terminated by triangular pyramids. It is of a white colour. Its specific gravity is 1.740.
Its taste is slightly alkaline.
It is soluble in 18 times its weight of water of the temperature of 60°, and 6 times its weight of boiling water.
It is composed, according to Bergman, of 17 parts of soda, 39 of acid, and 44 of water.
When exposed to the air, it effloresces slowly and slightly.
When heated, it swells, loses about four-tenths of its weight, becomes rosy, and then assumes the form of a light, porous, and very friable mass, known by the name of calcined borax; it then melts into a transparent glass, still soluble in water.
By compound affinity it is decomposed by Nitrat of mercury.
When two pieces of borax are struck together in the dark, a flash of light is emitted.
Borax has the property of facilitating the fusion of a great number of bodies. This property renders it useful in glass making, in assaying ores, and in soldering metals.
Borax turns syrup of violets green; it appears therefore to be supersaturated with alkali.
The real borat of soda, or the salt in which boracic acid and soda saturate each other, has not yet been examined with attention. According to Dr Withering, soda requires twice its weight of boracic acid to saturate it.
3. Borat of ammonia.—This salt has been examined only by Mr Fourcroy.
Its crystals are polyhedral pyramids.
It has a poignant urinous taste, and turns syrup of violets green. It dissolves readily enough in water.
When exposed to the air, it gradually loses its crystal-line form and becomes brown.
4. Borat of... 4. Borat of barytes.—Unknown.
5. Borat of lime.—It is difficultly soluble in water, and did not crystallize with Beaumé.
6. Borat of fritonites.—This salt was first formed by Dr Hope.—It is a white powder, soluble in about 130 parts of boiling water. The solution turns the syrup of violets green.
7. Borat of magnesia.—It assumes the appearance of small irregular crystals. It is soluble in acetic acid and formic acids. Alcohol decomposes it. It melts easily in the fire without being decomposed.
8. Borat of alumina.—It does not crystallize, and is scarcely soluble in water.
9. Borat of iron.—Its crystals are of a yellow colour, but the salt has never been examined with attention.
10. Borat of zinc.—This salt does not appear to be capable of crystallizing. By heat, it melts into a light green insoluble mass.
11. Borat of cobalt.—When oxyd of cobalt is melted with boracic acid, a bluish grey mass is produced. This, by lixiviation and evaporation, yields crystals of a reddish white colour and ramified form.
12. Borat of nickel.—A saline substance difficultly soluble.
13. Borat of lead.—When boracic acid and red oxyd of lead are melted together, the product is a fine greenish yellow, transparent, hard, insoluble glass.
14. Borat of tin.—When equal parts of boracic acid and tin filings are melted together, the product dissolved in water yields by evaporation transparent white polygonous crystals.
15. Borat of copper.—When borax is poured into a solution of sulphur of copper, borat of copper is precipitated in the form of a pale light green jelly, which when dried is with great difficulty soluble in water. It easily melts into a dark red vitreous substance. According to Palm, by long trituration of filings of copper and boracic acid in water, and then digesting the mixture, it dissolves, and crystals may be obtained from it.
16. Borat of bismuth.—A white powder, which melts into a white transparent permanent glass.
17. Borat of arsenic.—White oxyd of arsenic and boracic acid form a salt soluble in water and crystallizable.
**Sect. IX. Of Fluids.**
Those salts into which fluoric acid enters are called fluats. They were first formed by Scheele.
1. Fluat of potas. It forms a gelatinous mass almost without taste. It dissolves readily in water. When exposed to the fire it melts without any ebullition.
2. Fluat of soda. This salt resembles exactly the fluat of potas.
3. Fluat of ammonia. It crystallizes in small prisms. It is deliquescent, and is partly decomposed by heat. It is decomposed by
Nitrat of mercury,
— silver,
— lead.
4. Fluat of barytes. A powder which requires a large quantity of water to dissolve it.
5. Fluat of lime. This salt abounds in nature. It is known by the name of fluor spar.
It crystallizes most commonly in the form of cubes. It is tasteless and nearly insoluble in water. It is not altered by the air. Its specific gravity is about 3.1.
When exposed to a sudden heat it decrepitates. A very violent heat melts it into a white opaque mass.
When reduced to powder and heated it becomes phosphorescent; but it loses this quality altogether if it be heated red hot.
6. Fluat of fritonites. This salt was formed by Dr Hope; but its properties have not been examined.
7. Fluat of magnesia. It is not soluble in water except there be an excess of acid. In that case, by spontaneous evaporation, it forms hexagonal prisms, terminated by a low pyramid composed of three rhombohedral sides.
These crystals are hardly soluble in water. Alcohol dissolves a small portion of them. Heat does not decompose them.
8. Fluat of alumina. A saline mass; which is sweetish, clammy, and gelatinous.
9. Fluat of silica. Little is known concerning this singular combination, except that it can exist in a gaseous form, and that it deposits silica in crystals after a certain time.
10. Fluat of silica and potas or soda. This triple salt may be formed by pouring fixed alkali into a solution of fluat of silica. It contains an excess of acid. On evaporation it yields a kind of jelly, which when dry separates into gritty particles like sand. It is soluble in 96 parts of hot water. In the fire it readily melts into a white mass. If the heat be continued the acid separates, and there remains a transparent glass, which is soluble in water, and forms a liquor silicum.
11. Fluat of iron. It is incrustable; but when evaporated leaves a hard mass.
12. Fluat of zinc. It resembles that of iron.
13. Fluat of manganese. It may be formed by pouring fluat of ammonia into a solution of oxyd of zinc in fluats, any of the three mineral acids. It crystallizes.
14. Fluat of cobalt. A yellow gelatinous mass.
15. Fluat of nickel. It affords green crystals.
16. Fluat of lead. A sweet tailed powder.
17. Fluat of tin. A nauseous tailed jelly.
18. Fluat of copper. Blue crystals; some of them oblong, others cubic.
19. Fluat of arsenic. Small crystals.
20. Fluat of mercury. A powder. Before the blowpipe it melts into a yellow glass, most of which evaporates by a continued heat.
**Sect. X. Of Carbonats.**
The compounds into which the carbonic acid enters are called carbonats. They were first analysed by Dr Black.
1. Carbonat of potas. This salt is formed by saturating potas with carbonic acid, which is best done by exposing a solution of potas for a considerable time to carbonic acid gas.
It crystallizes, according to Bergman, in quadrangular prisms; the apexes of which are composed of two inverted triangles, converging like the roof of a house. According to Pelletier they are tetrahedral rhombohedral prisms, with dihedral summits. The complete crystal has eight faces, two hexagons, two rectangles, and four rhombs. It has an alkaline, but not a caustic taste.
It is soluble at the common temperature in about four times its weight of water. Boiling water dissolves this of its weight. Alcohol, even when hot, does not dissolve above parts of it.
According to Bergman, it is composed of 48 parts of potash, 20 of acid, and 32 of water. According to Pelletier, of 43 parts of acid, 40 of potash, and 17 of water. Bergman under-rated the quantity of acid from not observing that the salt loses part of its acid when heated. Even solution in hot water produces a separation of some acid.
It is not altered by exposure to the air.
Heat deprives it of its water and part of its acid, but does not decompose it completely. The following salts decompose it by compound affinity:
- Sulphate of lime, - Nitrate of barytes, - Barytes, - Soda, - Ammonia, - Magnesia, - Alumina, - Acetite of barytes, - Muriate of lime, - Lime, - Ammonia, - Magnesia, - Alumina, - Oxy-muriate of mercury, - Phosphat of lime,
Nitrate of lime,
When potash is saturated with carbonic acid it always lets fall a quantity of silica. Mr Pelletier has proposed this saturation as the best method of purifying potashes from that earth.
2. Carbonate of soda. This salt may be formed in the same manner with carbonate of potash.
Its crystals are five-sided prisms, with one of the angles frequently truncated, surmounted by dihedral pyramids with rhombooidal faces.
Its taste is precisely the same with that of carbonate of potash.
It is soluble in double its weight of cold water.
It is composed, according to Bergman, of 16 parts of acid, 25 of alkali, and 64 of water.
It effloresces when exposed to the air. Heat is incapable of decomposing it completely.
The following salts decompose it by compound affinity:
- Sulphate of ammonia, - Acetite of barytes, - Barytes, - Lime, - Magnesia, - Alumina, - Muriate of lime, - Nitrate of ammonia, - Lime, - Magnesia, - Alumina, - Lead,
3. Carbonate of ammonia. This salt forms octahedral crystals, having for the most part their two opposite apexes truncated.
Its taste and smell, though much weaker, are the same with those of pure ammonia. Like all the alkaline carbonates it converts vegetable blues to green, precisely as pure alkalies do.
It is soluble in rather less than twice its weight of cold water. Hot water dissolves its own weight of it.
According to Bergman it is composed of 43 parts of alkali, 45 of acid, and 12 of water.
When exposed to the air it becomes somewhat moist. The smallest heat is sufficient to evaporate it.
The following salts decompose it by compound affinity:
- Sulphate of alumina, - Acetite of barytes, - Nitrate of lime, - Muriate of lime, - Magnesia, - Alumina,
4. Carbonate of barytes. This salt has been found native.
Its crystals have been observed to assume four different forms; double fixed-fled and double four-sided pyramids, fixed-fled columns terminated by a pyramid with the same number of faces, and small radiated crystals an inch in length, and very thin, appearing to be hexagonal prisms, rounded towards the point.
Cold water dissolves part, and boiling water part of this salt. Water saturated with carbonic acid dissolves part.
According to Dr Withering, who first discovered it native, it is composed of 80 parts of barytes and 20 of acid. Bergman informs us, that artificial carbonate is composed of 7 parts of acid, 28 of water, and 65 of earth.
It is not altered by exposure to the air.
It is decomposed by the application of a very violent heat.
By compound affinity it is decomposed by the following salts:
- Sulphate of soda, - Nitrate of alumina, - Lime, - Muriate of lime, - Ammonia, - Magnesia, - Alumina, - Acetite of lime, - Lime, - Magnesia, - Alumina,
5. Carbonate of lime. This substance, under the common names of marble, chalk, lime stone, &c., exists in great abundance in nature, variously mixed with other bodies.
When pure, it is of a white colour, and has very little taste.
It is insoluble in pure water; but water saturated with carbonic acid dissolves part of it; from this solution it gradually precipitates as the acid leaves it in the form of small rhomboidal crystals.
It is composed, according to Bergman, of 34 parts of acid, 11 of water, and 55 of lime.
It suffers little or no alteration by being exposed to the air.
When exposed to heat, it first loses its water, and afterwards its acid separates as the heat is increased; but to separate the acid completely, a very strong heat is required.
The following salts decompose it by compound affinity:
- Sulphate of alumina, - Copper,
6. Carbonate of ironstones. This salt, which was first examined by Dr Hope, is insipid, and soluble in parts. Quantity of loss by driving off the gas by solution according to Wenzel:
| Element | Loss | |---------|------| | Zinc | 0.137 | | Iron | 0.009 | | Cobalt | 0.352 | | Lead | 0.157 | | Tin | 0.000 | | Copper | 0.174 | | Bismuth | 0.056 | | Antimony| 0.005 | | Mercury | 0.038 | | Silver | 0.158 | | Gold | 0.144 |
These determinations differ too widely from each other to be exact. It is obvious that part of the weight must be owing to adhering water, and very probably triple salts are formed, which must render the determination still more erroneous.
**Sect. XI. Of Acetites.**
The compounds which the acetous acid forms are called acetites.
1. Acetite of potash. Pliny is supposed, but probably without any reason, to have been acquainted with potash; this salt, because he recommends a mixture of vinegar and vine-ashes as a cure for a particular species of tumor. It was first clearly described by Raymond Plinius, Lully. It has received a great number of names; as, tartar, efflorescent salt of wine, regenerated tartar, diuretic salt, digestive salt of Sylvestris.
Its crystals are very white, and assume the form of thin plates.
It has a sharp warm taste.
It is soluble in about ten times its weight of water at the temperature of 60°. It is soluble also in alcohol.
According to Wenzel, 24 parts of acetous acid require for saturation 24 parts of potash. And from the experiments of Dr Higgins, it appears that acetite of potash is composed of 67 parts of alkali and 33 parts of acetous acid and water.
When exposed to the air it is very deliquescent. When heated, it melts as readily as wax; and if a very strong heat be applied, the acid is decomposed.
The following salts decompose it by compound affinity:
| Salt | Weight | |-----------------------|--------| | Sulphate of soda | | | Nitrate of ammonia | | | Lime | | | Ammonia | | | Magnesia | | | Alumina | | | Bismuth | | | Mercury | | | Lime | | | Alumina | |
2. Acetite of soda. This salt was first described by Mr Baron.
Its crystals are striated prisms, not unlike those of sulphate of soda.
It has a sharp taste, approaching to bitter.
It is soluble in 2.86 parts of water at the temperature of 60°.
According to Wenzel, 440 parts of acetous acid require for saturation 157 parts of soda.
It is not affected by exposure to the air.
When heated, it first loses its water of crystallization; in a strong heat it melts; and in a still stronger, its acid is destroyed. This salt can only be obtained in crystals when there is an excess of alkali in the solution.
The following salts decompose it by compound affinity:
- Sulphate of ammonia, - Nitrate of alumina, - Nitrate of ammonia, - Muriate of lime, - Magnesia,
3. Acetite of ammonia. This salt was formerly called spirit of Mindereur.
It is too volatile to be easily crystallized: It may, however, by gentle evaporation, be made to deposit needle-shaped crystals. Mr de Laflon crystallized it by sublimation*. When the sublimation is slow, it forms long, slender, flattened crystals, terminating in sharp points, of a pearl white colour, and about an inch and eight-tenths in length†.
It impresses the tongue at first with a sense of coldness, and then of sweetness, which is followed by a taste resembling that of a mixture of sugar and nitre, in which the sweet does not predominate over the the mawkish taste of the nitre ‡.
According to Wenzel, 240 parts of acetous acid saturate 244 of ammonia.
It is very deliquescent. It melts at 170°, and sublimes at about 250°.
When a watery solution of this salt is distilled, there comes over first a quantity of ammonia, next a quantity of acetous acid; and at last of the neutral salt itself. No such decomposition takes place when the crystals are distilled by a moderate heat*.
The following salts decompose acetite of ammonia by compound affinity:
- Sulphate of alumina, - Carbonate of soda, - Nitrate of silver §,
4. Acetite of barytes. This salt was first formed by Mr Morveau.
It is not easily crystallized. Morveau procured it in long prisms in groups.
It has a pleasant, somewhat acid taste, and always contains an excess of acid.
It is soluble in water, and does not deliquesce when exposed to the air †.
The following salts decompose it by compound affinity:
- Sulphate of potash, - Nitrate of alumina, - Lime, - Ammonia, - Magnesia, - Alumina, - Nitrate of potash, - Soda, - Lime, - Ammonia, - Magnesia,
5. Acetite of lime. This salt was first described accurately by Crollius. The ancients, however, used a mixture of lime and vinegar in surgery*.
It crystallizes in fine needles, of a glossy appearance like satin.
Its taste is bitter and sour, because it has an excess of acid.
It is soluble in water.
According to Wenzel, 240 parts of acetous acid require for saturation 125 of lime; according to Marey, 100 parts of acetite of lime contain 50 of lime†. From the experiments of Dr Higgins, it follows, that acetite of lime is composed of 35.7 parts of lime and 64.3 of acetous acid and water‡.
It is not altered by exposure to the air; at least Morveau kept some of it for a whole year merely covered with paper, and even quite uncovered for a month, without its undergoing any alteration§.
Heat decomposes it, and at the same time partly decomposes its acid.
The following salts decompose it by compound affinity:
- Sulphate of soda, - Nitrate of alumina, - Magnesia, - Alumina, - Nitrate of ammonia, - Magnesia, - Alumina, - Muriate of ammonia,
6. Acetite of strontites. This salt was first formed by Dr Hope. It forms small crystals, which are not thrown affected by exposure to the atmosphere. 49 parts of it are soluble in 122 parts of boiling water: It seems to be nearly as soluble in cold water. It renders vegetable colours green*.
7. Acetite of magnesia. This salt was first mentioned by Mr Wenzel.
It is not crystallizable; but forms by evaporation a viscous mass†.
It has a sweetish taste; leaving, however, a sense of bitterness‡.
It is very soluble both in water and alcohol*.
According to Wenzel, 240 parts of acetous acid require for saturation 123 parts of magnesia.
When exposed to the air, it deliquesces. Heat decomposes it.
The following salts decompose it by compound affinity:
- Sulphate of ammonia, - Alumina, - Nitrate of ammonia, - Alumina, - Muriate of ammonia, - Alumina,
8. Acetite of alumina. This salt can only be formed by digesting acetous acid on alumina recently precipitated.
By evaporation needle-shaped crystals are obtained, which are very deliquescent. According to Wenzel, 240 parts of acetous acid require 20 parts of alumina for saturation.
This salt is decomposed by compound affinity by the following salts:
- Nitrate of ammonia, - Muriate of ammonia, - Carbonate of barytes,
9. Acetite of jargonia. This salt may be formed by pouring acetous acid on newly precipitated jargonia. It has an astringent taste. It does not crystallize; but when evaporated to dryness, it forms a powder, which does not attract moisture from the air as acetite of alumina does†. It is very soluble in water and in alcohol‡. It is not so easily decomposed by heat as nitrat of jargonia, probably because it does not adhere so strongly to water.
10. Acetite of iron. This salt was mentioned by Schroeder and Juncker. It is composed of acetous acid and brown oxyd of iron.
Its solution forms by gentle evaporation small oblong crystals; but the greatest part of the salt assumes the form of a gelatinous mass.
It has a sweetish rypic taste.
According to Wenzel, 240 parts of acetous acid require for saturation 186 parts of iron.
Heat decomposes this salt; and it seems also to be gradually decomposed by exposure to the air.
11. Acetite of zinc. This salt was first mentioned by Glauber.
Its crystals are rhomboidal, and sometimes hexagonal plates, of a white colour, and the appearance of talk.
It is soluble in water. According to Wenzel, 240 parts of acetous acid require for saturation 195 parts of zinc.
It is not altered by exposure to the air. Heat decomposes it. When thrown upon burning coals, it explodes with a blue flame.
12. Acetite of manganese. This salt is not crystallizable; and when evaporated to dryness, it deliquesces. Is it not an acetate?
13. Acetite of cobalt. This salt is deliquescent. Its solution is of a fine red colour while cold; but becomes blue by being heated, and it recovers its former colour on cooling. According to Wenzel, 240 parts of acetous acid require for saturation 241 parts of cobalt.
14. Acetite of nickel. This salt forms rhomboidal cubes of a green colour. They are not deliquescent. Their taste is sweet.
15. Acetite of lead. This salt is mentioned by Isaac Hollandus and Raymond Lully. It is composed of acetous acid and white oxyd of lead.
It was formerly called sugar of lead, sugar of Saturn, salt of Saturn, vinegar of Saturn, extract of Saturn, &c.
Its crystals are flat parallelopipeds, terminated by two inclined planes approaching each other.
It has a sweet and somewhat astringent taste.
It is not very soluble in water; but acetous acid dissolves it abundantly.
According to Wenzel, 240 parts of acetous acid require for saturation 503 parts of lead.
When exposed to the air it becomes yellow, but undergoes no other alteration.
Heat decomposes it by destroying the acid. When distilled, the residuum takes fire spontaneously on exposure to the air. Paper dipped into acetite of lead forms excellent matches, which are not subject to go out, and which burn very slowly.
The following salts decompose it by compound affinity:
Muriat of ammonia, Phosphat of ammonia, Sulphat of copper, Oxalat of potas, Phosphat of soda, Malat of potas.
16. Acetite of tin. This salt was first described by Lemery.
Its crystals are prismatic needles in groups. According to Wenzel, 240 parts of acetous acid require for saturation 37 parts of tin.
17. Acetite of copper. This salt was known to the ancients, and various ways of preparing it are described by Pliny. It was formerly known by the names of crystals of Venus and verdigris.
It is of a deep green colour. Its crystals are rhomboidal.
It has a disagreeable coppery taste.
It is soluble in water and in alcohol.
According to Wenzel, 240 parts of acetous acid require 16 parts of copper for saturation.
It effloresces when exposed to the air. Heat decomposes it. It is used in painting.
18. Acetite of bismuth. This salt seems to have been first mentioned by Geoffroi. He called it sugar of bismuth.
It is most easily procured by mixing together the solutions of nitrat of bismuth and acetite of potas. It forms brilliant, talky, fivery crystals.
It has a sweetish taste. According to Wenzel, 240 parts of acetous acid require for saturation 15 parts of bismuth.
It does not deliquesce when exposed to the air. Heat decomposes it.
19. Acetite of antimony. It yields with difficulty small crystals. According to Wenzel, 240 parts of acetous acid require for saturation 1 part of antimony.
20. Acetite of arsenic. This salt forms small crystals in grains, hardly soluble in water.
21. Acetite of mercury. This salt is mentioned by Schroeder.
Its crystals are small thin plates.
It has a disagreeable taste, and excites coughing.
It is hardly soluble in water. According to Wenzel, 240 parts of acetous acid require for saturation 240 parts of mercury.
When exposed to the air it becomes black, owing to the reduction of the oxyd of mercury. Heat decomposes it.
22. Acetite of silver. This salt was perhaps first described by Margraf.
It is best formed by dropping acetite of soda or potas into a saturated solution of nitrat of silver.
It forms small oblong crystals, easily dissolved in water.
According to Wenzel, 240 parts of acetous acid require for saturation 10 parts of silver.
Heat decomposes it. It is decomposed by muriat of magnesia.
23. Acetite of gold. This salt is mentioned by Schroeder and Juncker.
24. Acetite of uranium. This salt was first formed by Klaproth.
Its crystals are regular four-sided slender prisms, terminated at both ends by regular quadrilateral pyramids; they are transparent, and of a beautiful topaz yellow colour.
Heat decomposes them; and what is singular, if they be heated gradually red hot, the oxyd which remains retains nearly the form of the crystals.
The compounds into which the acetite acid enters are called acetats. They are so imperfectly known at present, that we shall not attempt a description of them.
Sect. XII. Of Oxalats.
The compounds of which oxalic acid forms a part are are known by the name of oxalate. They were first described by Bergman.
1. Oxalate of potash. This salt crystallizes with difficulty. It is very soluble in water. When heated it falls to powder.
2. Acidulous oxalate of potash. The oxalic acid is also capable of combining with potash in excess, and forming another salt, called acidulous oxalate from its acid taste; or, to speak more accurately, this salt is formed by the combination of oxalate of potash with oxalic acid. This salt exists ready formed in oxalic acetylfilla or wood-ferret; from which it is extracted in some parts of Europe in great quantities. Hence it was formerly called salt of wood ferret. It is mentioned by Duclos in the Memoirs of the French Academy for 1668. Margraf first proved that it contained potash; and Scheele discovered that its acid is the oxalic. A great many interesting experiments had been previously made on it by Wenzel and Wiegler.
It may be formed, as Scheele has shown, by dropping potash very gradually into a saturated solution of oxalic acid in water: as soon as the proper quantity of alkali is added, acidulous oxalate is precipitated. But care must be taken not to add too much alkali, otherwise no precipitation will take place at all.
Its crystals are small opaque parallelopipeds.
It has an acid, pungent, bitterish, taste.
It is soluble in about ten times its weight of boiling water, but much less soluble in cold water.
It is not altered by exposure to the air. Heat decomposes it.
This salt is sold in this country under the name of efflorescent salt of lemons.
3. Oxalate of soda. This salt agrees very much with oxalate of potash. Its crystals are small, and soluble in water.
From Bergman's description, oxalic acid appears also capable of combining in excess with soda, and forming an acidulous oxalate.
4. Oxalate of ammonia. Its crystals are four-sided prisms, generally diverging from various points. They redden the infusion of turpentine.
They are easily soluble in water, but not in alcohol.
It is decomposed by nitric or barytes.
5. Oxalate of barytes. This salt does not crystallize except with excess of acid. The addition of potash, or even of water, deprives it of this excess, and then it crumbles into powder. It is insoluble in water.
6. Oxalate of lime. This salt does not crystallize. It is insoluble in water, but somewhat soluble in acids. It is composed of 43 parts of acid; 46 of lime, and 6 of water. Heat decomposes it.
7. Oxalate of ironites. This salt was first formed by Dr Hope. It is a white infusible powder; soluble in 1920 parts of boiling water. Heat decomposes it by destroying the acid.
8. Oxalate of magnesia. This salt is in the form of a white powder. It is scarcely soluble either in water or alcohol. It is composed of 35 parts of magnesia and 65 of acid and water. Heat decomposes it.
9. Oxalate of alumina. It is uncrystallizable; but furnishes on evaporation a yellowish pellucid mass. It is sparingly soluble in alcohol. It has a sweet astringent taste. It is composed of 44 parts of alumina and 56 of acid and water.
When exposed to the air it deliquesces; and if it has been previously well dried, its weight is increased by 1/4.
10. Oxalate of iron. This salt forms prismatic crystals of a yellowish-green colour. It has an astringent and sweet taste. It is very soluble in water.
It is composed of 45 parts of green oxyd, and 55 of acid and water. When exposed to heat it falls to powder.
From Bergman's description, the brown oxyd of iron appears also capable of combining with oxalic acid. The compound does not crystallize, and is nearly insoluble in water.
11. Oxalate of zinc. It is hardly soluble in water. It is composed of 75 parts of oxyd and 25 of acid.
12. Oxalate of manganese. It is composed of oxalic acid and white oxyd of manganese. It appears capable of crystallizing.
13. Oxalate of cobalt. This is a rose-coloured powder, insoluble in water, but soluble in oxalic acid; and capable, by that means, of crystallizing.
14. Oxalate of nickel. This is a green-coloured powder, hardly soluble in water. It is composed of two parts of acid and one of oxyd.
15. Oxalate of lead. It forms small crystalline grains. They are insoluble in alcohol, and nearly insoluble in water. They contain 55 parts of oxyd and 45 of acid.
16. Oxalate of tin. This salt forms prismatic crystals. It has an astringent taste. If the solution of this salt be quickly evaporated, it affords a mass resembling horn, and soluble in water.
17. Oxalate of copper. This salt is uncrystallizable. It is a bluish powder, insoluble in water, except with excess of acid. It is composed of 21 parts of copper and 29 of acid.
18. Oxalate of bismuth. This salt may be formed by dropping oxalic acid into a solution of nitrat of bismuth. It forms pellucid polygonous crystals. When oxyd of bismuth is dissolved by oxalic acid, the result is a white powder, scarcely soluble in water.
19. Oxalate of antimony. This salt forms crystalline grains, with difficulty soluble in water.
20. Oxalate of arsenic. This salt is composed of oxalic acid and white oxyd of arsenic. Its crystals are prisms very soluble in water and alcohol. It reddens turnsole. Heat sublimes it; and by a strong heat it may be decomposed.
21. Oxalate of mercury. A white powder hardly soluble in water, except with excess of acid.
22. Oxalate of silver. This salt may be formed by pouring oxalic acid into a solution of nitrat of silver. It is a white powder, scarcely soluble in water, and not at all in alcohol; but soluble in nitric acid. It becomes black by being exposed to the air, owing to the reduction of the oxyd.
23. Oxalate of platinum. This salt affords yellow crystals.
Sect. XIII. Of Tartrites.
The salts into which tartaric acid enters as an ingredient are known by the name of tartrites.
1. Acidulous oxalate of potash or tartar. This salt, which is composed of potash and an excess of tartaric acid, or rather of tartrite of potash and tartaric acid, It has been long known. It is obtained in a state of impurity at the bottom, and adhering to the sides of casks in which wine has fermented. It is called tartar, says Paracelsus, because it produces the oil, water, limestone, and salt, which burn the patient as Hell does. According to him, it was the principle of every disease and every remedy, and all things contain the germ of it.
Margraf and Rouelle first demonstrated that it contained potash ready formed; and Scheele first obtained tartaric acid from it in a state of purity.
Its crystals are very small and irregular. According to Montet, they are prisms, somewhat flat, and mostly with six faces. It has a strong acid taste. It is soluble in about 30 times its weight of boiling water. According to Bergman, it contains 23 parts of alkali and 77 of acid.
It is not altered by exposure to the air. Heat decomposes it, and at the same time destroys the acid. It is capable of forming a great many compounds:
1. Tartrate of potash. This salt may be formed by saturating the last described salt with potash. It was formerly called soluble tartar, because it is much more soluble in water than the acidulous tartrate of potash. It crystallizes most readily when there is a small excess of alkali in the solution. Its crystals are small oblongs. It has an unpleasant bitter taste. It is soluble in 4 parts of water, at the temperature of 40°.
2. Tartrate of soda. This salt has never been accurately examined.
3. Tartrate of potash and soda. This triple salt, formerly known by the name of salt of Seignette, because first formed by Mr. Seignette apothecary at Rochelle, is made by saturating tartar with soda.
Its crystals are prisms of eight or ten unequal sides, having their ends truncated at right angles. They are generally divided into two in the direction of their axes, and the base on which they stand is marked with two diagonal lines, so as to divide it into four triangles.
It has a bitter taste. It is almost as soluble as tartrate of potash.
It effloresces when exposed to the air. Heat decomposes it.
4. Tartrate of ammonia. The crystals of this salt are polygonous prisms, not unlike those of the last described salt.
It has a cooling bitter taste like that of nitre. It is easily soluble in water. Heat decomposes it.
5. Acidulous tartrate of ammonia. This salt may be formed by pouring tartaric acid into a solution of tartrate of ammonia. Like acidulous tartrate of potash it is very insoluble in water.
6. Tartrate of potash and ammonia. This triple salt may be formed by pouring ammonia into acidulous tartrate of potash.
Its crystals, according to Macquer, are prisms with four, five, or six faces; according to the Dijon academicians, parallelopipeds, with two alternate sloping faces.
It has a cooling taste. It is soluble enough in water. It effloresces in the air. Heat decomposes it.
7. Tartrate of barium. Unknown.
8. Tartrate of lime. This salt, first formed by Scheele, is a talc-like and almost infusible powder. By heat the acid is decomposed, and the pure lime remains behind.
9. Tartrate of strontites. This salt was first formed by Dr. Hope. Its crystals are small regular triangular tables, having the edges and angles sharp and well defined. It is infusible. It dissolves in 320 parts of boiling water.
It is not altered by exposure to the air. Heat decomposes it by destroying the acid.
10. Tartrate of magnesia. This salt is insoluble in water except there be an excess of acid present. It then affords by evaporation small crystals in the form of hexagonal truncated prisms.
It has a more saline taste, and is more fusible than tartrate of lime.
Heat first melts and afterwards decomposes it.
11. Tartrate of alumina. This salt does not crystallize, but forms by evaporation a clear transparent gummy mass. Its taste is astringent. It is soluble in water. It does not deliquesce in the air.
12. Tartrate of potash and alumina. This triple salt is formed by saturating tartar with alumina. It bears a very striking resemblance to the last described salt.
13. Tartrate of iron. This is a grey powder. When metallic tartaric acid is poured into a solution of sulphate of tartar-iron, feely crystals are formed by evaporation. These crystals are doublets composed of tartaric acid combined with sulphate of iron. This triple salt might be called tartar-sulphate of iron.
14. Tartrate of potash and iron. This triple salt was formerly called tartarized mixture of Mars, chalybeated tartar, and tartarized iron. It may be formed by boiling two parts of tartar and one of iron fillings, previously made up into a paste, in a proper quantity of water. The liquor by evaporation deposits crystals, which form the salt wanted.
15. Tartrate of zinc. This salt is not easily soluble in water.
16. Tartrate of potash and zinc. This triple salt, formed by combining tartar and oxyd of zinc, is very soluble in water.
17. Tartrate of lead. This salt, which is composed of tartaric acid and white oxyd of lead, is almost insoluble in water. Nitric acid dissolves it.
18. Tartrate of potash and lead. This salt, formed by combining white oxyd of lead with tartar, is very soluble in water.
19. Tartrate of tin. Unknown. The tartrate of potash and tin, composed of tartar and oxyd of tin, is capable of crystallizing.
20. Tartrate of copper. This salt is best formed by pouring tartaric acid into the solutions of muriatic or sulphuric acid; it precipitates in the form of blue crystals.
This salt forms the best kind of the pigment called Brunswick green.
21. Tartrate of potash and copper. This triple salt is also in the form of blue crystals.
22. Tartrate of bismuth. Small crystalline grains.
23. Tartrate of antimony. This salt has never been examined with attention.
24. Tartrate of potash and antimony, or tartar emetic. To this salt, which is perhaps the most powerful emetic known, a great deal of attention has been paid, and a vast number of methods have been tried to prepare it. These methods have been already described in the Encyclopaedia. It appears from the experiments of Mr. Bindheim, that if this salt be carefully prepared, the difference that results from the use of different oxyds is not so great as might have been expected.
It was first made known by Adrian in 1631. It is Sect. XVI. Of Lactats.
The neutral salts formed by the combination of the lactate acid with various bases are called lactats. They were first discovered by Scheele.
1. Lactat of potash. A deliquescent salt, soluble in alcohol. 2. Lactat of soda. This salt does not crystallize. It is soluble in alcohol. 3. Lactat of ammonia. Crystals which deliquesce. Heat separates a great part of the ammonia before destroying the acid. 4. Lactat of barytes. These salts deliquesce. The lactat of lime is soluble in alcohol. 5. Lactat of lime. 6. Lactat of alumina. 7. Lactat of magnesia. Small deliquescent crystals. 8. Lactat of iron. A brown solution. 9. Lactat of zinc. Crystals.
These salts have a very strong resemblance to malats. The only difference which Scheele observed was that the lactat of lime was insoluble in alcohol, while alcohol dissolved lactat of lime.
Sect. XVII. Of Saccholats.
The compounds into which the saccharic acid enters are called saccholats. They also were first discovered by Scheele.
1. Saccholat of potash. Small crystals, soluble in eight times their weight of boiling water. 2. Saccholat of soda. The same; soluble in five times their weight of boiling water. 3. Saccholat of ammonia. A salt which has a fourth taste. Heat separates the ammonia. 4. Saccholat of barytes. 5. Saccholat of lime. 6. Saccholat of magnesia. These salts are insoluble in water. 7. Saccholat of alumina.
Sect. XVIII. Of Gallats.
The compounds into which the gallic acid enters are denominated gallats. They were first attended to by the Dijon academicians and by Scheele.
1. Gallat of potash. We only know that these compositions are possible, and that their properties are different from those of all other salts. 2. Gallat of soda. 3. Gallat of ammonia. 4. Gallat of barytes. These salts are soluble in water, especially when there is excess of acid. 5. Gallat of lime. 6. Gallat of magnesia. This salt is a yellow powder, soluble in water and in alcohol. 7. Gallat of alumina. This salt, according to Bartholdi, exists ready formed in nut galls. It is very soluble in water. 8. Gallat of iron. This salt, which Mr Proult has discovered to be formed of gallic acid and brown oxyd of iron, is of a black colour, and does not seem capable of crystallizing. It is soluble in the three mineral acids, and by that means is deprived of its black colour. It is to this salt that ink partly owes its black colour. Gallat of iron is decomposed by alkalis.
We shall not attempt any farther account of this class of salts. Scarcely any addition has yet been made to the The experiments of Scheele which have been given already in the article Chemistry, Encyc.
Sect. XIX. Of Benzoats.
The compounds into which the benzoic acid enters have been called benzoats.
1. Benzoat of potash. This salt forms pointed feathery crystals. It has a saline sharp taste. It is very soluble in water. It deliquesces when exposed to the air.
2. Benzoat of soda. The crystals of this salt are larger, but its taste is the same with that of benzoat of potash. It is also very soluble in water. It effloresces in the air.
3. Benzoat of ammonia. This salt crystallizes with difficulty. Its crystals are feather-shaped. It deliquesces.
4. Benzoat of lime. This salt forms white, shining, pointed crystals, of a sweetish taste, and not easily soluble in water.
5. Benzoat of magnesia. Feather-shaped crystals, of a sharp bitter taste, and easily soluble in water.
6. Benzoat of alumina. An astringent salt.
7. Benzoat of iron. This salt forms yellow crystals. It has a sweet taste. It is soluble in water and alcohol. It effloresces in the air. Heat disengages the acid.
8. Benzoat of zinc. This salt forms arborescent crystals. It is soluble in water and alcohol. When exposed to the air it is dissipated. Heat decomposes it.
9. Benzoat of manganese. This salt, which is formed of benzoic acid and white oxide of manganese, crystallizes in small scales. It dissolves readily in water, with difficulty in alcohol. It is not altered by exposure to the air.
10. Benzoat of cobalt. Flat crystals.
11. Benzoat of lead. Very white crystals, soluble in water and alcohol. They are not altered by exposure to the air. Heat disengages the acid.
12. Benzoat of tin. This salt may be formed by pouring benzoat of potash into a solution of tin in the nitro-muriatic acid. The benzoat of tin is precipitated. It is soluble in hot water, but insoluble in alcohol. Heat decomposes it.
13. Benzoat of copper. Small crystals of a deep green colour. They are with difficulty soluble in water, and not at all in alcohol.
14. Benzoat of bismuth. This salt forms white needle-shaped crystals. They are soluble in water and in a very small proportion in alcohol. They are not altered by exposure to the air. Heat decomposes them.
15. Benzoat of antimony. Crystals which effloresce in the air, and are decomposed by heat.
16. Benzoat of arsenic. Small feather-shaped crystals. It is soluble in hot water, but crystallizes in the cooling. A moderate heat sublimes it; a strong heat decomposes it. Sulphur decomposes it. It is not decomposed by alkalis.
17. Benzoat of mercury. A white powder. It is insoluble in water, but dissolves in a small quantity in alcohol. It is not altered by exposure to the air. A small heat sublimes it; a greater decomposes it. It is decomposed by sulphur.
18. Benzoat of silver. This salt is soluble in water and also in a very small proportion in alcohol. It is not altered by exposure to the air, but the rays of the sun render it brown. Heat disengages its acid.
19. Benzoat of gold. Small irregular crystals, not easily soluble in water; insoluble in alcohol. It is not altered by exposure to the air. Heat decomposes it.
20. Benzoat of platinum. This salt forms small brownish crystals, with difficulty soluble in water; not soluble in alcohol. When exposed to heat, it is decomposed, and there remains behind a brown powder.
Sect. XX. Of Succinats.
The neutral salts, formed by the combination of the succinic acid with various bases, have been called succinats.
We shall not describe these salts, as we could not add much to the account given in the Appendix to the article Chemistry in the Encyclopedia. That account was taken from Mr Kier's Chemical Dictionary, and that gentleman borrowed it from Leonhardt.
Sect. XXI. Of Camphorats.
The neutral salts into the composition of which camphoric acid enters, have been denominated camphorats. The only chemist who has hitherto examined them is Bouillon la Grange; his experiments have been published in the 27th volume of the Annales de Chimie.
1. Camphorat of potash. To prepare this salt camphorat of potash is to be dissolved in water, and the solution saturated with camphoric acid. When the effervescence is over, the liquor is to be evaporated by a gentle heat to the proper consistence, and crystals of camphorat of potash will be deposited when the liquor cools.
Camphorat of potash is white and transparent; its crystals are regular hexagons. Its taste is bitterish and slightly aromatic.
Water at the temperature of 60° dissolves $\frac{1}{20}$th part of its weight of this salt; boiling water dissolves $\frac{1}{4}$th part of its weight.
It is soluble in alcohol, and the solution burns with a deep blue flame.
When exposed to moist air, it loses a little of its transparency, but in dry air it suffers no change.
When exposed to heat it melts, swells, and the acid is volatilized in a thick smoke, which has an aromatic odour. Before the blow-pipe it burns with a blue flame, and the potash remains behind in a state of purity.
By compound affinity this salt is decomposed by:
- Nitrat of barytes, - All the salts whose base is lime, - Nitrat of silver, - Sulphat of iron, - Muriat of tin, - Lead
2. Camphorat of soda. This salt may be formed precisely in the same manner with the camphorat of potash.
It is white and transparent; its taste is somewhat bitter; its crystals are irregular.
Water at the temperature of 60° dissolves less than of soda.
$\frac{1}{20}$th part of its weight of this salt; boiling water dissolves $\frac{1}{4}$th of its weight.
It is also soluble in alcohol.
When exposed to the air it loses its transparency, and effloresces. Camphorat effloresces slightly, but is never completely reduced to powder.
Heat produces the same effect upon it as on camphorat of potash; the acid burns with a blue flame, which becomes reddish towards the end.
By compound affinity it is decomposed by
Nitrat of lime, Muriat of lime, Silver, Iron, Muriat of magnesia, Sulphat of alumina, Barytes, Iron; and many other salts with metallic bases.
3. Camphorat of ammonia. This salt may be prepared by dissolving carbonat of ammonia in hot water, and adding camphoric acid slowly till the alkali is saturated. It must then be evaporated with a very moderate heat, to prevent the disengaging of ammonia.
It is very difficult to obtain this salt in regular crystals. When evaporated to dryness, there is obtained a solid opaque mass of a sharp and bitterish taste.
Water at the temperature of about 60° dissolves nearly 1/25th part of its weight of this salt; boiling water dissolves 1/4 of its weight. But this and the two salts above described are a good deal more soluble when there is excess of base.
It is entirely soluble in alcohol.
When exposed to the air it attracts moisture, but not in sufficient quantity to enable it to assume a liquid form.
When exposed to heat it swells, melts, and is converted into vapour; before the blow pipe it burns with a blue and red flame, and is entirely volatilized.
Most of the calcareous salts form triple salts with camphorat of ammonia.
It decomposes in part all the aluminous salts except the sulphat of alumina.
4. Camphorat of barytes. In order to prepare this salt, barytes is to be dissolved in water, and camphoric acid added to the solution; the mixture is then to be boiled, and afterwards filtered and evaporated to dryness.
Camphorat of barytes does not crystallize; when the evaporation is conducted slowly, the salt is deposited in thin plates one above another, which appear transparent while immersed in the liquor, but become opaque whenever they come into contact with the air.
It has very little taste, though it leaves at last upon the tongue a slight impression of acidity mixed with bitterness.
Water dissolves only a very small quantity of this salt; boiling water being capable of taking up only 1/25th part of it.
It is not altered by exposure to the air.
When exposed to heat it melts easily, and the acid is volatilized. When the heat is considerable, the acid burns with a lively blue flame, which becomes red and at last white.
It is decomposed by
Nitrat of potash, soda, lime, ammonia, and magnesia. Muriat of lime, potash, alumina, and magnesia. All the sulphats. Carbonat of potash and soda. Phosphat of potash, soda, and ammonia.
5. Camphorat of lime. This salt may be prepared by dropping into lime-water crystallized camphoric acid.
The mixture is then to be made boiling hot, passed through a filter, and evaporated to about 1/4th of its volume. On cooling camphorat of lime is deposited.
It has no regular shape; but if the evaporation has been properly conducted, it is in plates lying one above another. It is of a white colour, and has a taste slightly bitter.
Water at the temperature of 60° dissolves very little of this salt; boiling water is capable of dissolving about 1/25th part of its weight of it. It is insoluble in alcohol.
It is composed of 43 parts of lime, 50 of acid, and 7 of water.
When exposed to the air it dries and falls into powder.
When exposed to a moderate heat it melts and swells up; when placed on burning coals, or when heated in close vessels, the acid is decomposed and volatilized, and the lime remains pure.
When sulphuric acid is poured into a solution of this salt, it produces an insoluble precipitate; nitric and muriatic acids precipitate the camphoric acid.
It is decomposed by compound affinity by
Carbonat of potash, Nitrat of barytes, Muriat of alumina, Sulphat of alumina, Phosphat of soda.
6. Camphorat of magnesia. This salt may be prepared by pouring water on carbonat of magnesia, and then adding crystallized camphoric acid; heat is then applied, the solution is filtrated, and evaporated to dryness. The salt obtained is dissolved in hot water, passed through a filter, and evaporated by means of a moderate heat till a pellicle forms on the surface of the solution. On cooling the salt is deposited in thin plates. The second solution is to remove any excess of magnesia that may happen to be present.
This salt does not crystallize. It is white, opaque, and has a bitter taste.
It is scarcely more soluble in water than camphorat of lime.
Alcohol has no action on it while cold, but when hot it dissolves the acid and leaves the magnesia; and the acid precipitates again as the alcohol cools.
When exposed to the air it dries and becomes covered with a little powder; but this effect is produced slowly, and only in a warm place.
When this salt is placed on burning coals, the acid is volatilized, and the magnesia remains pure. Before the blow-pipe it burns like the other camphorats with a blue flame.
The nitrats, muriats, and sulphats, do not completely decompose this salt, if we except the nitrat of lime and muriat of alumina.
7. Camphorat of alumina. To prepare this salt, alumina, precipitated by means of ammonia, and well washed, is to be mixed with water, and crystals of camphoric acid added. The mixture is then to be heated, filtered, and concentrated by evaporation.
This salt is a white powder, of an acid bitterish taste, leaving on the tongue, like most of the aluminous salts, a sensation of astringency.
Water at the temperature of 60° dissolves about 1/25th part of its weight of this salt. Boiling water dissolves it
it in considerable quantities; but it precipitates again as the solution cools.
Alcohol, while cold, dissolves it very sparingly; but when hot it dissolves a considerable quantity of it, which precipitates also as the solution cools.
This salt undergoes very little alteration in the air; but it rather parts with than attracts moisture.
Heat volatilizes the acid; and when the salt is thrown on burning coals it burns with a blue flame.
It is decomposed by the nitrates of lime and barites.
Sect. XXII. Of Suberats.
The salts formed by the suberic acid have obtained the appellation of suberats. They have hitherto been examined only by Bouillon la Grange.
1. Suberat of potash. This salt ought to be formed by means of crystallized carbonat of potash.
It crystallizes in prisms, having four unequal sides. It has a bitter saltish taste, and it reddens vegetable blues. It is very soluble in water. Caloric melts it, and at last volatilizes the acid.
It is decomposed by most of the metallic salts, and by sulphate of alumina, muriate of alumina, and of lime; nitrate of alumina and of lime; and phosphate of alumina.
2. Suberat of soda. This salt does not crystallize. It reddens the tincture of turpentine. Its taste is slightly bitter. It is very soluble in water and in alcohol. It attracts moisture from the air. Caloric produces the same effect on it that it does on suberat of potash.
It is decomposed by the calcareous, aluminous, and magnesian salts.
3. Suberat of ammonia. This salt crystallizes in parallelopipeds. Its taste is saltish, and it leaves an impression of bitterness. It reddens vegetable blues.
It is very soluble in water. It attracts moisture from the air. When placed upon burning coals, it loses its water of crystallization, and swells up; and before the blow-pipe it evaporates entirely.
It is decomposed by the aluminous and magnesian salts.
4. Suberat of barytes. This salt does not crystallize. Heat makes it swell up, and melts it. It is scarcely soluble in water except there be an excess of acid.
It is decomposed by most of the neutral salts except the barytic salts and the fluors of lime.
5. Suberat of lime. This salt does not crystallize. It is perfectly white; it has a saltish taste; it does not reddens the tincture of turpentine.
It is very sparingly soluble in water except when hot; and as the solution cools most of the salt precipitates again.
When placed upon burning coals it swells up, the acid is decomposed, and there remains only the lime in the state of powder.
It is decomposed by
- The muriate of alumina, - The carbonat of potash and soda, - The fluors of magnesia, - The phosphates of alumina and soda, - The borat of potash,
All the metallic solutions.
6. Suberat of magnesia. This salt is in the form of a powder; it reddens the tincture of turpentine. It has a bitter taste; it is soluble in water, and attracts some moisture when exposed to the air.
When heated it swells up and melts; before the blow-pipe the acid is decomposed, and the magnesia remains in a state of purity.
It is decomposed by
- Muriate of alumina, - Nitrate of lime and alumina, - Borat of potash, - Fluor of soda, - Phosphate of alumina.
7. Suberat of alumina. This salt does not crystallize. When its solution is evaporated by a moderate heat in a wide vessel, the salt obtained is of a yellow colour, transparent, having a flaky taste, and leaving an impression of bitterness on the tongue. When too much heat is employed it melts and blackens. It reddens the tincture of turpentine, and attracts moisture from the air.
Before the blow-pipe it swells up, the acid is volatilized and decomposed, and nothing remains but the alumina.
It is decomposed by
- The carbonates of potash and soda, - The sulphate of iron, - The muriate of iron, - The nitrate of silver, mercury, and lead.
Suberic acid forms also compounds with the oxyds of silver, mercury, lead, copper, tin, iron, bismuth, arsenic, cobalt, zinc, antimony, manganese, and molybdenum; most of which are incrustable, and have an excess of acid.
Sect. XXIII. Of Prussiates.
The compounds into which the prussic acid enters are called Prussiates.
These substances, the most important of which are triple salts, have something very peculiar in their affinities. The prussic acid appears to have a stronger affinity for alkalies and earths than for metals, at least these substances are capable of decomposing metallic prussiates; yet acids scarcely decompose the metallic prussiates, while the weakest acid known decomposes the prussiates of alkalies and earths. These phenomena have not yet been satisfactorily accounted for.
1. Prussiate of potash. 2. Prussiate of soda. 3. Prussiate of ammonia. 4. Prussiate of lime. 5. Prussiate of barytes. 6. Prussiate of magnesia.
These salts were first obtained pure by Mr Scheele. They are soluble in water; but they are of little use, as mere exposure to the air decomposes them.
Prussic acid does not combine with alumina.
7. Prussiate of iron, or Prussian blue. This substance is composed, as Mr Prout has shown, of the prussic acid and brown oxyd of iron. With the green oxyd the prussic acid forms a white compound, which, however, becomes gradually blue when exposed to the atmosphere, because the oxyd absorbs oxygen and is converted into brown oxyd.
Prussiate of iron is a deep blue coloured powder. Prussian blue is insoluble in water, and scarcely soluble in acids. It is composed, according to the most accurate experiments hitherto made, of equal parts of oxyd of iron and prussic acid. It is not affected by exposure to the air. Heat decomposes it by destroying the acid, and the oxyd of iron remains behind.
The Prussian blue of commerce, besides other impurities, contains mixed with it a great quantity of alumina. Its use as a pigment, and the attempts which have been made to introduce it as a dye, are well known.
Prussic acid of iron may also exist in another state: It may have a superabundance of oxyd; its colour is then more or less yellow. To this state it may be reduced by digesting it with alkalies or any of the alkaline earths. These substances deprive it of part of its acid, but not of the whole.
This yellow prussic acid is soluble in acids.
Were we to attempt an explanation of this, and the other phenomena which the prussic acid displays in its combinations, we would conjecture, that this yellow prussic acid is the substance formed by the direct combination of brown oxyd of iron and prussic acid, and that the blue prussic acid is formed of the yellow prussic acid combined as an integrant with prussic acid: That the affinity between the prussic acid and oxyd of iron is much stronger than that between yellow prussic acid and prussic acid: that therefore alkalies and earths have a stronger affinity for prussic acid than the yellow prussic acid has, but a much weaker affinity than oxyd of iron, and perhaps every other oxyd; hence the apparent superiority of alkalies and earths in some cases, while in others they appear very inferior. We would suppose, then, that the prussic acid has a much stronger affinity for oxyd of iron, and perhaps for all other oxyds, than for other bodies; that the prussic acids, thus formed, are capable of combining with prussic acid; but that their affinity for it is much less than that of the alkalies and earths. This conjecture is supported by all the phenomena at present known; it would remove all the apparent anomalies which the combinations of this singular acid present, and reduce the whole of them under the known laws of affinity.
8. Prussic acid of potash and iron, commonly called Prussian alkali, or Prussian salt. This substance is a triple salt, composed of prussic acid, potash, and oxyd of iron combined together. To chemists and mineralogists it is one of the most important instruments ever invented; as, when properly prepared, it is capable of indicating whether any metallic substance (platinum excepted) be present in any solution whatever, and even of pointing out the particular metal, and of ascertaining its quantity: This it does by means of a compound affinity, which, after what has been said above, may be easily understood. The Prussian alkali may be conceived to be a combination of two substances, prussic acid of potash and blue prussic acid of iron. Now every metallic oxyd has a stronger affinity for prussic acid than potash has (and, in fact, seems to have a stronger affinity for it than for any other substance). If, therefore, there happen to be any oxyd in the solution, it immediately seizes the prussic acid with which the potash is combined, and by that means decomposes the triple salt. A prussic acid of the particular metal is formed, and, as most prussic acids of metals are insoluble, it is precipitated; and it indicates by its colour the particular metal, and by its weight the quantity of metal that happens to be present. At the same time, the blue prussic acid is also precipitated, and its weight must be deducted from the quantity of the precipitate.
In order to be certain of the accuracy of these results, it is necessary to have a Prussian alkali perfectly pure, and to be certain before hand of the quantity, or rather of the proportions of its ingredients. To obtain a test of this kind has been the object of chemists ever since the discoveries of Macquer pointed out its importance. It is to the use of impure tests that a great part of the contradictory results of mineralogical analyses by different chemists is to be ascribed.
There are two ways in which this test may be rendered impure, besides the introduction of foreign ingredients, which we do not mention, because it is obvious that it must be guarded against. 1. There may be a superabundance of alkali present, or, which is the same thing, there may be mixed with the Prussian test a quantity of pure alkali; or, 2. There may be contained in it a quantity of yellow prussic acid of iron, for which prussic acid of potash has also a considerable affinity.
If the Prussian test contain a superabundance of alkali, two inconveniences follow. This superabundant quantity will precipitate those earthy salts which are liable to contain an excess of acid, and which are only soluble by that excess: Hence alumina and barytes will be precipitated. It is to the use of impure tests of this kind that we owe the opinion, that barytes and alumina are precipitated by the Prussian alkali, and the consequent theories of the metallic nature of these earths. This mistake was first corrected, we believe, by Mr Klaproth.
Another inconvenience arising from the superabundance of alkali in the Prussian test is, that it gradually decomposes the blue prussic acid which the test contains, and converts it into yellow prussic acid. In what manner it does this will be understood, after what has been said, without any explanation.
On the other hand, when the Prussian alkali contains a quantity of yellow prussic acid of iron, as great inconveniences follow. This yellow prussic acid has an affinity for prussic acid, which, though inferior to that of the potash, is still considerable; and, on the other hand, the potash has a stronger affinity for every other acid than for the prussic. When, therefore, the test is exposed to the air, the carbonic acid, which the atmosphere always contains, afflicts by the affinity between the yellow prussic acid and the prussic acid, decomposes the prussic acid of potash in the test; and the yellow prussic acid is precipitated in the form of Prussian blue: And every other acid produces the same effect. A test of this kind, therefore, would indicate the presence of iron in every mixture which contains an acid (for a precipitation of Prussian blue would appear); and could not, therefore, be trusted to with any confidence.
We will not attempt to describe the various methods which different chemists have adopted of preparing this method; but shall satisfy ourselves with describing the former method of Klaproth, which answers the purpose completely. This we shall do nearly in the words of Mr Kirwan.
Prepare a pure potash, by gradually projecting into a large crucible heated to whiteness a mixture of equal parts of purified nitre and crystals of tartar; when the whole is injected, let it be kept at a white heat for half an hour, to burn off the coal.
Detach the alkali thus obtained from the crucible, reduce it to powder, spread it on a muffle, and expose it to a white heat for half an hour.
Dissolve it in five times its weight of water, and filter the solution while warm.
Pour this solution into a glass receiver, placed in a sand furnace, heated to 170° or 180°, and then gradually add the best Prussian blue in powder, injecting new portions according as the former becomes grey, and supplying water as fast as it evaporates; continue until the added portions are no longer discoloured, then increase the heat to 212° for half an hour.
Filter the ley thus obtained, and saturate it with sulphuric acid moderately diluted; a precipitate will appear; when this ceases, filter off the whole, and wash the precipitate.
Evaporate the filtered liquor to about one quarter, and set it by to crystallize; after a few days, yellowish crystals of a cubic or quadrangular form will be found mixed with some sulphate of potash and oxyd of iron; pick out the yellowish crystals, lay them on blotting paper, and redissolve them in four times their weight of cold water, to exclude the sulphate of potash.
7. Effay a few drops of this solution with barytic water, to see whether it contains any sulphuric acid, and add some barytic water to the remainder if necessary; filter off the solution from the sulphate of barytes, which will have precipitated, and set it by to crystallize for a few days; that the barytes, if any should remain, may be precipitated. If the crystals now obtained be of a pale yellow colour, and discover no bluish streaks when sprinkled over with muriatic acid, they are fit for use; but if they still discover bluish or green streaks, the solutions and crystallizations must be repeated.
These crystals must be kept in a well-stopped bottle, which to preserve them from the air should be filled with alcohol, as they are insoluble in it.
Before they are used, the quantity of iron they contain should be ascertained, by heating 100 grams to redness for half an hour in an open crucible; the prussian acid will be consumed, and the iron will remain in the state of a reddish brown magnetic oxyd, which should be weighed and noted: This oxyd is half the weight of the Prussian blue afforded by the Prussian alkali; its weight must therefore be subtracted from that of metallic precipitates formed by this test. Hence the weight of the crystals, in a given quantity of the solution, should be noted, that the quantity employed in precipitation may be known. Care must be taken to continue the calcination till the oxyd of iron becomes brown; for while it is black it weighs considerably more than it should.
9. Prussian of soda and iron. The only discernible difference between this salt and the last is, that it crystallizes differently.
10. Prussian of ammonia and iron. This triple salt has also been employed as a test; but it is not so easy to obtain it in a state of purity as the other two. It was discovered by Macquer, and first recommended by Meyer.
It forms flat hexangular crystals, soluble in water, and deliquesce in the air. Heat decomposes it like the other Prussians.
We shall not give any description of the triple salts formed by digesting the alkaline earths on prussian of iron; they are sufficiently known, and are not of any use except as tests; and in that respect they are inferior to that above described. They are all soluble in water, and are most of them capable of crystallizing.
11. Prussian of mercury. This salt, which was first formed by Scheele, is composed of the prussic acid mercury combined with the red oxyd of mercury. It may be formed by boiling the red oxyd of mercury with Prussian blue. It crystallizes in tetrahedral prisms, terminated by quadrangular pyramids, the sides of which correspond with the angles of the prism.
This salt is capable of combining with sulphuric and muriatic acids, and forming triple salts, which have not yet been examined.
Sect. XXIV. Of Formate.
The compounds into which the formic acid enters are called formates. We shall not describe them, as little has been added to the account already given in the Appendix to the article Chemistry in the Encyclopaedia.
Sect. XXV. Of Sebats.
The compounds into which the sebatic acid enters are called sebats. For our knowledge of this class of salts we are chiefly indebted to the celebrated Crell, who published a dissertation on the sebatic acid and its combinations in the Philosophical Transactions for 1780 and 1782.
1. Sebat of potash. This salt is of a white colour. Its crystals are quadrangular pyramids, of which two opposite sides are narrower than the others. It has a sharp saline taste like muriat of ammonia, but milder. It is soluble in water, insoluble in alcohol, and does not deliquesce when exposed to the air. Heat decomposes it.
2. Sebat of soda. This salt is white. Its crystals are pyramids, with three or four sides: a very moderate heat melts them.
3. Sebat of ammonia. This salt in taste and solubility resembles muriat of ammonia, but it differs from it in not being capable of subliming iron.
4. Sebat of lime. The crystals of this salt are hexagonal, terminated by a plane surface; they have a sharp, acid taste; are very soluble in water, but not in alcohol; they do not deliquesce.
5. Sebat of magnesia. A gummy, saline, uncrystallizable mass.
6. Sebat of alumina. A gummy saline mass, which does not crystallize, and has an astringent taste.
7. Sebat of iron. Needle-shaped crystals, which deliquesce.
8. Sebat of lead. Needle-shaped crystals, very soluble in water.
9. Sebat of tin. A white deliquescent salt.
10. Sebat of copper. This salt is capable of crystallizing, but is very deliquescent.
11. Sebat of antimony. A crystallizable salt, which does not deliquesce.
12. Sebat of arsenic. Small crystals.
13. Sebat of mercury. A white powder, very difficultly soluble in water.
14. Sebat of gold. Yellow crystals.
15. Sebat of platinum. Brownish yellow crystals.
The bombastic or compounds which the bombastic acid forms are still unknown. Sect. XXVI. Of Arseniates.
The compounds formed by the combination of the arsenic acid with bases are called arseniates. This class of salts was first discovered by Macquer; but little accurate was known concerning it till Scheele made known the arsenic acid.
An abstract of Scheele's experiments has been given in the article Chemistry, Encycl.
To his description of arsenites several additions might be made, but not of sufficient consequence to warrant a repetition of what has been given in that article; and without such a repetition these additions would scarcely be intelligible.
Sect. XXVII. Of Metallic Acid Salts.
It has been conjectured that all metals may be converted into acids by combining them with a sufficient quantity of oxygen. This conjecture has been verified in a considerable number of instances. We have seen the arsenic acid, the tungstic acid, the molybdic acid, and the new metallic acid of Vauquelin. Berthollet has discovered that platinum becomes an acid; and the same thing has been ascertained with regard to tin. Even those metallic oxyds which do not possess many of the characters of acids are capable of combining with alkalies and earths, and of forming peculiar neutral salts. These oxyds, therefore, perform the office of acids; and consequently must be considered as partaking of their nature, or rather as a kind of intermediate substances between acids and those bodies which unite only with acids.
Some of these neutral salts we shall proceed to enumerate.
1. Aurat of ammonia, or fulminating gold. This salt is composed of the oxyd of gold and ammonia. This compound may be formed by precipitating gold from nitro-muriatic acid by ammonia. The precipitate is fulminating gold. Bergman was the first who clearly demonstrated that this powder is composed of oxyd of gold and ammonia. When heated a little above the boiling temperature it explodes with astonishing violence. Chemists had made many attempts to explain the cause of this phenomenon, but without success, till Mr Berthollet discovered the composition of ammonia. After making that discovery, he proved, by a number of delicate and hazardous experiments, that during the fulmination the ammonia is decomposed, that its hydrogen combines with the oxygen of the oxyd and forms water, while the azot flies off in a gaseous form, and occasions the explosion.
2. Argentat of ammonia, or fulminating silver. This substance was discovered by Mr Berthollet. It may be formed by dissolving oxyd of silver in ammonia. It is a black powder. It possesses the fulminating property much more powerfully than the last described substance. The slightest friction makes it explode with violence. This property, as Mr Berthollet has proved, is owing to the same decomposition of ammonia and formation of water that causes the explosion of fulminating gold.
If a small retort be filled with the liquor from which the fulminating silver has been precipitated, and be made to boil, some azot is disengaged, and small opaque crystals are formed consisting of the same substance; which explode when touched, though they be covered with water. Nitrate and muriat of barytes precipitate silver from this salt.
3. Mercuriat of lime. Oxyd of mercury boiled with lime-water forms, by evaporation, small transparent yellow crystals.
4. Mercuriat of ammonia. Oxyd of mercury dissolves in ammonia in large quantity, and by evaporation furnishes a white salt.
5. Cuprat of ammonia. Oxyd of copper dissolves in ammonia. Mr Sage has described its crystallization. It is decomposed by lime and potash, and cuprat of lime and potash are formed.
6. Stannat of gold. When gold is precipitated by stannin it unites with it. Vogel and Beaumé first observed that the precipitate, which is purple, contained tin.
7. Plumbat of lime. Lime-water boiled on the red oxyd of lead dissolved it. This solution evaporated in a retort, gave very small transparent crystals, forming prismatic colours, and not more soluble in water than lime. It is decomposed by all the sulphats of alkalies and by sulphurated hydrogen gas. The sulphuric and muriatic acids precipitate the lead. It blackens wool, the nails, the hair, white of eggs; but it does not affect the colour of silk, the skin, the yoke of egg, nor animal oil. It is the lead which is precipitated on these coloured substances in the state of oxyd; for all acids can dissolve it. The simple mixture of lime and oxyd of lead blackens these substances; a proof that the salt is easily formed.
8. Zincat of ammonia. De Cassone has published a great number of experiments on the property which ammonia has of dissolving oxyd of zinc. Lime water and potash also dissolve it.
9. Antimoniat of potash. When antimony is detonated with nitre in a crucible, part of its oxyd unites with the potash of the nitre.
Chap. III. Of Hydrosulphurets.
Sulphurated hydrogen gas, which has been described in the first part of this article, possesses almost all the properties of acids. It combines with water, and the solution gives a red colour to vegetable blues. It decomposes soaps and sulphurets, and is capable of combining with alkalies, earths, and metallic oxyds, and of forming compounds, to which Mr Berthollet, to whom we are indebted for discovering them, has given the name of hydrosulphurets.
Before giving any account of these compounds, which we shall do from the paper of Berthollet just quoted, we beg leave to make a few previous observations, in order to rectify some inaccuracies into which we have fallen from not being acquainted with the experiments of that philosopher.
Sulphur is capable of combining with alkalies, earths, metals, and metallic oxyds, and forming the compounds known by the name of sulphurets. The alkaline, earthy, and even some of the metallic sulphurets, can only exist in a state of dryness; the instant they are moistened with water, a quantity of sulphurated hydrogen gas is formed, which combines with the sulphuret, and forms a new compound. To these triple compounds Mr Berthollet has given the name of hydrogenous sulphurets. All solutions of sulphurets in water are in fact hydrogenous sulphurets. Were it not for the formation and combination of sulphurated hydrogen, the alkaline sulphurets would... Almost all the metallic oxyds have a stronger affinity for sulphurated hydrogen than the earths have.
When the hydrofulphurets are prepared with the necessary precautions to prevent the contact of atmospheric air, they are colourless; but the action of the air renders them yellow.
If they be decomposed while they are colourless, by pouring upon them sulphuric acid, muriatic acid, or any other acid which does not act upon hydrogen, the sulphurated hydrogen gas exhales without the deposition of a single particle of sulphur; but if the hydrofulphuret has become yellow, some sulphur is always deposited during its decomposition, and the quantity of sulphur is proportional to the depth of the colour.
The yellow colour, therefore, which hydrofulphurets acquire by exposure to the atmosphere is owing to a commencement of decomposition. Part of the hydrogen of the sulphurated hydrogen abandons the sulphur, combines with the oxygen of the atmosphere, and forms water. By degrees, however, a portion of the sulphur is also converted into an acid; and when the proportion of sulphurated hydrogen is diminished, and that of the sulphur increased to a certain point, the sulphur and the hydrogen combine equally with oxygen.
If sulphuric or muriatic acids be poured upon a hydrofulphuret after it has been for some time exposed to the air, a quantity of sulphurated hydrogen gas exhales; sulphur is deposited, and after an interval of time sulphurous acid is disengaged. It is therefore sulphurous, and not sulphuric acid, which is formed while the hydrofulphuret spontaneously absorbs oxygen. This acid, however, is not perceptible till after a certain interval of time when separated from the hydrofulphuret by means of an acid; because as long as it meets with sulphurated hydrogen a reciprocal decomposition takes place. The oxygen of the acid combines with the hydrogen of the gas, and the sulphur of both is precipitated.
Sulphurated hydrogen is capable of combining with several of the metals, mercury, for instance, and silver; it combines with the greater number of the metallic oxyds, and forms hydrofulphurets, on which the alkalies have no action at the temperature of the atmosphere; but concentrated acids combine with the oxyds of these hydrofulphurets, and separate the sulphurated hydrogen in the form of gas.
In the greater number of these metallic oxyd hydrofulphurets, the tendency which oxygen and hydrogen have to combine occasions a partial decomposition of the sulphurated hydrogen, and brings the oxyds nearer to the metallic state. In some of these hydrofulphurets part of the sulphur also combines with oxygen, and forms sulphuric acid.
The alkaline hydrofulphurets precipitate all the metals from their combination with acids; they are therefore very valuable tests of the presence of metals in any solution, as they do not precipitate any of the earths except alumina and jargonia. The following table exhibits a view of the effect of hydrofulphuret of potash, hydrogenous sulphuret of potash, and water impregnated with sulphurated hydrogen gas, upon various metallic solutions. | Metallic Solutions | Solution of Hydrogenous sulphuret of Potash | Water impregnated with Sulphured Hydrogen Gas | Hydrofulphuret of Potash | |--------------------|---------------------------------------------|-----------------------------------------------|-------------------------| | Green sulphate of iron | A black precipitate, which becomes yellow by the contact of the air. | Becomes black. The liquor remains very deep coloured if there be an excess of sulphurated hydrogen. | A black precipitate. The potash separated. | | Red oxyd of iron | | | Becomes black. | | Sulphate of zinc | A white precipitate. | A white precipitate. | A white precipitate. | | Acetite of lead | A white precipitate, which by an addition becomes black. | A black precipitate. | A black precipitate. | | Red oxyd of lead | | Becomes black. | The potash separated. | | Nitrat of bismuth | | A black precipitate. | A black precipitate. | | Oxyd of bismuth | | Becomes black. | | | Nitrat of silver | A black precipitate. | A black precipitate. | A black precipitate. | | Sulphate of copper | A brown precipitate. | A black precipitate. | A black precipitate. | | Green oxyd of copper | | Becomes black. | Separation of the potash. | | Nitrat of mercury | In a great deal of water, a brown colour. | A brownish black precipitate. | A brownish black precipitate. | | Oxy-muriat of mercury | A white precipitate, which becomes black by addition. | A white precipitate, becoming black by an addition. | White, becomes black by addition. | | Red oxyd of mercury | | Blackish. | A heat produced which caused the hydrofulphuret to boil. The alkali separated (a). | | Muriat of tin | | | A black precipitate. | | Oxy-muriat of tin | A precipitation of sulphur, and of the oxyd. | No change. | A precipitation of white oxyd of tin, and a disengagement of sulphurated hydrogen gas. | | White oxyd of tin | | No change. | Disengagement of sulphurated hydrogen gas. | | Sulphate of manganese | | No change. | A white precipitate. | | Black oxyd of manganese | | The odour disappears. An excess of the water dissolves the oxyd. | Ammonia disengaged. Heat. The liquor boils (a). | | Nitrat of antimony | | | A reddish orange precipitate. | | Tartrate of antimony | A yellow orange precipitate. | An orange colour, but no precipitate. | An orange red precipitate, redissolved by an excess of hydrofulphuret. | | White oxyd of antimony | | Becomes yellow after some seconds. | The liquor loses its colour (a). |
(a) In these, hydrofulphuret of ammonia was used instead of hydrofulphuret of potash. ### Table continued.
| Metallic Solutions | Solution of Hydrogenous Sulphur of Potash | Water impregnated with Sulphurated Hydrogen Gas | Hydroalpheute of Potash | |--------------------|------------------------------------------|-------------------------------------------------|------------------------| | Oxide of antimony sublimed. | | Scarcely changes colour. | | | Solution of oxide of arsenic. | Sulphuret decomposed as by an acid. | Becomes somewhat muddy, and of a yellow colour. | A yellow colour, but no precipitate. | | Sulphate of titanium. | | | A precipitate of a deep green. | | Molybdenic acid. | | | A brown precipitate. |
### Chap. IV. Of Crystallization.
The word crystal in its strictest and proper sense signifies a transparent body possessed of a regular figure. But it is now used to denote a body which has assumed a regular figure whether it be transparent or not. Crystalization is the act by which this regular figure is formed.
As the greater number of crystals belong to the class of neutral salts, it may not be improper before we conclude this part of the article to make a few observations on the phenomena of crystallization.
As crystallization is confessedly nothing else than the regular arrangement of the particles of bodies, it is evident that before it can take place the particles of the body to be crystallized must be at some distance from each other, and that they must be at liberty to obey the laws of attraction. They may be put into this situation by three methods, solution, suspension, and fusion.
1. Solution is the common method of crystallizing salts. They are dissolved in water; the water is slowly evaporated, the saline particles gradually approach each other, combine together, and form small crystals; which become constantly larger by the addition of other particles till at last they fall by their gravity to the bottom of the vessel. It ought to be remarked, however, that there are two kinds of solution, each of which presents different phenomena of crystallization. Some salts dissolve in very small proportions in cold water, but are very soluble in hot water; that is to say, water at the common temperature has little effect upon them, but water combined with caloric dissolves them readily. When hot water saturated with any of these salts cools, it becomes incapable of holding them in solution; the consequence of which is, that the saline particles gradually approach each other and crystallize. Sulphate of soda is a salt of this kind. To crystallize such salts nothing more is necessary than to saturate hot water with them, and let it be to cool. But were we to attempt to crystallize them by evaporating the hot water, we should not succeed; nothing would be procured but a shapeless mass. Many of the salts which follow this law of crystallization combine with a great deal of water; or, which is the same thing, many crystals formed in this manner contain a great deal of water of crystallization.
There are other salts again which are nearly equally soluble in hot and cold water; common salt for instance. It is evident that such salts cannot be crystallized by cooling; but they crystallize very well by evaporating their solution while hot. These salts generally contain but little water of crystallization.
2. It appears, too, that some substances are capable of assuming a crystalline form merely by having their particles suspended in water, without any regular solution; at least it is not easy, on any other supposition, to explain the crystallizations of carbonat of lime sometimes deposited by waters that run over quantities of that mineral.
3. There are many substances, however, neither soluble in water, nor capable of being so minutely divided as to continue long suspended in that fluid; and which, notwithstanding, are capable of assuming a crystalline form. This is the case with the metals, with glass, and some other bodies. The method employed to crystallize them is fusion, which is a solution by means of caloric. By this method the particles are separated from one another; and if the cooling goes on gradually, they are at liberty to arrange themselves in regular crystals. There are many substances, however, which it has been hitherto impossible to reduce to a crystalline form, either by these or any other method. Whether this be owing to the nature of these bodies themselves, or to our ignorance of the laws by which crystals are formed, as is much more likely, cannot be determined.
The phenomena of crystallization seem to have attracted but little of the attention of the ancient philosophers. Their theory indeed, that the elements of bodies possess certain regular geometrical figures, may have been suggested by these phenomena; but we are ignorant of their having made any regular attempt to explain them. The schoolmen ascribed the regular figure of crystals to their substantial forms, without giving themselves much trouble about explaining the meaning of the term. This notion was attacked by Boyle; who proved, that crystals were formed by the mere aggregation of particles. But it still remained to explain why that aggregation took place? and why the particles united in such a manner as to form regular figures? These questions were answered by Newton. According to him, the aggregation is produced by the attraction which he had proved to exist between the particles of all bodies, and which acts as soon as these particles are brought within a certain distance of each other by the evaporation of the liquid in which they are dissolved. The regularity of their figures he explained by supposing, that while in a state of solution they were arranged in the liquid in regular rank and file; the consequence... Chemistry.
Crystallization of which, as they are acted upon by a power which at equal distances is equal, at unequal distances unequal, will be crystals of determinate figures.
This explanation, which is worthy of Newton, is now universally admitted as the true one, and has contributed much towards elucidating this important part of chemistry.
Still, however, there remain various phenomena relating to crystallization which it is no easy matter to explain.
It has been observed, that those salts which crystallize upon cooling, do not assume a crystalline form so readily if they are allowed to cool in close vessels. If a saturated solution of sulphate of soda, for instance, in hot water be put into a phial, corked up closely, and allowed to cool without being moved, no crystals are formed at all; but the moment the glass is opened, the salt crystallizes with such rapidity that the whole of the solution in a manner becomes solid. This phenomenon has been explained by supposing, that there is an affinity between the salt and caloric, and that while the caloric continues combined with it the salt does not crystallize; that the caloric does not leave the salt so readily when external air is not admitted, as glass receives it very slowly and parts with it very slowly. In short, the atmospheric air seems to be the agent employed to carry off the caloric; a task for which it is remarkably well fitted, on account of the change of density which it undergoes by every addition of caloric. This is confirmed by the quantity of caloric which always makes its appearance during these sudden crystallizations. This explanation might be put to the test of experiment, by putting two solutions of sulphate of soda in hot water in two similar vessels; one of glass, the other of metal, and both closed in the same manner. If the salt contained in the metallic vessel crystallized, which ought to be the case on account of the great conducting power of metals, while that in the glass vessel remained liquid, this would be a confirmation of the theory, amounting almost to demonstration.
On the contrary, if both solutions remained liquid, it would be a proof that the phenomenon was still incompletely understood.
Not only salts but water itself, which commonly crystallizes at 32°, may be made to exhibit the same phenomenon: it may be cooled much lower than 32 without freezing. This, as Dr Black has completely proved, depends entirely upon the retention of caloric.
If the regular form of crystals depends upon the aggregation of particles, and if during all crystallizations this aggregation goes on in the same manner, why have not all crystals the same form? Some have ascribed these differences to a certain polarity which the particles of bodies are supposed to possess, and which dispose each kind of particles to arrange themselves according to a certain law. Sir Isaac Newton appears rather to have ascribed it to the forms of the particles themselves; and this seems to be the real solution of the problem. For supposing that all particles have the same form, they must of course possess the same polarity; and therefore every crystal must have the same form.
It is impossible, then, to account for the different forms of crystals without supposing that the particles which compose them have also different forms. And if the particles of bodies have different forms, their regular aggregation must produce crystals of various shapes; and therefore their polarity, which is merely a supposition founded on this difference in the appearance of crystals, cannot be admitted. Suppose, for instance, that eight cubic particles were regularly arranged in water, and that by the gradual evaporation of the liquid were to approach, and at last to combine, it is evident that the crystal which they would produce would be a cube. Eight six-sided prisms would also produce a six-sided prism; and eight tetrahedrons would form a very different figure.
But it will be asked, if the figure of crystals depends entirely upon the form of the particles that compose them, how comes it that the same substance does not always crystallize in the same way, but presents often such a variety of forms that it is scarcely possible to reckon them? We answer, that these various forms are sometimes owing to variations in the ingredients which compose the integrant particles of any particular body. Alum, for instance, crystallizes in octahedrons; but when a quantity of alumina is added, it crystallizes in cubes; and when there is an excess of alumina it does not crystallize at all. If the proportion of alumina varies between that which produces octahedrons and what produces cubic crystals, the crystals become figures with fourteen sides; five of which are parallel to those of the cube and eight to those of the octahedron; and according as the proportions approach nearer to those which form cubes or octahedrons, the crystals assume more or less of the form of cubes or octahedrons. What is still more, if a cubic crystal of alum be put into a solution that would afford octahedral crystals, it passes into an octahedron; and on the other hand, an octahedral crystal put into a solution that would afford cubic crystals, becomes itself a cube. Now, how difficult it is a matter it is to proportion the different ingredients with absolute exactness must appear evident to all.
Another circumstance which contributes much to vary the form of crystals, is the different degree of concentration to which their solution has been reduced, and the rapidity or slowness with which they are formed. For it is too evident to require illustration, that when crystals are deposited very rapidly they must obstruct one another, and mix together so as very much to obscure the natural regularity of their form.
Even the nature of the vessel in which the crystallization is performed is not without some influence.
But, independent of these accidental circumstances, Mr Haug has shown that every particular species of crystal has a primitive figure, and that the variations of crystals are owing to the different ways in which the particles arrange themselves. Of this theory, which is certainly exceedingly ingenious, and even satisfactory, we shall attempt to give a short view.
Happening to take up a hexangular prism of calcareous spar, or carbonat of lime, which had been detached from a group of the same kind of crystals, he observed that a small portion of the crystal was wanting, and that the fracture presented a very smooth surface. Let \(a b c d e f g h\) (fig. 8.) be the crystal; the fracture lay obliquely as the trapezium \(p r u t\), and made an angle of 135°, both with the remainder of the base \(a b c e f h\) and with \(r u e f\), the remainder of the side \(i n e f\). Observing that the segment \(p u i n\) thus cut off had for its vertex \(i n\), one of the edges of the base \(a b c e f h\) of the prism, he attempted to detach may also be divided by sections parallel to the sides of the primitive crystal. It follows from this, that the parts detached by means of these sections are similar, and differ from one another only in size, which diminishes in proportion to the length that the division is carried. But the division of the crystals into similar solids has a term, beyond which we should come to the smallest particles of the body, which could not be divided without chemical decomposition. It is probable, therefore, that the form of the integrant particles of a body is the same with the primitive form of its crystals. Here, then, we have a method of discovering the form of the particles of bodies; and if this method could be applied to all substances whatever, it would enable us to ascertain the affinity of all bodies for each other by accurate calculation. It must be allowed, that several objections might be made to the conclusions of Mr Hauy; but his theory is, on the whole, so plausible, that it would certainly be worth while to extend it, and apply it to the calculation of affinities as far as it is susceptible of the application. If the crystals obtained by the above process be the primitive forms, it becomes a question of some consequence to determine in what manner the secondary forms are produced.
According to Hauy, all the parts superadded to the primitive crystals, in order to form the secondary crystal, consist of plates, which decrease regularly by the subtraction of one or more rows of integrant particles, in such a manner, that the number of these ranks, and consequently the form of the secondary crystal, may be determined by theory (c).
To explain this, let us suppose that EP (fig. 12.) represents a dodecahedron, terminated by equal and similar rhombs; that this dodecahedron is a secondary crystal, the primitive form of which is a cube: the situation of this cube in the dodecahedron may be conceived from fig. 13. The smaller diagonals DC, CG, GF, FD, of four sides of the dodecahedron, united round the same solid angle L, form the square CDFG. Now there are six fold angles, composed of four plains, to wit, the angles L, O, E, N, R, P (fig. 12.); and consequently, by making sections through the smaller diagonals of the sides that form these angles, six squares will be made apparent, which are the six sides of the primitive cube, three of which are represented in fig. 13. CDFG, ABCD, BCGH.
This cube being composed of cubic integrant particles, each of the pyramids, LCDFG for instance (fig. 13.) which repose upon its sides, must also, according to the theory, be composed of similar cubic particles. To make this appear, let us suppose that ABFG (fig. 14.) is a cube composed of 729 small cubes: Each of its sides will consist of 81 squares, being the external sides of as many cubic particles, which together constitute the cube. Upon ABCD, one of the sides of this cube, let us apply a square lamina, composed of cubes equal to those of which the primitive crystal consists, but which has on each side a row of cubes less than the outermost layer of the primitive cube. It will of course be composed of 49 cubes, 7 on each side; so that its lower base on FG (fig. 15.) will fall exactly on the square marked with the same letters in fig. 14.
Above this lamina let us apply a second lamina (fig. 16.), composed of 25 cubes; it will be situated exactly above the square marked with the same letters (fig. 14.). Upon this second let us apply a third lamina v x y z (fig. 17.), consisting only of 9 cubes; so that its base shall rest upon the letters v x y z (fig. 14.). Lastly, on the middle square r let us place the final cube r (fig. 18.), which will represent the last lamina.
It is evident, that by this process a quadrangular pyramid has been formed upon the face ABCD (fig. 14.), the base of which is this face, and the vertex the cube r (fig. 18.). By continuing the same operation on the other five sides of the cube, as many similar pyramids will be formed; which will envelop the cube on every side.
It is evident, however, that the sides of these pyramids will not form continued planes, but that, owing to the gradual diminution of the laminae of the cubes which compose them, these sides will resemble the steps of a stair. We can suppose, however (what must certainly be the case), that the cubes of which the nucleus is formed are exceedingly small, almost imperceptible; that therefore a vast number of laminae are required to form the pyramids, and consequently that the channels which they form are imperceptible. Now DCBE (fig. 19.) being the pyramid resting upon the face ABCD (fig. 14.), and CBOG (fig. 19.) the pyramid applied to the next face BCGH (fig. 14.), if we consider that every thing is uniform from E to O (fig. 19.) in the manner in which the edges of the laminae of superposition (as the Abbé Haüy calls the laminae which compose the pyramids) mutually project beyond each other, it will readily be conceived, that the face CEB of the first pyramid ought to be exactly in the same plane with the face COB of the adjacent pyramid; and that therefore the two faces together will form one rhomb ECOB. But all the sides of the five pyramids amount to 24 triangles similar to CEB; consequently they will form 12 rhombs, and the figure of the whole crystal will be a dodecahedron, similar to that represented in fig. 12. and 13.
If the decrease of the laminae of superposition took place according to a more rapid law, if each lamina had on its circumference two, three, or four rows of cubes less than the inferior lamina—in that case, the pyramids produced being lower, their adjacent faces would no longer form one plane; and therefore the surface of the secondary crystal would consist of 24 isosceles triangles, all inclined towards each other.
In this manner Mr Haüy has shewn, that a variety of secondary crystals are formed, and that their forms vary by means of slight variations in the ratio of the decrement. Dodecahedral sulphuret of iron, for instance, is formed from a cubic nucleus, by the addition of laminae, decreasing, as in the example given above, with this difference, that from every lamina laid upon the face ABCD (fig. 14.) only one row of cubes are subtracted at the sides AD and BC respectively; whereas two rows are subtracted at each of the sides AB and CD. The consequence of this more rapid decrement on two parallel sides than on the other two will be, that the pyramid raised on the face ABCD (fig. 14.), instead of terminating in a single cube as in the example given above, will terminate in a range of cubes; or (supposing the cubes infinitely small) instead of terminating in a point, it will terminate in a ridge. The pyramid will therefore have for its two sides, contiguous to AB and DC, two trapeziums, and for its sides, contiguous to AD and BC, two triangles. Let us suppose also, that with regard to the laminae of superposition which arise on the face BCGH (fig. 14.), the decrements follow the same law, and that each lamina decreases by two rows of cubes towards the lines BC and HG, and only by one row towards the lines CG, BH: The pyramid, in that case, will be placed in a direction opposite to the pyramid on ABCD, the ridge at the vertex of it running parallel to BC: the vertex of the pyramid raised upon CDFG must be parallel to CG: the pyramids on the three other sides of the cube ought to stand each like that which arises on the opposite face.
The sides of all the six pyramids thus formed amount to twelve trapeziums and twelve triangles. Every triangle is evidently contiguous and in the same plane with a trapezium of the nearest pyramid; consequently the secondary crystal thus formed consists of twelve sides, each of which is a pentagon.
Several other examples have been given by Mr Haüy; but these are sufficient to show in what manner the various secondary forms of crystals are constructed, according to the theory of that ingenious philosopher.
In his researches on this subject, Mr Haüy perceived, that some crystals assumed secondary forms which could not be accounted for by any decrement whatever along the edges. Thus, for instance, some bodies, the primary form of which is cubic, are sometimes found crystallized in regular octagons. Mr Haüy explains the formation of these secondary crystals, by supposing that the decrement took place parallel, not to the edges, but to the diagonals of the faces of the primary cubes.
In order to comprehend this, let us suppose ABCD (fig. 20.) to be the surface of a lamina composed of small cubes, the bases of which are represented by the little squares in the figure. It is evident, that the cubes a, b, c, d, e, f, g, h, i, are in the direction of the diagonal of the square ABCD; that the row of cubes q, r, s, t, u, v, w, x, y, z, is parallel to the diagonal; as also the row n, o, p, q, r, s; and that the whole figure might be divided into rows of squares, each of which would be parallel either to the diagonal AC or DB.
Now we may conceive that the laminae of superposition, instead of decreasing by rows of cubes parallel to the edges AB, AD, decrease by rows parallel to the diagonals.
Let it be proposed to construct around the cube ABGF (fig. 21.), considered as a nucleus, a secondary solid, in which the laminae of superposition shall decrease on all sides by single rows of cubes, but in a direction parallel to the diagonals. Let ABCD (fig. 22.), the superior base of the nucleus, be divided into 81 squares, representing the faces of the small cubes of which it is composed. Figure 23. represents the superior surface of the first lamina of superposition; which must be placed above ABCD (fig. 22.), in such a manner that the points a', b', c', d' (fig. 23.) answer to the points a, b, c, d, (fig. 22.). By this disposition the squares Aa, Ba, Ca, Da (fig. 22.), which compose the four outermost rows of squares parallel to the diagonals AC, BD, remain uncovered. It is evident also, that the borders QV, ON, IL, GF (fig. 23.), project by one range beyond the borders AB, AD, CD, BC (fig. 22.), which is necessary, that the nucleus may be enveloped towards these edges: For if this were not the case, The superior face of the second lamina will be $A'G'L'K'$ (fig. 24.). It must be placed so that the points $a', b', c', d'$ correspond to the points $a, b, c, d$ (fig. 23.), which will leave uncovered a second row of cubes at each angle, parallel to the diagonals AC and BD. The solid still increases towards the sides. The large faces of the laminae of superposition, which in fig. 23., were octagons, in fig. 24., arrive at that of a square; and when they pass that term they decrease on all sides; so that the next lamina has for its superior face the square $B'M'L'S'$ (fig. 25.), less by one range in every direction than the preceding lamina (fig. 24.). This square must be placed so that the points $e', f', g', h'$ (fig. 25.) correspond to the points $e, f, g, h$ (fig. 24.).
Figures 26, 27, 28, and 29, represent the four laminae which ought to rise successively above the preceding; the manner of placing them being pointed out by corresponding letters, as was done with respect to the three first laminae. The last lamina $x$ (fig. 30.) is a single cube, which ought to be placed upon the square $x$ (fig. 29.).
The laminae of superposition, thus applied upon the side $ABCD$ (fig. 22.), evidently produce four faces, which correspond to the points $A, B, C, D$, and form a pyramid. These faces, having been formed by laminae, which began by increasing, and afterwards decreased, must be quadrilaterals of the figure represented in fig. 31.; in which the inferior angle $C$ is the same point with the angle $C$ of the nucleus (fig. 21. and 22.); and the diagonal $LQ$ represents $L'G'$ of the lamina $A'G'L'K'$ (fig. 24.). And as the number of laminae composing the triangle $LQC$ (fig. 31.) is much smaller than that of the laminae forming the triangle $ZLQ$, it is evident that the latter triangle will have a much greater height than the former.
The surface, then, of the secondary crystal thus produced, must evidently consist of 24 quadrilaterals (for pyramids are raised on the other 5 sides of the primary cube exactly in the same manner), disposed 3 and 3 around each solid angle of the nucleus. But in consequence of the decrement by one range, the three quadrilaterals which belong to each solid angle, as $C$ (fig. 21.) will be in the same plane, and will form an equilateral triangle $ZIN$ (fig. 32.). The 24 quadrilaterals, then, will produce 8 equilateral triangles; and consequently the secondary crystal will be a regular octagon. This is the structure of the octahedral sulphuret of lead and of muriatic acid.
Decrements which take place in this manner have been called by Mr Haüy decrements on the angles.
There are certain crystals in which the decrements on the angles do not take place in lines parallel to the diagonals, but parallel to lines situated between the diagonals and the edges. This is the case when the sub-crystalline tracts are made by ranges of double, triple, &c. molecule. Fig. 33. exhibits an instance of the subtractions in question; and it is seen that the molecule which compose the range represented by that figure are afforded in such a manner as if of two there were formed only one; so that we need only to conceive the crystal composed of parallelopipeds having their bases equal to the small rectangles $abcde, defgh, higl$, &c. to reduce this case under that of the common decrements on the angles. To this particular kind of decrement Mr Haüy has given the name of intermediate.
In other crystals the decrements, either on the edges or on the angles, vary according to laws, the proportion of which cannot be expressed but by the fraction $\frac{3}{4}$ or $\frac{1}{2}$. It may happen, for example, that each lamina exceeds the following by two ranges parallel to the edges, and that it may at the same time have an altitude triple that of a simple molecule. Figure 34. represents a geometrical section of one of the kinds of pyramids which would result from this decrement; the effect of which may be readily conceived, by considering that $AB$ is a horizontal line taken on the upper half of the nucleus, $a \approx r$ the section of the first lamina of superposition, $g'f'c'n$ that of the second, &c. These decrements Mr Haüy has called mixed.
These two last species of decrements occur but rarely; Mr Haüy found them only in certain metallic substances.
All the metamorphoses to which crystals are subjected depend, according to Mr Haüy, on the laws of structure just explained, and others of the like kind. Sometimes the decrements take place at the same time on all the edges; as in the dodecahedron having rhombuses for its planes, as before mentioned; or on all the angles, as in the octahedron originating from a cube. Sometimes they take place only on certain edges or certain angles. Sometimes there is an uniformity between them; so that it is one single law by one, two, three ranges, &c. which acts on the different edges, or the different angles. Sometimes the law varies from one edge to the other, or from one angle to the other; and this happens above all when the nucleus has not a symmetrical form; for example, when it is a parallelopipedon, the faces of which differ by their respective inclinations, or by the measure of their angles. In certain cases the decrements on the edges concur with the decrements on the angles to produce the same crystalline form. It happens also sometimes that the same edge, or the same angle, is subjected to several laws of decrement that succeed each other. In short, there are cases where the secondary crystal has faces parallel to those of the primitive form, and which combine with the faces produced by the decrements to modify the figure of the crystal.
The crystals arising from a single law of decrement have been called by Mr Haüy simple secondary forms; those which arise from several simultaneous laws of decrement he has called compound secondary forms.
"If amidst this diversity of laws (he observes), sometimes inflated, sometimes united by combinations more or less complex, the number of the ranges subtracted were itself extremely variable; for example, were these decrements by twelve, twenty, thirty, or forty ranges, or more, as might absolutely be possible, the multitude..." The fecundity of the laws on which the variations of crystalline forms depend, is not confined to the producing of a multitude of very different forms with the same molecules. It often happens also, that molecules of different figures arrange themselves in such a manner as gives rise to like polyhedra in different kinds of minerals. Thus the dodecahedron with rhombuses for its planes, which we obtained by combining cubic molecules, exists in the granite with a structure composed of small tetrahedra, having isosceles triangular faces; and I have found it in sparry fluor (flint of lime), where there is also an assemblage of tetrahedra, but regular; that is to say, the faces of which are equilateral triangles. Nay more, it is possible that similar molecules may produce the same crystalline form by different laws of decrement. In short, calculation has conducted me to another result, which appeared to me still more remarkable, which is, that, in consequence of a simple law of decrement, there may exist a crystal which externally has a perfect resemblance to the nucleus, that is to say, to a solid that does not arise from any law of decrement.*
Such is a short view of the theory by which Mr. Haüy explains the various crystalline forms of the same substance. We would with pleasure have entered more into detail, had not most of his examples been deduced from substances which belong rather to mineralogy than to the elements of chemistry. This theory, to say no more of it, is, in point of ingenuity, inferior to few; and the mathematical skill and industry of its author are entitled to the greatest applause.
But what we consider as the most important part of that philosopher's labours, is the method which they point out of discovering the figure of the integrant particles of crystals; because it may pave the way for calculating the affinities of bodies, which is certainly by far the most important part of chemistry. This part of the subject, therefore, deserves to be investigated with the greatest care.
Mr. Haüy has found, that the primitive form of all the crystals which he has examined may be reduced to six: 1. The parallelopipedon in general, comprehending the cube, the rhomboïd, and all solids terminated by six sides parallel two and two; 2. The regular tetrahedron; 3. The octahedron with triangular sides; 4. The hexagonal prism; 5. The dodecahedron bounded by rhombs; 6. The dodecahedron bounded by isosceles triangles. Were we to suppose that these primitive forms are exactly similar to the form of the integrant particles which compose them, it would follow, that the integrant particles of all the crystals hitherto formed have only six different forms. This supposition, however, is not probable; because the same nucleus has been discovered in different species of minerals, and because we can easily conceive integrant particles of different forms combining in such a manner as to compose nuclei of the same figure, just as we have seen that different primitive forms are capable of producing the same secondary form. Still, therefore, in endeavouring to discover the integrant particles of bodies, there are difficulties to remove, which hitherto, at least, have been unmountable. But the theory of Mr. Haüy may be considered as a first step towards the discovery and a step in researches of so difficult a nature is of very great consequence. We have now finished the three first parts of this article, which comprehend all the elementary part of chemistry. We ought now to proceed to the fourth part, which was to consist of a chemical examination of substances as they exist in nature in the mineral, vegetable, and animal kingdoms; but this, for various reasons, we shall defer till we come to the words MINERALOGY, and Animal and Vegetable Substances.
We shall finish this article with a few remarks upon the chemical nomenclature, which for some time past has been an object of serious attention.
Chemistry was unfortunately first cultivated by a set of ignorant men, filled with the highest notions of their own importance, and buoyed up with the mighty feats which they were to perform by their art. The little which they did know they were anxious to conceal; and their anxiety was no less to inspire the world with high ideas of their knowledge and power. The consequence of this was, that they loaded chemistry with the most ridiculous and whimsical names that can well be conceived.
Lover of sulphur, mercury of life, burned moon, bitter of antimony, the double secret, the coralline secret, the secret of vitriol, the wonderful salt, the secret salt, the salt with many virtues, the salt of two ingredients, the foliated earth of tartar, were the names by which they distinguished some of the most familiar preparations; and, were it worth while, a great many more names of the same stamp might easily be added.
As soon as chemistry had attracted the attention of men of science, the absurdity of its nomenclature was felt, and several partial improvements were at different times made in it. Mecquer, in particular, discarded many of the ancient names, and substituted others less exceptionable in their place.
But soon after the publication of the first edition of his Dictionary, an evil began to be felt severely, which never could have occurred to the earlier chemists. Hitherto the number of objects which had engaged the attention of those who cultivated the science had been very limited; the acids amounted only to five, the earths to four, the metals to twelve or fourteen, and the neutral salts scarcely exceeded twenty or thirty. To remember names so small a number of bodies, however ridiculous they happened to be, was not very difficult matter. But about that time, in consequence chiefly of the discovery of fixed air by Dr Black, which laid the foundation of pneumatic chemistry, the science began to extend itself, and to enlarge its boundaries with inconceivable rapidity. The number of bodies connected with it, and which it had to describe, soon became immense; and if every one of them received names not dependant upon one another, the most retentive memory could not have remembered the thousandth part of them.
The difficulty of studying chemistry from that time till the year 1782 must have been very great; it was even perceived and complained of by the masters of the science. In 1782 Mr de Morveau, who had undertaken the chemical part of the Encyclopédie Méthodique, published in the Journal de Physique a new chemical nomenclature, and at the same time invited all those persons who were fond of chemistry, and interested in its progress, to propose objections and improvements.
This new nomenclature was formed agreeably to the five following rules:
1. Every substance ought to have a name, and not to be denoted by a phrase. 2. Names ought to be as much as possible conformable to the nature of the things signified by them. 3. When the character of a substance is not well enough known to determine the denomination, a name which has no meaning is preferable to one which conveys a false idea. 4. In the choice of new words, those ought to be preferred which have their roots in the dead languages most generally known, that the word may be easily figured by the sense, and the sense by the word. 5. The new words ought to be as suitable as possible to the genius of the languages for which they are formed.
This nomenclature was approved of by Mecquer, and by Bergman, who had himself proposed one upon a plan not very different (p). He wrote to Morveau, and exhorted him to prosecute his undertaking with courage. "Do not spare (says he) a single improper denomination; those that are already learned will be always for, and those that are not will learn the sooner."
This nomenclature was adopted by several chemists, and it was used in the greatest part of the first volume of the chemical part of the Encyclopédie Méthodique; but the new discoveries in chemistry had produced a more accurate method of reasoning, and had enabled Lavoisier to explain the phenomena of the science without the assistance of the hypothetical principle of phlogiston, which had hitherto been necessary. As the language, even in its improved state, was accommodated to this principle, and presupposed its existence, new changes became evidently necessary, in order that, according to Morveau's rule, the words might denote the most essential properties of the things intended to be signified. Accordingly, when Morveau was in Paris in 1787, Lavoisier, Berthollet, and Fourcroy, agreed to labour in concert with him to bring the chemical nomenclature still nearer to perfection. These philosophers, assisted by the mathematicians of the Royal Academy and by several chemists, formed a new nomenclature, which they made public in 1787.
For some time little attention was paid to this nomenclature by foreign chemists, and it seemed generally to be disapproved. The adherents of the phlogistic system in France, who were exceedingly numerous, viewed it as an engine artfully formed to undermine and destroy their favourite theory. They resolved, therefore, unanimously, to crush, if possible, this new instrument, which they considered as
in nostris fabricata machina miror,
Instituta domus, venturaque defecerit urbi.
And for this purpose they exerted themselves with a vigour, which was only equalled by the zeal and indefatigable exertions of their antagonists. A kind of civil war was thus kindled in the republic of letters, which was carried on with great animosity; and posterity will see, with regret, men of undoubted genius at times divesting themselves of the armour of truth and of candour, and endeavouring to serve their party, and stab their adversaries with darts steeped in the poison of calumny and falsehood. This contest, however, which was not confined to France, was productive of good effects, which infinitely surpassed all the bad ones.
See his thoughts on a natural history of fossils in the 4th vol. of his Opusc. occasioned an accumulation of facts, produced a rigid examination of theories and opinions, introduced an accuracy into chemical experiments which has been of the most essential service, and gave that tone and vigour to the cultivators of chemistry which have brought to light the most sublime and unlooked-for truths. It deserves attention, and the fact is no inconsiderable evidence in favour of the antiphlogistic theory, that almost all the illustrious chemists who at present adhere to it declared originally against it. Berthollet, Moreau, Black, Kirwan, and many other chemists who are now its ablest defenders, were at first its most powerful opponents.
"This system had hardly been published in France (says Dr Priestley, who still continues to adhere to the doctrine of phlogiston) before the principal philosophers and chemists of England, notwithstanding the rivalry which has long subsisted between the two countries, eagerly adopted it. Dr Black in Edinburgh, and as far as I hear all the Scots, have declared themselves converts, and, what is more, the same has been done by Mr Kirwan, who wrote a pretty large treatise in opposition to it. The English reviewers of books, I perceive, universally favour the new doctrine. In America, also, I hear of nothing else. It is taught, I believe, in all the schools on this continent, and the old system is entirely exploded. And now that Dr Crawford is dead, I hardly know of any person except my friends of the Lunar Society at Birmingham, who adhere to the doctrine of phlogiston; and what may now be the case with them in this age of revolutions, philosophical as well as civil, I will not at this distance answer for.
"It is no doubt time, and of course opportunity of examination and discussion, that gives stability to any principles. But this new theory has not only kept its ground, but has been constantly and uniformly advancing in reputation more than ten years, which, as the attention of so many persons, the best judges of everything relating to the subject, has been uninterruptedly given to it, is no inconsiderable period. Every year of the last twenty or thirty has been of more importance to science, and especially to chemistry, than any ten in the preceding century."
We have endeavoured in the preceding article to state the different theories which have successively made their appearance in chemistry with as much fairness as possible. If we have succeeded, the reader will be enabled to judge for himself which of these theories is the most consistent with truth; or rather, if we have succeeded, he will join with us in thinking that the theory of Lavoisier is in most points an accurate account of what takes place in nature.
This we consider as a sufficient reason for having adopted the new nomenclature; for as Moreau long ago observed, most of the objections that were made to it were rather levelled at the doctrine of those who formed it, than at the nomenclature itself. Its superiority to every other nomenclature cannot be disputed for an instant; and the vast facility which it has added to the acquisition of chemistry, must be acknowledged by every one who knows anything about the science. The table of the new nomenclature will not be expected here, as it has been already given in the Appendix to the article Chemistry in the Encyclopaedia. At any rate, it would have been unnecessary, as we have used the new names all along; and therefore our readers must by this time be well acquainted with them.
Upon the almost infinite number of criticisms which have been made on the new nomenclature, and the many new terms which since its publication have been successively proposed, we do not mean to enter. Few of these terms can bear a comparison with the French nomenclature, and still fewer have any claim to be preferred to it; and the philosophers who persist in these useless innovations, are more probably actuated by the desire of appearing to have a share in the great revolution which chemistry has undergone, than by any hopes of being able to improve the accuracy or the elegance of its language. How few have displayed the magnanimity of an illustrious philosopher of our own country, who, though he had invented a new nomenclature himself, exhorted his pupils not to use it, but to adopt that of the French chemists, which was likely soon to come into universal use.
Even the etymological remarks which have been made on the new nomenclature, we consider as either of little consequence or as ill-founded. The philosophers who formed it have displayed a sagacity and a moderation which could not be excelled, and have, upon the whole, formed a language much more systematic and much more perfect, than could have been expected; and whoever compares it with the nomenclature proposed in 1782 by Moreau, will see how great a share of it is due to that illustrious and candid philosopher.
Notwithstanding what we have here said, we would not be understood to consider the new nomenclature as already arrived at a state of such absolute perfection, that no alteration whatever can be made in it except for the worse. Such perfection belongs not to the works of man; nor if it did, could it be expected in this case, if we consider for a moment the present state of chemistry. New discoveries must occasion additions and alterations in the nomenclature; but the authors of the new nomenclature have given us the rules by which changes and additions are to be made; and if they are adhered to, we may expect with confidence that the language of chemistry will in its advancement to perfection keep pace with the science. We have in the preceding article ventured in an instance or two to adopt little improvements that have been suggested by later writers. We have taken the liberty, too, of choosing, from the variety which the British chemists have proposed, that mode of spelling each of the terms which appeared to us most agreeable to the English idiom, and most conformable to analogy: Whether or not we have made a proper choice must be left for others to determine.
Erratum in the article Chemistry.
In page 257, dele the whole account of Adamanta, the existence of which as a peculiar earth has been destroyed by the subsequent experiment of Kloepel. It may be proper to mention, that in that section, line 28, infusible ought to be fusible. INDEX.
A
Alumina, felspar of, n° 847. soap of, 594. fulberat of, 836. fulphat of, 627. fulphite of, 665. tartrite of, 811.
Amalgam, what, 93. Amber, 502. Ammonia, Part II. ch. iv. sect. 3. acetite of, 779. aurat of, 849. benzoat of, 820. borat of, 725. camphorat of, 825. carbonat of, 770. citrat of, 813. cuprat of, 852. fluat of, 761. laetat of, 817. malat of, 816. mercuriat of, 851. muriat of, 607. nitrat of, 670. oxalat of, 804. phosphat of, 739. pruflat of, 837. saccholat of, 818. sebat of, 846. soap of, 591. fulberat of, 832. fulphat of, 627. fulphite of, 661. tartrite of, 810. zincat of, 855.
Animal acids, 549. Antimony, Part I. ch. iii sect. 10. acetite of, 794. benzoat of, 822. muriat of, 716. nitrat of, 687. oxalat of, 806. sebat of, 848. fulphat of, 650. tartrite of, 812.
Antiphlogistic theory, p. 277. note.
Ants, acid of, Part II. ch. v. sect. 29.
Apalum, n° 240. Aquafortis, 407. Aqua regia, p. 224. note. Arcanum duplicatum, n° 624. tartari, 777.
Arseniate, 552, and Part III. ch. ii. sect. 26. Arsenic, Part I. ch. iii. sect. 12. acetite of, 795. benzoat of, 822. borat of, 758.
Arsenic, fluat of, n° 767. muriat of, 717. nitrat of, 688. oxalat of, 806. phosphat of, 740. sebat of, 848. fulphat of, 651. tartrite of, 812. acid, 550.
Atmospheric air, composition of, 53. Aurum musivum, 120. Ayutrum, 240. Azot, Part I. ch. ii. sect. 5. how combined with oxygen, 421.
B
Balsam of sulphur, 370. Balm of Peru, soap of, 609. Barytes, Part I. ch. iv. sect. 3. acetite of, 780. borat of, 725. camphorat of, 826. carbonat of, 771. citrat of, 814. fluat of, 762. laetat of, 817. malat of, 816. muriat of, 699. nitrat of, 671. oxalat of, 805. oxymuriat of, 724. phosphat of, 731. pruflat of, 838. saccholat of, 818. soap of, 595. fulberat of, 834. fulphat of, 628. fulphite of, 661.
Barytic water, 209. Beer, when first known, 340. Bell metal, 122. Benzoats, 501, and Part III. ch. ii. sect. 19. Benzoic acid, Part II. ch. v. sect. 20. Benzoin, 499. soap of, 608. Bergman, character of, 114. Bijmut, Part I. ch. iii. sect. 11. acetite of, 793. benzoat of, 822. borat of, 757. muriat of, 715. nitrat of, 686. oxalat of, 806. fulphat of, 649. tartrite of, 812.
Black, Dr., discovers latent heat, 268. discovers the composition of the carbonates, 200, 373. Black bodies soonest heated by light, 325. lead, 109. Blende, p. 247, note. Blue, liquid, n° 513. Boiling point of water, experiments on, 337, 338. Bologna stone, 679. Bombay acid, 546. Boracic acid, Part II. ch. v. sect. 8. Borats 447, and Part II. ch. ii. sect. 8. Borax, 441, 744. Borbonium, 240. Brafs, 140. Brittlefes, to what owing, 303. Bronze, 122. Brunswick green, 812.
C
Calcium, 134. Calcarous acid, 457. Calcantum, 641. Calcination, 61. Calomel, 718, 725. Calorie, Part I. ch. v. whether a substance, 241, 312. equilibrium of, 246. of fluidity, 269. of evaporation, 270. methods of obtaining, 292. whether the same with light, 328. Calorimeter, 265. Calx, 61. Camphor, 506. Camphorate, 510, and Part III. ch. ii. sect. 21. Camphoric acid, Part II. ch. v. sect. 22. Canton's pyrophorus, 320. Capacity for caloric explained, 262. Carbon, Part I. ch. ii. sect. 3. attempts to decompose, 44. Carbonate, 462, and Part III. ch. ii. sect. 10. Carbonated hydrogen gas, 42, and Part III. ch. iii. Carbonated azotic gas, 50. Carbonic Chemistry
Carbonic acid, 32, and Part II. ch. v. sect. 10.
Carburets, no. 35.
Carburet of iron, 100.
Manganese, 175.
Zinc, 139.
Cavallio's experiments on light, 345.
Cavendish, Henry, discovers the composition of water, 141.
And of nitric acid, 409.
Camphor, acidum, 374.
Cementation, 113.
Chalybeated tartar, 812.
Charcoal, conducting power of, 252.
Chemistry, definition of, 1.
Chromatic acid, Part II. ch. v. sect. 35.
Chromatium, 189.
Glauber, 91.
Citrates, 478, and Part III. ch. ii. sect. 14.
Citric acid, 476.
Cobalt, Part I. ch. iii. sect. 13.
Acetate of, 790.
Benzoate of, 822.
Borat of, 752.
Fluor of, 767.
Muriat of, 710.
Nitrat of, 680.
Oxalat of, 826.
Soap of, 598.
Sulphate of, 646.
Cobalt, 570.
Cold, method of producing, 280.
Why produced by mixtures, 282.
Colour affects the heating of bodies by light, 335.
Colouring matter of Prussian blue, 533.
Combination explained, 293.
Common salt, 696.
Compound affinity, 583.
C. around bodies, Part II.
Condensation diminishes specific caloric, 303.
Conducting powers of bodies, 251, 286.
Contact, in absolute, 568.
Copper, Part I. ch. iii. sect. 5.
Acetate of, 792.
Benzoate of, 822.
Borat of, 756.
Citrat of, 815.
Fluor of, 767.
Muriat of, 714.
Nitrat of, 685.
Oxalat of, 826.
Sefat of, 848.
Soap of, 602.
Sulphate of, 684.
Emetic tartar, 812.
Empyrean air, 6.
Epsom salt, 633.
Equilibrium of caloric, 246.
Ether, 355.
Ethiopic mineral, 90.
Eudiometer, 420.
Euler's theory of light, 315.
Expansion of bodies, table of, 242.
Extract of Saturn, 799.
Fat, acid of, 543.
Feathers, why a warm covering, no. 260.
Ferriprussic salt of Sylvius, 695.
Fire damp, 36.
Fixed air, 209, 457.
Ammonia, 701.
Oil, 361.
Fluors, 455, and Part III. ch. ii. sect. 9.
Fluids, non-conductors of caloric, 256.
Fluor, 449.
Fluoric acid, Part II. ch. v. sect. 9.
Formic acid, 529.
Formica rufa, 539.
Franklin's experiments on the heating of bodies by light, 325.
Friction, caloric produced by, 377, 319.
Fuming gold, 849.
Silver, 830.
Furs, in what their warmth consists, 260.
Fusible spar, 449.
Fusible, 867.
Gallate, 498, and Part III. ch. ii. sect. 18.
Gallie acid, Part II. ch. v. sect. 19.
Galls, 493.
Gas explained, 5, 457.
Gaseous form of bodies, to what owing, 279.
Gases, not heated red hot, 327.
Glass, 377.
Conducting power of, 253.
Antimony, 145.
Glauber's salt, 626.
Glucina, 238.
Gold, Part I. ch. iii. sect. 1.
Acted on by nitric acid, 413.
Fuming, 848.
Acetate of, 798.
Benzoate of, 822.
Sefat of, 849.
Soap of, 605.
Tannat of, 853.
Guaiac, soap of, 610.
Gunpowder, 667.
Gypsum, 630.
Hartshorn, 382.
Hauy's theory of crystallization, 872.
Heat, Part I. ch. v.
Makes bodies luminous, 326.
Hepatic gas, 40.
Hot bodies lighter than cold, 248.
Honi poun, 441.
Hutton's theory of light, 295.
Explanation of the parent reflecting cold, page note.
Hydrogen gas, Part I. ch. i. sect. 4.
Hydrogenous sulphurites, 831.
Hydrogalliborate, Part III. iii.
I
Jame's powder, 742.
Jargon, 243.
Jargonite, Part I. ch. iv. sect. & page 363, acetite of, 781.
Muriat of, 706.
Nitrat of, 677.
Sulphat of, 640.
Ice, 335.
Inflammable air, page 217.
Iron, Part I. ch. iii. sect. 113.
Cold short, 108.
Wrought, 111.
Acetite of, 786.
Benzoate of, 822.
Borat of, 750.
Carbonat of, 776.
Citrat of, 815.
Fluor of, 767.
Green sulphat of, 641.
Lactat of, 817.
Malat of, 816.
Muriat of, 707.
Nitrat of, 678.
Oxalat of, 806.
Phosphat of, 736.
Pruffat of, 539.
Red sulphat of, 642.
Sefat of, 848.
Soap of, 601.
Sulphate of, 666.
Tartrate of, 812.
Irvine, Dr., his theory of heat theorem to discover real zero, 272.
Kirwan's theory of phlogiston, 299.
Experiments on strength of ac 497, 511.
L
Lac, white, 517.
Laetic acid, Part II. ch. vi. 24.
Lattre, 486, and Part III. ii. sect. 16.
Laetic acid, Part II. ch. vi. sect.
Lana philosophica, page note.
Latent caloric, no. 269.
Lavoisier and Laplace, CHE
CHERUBIM were emblematical figures; of which an account, a very vague one indeed, has been given in the Encyclopaedia Britannica. We are far from thinking ourselves qualified to improve that account, or to explain emblems in the Jewish worship, which even Josephus did not understand; and we certainly should not have refused the subject, but to gratify a numerous class of our readers, and to comply with the request of some highly respected friends.
The followers of Mr Hutchinson, who are firmly persuaded that their matter brought to light from the writings of the Old Testament many important doctrines which had lain concealed from all the piety, all the industry, and all the learning of 1700 years, believe that, among other things, he and they have been able to ascertain the form and the import of the Hebrew Cherubim. Their discoveries on this subject, as we have been told by better judges than we pretend to be, are more clearly stated by Mr Parkhurst in his Hebrew Lexicon, than by any other writer of that school. We shall therefore lay before our readers his doctrine respecting the form of the artificial cherubs, as well as of their emblematical meaning; and submit a few remarks, which the nature of his reasoning has forced from us.
"First, then, as to the form of the artificial cherubs in the tabernacle and temple, Moses (says our author) was commanded (Exod. xxv. 18, 19). 'Thou shalt make two cherubs: of beaten gold shalt thou make them at the two ends of the mercy-seat. And thou shalt make one cherub at the one end, and the other Cherubim, cherub at the other end: out of the mercy-seat (Margin Eng. Translat. of the matter of the mercy-seat) shall ye make the cherubs at the two ends thereof.' All which was accordingly performed (Exod. xxxvii. 7, 8.), and these cherubs were with the ark placed in the holy of holies of the tabernacle (Exod. xxvi. 33, 34. xl. 23.) as those made by Solomon were afterwards in the holy of holies of the temple (1 Kings vii. 23, 27.)
We may observe that in Exodus Jehovah speaks to Moses of the cherubs as of figures well known; and no wonder, since they had always been among believers in the holy tabernacle from the beginning. (See Gen. iii. 24. Wild. ix. 8. And though mention is made of their faces (Exod. xxv. 20. 2 Chron. iii. 13.), and of their wings, (Exod. xxv. 22. 1 Kings viii. 7. 2 Chron. iii. 11, 12.) yet neither in Exodus, Kings, nor Chronicles have we any particular description of their form. This is however very exactly, and, as it were, anxiously supplied by the prophet Ezekiel, ch. i. 5. 'Out of the midst thereof (i.e. of the fire infolding itself, ver. 4.) ran the likeness of four living creatures or animals; and over the likeness of a man (being) with them.'
This last Hebrew expression cannot mean that they, i.e. the four animals, had the likeness of a man, which interpretation would indeed make the prophet contradict himself (comp. ver. 10.), but it imports that the likeness of a man in glory, called (verse 26.) and cherubs, and particularly described in that and the following verses, was with them. Ver. 6. And there were four faces to one (or similitude), and four wings to one, to them. So there were at least two compound figures. Ver. 10. And the likeness of their faces; the face of a man, and the face of a lion, on the right side, to them four; and the face of an ox to them four; and the face of an eagle to them four. Ezekiel knew (ch. x. 1—10.) that these were cherubs. Ver. 21. Four faces to one (cherub) and four wings to one. This text also proves that the prophet saw more cherubs than one, and that each had four faces and four wings. And we may be certain that the cherubs placed in the holy of holies were of the form here described by the priest and prophet Ezekiel, because we have already seen from Exodus, 1 Kings, and 2 Chronicles, that they likewise had faces and wings, and because Ezekiel knew what he saw to be cherubs, and because there were no four-faced cherubs anywhere else but in the holy of holies; for it is plain, from a comparison of Exod. xxvi. 1, 31. 1 Kings vi. 29, 32. and 2 Chron. iii. 14. with Ezekiel xii. 18, 19, 20. that the artificial cherubs on the curtains and veil of the tabernacle, and on the walls, doors, and veil of the temple, had only two faces; namely, those of a lion and of a man.
For it must be observed further, that, as the word כְּרָב is used for one compound figure with four faces, and כְּרָבוֹת in the plural for several such compounds (see Exod. xxv. 18, 19. xxxvii. 8. 1 Kings vi. 23—26.), so is כְּרָב applied to one of the cherubic animals, as to the ox, Ezek x. 14.; (compare ch. i. 10.) to the coupled cherub, or lion-man, Ezek xlii. 18.; and כְּרָבוֹת to several of the cherubic animals, as to several oxen, 1 Kings vii. 36. (compare ver. 29.) to several coupled cherubs, Exod. xxvi. 1. 1 Kings vi. 34, 35. &c. I proceed to show
Secondly, of what the cherubs were emblems, and with what propriety.
That the cherubic figures were emblems or representatives of something beyond themselves is, I think, agreed by all, both Jews and Christians. But the question is, of what they were emblematical? To which I answer in a word, Those in the holy of holies were emblematical of the ever-blessed Trinity in covenant to redeem man, by uniting the human nature to the Second Person; which union was signified by the union of the faces of the lion and of the man in the cherubic exhibition, Ezek. i. 10. compare Ezek. xlii. 18, 19. The cherubs in the holy of holies were certainly intended to represent some beings in heaven, because St Paul has expressly and infallibly determined that the holy of holies was a figure or type of heaven, even of that heaven where is the peculiar residence of God. (Heb. ix. 24.) And therefore these cherubs represented either the ever-blessed Trinity with the man taken into the essence, or created spiritual angels. The following reasons will, I hope, clearly prove them to be emblematical of the former, not of the latter:
1st. Not of angels; because (not now to insist on other circumstances in the cherubic form) no tolerable reason can be assigned why angels should be exhibited with four faces apiece.
2ndly. Because the cherubs in the holy of holies of the tabernacle were, by Jehovah's order, made out of the matter of the mercy-seat, or beaten out of the same piece of gold as that was' (Exod. xxv. 18, 19. xxvi. 37. 9.). Now the mercy-seat, made of gold and crowned, was an emblem of the Divinity of Christ (See Rom. iii. 25.). The cherubs therefore represented not the angelic, but the Divine nature.
3rdly. The typical blood of Christ was sprinkled before them on the great day of atonement (compare Exod. xxxvii. 9. Lev. xvi. 14. Heb. ix. 7, 12.) And this cannot in any sense be referred to created angels, but must be referred to Jehovah only; because,
4thly. The high priest's entering into the holy of holies on that day, represented Christ's entering with his own blood into heaven to appear in the presence of God for us' (Heb. ix. 7, 14.). And,
5thly. When God raised Christ (the humanity) from the dead, he set him at his own right hand in the heavenly places, far above, ὑπεράνω, all principality and power, and might and dominion, and every name that is named, not only in this world, but also in that which is to come (Eph. i. 21.). Angels and authorities and powers being made subject unto him' (1 Peter iii. 22.)
The prophet Ezekiel says (ch. x. 20.), 'This is the living creature, (which must mean one compound figure, comp. ver. 14.) that I saw instead of, a substitute of, the Aleim of Israel.' It is said, may refer either to situation or substitution, (see Gen. xxx. 2. l. 19.) as the sense requires. Here, notwithstanding what is said ver. 10. the latter sense is preferable; because it was the glory of the God of Israel, i.e., the God-man in glory, (compare ch. i. 26.) not the Aleim (the Trinity) of Israel that were over the cherubim; and the text says not, these were the living creatures, but, this was the living creature, which I saw ἐν τῷ ἀέρι. Now the glory was over both the cherubim, ver. 19. but one compound cherub only was a substitute of the Aleim.
If it should be here asked, Why then were there two compound cherubs in the holy of holies? I answer, Had there not in this place been two compound cherubs, it would have been naturally impossible for them to represent what was there designed; for otherwise, all the faces could not have looked inwards toward each other, and down upon the mercy seat, and on the interceding high priest sprinkling the typical blood of Christ, (see Exod. xxxvii. 9.) and at the same time have looked outward toward the temple, ἐκ τοῦ ἔσω ἐκεῖνος ἐξελθὼν, to the outer house,) 2 Chron. iii. 13. Or, in other words, the Divine Persons could not have been represented as witnessing to each other's voluntary engagements for man's redemption, as beholding the sacrifice of Christ's death, typified in the Jewish church, and at the same time as extending their gracious regards to the whole world. (See Isa. liv. 5. and Spearman's Enquiry, p. 382. edit. Edinburgh.
The coupled cherub, or lion-man, on the veil and curtains of the outer tabernacle, and on the veil, doors, and walls of the temple, accompanied with the emblematic palm tree, is such a striking emblem of the lion of the tribe of Judah (Rev. v. 5.) united to the man Christ Jesus, as is easy to be perceived, but hard to be evaded. These coupled cherubs appropriate the tabernacle or temple and their veils as emblems of Christ, and express in visible symbols what he and his apostles do in words. See John ii. 19, 21. Heb. viii. 2. ix. 11. And as the texts just cited from the New Testament afford us divine authority for asserting that the outer tabernacle or temple was a type of the body of Christ, so they furnish us with an irrefragable argument to prove that the cherubs on their curtains or walls could not represent angels. For did angels dwell in Christ's body? No surely; 'But in him dwelt all the fulness of the Godhead bodily.' (Col. ii. 9.)
"I go on to consider the propriety of the animals in the cherubim exhibition representing the Three Persons in the ever-blessed Trinity. And here to obviate any undue prejudice which may have been conceived against the Divine Persons being symbolically represented under any animal forms whatever, let it be remarked that Jehovah appeared as three men to Abraham, (Gen. xxiii.) that the terpent of brazen set up by God's command in the wilderness was a type or emblem of Christ, Gethsemane, lifted up on the cross (comp. Num. xxxi. 1—9, with John iii. 14, 15;) that at Jesus' baptism the Holy Spirit descended in a bodily shape, like a dove, upon him (Luke iii. 21, 22;) that Christ, as above intimated, is expressly called 'the lion of the tribe of Judah' (Rev. v. 5;) and continually in that symbolical book set before us under the similitude of a lamb. All these are plain scriptural representations, each of them admirably suited, as the attentive reader will easily observe, to the particular circumstances or specific design of the exhibition. Why then should it appear a thing incredible, yes why not highly probable, that Jehovah Aleinu should, under the typical state, order his own Persons and the union of the manhood with the essence to be represented by animal forms in the cherubim of glory? Especially if it be considered that the three animal forms, exclusive of the man (who stood for the very human nature itself) are the chief of their respective genera: the ox or bull, of the tame or gramivorous; the lion, of the wild or carnivorous; and the eagle, of the winged kind.—But this is by no means all: For as the great agents in nature, which carry on all its operations, certainly are the fluid of the heavens, or, in other words, the fire at the orb of the sun, the light issuing from it, and the spirit or grotos air constantly supporting, and concurring to the actions and effects of the other two; so we are told (Psal. xix. 1,) that יָרְבוּ הַשֶׁבֳּרִים (the heavens) are the means of declaring, recounting, or particularly exhibiting the glory of God, even his eternal power and godhead, as St Paul speaks, Rom. i. 20. And accordingly Jehovah himself is sometimes, though rarely (I presume for fear of mistakes) called by the very name יָרְבוּ or יָרְבוּ heavens in the Old Testament, see 2 Chron. xxix. 20. (comp. 2 Kings xix. 14. Isa. xxxvii. 15.) Dan. iv. 23. or 26.; as he is more frequently expressed by יָרְבוּ heaven in the New. (See Mat. xxi. 25. Mark xi. 50, 51. Luke xv. 18, 21. xxii. 4, 5. John iii. 27.) Yet not only so, but we find in the Scriptures both of the Old and New Testament, that the Persons of the eternal Three and their economical operations in the spiritual, are represented by the three conditions of the celestial fluid and their operations in the material world. Thus the peculiar emblem of the Word or Second Person is יָרְבוּ or light, and he is and does that to the souls or spirits of men which the material or natural light is and does to their bodies. (See inter al. 2 Sam. xxiii. 4. Isa. xlix. 6. lx. 1. Mal. iv. 2. or iii. 20. Luke i. 78. ii. 32. John Cherubim. i. 4—9. vii. 12. xii. 35, 36, 46.) The Third Person has no other distinctive name in scripture but ru in Hebrew, and ὁ ἅγιος in Greek, (both which words in their primary sense denote the material spirit or air in motion,) to which appellation the epithet ὁ ἅγιος ὁ ἅγιος holy, or one of the names of God, is usually added: and the actions of the Holy Spirit, in the spiritual system are described by those of the air in the natural. (See John iii. 8. xx. 22. Acts ii. 2.) Thus, then, the Second and Third Persons of the ever-blessed Trinity are plainly represented in scripture by the material light and air. But it is further written, Jehovah thy Aleinu is a consuming fire. Deut. iv. 24. (Comp. Deut. ix. 23. Heb. xii. 29. Psa. xli. 10. lxviii. 21. Nah. i. 2.) And by air, derived either immediately or mediately from heaven, were the typical sacrifices consumed under the old dispensation. Since, then, Jehovah is in scripture represented by the material heavens, and even called by their name, and especially by that of fire, and since the Second and Third Persons are exhibited respectively by the two conditions of light and spirit, and since fire is really a condition of the heavenly fluid as much distinct from the other two as they are from each other, it remains that the peculiar emblem of the First Person (as we usually speak) of the eternal Trinity, considered with respect to the other two, be the fire.
"Bearing then in mind that the personality in Jehovah is in scripture represented by the material Trinity of nature; which also, like their divine antitype, are of one substance, that the primary scriptural type of the Father is fire; of the Word, light; and of the Holy Ghost, spirit, or air in motion; we shall easily perceive the propriety of the cherubim's emblems. For the ox or bull, on account of his horns, the curling hair on his forehead, and his unrelenting fury when provoked (see Psa. xxii. 13.) is a very proper animal emblem of fire; as the lion from his usual tawny gold-like colour, his flowing mane, his shining eyes, his great vigilance and prodigious strength, is of light; and thus likewise the eagle is of the spirit or air in action, from his being chief among fowls, from his impetuous motion, (see 2 Sam. i. 23. Job ix. 26. Jer. iv. 13. Lam. iv. 19.) and from his towering and surfeiting flights in the air (see Job xxxiii. 27. Psa. xxiii. 5. xxx. 19. Isa. xli. 21. and Bodart, vol. iii. page 173.) And the heathen used these emblematic animals, or the like, sometimes separate, sometimes joined, in various manners, as representatives of the material Trinity of nature, which they adored. These particulars Mr Hutchinson has proved with a variety of useful learning, vol. vii. p. 381. &c. and any person who is tolerably acquainted with the heathen mythology will be able to increase his valuable collection with many instances of the same kind from modern as well as ancient accounts of the pagan religions.
"Thus, then, the faces of the ox, the lion, and the eagle, representing at second hand the Three Persons of Jehovah, the Father, the Word, and the Holy Spirit; and the union of the divine light with man being plainly pointed out by the union of the faces of the lion and the man (see Ezek. i. 10. ali. 18.), we may safely assert, that the cherubim of glory (Heb. ix. 5.) in the holy of holies were divinely instituted and proper emblems of the Three Eternal Persons in covenant to redeem..." cherubim, redeem man, and of the union of the divine and human natures in the person of Christ. And we find (Gen. iii. 24.) that immediately on Adam's expulsion from paradise, and the cessation of the first or paradisiacal dispensation of religion, Jehovah Aleim himself set up these emblems, together with the burning flame rolling upon itself, to keep the way to the tree of life; undoubtedly, conferring the services performed before them, not to hinder, but to enable, man to pass through it.
Thus far Mr Parkhurst; and to his dissertation where is the man who will deny the merit of erudition, combined with ingenuity? To the latter part of his reasoning, however, objections obtrude themselves upon us of such force, that we know not how to answer them. The reader observes, that, according to this account, the cherubim are only at second hand emblematical of the Holy Trinity, and that the primary emblem is that fluid which the author conceives to fill the solar system, and to be one substance under the different appearances or modifications of fire, light, and gross air. But unfortunately for this reasoning, we are as certain as we can be of any matter of fact, that fire and air are not one substance; that the gross air itself is compounded of very different substances; and that even light is a different substance from that which causes in us the sensation of heat, and to which modern chemists have given the name of caloric (See Chemistry Index in this Supplement). We admit, that the primary atoms of all matter may be substances of the same very kind, though we do not certainly know that they are; but this makes nothing for our author's hypothesis; because the sun and all the planets must, in that case, be added to his one substance, which would no longer appear under a triple form. Could it indeed be proved, that all men from Adam downwards, who made use of cherubim figures for the very same purpose with the ancient Jews, believed that fire, air, and light, are different modifications of the same substance, their belief, though erroneous, would be a sufficient foundation for our author's reasoning; but of this no proof is attempted, and certainly none that is satisfactory could be brought.
Our learned author, indeed, takes much for granted without proof. He has not proved, that anywhere the bull was the emblem or hieroglyphic of fire, the lion of light, or the eagle of air. We do not, it must be owned, know that such hieroglyphics were not used in Egypt and other countries before the introduction of alphabetical characters; but unless they were so used by Adam, all that is here said of the propriety of these emblems must go for nothing: Indeed we see not their peculiar propriety. The tawny colour, flowing mane, and fierceness of the lion, might, for any thing that we can perceive to the contrary, represent fire as fitly as the horns, curling hair, and fury of the bull; and if it be true, as is generally said, that the eagle can look readily on the sun, he seems, of all the three, to be the fittest emblem of light.
But there are other objections to this interpretation of the word cherubim. The four animals in the Revelation, which were undoubtedly cherubim, as well as the four and twenty elders, fell down before the Lamb, and worshipped God. Now, says Dr Gregory Sharp, "it is scarce to be conceived, if these four beasts were representatives of the divine persons, that they could with any propriety, or without the greatest solecism, be said and described to fall down before and worship other emblematical representations of the same divine nature and perfections: And therefore, whatever these beasts were emblems of, they could not be cherubim in Mr Hutchinson's sense of that word; it being as contrary to the rational explanation of a vision to say that one emblem of the divinity should worship another emblem of it, as it is contrary to the reason of mankind, and to all our notions either of the Godhead or of worship, to say that the Trinity worshipped the Trinity, or any one Person in the Trinity."
This objection is admitted by our learned author to be a very plausible one. To us it appears unanswerable. He answers it, however, in the following words:
"Let it be carefully observed, that these representations in Rev. ch. v. and xix. are not only vitual but hieroglyphical, and therefore must be explained according to the analogy of such emblematical exhibitions; and as at ver. 6. 'the lamb, as it had been slain, having seven horns and seven eyes, standing in the midst of the throne, and of the four animals, and of the four-and-twenty elders,' is evidently symbolical of the Lamb of God now raised from the dead, and invested with all knowledge and power both in heaven and in earth; so the four animals falling down before him (ver. 8.), and, as it is expressed (ch. xix. 4.), 'worshipping God who sat upon the throne,' must, in all reason, be explained symbolically likewise, not from any abstract or metaphysical notions we may have framed to ourselves of worship in general, but from the specific and peculiar circumstances of the case before us. Thus likewise, when in 1 Chron. xxix. 20. 'All the congregation worshipped Jehovah and the king, namely David, the worship to both is expressed by the same strong phrase—proliferated themselves to, LXX., ἀποκατεστήσαντο; yet surely no one will say that the people meant to worship David as God, but only to acknowledge him as king. So Adonijah, who had contested the crown with Solomon, came, and worshipped King Solomon, (1 Kings i. 53,) not as God doubtless, but as king, thereby surrendering his own claim to the throne. However contrary therefore it may be to the reason of mankind, and to all our notions either of the Godhead or of worship, to say that the Trinity worshipped the Trinity, or any one Person of the Trinity, i.e. with divine worship as a creature worships his Creator; yet it is by no means contrary to the rational and scriptural explanation of an emblematic vision, to say that the hieroglyphical emblems of the whole ever-blessed Trinity fell down and worshipped the hieroglyphical emblem of the God-man, or God who sat upon the throne. Since such falling down, proliferation, or worshipping, was the usual symbolical act, as it still is in the east, not only of divine worship, but of acknowledging the regal power to be in the person so worshipped; and these acts of the cherubic animals in Rev. v. 6. xix. 4. meant nothing more than either a cession of the administration of all divine power to Christ God-man, or a declaration of the divine Persons, by their hieroglyphical representatives, that He must reign till all his enemies were made his footstool. Comp. Mat. xxviii. 18. 1 Cor. xv. 25."
With every inclination to honour the memory of Mr Parkhurst, who was certainly a scholar, and, which is of more value, a pious and a good man, we cannot help considering this answer as mere trifling. In the 18th Psalm, the Lord is said to "ride upon a cherub;" and in Ezekiel, chap. i., there is said to have been over the heads of the cherubim a throne, and upon that throne the likeness or appearance of a man, whom we take to be the Son of God incarnate. But is there any country in which the regal power of the sovereign is acknowledged by his riding, not upon his subjects, but upon other co-equal sovereigns? or, in which it is the custom for the sovereign to place his viceroy (for such our Saviour in his human nature certainly is) in his throne above himself?
We must therefore confess, that we know not of what the cherubic figures were emblematical, and that he who labours to establish the doctrine of the ever blessed Trinity by such criticisms and reasonings as those which we have examined, is either a secret enemy to that doctrine, or a very injudicious friend.