GENERAL VIEW OF THE PROGRESS OF CHEMICAL SCIENCE

GENERAL VIEW OF THE PROGRESS OF CHEMICAL SCIENCE, FROM THE EARLY AGES TO
THE END OF THE SEVENTEENTH CENTURY.

THE phenomena of the universe present a series of changes, of which the regularity and harmonious succession excite the surprise of superficial observers, and awaken the admiration and attention of the philosophic mind.

These changes are either accompanied by visible motion susceptible of measurement, and relate to the exterior forms and mechanical characters of bodies, or they depend upon the mutual agencies of the elementary principles of matter, upon its composition, upon its susceptibility of acquiring new properties by entering into new combinations.

The investigation of the former phenomena belongs to the mechanical philosopher; to trace the causes of the latter, and to discover the laws to which they are obedient, is the business of chemical science.¹

Chemistry, considered as a branch of scientific inquiry, is not of ancient date.¹ Founded upon principles deduced from experiment and observation, centuries were

physique expérimentale, qui ne considère que les propriétés extérieures des corps doués d'un volume, et d'une masse qu'on peut mesurer, tandis que la Chimie ne s'attache qu'aux propriétés intérieures, et n'agit que sur des molécules, dont le volume et la masse ne peuvent pas être soumis aux mesures et aux calculs." (Fourcroy, Système des Connoissances Chimiques, Vol. I. p. 4.)

"Die Chemie ist eine Wissenschaft die uns die wechselseitige wirkungen der einfachern Stoffe in der Natur, die zusammensetzung der Körper aus ihren und nach ihren verschiedenen Verhältnissen, und die Art und Weise kennen lehrt, sie zu trennen, oder sie wieder zu neuen Körperarten zu verbinden." (Gren. Systematisches handbuch der Chemie, p. 1. Halle, 1794.)

"Chemistry is that science which treats of those events or changes in natural bodies, which are not accompanied by sensible motions." (Thomson, System of Chemistry, fifth edition, p. 2.)

Most of the substances belonging to our globe are constantly undergoing alterations in sensible qualities, and one variety of matter becomes, as it were, transmuted into another. Such changes, whether natural or artificial, whether slowly or rapidly performed, are called chemical;—thus the gradual and almost imperceptible decay of the leaves and branches of a fallen tree exposed to the atmosphere, and the rapid combustion of wood in our fires, are both chemical operations.

"The object of chemical philosophy is to ascertain the causes of all phenomena of this kind, and to discover the laws by which they are governed." (Davy, Elements of Chemical Philosophy, p. 1.)

In the edition of Johnson's Dictionary, now publishing by the Rev. H. J. Todd, the erroneous and antiquated definition of Boerhaave is very improperly retained. "An art whereby sensible bodies contained in vessels, or capable of being contained therein, are so changed by means of certain instruments, and principally fire, that their several powers and virtues are thereby discovered, with a view to philosophy or medicine."

The derivation of the word Chemistry can scarcely be said to have been ascertained. The most plausible guesses are the following: from χρῖν to melt, or χρῖν juice; from kema, an oriental word signifying black; from χῆμης, the name of a person eminently skilled in the sciences; from Chémi, the Coptic name of Egypt, where the art is supposed to have had its rise.

According to Bryant (Ancient Mythol.), it is derived from chemia, and that word from Cham.

The Rev. Mr Palmer, Professor of Arabic at Cambridge, has given the following etymology: "Al-chemy, or more properly Al-kemy, the knowledge of the substance or composition of bodies, so named from the substantive (Kyamon), that is, the substance or constitution of any thing; from the root (Kama). Golius. Lexicon." (Thomson's Chemistry, 5th edit. p. 4. Note.)

Conversing upon this subject with Dr Thomas Young, he remarked, that the Egyptians probably neither knew nor cared much about the composition of bodies; and that the term Chemistry, as referring to the secret art of transmutation, was probably derived from the Coptic root hems or chems, signifying obscure, dark. The German word geheim, secret, he said, was perhaps of the same root.

"Hæc ars varia accepit nomina, nam omnium primò dicta fuit τὴν πενητήν, et antiquis illis temporibus per hanc vocem significabant artem vilia metalla in aurum convertendi, et ejus artifices πενηταί vocari Zozi-mus dicit. Veteres Ægyptios hanc artem Chimoet vocasse Josephus Scaliger ibi ostendit, sed postea Græci hanc artem χρυσίην dixerunt, Arabibus vero, Alchemia." (Boerhaave, Institutiones Chemicæ.)

"Tout ce qu'on a dit de l'antique origine de la Chimie, sur les premiers hommes qui ont travaillé les métaux, taillé et poli les pierres dures, fondu les sables, dissous et cristallisé les sels, ne montre à un esprit exact et sévère qu'une vaine et ridicule prétension, semblable à cette par laquelle on voudrait reconnoître

consumed in their accumulation and systematic arrangement; but, as an art, chemistry is readily traced to periods of remote antiquity; for it is obvious that the chemical changes of matter must have been rendered subservient to the wants of mankind in the earliest ages of the world.

Metallurgy is among the most ancient of the arts, and Tubal Cain, the instructor of workers in iron and brass, has thence been called the inventor of chemistry. Others have preferred the claims of Noah, to whom the invention of wine has been attributed; but these, and other arts alluded to in Sacred Writ, such as dyeing, gilding, and embalming, which have been adduced as instances of chemical knowledge in the time of Moses, prove nothing more than that such processes were practised at that period, independent of each other, and quite unconnected by the slightest reference to general principles.¹

It is probable that the early mythological systems of the Egyptians contained some allusions to the chemical changes of matter, and to them the first speculations on the art of transmutation have been attributed. Hermes, or Mercurius Trismegistus, the favourite minister of the Egyptian king Osiris, has been celebrated as the inventor of this art, and the first treatise upon it has been attributed to Zosymus, of Chemnis or Panopolis in Egypt. The inhabitants of Sydon and Tyre, those renowned seats of the commerce of the ancient world, seem to have been skilled in some chemical manufactures; they made glass and artificial gems, and excelled in dyeing purple.

Egypt maintained its superiority in arts until the invasion of Alexandria by the Saracens, when the celebrated library collected by the Ptolemies, with great diligence and at enormous expence, was burned by the orders of Caliph Omar.² The alchemical

les élémens de la géométrie dans l'ouvrage grossier du sauvage qui use les fragmens du rocher, qui leur donne des formes à peu près régulières pour les rendre utiles à ses premiers besoins." (Fourcroy, Discours Préliminaire.)

works had been previously destroyed by Diocletian in the fourth century, lest the Egyptians should acquire by such means sufficient wealth to withstand the Roman power. On the present occasion, about seven hundred thousand volumes were seized, which we are told supplied six months' fuel for forty thousand baths, that contributed to the health and convenience of the populous capital of Egypt.

When philosophy declined in Egypt and in the East, Greece became the principal seat of learning and of the arts; but the systems of their early philosophers, of Thales¹ the founder of the Ionic sect, of Anaximander, and Anaximenes, breathe the sentiments of the Egyptian schools. By Thales water was considered as the source of all things, as the universal element. The opinions of Anaximander, in themselves unintelligibly obscure, received some elucidation from his successor Anaximenes; they regarded air and fire as the first rudiments of matter.

The result of the Macedonian war introduced Grecian philosophy into Italy, and the doctrines of Plato,² and Aristotle, and Theophrastus, prevailed in the school of Rome.

Among the early Roman philosophers, Lucretius³ stands preeminent; but his opinions had been formed at Athens, in the Stoic school of Zeno, and he early imbibed the doctrines of Empedocles and Epicurus, which are expounded with superior genius and admirable ingenuity in his masterly poem on the Nature of Things.

The celebrated Natural History of the elder Pliny, written in the first century of the Christian era, contains an account of the rise and progress of the arts and sciences previous to that period, which, though not always accurate, often obscure, and sometimes unintelligible, abounds in instructive documents and interesting remarks. It is written, not in the elevated, refined, and elegant style of the Augustan age, but in the language of the laborious and liberal historian, frequently led by the extent of his inquiries to subjects which he is incompetent to manage, and upon which his opinions are incorrect, his conjectures vague, his assertions ill-founded.

The origin of many of the follies and mysteries of Alchemy may perhaps be referred with most propriety to the New Platonists, whose rise marked the declining age of learning towards the end of the third century of the Christian era. These philosophers, celebrated for their metaphysical disputes and superstitious notions, credited the existence of demons and spirits, with whom they claimed familiar intercourse. Ne-

glecting useful knowledge, they exhausted their strength in verbal disputes, and in attempts to discover the secrets of the invisible world; thus gradually converting the study of philosophy into that of demonology and magic. "Several of these masters," says Gibbon, "Ammonius, Plotinus, Amelius, and Porphyry, were men of profound thought and intense application: but, by mistaking the true object of philosophy, their labours contributed much less to improve than to corrupt the human understanding."

Porphyry died about the time of Diocletian's abdication. The life of his master, Plotinus, which he composed, gives a complete idea of the genius of the sect, and the manners of the Professors. This curious piece is inserted in Fabricius. (Bibliotheca Græca, Tom. IV.) When the cultivated part of Europe was overwhelmed by the barbarous nations, all records of arts and sciences possessed by the Greeks, and by their Roman successors, were swept away in the general destruction, and now the Arabians became the protectors of philosophy, and the promoters of its pursuits. To them, Chemistry, regarded as a distinct branch of experimental philosophy, owes its origin, and several circumstances co-operated to render its progress rapid, which are important in their relation to the subsequent advances of the science. Among these the mysteries of Alchemy, so well adapted to the genius of that age and people, are the most remarkable. Of this occult art, the two leading objects were the transmutation of common metals into gold and silver, and the discovery of the universal medicine, which, by the removal and prevention of disease, should confer immortality upon the possessors of the secret.

The origin of these chimerical notions has been variously accounted for. The idea of transmutation may plausibly be referred to the various processes to which natural bodies were submitted by the astrological experimentalists of the seventh and eighth centuries. Observing the change of properties in metallic ores by exposure to heat, and the production of malleable and useful metals from their brittle and useless compounds, it is not surprising that superficial observation and incorrect reasoning should lead to a belief in their production and transmutation; and such speculations, not without apparent foundation, holding out attraction to the ambitious, and hope to the needy, would soon excite notice and command followers. That this was the case, the records of those times amply testify.

The pursuit of the other object may be referred to the success attending the medical employment of many of the chemical preparations. Pharmacy was becoming enriched by the introduction of chemical compounds; and remedies for diseases, before deemed incurable, were occasionally discovered among the products of

the furnace. Hence, perhaps, the possibility of the existence of an universal remedy might occur to those under the infatuations of the black art.

The earliest of the true Alchemists, whose name has reached posterity, is Geber,¹ supposed to have been an Arabian prince of the seventh century. The works attributed to Geber, several of which have been published in Latin translations by Golius, and others in English by Russell, are numerous and curious. They abound in the cant and jargon of the hidden art. Some have asserted his pretensions to the possession of the universal medicine, for he speaks of curing disease. But this seems a mere metaphorical expression, relating to transmutation. "Bring me," says he, "the six lepers, that I may cleanse them;" by which he doubtless would imply the conversion of silver, mercury, copper, iron, tin, and lead, into gold,—there being only these seven metals known at that period. Dr Johnson supposes that the word Gibberish, anciently written Geberish, was originally applied to the language of Geber and his tribe.

The elder Mesue and Avicenna,² physicians of the ninth and tenth centuries, have given some account of the Chemistry of their age, but their works relate chiefly to medicine. Indeed, it is probable that the writings now extant in the name of the former are spurious.

The twelfth, thirteenth, and fourteenth centuries, abound in writers on the secrets of Alchemy; and the happy few to whom fate and metaphysical aid had granted the discovery of the great secret, assumed the title of adepts, a character which required to be sustained by superior feats of deception and duplicity.

About this period, several circumstances happily concurred, favourable to the diffusion of learning and the arts, which began again to dawn in Europe with promising splendour.

The extravagant expeditions of the Crusaders tended, in these respects, to the most extensive, beneficial, and permanent consequences. In their progress to Palestine, these ardent followers of the Cross traversed countries which, compared with their own, were cultivated, civilized, and refined. Their minds and manners were thus enlarged and improved, and new customs and institutions attracted their notice.

In Constantinople, then the largest and most magnificent of European cities, some traces of ancient elegance and refinement were still to be found, and many of the natural products and of the manufactures of the East were offered to their notice.¹

We accordingly discover in these superstitious and enthusiastic expeditions the source of many improvements, which afterwards raised Europe to the highest rank among nations; which tended to dispel barbarism, to mitigate the fury of war, and to extend commerce; and which ultimately led to the cultivation of the useful and fine arts, and to the diffusion and exaltation of science.

Another event occurred about this period, which miraculously facilitated the acquisition and propagation of learning, namely, the invention of printing, which, as it were by superhuman mediation, advanced so rapidly to perfection, that the finest specimens of typography are to be found among the early efforts of the art. It was introduced into England by the Earl of Rivers, in the reign of Edward IV.²

Of the earlier writers on Chemistry, no one is more deserving notice than the celebrated Roger Bacon, a native of Somersetshire, who flourished in the thirteenth century. His writings, though troubled and polluted by the reigning absurdities of Alchemy, contain many curious facts and judicious observations. To him the discovery of gunpowder has, with all appearance of justice, been attributed.³ "From saltpetre and other ingredients," he says, "we are able to form a fire which will burn to any distance." And again, alluding to its effects, "a small portion of matter, about

the size of the thumb, properly disposed, will make a tremendous sound and corruscation, by which cities and armies might be destroyed." And again, in the same work, is a passage which, though somewhat enigmatical, is supposed to divulge the secret of this preparation. "Sed tamen salis petræ, luru mone cap urbre, et sulphuris, et sic facies tonitrum si scias artificium." The anagram is convertible into carbonum pulvere. Such are the claims of Roger Bacon to a discovery which soon changed the whole art of war.

The works of Bacon most deserving perusal are the Opus Majus, edited by Dr Jebb in 1733; and his Epistola de secretis Operibus Artis et Naturæ, et de nullitate Magicæ. Paris, 1532. The former, addressed to Pope Clement IV., breathes sentiments which would do honour to the most refined periods of science, and in which many of the advantages likely to be derived from that mode of investigation insisted upon by his great successor Chancellor Bacon, are anticipated.

Raymond Lully, Arnold of Villanova,¹ John de Rupescissa, and Isaac and John of Holland,² were Alchemists of the thirteenth, fourteenth, and early part of the fifteenth century. Their writings are extremely numerous; and they each treat of the philosopher's stone, and other secrets of the occult science.

Basil Valentine of Erfurt, who wrote towards the end of the fifteenth century, is deserving of more attention, and ranks among the first who introduced metallic preparations into medicine. In his Curvus Triumphalis Antimonii,³ after setting forth the chemical preparations of that metal, he enumerates their medicinal effects. According to the notions of the age, he boasts of supernatural assistance; and his work furnishes a good specimen of the controversial disputes between the chemical physicians and

those of the school of Galen,—the former being attached to active remedies, the latter to more simple and inert medicines. The Chariot of Antimony opens with the most pious exhortations to prayer and contemplation, to charity and benevolence. But the author, soon forgetting himself, breaks out in the following strain of virulent invective. “ Ye wretched and pitiful medicasters, who, full of deceit, breathe out I know not what Thrasonick brags,—infamous men, more mad than Bacchanalian fools! who will neither learn, nor dirty your hands with coals! you titular doctors, who write long scrolls of receipts; you apothecaries, who with your decoctions fill pots no less than those in princes’ courts, in which meat is boiled for the sustenance of some hundreds of men; you, I say, who have hitherto been blind, suffer a collyrium to be poured into your eyes, and permit me to anoint them with balsam, that this ignorance may fall from your sight, and that you may behold truth as in a clear glass. But,” says Basil Valentine, after a long exhortation in this strain, “ I will put an end to my discourse, lest my tears, which I can scarcely prevent continually falling from my eyes, should blot my writing, and, whilst I deplore the blindness of the world, blemish the lamentation which I would publish to all men.”

Such is the trash in which these authors abound, and in which curious facts and ingenious speculations are often enveloped.

Basil Valentine was succeeded by the more celebrated Paracelsus, a native of a village near Zurich in Switzerland.¹ In this remarkable person, all the follies and extravagance of the Alchemists were united;—he pretended to the discovery of the grand secret of the universal remedy; and his writings, which are very numerous, overflow with the whims and oddities of the sect; his zeal was more directed to the acquisition of popularity than to the advancement of science; his enthusiasm was ever misemployed; and he sought the elevation of his own character in the abuse and deprecation of his predecessors and contemporaries. He terminated a life, stained with every vice, and deficient in every virtue, in the year 1541, at an obscure inn at Saltzbourg, in Bavaria.

In the history of medicine, Paracelsus deserves more honourable mention; for he enriched the Materia Medica with many powerful remedies, derived from the mineral world, among which several preparations of mercury deserve especial notice; nor was he unacquainted with the virtues of opium, and other powerful drugs of vegetable origin. These he administered with a daring but often successful hand, and gained such celebrity, that, in 1527, he was promoted by the magistracy of Basle to the office of Professor of Physic. In this he expounded his own doctrines, asserting that that which was denied him from above had been granted by the infernal deities; and that to them he was indebted for those great secrets of physic and philosophy which he should divulge for the advantage and salvation of his hearers. Paracelsus, however, soon became weary of his situation, and terminated his professorial career, which was ill suited to his genius and inclinations, in the year 1528; he left Basle, and his subsequent life was one disgusting scene of dissolute irregularity.

The last person whose name deserves to remain upon the chemical records of the sixteenth century is Van Helmont of Brussels, born in 1577,¹ who, at an early age, made considerable progress in philosophical studies. As a physician, he adopted the doctrines of the chemical school, and rejected those of Aristotle and Galen; he effected cures so numerous and surprising, that he was accused by the inquisition of employing supernatural means, which induced him to retire into Holland. The writings of Van Helmont are chiefly upon medical subjects; those connected with chemistry contain some curious speculations respecting aeriform fluids, which he calls gases, a term now in common use. He also speaks of a subtle invisible agent, called Blas, which, he says, is an ethereal emanation from the heavenly bodies. "Winds are air agitated by the Blas of the stars."²

The doctrine of the Four Elements, as established by the ancient philosophers, underwent several alterations in the hands of the chemists of the sixteenth century. The former regarded Earth, Water, Air, and Fire, as the universal rudiments of all matter, and assigned to each its particular station in the universe. Earth tended towards the centre, water to the surface of the globe; air occupied a middle station between water and fire, which last was considered as the most rare, subtle, and active of all things;

it was supposed to constitute the heavenly bodies, and to confer life and action upon the other principles, to various combinations of which the different productions of nature were referred.

Basil Valentine, Paracelsus, and Van Helmont, speak of Salt, Sulphur, and Mercury, as the elementary principles of bodies; but the passages in their works referring to this hypothesis, are too dark and absurd to merit quotation; it was, however, adopted by several of their contemporaries and successors.

During the sixteenth century, some progress was made in the elucidation of the chemical arts, especially of Metallurgy, upon which subject the works of Agricola,¹ and of Lazarus Erckern, merit particular notice. The former has detailed, at considerable length, the various operations employed in mining, and his descriptions are at once correct and elegant; but his attempts at theory are deeply tinctured with the prevailing follies of the age. Agricola, who died at Chemnitz in 1555, was succeeded by Erckern, superintendent-general of the German mines; "he is an experienced, candid, and honest writer, relates nothing but what he had himself seen, without a word of theory or reasoning, and every where speaks as if he were sitting before the furnace and relating what passed."²

After wading through the thick fog of alchemical speculation, which envelopes the writers of this period, it is a relief to meet with one whose details are thus intelligible, and who adheres to matter of fact.

The periods we have now considered teemed with searchers for the philosopher's stone,—the elixir of life,—and the universal medicine. Of these such have hitherto only been noticed as conducted, by their experiments and discoveries, to the progress of chemical science.

The records of the fifteenth and sixteenth centuries present a motley group of these adventurers solely devoted to the occult art of transmutation. Some were open impostors; others deluded believers; but their respective histories are, in general, so similar,

that an account of one will suffice:¹ Bernard Trevisan, who was born at Paris early in the fifteenth century, and who suffered severely under this intellectual epidemic, may be cited for the purpose. He commenced his career with the unsuccessful repetition of certain processes of transmutation described by Rhazes, in which he expended eight hundred crowns. The perusal of Geber's treatise on the perfection of the metals rekindled his hopes, and, after wasting two thousand crowns upon apparatus and materials, this experiment proved as fruitless as the former. The writings of Ruspescissa, Archelaus, and Sacrobosca, shortly afterwards engaged his notice; and, to ensure success, he associated himself with a monk, and performed a variety of silly but laborious experiments, at the expence of more than a thousand crowns. He submitted the same portion of spirit of wine to three hundred distillations, and was engaged during a period of twelve years, in a series of fruitless and unmeaning operations upon alum, common salt, and copperas. At length he quitted his native country for Italy; thence he proceeded to Spain and Turkey, in search of the adepts of the art, from whom he hoped to acquire the secret, and reimburse himself. Thus having squandered the scanty remains of his broken fortune, and reduced nearly to beggary, he retired to the isle of Rhodes, where he entered the service of Arnold of Villa Nova, from whom he states that he obtained that which he had so long searched for. So true is that definition of Alchemy, which describes it as an art without principle, which begins in falsehood, proceeds in labour, and ends in beggary.

Entering upon the seventeenth century, the historian of Experimental Science must ever pause to pay a tribute of gratitude and respect to the celebrated Francis Bacon; a man whose faults as a statesman have been eclipsed to the eyes of posterity, by the brilliancy and excellence of his philosophical character.

It may commonly be observed, that those who are gifted by nature with superior genius or uncommon capacity,—who are destined to reach the meridian of science,

or to attain exalted stations in the learned professions, have exhibited early symptoms of future greatness: either indefatigable industry, or extraordinary sagacity, or ardent enthusiasm, have marked their entrance into the affairs of life. At the age of sixteen, Bacon was distinguished at Cambridge; and, very shortly afterwards, struck with the frivolous subtlety of the tenets of Aristotle, he appears to have turned his mind into that channel which led on to future eminence. The solid foundation of his scientific character is the Instauration of the Sciences. It opens with a general and philosophical survey of the subject; whence he proceeds to infer the futility of the ancient philosophical systems, and to point out Induction, from sober and severe experiments, as the only road to truth. Pursue this, he says, and we shall obtain new powers over nature; we shall perform works as much greater than were supposed practicable by natural magic, as the real actions of a Cæsar surpassed the fictitious ones of a hero of romance.

Speculative philosophy he likens to the lark, who brings no returns from his elevated flights; experimental philosophy to the falcon, who soars as high, and returns the possessor of his prey.

Illustrations of the new method of philosophizing, and the mode of arranging results, conclude this admirable and unrivalled performance.

To do justice to this work, we must, for a moment, forget the present healthy and vigorous constitution of science, and view it deformed and sickly in the reign of Elizabeth. We shall then not be surprised at the irrelative observations and credulous details which occasionally blemish this masterly production of the human mind.

But the history of Lord Bacon furnishes other materials for reflection. Upon the accession of James I., he became successively possessed of the highest honours of the law, and acquired great celebrity as a public speaker and a man of business; yet, amidst the harassing duties of his laborious avocations, he still found time to cultivate and adorn the paths of science, the pursuit of which furnished employment for his scanty leisure and relaxation in his professional toils; and, when ultimately disgraced, "his genius, yet unbroken, supported itself amidst involved circumstances and a depressed spirit, and shone out in literary productions." Nor should the munificence of his royal master remain unmentioned, who, after remitting his fine, and releasing him from his prison in the Tower, conferred upon him a large pension, and used every expedient to alleviate the burden of his age, and to blunt the poignancy of his sufferings.

After the death of Lord Bacon, which happened in April 1626, in the 66th year of his age, the records of science begin to assume a brighter aspect; and we discern true knowledge emerging from the dungeons of scholastic controversy, and shaking off the shackles of polemical learning.

The philosophers by fire, as the Chemists were emphatically termed, no longer exclusively engaged in seeking for the elixir of life, and the stone of transmutation, began to direct their endeavours towards more attainable and useful objects. They availed themselves of the accumulated facts collected by the misguided zeal and barren labours of their predecessors, and combined these useless and unseemly materials into the foundations of a beautiful and useful department of knowledge; but their progress was slow, and not unfrequently interrupted by relapse into the follies of Alchemy.

Glauber of Amsterdam,¹ and in this country the Honourable Robert Boyle, are characteristic writers of the middle of the seventeenth century. The former has detailed many curious and interesting facts respecting neutral salts, acids, and animal and vegetable substances; but his descriptions are darkened by the language of the adepts, and valuable truths are disguised by being blended with the unintelligible jargon of the black art.

The perusal of Glauber's chemical works leads to some surprise at the multitude of facts with which he was acquainted, and, among them, we meet with discoveries which have been considered of modern date. He particularly describes the production of vinegar during the destructive distillation of wood. (Miraculum Mundi, p. 1.) The following may be selected from among many similar passages in his writings, as exhibiting the active and original turn of mind of this keen and curious inquirer, and as containing the germ of many truths which have been more fully developed in our own time.

"But what other things the said juice of wood is able to effect, we cannot here declare, by reason of our intended brevity; yet this I will add, that, if this acid spirit be rectified, it may be used in the preparation of good medicines; in mechanic arts; in the making of many fair colours from the extraction of metals, minerals, and stones; and for all things for which common vinegar is used; yea, far more commodiously, because it much exceedeth common wine and beer vinegar in sharpness."

He also mentions the tar produced in the same process, which he recommends as

efficacious in preserving wood that is exposed to weather, and speaks of it, when mixed with ashes, as a profitable and quickly acting manure. He further points out the method of concentrating the vinegar of wood by exposure to cold, "which freezes the phlegm only, but the sharp spirit is not turned into ice, but remaineth in the middle of the hogshead, so sharp that it corrode metals like aqua-fortis. If hop-poles be dipped in the oil, it not only preserves them, but fattens the plant; and as insects abhor these hot oils, if they be applied to the bark of fruit-trees, it will defend them from spiders, ants, canker-worms, and other insects; by this means also rats and mice may be prevented from creeping up hovel-posts, and devouring the grain." Glauber details a number of experiments relating to the action of this vinegar of wood, on limestone, and notices the uses of its compounds; and that he was accurately acquainted with its superior acidity, appears from the following quotation: "It is said that Hannibal made a passage through the Alps for himself and his army, softening the rocks by the benefit of vinegar. What vinegar that was, histories do not mention. Perhaps it was the vinegar of wine; but if he had had the vinegar of wood, he might sooner have attained his desire."

These shrewd remarks and useful observations are thickly scattered through the verbose pages of Glauber. He enriched the laboratory with new agents, and into medicine he introduced several new and useful remedies. Upon the arts he bestowed many improvements, and was among the first who seriously endeavoured to benefit agriculture by the medium of experimental chemistry.

Boyle¹ has left voluminous proofs of his attachment to scientific pursuits, but his experiments are too miscellaneous and desultory to have afforded either brilliant or useful results; his reasoning is seldom satisfactory; and a broad vein of prolixity traverses his philosophical works. He was too fond of mechanical philosophy to shine in Chemistry, and gave too much time and attention to theological and metaphysical controversy to attain any excellence in either of the former studies. He who would do justice to Boyle's scientific character, must found it rather upon the indirect benefits which he conferred, than upon any immediate aid which he lent to science. He exhibited a variety of experiments in public, which kindled the zeal of others more capa-

ble than himself. He was always open to conviction; and courted opposition and controversy, upon the principle that truth is often elicited by the conflict of opinions. His disposition was ever amiable, mild, and generous, and he was at once the patron of learning and of virtue.

The merit of bringing Hooke¹ before the public, and of pointing out to him the road to eminence, is chiefly due to Mr Boyle, who, in the troublesome and bigotted periods of the commonwealth and protectorship, associated himself with a few philosophical friends at Oxford, for the purpose of promoting experimental inquiry. Hooke, who enjoyed the advantage of having been educated at Westminster school, under Dr Busby, was introduced in the year 1655 to this select society, where his original and inventive genius was soon discerned and called into action. Boyle engaged him as his operator and assistant, and his talents were turned, with great success, to the invention and improvement of philosophical instruments, and to many important subjects connected with the mechanical arts.

It was about this period that the physical properties of the atmosphere began to attract notice, and that the favourite scholastic notion of Nature's abhorrence of a vacuum was called into question. Galileo was perhaps the first who broke this spell of Aristotelian philosophy; and in the year 1644, the grand discovery of atmospheric pressure, and its variation, was announced by Torricelli, the celebrated inventor of the barometer.² The idea of constructing a machine for the purpose of rarefying air, first

occurred to Otto Guericke, who, after many fruitless attempts, succeeded by means of a sucking pump, in withdrawing a considerable portion of air from the interior of a copper ball. With this awkward and imperfect air-pump, he performed several notable experiments. One of these is often exhibited at the present day. It consists in exhausting a hollow brass globe, composed of two hemispheres, closely fitted to each other. When a portion of the interior air is removed, the pressure of the exterior atmosphere is such as to resist considerable force applied to separate the hemispheres. This is called the Magdeburgh experiment, and was first publicly exhibited in the year 1654 before the deputies of the empire, and foreign ministers assembled at the diet of Ratisbon. This original air-pump, invented by the Burgomaster of Magdeburgh, was greatly improved by Hooke, who, in conjunction with Boyle, performed by its means a variety of new and important experiments, illustrative of the mechanical properties of the atmosphere, which, at a subsequent period, tended considerably to the progress of pneumatic chemistry.

The works of Hooke, chiefly interesting to the chemist, are his Micrographia and Lampas, the former published in 1664, the latter in 1677. They contain anticipations of many of the subsequent changes and improvements of chemical theory, which will be noticed in a future page of this history.

Both the private and public character of Dr Hooke exhibit many faults, and are stained with many blemishes. His temper was peevish, reserved, and mistrustful; and he wanted that candour and dignity of mind which should raise the philosopher above the level of ordinary men. He was born at Freshwater, in the Isle of Wight, in 1635, and died in London in the year 1702.

Immediately after the Restoration, the gentlemen who formed the Philosophical Society at Oxford adjourned to London, where they held their meetings in Gresham College, and considerably extended the number of their members. The King, who himself loved science, countenanced and patronised their proceedings; and, on the 15th of July 1662, granted a royal charter, constituting them a body corporate, under the name of The Royal Society of London, for promoting Natural Knowledge. In the year 1665 was published the first number of the Philosophical Transactions, of which work, justly regarded as the standard of English science, a volume has been published annually since the year 1762.

This laudable and rare example of Charles the Second was followed by Lewis the Fourteenth of France; and in the year 1666 the Royal Academy of Sciences was instituted at Paris, under the immediate protection of that monarch. Neither was the

patronage cold, nor the honours empty, which were bestowed by Lewis on the followers of science. Salaries he conferred upon scientific bodies, and pensions upon learned men, "a generosity," says Hume, "which does great honour to his memory, and in the eyes of all the ingenious part of mankind will be esteemed an atonement for many of the errors of his reign. We may be surprised," continues the historian, "that this example should not be more followed by Princes, since it is certain that bounty so extensive, so beneficial, and so much celebrated, cost not this monarch so great a sum as is often conferred upon one useless overgrown favourite or courtier." Happily for the scientific character of Britain, the genius, talents, and exertions of individuals have ever been sufficient to counterbalance such advantages; and thus nurtured and protected, the growth of science has not been less rapid or vigorous than where she has enjoyed the sunshine of royal favour.

With the great and unrivalled name of Newton, we close the records of the seventeenth century. To him Chemistry is indebted for the first correct views respecting the nature of combination; a subject which had little engaged the attention of the more sensible experimentalists of the preceding periods, and which was formerly attributed to the occult qualities of the Aristotelians, and afterwards to the mechanical forms of the particles of bodies.¹

Chemical affinity was referred by Newton to the different attractive powers of the different kinds of matter in regard to each other. Salt of tartar becomes moist by exposure to air, because that salt attracts the humidity of the atmosphere. Muriatic acid unites with salt of tartar by virtue of their respective attractions; but when oil of vitriol is poured upon this compound, the former acid is displaced by the superior attraction of the latter. Silver dissolved in aqua-fortis is separated from that menstruum by the superior attraction of quicksilver; in like manner copper separates quicksilver; and iron, copper. Referring to these and other similar instances, "does not this" says he "argue, that the acid particles of the aqua-fortis are attracted more strongly by iron than by copper, by copper than by quicksilver, and by quicksilver than by silver?" Such are the simple but clear, and, in most instances, correct suggestions relating to the subject of attraction, which Chemistry owes to the great luminary of Mechanical Philosophy.

In tracing the history of Chemistry from early times, through the dark ages, to the

beginning of the last century, I have only noticed such authors as conduced by the weight or novelty of their writings, the importance of their discoveries, or the example of their zeal, to the more immediate progress and elucidation of this department of philosophy. The annals of a period so extensive must necessarily record a host of experimentalists, to whose researches it would upon the one hand be impossible to do justice; and whose names, on the other, it would be useless to repeat. It may however be remarked, that alembics, and other complex distillatory apparatus, were employed by the alchemical physicians who flourished between the ninth and thirteenth centuries. Mesue mentions the distillation of rose-water, and the production of spirit of wine is noticed by Raymond Lully. At this time, too, furnaces of peculiar construction, and a variety of complex apparatus and accoutrements, were introduced into the laboratory.

During the fifteenth and sixteenth centuries, Alchemy was at its acmé, and many were the unwary and avaricious who were entrapped by the golden prospects and plausible mysticism of the art. Among them was that admirable artist Mazzuoli of Parma, better known under the name of Parmagiano.

Curious discoveries and useful inventions multiplied rapidly during the seventeenth century. Kunckel, in Saxony, successfully promoted the Chemistry of the Arts. In 1669, Brandt of Berlin discovered Phosphorus, and about the same time Homberg accidentally produced a spontaneously inflammable compound, which he called Pyrophorus. In 1674 the elder Lemery acquired great and deserved fame at Paris as a chemical lecturer. He was the first who threw aside the affected and pompous diction habitually indulged in by his predecessors and contemporaries, and adopted a simple and perspicuous style, which at once tended to the ready diffusion of his subject, and to its permanent popularity. When he published his course, "it sold" says Fontenelle "like a novel or a satire."

The establishment of literary and scientific societies during this age was another grand step towards the promotion of knowledge, and the period was particularly propitious to their progress. Bacon, Galileo, and Kepler, had opened that road to truth which was so eagerly and successfully pursued by Boyle, Hooke, and Mayow, in this country, and in which the miraculous mind of Newton displayed its brilliant powers. In Germany, Beccher and Stahl are entitled to particular mention. The suggestions of the former, who was a man of an acute and inquisitive turn of mind, led the latter into that train of speculation which terminated in producing the Phlogistic Theory, and which will presently be more particularly considered. Homberg, Geoffroy, and

the two Lemerys, were zealous followers of experimental chemistry in France, at the establishment of the Royal Academy of Sciences. In short, the independent zeal and healthy activity in scientific pursuit, which has since marked its progress in Europe, became manifest early in the seventeenth century; and the causes I have attempted to unfold contributed to the splendour which it began to acquire about the end of that important era in the general history of the world. The clouds of ignorance and error quickly dispersed before this happy dawn of true knowledge; and science, no longer enveloped in scholastic mystery and absurd speculation, began to display those inherent charms, which gained her the courtship and admiration of every liberal and cultivated mind, and which laid the foundation of that extended dominion which she acquired in the succeeding age.¹

STATE OF CHEMISTRY AT THE OPENING OF THE EIGHTEENTH CENTURY.—OPINIONS OF BECCHER AND STAHL RESPECTING THE PHENOMENA OF COMBUSTION, COMPARED WITH THE VIEWS OF REY AND MAYOW.—PNEUMATIC CHEMISTRY OF HAILES AND BOERHAAVE.—INVENTION OF THE THERMOMETER.

THE history of the progress of Chemistry during the seventeenth century presents many active and able inquirers, whose researches tended to develop new properties and combinations of bodies; but their attempts at theory and generalization were, with few exceptions, absurd and abortive. They consisted in wild hypothesis and vague speculation, and were founded, not upon the sober and steady basis of truth, but upon the unreal and tottering visions of the imagination. The spirit of Lord Bacon was slow in animating experimental philosophy, until Newton rose to surprise and illumine the world. It then assumed a new and cheerful aspect, and quick was its growth, and illustrious its progress, under the invigorating influence of that sun of science.

Although Chemistry does not lie under the same weighty obligations to Newton as

mechanical philosophy, he conferred upon it a great and lasting benefit, by the disclosure of those clear and simple views which have already been alluded to.¹ The important deductions, too, which flow in easy perspicuity from his experimental researches, soon became general models of imitation; and the new style which we discern in the philosophical authors of the early part of the eighteenth century throughout Europe, may, in a great measure, be referred to the lofty example before us.

No sooner was the spell of Alchemy broken, than the phenomena of combustion began to attract the notice of the early chemical theorists. The influence of the air upon this process had been long observed, and many of the changes suffered by the com-

bustible had been examined with a surprising degree of acuteness and precision; for fire was almost the only agent employed at that period to effect combination and decomposition. These inquiries constitute a prominent feature in the history of Chemistry. It may therefore be requisite to pursue them with a minute attention, which may at first appear tedious, but which will gain in importance and interest as they proceed.

The first speculations in theoretical Chemistry deserving attention, are those of John Joachim Beccher of Spire, who died in England in 1685. He gained considerable celebrity at Vienna and Haerlem, for improvements in arts and manufactures, but was induced to retire to this country, in consequence of the jealousy of rivals, and the neglect of those upon whom he had conferred benefits. His works abound in shrewd and witty remarks, and in deep and curious reasoning,—in frivolous subtlety, and in weighty and sensible observations. His hypothesis respecting the origin of the varieties of matter, from the mutual agencies and combinations of a few elementary principles, though unnecessarily blended with scriptural history, are characterized by considerable brilliancy of thought and originality of invention. They are detailed at great length in his Physica Subterranea, which treats on the original creation of matter, and the transition and interchange of elements. The Institutiones Chemicæ, or Oedipus Chemicus, of this author, is another curious production, containing the history of the chemical elements, and describing the leading operations of the laboratory. Earth was the favourite element of this philosopher, of which he supposed three varieties to exist, namely, a vitrifiable, a metallic, and an inflammable earth. Of these the various productions of nature were formed.¹

But the most celebrated chemical theorist of the latter part of the seventeenth century is Ernest Stahl, born at Anspach in Franconia, in 1660. He adopted many of the opinions of Beccher respecting the cause of inflammability, and upon these foundations reared the celebrated System of Phlogiston, according to which, inflammability is supposed to depend upon the presence of a highly subtile and elastic matter, which, at certain temperatures, is thrown into violent motion, and appears under the form of flame or fire. Combustion is the separation of this principle, and bodies contain it in various proportions. Charcoal, for instance, when burned, leaves scarcely any residuum, and is, therefore, nearly pure phlogiston. Antimony, when burned, affords a large proportion of earthy matter. If this earth be heated with charcoal, or other matter abounding in phlogiston, antimony is regenerated; this metal, therefore, is a compound of earth and phlogiston.

If sulphuric acid, which is not inflammable, be distilled with oil of turpentine, which is extremely so; or, in other words, if phlogiston be added to sulphuric acid, sulphur is obtained. Sulphur, therefore, is a compound body, consisting of sulphuric acid and phlogiston. If sulphur and common potash be fused together, a brown compound is obtained, formerly called liver of sulphur, and the same product results when charcoal is heated with Glauber's salt, which consists of soda combined with sulphuric acid. Such was Stahl's explanation of the phenomena of combustion, and such the apparently plausible experimental proofs upon which it was founded.¹

In Germany and in France, the phlogistic doctrine was received with that thoughtless and eager enthusiasm which suffers the blaze of novelty to eclipse the steady light of truth, and which is rather captivated by plausible exterior than by internal excellence. Even in this country the experiments of Boyle and of Hooke, if not forgotten, were over-

tatem in hoc opere," says he, "quam barbaram esse fateor, ob materiem et ob scriptionem, in specie scriptionis modum: ex ore enim dictantis totum opus conceptum est. Sic rebus attentus, verba neglexi." This is at once an example and apology.

looked, and hypothesis for a time gained the ascendancy over facts; for it had been most satisfactorily demonstrated by those experimentalists, that bodies will not burn if air be excluded, and that, during combustion, a portion of the air is consumed by the burning body. Even at an earlier period, the same observation had been most pointedly dwelt upon and another equally important circumstance ascertained, namely, the increase of weight sustained by metals during their calcination. As early as 1629, Brun, an Apothecary, resident in the town of Bergerac in France, melted two pounds six ounces of tin, and in six hours the whole was converted into a calx, which weighed seven ounces more than the tin employed. Brun, surprised at this circumstance, communicated it to John Rey,¹ a physician of Perigord, who, in 1630, published a Tract upon the subject, in which he refers the increase of weight to the absorption and solidification of air: "Thus," says Rey, in the fanciful language of the period, "have I succeeded in liberating this surprising truth from the dark dungeons of obscurity; which was vainly but laboriously sought after by Cardan, Scaliger, Faschius, Cæsalpinus, and Libavius. Others may search for it, but in vain, unless they pursue the royal road which I have cleared. The labour has been mine,—the profit is the reader's,—the glory is from above."

But amongst the authors whose researches tended to conclusions diametrically opposite to those of Stahl and his associates, and whose writings abound in anticipations of modern discoveries, no one stands so conspicuous as our countryman John Mayow.² His tracts, published at Oxford in 1674, relating to chemical, physiological, and medical subjects, abound in traits of original and inventive genius, and furnish the prototype of many discoveries, which have conferred great and lasting renown upon succeeding labourers in the field of Chemistry. It is the treatise upon nitre and the nitro-aerial spirit to which I principally allude, and of which it may be proper to give a short but connected sketch.

The atmosphere, he observes, contains a certain nitro-saline matter, a spirit, vital, igneous, and fermentative, which exists in, and may be obtained from nitre; that it supports combustion, but is itself incombustible; that it exists in nitric acid; that when antimony is exposed to the joint operation of heat and air, it imbibes the nitro-aerial particles, whence its increase in weight; and that a similar change may be effected by nitre or by nitric acid; that acidity depends upon the absorption of the same principle which in sulphuric acid is combined with sulphur, either during combustion, or during the exposure of pyrites to air: that fermentation is referable to a very similar cause: that it is necessary to vegetation, and present in all cases of combustion; that it is absorbed by animals during respiration; and that the same substance which contributes to the support of flame, is likewise required for the support of life. Mayow also was acquainted with the evolution of air during the action of nitric and vitriolic acids upon iron, and points out a mode of collecting it, in bottles inverted in vessels of the dilute acids. He observes that the air generated in these experiments, although expansible by heat, is probably different from the atmosphere, as is also the air which an animal has breathed, and in which a candle has burned.

These are a few of the important facts dwelt upon by Mayow, respecting the nature of the atmosphere, and of the cause of combustion. That they were not at the time opposed to the purely speculative notions of Stahl is truly remarkable, for they explain, in conjunction with the observations of Rey and others, the great obstacle to the phlogistic hypothesis, the increase of weight in the burning body; they show the real cause of the necessity of the presence of air, which, if combustion consisted in the mere evolution of the subtile principle of fire, could not be required; and they adduced experimental evidence, where Stahl merely surmised.

Another active inquirer occurs in this page of chemical history; one whose researches cleared the way for the great discoveries of the succeeding era, and to whom the merit is justly due of having opened a mine in the field of nature; who indulged, not in the speculative and metaphysical frivolities which characterize the productions of most of his predecessors, and many of his contemporaries, but followed nature with a steady and unerring step, and recorded his observations in a concise, unadorned and unaffected style. This was the Reverend Dr Stephen Hales.¹ He was the first

who instituted researches into the physiology of vegetation, a subject which he pursued with considerable ardour and perseverance. He also made a variety of experiments upon the extrication of air during the exposure of animal, vegetable, and mineral substances to heat. In perusing his Essays on these subjects, we frequently find him upon the verge of those splendid discoveries which fell to the lot of his fellow-labourers and successors; but the erroneous nature of his preconceived opinions induced him to take for granted that which experiment should have determined, and to rest satisfied with results which, had they been followed up, would inevitably have led to the most important and novel facts. His experiments do credit to his industry, but his conclusions betray feebleness of judgment. If, instead of regarding the various gaseous products obtained from the substances he operated upon, as consisting of common air contaminated by their effluvia, he had submitted them to more close investigation, he would doubtless have run a more brilliant and successful career. He is justly regarded as the founder of Pneumatic Chemistry, but he contributed few materials to the superstructure.

Herman Boerhaave,¹ of Leyden, who was a contemporary of Hales, pursued a

than one occasion, in order that he might attend to his humble parochial duties, and continue his scientific pursuits.

He directed his attention to the quantity of moisture imbibed and emitted by different plants, and to the circulation of the sap, which, he says, put him upon making a more particular inquiry into the nature of a fluid which is so absolutely necessary for the support of the life and growth of animals and vegetables.

His Specimen of an Attempt to analyse the Air by Chymiostatical Experiments displays extraordinary ingenuity in the contrivance of experiments and apparatus. It was his misfortune to consider the various gases which he procured as mere modifications of atmospheric air. Philos. Trans. Statical Essays, London, 1731.

¹ Boerhaave was born in December 1668, at a village near Leyden. He died in September 1738. He was an eminent ornament of medicine, as well as of chemical science. His oration upon resigning the office of Governor of the University of Leyden has been justly eulogised by Johnson. (Life of Boerhaave.) He here declares in the strongest terms (says his eloquent biographer) in favour of experimental knowledge, and reflects with just severity upon those arrogant philosophers, who are too easily disgusted with the slow methods of obtaining true notions by frequent experiments, and who, possessed with too high an opinion of their own abilities, rather choose to consult their own imaginations than inquire into nature, and are better pleased with the charming amusement of forming hypotheses than the toilsome drudgery of making observations.

The emptiness and uncertainty of all those systems, whether venerable for their antiquity, or agreeable for their novelty, he has evidently shown; and not only declared, but proved, that we are entirely ignorant of the principles of things, and that all the knowledge we have is of such qualities alone as are discoverable by experience, or such as may be deduced from them by mathematical demonstration.

Boerhaave's contributions to physic were large and valuable. His principal chemical work is the Elementa Chemica, of which a good translation, with notes, was edited in 1753 by Dr Shaw. This work he

similar train of inquiries; but, although many of his experiments were new and well conceived, he was not more happy in his conclusions, nor more fortunate in his discoveries. He attributed the elasticity of air to its union with fire, and considered its ponderable matter as susceptible of chemical combinations; but the existence of different aeriform fluids escaped his notice.

The philosophers whose names have been now recorded, not only greatly added to the stock of chemical facts collected by their predecessors, but conferred new life and vigour upon the science by their occasional incursions into the regions of theory and rational speculation:—in this light, the works of Rey, Mayow, and Stahl, deserve particular attention; the two former for correctness and precision, the latter for boldness and ingenuity.

About this period the Thermometer was brought to perfection, which tended materially to the progress of that most refined and difficult branch of Chemical Philosophy, relating to the nature and effects of heat. The researches, on this subject, will presently form an important feature in our history, which renders it proper to notice this instrument of such consequence in their prosecution.

That bodies change in bulk, with variations of temperature, must have been noticed at a very early period; but there can be little doubt, that the idea of constructing an instrument for measuring these variations first occurred to Santorio,¹ Professor of Medicine, in the University of Padua, in the beginning of the seventeenth century; he is also celebrated for his Medico-statical experiments, which are well burlesqued in one of the early numbers of the Spectator.²

dedicated to his brother, who was intended for the medical profession, but went into the church; while Boerhaave, who originally studied divinity, relinquished it for physic and chemistry. Alluding to this circumstance, "Providence," says he, "has changed our views, and consigned you to religious duties, while I, whose talents were unequal to higher objects, am humbly content with the profession of physic."

In the Elementa, and in several of his Orationes, are admirable remarks upon the useful application of Chemistry to other branches of knowledge. His observations upon its usefulness and necessity to the medical practitioner, may be well enforced at the present day; for, excepting in the Schools of London and Edinburgh, Chemistry, as a branch of education, is either entirely neglected, or, what is perhaps worse, superficially and imperfectly taught. This is especially the case at the English Universities, and the London Pharmacopœia is a record of the want of chemical knowledge, where it is most imperiously required.

Santorio's thermometer consisted of a tube, blown at one end into a bulb, and with the other open extremity immersed into water. In cold weather the confined air contracted and the water rose in the tube—in a warm atmosphere the air expanded and the fluid fell. Santorio observed some other particulars connected with the operation of this thermometer, among which the increased influence of the sun's rays, when the bulb was blackened, deserves notice.

The Academicians del Cimento, whose early labours have already been mentioned, materially altered and improved the thermometer, by employing a liquid to measure temperature, instead of air, the changes of bulk in which, in a moderate range of temperature, are so considerable as to render the instrument extremely bulky and otherwise inconvenient. They generally used spirit of wine, and fixed a scale of degrees to the tube, with a view to ascertain its variations in bulk with greater precision. These instruments soon acquired considerable celebrity, and were largely circulated under the appellation of the Florence Glass. In this state the uses of the thermometer were extremely limited, no two instruments corresponded, and there being a free communication between the fluid and the external air, it was liable to evaporation,—yet was this thermometer much preferable to the over-sensible and bulky instrument of Santorio. There was another objection to spirit of wine, arising out of the readiness with which it assumes an elastic state, and which renders it unfit for measuring temperatures even below the heat of boiling water. Sir Isaac Newton, therefore, suggested the use of linseed oil, which, however, is extremely ill adapted to the purpose on account of its unctuousity, and the ease with which it solidifies. Quicksilver was first recommended by Roemer,¹ the eminent Danish philosopher, who discovered the motion of light; it was also employed by Dr Halley, and is now generally used. The advantages of this fluid metal in the construction of the thermometer are manifold; it retains its liquid state at very high and very low temperatures, and has the peculiar excellence of expanding very equally for equal increments of heat, which is far from the case with spirit of wine.

But the great improver of the thermometer was Fahrenheit,² a merchant of Dantzic, who, having failed in business, and being attached to chemical and mechanical pursuits, was obliged to gain a livelihood by making and selling these instruments. Fahrenheit used both spirit of wine and quicksilver, and hermetically sealed the tube containing the fluid; he also greatly improved the method of graduation, by establishing

two points as the extremes of his scale, and subdividing the intermediate portion into a given number of degrees.

The division of the thermometric scale had occupied the attention of several learned and ingenious men; but it was Fahrenheit who pointed out the most accurate means of accomplishing this purpose. The curious circumstance of the water running from melted snow being always of the same temperature, appears first to have occurred to Güricke of Magdeburgh, but was first applied to the graduation of thermometers by Sir Isaac Newton. Dr Hooke had observed that the quicksilver in the tube of the thermometer, plunged into boiling-water, always rose to the same height; accordingly, if a mercurial thermometer be put into melting snow, and the point at which the fluid stands, marked upon the tube, and then transferred to boiling-water, and that point also marked, and if the intermediate space be subdivided into any number of equal degrees, 100 for instance, it follows that, provided proper precautions have been taken in selecting and filling the tube, every thermometer so constructed will indicate the same degree, when applied to bodies of the same temperature. With regard to the boiling point, Fahrenheit observed it to differ under different degrees of atmospheric pressure, and pointed out the necessity of fixing it at a mean barometrical altitude. He had also noticed, that a degree of cold much more intense than that of ice might be procured by a mixture of snow and salt; and conceiving this to be extreme cold, he commenced his scale from that point, which is $32^\{\backslash circ\}$ below the freezing of water. Accordingly, Fahrenheit's scale commences at $0^\{\backslash circ\}$, the temperature of his freezing mixture; the freezing point of water is marked $32^\{\backslash circ\}$, and the boiling point $212^\{\backslash circ\}$; the space between the freezing and boiling of water being divided into $180^\{\backslash circ\}$. The graduation of thermometers received its greatest improvement in 1742, by Celsius of Sweden, who commenced the scale at the freezing of water, and divided the space between it and the boiling point into $100^\{\backslash circ\}$. This is the centigrade scale, now used in France. Reaumur's scale, in which the point of congelation is marked $0^\{\backslash circ\}$, and that of boiling-water $80^\{\backslash circ\}$, is used in some parts of the European Continent; and in Russia the descending scale of Delisle is sometimes employed, in which the boiling point of water is $0^\{\backslash circ\}$, the freezing $150^\{\backslash circ\}$. These scales have each their merits and defects. In the event of innovation, the interval between the freezing and boiling of mercury, might be divided into 1000 equal parts; the former being $40^\{\backslash circ\}$ below $0^\{\backslash circ\}$ of Fahrenheit, the latter about $+670^\{\backslash circ\}$. The degrees would thus be sufficiently small to be expressed without fractions; and the commencement of the scale,

which is about the lowest natural temperature, would be so low, as to preclude the frequent necessity of expressing negative degrees.¹

From this sketch of the history of the thermometer, it is obvious, that its operation depends upon the circumstance of fluids diminishing in bulk by diminution of temperature, and the contrary; which is really the case with all fluids except water. This important fact was observed by the Florentine Academicians in their early experiments, and it is among the most curious and interesting discoveries of that zealous and active association of experimentalists. Having filled a large thermometer tube with water, they plunged it into a mixture of salt and snow. The water presently began to contract in bulk, and descend in the tube; but, instead of continuing to do so, till it reached the freezing point, after a short time it commenced expanding; the expansion went on till a portion of the water froze, and was then very suddenly increased.²

The temperature at which water thus begins to expand by cooling is 40° Fahrenheit, and water cooled down to 32°, that is, 8° below 40°, occupies the same space as

when heated to $8^\{\backslash circ\}$ above $40^\{\backslash circ\}$; in other words, the density or specific gravity of water is at its maximum at $40^\{\backslash circ\}$.

When in the year 1683 Dr Croune repeated this experiment before the Royal Society, Hooke attributed the effect, not to any peculiarity in the expansibility of water, but to a rapid and sudden contraction of the glass bulb, which would force the water upwards in the tube; ¹ a conclusion amply disproved by other forms of the experiment, especially by that suggested by Dr Hope² of Edinburgh, in which a freezing mixture was applied to the surface of water at $60^\{\backslash circ\}$ contained in a tall cylindrical glass jar. The water was cooled throughout to $40^\{\backslash circ\}$, and then the surface sunk to $32^\{\backslash circ\}$, and froze. But when the freezing mixture was applied to the bottom of the jar, the water became cooled throughout to $32^\{\backslash circ\}$. If the cold be applied to the centre of the vessel, as long as the water is above $40^\{\backslash circ\}$, the warmer part will always be at the top, but below $40^\{\backslash circ\}$ the arrangement is reversed, and the warmer part being then most dense, occupies the lower half of the vessel, and the colder portion floats upon it.

The influence of this singular anomaly, which has thus been demonstrated by unanswerable experiments, is of great extent and importance. In most of the cases in

The following is Dr Birch's memorandum relating to this experiment:

February 6, 1683.

A letter of Mr Musgrave to Mr Aston, dated at New College, Oxford, was read, containing, among other things, several experiments about freezing, as that two inches of water in a tube $\backslash frac\{1\}\{2\}$ inch diameter, expanded itself, upon freezing, $\backslash frac\{2\}\{3\}$ higher; that a tube one inch diameter filled 6 inches, rose upon freezing, $\backslash frac\{2\}\{3\}$ of an inch; and that half a pint of water, upon freezing, lost in weight 5ij. $\backslash text\{ij.\; gr.\; viij.\}$

Dr Croune said, that having weighed three ounces of water, he found it, after freezing, to differ a scruple and half.

Sir Christopher Wren remarked, that if water were suddenly frozen, there would be less difference in weight.

Dr Croune said, that he observed water which he had put into a bolt-head, to rise higher before there was anything of freezing in it.

Mr Hooke attributed the rising of the water in the neck of the bolt-head, to the shrinking of the glass.

Dr Croune said, that the glass had been long in the cold, before, and that the water rose immediately.

Dr Wallis proposed, that an empty glass might be cooled well in a freezing liquor, in order that it might have its contraction before the water be put into it.

This was done immediately by Mr Hunt, and the water being put into a small bolt-head, rose about $\backslash frac\{1\}\{2\}$ of an inch in the neck, though the air at that time was very warm. (Birch's History of the Royal Society, Vol. IV. p. 253.)

which nature deviates from her usual established laws, philosophy has discovered happy consequences in her aberration; and where such discovery has not been made, investigation should be upon the alert to trace the clue that is presented.

If water were obedient to the same laws of refrigeration as other less universal liquids, such as spirit, oils, and quicksilver, it must be evident, that, during the winter's cold, our rivers and lakes, instead of presenting a superficial stratum of ice, would soon become solid throughout; the continuous influence of the summer's sun would be required to produce their fluidity, and the inhabitants of the waters would annually risk extermination.

These effects are obviated by the peculiarity observed by the Academicians del Cimento. As the temperature of the earth is in winter always greater than that of the atmosphere, the cooling of large bodies of water must take place from above, by the contact of cold air and chilling blasts. The whole mass will thus be lowered to 40°, after which, the water becoming specifically lighter as it becomes colder, remains upon the surface where it sinks to 32°, and is converted into a film of ice, which being a bad conductor of heat, thickens slowly, and affords further protection to the warmer fluid beneath. Those who in winter's cold accidentally fall through the ice, are surprised by the comparative warmth of the water below, and the aquatic animals that in summer sport upon the surface of their element, retire in winter to the more genial retreats which nature has thus provided.

In tracing the progress of Chemistry through its dark and early periods, the historian necessarily traverses a rugged and barren path; his chief object must be to advance, and the shortest is generally the safest road. Reaching the age of Alchemy, the prospect, though improved, is not such as to demand a very deliberate survey: its fictions, however, like those of romantic chivalry, have somewhat of reality for their basis, and by the mere increase of experimental inquiry, contributed essentially to the growth of chemical knowledge. As a science, its progress was languid until the middle of the seventeenth century, when it began to shake off the lethargy in which it had been sunk, and was turned with eager curiosity to new and more useful objects.

In the dross of the alchemical furnaces many scattered treasures were discovered, the value of which was greatly enhanced by arrangement and systematic combination. New views were thus opened to the Experimentalist; and authors, dismissing the florid exuberancies and pompous affectation of their predecessors, cultivated an unadorned and simple style, more becoming the dignity of scientific narration.

These circumstances contributed to confer a prosperous aspect on Chemical Philo-

sophy at the commencement of the eighteenth century. It was applied to the arts, and to them it gave an unexpected and vigorous impulse. It was directed to the investigation of nature, and there it discovered new beauties. It found "tongues in trees, books in the running brooks, sermons in stones, and good in everything."

THE discoveries of Dr Joseph Black form a most important epoch in the history of Chemical Philosophy; they embrace two leading subjects,—the one relating to the causticity of the earths and alkalies—the other to the operation of heat in changing the state of bodies; in rendering solids liquids; and converting liquids into elastic or aeriform fluids.

Regarding these researches as isolated specimens of inductive philosophy, they have rarely been equalled: as influencing the progress of Chemistry, by disclosing the hidden cause of many very intricate phenomena, they have never been surpassed; and, by a happy combination of circumstances, we trace in them the distant but fertile source of those gigantic improvements of the arts, in which the perfection of the steam-engine is involved.

Of a man whose scientific character is thus pre-eminent, and in whose attainments his country has just reason to exult, history has recorded a brief but interesting memorial.¹

Dr Joseph Black was sprung from a Scottish family, transplanted first to Ireland and then to France, where he was born in 1728, on the banks of the Garonne. When twelve years of age, he was sent for education to Belfast, and afterwards to the University of Glasgow, where he entered upon the study of Physic, under the guidance of that bright ornament of medical science, Dr William Cullen. In 1750 he removed to Edinburgh; four years afterwards, he took the degree of Doctor of Physic; and, in

1756, published his Experiments on Magnesia, Quicklime, and some other alkaline substances, in the Physical and Literary Essays.¹ In the same year Dr Cullen, having removed to Edinburgh, Dr Black returned to Glasgow to fill the Medical and Chemical chair of that University, where he was received with open arms both by the Classes and Professors. In 1764, he brought his ideas respecting the combinations of heat with ponderable matter to perfection. Speculations upon this subject had occupied his mind during a considerable period, but the difficulties of the inquiry, and the time necessarily consumed in other professional avocations, had considerably interfered with the pursuit.

In 1766, he was appointed to the Chemical Chair of Edinburgh, an office which he filled with such talent, industry, and perseverance, as not only drew an immense course of hearers to his class, but tended to confer upon chemistry a degree of popularity and importance, which has been greatly conducive to its promotion and extension. "His discourse," says his biographer, Professor Robison, "was so plain and perspicuous, his illustrations by experiment so apposite, that his sentiments on any subject never could be mistaken; and his instructions were so clear of all hypothesis or conjecture, that the hearer rested on his conclusions with a confidence scarcely exceeded in matters of his own experience."¹ In short, Dr Black, in his professorial capacity, was entitled to every praise, and he contributed most essentially to the foundation and increase of the reputation which the University of Edinburgh has acquired and maintained. Nor was his private character at variance with his public excellence; he was mild, amiable, and fond of conversation, whether serious or sportive; and he was not above uniting to the highest philosophical attainments, most of the

elegant accomplishments of life. In his advanced age he often expressed a hope that he might not linger in protracted sickness, on account of the distress which, in such cases, is suffered by attending friends; and his death, which happened in his 71st year, in November 1799, is on this account the more remarkable. He was taking some milk and water, and having the cup in his hand, when the last stroke of his pulse was to be given, had set it upon his knees, and in this attitude expired without the smallest agitation.

The writings of Black, though lamentably few, are masterpieces of scientific composition. Newton was his model, and he was the first who transferred into chemistry the severe system of inductive logic, which marks the productions of that great master of natural philosophy. "In no scientific inquiries, since the date of the Principia and Optics, do we find so great a proportion of pure ratiocination, founded upon the description of common facts, but leading to the most unexpected and important results, as in the two grand systems of Black." Averse to all hypothesis, and aware of the multitudinous facts upon which a theory that is to stand firm must be founded, Dr Black was unwarrantably slow in the formal public disclosure of his admirable researches. His tenets were fully and freely delivered to his pupils; but he very rarely intruded upon the public as an author; and his splendid achievements in the philosophy of heat are chiefly developed in his posthumous works. This silence, arising out of an over-cautious modesty which marked all his proceedings, was not favourable to the reputation of Dr Black. Faulty and incomplete copies of his lectures were circulated among his friends and admirers, which afterwards reached the hands of those who deserve another name, and by whom they were not very honourably employed.

The first researches of Dr Black, which it will be necessary to attend to, explain the cause of causticity in earths and alkalies. When chalk or limestone, which are mild insoluble tasteless substances, are heated to redness in the open fire, they are converted into quicklime, a body corrosive, soluble in water, and having an acrid flavour. Stahl, Macquer,¹ and Meyer, attributed this change to some substance absorb-

ed from the fire,—to an acrid acid,¹—to phlogiston, and other creatures of the imagination. Dr Black's mind was turned to this subject in consequence of the discovery of magnesia. This substance made its first appearance as an Arcanum in Italy, in 1707. Valentine showed that it might be obtained from the mother-liquor of nitre, but it was supposed to be lime, until Hoffman, in 1720, pointed out several peculiarities by which it is distinguished from that earth. Hoffman prepared magnesia from bittern, or the saline liquor which remains after the separation of common salt from sea water; to this he added an alkali which precipitated the earth.² The substance which thus exists in bittern, is a compound of magnesia and sulphuric acid. It was first obtained from certain mineral springs in the neighbourhood of Epsom in Surrey, and thence called Epsom salt, but was sold at a very high price, in consequence of the small quantities so procured, until the manufacturers in the neighbourhood of Lymington obtained it from sea water; it was then largely exported to the Continent under the name of English salt.

Epsom salt was indeed long confounded with Glauber's salt, and a fraud of the manufacturers here, and in Germany, tended to keep up the confusion; for at that period Glauber's salt was rare in England, and large crystals of Epsom salt were sold under that name; but in Germany, where Epsom salt was not common, Glauber's salt, in

d'âcre."—"On le combine avec la partie la plus âcre, la plus subtile, et la plus saline de la chaux."—"Nous n'entreprendrons point ici d'expliquer pourquoi le sel alcali, que l'on combine avec la chaux, acquiert une si grande causticité. Cette question nous paroît une des plus delicates et des plus difficiles à résoudre que nous offre la Chimie. Elle tient à celle des propriétés alcalines de la chaux, et on ne peut guères espérer de la résoudre, que quand on aura acquis sur la nature de cette substance, beaucoup plus de lumières que nous n'en avons à présent." Élemens de Chimie Pratique, pp. 179. 182.

¹ J. F. Meyers, Chemische versuche zur näheren erkentniss des ungelöschten kalks; der elastischen und elektrischen Materie, des allerreinsten feuerwesens, und der ursprünglichen allgemeinen säure. Hannover, 1764. In this dissertation, though published subsequently to Black's essay, the causticity of the alkalis and lime is referred to the absorption of a principle which the author calls Causticum, or Acidum pingue. Between the years 1760 and 1772, a great variety of dissertations were published in Germany upon this question, some in support of Black's doctrine, others in favour of Meyers's hypothetical absurdities. See Gren's Systematisches Handbuch der Gesamten Chemie. Halle, 1794. § 437.

² Observ. Phys. Chem. 1722.

Hoffman was the most celebrated Chemical Physician of the age. He was born at Halle in Saxony, in 1660, and died in 1742. His writings, which are voluminous, are also valuable. In 1749, they were eked out by the Genevese Booksellers into nine folio volumes. The following are his leading Essays in Chemistry:

Dissertationes de Generatione Salium,—De Natura Nitri,—De Cinnabare Antimonii,—De Mirabili Sulphuris Antimonii fixati efficacia,—De Mercurio et Medicamentis Mercurialibus. Observationum Physico-Chemicarum Collectio. Libri iii.

small crystals, was vended as English or Epsom salt. Pott of Berlin, and Du Hamel of Paris, were led into a comedy of errors in consequence of mistaking the nature of these bodies.

Dr Black found that, when magnesia was prepared by precipitating a solution of Epsom salt by a mild alkali, that it effervesced with acids; but that when heated to redness it lost weight, and then dissolved without effervescence. This fact, which also holds good in respect to lime, induced him to believe that, instead of gaining any thing in the fire, something was lost by these earths. He, therefore, distilled some magnesia in a retort, but found, that although it lost weight as before, nothing but a relatively small quantity of water was found in the receiver. The experiments of Dr Hales now rushed into his mind, and it occurred to him, that some gaseous or aeriform body had escaped from the earth, and that this was the cause of its effervescing with acids,—a circumstance previously ascribed to the collision of the acid and earthy particles. He therefore put some magnesia not calcined into a bottle, with a bent tube attached to it; and thus, during the action of the acid, obtained a large quantity of an elastic fluid, in a vessel inverted in water; he found, too, that chalk, and common alkali, yielded the same kind of air. The air thus existing in these substances Dr Black called fixed air; and he proved it to be the cause of mildness in earths and alkalies. If lime be added to a mild alkali, the lime absorbs its fixed air, and renders it caustic,—an effect formerly attributed to the transfer of the fiery particles of the lime.

In the year 1750, Venel observed that selters, and other sparkling waters, when placed under the receiver of an air-pump, gave out a large quantity of air, and became flat and insipid, and he imitated them by dissolving common soda in water, and adding muriatic acid, which produced an effervescence and gave it briskness.¹ These experiments were a little antecedent to Dr Black's publication, but they by no means anticipated his discoveries.² In 1764 the conclusions of Black were verified, and his

views extended, by Dr Macbride of Dublin, who pointed out several new properties of fixed air, and demonstrated its existence in the atmosphere; for lime exposed to air gradually loses its causticity, and becomes effervescent. The operation of quicklime as a manure depends upon its power of rendering the inert vegetable matter of the soil soluble and fit for the nourishment of young plants; an effect which it does not produce when combined with fixed air, or in the state of chalk: hence the lime should be spread quickly over the land, and not left in heaps exposed to the air, by which, as Dr Macbride has shown, it is rendered mild, and of comparatively small effect.¹

Such are the principal features of Dr Black's researches respecting the cause of mildness and causticity in earthy and alkaline substances. They constitute an important body of chemical evidence, and are established upon the satisfactory basis of analytical and synthetic proofs.

I now turn to his more elaborate investigation into the effects of heat; to inquiries so momentous in their influence upon the advancement of experimental philosophy, so replete with difficulties, and so masterly in their execution, as to raise them to the highest efforts of the human mind. I have deemed a rapid glance at the discovery of fixed air sufficient for our present purpose; for occasions will afterwards offer of descending more largely upon its nature and properties; but the investigation now before us, is that from which the towering and durable greatness of Black's name has been principally derived; and it was begun, continued, and completed, by the labour of his own hands.

In speaking of the graduation of thermometers, it was mentioned, that if snow or ice be brought into a warm atmosphere, and suffered to thaw slowly, the water which

waters of Pyrmont, Spa, and others, imparting to them that pungent taste, from which they were denominated acidulae, and likewise that volatile principle on which their virtues chiefly depend."

Mr Lane was the first who ascertained the solubility of iron in water, impregnated with fixed air. Phil. Trans. 1769. "By this means," says Sir John Pringle in his discourse on the different kinds of Air, delivered at the anniversary meeting of the Royal Society, November 30, 1773, "the nature of the metallic principle in mineral waters was clearly explained, and the whole analysis of those celebrated fountains, so often attempted by Chemists and others, and still eluding their laboured researches, was thus, in the most simple manner, brought to light."

¹ Macbride's Experimental Essays, 1764. The merit of this performance induced the University of Glasgow to bestow the degree of Doctor of Physic on the author.

Dr Macbride introduced some important improvements into the art of Tanning, and was the first who employed lime water in the preparatory operations of that process. He was born in the county of Antrim in 1726, and died in 1778.

runs from it is always at one temperature, that of $32^\{\backslash circ\}$ of Fahrenheit's scale. This and similar cases seem to have occupied the early thoughts of our philosopher; for his biographer informs us, that, in the oldest parcels of his notes, he found queries relating to this subject. How does it happen that, although heat is constantly flowing from surrounding bodies to the ice, its temperature is not increased? Water at $32^\{\backslash circ\}$, when brought into a room at $60^\{\backslash circ\}$, goes on increasing in temperature till it attains that of the circumambient air; but the ice, though exposed to exactly similar sources of heat, remains at $32^\{\backslash circ\}$. Why, when water is cooled several degrees below its freezing point, does its temperature suddenly rise to that point, the instant that it congeals? or why is it, that, when a vessel of water is put upon the fire, a thermometer plunged into it continues to indicate increase of heat until it rises to $212^\{\backslash circ\}$; and the water then boils, but does not become hotter, although it remains upon the fire, and has all its former opportunities of acquiring heat? Such were the queries which Dr Black has most happily resolved.

In regard to the liquefaction of ice, he has demonstrated that, when solids pass into the liquid state, the change is always accompanied with the absorption of heat, which is concealed or becomes latent in the liquid, and is not indicated by the thermometer, which instrument, therefore, is no measure of the absolute quantity of heat. A variety of interesting and curious experiments were undertaken with a view to ascertain the quantity of thermometric heat, which thus becomes latent during the conversion of ice into water. A pound of snow at $32^\{\backslash circ\}$ was mixed with a pound of water at $172^\{\backslash circ\}$; the snow was melted, and the temperature of the mixture was only $32^\{\backslash circ\}$; so that here $140^\{\backslash circ\}$ of thermometric heat had disappeared; their effect being, not to raise the temperature of the snow, but to convert it into water. We should say, therefore, from this experiment, that water at $32^\{\backslash circ\}$ is a compound of ice, and $140^\{\backslash circ\}$ of heat as indicated by the thermometer. If water, at the temperature of $32^\{\backslash circ\}$, be mixed with an equal weight of warm water, suppose at $200^\{\backslash circ\}$, the resulting temperature will be the mean; $232\; \backslash div\; 2\; =\; 116$; but if we use ice, the temperature will not be the mean, for $140^\{\backslash circ\}$ of heat must be subtracted from the warm water, which heat is consumed in liquefying the ice; the result, therefore, will be the same as if water at $32^\{\backslash circ\}$ and $60^\{\backslash circ\}$ were mixed, giving a mean of only $45^\{\backslash circ\}$.

These experiments at once demonstrated the cause of many facts respecting the production of heat and cold, which, though long known, remained without any plausible explanation.

When solids become fluids, the production of cold is more or less evident, according to the rapidity of the change. Those saline bodies, for instance, which are very rapidly soluble in water, generate during their solution a considerable intensity of cold, for to become fluid they must absorb heat. When snow and salt are suddenly blended, there is an instant liquefaction, and the temperature of the substances being already low, a degree of cold equal to $0^\{\backslash circ\}$ of Fahrenheit is obtained. The production of cold by mixing snow and muriate of lime, a very soluble salt, is $-40^\{\backslash circ\}$ Fahrenheit, and sufficient to freeze quicksilver even in a comparatively warm atmosphere. A mixture of 5 parts of sal ammoniac in powder, and 5 parts of nitre with 16 of water, sink the thermometer from $50^\{\backslash circ\}$ to $10^\{\backslash circ\}$. Equal parts of nitrate of ammonia and water produce a more intense cold, and by a clever successive application of these freezing mixtures, the intense degree of cold of $-91^\{\backslash circ\}$. Fahrenheit has been artificially exhibited. This is $123^\{\backslash circ\}$ below the freezing of water, and $40^\{\backslash circ\}$ below the greatest natural cold hitherto observed, which was at Hudson's Bay, where the spirit thermometer has been seen at $50^\{\backslash circ\}$.

There are many counter illustrations of this doctrine of latent heat; in which heat is evolved during the conversion of liquids into solids. If oil of vitriol be poured upon magnesia, there is a sudden solidification of the acid by its union with the earth, and a considerable rise of temperature ensues. Water poured upon quicklime produces a similar phenomenon; and when water at perfect rest is exposed in a covered vessel to an intensely cold atmosphere, its temperature may be reduced to many degrees below its freezing point: A slight agitation causes it suddenly to become ice, and at that instant the temperature rises to $32^\{\backslash circ\}$. A somewhat similar case is the sudden crystallization of saline solutions, during which their latent heat becomes sensible to the feeling, and is indicated by the thermometer.

In Dr Black's theory of latent heat, it is assumed that heat is matter; that it is a substance of excessive tenuity, existing in variable proportions in bodies; that when in a free state it affects our senses, and the thermometer, but that it occasionally enters into union with other substances, or is separated from them, consistent with the usual laws of chemical attraction. Thus, in fluids, it is combined or latent, but when they are converted into solids, it is separated in a free or sensible state. The other view of the question represents heat as the result of a vibrating motion among the particles of bodies; the vibrations being most rapid and extensive in the hottest bodies. In fluids the vibrations are accompanied by a motion of the particles round their own axes; and when solids pass into the fluid state, the vibratory motion or temperature is in part lost, by the communication of the rotatory motion to the particles.

Each of these hypotheses has had its able defenders and advocates; the ideas of Newton seem to have been favourable to the latter, and many facts may be adduced in its support. The strongest are the imponderability of heat, and its continuous extrication by friction. That we discover no increase of weight in a heated body may be attributed to the insufficiency of our instruments, but its unlimited production in a variety of cases, though consonant with the hypothesis of vibration, ill agrees with that of a specific form of matter.

If a soft iron nail be beaten upon the anvil, it becomes hot and brittle, and it cannot again be rendered malleable till it has been resoftened by exposure to the fire. By those who favour the notion of a matter of heat, this has been called an experimentum crucis. The matter of heat, say they, is squeezed out of the nail, as water out of a sponge, but it is reabsorbed in the fire. In this experiment, however, it must be recollected, that the mechanical arrangement of the particles of the iron is considerably altered; it is rendered very brittle; and hence, perhaps, its insusceptibility of becoming again hot till restored to its former state or texture by the expansive power of fire.

It was not until the publication of the researches which have just been considered, that a variety of curious circumstances concerning congelation were understood. The gradual progress in the freezing of large bodies of water has been shown to depend in some measure upon the remarkable anomaly respecting its maximum of density; but it is also materially connected with the phenomena of latent heat; for water, before it can become ice, must part with a quantity of heat, which, if suddenly evolved, would raise the thermometer $140^\{\backslash circ\}$. It must also be obvious, that the process of thawing suffers a similar retardation, for ice requires for its conversion into water, the absorption of $140^\{\backslash circ\}$. of sensible heat.

Thus we see that sudden congelation and sudden liquefaction are alike prevented; that the process must be gradual, and consequently productive of none of those evils which would result from a more rapid change.

One of the great advantages of irrigation, or meadow watering, is also explained by a reference to these principles. In an irrigated meadow, the surface of the water may be frozen; but as water at $40^\{\backslash circ\}$ is heavier than at $32^\{\backslash circ\}$, the former will be its temperature in contact with the grass; and it is a temperature perfectly congenial to the functions of vegetable life. Sir Humphrey Davy examined the temperature in a water meadow near Hungerford, in Berkshire, by a very delicate thermometer. The temperature of the air, at seven in the morning, was $29^\{\backslash circ\}$. The water was frozen above the grass; the temperature of the soil at the roots of the grass was $43^\{\backslash circ\}$. Thus, by the peculiarity in the re-

frigeration of water, by the defence afforded by the stratum of ice, and by the laws of congelation, the vegetables are not merely protected from the effects of an intensely cold atmosphere, but likewise from the injurious influence of sudden changes of temperature.

Congelation is to surrounding bodies a source of heat, and there is no inconsiderable mitigation of the extreme cold of air wasted over large bodies of water, by the transfer of latent to sensible heat, which must occur before they can freeze.

The theory of freezing mixtures has led to considerable improvements of their applications, and many new and curious discoveries have resulted in pursuing this inquiry. Indeed, whatever tends to disclose the laws of nature cannot ultimately fail of subjecting her more or less to the uses of life, and of manifesting more and more the wisdom of the Creator.

Having established the above facts respecting the cause of fluidity, Dr Black proceeded to the second part of his inquiry, relating to vaporisation, and pursued it with the same abilities and success.¹ Finding the thermometer to remain stationary at 212° in boiling water, he conceived the process of ebullition to be in some respects analogous to that of liquefaction, and that the heat which did not raise the temperature of the water, entered into union with it, and became latent in the steam. If this

were the case, it should be re-evolved during the condensation of steam; and thus a method was devised of ascertaining its thermometric quantity. Dr Black's experiments on this subject were very numerous. I shall allude to such as put the phenomenon in the clearest light, and are perfectly unconnected with hypothesis.

He noted the time consumed for raising a certain quantity of water to its boiling point, and then kept up the same heat till the whole was evaporated, and marked the time consumed by the process. It was thus easily computed what the temperature would have been, supposing the rise to have gone on above $212^\{\backslash circ\}$ in the same ratio as below it. The water was originally at $50^\{\backslash circ\}$; it boiled in four minutes, and in twenty minutes was all evaporated. In four minutes, therefore, it had gained $162^\{\backslash circ\}$ for $50^\{\backslash circ\}\; +\; 162\; =\; 212$; and in twenty minutes would have gained $162\; \backslash times\; 5\; =\; 810^\{\backslash circ\}$; which may, therefore, be considered as the equivalent thermometric expression of the latent heat of the steam. Another good illustration of the absorption of heat in the production of steam, is furnished by heating water under compression. It may then be raised many degrees above its ordinary boiling point; but, on removing the pressure, a portion of steam rushes out, and the remaining water has its temperature lowered to $212^\{\backslash circ\}$.¹

Hence we learn, that the conversion of water into vapour is attended with a great loss of heat to the surrounding bodies; and although the perceptible temperature of water and steam are identical, the latter contains heat equivalent to between $800$ and $900^\{\backslash circ\}$ of perceptible or thermometric temperature. When steam is reconverted into water, this large quantity of heat is again given out; and hence a small portion of steam is capable of heating a large body of water to its boiling point. The knowledge of this fact is of great economical importance; and in breweries and other manufactories, where large bodies of water are required to be boiled, the steam, instead of being suffered, as formerly, to pass off into the air, is conveyed by pipes into other vessels of water, which it heats during its condensation. In the same way, rooms and houses are warmed by the heat evolved during the condensation of steam, in iron or copper tubes which traverse the building, and the method is at once safe and effectual.

It is in consequence of the latent heat of steam, that, in the process of distillation, we are obliged to present so large a surface for condensation; and it is not difficult, by the help of a still, to calculate the latent heat of steam. If, for instance, one hun-

dred gallons of water at $50^\{\backslash circ\}$ be mixed with one gallon at $212^\{\backslash circ\}$, the temperature of the water will be raised above $1\backslash frac\{1\}\{2\}^\{\backslash circ\}$. If, by the common still-tub, one gallon of water be condensed from the state of steam by one hundred gallons of water at $50^\{\backslash circ\}$, in that case the water will be raised $11^\{\backslash circ\}$, which is about $9\backslash frac\{1\}\{2\}^\{\backslash circ\}$ degrees more than in the former instance. Hence it appears, that the heat imparted to a hundred gallons of cold water by eight pounds of steam, would, if it could be condensed into one gallon of water, raise it $950^\{\backslash circ\}$.

The average of the various experiments which have been made on this subject, warrants us in placing the latent heat of steam between $900^\{\backslash circ\}$ and $1000^\{\backslash circ\}$.

These facts demonstrate that the condensation of vapour is always a heating process, and that its formation must equally be attended with the production of cold.

¹ About the year 1774, it was observed by Dr Cullen, that a thermometer moistened with spirit of wine or ether, sinks many degrees during the evaporation of those fluids; with others, the thermometer may be made to fall from $60^\{\backslash circ\}$ to $0^\{\backslash circ\}$. The cause of this is sufficiently explained by Dr Black's theory; the ether and spirit readily pass into vapour, which requires a certain quantity of heat for its production; this is taken from the bodies it happens to be in contact with, as from the thermometer or the hand; hence the cold perceived when these fluids are applied to the body, and the advantage which results from their application in cases of burns, and inflammations. These circumstances led Dr Cullen to accelerate the evaporation of these fluids, by exposing them under the receiver of the air-pump; by placing a flask half full of ether

in a tumbler of water, it was found that, during the process of exhaustion, the evaporation was so rapid from the ether in the flask, as to convert the surrounding water into ice.¹

This part of the philosophy of heat, regarded in its connection with the phenomena of nature, opens pleasing views of her order and economy. In the constant evaporation from the earth's surface, from rivers, lakes, and the sea, we discern an unfailing cause of equalization of heat; the vapour thus formed, ascending to colder regions, there becomes a source of increase of temperature, and, re-assuming fluidity, is thrown upon the earth in fertilizing showers, or forming torrents among the mountains, and rivers in the valleys, is returned to the parent ocean, and again becomes active in a similar cycle of changes.

But besides these obvious and complete changes in the state of matter connected with the evolution or absorption of heat, there are others in which similar alteration of temperature is observed, without a positive change of form. Whenever the density of a body, whether solid, liquid, or aeriform, is varied, there is an equivalent variation in its latent heat. The specific gravity of soft iron is increased by hammering, and heat is evolved during the operation. A piece of Indian rubber, suddenly extended, becomes warm. If water be mixed with oil of vitriol, the density of the water is increased, and there is a very considerable augmentation of temperature. If air be suddenly compressed, it retains its elastic state, but becomes violently heated; on the other hand, if air be quickly rarified, there is an equivalent reduction in its tempera-

ture. In these cases, bodies are said to change their capacities for heat; increase of density is attended with a diminution of capacity for heat; and diminution of density with an increased capacity. The phenomena thus presented are such as the doctrine of latent heat would lead us to expect. When a fluid is converted into a solid, there is a copious evolution of heat; when a fluid approximates to a solid state, or where its density is increased, we might expect that heat would also be evolved.¹

The last train of investigation, in regard to heat, which occupied Dr Black's thoughts, related to the different quantities of heat contained in different substances of the same temperature, without relation to change of density or state. A reference to an experiment will perhaps render this point more intelligible. If, for instance, a given quantity of boiling water, surrounded with ice, in sinking from $212^\{\backslash circ\}$. to $32^\{\backslash circ\}$., melts one pound of ice, and if the same quantity of olive oil, in passing from the same to the same temperature melts only half a pound of ice, we should conclude, that, although the thermometric temperature of the two fluids is similar, the actual quantity of heat contained in the water, and ascertainable by its effects upon the ice, is twice that contained in the oil. To signify the quantity of heat thus contained in different bodies of the same temperature, the term specific heat has been employed—we thus should state, from the result of the experiment alluded to, the specific heat of water to be 2, that of olive oil 1. Irvine, Crawfurd, Wilcke, Lavoisier, and several eminent Experimentalists of the present day, have engaged themselves in researches on this subject, but the inquiry originated with Dr Black, in the year 1762.

In these limited observations upon the discoveries of Black, I hope to have rendered myself intelligible upon those main points of his investigations, which constitute the foundation of some of the most important and refined doctrines of chemical science. The distinct object of this discourse being to record the march of chemical discovery, and not to unfold the principles of the science, it would be unwise to indulge in more extended incursions upon this fertile ground, or to trace the great trunk of his researches to its extreme ramifications. But a partial glance at the facts disclosed will show even a superficial observer the obligations we are under to the discoveries of this eminently modest and unassuming Philosopher. Of many of the most intricate phenomena of nature they furnished new, easy, and luminous explanations; and to the arts

they were of unparalleled benefit; for, by developing their connection, not with the shallows merely, but with the depths of science, a new road was opened to their improvement and perfection.

Among the learned lookers-on of this period we discern many who, with independent and liberal minds, loved and patronized science for its own sake, and they were pleased at its rapid progress under the auspicious guidance of Black. Others, actuated by motives illiberal and interested, countenanced science solely upon the selfish principle of gain; the puerile and short-sighted question of cui bono was constantly on their lips; but even they have been silenced by the application of Black's discoveries.¹

OF the various discoveries, which it is the object of this Dissertation to unfold, none have been more important in their consequences than those relating to the composition of atmospheric air, a subject which the ancients seem not to have thought upon, since they regarded it as an element or ultimate principle of matter.¹ In this, as in most other branches of experimental science, the advances of the human mind

the steam, it became absolutely necessary to keep up the temperature of the cylinder constantly at the boiling point of water; this he was enabled to attain, by connecting with it another vessel, exhausted of air, and immersed in cold water, into which, when communicated with the cylinder, the steam, being an elastic fluid, instantly rushes and is condensed, and, on closing its connection with the cylinder, the steam, again admitted there, now operates with full force, and suffers no further condensation. To carry off the water from this second vessel, which he calls the condenser, and to perpetuate the vacuum, Mr Watt attached to it a pump by which both the air and condensed water are removed. The engine thus altered produced the same power as one of equal dimensions on Newcomen's plan, with rather less than one-third the quantity of steam; hence was a considerable hindrance to the use of the engine materially diminished, namely, the expence of fuel. But great as was this improvement, it forms a small part of the successful achievements of Mr Watt in this department of mechanics; he amended the apparatus for boring the cylinders, and improved every part of the working gear of the engine; and he infinitely extended its applications and utility, by applying the power of steam to produce motion round an axis; but their enumeration would lead me out of the bounds of chemistry. I, therefore, hasten to the invention which may be said to have perfected the steam-engine. Steam had hitherto only been used to force the piston down,—it was returned by a weight attached to the other end of the beam. Mr Watt, in 1782, constructed an engine in which steam was used to elevate as well as to depress the piston, an alternate vacuum being formed above and below it, by the condenser, as before. An engine upon this plan, executed at Mr Watt's manufactory at Soho, near Birmingham, was first employed at the Albion Mills in 1788.

An excellent sketch of the history of the steam-engine will be found in the Edinburgh Review, Vol. XIII. p. 311.

¹ Thus Lucretius,—

Aera nunc igitur dicam, quid corpore toto
Innumenabiliter privas mutatur in horas:
Semper enim, quodquomque fuit de rebus, id omne
Aeris in magnum fertur mare, qui nisi contra
Corpora retribuat rebus, recreetque fluentis,
Omnia jam resoluta forent, et in aera vorsa,
Haud igitur cessat gigni de rebus, et in res
Recidere assidue, quoniam fluere omnia constat.

De Rerum Natura, Lib. V. v. 274.

have been very gradual: Mayow, in 1674, was upon the very brink of that stream of discovery, which, in 1774, carried Dr Priestley into the fastnesses of Pneumatic Chemistry. Hales, by showing the mode of disengaging and collecting gaseous fluids, removed many of the most serious obstacles which encumbered this path of research; he was followed by Boerhaave, and afterwards by Black, who, having reached the discovery of fixed air, turned into another road of investigation. Neither Mayow, therefore, nor Hales, nor Boerhaave, nor Black, were very diligent cultivators of Pneumatic Chemistry; they had, indeed, opened the mine, but did not explore it; its treasures were reserved for those whose labours we are now about to recount, and were chiefly borne away by the diligent dexterity of Dr Joseph Priestley.

If we trust the quotations of Rey already cited, the necessity of air, in the process of combustion, was not only observed, but inquired into by Cæsalpinus¹ and Libavius,² as far back as the sixteenth and early part of the seventeenth century. Mayow insisted that a part only of the atmosphere was concerned in the phenomena of combustion, and found that air in which bodies had burned became unfit for the respiration of animals.³ As soon as it had been ascertained that, in the phenomena of combustion and respiration, a portion of fixed air was generated, the extinction of burning bodies, and the death of animals immersed in air, thus rendered foul, were referred to the presence of that gaseous body, its noxious qualities having been amply proved by Black and

others; and this opinion seemed to be sanctioned by the discovery, that air thus tainted by respiration and combustion, might, in some measure, be restored to purity by exposure to the action of lime water, which absorbed the fixed air.

In 1772, Dr Rutherford, Professor of Botany in the University of Edinburgh, published a thesis on fixed, or, as it was then called, mephitic air, from which the following passage is extracted.¹ "By the respiration of animals, healthy air is not merely rendered mephitic, but also suffers another change. For, after the mephitic portion is absorbed by a caustic alkaline lixivium, the remaining portion is not rendered salubrious, and although it occasions no precipitate in lime water, it nevertheless extinguishes flame, and destroys life."

Thus we have traced the discovery of two gaseous fluids differing from common air: fixed air, discovered by Black, and azote, as it has since been called, by Rutherford. The former, a component part of chalk, and of the mild alcalis, the product of the combustion of charcoal, and of the respiration of animals; the latter an ingredient of atmospheric air.

It would be a wearisome and unprofitable occupation to record, even in brief terms, the transactions of a set of cavilling philosophers who started up in this country, and elsewhere, about the present period of our history; their names have sunk into oblivion, and their works were only read while recommended by novelty. Some of them I have reluctantly perused, and have found that they are rather calculated to weary the attention than to satisfy curiosity, or impart information.

I therefore hasten to one of the most remarkable and splendid epochs of chemical science, adorned by discoveries which have been rarely equalled, either in number or importance, and ushered in by a series of sterling facts and memorable investigations. The well known names of Priestley, Scheele, Cavendish, and Lavoisier, now appear upon the stage, and it will be an arduous but gratifying task to follow them through their respective parts. In this recital, a strict adherence to the dates of discoveries would neither be convenient nor useful, and I shall rather therefore deviate a little on this point, than cloud the perspicuity of my narrative, or cramp it by chronological strictness.

Dr Priestley's character was of so composite an order as to defy brief description or superficial delineation; he was a politician, a divine, a metaphysician, and a philosopher; and in each of these callings he displayed abilities of a peculiar and occasionally exalted description. His copious and important contributions to chemical science are the more surprising, when it is remembered that his philosophical pursuits were merely resorted to as a relaxation in his theological studies; that his mind was under the constant agitation of controversy and dispute; that he was too impatient for deep research, and too hasty for premeditated plans. But, with all these bars against him, he was a thriving wooer of science: he made more of his time than any person of whom I ever read or heard; and possessed the happy and rare talent of passing from study to amusement, and from amusement to study, without occasioning any retrograde movement in the train and connection of his thoughts.

There is another important feature in Dr Priestley's character, which may tend to throw some light upon his controversy with the French school: He possessed the strictest literary and scientific honesty; he makes frequent mention of his predecessors and contemporaries, and enumerates the ideas which he borrowed from them, and the experiments they suggested, with more than necessary accuracy and minuteness. His attachment to Chemistry seems to have been formed at Leeds,¹ about the year 1768, and between that period and the year 1772 he had added several new and highly important facts to the science, which are detailed in a long communication presented to the Royal Society in the spring of that year. It is here that he relates those research-

es respecting the influence of vegetation upon the atmosphere, which led to entirely new views of the physiology of plants, and which displayed, in a striking light, some of those masterly and beneficent adjustments of nature, by which the different members of the creation are made to minister to each other's wants, and thus preserve that eternal harmony which marks the natural world.

As combustion and respiration were connected with the deterioration of air, it occurred to Dr Priestley to ascertain how far the growth of vegetables might be productive of similar effects.

"One might have imagined," says he, "that since common air is necessary to vegetable as well as to animal life, both plants and animals would affect it in the same manner; and I own I had that expectation when I first put a sprig of mint into a glass jar, standing inverted in a vessel of water; but when it had continued growing there for some months, I found that the air would neither extinguish a candle, nor was it at all inconvenient to a mouse which I put into it."

In experiments of this kind, Dr Priestley points out the necessity of often withdrawing the dead and dying leaves, lest, by their putrefaction, they should injure the air; he also hints at the noxious powers of some plants, especially the cabbage, of which he kept a leaf in a glass of air for one night only, and in the morning a candle would not burn in it.¹

Dr Priestley also extended his experiments to the influence of plants upon air vitiated by animal respiration and by combustion, and found that they in general did not only not contaminate the air, but that they actually restored to purity that which had been rendered impure by flame and breathing; and by showing that this change was

effected by groundsel as perfectly as by mint, proved it independent of the aromatic oil to which some in their ignorance had been willing to refer it.

That actual vegetation was necessary, and the mere vegetable insufficient, he proved by exposing the pulled leaves of a mint plant to air, which were unproductive of the regeneration effected by the growing sprig.

Dr Priestley concluded from these experiments, that the noxious air resulting from combustion, and from the breathing of the different animal tribes, formed part of the nourishment of plants; and that the purity of our atmosphere, and its fitness for respiration, were materially dependent upon the functions of growing vegetables.

Mayow in 1674, and Hales in 1724, had observed the production of gaseous matter during the action of nitric acid upon the metals. I have before alluded to the very rude manner in which Mayow collected it. Hales ascertained its singular property of producing red fumes when mixed with common air. Dr Priestley resumed these inquiries, and pursued them with clever activity: he found, that, on mixing one hundred parts, by measure, of common air, with one hundred of the air procured by the action of nitrous acid on copper, which he called nitrous gas, red fumes were produced, and there was a diminution of bulk equal to ninety-two parts in the two hundred; so that one hundred and eight parts only remained.

When fixed air was thus mixed with nitrous air, there was no diminution; when air, contaminated by combustion or respiration, was used, the diminution was less than with purer air; and with air taken from different situations, Dr Priestley thought he obtained rather variable results. Hence the beautiful application of nitrous air to the discovery of the fitness of other species of air, for combustion and respiration.

It was for these discoveries that the Council of the Royal Society honoured Dr Priestley by the presentation of Sir Godfrey Copley's medal, on the 30th of November 1733.¹

Sir John Pringle, who was then President, delivered, on this occasion, an elaborate and elegant discourse upon the different kinds of air, in which, after expatiating upon the discoveries of his predecessors, he points out the especial merits of Priestley's investigations : In allusion to the purification of a tainted atmosphere by the growth of plants, the President has thus expressed himself :

" From these discoveries we are assured, that no vegetable grows in vain ; but that, from the oak of the forest to the grass of the field, every individual plant is serviceable to mankind ; if not always distinguished by some private virtue, yet making a part of the whole which cleanses and purifies our atmosphere. In this the fragrant rose and deadly nightshade co-operate ; nor is the herbage nor the woods that flourish in the most remote and unpeopled regions unprofitable to us, nor we to them, considering how constantly the winds convey to them our vitiated air, for our relief and for their nourishment. And if ever these salutary gales rise to storms and hurricanes, let us still trace and revere the ways of a beneficent Being, who not fortuitously, but with design, not in wrath, but in mercy, thus shakes the water and the air together, to bury in the deep those putrid and pestilential effluvia which the vegetables on the face of the earth had been insufficient to consume." ¹

Mr Martin Folkes. The discourses, however, which he and his successors delivered, were very short, and were only inserted in the minute books of the Society ; none of them had ever been printed before Sir John Pringle was raised to the chair of the Society." Chalmers's Biographical Dictionary.—Life of Pringle.

Dr Franklin, in a letter upon the subject of this discovery to Dr Priestley, has expressed himself as follows :

" That the vegetable creation should restore the air which is spoiled by the animal part of it, looks like a rational system, and seems to be of a piece with the rest. Thus, fire purifies water all the world over. It purifies it by distillation when it raises it in vapours, and lets it fall in rain ; and farther still by filtration, when, keeping it fluid, it suffers that rain to percolate the earth. We knew before that putrid animal substances were converted into sweet vegetables when mixed with the earth and applied as manure ; and now, it seems that the same putrid substances, mixed with the air, have a similar effect. The strong thriving state of your mint, in putrid air, seems to show that the air is mended by taking something from it, and not by adding to it. I hope this will give some check to the rage of destroying trees that grow near houses, which has accompanied our late improvements in gardening, from an opinion of their being unwholesome. I am certain, from long observation, that there is nothing unhealthy in the air of woods ; for we Americans have everywhere our country habitations in the midst of woods, and no people on earth enjoy better health, or are more prolific." Phil. Trans. 1772, page 199.

Notwithstanding these researches, which have exposed some very curious facts relative to the chemical physiology of plants, it must be confessed that the causes of the renovation and equality of our atmosphere are yet by no means ascertained ; for, although some growing vegetables do, under certain circumstances, purify the air (by the absorption of carbon and the evolution of oxygen), yet, when in a state of decay, they invariably add to its contamination, and a general view of the subject would induce us to conclude,

Such were Dr Priestley's researches, and such the views to which he had been led previous to the year 1773, when he undertook the examination of the air which rises from red lead, and from red precipitate of quicksilver, when those substances are exposed to heat. This, indeed, was one of the topics upon which Hales had touched before him, but it was passed over with that hasty and superficial carelessness of which his experimental proceedings furnish so many instances, and in which he so often lost the substance by grasping at the shadow.

Dr Priestley cast his keenest eye upon the prospect now before him, and as the various objects came into view, he followed them up with more than his ordinary diligence and usual sagacity. The track he had entered upon was, indeed, of such abundant promise, as would have insnared the attention and excited the curiosity of one less awake than our author to its interest and novelty. But he, already well initiated in the management of æriform fluids, proceeded with a rapidity which left his associates far behind, and carried him, in proud and undisputed precedence, to the goal of discovery.

The 1st of August 1774 is a red-letter day in the annals of Chemical Philosophy, for it was then that Dr Priestley discovered dephlogisticated air. Some, sporting in the sunshine of rhetoric, have called this the birth-day of Pneumatic Chemistry; but it was even a more marked and memorable period; it was then (to pursue the metaphor) that this branch of the science, having eked out a sickly and infirm infancy in the ill-managed nursery of the early Chemists, began to display symptoms of an improving constitution, and to exhibit the most hopeful and unexpected marks of future importance.

Dr Priestley's original opinion, that all kinds of factitious air were noxious, seems first to have been shaken by observing that a candle would burn in air procured by distilling nitre in a gun barrel; but the first experiment, which led to a very satisfac-

that they do as much harm as good, at least, if recent experiments connected with this subject are to be considered as correct.

These are the prominent features of Dr Priestley's first communication to the Royal Society respecting the different kinds of air, and had he bestowed no other contribution upon chemistry, the facts here detailed would have entitled him to a conspicuous place among the benefactors of the science. The paper is divided into several sections, in which he discusses the nature and properties of fixed air; of the air contaminated by the combustion of candles and of brimstone; of inflammable air; of air infected with animal respiration or putrefaction; of air exposed to the action of mixtures of iron filings and sulphur; of nitrous air; of air in which metals have been calcined, and which has been exposed to the action of white-lead paint; and of air procured by spirit of salt.

tory result, was conducted as follows. A glass jar was filled with quicksilver, and inverted in a basin of the same; some red precipitate of quicksilver was then introduced, and floated upon the quicksilver in the jar; heat was applied to it in this situation by a burning lens, and "I presently found that air was expelled from it very readily. Having got about three or four times as much as the bulk of my materials, I admitted water into it, and found that it was not imbibed by it. But what surprised me more than I can well express, was, that a candle burned in this air with a remarkably vigorous flame, very much like that enlarged flame with which a candle burns in nitrous air exposed to iron or liver of sulphur; but, as I had got nothing like this remarkable appearance from any kind of air besides this peculiar modification of nitrous air, and I knew no nitrous acid was used in the preparation of mercurius calcinatus, I was utterly at a loss how to account for it."¹

He afterwards obtained the same kind of air by exposing red lead and several other substances to heat, and made a number of well-devised experiments upon its properties.

Those who, for the first time, witness the effect of this air upon burning bodies, will best picture to themselves the emotion and surprise of its discoverer, when he plunged a burning taper into it. The splendour of the flame was magnificently increased, the consumption of the wax was extremely rapid, and the heat evolved much more considerable than in common air. He found, in short, that, in all cases of combustion, the process was infinitely more rapid and perfect in this kind of air, than in the ordinary atmosphere;² and he was thence induced to apply the term dephlogisticated to the gas he had thus obtained. He regarded it as air deprived of phlogiston, and thus accounted for its eager attraction for that principle which, during combustion, bodies were imagined to throw off. On the contrary, he accounted for

the extinction of flame by the air discovered by Rutherford, and since termed azote¹ or nitrogen,² upon the idea that that aeriform fluid was charged or saturated with phlogiston, and he therefore called it phlogisticated air.³

In enumerating the higher merits of Dr Priestley as a discoverer, we must not forget the minor advantages which his ingenuity bestowed upon experimental Chemistry. He supplied the Laboratory with many new and useful articles of apparatus, and the improved methods of managing, collecting, and examining gaseous fluids, were chiefly the results of his experience. He was the first who, with any chance of accuracy, endeavoured to ascertain the relative or specific gravities of the different kinds of air then known; he observed that dephlogisticated air was rather heavier, and phlogisticated air somewhat lighter, than that of the atmosphere; nitrous air he conceived to be nearly of the same specific gravity. His experiments were made by the help of a delicate balance and exhausted flask.

The influence upon the respiration of animals of a species of air marked by the eminent perfection with which it supports combustion, did not escape Dr Priestley's notice. On applying to it his test of nitrous air, he found the absorption produced on mixture greater than with atmospheric air; whence he conjectured its superior fitness for the support of life; he introduced mice into it, and found that they lived longer than in an equal bulk of atmospheric air; he then had the curiosity to taste the gas himself, and after two or three respirations, he felt, or fancied he felt, a peculiar sensation of lightness and ease of the chest. "Who can tell," says he, "but that in time this pure air may become a fashionable article in luxury.—Hitherto only two mice and myself have had the privilege of breathing it." To this he foolishly adds, that "the air which nature has provided for us is as good as we deserve."

We have not yet exhausted Dr Priestley's discoveries, but have seen enough to establish his claims to the title of a great benefactor to chemical science. If we compare him with his predecessor Black, he falls short in depth of judgment, but in quickness of conception, and industry of pursuit, he excels even such a standard of comparison. The one climbed the hill of discovery with slow and cautious steps, and

calmly enjoyed the surrounding views; the other made a more rapid ascent, but was giddy when he reached the summit; hence those distortions and misconceptions, those erroneous notions and hasty conclusions which he who turns over the philosophical writings of Dr Priestley cannot fail to discern.

Upon the other productions of his pen, metaphysical, political, and moral, it is neither my province nor inclination to dwell; they abound in the defects, but are deficient in the merits, of his tracts upon chemical subjects.

From the commencement to the termination of his busy career, Dr Priestley was a staunch supporter of the unintelligible system of phlogiston; he adopted it in all its original incoherence and absurdity; and the last of his scientific publications was a tract in its defence, in which are adduced a variety of objections to the revived hypotheses of Rey and Mayow, and Hooke, which having long lain dormant, were at this time erupted into the chemical world under the specious title of the French theory.¹

It will not be denied that the leading facts just detailed threw considerable light upon the nature and properties of atmospheric air; but those who have entitled Dr Priestley the discoverer of its composition, have somewhat overstepped the bounds of correctness.

He seems, indeed, to have possessed no just notions of the difference between phlogisticated and dephlogisticated air; and, instead of regarding them as distinct chemi-

cal principles, adopted the notion of one elementary substance, charged, in the one instance, with the imaginary essence of inflammability, and free from it in the other. In these inquiries, he frequently verges upon more correct and refined views, but has no sooner entered the right path, than phlogiston, like an ignis fatuus, dances before his eyes, and leads him into the marshy mazes of error.

In the preceding investigations, Dr Priestley followed those methods of collecting aeriform fluids over water, which Hales and others had employed before him: he now ascertained that there were some gases absorbed by or soluble in water. Mr Cavendish, one of the most eminent Philosophers of that day, had announced this circumstance, and was puzzled by it; but Dr Priestley, with his usual and dexterous ingenuity, overcame the difficulty, by employing quicksilver instead of water, over which fluid metal he preserved and examined several kinds of air, which are instantly deprived of their elastic state by the contact of water.

The first permanently elastic fluid of this description which he examined, was the muriatic acid; he obtained it by heating copper in the fluid acid, or common spirit of salt, and called it marine acid air.

He immediately ascertained its absorption by water, and its powerful acidity; he found it incapable of supporting flame, and extremely destructive of animal life. He examined the action of a variety of substances upon this gas, and ascertained the remarkable rapidity with which it is absorbed by charcoal, and several vegetable and animal substances. Some unsuccessful attempts were made to ascertain the specific gravity of this gas, from which Dr Priestley correctly concluded, however, that it was a little heavier than air.

The success attending these experiments, and the readiness with which he procured and retained the gaseous muriatic acid, led him to extend his trials to other acids, when he found, that, by acting upon vitriolic acid by inflammable substances, he could procure from it a permanently elastic fluid, to which he gave the name of vitriolic acid air; he found that, like the marine acid air, it was rapidly absorbed by water, and must be collected and preserved over quicksilver; that it was nearly twice as heavy as atmospheric air; that it extinguished flame, and was instantly fatal to animal life; that it reddened vegetable blues, and destroyed most colours. This air is, in fact, produced by burning sulphur in the atmosphere, and straw, wool, and other materials, are frequently bleached by exposing them to its fumes.¹

Having thus obtained permanent aeriform fluids, having acid qualities, it occurred to Dr Priestley, that the volatile alkali, the substance which gives pungency to salvolatile, spirit of hartshorn, and similar compounds, might be also procured in a pure and isolated gaseous form; and, after several unsuccessful trials, he succeeded, by heating a mixture of quicklime and sal ammoniac, when a great quantity of air escaped, permanent over quicksilver, but, like the acid gases, rapidly absorbed by water.

The odour of this gas was pungent in the extreme, and it possessed the property of salvolatile, smelling salts, and similar substances, of turning vegetable blues to green. After several experiments, in which the absorbing powers of different substances in regard to this air, were tried, Dr Priestley became impatient to discover the effect of mixing it with the acid airs just described,—he imagined that he should form a neutral air. On putting this notion, however, to the proof of experiment, he was surprised to observe that when marine acid air, and the volatile alkaline air, were mixed in due proportions, they were wholly condensed into a solid. And with sulphureous air a very similar result was afforded.

Dr Priestley concluded that alkaline air was considerably lighter than acid air, because, on mixing them over mercury, he observed the former to float above the latter;

discovery of Vitriolic Acid Air, to show the exactness with which he acknowledges the hints and assistance of others:

“ My first scheme was to endeavour to get the vitriolic acid in the form of air, thinking that it would probably be easy to confine it by quicksilver, for, as to the nitrous acid, its affinity with quicksilver is so great that I despaired of being able to confine it to any purpose. I, therefore, wrote to my friend Mr Lane to procure me a quantity of volatile vitriolic acid,” &c. “ Seeing Mr Lane the winter following, he told me, that if I would only heat any oily or greasy matter with oil of vitriol, I should certainly make it the very thing I wanted, viz. the volatile or sulphureous vitriolic acid; and, accordingly, I meant to have proceeded upon this hint, but was prevented from pursuing it by a variety of engagements.

“ Some time after this I was in company with Lord Shelburne, at the seat of Mons. Trudaine, at Montigny, in France; where, with that generous and liberal spirit by which that nobleman is distinguished, he has a complete apparatus of philosophical instruments, with every other convenience and assistance for pursuing such philosophical inquiries as any of his numerous guests shall chuse to entertain themselves with. In this agreeable retreat I met with that eminent philosopher and chemist, Mons. Montigni, Member of the Royal Academy of Sciences; and conversing with him upon this subject, he proposed our trying to convert oil of vitriol into vapour, by boiling it on a pan of charcoal in a cracked phial. This scheme not answering our purpose, he next proposed heating it together with oil of turpentine. Accordingly, we went to work upon it, and soon produced some kind of air confined with quicksilver; but our recipient being overturned by the suddenness of the production of the air, we were not able to catch any more than the first produce, which was little else than the common air which had lodged on the surface of the liquor, and which appeared to be a little phlogisticated by its not being much affected by a mixture of nitrous air.”

on putting a lighted candle into alkaline air the flame was enlarged, and a portion of the air appeared to burn with flame.

We have now considered the principal discoveries of Dr Priestley, upon which his title to originality rests, and it must be allowed that they are not less important than numerous. If we even consider them merely as insulated facts, they are of a very superior character, and tended greatly to enlarge our knowledge of the chemical elements of matter; but the new views of many natural and artificial phenomena, which they exposed, and which before were buried in deep obscurity, confer upon them a more exalted aspect, and have obtained for them the deserved meed of universal admiration. In perusing Dr Priestley's tracts, we find the thread of the narrative occasionally knotted with conceit, and weakened by garrulity; but these blemishes are compensated by prevailing candour and perspicuity of style: he had greatly extended the boundaries of science, and was awake to the importance of his conquests; but resisted that febrile thirst of innovation and reform, which was endemic among contemporary Chemists.

"At present," says he, in the Preface to his third volume of Experiments and Observations, relating to various branches of Natural Philosophy, "At present all our systems are in a remarkable manner unhinged by the discovery of a multiplicity of facts, to which it appears difficult or impossible to adjust them: We need not, however, give ourselves much concern on this account. For when a sufficient number of new facts shall be discovered, towards which even imperfect hypotheses will contribute, a more general theory will soon present itself, and perhaps to the most incurious and least sagacious eye. Thus, when able navigators have, with great labour and judgment, steered towards an undiscovered country, a common sailor, placed at the mast head, may happen to get the first sight of land. Let us not, however, contend about merit, but let us all be intent on forwarding the common enterprise, and equally enjoy any progress we may make towards succeeding in it, and, above all, let us acknowledge the guidance of that great Being, who has put a spirit in man, and whose inspiration giveth him understanding." With this quotation, sufficiently characteristic of his general style, I shall take leave of Dr Priestley, and introduce another hero of chemical history, his contemporary and great rival, Scheele.

AMONG those whose names became eminent in the history of chemical science during the first half of the eighteenth century, Margraaf and Bergman are entitled to particular mention. The former was a pupil of the once celebrated Neumann,¹ a man whose works are now not much thought of, but who did considerable service to the Chemistry of his day, and was evidently possessed of great diligence and some capacity. In 1733, Margraaf² pursued chemistry under Juncker at Halle, and, having returned to Berlin in 1738, we find several of his contributions in the Transactions of the Scientific Society of that capital. Subsequent to that period, his works were collected and published at Paris in 1762. They contain a great body of information, at that time novel and important, but they are chiefly entitled to notice as furnishing specimens of the art of analysis, which was afterwards carried to greater perfection by Bergman,³ who, indeed, may be considered as the first who pointed out the true objects of that branch of the science, and who aimed at conferring upon it the statistical accuracy which has since rendered it so important and useful.

But Bergman was something more than a diligent experimentalist and acute reasoner; he was also an active patron of science, and had the merit of rescuing Scheele

from his obscure situation, and of discerning that talent and genius in the bud which afterwards was so vigorously fruitful.

If we compare Scheele with our own countrymen, we discern him possessed of the accuracy and cool judgment of Black, conjoined with the inquisitive and busy activity of Priestley, and his success in the pursuit of science was such as might be expected to flow from this happy and rare union of opposite talents. In the number of his discoveries, their weight, and novelty, he has indeed very few equals; nor has their splendour been tarnished by time, or dimmed by the brilliant light of modern investigation.

Scheele is among the fortunate few, who, starting from an obscure original, have attained the zenith of scientific eminence. He was born in 1742 at Stralsund, where his father was a tradesman. His youthful days were passed in the house of an Apothecary at Gottenburgh, where, by singular perseverance, and that kind of industry which is prompted by strong natural inclination, he acquired a valuable stock of chemical information. In 1773, having removed to Upsal, accident brought him acquainted with Bergman, who became his friend and patron, and to whose honour be it told, that, when Scheele's reputation afterwards rose to such a height as threatened to eclipse his own, instead of listening to the voice of jealousy, which, on such occasions, is too common a frailty, he became more zealous in behalf of his rival, and more indefatigable in the service of his friend. Scheele afterwards removed to Köping, in the neighbourhood of Stockholm, where he died in 1786.

No adventitious aid, however, can be said to have contributed to Scheele's greatness. On the contrary, obstacles were opposed to his progress which would have damped the ardour, and checked the flight, of less aspiring and persevering minds; and much of his useful life was spent, "not in the soft obscurities of retirement, or under the shelter of academic bowers, but amid inconvenience and distraction, in sickness and in sorrow."

Scheele's first publication, which appeared in the Stockholm Memoirs¹ for the year 1771, relates to the analysis of fluor spar. The peculiarities of this substance were first noticed in 1768 by Margraaf, but the discovery of the principle upon which they depend was reserved for the superior sagacity of Scheele, who demonstrated in it the existence of lime, and an acid till then unknown, which he called fluoric acid.

Scheele had applied acid of vitriol with great success to the analysis of a variety of substances, and on exposing powdered fluor spar to its action in a glass retort, he obtained the new body in question. The fluoric is one of the few acids which rapidly corrode glass; it dissolves silicious earth, a component part of glass, and forms with it an æriform compound, permanent until it touches water, when part of the silicious earth is deposited. Scheele, not aware of this fact, at first conceived that silicious earth was a compound of fluoric acid and water, for, on evolving the gas in a glass retort, and allowing it to pass into water, every bubble was coated with a film of flint; but he afterwards learned, that it was derived from the retort, which is soon eaten into holes. It is this property of fluoric acid which has led to its employment for the purpose of etching upon glass.

Scheele was next occupied in a series of researches on manganese, a mineral substance abundant in many parts of the world, but of which the nature was unknown until the appearance of his Dissertation upon it in 1774. This tract is full of important facts, and glitters with brilliant discoveries. We are here first informed that manganese is a metallic calx; that in its crude state it often contains a peculiar earth, to which the name barytes has since been applied; that the volatile alkali contains nitrogen as one of its essential component parts. But the most remarkable novelty announced in this Essay, is the discovery of a peculiar gaseous fluid of a yellow colour, which Scheele considered as the basis of the muriatic acid, conceiving the addition of phlogiston requisite to the restoration of its acid properties. This dephlogisticated marine acid, as its discoverer termed it, was examined by him with some precision, and many of its leading characters ascertained, especially its power of destroying colour, which has since rendered it of so much importance to the bleacher. It has since been termed oxymuriatic acid, and more recently chlorine. Besides the valuable facts to which I have now alluded, Scheele's Essay on Manganese contains others of considerable interest and importance. There can be little doubt that he discovered azote about the same time as Dr Rutherford. He obtained it by exposing compounds of sulphur, and the alkalies and earths, to confined portions of atmospheric air. He found a part was absorbed, and that the remainder, though not fixed air, was still incapable of supporting combustion. He went a step farther, and demonstrated the existence of azote in the volatile alkali or ammonia, from which he obtained it by the action of certain compounds of manganese.

For our knowledge of the method of obtaining tartaric and citric acids in their pure

state from tartar and lemon juice, we are also indebted to Scheele, and for a variety of curious and interesting documents relating to some of the metallic acids, and their combinations. A compound of one of the acids of arsenic and copper was particularly described by him, and recommended as a green pigment; he prepared it by adding to a solution of blue vitriol, an alkaline solution of white arsenic.

His chemical tracts on the nature and properties of milk, his observations on ether, on the preservation of vinegar, on Prussian blue, and on the nature of the acid matter in various fruits, are all entitled to the highest praise. A just notion of their excellence may be formed by comparing them with the essays of the ablest Chemists of the present day: in regard to experimental accuracy and just conclusion, they generally stand this severe test; no small merit, when his humble means and deficient education are thrown into the balance against him.

But, of the various works of Scheele, that which is most decidedly characteristic of an inventive and original genius, is his Chemical Observations and Experiments on Air and Fire. Every page of this treatise has its merits, and they are distinct and peculiar; sometimes we are struck with the sagacity of his inductions, at others, with the appropriateness of his experiments. The facts are detailed in intelligible, clear, and distinct arrangement; the theoretical speculations are adduced with that caution and modesty which ensures attention, and often commands acquiescence. Nor is this essay deficient in original discoveries of the highest class. He obtained oxygen from manganese without any knowledge of Priestley's prior claims; he calls it empyreal air, and has detailed its properties and several modes of procuring it, with becoming accuracy and minuteness. Upon the composition of the atmosphere, and of metallic calces, he dwells at considerable length, and relates several remarkable facts concerning the chemical powers of the prismatic rays, and the radiation of terrestrial heat.¹

From one who wrote in that twilight period, when chemical philosophy was emerging from error and absurdity, we are not to expect the logical accuracy required at the present day. Scheele is sometimes hasty, and occasionally unintelligible; but seldom careless, and never ridiculous. Different men will form different estimates of Scheele's talents, and although I cannot agree with a contemporary biographer who designates

him "as the brightest ornament of human nature, and the most extraordinary man that ever existed;" it will, I think, be generally admitted, that he was an acute and industrious philosopher, and an upright honourable man.

Of the Chemical Philosophers that adorned the last age, the Honourable Henry Cavendish¹ stands foremost in the first rank.

While Priestley and Scheele were extending the boundaries of knowledge, and pursuing that brilliant career of which I have just presented an outline, Cavendish was not less successfully employed in another train of investigation.

Van Helmont, Mayow, and Hales, had, by a series of crude and imperfect experiments, demonstrated the existence of inflammable aeriform fluids; but the nature of the peculiar principle to which they owe their inflammability had been but very imperfectly ascertained till Cavendish turned his mind to the subject, and published upon it in the Philosophical Transactions for 1776. The paper I allude to consists of three tracts, relating to inflammable, fixed, and nitrous air. The first is chiefly entitled to attention from its originality and importance; in the others he had been anticipated by Mayow and Black, or excelled by Priestley, Scheele, and others of his contemporaries.

By acting with dilute acids upon iron, zinc, and tin, Mr Cavendish obtained an inflammable elastic fluid. He found that it was afforded in the largest quantity by zinc, and that iron yielded more than tin; and he particularly mentions that the state of dilution, and quantity of the acid, provided it was sufficient to effect the solution of the metal, did not affect the quantity or quality of the air. He discovered in the gas thus obtained several characters, which at once distinguished it from the other varieties of air then known. It was not absorbable by water, it extinguished flame, and was fatal to animal life; but, when a candle was presented to it, it inflamed; and, when pure, burned with a blue lambent light. It was found to be the lightest known form of ponderable matter. Mr Cavendish considered it as about eleven times lighter than atmospheric air; but subsequent experiments have shown that, when it is rendered perfectly dry, and collected in a state of purity, it is about thirteen times lighter than atmospheric air. Compared with oxygen or dephlogisticated air, its relative weight is as 1 to 15.²

He next proceeded to examine the results afforded by burning mixtures of inflammable and common air; and found that, in the proportion of one part of the former to about three of the latter, the mixture exploded on the contact of flame, and that, when the vessel in which this inflammation was performed was previously dry, it always became moist after the explosion.

This circumstance was noticed by Macquer in 1766, and shortly after by Priestley, but that water was the result of the combustion, seems first to have occurred to Mr Watt, who suggested the idea to Dr Priestley in 1783.

In January 1784, Mr Cavendish presented a paper to the Royal Society, entitled Experiments on Air, in which, after some preliminary remarks, he advertises to Mr Warltires' experiments, related by Dr Priestley, upon the formation of dew during the combustion of inflammable with common air, which by that gentleman was referred to the deposition of the air's moisture during its phlogistication; for by the Chemists of that period, inflammable air seems to have been considered identical with phlogiston.

The method in which Mr Cavendish pursued this inquiry was not less new than satisfactory, and the body of evidence adduced, so conclusive as to convince the most sceptical mind of the accuracy of his deductions.

To ascertain the nature of the products of the combustion of inflammable air, he had recourse to two plans: he burned it slowly and rapidly,—in the one instance, a stream of the air issuing from a small tube, was inflamed in contact with the atmosphere, or oxygen; in the other, the two gases were mixed, and suddenly detonated; and he found that, proper precautions having been taken to exclude extraneous bodies, the result was perfectly pure water; "it had no taste nor smell, and left no sensible sediment when evaporated to dryness, neither did it yield any pungent smell during the evaporation; in short, it seemed pure water."¹ His grand discovery of the composition of water necessarily led to a variety of others, scarcely inferior in im-

venient on account of its weight; and the flame required for the rarefaction of the air inclosed in the balloon, was dangerous in the extreme—by confining inflammable air in a silk bag, of sufficient dimensions, its small specific gravity enables it to float in our atmosphere. The first ascent, with a balloon filled with hydrogen, was performed in France by M. Charles, on the 1st of December 1783—he rose to the enormous height of 10,500 feet above the earth's surface. There is a passage in Dewynt's Sermons, published in 1658, from which it has been concluded, that balloons were known at that early period.

portance, and it tended to the elucidation of a variety of intricate phenomena in nature and art, in which that universal fluid is concerned. It was verified and established by the analytic and synthetic researches of many modern Chemists, and it became a great organ in subverting the phlogistic doctrine.

In the synthetic experiments proving the composition of water, originally devised and executed by Cavendish, he frequently observed the production of acid matter; the water formed was sour to the taste, and reddened vegetable blues; and he ascertained that these effects arose from the presence of a portion of nitrous acid. Whence this was derived remained to be proved,—whether the elements which, in one proportion, formed water, produced, in another proportion, the nitric acid, or whether it resulted from other causes. In a paper read before the Royal Society, in June 1785, Mr Cavendish sets this curious and interesting question at rest, and develops the source of the acid which appeared in his former investigations. It arose from the presence of a portion of azote which, when made to unite with oxygen, produced nitric acid. The atmosphere has already been shown to consist of azote and oxygen,—these gases are there merely mechanically mixed; when they are made to combine in the presence of water, nitric acid results.

This curious fact was proved by several experiments. That which is most simple, and most satisfactory, consisted in confining a small portion of atmospheric air in a bent tube over quicksilver, and passing the electric spark for some hours through the mixture. A diminution took place in its bulk, the mercury was corroded, and, on introducing a solution of potash, it became saturated, and yielded nitre on evaporation, a salt composed of potash and nitric acid.

These are the principal discoveries with which Cavendish enriched the science of Chemistry; they relate to the properties of hydrogen or inflammable air, to the composition of water, and to the constitution of the nitric acid. They are detailed in three communications to the Royal Society; the first stands in the Philosophical Transactions for 1766; the other two in the volumes for 1784 and 1785.

Those who have heard Mr Cavendish designated the Newton of Chemistry, and have only hastily perused his tracts, or witnessed imperfect illustrations of his researches, may perhaps regard him less worthy that honourable and high distinction than his contemporaries Priestley and Scheele; but a more careful examination of his writings, and a comparison of his reasoning and methods of research with those of even his most eminent fellow-labourers in science, will unanswerably support his claims, and display such peculiar and varied excellence, as must justify the highest

encomiums and most elaborate eulogies which have been bestowed on his exalted name. In his philosophical proceedings, the severest scrutineer is challenged to detect a single false step, for every conclusion he has formed, every theory that he has advanced, even every sentence he has written, will bear microscopic examination. Aware that there was no royal road to philosophic truth, he relied solely upon the light of experiment, in the path of induction, and from this he never deviates. If he excelled not his contemporaries in the number of his discoveries, he certainly equalled them in their importance, and went far before them in statistical accuracy and mathematical precision : but as a Philosopher he scarcely admits of comparison ; in him most of the defects of his contemporaries were absent, and their talents concentrated ; he was " himself alone." In Cavendish science may boast of a follower not less disinterested than successful : his affluence was princely, and his family noble ; it was therefore not the desire of distinction in society, nor the more imperious call of necessity, but the thirst for knowledge, and love of truth, that summoned him to her banners.

Mr Cavendish did not lisp in the language of science ; it was, indeed, late before he appeared as a candidate for philosophic fame. His first paper was published in the Transactions of the Royal Society for 1766, when he was in his 36th year, a period of life at which Black, Priestley, and Scheele, had already acquired no inconsiderable celebrity. He was not confined to Chemistry only ; Electricity and subjects connected with Meteorology and Astronomy often occupied his thoughts and employed his pen : his last essay is on the division of astronomical instruments, published in the Philosophical Transactions for 1809. He was then in his 78th year, and in full possession of bodily activity and mental energy. After a few days illness, he expired on the 4th of February 1810, in the 79th year of his age.

In private life, he was unambitious, unassuming, bashful, and reserved : he was peevishly impatient of the inconveniences of eminence ; he detested flattery, and was uneasy under merited praise ; he, therefore, shunned general society, and was only familiar in a very limited circle of friends. Here he bore his great faculties always meekly : his conversation was lively, varied, and instructive ; upon all subjects of science he was at once luminous and profound ; and in discussion, wonderfully acute.

We are now about to enter upon that period of our history at which the science was reformed and modified by the French school. Of this chemical revolution I shall endeavour to present a faithful though faint outline. I shall attempt to show the grounds of innovation, to expose the weak parts of the plan, to exhibit its merits, and to com-

pare it with former theories. In the meantime, it may not be improper to take a rapid survey of the ground we have gone over, and to enumerate the materials already in the hands of the reformers.

In the early hypotheses respecting the phenomena of combustion, they were conceived to depend upon the separation of a peculiar principle, called by Stahl and his associates phlogiston; but the fallacy of these views was shown by Mayow, who, with his predecessor Rey, demonstrated the necessity of atmospheric air in the process. The attention of Chemists was drawn from these subjects early in the eighteenth century, by the new train of investigation in which Dr Black had successfully embarked, and the field of Pneumatic Chemistry, which was so eminently cultivated by Priestley, Scheele, and Cavendish, absorbed universal attention.

The ideas of the ancients concerning the Elements were now completely subverted. The air we breathe was proved to consist of two distinct æriform fluids—the one a powerful supporter of combustion and respiration, the other extinguishing flame and exterminating life. Water, so long considered as a primitive body, had been resolved into simpler forms of matter; in short, novelties of the most attractive kind presented themselves on every side.

The discovery of hydrogen was seized upon by the advocates of phlogiston, as supporting their hypothesis, and it was generally considered as identical with that substance, which had long been hypothetical, but was now exhibited in a tangible form. The reduction of the metallic calces, by hydrogen, was considered as a powerful argument in favour of these notions, and wherever phlogiston had been supposed to be absorbed or evolved, hydrogen seemed to play the part of that imaginary principle.

The views of Priestley and Scheele were combated by a host of petty controversialists, whose names are yet extant, but whose writings are sunk into oblivion—they brought into the field an army of words, but not a single observation, founded upon fact or experiment. Mr Cavendish was more strenuously and respectably opposed: among those who stood up against his theoretical views, Mr Kirwan deserves especial mention, for he laid other departments of Chemistry under considerable obligations; but his arguments and learning were of little avail against the tried and sterling facts which he questioned; they are no creditable records to the author, but serve to show the feebleness of subtilty when opposed to the strength of truth.

AMONG the eminent scientific characters who adorned the last century, Lavoisier has always been looked upon with high consideration. That his talents were shining, and his career brilliant, cannot be denied; but that he has those high claims to originality which we have been obliged to allow his exalted rivals, has been doubted by the generality of historians, and denied by those who have had access to the most correct information. I shall briefly notice his most important investigations, and afterward endeavour to sketch his character as a Philosopher.

The phenomena of combustion were with Lavoisier, as with his predecessors in the field of theoretical chemistry, a leading object of attention; and the theory of latent heat, devised by Dr Black, was assumed as the ground-work of his new views.

It has already been stated, that, during the conversion of solids into fluids, and of fluids into vapours, there is a considerable absorption of heat; and that, on the other hand, when vapours and liquids are restored to the fluid and solid form, the heat which they contained is evolved, or passes from the latent to the sensible or thermometric state. These views were assumed by the French school as the basis of their theory of combustion. The gas called by Priestley dephlogisticated air, and by Lavoisier oxygen, was regarded as a compound of a peculiar ponderable basis, united to the matter of light and heat. During the process of combustion, the basis was represented as combining with the combustible, augmenting its weight, and changing its properties; whilst the imponderable elements of the gas, the light and heat, were said to be developed in the form of flame.

Lavoisier instituted an extended and beautiful series of researches connected with this subject. Dr Ingenhouz had devised the brilliant experiment of burning iron wire in oxygen, but had neglected any inquiry into the change suffered by the gas and the metal. Lavoisier ascertained that the iron was converted into the black brittle substance, called martial ethiops by the old chemists, and that 100 grains of iron absorbed about 100 cubical inches of the gas, and increased 35 grains in weight. Hence martial ethiops appeared to be a compound of oxygen and iron.

Phosphorus was burned in the same manner. There was a considerable absorption

of the gas, and it appeared that the phosphorus had sustained a precisely equivalent increase of weight.

The general conclusions deduced from these experiments were bold, but incorrect. It was assumed that oxygen must be present in all cases of combustion; that the base of the gas always unites to the burning body, and that the heat and light essential to the aeriform state of the oxygen are consequently thrown off, or rendered sensible. With regard to the necessity of the presence of oxygen, it may be remarked, that the cases are very numerous in which bodies burn, and vividly too, independent of that principle, although it is perfectly true that, in the generality of instances, oxygen feeds the flame.

It is, therefore, more philosophical to consider combustion, or the evolution of heat and light, as a general result of intense chemical action, and as ensuing in all cases where it may be conceived that the corpuscles of bodies are thrown into violent motion, than as depending upon the presence of any distinct substance, or ensuing from the mutual actions of any appropriate forms of matter.

But farther; there are many cases in which oxygen unites to bodies, without the evolution of heat and light, as during the gradual change of some of the metals by exposure to air. And there are numerous instances in which vehement combustion ensues, not only where there is no condensation of air, but where gaseous matter is positively produced, as in the inflammation of gunpowder; and hence the theory of latent heat, as applied to the composition of gases, is insufficient to account for the phenomena.

Another weak part of the French hypothesis is that relating to the evolution of light, which, if derived from the gas, should be proportional to its consumption or solidification, whereas it depends chiefly on the combustible. Richter, Delameterie, and Gren, regarded the gas as affording the heat only, which is proportional to the quantity consumed; and they supposed the evolution of light to be derived from the combustible, and several modern chemists have espoused this explanation. Phosphorus emits much more light than hydrogen, but consumes less oxygen; hence we should regard phosphorus as containing more combined light than hydrogen. This hypothesis involves several unnecessary suppositions; but these cannot be discussed without reference to subjects which are excluded by the limits of this discourse. It may, however, here be observed, how nearly the French theory of combustion agrees with that of Rey and Mayow, in referring the increase of weight of the

combustible, to the fixation of air: this was the great obstacle in the phlogistic hypothesis, and Rey and Lavoisier overcame it by the same means.

Oxygen was not merely considered by the French school as necessary to combustion, but also as an essential ingredient in all acids (whence the term oxygen); but there are many acids in which no oxygen can be proved to exist, and it is now known even to form a component part of the alkalies and earths. 'If sulphur be burned in oxygen, it produces sulphurous acid gas: if potassium be heated in sulphurous acid gas, it robs the sulphur of its oxygen, and is converted into potash; here oxygen is seen alternately producing an acid and an alkali,—the result depending not upon the oxygen, but upon the base with which it combines.

In detailing the discoveries of Dr Black, I was led to notice his researches concerning the production of fixed air. This gas was also examined with much attention by Priestley, Scheele, and Cavendish, and they have each made important additions to our knowledge of its sources and properties.

Lavoisier's inquiries respecting the composition of fixed air, and its production during the combustion of charcoal and of the diamond, were highly important as connected with his general theoretical views. Black had indeed ascertained that burning charcoal produced fixed air, but rested satisfied with the mere fact, and pursued not the inquiry which it naturally suggested, and which was eagerly taken up by Lavoisier at an early period of his scientific career. He burned a given weight of charcoal in a given proportion of oxygen gas confined over quicksilver, and when the vessel had cooled, he introduced a solution of potash, which absorbed the fixed air. He thus ascertained the bulk of the fixed air generated by the charcoal, and the bulk of oxygen consumed; and, by weighing the residuum of the charcoal, he found the quantity lost by its combustion. From such experiments, he was led to regard fixed air as composed of oxygen and charcoal, in the proportions by weight of about 70 of the former and 30 of the latter. Soon after the discovery of fixed air by Black, it was demonstrated by Keir, Bergman, and Fontana, to possess acid properties; hence it was occasionally termed aerial acid, cretaceous acid, and mephitic acid. Consistently with the principles of the new nomenclature, it received from Lavoisier the name of carbonic acid, a term implying that it is composed of charcoal and oxygen; and this it has since retained.

The production of fixed air, or, as we may now call it, carbonic acid, during the combustion of diamond, is one of the most remarkable and important discoveries with which Lavoisier enriched chemical science. The destruction of this precious gem by

fire was demonstrated by the Florentine academicians as early as 1690 ; they exposed a diamond to the focus of a burning lens, and found that it was entirely evaporated ; and Francis the First, of Germany, witnessed the same phenomenon in the heat of a furnace. Lavoisier proved that the diamond underwent no change when air was excluded ; and that, when ignited in oxygen gas, it produced carbonic acid ; whence the inevitable conclusion that the diamond and charcoal are identical in their nature ; and that the vast difference in their appearance and mechanical qualities is the result of aggregation ; that the one is crystallized, the other in a less indurated form. Unprecedented as such an idea may seem, it is not only warranted by the experiments of Lavoisier and others, but also in some degree supported by analogy. Thus, when argillaceous earth, which is a white pulverulent substance, is aggregated by mechanical attraction into a crystalline form, it constitutes the sapphire, one of the hardest and least destructible of the gems. In one state, the earth is soft, and readily soluble in acids ; in the other, its insolubility equals its induration : but there is one invincible anomaly relating to the conducting power of the diamond and charcoal in regard to electricity ; the former ranks among the non-conductors, the latter is a conductor ; and hitherto mechanical texture has not been shown, in any analogous cases, to interfere with the power of conducting electricity.

Among those who have further explored the phenomena of the combustion of the diamond, and who have verified and extended the original views of Lavoisier, we find the names of the most eminent European Philosophers. Few subjects in Chemistry have been so eagerly pursued, and the united results of different experimentalists have rarely tallied with the precision which these researches present.¹

The discoveries of Rutherford and of Priestley, in the years 1772 and 1774, had dis-

closed the elements of atmospheric air, and several experiments respecting the proportions in which they are blended, had been instituted by these, and other Philosophers. In the year 1775, Lavoisier resumed these inquiries, with a masterly and decisive hand; he heated mercury in contact with a known portion of atmospheric air; it gradually acquired a red film, which after some days ceased to form, and the metal remained unaltered; he then withdrew the fire, and suffered the vessels to cool; he found that the air had diminished in bulk, and that the quicksilver had increased in weight; that the loss of the former was equivalent to the gain of the latter—which had absorbed the oxygen of the air, leaving the azote unaltered. By such investigations he arrived, with tolerable precision, at the proportion in which these gases exist in common air, and found, that, by mixing forty-two parts, by measure, of azote with eight parts, by measure, of oxygen, he produced a compound precisely resembling our atmosphere, in its power of supporting combustion and respiration, and of contributing to the calcination of the metals.

Besides these researches and discoveries, Lavoisier was the author of many scientific papers in the Memoirs of the Parisian Academy. Of these a brief and hasty notice will suffice, as they relate not to the great reform of chemical theory, in which he was so conspicuous an actor, and upon which his fame and reputation have chiefly been raised.

In 1764, the French Government proposed, as a prize question, "Which is the best method of illuminating the streets of a large metropolis?" It was answered by Lavoisier; and he was rewarded with an honorary medal. In 1768, he became a member of the Academy. In 1770, he controverted a prevailing opinion respecting the convertibility of water into earth; and, two years afterwards, published an ingenious geological essay upon the changes and stratification of the globe. In 1774, he entered upon the grand field of discovery which has occupied so much of our attention, and published an ingenious and comprehensive view of Pneumatic Chemistry. A few years afterwards, his theory of acidity, of combustion, and of oxidizement; his experiments upon the composition of water, and of the atmosphere, and his views respecting the nature and affections of heat, were successively presented to the public; and, in 1789, his work entitled Éléments de Chimie was given to the world. It contains a full account of his theoretical views and experimental researches.

Lavoisier was an earnest promoter of the Chemistry of the Arts. He turned his attention to the improvement of several manufactures, and his labours were rewarded by considerable success. Agriculture was with him a favourite pursuit, and he en-

deavoured to improve its processes by experimental research. He was an able Political Economist; and, for a few years, filled the office of a Commissioner of the National Treasury, with honour to himself, and benefit to his country.

The moral and social character of Lavoisier was of the most estimable cast. Contemporary historians agree in eulogizing his mild, amiable, and obliging manners; in extolling his liberality, and in praising him, as the encourager of deserving ingenuity, and the ardent patron of science and the arts.

Through the scenes of the Revolution, such a man could not expect to pass unmo- lested. He was rich, and therefore criminal; virtuous, and consequently offensive. In short, because his public character and private life were equally unimpeachable and blameless, he was marked out for destruction, and murdered upon the scaffold on the 8th of May 1794, in his native city of Paris, and in the 51st year of his age.

Upon these acts of iniquitous barbarity and inhuman treachery, equally degrading to the individual performers and to the beholding nation, it is neither my business nor inclination to dwell; the recital of particulars would excite disgust rather than interest; and would rather shock than inform.

We must now divest ourselves of the impressions naturally arising out of the virtues, the eminence, and the misfortunes of Lavoisier, and with unmixed attention steadily reflect upon his philosophical character. By some he has been extolled as the most original, inventive, and exalted genius of his age; by others stigmatized as an univer- sal and dishonourable plagiarist; but these are the extremes of panegyric and male- volence, each equidistant from candour and from truth. He was doubtless an acute, sagacious, and useful Philosopher; his zeal for the welfare of science was unremitting and exemplary, and his affluence enabled him to pursue it upon an extensive and splendid scale. As an original discoverer, he bends before Black and Priestley, and was inferior to Cavendish and Scheele; but, as a theorist, he has few equals; he was comprehensive, successful, and clear. If time has shaken his opinions, and loosened his speculations, the change must be referred to the imperfect and progressive state of Chemistry, rather than to their inherent futility. In Natural Philosophy, the systems of Pythagoras, Ptolemy, Descartes, and others, have successively yielded to the satisfactory and apparently stable simplicity of the Newtonian doctrines; but the Newton of Chemistry is yet to come.

It must be regretted, that those who have censured Lavoisier with the uncandid and unacknowledged appropriation of the thoughts of others, have some grounds for

the accusation. In bringing forward his theory of combustion, why did he smother the lucid opinions of Rey and Mayow? why refuse praise and acknowledgment to Black, and Scheele, and Cavendish? or, why appropriate the discovery of oxygen, in the face of the prior, indisputable, and known claims, of his friend and contemporary Priestley? These are questions we cannot now answer; but, those who have grounded harsh, indiscriminate, and severe censure, upon such accusations, have neither been animated by the independent spirit of true philosophy, nor guided by the unbiased love of truth. It must be remembered, that Lavoisier was never fairly confronted by these rivals and antagonists; that unintentional inadvertency often accompanies scientific ardour; that, in the eagerness of pursuit, he may have neglected that which, in a calmer hour, he would have seen, regretted, and acknowledged; and that, in the hurry of discussion and heat of controversy, he was suddenly summoned to eternity.¹

I insert a long quotation, that there may be no misunderstanding upon the subject.

After stating the prevailing phlogistic notions entertained at that period, he proceeds as follows: "Tel étoit l'état des connoissances, lorsqu'une suite d'expériences, entreprises en 1772 sur les différentes espèces d'air, ou de gaz qui se dégagent dans les effervescences et dans un grand nombre d'opérations chimiques, me firent connoître, d'une manière démonstrative, quelle étoit la cause de l'augmentation de poids, qu'acquérièrent les métaux lorsqu'on les expose à l'action du feu. J'ignorais alors ce que Jean Rey avoit écrit à ce sujet en 1630; et quand je l'aurois connu, je n'aurois pu regarder son opinion à cet égard, que comme une assertion vague, propre à faire honneur au génie de l'auteur, mais qui ne dispensait pas les chimistes de constater la vérité de son opinion par des expériences. J'étois jeune, j'étois nouvellement entré dans la carrière des sciences, j'étois avide de gloire, et je crus devoir prendre quelques précautions pour m'assurer la propriété de ma découverte. Il y avoit à cette époque, une correspondance habituelle entre les savans de France et ceux d'Angleterre; il regnoit entre les deux nations, une sorte de rivalité qui donnoit de l'importance aux expériences nouvelles, et qui portoit quelquefois les écrivains de l'une ou de l'autre nation, à les contester à leur véritable auteur; je crus donc devoir déposer, le 1^er Novembre 1772, l'écrit suivant cacheté, entre les mains du Secrétaire de l'Académie. Ce dépôt a été ouvert à la séance du 5^me Mai suivant, et mention du tout a été faite en tête de l'écrit. Il étoit conçu en ces termes:—

"Il y'a environ huit jours que j'ai découvert, que le soufre en brûlant, loin de perdre de son poids, en acquéroit au contraire; c'est à dire, que d'une livre de soufre, on pouvoit retirer beaucoup plus d'une livre d'acide vitriolique, abstraction faite de l'humidité de l'air; il en est du même du phosphore: cette augmentation de poids vient d'une quantité prodigieuse d'air qui se fixe pendant la combustion, et qui se combine avec les vapeurs.

Though these considerations do not exculpate our philosopher, they must be allowed to extenuate his imputed failings—they should induce us rather to soften the asperities of his scientific character, than to magnify its faults—instead of rejoicing that he was not perfect, we should delight in his excellence, and should estimate his character as a Philosopher, not so much by the means he employed, as by the noble effects produced.

Among many other subjects which engaged the attention of Lavoisier and his associates, that of reforming the nomenclature of Chemistry deserves to be noticed as highly beneficial to the promotion of the science, and as tending materially to facilitate its acquisition. I am inclined, however, to think that, upon this point, too much credit has been given to the French school; rage for innovation, and not zeal for improvement, seems often to have guided the undertaking; and terms, once deemed faultless, now appear not less absurd and objectionable than the fanciful names employed by the alchemical writers.

As principals in the formation of the new nomenclature, we find the names of Guyton Morveau¹ and Fourcroy, two men who may certainly be considered as ornaments of their age and country. The former, amidst varied avocations, prosecuted Chemistry

“ Cette découverte que j'ai constatée par des expériences que je regarde comme décisives, m'a fait penser que ce qui s'observoit dans la combustion du soufre et du phosphore, pouvoit bien avoir lieu à l'égard de tous les corps qui acquièrent du poids par la combustion et la calcination : et je me suis persuadé, que l'augmentation de poids des chaux métalliques, tenoit à la même cause. L'expérience a complètement confirmé mes conjectures : j'ai fait la reduction de la litharge dans des vaisseaux fermés, avec l'appareil de Hales, et j'ai observé qu'il se dégagéoit, au moment du passage de la chaux en métal, une quantité considérable d'air, et que cet air formoit un volume au moins mille fois plus grand que la quantité de litharge employée. Cette découverte me paroissant une des plus intéressantes qui ait été faite depuis Stahl, j'ai cru devoir m'en assurer la propriété, en faisant le présent dépôt entre les mains du Secrétaire de l'Académie, pour demeurer secret jusqu'au moment où je publierai mes expériences.”

(Signé) “ LAVOISIER.”

“ En rapprochant cette première notice de celle que j'avois déposée à l'Académie le 20^me Octobre précédent, sur la combustion du phosphore, du mémoire que j'ai lu à l'Académie à sa séance publique de Pâques 1773, enfin, de ceux que j'ai successivement publiés, il est aisé de voir, que j'avois conçu dès 1772, tout l'ensemble du système que j'ai publié depuis sur la combustion. Cette théorie à laquelle j'ai donné de nombreux développemens en 1777, et que j'ai portée, presque dès cette époque à l'état où elle est aujourd'hui, n'a commencé à être enseignée par Fourcroy, que dans l'hiver de 1786 à 1787; elle n'a été adoptée par Guyton Morveau, qu'à une époque postérieure; enfin, en 1785 Berthollet écrivoit encore dans le système du phlogistique. Cette théorie n'est donc pas, comme je l'entends dire, la théorie des Chimistes Français: elle est la mienne, et c'est une propriété que je réclame auprès de mes contemporains et de la postérité.”

with successful diligence, and, had he given nothing else to the science, his name deserves to be transmitted to posterity, as the inventor of the means of destroying infection by acid vapours, the efficacy of which he first pointed out in the year 1773. His first essay on the reform of nomenclature was published in the Journal de Physique for May 1782, and although it was strenuously opposed by the colossal power of the Royal Academy of Paris, the plan was not only afterwards approved, but prosecuted by the eminent Chemists of that metropolis. The different papers and correspondence relating to this subject are, in many respects, curious and interesting from the difference of opinion which prevailed respecting the terms he adopted, and the ultimate benefit likely to result from the reformation.

Fourcroy¹ is a well known name in the chemical world; his works rank among the most celebrated which France has produced in the science of Chemistry, though they are sometimes deficient in candour, and sometimes in correctness. His labours were important, and his discoveries numerous, but they are, in many respects, so closely interwoven with those of contemporary Philosophers, that I have deemed it expedient to waive farther notice respecting their objects and merits.

I have now brought my narrative to the conclusion of the last century, about which period Electricity began to assume importance as a chemical agent, and the Voltaic apparatus became a necessary implement of the laboratory. To this source, the new aspect which chemical science now wears, may principally be referred, and the historian, who shall in aftertimes record the advances that have been made in Chemistry during the last eighteen years, will recite triumphs of the human mind never excelled, and rarely equalled.—I am apprehensive that the inquisitive eye will detect several omissions in the foregoing pages, although I have diligently endeavoured to record every important event in the general history of the science. Of many who have attained deserved eminence in the exclusive pursuit of its distinct branches, no mention has been made: I have looked with attention into their works, and am well aware of their individual merits; but I should have swerved from the principal object of this Dissertation, that of recording discoveries, had I attempted even the superficial enumeration of their infinitely varied applications.

Page 23, line 16, for potash read soda.

Page 53, last line, for 1733 read 1773.