The Life of Sir Humphry Davy, Bart. LL.D., Volume 2 (of 2)

by John Ayrton Paris

A SKETCH OF THE HISTORY OF CHEMICAL SCIENCE, WITH A VIEW TO EXHIBIT THE REVOLUTIONS PRODUCED IN ITS DOCTRINES BY THE DISCOVERIES OF SIR HUMPHRY DAVY.

The rapidity with which chemical opinions have risen into notice, flourished for a while, and then fallen into disrepute, to be succeeded by others equally precarious in their tenure and ephemeral in their popularity, are circumstances which the superficial reasoner has ever deplored, and the Sciolist as constantly converted into arguments against the soundness of the science which produced them. The leaves of a season will sprout, expand, and wither; and the dry foliage will be pushed off by the propulsion of new buds; but this last change is not effected in them, until they have absorbed the light and dews of heaven for the nourishment of the plant that bore them; and when even they shall have fallen to the earth, they will farther supply its spreading roots with fresh soil for its future growth and healthy developement; and entering into new combinations, will re-appear in the same tree under fresh forms of usefulness and symmetry. In like manner, chemical theories are but for a season; they are nothing more than general expressions of known facts; they may delight by their ingenuity, as vegetable forms captivate by their beauty, but their real and substantial use is to extend science; and as facts accumulate under their operation, they must give way to others better adapted to the increased growth and expansion of knowledge; nor does the utility of theories cease with their rejection,—they afford objects of analogy and comparison which assist the philosopher in his progress to truth, while their elements furnish materials for future arrangements. Were it otherwise, we should behold science in its advancement as a shapeless mass, enlarging by constant appositions, but without a single sign of growth or inward sympathy.

If chemical theories have undergone more rapid and frequent changes than those of other branches, the circumstance has arisen from the rapid manner in which new and important facts have been successively added to the general store.

Whatever may be the vices attributed to Chemistry on such occasions, they have belonged to the philosophers engaged in its pursuit, and are no evidence of the frailty of the science itself; and here it must be admitted, that there exists in one portion of mankind a self-love which cannot patiently submit to a change of opinions of which they are either the authors or defenders, while in another there predominates a timidity which naturally leads them, amidst the storm of controversy, to cling to the wreck of a shattered theory, rather than to trust themselves to a new and untried bark.

In our review of the history of Science, we have frequently to witness how the wisest philosopher has strained truth, for the support of a favourite doctrine, and measured and accommodated facts to theory, instead of adapting theories to facts—but this vice does not belong exclusively to chemical philosophers. Huygens, the celebrated Dutch Astronomer, from some imaginary property in the number six, having discovered one of Saturn's moons, absolutely declined looking for any more, merely because that one, when added to the four moons of Jupiter, and to the one belonging to the Earth, made up the required number.

Such reflections naturally arise on viewing, with a philosophic eye, the progress and modifications of chemical opinions; and it is essential that they should be duly appreciated upon the present occasion; for, before any just estimate can be formed of the talents and services of Sir Humphry Davy, we must thoroughly consider, in all their bearings and relations, the various prejudices with which he had to contend in his efforts to modify a gigantic theory, which enjoyed an unrestrained dominion in the chemical world, and for many years continued to be the pride of France and the admiration of Europe.

It would be quite foreign to the plan of this sketch,[132] which the reader must consider as wholly subservient to the object that has been announced, to enquire how far the ancients, in their metallurgical processes, can be said to have exercised the arts of chemistry. Equally vain would it be to enter into a history of that system of delusion and imposture, so long practised under the denomination of Alchymy. It is only necessary to consider Chemistry in its dignified and purely scientific form; and we have only to notice those commanding discoveries and opinions which led to the developement of that system, which the genius of Davy was destined to modify.

The origin of Chemistry, as a science, cannot be dated farther back than about the middle of the seventeenth century; and Beccher, the contemporary of Boyle, who was born at Spires in 1635, was unquestionably the first to construct any thing like a general theory. He formed the bold idea of explaining the whole system of the earth by the mutual agency and changes of a few elements. And by supposing the existence of a vitrifiable, a metallic, and an inflammable earth, he attempted to account for the various productions of rocks, crystalline bodies, and metallic veins, assuming a continual interchange of principles between the atmosphere, the ocean, and the solid surface of the globe, and considering the operations of nature as all capable of being imitated by art.

Albertus Magnus had advanced the opinion that the metals were earthy substances impregnated with a certain inflammable principle; but Beccher supported the idea of this principle not only as the cause of metallization, but likewise of combustibility. Stahl, however, one of the most extraordinary men that Germany ever produced, having adopted and amplified this theory, carried off the entire credit of being its founder, and it is universally spoken of as the Stahlian Theory.

This theory forms so important a feature in the history of chemistry, and so long maintained its ascendency in the schools, that it will be necessary to give the reader a short summary of its principles. It assumed that all combustible bodies are compounds: one of the constituents being volatile, and therefore easily dissipated during the act of combustion; while the other, being fixed, constantly remained as the residue of the process. This volatile principle, for which Stahl invented the term Phlogiston, was considered as being identical in every species of combustible matter; in short, it was supposed that there was but one principle of combustibility in nature, and that was the imaginary phantom Phlogiston, which for nearly a century possessed the schools of Europe, and, like an evil spirit, crossed the path of the philosopher at every step, and by its treacherous glare allured him from the steady pursuit of truth; for, whether a substance were combustible or not, its nature could never be investigated without a reference to its supposed relations with Phlogiston; its presence, or its absence, was supposed to stamp a character upon all bodies, and to occasion all the changes which they undergo. Hence chemistry and combustion came to be in some measure identified; and a theory of combustion was considered the same thing as a theory of chemistry.

The identity of Phlogiston in all combustible bodies was founded upon observations and experiments of so decisive a nature, that after the existence of the principle itself was admitted, they could not fail to be satisfactory. When phosphorus is made to burn, it gives out a strong flame, much heat is evolved, and the phosphorus is dissipated in fumes, which, if properly collected, will quickly absorb moisture from the atmosphere, and produce an acid liquid known by the name of phosphoric acid. Phosphorus then must consist, say the Stahlians, of Phlogiston and this acid. Again—If this liquid be evaporated to a dry substance, mixed with a quantity of charcoal powder, and then heated in a vessel from which the external air is excluded, a portion, or the whole of the charcoal will disappear, and phosphorus will be reproduced, possessing all the properties that it had before it was subjected to combustion. In this case, it was supposed that the charcoal restored the phlogiston. There was much plausibility in all this, as well as in the reasoning which followed. Since we may employ, with equal success, any kind of combustible body for the purpose of changing phosphoric acid into phosphorus, such as lamp-black, sugar, resin, or even several of the metals, it was concluded that all such bodies contain a common principle which they communicate to the phosphoric acid; and since the new body formed is in all cases identical, the principle communicated must also be identical. Hence combustible bodies contain an identical principle, and this principle is Phlogiston.

The same theory applied with equal force to the burning of sulphur and several of the metals, and to their reconversion by combustible bodies.

When lead is kept nearly at a red-heat in the open air for some time, it is converted into a pigment called red lead; this is a calx of lead. To restore this calx again to metallic lead, it is only necessary to heat it in contact with almost any combustible matter; all these bodies therefore must contain one common principle, which they communicated to the red lead, and by so doing reconverted it to the state of metal. Metals then were regarded as compounds of calces and phlogiston. Thus far the theory works glibly enough; but now comes a startling fact, which was long unnoticed by the blind adherents of Stahl, or, if noticed, intentionally overlooked. It was observed very early, that when a metal was converted into a calx, its weight was increased. When this difficulty first forced itself upon the attention of the Phlogistians, it was necessary that they should either explain it, or at once abandon their theory. They accordingly endeavoured to evade the difficulty, not only by asserting that phlogiston had no weight, but that it was actually endowed with a principle of levity.

It was not possible, however, that any rational notions should have been entertained upon the subject of combustion, at a period when the composition of the atmosphere even was unknown. Let us therefore follow the stream of discovery, skimming the surface merely, as it flowed onward towards quite a new field of science—Pneumatic Chemistry.

Boyle and Hooke, who had improved the air-pump invented by Otto de Guericke, of Madenburgh, first used this apparatus for investigating the properties of air; and they concluded from their experiments that air was absolutely necessary to combustion and respiration, and that one part of it only was employed in these processes; and Hooke formed the sagacious conclusion, that this principle is the same as the substance fixed in nitre, and that combustion is a chemical process, the solution of the burning body in elastic fluid, or its union with this matter.

Mayow, of Oxford, in 1674, published his treatises on the Nitro-aërial spirit, in which he advanced opinions similar to those of Boyle and Hooke, and supported them by a number of original and curious experiments.

Dr. Hales, about 1724, resumed the investigations commenced with so much success by Boyle, Hooke, and Mayow; and endeavoured to ascertain the chemical relations of air to other substances, and to ascertain by statistical experiments the cases in nature, in which it is absorbed or emitted. He obtained a number of curious and important results; he disengaged elastic fluids from various substances, and drew the conclusion, that air was a chemical element in many compound bodies, and that flame resulted from the action and reaction of aërial and sulphurous particles; but all his reasonings were contaminated with the notion of one elementary principle constituting elastic matter, and modified in its properties by the effluvia of solid or fluid bodies.

The light of Pneumatic science which had dawned under Hooke, Mayow, and Hales, burst forth in splendour under the ascendency of that constellation of British science, Black, Cavendish, and Priestley.

In 1756, Dr. Black published his researches on calcareous, magnesian, and alkaline substances, by which he proved the existence of a gaseous body, perfectly distinct from the air of the atmosphere. He showed, that quick-lime differed from marble and chalk by not containing this substance, which he proved to be a weak acid, capable of being expelled from alkaline and earthy bodies by stronger acids.

As nothing is more instructive than to enquire into the circumstances which have led to a great discovery, I quote with pleasure the following passage from Dr. Thomson's History of Chemistry.

"It was the good fortune of chemical science that, at this time (1751), the opinions of professors were divided concerning the manner in which certain lithonthriptic medicines, particularly lime-water, acted in alleviating the excruciating pains of the stone and gravel. The students usually partake of such differences of opinion: they are thereby animated to more serious study, and science gains by their emulation.

"All the medicines which were then in vogue as solvents of calculi had a greater or less resemblance to caustic potash or soda; substances so acrid, when in a concentrated state, that in a short time they reduce the fleshy parts of the animal body to a mere pulp. They all seemed to derive their efficacy from quick-lime, which again derived its power from the fire. It was therefore very natural for them to ascribe its power to igneous matter imbibed from the fire, retained by the lime, and communicated by it to alkalies which it renders powerfully acrid. It appears from Dr. Black's note-books, that he originally entertained the opinion, that caustic alkalies acquired igneous matter from quick-lime. In one of them, he hints at some way of catching this matter as it escapes from lime, while it becomes mild by exposure to the air; but on the opposite blank page is written, 'Nothing escapes—the cup rises considerably by absorbing air.' A few pages further on, he compares the loss of weight sustained by an ounce of chalk when calcined, with its loss while dissolved in muriatic acid.

"These experiments laid open the whole mystery, as appears by another memorandum. 'When I precipitate lime by a common alkali, there is no effervescence: the air quits the alkali for the lime; but it is lime no longer, but c. c. c: it now effervesces, which good lime will not.'—What a multitude of important consequences naturally flowed from this discovery! He now knew to what the causticity of alkalies is owing, and how to induce it, or remove it, at pleasure. The common notion was entirely reversed. Lime imparts nothing to the alkalies; it only removes from them a peculiar kind of air (carbonic acid gas) with which they were combined, and which prevented their natural caustic properties from being developed. All the former mysteries disappear, and the greatest simplicity appears in those operations of nature which before appeared so intricate and obscure."

Dr. Thomson afterwards observes,—"The discovery which Dr. Black had made, that marble is a combination of lime and a peculiar substance, to which he gave the name of fixed air, began gradually to attract the attention of chemists in other parts of the world. It was natural, in the first place, to examine the nature and properties of this fixed air, and the circumstances under which it is generated. It may seem strange and unaccountable that Dr. Black did not enter with ardour into this new career which he had himself opened, and that he allowed others to reap the corn after having himself sown the grain. Yet he did take some steps towards ascertaining the properties of fixed air; though I am not certain what progress he made. He knew that a candle would not burn in it, and that it is destructive to life, when any living animal attempts to breathe it. He knew that it is formed in the lungs during the breathing of animals, and that it is generated during the fermentation of wine and beer. Whether he was aware that it possesses the properties of an acid, I do not know; though with the knowledge which he possessed that it combines with alkalies and alkaline earths, and neutralizes them, or at least blunts and diminishes their alkaline properties, the conclusion that it partook of acid properties was scarcely avoidable. All these, and probably some other properties of fixed air, he was in the constant habit of stating in his lectures from the very commencement of his academical career; though, as he never published any thing on the subject himself, it is not possible to know exactly how far his knowledge of the properties of fixed air extended. The oldest manuscript copy of his lectures that I have seen was taken down in writing in the year 1773; and before that time Mr. Cavendish had published his paper on fixed air and hydrogen gas, and had detailed the properties of each. It was impossible from the manuscript of Dr. Black's lectures, to know which of the properties of fixed air stated by him were discovered by himself, and which were taken from Mr. Cavendish."

An idea so novel and important as that of an air possessing properties quite different from that of the atmosphere, existing in a fixed and solid state in various bodies, was not received without doubt, and even opposition. Several German enquirers endeavoured to controvert it. Meyer attempted to show that limestone became caustic, not by the emission of elastic matter, but by combining with a peculiar substance in the fire; the loss of weight, however, was wholly inconsistent with such a view of the question: and Bergman at Upsal, Macbride in Ireland, Keir at Birmingham, and Cavendish in London, fully demonstrated the truth of the opinion of Black, and a few years were sufficient to establish his theory upon an immutable foundation, and to open a new road to most important discoveries.

The knowledge of one elastic fluid, entirely different in its properties from air, very naturally suggested the probability of the existence of others. The processes of fermentation which had been observed by the ancient chemists, and those by which Hales had disengaged and collected elastic substances, were now regarded under a novel point of view; and the consequence was, that a number of new bodies, possessed of very extraordinary properties, were discovered.

Mr. Cavendish, about the year 1765, invented an apparatus for examining elastic fluids confined by water, which has since been called the hydro-pneumatic apparatus. He discovered inflammable air, and described its properties; he ascertained the relative weights of fixed air, inflammable air, and common air, and made a number of beautiful and accurate experiments on the properties of these elastic substances.

Dr. Priestley, in 1771, entered the same path of enquiry; and principally by repeating the processes of Hales, added a number of most important facts to this department of chemical philosophy. He discovered nitrous air, nitrous oxide, and dephlogisticated air, (oxygen) and by substituting mercury for water in the pneumatic apparatus, ascertained the existence of several aëriform bodies which are rapidly absorbable by water; such as muriatic acid gas, sulphurous acid gas, and ammonia.

Scheele, independently of Priestley, also discovered several of the aëriform bodies; he ascertained likewise the composition of the atmosphere; he brought to light fluoric acid, prussic acid, and the substance which he termed dephlogisticated marine acid, the oxy-muriatic acid of the French school, and the chlorine of Davy.

Sir Humphry Davy, in the preface to his Chemical Philosophy, observes that Black, Cavendish, Priestley, and Scheele, were undoubtedly the greatest chemical discoverers of the eighteenth century; and that their merits are distinct, peculiar, and of the most exalted kind. He thus defines them:

"Black made a smaller number of original experiments than either of the other philosophers; but being the first labourer in this new department of the science, he had greater difficulties to overcome. His methods are distinguished for their simplicity; his reasonings are admirable for their precision; and his modest, clear, and unaffected manner is well calculated to impress upon the mind a conviction of the accuracy of his processes, and the truth and candour of his researches.

"Cavendish was possessed of a minute knowledge of most of the departments of Natural Philosophy: he carried into his chemical researches a delicacy and precision, which have never been exceeded: possessing depth and extent of mathematical knowledge, he reasoned with the caution of a geometer upon the results of his experiments; and it may be said of him, what, perhaps, can scarcely be said of any other person, that whatever he accomplished, was perfect at the moment of its production. His processes were all of a finished nature; executed by the hand of a master, they required no correction; the accuracy and beauty of his earliest labours even have remained unimpaired amidst the progress of discovery, and their merits have been illustrated by discussion and exalted by time.

"Dr. Priestley began his career of discovery without any general knowledge of chemistry, and with a very imperfect apparatus. His characteristics were ardent zeal and the most unwearied industry. He exposed all the substances he could procure to chemical agencies, and brought forward his results as they occurred, without attempting logical method or scientific arrangement. His hypotheses were usually founded upon a few loose analogies; but he changed them with facility; and being framed without much effort, they were relinquished with little regret. He possessed in the highest degree ingenuousness and the love of truth. His manipulations, though never very refined, were always simple, and often ingenious. Chemistry owes to him some of her most important instruments of research, and many of her most useful combinations; and no single person ever discovered so many new and curious substances.

"Scheele possessed in the highest degree the faculty of invention; all his labours were instituted with an object in view, and after happy or bold analogies. He owed little to fortune or to accidental circumstances: born in an obscure situation, occupied in the duties of an irksome employment, nothing could damp the ardour of his mind, or chill the fire of his genius; with very small means, he accomplished very great things. No difficulties deterred him from submitting his ideas to the test of experiment. Occasionally misled in his views, in consequence of the imperfection of his apparatus, or the infant state of the enquiry, he never hesitated to give up his opinions the moment they were contradicted by facts. He was eminently endowed with that candour which is characteristic of great minds, and which induces them to rejoice as well in the detection of their own errors, as in the discovery of truth. His papers are admirable models of the manner in which experimental research ought to be pursued; and they contain details on some of the most important and brilliant phenomena of chemical philosophy."

The discovery of the gases, of a new class of bodies more active than any others in most of the phenomena of nature and art, could not fail to modify the whole theory of chemistry, and, under the genius of Lavoisier, it ultimately led to the establishment of those new doctrines, which it is the principal object of this history to expound; but before this task can be accomplished, it will be necessary to consider the rise and progress of opinion concerning chemical attraction, and heat and light, since these subjects are too intimately interwoven with the anti-phlogistic system to be separated from any examination of its principles.

Boyle, says Sir Humphry Davy, was one of the most active experimenters, and certainly the greatest chemist of his age. He introduced the use of tests, or re-agents, active substances for detecting the presence of other bodies: he overturned the ideas which at that time were prevalent, that the results of operations by fire were the real elements of things; and he ascertained a number of important facts respecting inflammable bodies, and alkalies, and the phenomena of combination; but neither he nor any of his contemporaries endeavoured to account for the changes of bodies by any fixed principles.

The solutions of the phenomena were attempted either on rude mechanical notions, or by occult qualities, or peculiar subtile spirits or ethers, supposed to exist in the different bodies. And it is to the same great genius who developed the laws that regulate the motions of the heavenly bodies, that chemistry owes the first distinct philosophical elucidations of the powers which produce the changes and apparent transmutations of the substances belonging to the earth.

"Sugar dissolves in water, alkalies unite with acids, metals dissolve in acids. Is not this," says Newton, "on account of an attraction between their particles? Copper dissolved in aqua fortis is thrown down by iron. Is not this because the particles of the iron have a stronger attraction for the particles of the acid, than those of copper; and do not different bodies attract each other with different degrees of force?"

In 1719, Geoffroy endeavoured to ascertain the relative attractive powers of bodies for each other, and to arrange them, under the form of a table, in an order in which these forces, which he named affinities, were expressed.

Concerning the nature of heat, there are two opinions which have ever divided the chemical world. The one considers it merely as a property of matter, and that it consists in an undefinable motion, or vibration of its particles; the other, on the contrary, regards it as a distinct and subtile substance, sui generis. Each of these opinions has been supported by the greatest philosophers, and for a long period the arguments on both sides appeared equally plausible and forcible. The discovery of Dr. Black, however, gave a preponderance to the scale in favour of its materiality.

"It was during his residence in Glasgow, between the year 1759 and 1763," says Dr. Thomson, "that he brought to maturity those speculations concerning the combination of heat with matter, which had frequently occupied a portion of his thoughts."

Before Dr. Black's discovery, it was universally supposed that solids were converted into liquids by a small addition of heat, after they have been once raised to the melting point, and that they returned again to the solid state on a very small diminution of the quantity of heat necessary to keep them at that temperature. An attentive view, however, of the phenomena of liquefaction and solidification gradually led this sagacious philosopher to a different conclusion. By observations which it is unnecessary to detail, he became satisfied that when ice is converted into water, it unites with a quantity of heat, without having its temperature increased; and that when water is frozen into ice, it gives out a quantity of heat without having it diminished. The heat thus combined, then, is the cause of the fluidity of the water; and as it is not sensible to the thermometer, Dr. Black called it latent heat.

There is such an analogy between the cessation of thermometric expansion during the liquefaction of ice, and during the conversion of water into steam, that there could be no hesitation about explaining both in the same way. Dr. Black, therefore, immediately concluded that, as water is ice united to a certain quantity of latent heat, so steam is water united to a still greater quantity.

This beautiful theory enables us to understand phenomena in nature which were previously quite inexplicable. We now comprehend how the thaw which supervenes after intense frost, should so slowly melt the wreaths of snow and beds of ice. Had, indeed, the transition of water from its solid into its liquid state not been accompanied by this great change in its relation to heat, every thaw would have occasioned a frightful inundation, and a single night's frost must have solidified our rivers and lakes. Neither animal nor vegetable life could have subsisted under such sudden and violent transitions. It would appear, then, that water, during the act of freezing, is acted upon by two opposite powers: it is deprived of heat by exposure to a medium whose temperature is below 32°; and it is supplied with heat by the evolution of that principle from itself, viz. of that portion which constituted its fluidity. As these powers are exactly equal, the temperature of the water must remain unchanged till the latent heat, necessary to its fluidity, is all evolved.

Although these facts have been admitted by all, it has been contended by many that the absorption of heat by bodies is the necessary effect, and not the efficient cause, of change of form,—the consequence of what has been called a change of their capacity: thus ice, it is supposed, in becoming water, has its capacity for heat increased, and the absorption of heat is a consequence of such increased capacity. This theory, however, is deficient, inasmuch as it fails to explain the cause of that change of form, which is assumed to account for the increase of capacity.

Light, like heat, has been considered by some philosophers as a subtile fluid filling space, and rendering bodies visible by the undulations into which it is thrown; while others, with Newton at their head, regard it as a substance consisting of small particles, constantly separating from luminous bodies, moving in straight lines, and rendering objects visible by passing from them and entering the eye. The late experiments of Dr. Young would incline us to prefer the undulatory to the corpuscular hypothesis.

By this preliminary sketch, the reader has been prepared for viewing with advantage the theory of Lavoisier; in the construction of which he will see little more than a happy generalization of the several discoveries which have been enumerated. Indeed, this observation will apply to all great systems of philosophy; facts, developed by successive enquirers, go on accumulating, until, after an interval, a happy genius arises who connects and links them together; and thus generally receives that meed of praise which, in stricter justice, would be apportioned and awarded to the separate contributors. It is far from my intention to disparage the merits of Lavoisier; but the materials of his system were undoubtedly furnished by Black, Priestley, and Cavendish.

The most important modification of the phlogistic theory—for there were several others—may be said to be that suggested by Dr. Crawford. Dr. Priestley had found that the air in which combustibles were suffered to burn till they were extinguished, underwent a very remarkable change, for no combustible would afterwards burn in it, and no animal could breathe it without suffocation. Dr. Crawford, like many others, concluded, that this change was owing to phlogiston; but he for the first time applied Dr. Black's doctrine of latent heat, for the explanation of the origin of the heat and light which appear during the process. According to this philosopher, the phlogiston of the combustible combines, during combustion, with the air, and at the same time separates the caloric and light with which that fluid had been previously united. The heat and the light, then, which appear during combustion, exist previously in the air. This theory was very different from Stahl's, and certainly a great deal more satisfactory; but still the question—What is phlogiston? remained to be answered.

Mr. Kirwan attempted to answer it, and to prove that phlogiston is no other than hydrogen.

This opinion, which Mr. Kirwan informs us was first suggested by the discoveries of Dr. Priestley, met with a very favourable reception from the chemical world, and was adopted, amongst many others, by Mr. Cavendish. The object of Mr. Kirwan was to prove, that hydrogen exists as a component part of every combustible body; that during combustion it separates from the combustible body, and combines with the oxygen of the air. At the same time, Lavoisier was engaged in examining the experiment of Bayen, and those of the British philosophers. Bayen, in 1774, had shown that mercury converted into a calx, or earth, by the absorption of air, could be revived without the addition of any inflammable substance; and hence he concluded, that there was no necessity for supposing the existence of any peculiar principle of inflammability, in order to account for the calcination of metals; but he formed no opinion respecting the nature of the air produced from the calx of mercury. Lavoisier, in 1775, showed that it was an air, which supported flame and respiration better than common air, which he afterwards named oxygen: the same substance that Priestley and Scheele had procured from other metallic bodies the year before, and had particularly described.

Lavoisier also discovered that the same air is produced during the revivification of metallic calces by charcoal, as that which is emitted during the calcination of limestones; hence he concluded, that this elastic fluid is composed of oxygen and charcoal: and from his experiments on nitrous acid and oil of vitriol, he also inferred that this gas entered into the composition of these substances.

Lavoisier was now enabled to explain the phenomena of combustion, without having recourse, to phlogiston: a principle merely supposed to exist, because combustion could not be explained without it.

His new theory depends upon the two laws discovered by himself and Dr. Black; viz. that when a combustible is raised to a certain temperature, it begins to combine with the oxygen of the atmosphere, and that this oxygen during its condensation lets go the latent caloric, and the light with which it was combined while in the gaseous state. Hence their appearance during every combustion. Hence also the change which the combustible undergoes in consequence of combustion.

It followed from this view, that the metallic calces were combinations of metals with oxygen; and on examining the products of certain inflammable bodies, and finding them to be acid, the conclusion was extended by a plausible analogy to other acids whose bases were unknown, and the general proposition was established that oxygen was the universal principle of acidity; that acids resulted from the union of a peculiar combustible base, called the radical, with the common principle, oxygen, technically termed the acidifier.

These views, regarding the phenomena of combustion and acidification, may be considered as constituting what has been termed the Anti-phlogistic system.

It was some time, however, after this system was promulgated, before its author was able to gain a single convert, notwithstanding his unwearied assiduity, and the great weight which his talents, his reputation, his fortune, and his situation naturally gave him.

At length, M. Berthollet, at a meeting of the Academy of Sciences in 1785, solemnly renounced his old opinions, and declared himself a convert. Fourcroy followed his example; and two years afterwards Morveau, during a visit to Paris, was prevailed upon to embrace the new doctrine.

The theory of Lavoisier, soon after it had been framed, received an important confirmation from the two grand discoveries of Mr. Cavendish, respecting the composition of water and nitric acid, and the elaborate and beautiful investigations of Berthollet into the nature of ammonia; by which, phenomena, before anomalous, were shown to depend upon combinations of aëriform matter.

The notion of phlogiston, however, was still defended with remarkable tenacity by many distinguished philosophers. Mr. Kirwan, who considered hydrogen as the universal principle of combustibility, undertook to prove that this element entered into the composition of every body of the kind: a single exception, of course, must necessarily prove fatal to the theory. Mr. Kirwan, fortunately for the French chemists, founded his reasonings on the inaccurate experiments of other chemists; and thus did he promote the popularity of the anti-phlogistic system by the weakness of the arguments by which he assailed it.

Lavoisier and his associates saw at once the important uses which might be made of this essay: by refuting an hypothesis which had been embraced by the most respectable chemists in Europe, their cause would receive an éclat which would make it irresistible. The essay was accordingly translated into French, and each of the sections into which it was divided was accompanied by a refutation.

Four of the sections were refuted by Lavoisier, three by Berthollet, three by Fourcroy, two by Morveau, and one by Monge.

Mr. Cavendish, in a paper communicated to the Royal Society in the year 1784, drew a comparison between the phlogistic and anti-phlogistic theories, and showed that each of them was capable of explaining the phenomena in a satisfactory manner; he however, at the same time, gave the reasons which induced him to prefer the earlier view. In the execution of this task, unlike Mr. Kirwan, he never advanced a single opinion which he had not put to the test of experiment; and he never suffered himself to go any farther than his experiments would warrant. This paper, therefore, the French chemists were unable to refute, and they were accordingly wise enough to pass it over without notice. Had it been possible to have preserved the phlogistic hypothesis, Mr. Cavendish would have saved it—

"Si Pergama dextrâ
Defendi possent, etiam hâc defensa fuissent."

"Sooner or later," says Sir Humphry Davy, "that doctrine which is an expression of facts, must prevail over that which is an expression of opinion. The most important part of the theory of Lavoisier was merely an arrangement of the facts relating to the combinations of oxygen: the principle of reasoning which the French school professed to adopt was, that every body which was not yet decompounded, should be considered as simple; and though mistakes were made with respect to the results of experiments on the nature of bodies, yet this logical and truly philosophical principle was not violated; and the systematic manner in which it was enforced was of the greatest use in promoting the progress of science."

Till 1786, there had been no attempt to reform the nomenclature of chemistry; the names applied by discoverers to the substances which they made known were still employed. Some of these names, which originated amongst the alchymists, were of the most barbarous kind; few of them were sufficiently definite or precise, and most of them were founded upon loose analogies, or upon false theoretical views.

"It was felt by many philosophers, particularly by the illustrious Bergman, that an improvement in chemical nomenclature was necessary; and in 1787, MM. Lavoisier, Morveau, Berthollet, and Fourcroy, presented to the world a plan for an almost entire change in the denomination of chemical substances, founded upon the idea of calling simple bodies by some names characteristic of their most striking qualities, and of naming compound bodies from the elements which composed them." There was, besides, a secret feeling in the breasts of the associated chemists, which, no doubt, had its influence in suggesting and promoting such a scheme. The views of Lavoisier had so changed the face of chemistry, as almost to have rendered it a new science: by adopting a new nomenclature, they identified, as it were, all the discoveries of the day with the new theory, and thus appropriated to France the original and entire merit of the system.

It is impossible to pass over this subject without a comment. Lavoisier was unquestionably indebted to Dr. Black for the support, if not for the suggestion, of the most brilliant part of his theory of combustion; and yet he attempted even to conceal the name of the discoverer of latent heat.

How far Lavoisier was really culpable, and whether he did not intend to do full justice to all the claims of his predecessors, cannot now be known; as he was cut off in the midst of his career, while so many of his scientific projects remained unexecuted. From the posthumous works of Lavoisier, there is some reason for believing that, if he had lived, he would have done justice to all parties; but there is no doubt that Dr. Black, in the mean time, thought himself aggrieved by the publication of several of Lavoisier's papers in the "Mémoires de l'Académie," and that he formed the intention of doing himself justice, by publishing an account of his own discoveries: this intention, however, was unfortunately thwarted and prevented by bad health. But to return to the subject of nomenclature. Sir H. Davy continues—"The new nomenclature was speedily adopted in France; under some modifications, it was received in Germany; and, after much discussion and opposition, it became the language of a new and rising generation of chemists in England. It materially assisted the diffusion of the anti-phlogistic doctrine, and even facilitated the general acquisition of the science; and many of its details were contrived with much address, and were worthy of its celebrated authors."

On the general adoption of this new theory of chemistry, it must be admitted that its authors displayed an intemperate triumph wholly unworthy of them. They held a festival, at which Madame Lavoisier, in the habit of a priestess, burnt the works of Stahl on an altar erected for the occasion, while solemn music played a requiem to his departed system!

Sir Humphry Davy, in speaking of the merits of Lavoisier, observes that "he must be regarded as one of the most sagacious of the chemical philosophers of the last century; indeed, except Cavendish, there is no other enquirer who can be compared to him for precision of logic, extent of view, and sagacity of induction. His discoveries are few, but he reasoned with extraordinary correctness upon the labours of others. He introduced weight and measure, and strict accuracy of manipulation into all chemical processes. His mind was unbiassed by prejudice; his combinations were of the most philosophical nature; and in his investigations upon ponderable substances, he has entered the true path of experiment with cautious steps, following just analogies, and measuring hypotheses by their simple relations to facts."

It will be scarcely possible for a future generation of philosophers to imagine with what an undisciplined ardour the anti-phlogistic system, thus enhanced by a new and fascinating nomenclature, was supported throughout Europe. Facts only were appreciated in proportion to the evidence they furnished of its truth; and a discovery even required the sanction of its authority as the passport to notice and regard. The least expression of doubt, as to the validity of any point in its doctrines, exposed the sceptic to a host of assailants, and fortunate was he if he escaped the fate of Peter Ramus, or of those who ventured to question the infallibility of that great despot of another age, Aristotle.

In no country of Europe did this feeling manifest itself to a greater extent than in England. There was perhaps a political prejudice co-operating upon the occasion: it is very difficult, under any circumstances, to avoid connecting the man and his works. The fate of Lavoisier[133] was truly affecting, and by a species of retributive justice, he received the sympathy of the world in the homage paid to his system; while the atrocity of his assassination, on which every Englishman dwelt with horror, appeared to be thus heightened by every praise bestowed upon his merits.

It is not the least surprising circumstance in the history of this system, that with such a blind and idolatrous admiration of its principles, so few facts should have been distorted. It is true that, from the belief that combustion could never take place without the presence of oxygen, the elementary principle of Scheele became, according to these views, a compound of oxygen and an acid; and the name of dephlogisticated marine acid was exchanged for that of oxy-muriatic acid, a circumstance which spread a cloud of error over the science, and perhaps retarded its progress in a greater degree than is generally imagined. In like manner, the chemist neglected to avail himself of the hint which, under other impressions, would have proved an important clue to discovery, viz. the acid properties of sulphuretted hydrogen.

We have now arrived at that stage in our history, when it may with propriety and advantage be asked—What has Davy done in correcting error, or in advancing truth?

The answer to this question will be nothing more than a summary of those discoveries which have been successively investigated during the progress of the present work.

The new doctrines of chemistry were highly instrumental in encouraging more extended investigations into all the different productions of nature and art; and we may observe, that one of the first efforts of Sir Humphry Davy was to improve our knowledge of the nature and habitudes of the tanning and astringent principles of vegetables,—an enquiry which had been commenced by Seguin and Proust. In pursuing even the most beaten path, he was sure to discover objects of novelty. Look at his early experiments on the cane, and on the straw of wheat, barley, and hay, and we shall see how magically he raised from their ashes a new flower of knowledge. He soon, however, quitted the track of other experimentalists; although we learn from the whole tenor of his researches, that he could obey as well as he could command, and he could act in the ranks, although he more frequently appeared as a general in the field of science.

Sir Humphry Davy has observed, that "at the time when the anti-phlogistic theory was established, electricity had little or no relation to chemistry. The grand results of Franklin respecting the cause of lightning, had led many philosophers to conjecture, that certain chemical changes in the atmosphere might be connected with electrical phenomena; and electrical discharges had been employed by Cavendish, Priestley, and Van-Marum, for decomposing and igniting bodies; but it was not till the era of the wonderful discovery of Volta, in 1800, of a new electrical apparatus, that any great progress was made in chemical investigation by means of electrical combinations.

"Nothing tends so much to the advancement of knowledge as the application of a new instrument. The native intellectual powers of men in different times are not so much the causes of the different success of their labours, as the peculiar nature of the means and artificial resources in their possession. Independent of vessels of glass, there could have been no accurate manipulations in common chemistry: the air-pump was necessary for the investigation of the properties of gaseous matter; and without the Voltaic apparatus, there was no possibility of examining the relations of electrical polarities to chemical attractions."

There is a candour in this statement which we cannot but admire. Nor does the admission diminish the glory of him who, by the application of such new instruments of research, was enabled to penetrate into the hidden mysteries of Nature. What avails the telescope, without the eye of the observer?

To Davy, the Voltaic apparatus was the golden branch, by which he subdued the spirits that had opposed the advance of former philosophers; but what would its possession have availed him, had not his genius, like the ancient Sibyl, pointed out its use and application?

It will be seen that he was thus enabled, not only to discover laws which are in constant operation, modifying the forms of matter, and influencing all the operations of chemistry, but, by applying them, to determine the elements of the fixed alkalies to be oxygen and a metallic base: a fact obviously opposed to the idea of oxygen being the general principle of acidity; for here it was the principle of alkalinity, if it may be so expressed. This was shaking the corner-stone of the edifice, and his subsequent researches into the nature of oxy-muriatic acid may be said to have overthrown it; for if either of the elements of this body can be considered as the acidifier, it is hydrogen. The consequences which flowed from this truth were of the highest importance, not only in correcting errors, which the progress of discovery, instead of rectifying, was actually multiplying, but in leading to the developement of new bodies. Iodine might have been recognised as an elementary body; but its relations to oxygen and hydrogen would probably have remained unknown, had not a knowledge of the true character of chlorine assisted the enquiry.

The same observation will apply to the recently discovered body, Bromine. In like manner has the chemist been led, by the chloridic theory, to a more accurate acquaintance with the composition of the fluoric, hydriodic, and hydrocyanic acids; while he has also learnt that hydrogen alone can convert certain undecompounded bases into well characterised acids, without the aid of oxygen. The same discovery has completely changed all our opinions with regard to a very important series of saline combinations, and developed the existence of new compounds of a most interesting description.

Thus, then, has the acidifying hypothesis of Lavoisier been overturned, and a new theory constructed out of its ruins, which acknowledges no distinct element as the one imparting to matter the characters of an acid.

Equally complete has been the downfall of the theory of combustion. The discovery of the true nature of chlorine was, in itself, sufficient to show that bodies might combine, with the phenomena of heat and light, without the presence of oxygen; but Davy has brought a mass of evidence from other sources in proof of the same truth. He has shown that, whenever the chemical forces which determine either composition or decomposition are energetically exercised, the phenomena of combustion, or incandescence, with a change of properties, are displayed. He has therefore annulled the distinction between supporters of combustion and combustibles, since he has shown that, in fact, one substance frequently acts in both capacities, being a supporter apparently at one time, and a combustible at another. But in both cases the heat and light depend on the same cause, and merely indicate the energy and rapidity with which reciprocal attractions are exerted. Thus sulphuretted hydrogen is a combustible with oxygen and chlorine; a supporter with potassium. Sulphur, with chlorine and oxygen, has been called a combustible basis; with metals, it acts the part of a supporter. In like manner, potassium unites so powerfully with arsenic and tellurium, as to produce the phenomena of combustion. Nor can we ascribe the appearances to the liberation of latent heat, in consequence of condensation of volume. The protoxide of chlorine, a body destitute of any combustible constituent, at the instant of decomposition evolves light and heat with explosive violence; and its volume becomes one-fifth greater. Chloride and iodide of azote, compounds alike destitute of any inflammable matter, according to the ordinary belief, are resolved into their respective elements with tremendous force of inflammation; and the first expands into more than six hundred times its bulk. Now, instead of heat and light, a prodigious degree of cold ought to accompany such an expansion, according to the hypothesis of latent heat. Other instances might be cited, and other arguments adduced on the same subject, but time and space fail me.[134]

Such, then, are the facts developed by the experimental researches of Sir Humphry Davy; from which it follows, that—

1. Combustion is not necessarily dependent on the agency of oxygen.

2. That it cannot be regarded as dependent upon any peculiar principle or form of matter, but must be considered as a general result of intense chemical action.

3. That the evolution of light and heat cannot be ascribed simply to a gas parting with its latent store of those ethereal fluids.

4. That, since all bodies which act powerfully upon each other are in the opposite electrical relations of positive and negative, the evolution of heat and light may depend upon the annihilation of these opposite states, which will happen whenever they combine.

Thus has Sir H. Davy, by refuting the opinions of the French philosophers, respecting the relations of oxygen to the phenomena of combustion, and the nature of its products, removed the pillars on which the fabric of the anti-phlogistic rested, and reduced the generalization of Lavoisier to isolated collections of facts; the sound logic, however,—the pure candour, the numerical precision of inference which characterise the labours of the French philosopher, will cause his name to be held in everlasting admiration. The downfall of his doctrine is the natural result of the progress of truth; the same fate may attend our present systems, but the facts discovered through their means are unchangeable and eternal; and it is upon them alone that the fame of the chemist must ultimately rest.

In sciences collateral to chemistry, the researches of Davy have cast a reflected lustre. In geology, his discovery of the composition of the earths, has opened a new path of investigation; while his examination of the water and gaseous matter so frequently enclosed in the cavities of quartz, has given no small degree of support to the hypothesis of the Plutonists; above all, his results connected with the decomposition and transfer of different elements by Voltaic influence, has already explained many phenomena relating to metallic veins; and the late researches of Mr. Fox must lead us to the conclusion, that electric powers are still in operation in the recesses of the earth; and that mineral veins are not only the cabinets of Nature, but still her active laboratories.

These cursory observations upon the discoveries of Sir H. Davy relate merely to the changes they have effected in the general theory of chemistry. I might recapitulate the numerous researches by which he has extended our knowledge upon particular subjects; but I have so fully entered into the consideration of them in the body of my work, that I consider such a tax upon the patience of my reader would be both unfair and unnecessary.

I shall therefore conclude my long and arduous labour, by enumerating the different memoirs communicated by this distinguished philosopher to the Royal Society; and also the several works which he published at different periods of his brilliant but too fleeting career.

1. An Account of some Galvanic Combinations, formed by single metallic plates and fluids, analogous to the Galvanic Apparatus of M. Volta.Read June 18, 1801.

2. An Account of some Experiments and Observations on the constituent parts of certain Astringent Vegetables, and on their operation in Tanning.February 24, 1803.

3. An Account of some Analytical Experiments on a Mineral Production from Devonshire, consisting principally of Alumina and Water.February 28, 1805.

4. On a Method of analysing Stones containing a fixed Alkali, by means of Boracic acid.May 16, 1805.

* For the above papers, the Society awarded him the
Copley Medal.

5. The Bakerian Lecture.—On some Chemical agencies of Electricity.November 20, 1806.

** For this memoir, he received the prize of the
French Institute.

6. The Bakerian Lecture.—On some new Phenomena of Chemical Changes produced by Electricity, particularly the Decomposition of the Fixed Alkalies, and the exhibition of the new substances which constitute their bases; and on the general nature of Alkaline bodies.Read November 19, 1807.

7. Electro-chemical Researches on the Decomposition of the Earths; with Observations on the Metals obtained from the Alkaline Earths; and on the Amalgam procured from Ammonia.June 30, 1808.

8. The Bakerian Lecture.—An Account of some new Analytical Researches on the nature of certain bodies, particularly the Alkalies, Phosphorus, Sulphur, Carbonaceous matter, and the Acids hitherto uncompounded; with some general Observations on Chemical Theory.December 15, 1808.

9. New Analytical Researches on the nature of certain bodies; being an Appendix to the Bakerian Lecture for 1808.February 1809.

10. The Bakerian Lecture for 1809. On some new Electro-chemical Researches on various objects, particularly the metallic bodies from the Alkalies and Earths; and on some combinations of Hydrogen.November 16, 1809.

11. Researches on the Oxy-muriatic Acid, its nature and combinations; and on the elements of Muriatic Acid; with some Experiments on Sulphur and Phosphorus, made in the Laboratory of the Royal Institution.Read July 12, 1810.

12. The Bakerian Lecture for 1810. On some of the Combinations of Oxy-muriatic Gas and Oxygen, and on the chemical relations of those principles to inflammable bodies.November 15, 1810.

13. On a Combination of Oxy-muriatic Gas and Oxygen Gas.February 21, 1811.

14. On some Combinations of Phosphorus and Sulphur, and on some other subjects of Chemical Enquiry.June 18, 1812.

15. On a new Detonating Compound; in a letter to Sir Joseph Banks, Bart. F.R.S.November 5, 1812.

16. Some further Observations on a new Detonating substance.July 1, 1813.

17. Some Experiments and Observations on the Substances produced in different chemical processes on Fluor Spar.July 8, 1813.

18. An Account of some New Experiments on the Fluoric Compounds; with some Observations on other objects of Chemical Enquiry.February 13, 1814.

19. Some Experiments and Observations on a new Substance, which becomes a Violet-coloured Gas by heat.January 20, 1814.

20. Further Experiments and Observations on Iodine.Read June 16, 1814.

21. Some Experiments on the Combustion of the Diamond, and other Carbonaceous Substances.June 23, 1814.

22. Some Experiments and Observations on the Colours used in Painting by the Ancients.February 23, 1815.

23. Some Experiments on a solid Compound of Iodine and Oxygen, and on its Chemical Agencies.April 20, 1815.

24. On the Action of Acid upon the Salts usually called Hyper-Oxymuriates, and on the Gases produced from them.May 4, 1815.

25. On the Fire-damp of Coal Mines, and on methods of lighting the Mine, so as to prevent Explosion.November 19, 1815.

26. An Account of an Invention for giving Light in Explosive Mixtures of Fire-damp in Coal Mines, by consuming the Fire-damp.January 11, 1816.

27. Further Experiments on the Combustion of Explosive Mixtures confined by Wire Gauze, with some Observations on Flame.January 25, 1816.

28. Some Researches on Flame.January 16, 1817.

29. Some New Experiments and Observations on the Combustion of Gaseous Mixtures; with an account of a method of preserving a continued Light in Mixtures of inflammable Gases and Air, without Flame.Read January 23, 1817.

*** For the preceding five papers, the Rumford
Medals were awarded to him.

30. On the fallacy of Experiments in which Water is said to have been formed by the decomposition of Chlorine.February 12, 1818.

31. New Experiments on some of the combinations of Phosphorus.April 9, 1818.

32. Some Observations on the formation of Mists in particular situations.February 25, 1819.

33. On the Magnetic Phenomena produced by Electricity.November 16, 1820.

34. Some Observations and Experiments on the Papyri found in the ruins of Herculaneum.March 15, 1821.

35. Further Researches on the Magnetic Phenomena produced by Electricity; with some new Experiments on the properties of Electrified bodies, in their relations to conducting powers and temperature.July 5, 1821.

36. On the Electrical Phenomena exhibited in vacuo.December 20, 1821.

37. On the state of Water and Aëriform matter in cavities found in certain Crystals.Read June 13, 1822.

38. On a new Phenomenon of Electro-Magnetism.March 6, 1823.

39. On the application of Liquids formed by the condensation of Gases, as mechanical Agents.April 17, 1823.

40. On the changes of volume produced in Gases, in different states of density, by Heat.May 1, 1823.

41. On the Corrosion of Copper Sheathing by sea-water; and on methods of preventing this effect, and on their application to ships of war and other ships.Jan. 24, 1824.

42. Additional Experiments and Observations on the application of Electrical Combinations to the preservation of the Copper Sheathing of ships, and to other purposes.June 17, 1824.

43. Further Researches on the preservation of Metals by Electro-chemical means.June 9, 1825.

44. The Bakerian Lecture for 1826.—On the Relation of Electrical and Chemical changes.June 3, 1826.

**** For this memoir, the Royal Society conferred upon him the Royal Medal.

45. On the Phenomena of Volcanoes.March 20, 1828.

46. Account of some Experiments on the Torpedo.November 20, 1828.

HIS PUBLISHED WORKS ARE,

"Experimental Essays on Heat, Light, and on the Combinations of Light, with a new Theory of Respiration," &c. Published in Contributions to Physical and Medical Knowledge, by T. Beddoes, M.D. 1799.

"Researches Chemical and Philosophical, chiefly concerning Nitrous Oxide, and its Respiration." 1800.

"A Syllabus of a Course of Lectures."

"An Introductory Lecture." 1801.

"Elements of Chemical Philosophy." 1812.

"Elements of Agricultural Chemistry." 1813.

"On the Safety Lamp for Coal Miners; with some Researches on Flame." 1818. (Several Editions.)

"Salmonia; or Days of Fly-Fishing."

"Consolations in Travel; or the Last Days of a Philosopher."