Again, Lavoisier showed that the atmospheric air consists of pure or vital air, and of an unvital air, which he thence called azot. The vital air he found to be the agent in combustion, acidification, calcination, respiration; all these processes were analogous; all consisted in a decomposition of the atmospheric air, and a fixation of the pure or vital portion of it. But he thus arrived at the conclusion, that this pure air was added, in all the cases in which, according to the received theory, phlogiston was subtracted, and vice versa. He gave the name of oxygen ( principe oxygène) to the substance which thus unites itself with metals to form their calces, and with combustible substances to form acids.' A new theory was thus produced, which would account for all the facts which the old one would explain, and had besides the evidence of the balance in its favour. But there still remained some apparent objections to be removed. In the action of dilute acids on metals, inflammable air was produced. Whence came this element? The discovery of the decomposition of water sufficiently answered this question, and converted the objection into an argument on the side of the theory: and thus the decomposition of water was, in fact, one of the most critical events for the fortune of the Lavoisierian doctrine, and one which, more than any other, decided chemists in its favour. In succeeding years, Lavoisier showed the consistency of his theory with all that was discovered concerning the composition of alcohol, oil, animal and vegetable substances, and many other bodies. It is not necessary for us to consider any further the evidence for this theory, but we must record a few circumstances respecting its earlier history. Rey, a French physician, had in 1630, published a book, in which he inquires into the grounds of the increase of the weight of metals by calcination. He says, 'To this question, then, supported on the grounds already mentioned, I answer, and maintain with confidence, 2 Mém. Ac. Par. 1781, p. 448. 3 Thomson, I↑ Chem. ii. 95. that the increase of weight arises from the air, which is condensed, rendered heavy and adhesive, by the heat of the furnace.' Hooke and Mayow had entertained the opinion that the air contains a nitrous spirit,' which is the supporter of combustion. But Lavoisier disclaimed the charge of having derived anything from these sources; nor is it difficult to understand how the received generalizations of the phlogistic theory had thrown all such narrower explanations into obscurity. The merit of Lavoisier consisted in his combining the generality of Stahl with the verified conjectures of Rey and Mayow. No one could have a better claim, by his early enthusiasm for science, his extensive knowledge, and his zealous labours, to hope that a great discovery might fall to his share, than Lavoisier. His father, a man of considerable fortune, had allowed him to make science his only profession; and the zealous philosopher collected about him a number of the most active physical inquirers of his time, who met and experimented at his house one day in the week. In this school, the new chemistry was gradually formed. A few years after the publication of Priestley's first experiments, Lavoisier was struck with the presentiment of the theory which he was afterwards to produce. In 1772, he deposited with the secretary of the Academy, a note which contained the germ of his future doctrines. 'At that time,' he says, in explaining this step, there was a kind of rivalry between France and England in science, which gave importance to new experiments, and which sometimes was the cause that the writers of the one or other of the nations disputed the discovery with the real author.' In 1777, the editor of the Memoirs of the Academy speaks of his theory as overturning that of Stahl; but the general acceptance of the new opinion did not take place till later. 4 Biogr. Univ. (Cuvier.) 5 Thomson, ii. 99. Sect. 2.-Reception and Confirmation of the Theory of Oxygen. THE Oxygen theory made its way with extraordinary rapidity among the best philosophers.6 In 1785, that is, soon after Cavendish's synthesis of water had removed some of the most formidable objections to it, Berthollet, already an eminent chemist, declared himself a convert. Indeed it was soon so generally adopted in France, that Foureroy promulgated its doctrines under the name of La Chimie Française,' a title which Lavoisier did not altogether relish. The extraordinary eloquence and success of Fourcroy as a lecturer at the Jardin des Plantes, had no small share in the diffusion of the oxygen theory; and the name of 'the apostle of the new chemistry' which was at first given him in ridicule, was justly held by him to be a glorious distinction.7 Guyton de Morveau, who had at first been a strenuous advocate of the phlogistic theory, was invited to Paris, and brought over to the opinions of Lavoisier; and soon joined in the formation of the nomenclature founded upon the theory. This step, of which we shall shortly speak, fixed the new doctrine, and diffused it further. Delametherie alone defended the phlogistic theory with vigour, and indeed with violence. He was the editor of the Journal de Physique, and to evade the influence which this gave him, the antiphlogistians established, as the vehicle of their opinions, another periodical, the Annales de Chimie. In England, indeed, their success was not so immediate. Cavendish,' in his Memoir of 1784, speaks of the question between the two opinions as doubtful. 'There are,' he says, 'several Memoirs of M. Lavoisier, in which he entirely discards phlogiston; and as not only the foregoing experiments, but most other phenomena of nature, seem explicable as well, or nearly as well, upon this as upon the commonly believed 6 Thomson, ii. 130. 7 Cuvier, Eloges, i. p. 20. principle of phlogiston,' Cavendish proceeds to explain his experiments according to the new views, expressing no decided preference, however, for either system. But Kirwan, another English chemist, contested the point much more resolutely. His theory identified inflammable air, or hydrogen, with phlogiston; and in this view, he wrote a work which was intended as a confutation of the essential part of the oxygen theory. It is a strong proof of the steadiness and clearness with which the advocates of the new system possessed their principles, that they immediately translated this work, adding, at the end of each chapter, a refutation of the phlogistic doctrines which it contained. Lavoisier, Berthollet, De Morveau, Fourcroy, and Monge, were the authors of this curious specimen of scientific polemics. It is also remarkable evidence of the candour of Kirwan, that notwithstanding the prominent part he had taken in the controversy, he allowed himself at last to be convinced. After a struggle of ten years, he wrote 10 to Berthollet in 1796, 'I lay down my arms, and abandon the cause of phlogiston.' Black followed the same course. Priestley alone, of all the chemists of great name, would never assent to the new doctrines, though his own discoveries had contributed so much to their establishment. He saw,' says Cuvier, 11 without flinching, the most skilful defenders of the ancient theory go over to the enemy in succession; and when Kirwan had, almost the last of all, abjured phlogiston, Priestley remained alone on the field of battle, and threw out a new challenge, in a memoir addressed to the principal French chemists.' It happened, curiously enough, that the challenge was accepted, and the arguments answered by M. Adet, who was at that time (1798,) the French ambassador to the United States, in which country Priestley's work was published. Even in Germany, the birthplace and home of the phlogistic theory, the struggle was not long protracted. There was, indeed, a con 10 Pref. to Foureroy's Chemistry, xiv. 11 Cuvier, Eloge de Priestley, p. 208. troversy, the older philosophers being, as usual, the defenders of the established doctrines; but in 1792, Klaproth repeated, before the Academy of Berlin, all the fundamental experiments; and the result was a full conviction on the part of Klaproth and the Academy, that the Lavoisierian theory was the true one.'12 Upon the whole, the introduction of the Lavoisierian theory in the scientific world, when compared with the great revolution of opinion to which it comes nearest in importance, the introduction of the Newtonian theory, shows, by the rapidity and temper with which it took place, a great improvement, both in the means of arriving at truth, and in the spirit with which they were used. Some English writers 13 have expressed an opinion that there was little that was original in the new doctrines. But if they were so obvious, what are we to say of eminent chemists, as Black and Cavendish, who hesitated when they were presented, or Kirwan and Priestley, who rejected them? This at least shows that it required some peculiar insight to see the evidence of these truths. To say that most of the materials of Lavoisier's theory existed before him, is only to say that his great merit was, that which must always be the great merit of a new theory, his generalization. The effect which the publication of his doctrines produced, shows us that he was the first person who, possessing clearly the idea of quantitative composition, applied it steadily to a great range of well-ascertained facts. This is, as we have often had to observe, precisely the universal description of an inductive discoverer. It has been objected, in like manner, to the originality of Newton's discoveries, that they were contained in those of Kepler. They were so, but they needed a Newton to find them there. The originality of the theory of oxygen is proved by the conflict, short as it was, which accompanied its promulgation; its 12 Thomson, vol. ii. p. 136. 13 Brande, Hist. Diss. in Enc. Brit. p. 182. Lunn, Chem. in Enc. Met. p. 596. |