S2 Biographical Account of [Aug. 



hesitated for some time to what branch of science he should 

 devote his chief attention. Mathematics first caught his fancy, 

 and were enlisting him under their banners, when the brilliant 

 discoveries of Dr. Black and his followers in the pneumatic 

 career came to his knowledge, and determined him to make 

 choice of chemistry. In 1774 he published a volume of essays, 

 in which he gives an historical detail of the labours of his pre- 

 decessors in this department of the science, and confirms the 

 theory of Dr. Black by his own experiments. 



His great wealth, his situation, his excellent education, his 

 mathematical precision, his general views, and his persevering 

 industry, all contributed to ensure his success. A comparison 

 of the Stahlian theory with the discoveries in chemistry made by 

 his contemporaries in Britain and Sweden, soon satisfied him of 

 its insufficiency to explain the phenomena of the science. The 

 opinion on the subject which he finally adopted, namely, that 

 phlogiston is a creature of the imagination, and that combustion 

 is occasioned by the union of oxygen with the burning body, 

 must have been brought into a definite form after the year 1774, 

 because it was not til! that year that oxygen gas was discovered 

 by Dr. Priestley ; and it is too obvious to require any proof that 

 his opinion respecting the combination of oxygen in cases of 

 combustion could not precede his knowledge of the existence of 

 that principle. This I conceive to be a sufficient answer to the 

 remarks of M. Berthollet, and several other gentlemen, upon an 

 observation of mine in the first volume of my System of Che- 

 mistry, that Bayen's paper on mercury, published in 1774, first 

 suggested to Lavoisier his theory of combustion. This observation 

 was borrowed from M. Delametherie, whose history of the pro- 

 gress of the antiphlogistic theory published in the Journal de 

 Physique, as far as I am able to judge, is accurate. 



Be this as it may, there can be no doubt that he was in pos- 

 session of the first hint of his theory at least as early as the year 

 1775. He revolved it in his mind with the utmost perseverance 

 for ten years, repeated all the important chemical experiments 

 of others, and contrived a great many of his own with reference 

 to his peculiar theory, and at last succeeded in demonstrating by 

 indisputable experiments a theory almost the reverse of that of 

 Stahl ; namely, that we have no evidence of the existence of the 

 substance called phlogiston, and that in all cases of combustion 

 oxygen unites with the burning body. If the opinion lately 

 advanced by Sir Humphry D<ivy, and which, to me at least, 

 appears founded upon very strong, though not perhaps decisive 

 evidence, be adopted ; namelv, that chlorine or oxymuriatic 

 acid is a simple substance, and muriatic acid a compound of 

 hydrogen and chlorine, we must in that case modify the theory 

 of Lavoisier, and admit combustion to take place during the 



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