LECTURE V.] HISTORY OF CHEMISTRY. 8 1 



oxygen to the latter. Finally, he points out to chemists the 

 many hypothetical substances to which it is necessary to have 

 recourse in order to preserve the older view, whereas the new 

 one explains the facts in the simplest manner. 



Gay-Lussac and Thenard do not admit this. In 1811, 

 when they publish their investigations in full, under the title : 

 Recherches physico-chimiques, they place the two theories side by 

 side, and show how both suffice to explain the facts. 54 Never- 

 theless, they declare against the new system, and the reason 

 they give for doing so, deserves to be mentioned. If chlorine 

 were a simple substance, dry sodium chloride would necessarily 

 decompose water when it dissolved in it, in order that muriate 

 of soda might be produced ; and this they consider more than 

 unlikely. Moreover they held Lavoisier in too high esteem to 

 abandon lightly any such doctrine as the one advanced by him 

 that all acids contain oxygen. 



But their resistance did not avail them long ; the force of 

 facts was stronger than they were, and Gay-Lussac was far too 

 clear-headed a thinker to be blind to them. The facts thaf 

 made him an adherent of Davy's view, in 1813, were especially 

 his own experiments upon iodine, 55 which had been discovered 

 by Courtois and described by Clement, 56 and whose analogy 

 with chlorine he recognised and emphasised ; and further, the 

 discovery of hydriodic acid. From this time onwards, the new 

 theory gains ground, and even Berzelius is unable to alter the 

 current of opinion, although he puts himself to every conceiv- 

 able pains, in a paper published in 1815, to deter chemists from 

 the threatened step. 57 After pointing out that the hypothesis 

 of muriaticum is still in a position to explain the facts, he 

 draws attention to the fact that it, alone, is in agreement with 

 the general theory of acids ; whereas, on the assumption that 

 there is no oxygen present in hydrochloric acid, a distinction is 

 drawn between this compound and the other acids, to which, 

 nevertheless, it shows the greatest resemblances. The salts 



54 Rech. phys. chim. 2, 94. 55 Ann. Chim. 91, 5. 56 Moniteur 

 1813, Nos. 336 and 346. 57 Ann. Phil. 2, 254; Schweigger's Journal, 

 14, 66, 



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