ISOMERIC CHANGE 619 



The use of copper oxide was introduced by Gay Lussac in 1815, 

 but was only developed into a perfect method some years later 

 in the hands of Dumas and Liebig. So uncertain, indeed, were 

 the results of organic analysis considered to be that Berzelius 

 in 1819 was actually able to ridicule the idea that organic com- 

 pounds could exist which contained only carbon and hydrogen, 

 and no oxygen, in spite of the fact that this had been established 

 by the repeated analyses of de'Saussure. It is therefore little 

 wonder that when Liebig, working in Gay Lussac's laboratory, 

 found that siver fulminate had the same percentage composition 

 as the silver cyanate discovered and analysed by Wohler in 

 1822, the result was not accepted until the analyses had been 

 repeated and confirmed by both investigators. Even then 

 Berzelius, whose custom it was in his annual reports to sit in 

 judgment on the work of all his contemporary chemists, could 

 not be persuaded to pass a favourable verdict until his own 

 experiments had demonstrated in 1830 that racemic acid — dis- 

 covered by Kestner (1822) as a by-product in the separation of 

 tartaric acid from argol and investigated by Gay Lussac in 

 1826 — was identical in composition with Scheele's tartaric acid, 

 although showing marked differences in its physical properties. 

 Being thus convinced by his own experience of the reality of 

 the phenomenon, he proposed in his Annual Report of 183 1 

 that substances which thus combine identity of composition 

 with distinct physical and chemical characteristics should be 

 described by the word Isomeric. 



Polymerism. — Whilst the discussion in reference to the com- 

 position of the cyanates and fulminates was still in progress, an 

 equally striking example of a similar kind was forthcoming from 

 the work of Faraday on the hydrocarbons condensed in the 

 manufacture of "portable gas." The discovery of the hydro- 

 carbon benzene in the liquid portion was followed in 1825 by 

 the investigation of a more volatile substance which escaped in 

 the form of vapour when the liquid was removed from the 

 gas-holders. This vapour had the same composition as ole- 

 fient gas, and like it combined with its own volume 0/ 

 chlorine ; but its density was twice as great, and its chloride 

 contained only half as much chlorine. In this case, it was clear 

 that the two compounds differed in molecular complexity, 1 and 

 in order to avoid confusion Berzelius proposed in 1832 to restrict 



1 Ethylene = C 2 H, ; butylene = C 4 H 8 . 



