ISOMERIC CHANGE 631 



611 ; 1898, 73, 422); and that by careful drying it was 

 possible also to prevent the dissociation of mercurous chloride 

 {Trans. 1900, 77, 646) and of nitrogen trioxide (Trans. 1907, 

 91, 1862). The extraordinary care which Baker used in 

 order to ensure successful results suggested that it might 

 be extremely difficult to repeat in the case of reversible 

 isomeric changes his achievements in preventing dissociation 

 by the removal of impurities. It was, therefore, a matter 

 of special gratification when it was found possible by making 

 use of chloroform as a solvent — without taking any exceptional 

 means to secure the absolute purity of the materials — to arrest 

 the isomeric change of nitrocamphor during a period of 

 two or three weeks (Trans. 1899, 75, 219). These isolated 

 observations were subsequently explained by the presence 

 in the chloroform of an impurity (carbonyl chloride) which 

 interacted with the catalyst (ammonia) normally associated 

 with the nitro-compound, in such a way as to destroy its 

 power to initiate chemical change (Trans. Chem. Soc. 1908, 93, 

 119). Up to the present this "arrest" of the oscillatory 

 isomeric change has only been observed in the case of nitro- 

 camphor dissolved in chloroform, benzene, carbon disulphide, 

 or ether, but there can be little doubt that the phenomenon 

 is a general one, and that— contrary to the original suggestion 

 of Butlerow — a " condition of equilibrium depending on 

 incessant isomeric change " is possible only in presence of 

 some third substance possessing definite catalytic properties. 

 In this class may be placed a number of oxygenated solvents, 

 such as water, the alcohols and the organic acids, but when 

 inert hydrocarbons are used, the further addition of moisture, 

 alkali, base or acid is necessary to establish a condition of 

 equilibrium. That Butlerow was not able to foresee this 

 development of his theory is not surprising in view of the 

 fact that the first of the observations quoted above in illus- 

 tration of the importance of moisture in promoting chemical 

 change was not made until six years after the appearance 

 of his paper. In every other respect his conceptions hold 

 good at the present day, and although erroneous views have 

 frequently been advocated by later writers, the one outstanding 

 feature of the succeeding thirty years' work has been its 

 complete corroboration of the ideas he expressed so clearly 

 in 1877. 



