WORK ABSORBED IN ELECTROLYSIS. 39 



the process of heating during the dissociation. In these two 

 cases, effectively, the molecules become grouped according to 

 the various forces in action : degrees of heat in these ; electro- 

 motive forces in those. 



Sprague's law is the converse of that which M. Berthelot 

 designated by the name of " principle of the maximum work," 

 and which he enumerated as follows : " Any chemical change 

 obtained without the interference of a foreign energy has a ten- 

 dency towards the production of the substance or the system of 

 substances which develop the greatest heat." 



LIMITS OF ELECTROLYSIS. M. Berthelot has carried on 

 some interesting experiments concerning the decomposition of 

 a certain number of electrolytes, and he has deduced from them 

 the following conclusions : 



1. In the generality of cases, the decomposition of electro- 

 lytes takes place as soon as the smallest sum of the necessary 

 energies that is to say, in accordance with the quantities of heat 

 is present. The said sum is calculated taking into account all 

 the reactions effected during the passage of the current, without 

 it being necessary to make a distinction between the reactions 

 called primitives and the reputed secondary reactions. 



2. The limit of forces is uncertain whenever polarisation 

 arises. In order to take this conclusion into account and ascer- 

 tain if it is in accordance with the common law, it would be 

 necessary to know the real nature of the compound substances 

 which it brings into action, and the heat due to their combi- 

 nation. 



We have condensed in the table given, page 58, the experi- 

 ments of M. Berthelot. They have the great merit of throwing 

 light on a few points concerning the real actions taking place in 

 electrolytic baths, which had until then remained obscure. 



OF THE USE OF SOLUBLE ANODES. In nearly all the indus- 

 trial applications of electrolysis, the platinum or carbon anodes 

 are replaced by soluble anodes ; the result is to maintain the 

 chemical neutrality of the liquors and to suppress the work 

 necessitated by the decomposition. 



In the case of sulphate of copper, if the anode is a plate of 

 copper, it will receive some oxygen and sulphuric acid which 



