38 ELECTROLYSIS. 



trary, often a very difficult thing to estimate all the chemical 

 phenomena which accompany a decomposition ; and notwith- 

 standing the tables setting forth the chemical and calorific equi- 

 valents, it is only with great difficulty that the accurate total 

 of all the energies contributing to the electrolytic phenomena 

 can be ascertained. It is therefore desirable, for every applica- 

 tion, not to undertake an industrial operation before having 

 previously conducted some laboratory experiments and carefully 

 examined the actions which take place and the definite results 

 to which they give rise. 



To complete this chapter and assist the operator in his re- 

 searches, we will give a few summary directions respecting the 

 use of soluble anodes, the law of the lesser energy of Sprague, 

 the limits of electrolysis of Berthelot, and some details on 

 M. Marchese's calculations for estimating the resistances of an 

 electric circuit. 



SPRAGUE'S LAW. M. Sprague's law on electrolysis can be 

 formulated as follows : 



The substances which in becoming freed absorb the smallest 

 quantity of intrinsic energy are those which are liberated at the 

 electrodes. 



This amounts to saying that any molecule, electrolyte or not, 

 in the neighbourhood of the points at which the current enters the 

 electrolyte or goes out of it, will be ranged within the polar cir- 

 cuit, provided a portion of the said molecule can combine itself 

 with the veritable ion which is turned towards the electrode and 

 the other portion may constitute a free molecule absorbing less 

 energy than the ion of the electrolyte would itself absorb from 

 becoming liberated, or else provided the veritable ion could be 

 introduced into the other molecule with a less expenditure of 

 energy than that required to allow of its constituting a free 

 molecule. The substances liberated can thus be recombined 

 anew by those which are in contact with the electrodes, as they 

 are no more simply separated in a state of ions or radicals result- 

 ing from molecules previously existing, although this latter action 

 is the fundamental type and general action of electrolysis. 



This new conception establishes an analogy between the 

 effects of electricity passing through a liquid and those due to 



