ELECTROLYTIC LAWS. 23 



posing produced more work than was required for their decom- 

 position, the result would be the creation of energy, which is 

 quite as impracticable as the realisation of perpetual motion. 



ELECTROMOTIVE FORCES. Faraday's law respecting the 

 quantities of substances liberated by one unit of intensity, and 

 the preceding one as regards the work required for effecting a 

 chemical decomposition, establish that, to electrolyse a given 

 compound it is necessary to use a given electromotive force, and 

 whatever may be the intensity of the current, no decomposition 

 of the electrolyte occurs if that electromotive force is not reached. 



Calling E the electromotive force necessary for the decom- 

 position of the bath, and Q the number of coulombs flowing 

 through the bath, the work of decomposition will be expressed 



by the formula : 



( ) "F 1 



W = ^pr kilogrammetres, 

 y * oJ. 



whence 



^ W x 9-81 



IT 



If z is the electro-chemical equivalent of the liberated sub- 

 stance, the total weight liberated by Q coulombs will be equal 

 to Q z. Calling H the number of calories emitted by one gramme 

 of the substance liberated by the electrolysis for returning to the 

 state of combination it was in at the beginning of the operation, 

 the heat produced by Q z will be Q z H, and, as the mechanical 

 equivalent of heat is 0*424 kilogrammetres for one calory 

 (gramme-degree), the corresponding work will therefore be 

 W = 0-424Q0H kilogrammetres. 



As we have already shown that 



"9-81 ' 

 after simplifying we will have 



E = 4- 15944 zH volts. 



THOMSON'S LAW. Thomson's law is but a paraphrase of the 

 above formula ; it can be thus formulated : The electromotive 

 force of an electrolyte is, in absolute measure, equal to the 

 mechanical equivalent of the chemical action to which an 

 electro-chemical equivalent of the decomposed metal is subject. 



