ELECTROLYTIC LAWS. 25 



which corresponds to it in the chemical reactions. We found, 

 fur example, that the electromotive force of a Daniell cell is 

 proportional to the heat which corresponds to the substitution 

 of one equivalent of copper to one equivalent of zinc, and that 

 consequently it is relatively measured by 25 calories, whereas 

 tlu- equivalent of hydrogen combining with the equivalent of 

 oxygen produces 34 5 calories. 



" There results, from the foregoing, the fact that a Daniell 

 crll is not capable of decomposing one equivalent of water in the 

 same time that one equivalent of zinc is dissolved in the cell." 



Dr. Jahn adds : 



"As according to an acknowledged principle in thermo- 

 chemistry the decomposition of one combination absorbs exactly 

 the same quantity of heat as evolved by its formation, the de- 

 composition of 9 grammes of water requires about 34 5 calories, 

 that is to say, a quantity of heat which a Daniell cell can in no 

 case furnish by the dissolution of one equivalent of zinc. I par- 

 ticularly insist on this latter restriction as it has been a frequent 

 custom to give this proposition the appearance of an impossibility 

 for a Daniell cell to decompose water. But this is contradicted 

 by experience." 



Of all the theories and laws applied to electrolysis, Dr. Jahn 

 only accepts those of Faraday, that of the conservation of energy 

 and that of the electro-chemical equivalence. We are exactly 

 of his opinion, and it is -precisely because we accept these laws 

 tli at we dispute his reasoning. 



If we admit, for one moment, that it is possible to decompose 

 water with an electromotive force of one volt, as, according to 

 Faraday, one ampere will always liberate the same quantity 

 of water, viz. 00000009328 kilogramme per second, the work 

 necessary for the decomposition of one kilogramme of water 

 will be: 



W = 9-81 x 0-00000009328 = 109280 kil gmmetrea 



On the other hand the combustion of the hydrogen contained in 

 one kilogramme of water corresponds to 



111 x 34-5 x 424 = 1623708 kilogrammetre*. 



