516 e/! TFi Gibbs — Eqtdlibriuni of Heterogeyieous Substances. 



the electromotive force of the cell is exactly equal to its diminution 

 of energy per unit of electricity transmitted. But such a coincidence 

 is far less significant than the fact that an absorption of heat has been 

 observed. With acid containing about seven equivalents of water 

 (HNOg + VHO), M. Favre has found 



(F"_ F') zJe=z 46781 '•*'•, J6 = -41824'^^'-, J ^ = 4957™'-; 

 and with acid containing about one equivalent of water (HNOg+HO), 



(17"— F')//e= 49847""'-, Z/f = — 52714^'="-, J ^ = -2867'^"'-. 

 In the first example, it will be observed that the quantity of heat 

 absorbed in the cell is not small, and that the electromotive force is 

 nearly one-eighth greater than can be accounted for by the diminu- 

 tion of energy in the cell. 



This absorption of heat in the cell he has observed in other cases, 

 in which the chemical processes ai-e much more simple. 



For electrodes of cadmium and platinum in hydrochloric acid his 

 experiments give* 



( Y"— V') Ae — 9256"="-, Jf = — 8258"^'-, 



J TTp^ — 290'^"'-, Z/^=:1288'"'-. 



In this case the electromotive force is nearly one-sixth greater than 

 can be accounted for by the diminution of energy in the cell with the 

 work done against the pressure of the atmosphere. 



For electrodes of zinc and platinum in the same acid one series of 

 experiments givesf 



(|7"_ V) Ae— 16950^'"-, Ae= — 16189'=*'-, 



JTrp^-290'^^'''-, J^^iosr""-; 



and a later series,J 



(F"- F')^e==16738'^'''-, Z/«= — 17702'='''-, 



z/TFp = -290^-^'-, z/(2=-674'^="-. 



In the electrolysis of hydrochloric acid in a cell with a porous par- 

 tition, he has found§ 



* Comptes Rendris, t. Ixviii, p. 1.S05. The total heat obtained in the whole circuit 

 (indudiug the cell) when all the electromotive worlt is turned into heat, was ascer- 

 tained by direct experiment. This quantity, 7968 calories, is evidently represented by 

 ( V"- V) Ae - AQ, also by - Ap + A Wv- [See (691).] The value of { V" — V')Ae 

 is obtained by adding A^, and that of — Ae by adding — A Wp, which is easily esti- 

 mated, being determined by the evolution of one kilogramme of hydrogen, 



\ Ibid. 



J Me7n. Savants fyrang., loc. cit., p. 145, 



§ Ihid, p. 142. 



