EQUILIBRIUM OF HETEROGENEOUS SUBSTANCES. 345 



and sometimes cold is produced.* When neither is produced, of course 

 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 

 (HNO 6 +7HO) [HNO 3 +3JH 2 O], M. Favre has found 



(V"- V')ke = 46781 caL , Ae = -41824 caL , AQ = 4957 ca1 ;,; 

 and with acid containing about one equivalent of water 



(HNO 6 +HO) [HNO 3 + JH 2 O], 



( v ff - V) Ae = 49847 cal - , Ae = - 52714 cal , AQ = - 2867 caL . 

 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 diminution 

 of energy in the cell. 



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

 in which the chemical processes are much more simple. 



For electrodes of cadmium and platinum in hydrochloric acid his 

 experiments givet 



(F"_ F')Ae = 9256 caL , Ae= -8258 ca1 -, 



AFp= -290^-, AQ = 1288 caL . 



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 gives \ 



(V- F')Ae = 16950 ca1 -, Ae= -16189 cal , 



AF P = -290 cal , AQ = 1051 cal ; 



i 



and a later series, 



(7"_ F')Ae = 16738 caL , Ae= -17702^, 



A W P = - 290 cal - , AQ = - 674 caL . 



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

 partition, he has found \\ 



= 2113 caU , 



* M6m Savants Etrang., loc. cit., p. 93; or Comptes Eendus, t. Ixix, p. 37, and 

 t. Ixxiii, p. 893. 



t Comptes Rendus, t. Ixviii, p. 1305. The total heat obtained in the whole circuit 

 (including the cell) when all the electromotive work is turned into heat, was ascertained 

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

 ( V" - V) Ae - AQ, also by - Ae + A W f . (See (691 ). ) The value of ( V" - V) Ae is obtained 

 by adding A$, and that of - Ae by adding - A W f , which is easity estimated, being 

 determined by the evolution of one kilogramme of hydrogen. 



I Ibid. 



M4m. Savants Etrang. , loc. cit. , p. 145. 



\\Ibid., p. 142. 



