Chemical Affinity in terms of Electromotive Force. 383 

 Electro-zinc and Amalgamated Copper. 



During 1st 

 minute. 



During 8th 

 minute. 



During 15 th 

 minute. 



} +5-4 

 } +5-4 

 } +5-5 



+6-9 

 4-5-5 

 +4-3 



4-7-8 

 +5-8 

 4-5-1 



4-11-1 

 + 8-0 



-f 5-8 



Average of 

 all obser- 

 vations. 



1 4-5-4 



4-5-5 



+6-1 



4- 7-9 



General average = + 6 '2. 



Heat developed during Intermixture of Solutions of Zinc 

 {Copper or Cadmium) Sulphates or Chlorides of different 

 Strengths. 



160. The results above described show that when two solu- 

 tions of different strengths, but containing the same metallic 

 salt, are allowed to intermix by diffusion, plates of the metal 

 contained in the salt immersed in the two solutions respectively 

 acquire different potentials, the potential-difference set up with 

 any given pair of solutions being to some extent dependent on 

 the surface- characters of the plates employed, but being, cwteris 

 paribus, greater the greater the difference between the strengths 

 of the solutions, the plates immersed in the stronger solution 

 acquiring the higher potential. It is evident that if there is 

 a development of heat during intermixture of the solutions 

 used, the work done by a current developed on connecting 

 the plates by a conductor may reasonably be supposed to be 

 done in virtue of this heat-development, just as the work done 

 by an ordinary voltaic couple is done in virtue of the heat 

 developed by the chemical actions taking place therein. Ac- 

 cordingly it becomes of interest to determine precisely what 

 amounts of heat are actually generated during intermixture 

 in order to see what relationships hold between the electro- 

 motive forces actually generated and those corresponding to 

 the heat-developments. 



The required " heats of intermixture" are readily calcu- 

 lable from the values representing the "heats of dilution" 

 obtained by measuring the amounts of heat produced when 

 solutions of metallic salts are diluted to known extents by 

 means of water. If h 1} h 2 , h B respectively represent the heats 

 of dilution of gramme-molecules of the three solutions MS0 4 

 2«H 2 0, MS0 4 26H 2 0, and MS0 4 (a + 6)H ? to the same 

 further extent, then H, the heat produced by mixing a gramme- 

 molecule of the first solution with one of the second so as to 



