Chemical Affinity in terms of Electromotive Force. 301 



Difference of Potential set up between Solutions of 5'0CdSO 4 

 100 H 2 and nCdS0 4 100 H 2 0. 





Amalgamated 



cadmium 



fluid. 



Electro- 

 cadmium. 



Bright 

 cadmium. 



Amalgamated 



cadmium, 



crystalline. 



tt=50 





 101 

 151 

 20-9 

 256 

 304 







99 

 139 

 19-2 

 23-8 

 28-5 







10-5 

 138 

 18-4 

 22-4 

 25-8 







71 

 10-6 

 15-8 

 183 

 20-6 



3-0 



2-0.. 



10 



05 



0-235 



Difference of Potential set up between Solutions of 2 - 0CdSO 4 

 100 H 2 and «CdS0 4 100H 2 O. 





Amalgamated 



cadmium, 



fluid. 



Electro- 

 cadmium. 



Bright 

 cadmium. 



Amalgamated 

 cadmium, 

 crystalline. 



n=2i) 







5-8 

 10-5 

 15-3 







53 



99 



14-6 







4-6 



8-6 



12-0 





 52 



77 

 106 



= 10 



= -5 



= -235 



Curves 1 to 4 (figs. 3 and 4) represent these sets of values 

 respectively : it is noticeable that the curve obtained with 

 crystalline amalgam plate -surfaces underlies the others. 



On contrasting the first of these tables with that similarly 

 obtained with zinc sulphate (§ 153), and the second with that 

 obtained with copper sulphate (§ 154), it is evident that with 

 certain kinds of plates the effect of an increase in strength of 

 solutions (both being always of equal strength) is to produce 

 an increase in E.M.F. in zinc-cadmium-sulphate cells or 

 cadmium-copper-sulphate cells ; and with other kinds of plates 

 to produce a decrease : i. e. the values of a and b in the 

 formula 



E = e + a— b 



are such that in certain cases a > b and in others b > a, precisely 

 as is found with zinc-copper-sulphate cells. It is noticeable 

 that even in the most extreme cases the difference between a 

 and b is never very great, rarely exceeding a few millivolts. 



[To be continued.] 



