Chemical Affinity in terms of Electromotive Force. 197 



details of these experiments and of others allied thereto will 

 be discussed in a future paper. 



1000 2000 3000 4000 



Microamp feres per square centimetre. 



Effect of varying the Size of one of the Plates, the other 

 remaining constant. 

 124. The experiments described in Part V. (§ 115) were 

 repeated with various cells containing copper-cadmium or 

 zinc-cadmium plates instead of zinc-copper ones. The follow- 

 ing values obtained in four such experiments illustrate the 

 results obtained, indicating that the effect of halving the area 

 of the plate on which metal is deposited is, as "with the Daniell 

 cells, greater than the effect of halving the area of the dissolved 

 plate, when the former plate is not mercurialized*. The zinc- 

 cadmium cells, however, differ from ordinary Daniell cells in 

 this respect — that, whilst amalgamating the copper plate of a 

 Daniell cell does not materially alter the relative effect of 

 halving its area, amalgamating the cadmium plate of a zinc- 

 cadmium cell greatly diminishes the relative effect of halving 

 its area, in such sort that, when solid crystalline amalgam is 

 used, the effect of halving the area of the cadmium plates, 

 instead of exceeding, becomes sensibly equal to the effect of 

 halving the area of the zinc plate, whilst when liquid amal- 



* It is noteworthy in this connexion, that when nearly pure wrought- 

 iron plates, immersed in ferrous sulphate solution, replace the zinc plates 

 and zinc sulphate solution of normal Daniell cells, the effect of halving the 

 area of the iron plates sometimes exceeds that produced hy halving the 

 area of the copper plates 



