Chemical Affinity in terras of Electromotive Force. 209 



Daniell cell largely raises the position of the curve, the effect 

 of substituting copper for zinc in a zinc-silver cell is very much 

 less marked. In other "words, the nature of the dissolved metal 

 affects the rate of decrease in E.M.F. with increasing current- 

 density much less than does the nature of the deposited metal ; 

 whilst the less the heat of formation of the salt of the latter that 

 is decomposed by the passage of the current, the more rapid 

 appears to be the rate of fall in the E.M.F. of the cell as the 

 current-density increases. As regards the first part of this 

 general conclusion, it is precisely what also results from the 

 majority of the previously described experiments on the effect 

 of halving the area of the dissolved plate, as compared with 

 that produced by halving the area of the plate on which metal 

 is deposited. The following experiments with cells containing 

 silver plates also give the same general results. 



Effect of Varying the Size of one of the Plates in Cells con- 

 taining Silver as one of the Metals, the other Plate remaining 

 unaltered. 



131. By operating in the way described in § 115, the fol- 

 lowing results were obtained in four sets of observations with 

 zinc-silver and copper-silver cells, showing that, in all cases, 

 halving the area of the silver plate produces a sensibly greater 

 decrease in the E.M.F. set up with a constant rate of current- 

 flow than is effected by halving the area of the plate opposed 

 to the silver. 



Zi>-c-Silver. 



CoPPER-SlLTEE. 



Amalgamated .^^mated , Amalgamated 



.-, . . 6 , . zinc — crystalline zinc — crystalline 



Current- zinc — electro- , „r ., 



density, silver. amalgamated 



in micro- 



silver. 



crystalline Electro-copper- 

 amalgamated '■ electro-silver, 

 silver. 



amperes 



Effect of halving Effect of halvingJEffect of halvingEffect of halving 





area of area of area of area of 



Zinc. J Silver, j Zinc. 



Silver. • Zinc. 



| 



Silver. Copper. 



Silver. 



1000 



1 -009 I -Oil -007 



026 ' -008 



■019 -004 



•011 



2000 



•012 -024 1 '009 



•045 ; -012 



•036 -010 



•023 



3000 



•014 -038 -Oil 



•059 i -015 



■047 -017 



•028 



5000 



•016 -064 -020 



•103 1 -021 



■070 



8000 



i -028 -093 -038 



•186 ' -029 



•122 



10000 





I -034 



151 



Summary of Results. 

 132. The foregoing results may be thus summarized : — 

 Cells containing zinc and cadmium or cadmium and copper 

 Phil Mag. S. 5. Vol. 14. No. 87. Sept. 1882. P 



