Chemical Affinity in terms of Electromotive Force. 285 



Effect of increasing the strength of the Copper-sulphate solu- 

 tion relatively to that of the Zinc-sulphate. 



1-010 

 1-010 



1050 

 1-090 



1-090 { 

 #1-176 [ 

 •1-176 { 

 #1-175 { 



Electro. 

 Bright. 



Electro. 

 Bright. 



Electro. 

 Bright. 



Electro. 

 Bright. 



1-129 

 1-135 



1-132 



1-141 



1-126 

 1-133 



1-123 



1-128 



1-114 

 1-120 



1-114 

 1-120 



1-114 

 1-120 



1-114 

 1-120 



■015 

 ■015 



•oso =0-188 



•if=-ioo 



:s=-ioo 



•015 



•018 

 •021 



•0195 



•012 

 •013 



•0125 



•009 

 •008 



•0085 



It is evident from these figures that the accumulation 

 round the zinc plate of zinc sulphate, and the exhaustion of 

 the copper sulphate in the solution round the copper plate, 

 even if carried out to the utmost possible extent, could not 

 diminish the E.M.F. of a Daniell cell by more than -03 to -04 

 volt; Avhilst it is hardly probable, even with tolerably rapid 

 currents, that the accumulation would suffice to diminish 

 the E.M.F. by more than half that amount — a diminution 

 almost negligible in comparison with the much larger amounts, 

 0'1 volt and upwards, found above to be due to this cause of 

 diminution and non-adjuvancy jointly. 



It is noticeable in passing that the above figures show that 

 when two solutions of zinc and copper sulphates interdiffuse, 

 the E.M.F. set up (like that produced by the interdiffusion of 

 two zinc-sulphate, or of two copper-sulphate solutions, as studied 

 by Moser) is of such a character that the stronger solution 

 acquires the higher potential; the actual value of the E.M.F. 

 developed also is less for a given difference in specific gravity the 

 stronger the sohdions, and, so far as the two sets of results can 

 be compared, agrees fairly with the values deducible from 

 Moser' s experiments — indicating that the difference between 



the E.M.F. set up when two different solutions of | zmc 



sulphate diffuse into a constant C ° ^c !" sm P nate solution is 



substantially the same as the E.M.F. set up when these two 



different copper f sulphate solutions diffuse into each other. 



* Solution almost saturated at ordinary temperatures. 



