Chemical Affinity in terms of Electromotive Force. 199 



Effect of substituting Amalgamated Silver (fluid) for 

 Bright Silver. 



Maximum ... +'102 +'110 +'105 



Minimum ... +"092 +'095 +'092 



Range -010 -015 '013 



Average +'099 +'101 +-1025 



Considering the perceptibly wider ranges of variation in 

 these experiments than those usually observed in the zinc- 

 cadmium-copper cells previously described, it is evident that 

 the effect of varying the nature of the silver plate is sensibly 

 independent of the nature of the other metal. 



Sometimes, but not invariably, the amalgamated silver 

 plates became solid and crystalline (greenish yellow) on the 

 surface : this result was apparently brought about much more 

 rapidly when the silver was immersed in concentrated zinc 

 sulphate solution than under any other of the conditions ob- 

 taining in the various experiments. "When this change took 

 place the E.M.F. set up by opposing such a plate to zinc in 

 cells containing sulphates of zinc and silver was always inter- 

 mediate between that set up in the same fluids by plates of 

 bright silver and of fluid amalgamated silver. The average of 

 several comparisons was as follows : — 



Effect of substituting Amalgamated Silver (solid) for 

 Bright Silver. 



Maximum +'025 



Minimum +'014 



Eange -011 



Average +'021 



In this respect silver is analogous to cadmium when the 

 latter is opposed to zinc (§ 121) ; but the average amounts 

 of increase in E.M.F. due to fluid and solid amalgam are in 

 each instance considerably greater with silver than with cad- 

 mium (*099 and '021 for silver as compared with -043 and 

 •016 for cadmium). 



On substituting electro- for bright cadmium in the cadmium- 

 silver cells, identically the same average effect was observed 

 as in the cadmium-copper cells (§ 119), viz. an increase in the 

 E.M.F. of from -002 to '006, averaging -004 volt. Similarly, on 

 substituting amalgamated for electro-copper in the copper-silver 

 cells, practically the same numerical difference in the E.M.F. 

 was brought about as was formerly observed in the zinc- 

 copper cells (§ 107) and the cadmium-copper cells (§ 119), 

 but in the opposite direction, the E.M.F. being raised in the 



