198 Dr. C. R. A. Wright on the Determination of 



gam is used the effect of halving the area of the cadmium 

 plate hecomes sensibly less than the effect of halving that of 

 the zinc plate. 



Current, 

 in micro- 

 amperes. 



Cadmium- Copper. I Zinc-Cadmium. 



Bright cadmium — 

 Electro-copper. 



Amalgamated zinc — 

 Electro-cadmium. 



Amalgamated zinc — 



Fluid amalgamated 



cadmium. 



Amalgamated zinc — 



Solid amalgamated 



cadmium. 



Effect of halving 

 area of 



Effect of halving 

 area of 



Effect of halving 

 area of 



Effect of halving 

 area of 



Cadmium. 



Copper. 



Zinc. 



Cadmium. 



Zinc. 



Cadmium. 



Zinc. 



Cadmium. 



1000 



2000 



5000 



10000 



20000 



•005 

 •010 

 •016 

 •020 

 •039 



•008 

 •013 

 •022 

 •031 

 •051 



•004 

 •007 

 •012 

 •020 

 •030 



•005 

 •008 

 •013 

 •025 

 •040 



•005 

 •009 

 •018 

 •027 

 035 



•003 

 •005 



•on 



015 

 •022 



•005 



■on 



•021 

 026 

 •032 



•006 

 •015 

 019 

 •025 

 032 



II. Cells containing Silver as one of the Metals, the Salts used 

 being Sulphates. 



125. Three sets of cells, after Eaoult's pattern, were con- 

 structed, containing respectively zinc-silver, cadmium-silver, 

 and copper-silver couples, the respective plates being immersed 

 in solutions of silver sulphate saturated at ordinary tempera- 

 tures, and of copper and zinc sulphate of strengths molecularly 

 equal thereto (the silver solution contained 7*25 grammes of 

 Ag 2 S0 4 per litre, and had a sp. gr. near to 1*0067); the com- 

 position was uniformly MSO 4 2360H 2 O. 



On making series of determinations of the E.M.F.'s of these 

 cells, the following results were arrived at as the effects of 

 varying the nature of the silver surfaces, deduced from the 

 average values of a large number of observations (upwards of 

 50 sets of comparisons). 



Effect of substituting Electro-Silver for Bright Silver. 



Zinc opposed. Cadmium opposed. Copper opposed. 

 Maximum ... +-017 +'015 +-012 



Minimum ... +-003 +-005 +-004 



Range -014 -010 -008 



Average +-008 4- -009 4- -0075 



