208 



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



Fluid surrounding 



Zinc-sulphate solu- 



Zinc-sulphate solu- 



Zinc-sulphate solu- 



1 



the zinc plates. 



tion, sp. gr. 1 "42 



tion, sp. gr. 1*42. 



tion, sp. gr. 1*10 



Fluid surrounding 



} 





{ 



Copper sulpha! 

 sol., sp. gr. I'll 



the copper plates 





Nature of silver Electro-silver (cry- 



Solid crystallized Solid crystallized 



Electro-silver (cr 



plates. 



stalline. 



amalgam. 



amalgam. 



stalline). 



Eesistance, in 



] 









ohms, of column 

 of fluid between 



66-9 

 1-500 



76-0 

 1-511 



766 

 1-546 



710 



Maximum E.M.F. 



•401 



Current-density, 



Observed amounts of fall in Electromotive Force. 



in microamperes. 





20 







•012 



•005 



50 



•016 



•010 



•021 



•on 



100 



•025 



•018 



•026 



■019 



200 



•041 



•036 



•037 



030 



400 



•062 



•067 



•059 



•047 



600 



•080 



•097 



•077 



•063 



1000 



•116 



•144 



•112 





2000 



•209 



•258 



•177 





These numbers are represented graphically by the curves 

 marked respectively V., VI., VII., and VIII. in the figure. 



On trying experiments, like those described in § 110, to see 

 how far the falling-off in E.M.F. when a current is generated 

 could be due to the accumulation of zinc (cadmium or copper) 

 sulphate round the plate opposed to the silver, it was found 

 that the maximum possible effect due to this cause could not 

 exceed about '04 volt with zinc and cadmium, and "02 with 

 copper. These experiments, and others of a similar nature, 

 will be discussed in a future paper. 



On comparing the eight curves represented in the figure 

 with those previously described as obtained with various forms 

 of Daniell cell (Part V. § 105), it is noticeable, first, that the 

 curves obtained with the zinc-cadmium cells underlie all the 

 others (I., II., and III.); secondly, that the curve with the 

 cadmium-copper cell (IV.) is practically identical with one of 

 the Daniell-cell curves — indicating consequently that, whilst 

 the substitution of copper for cadmium in a zinc-cadmium 

 cell raises the position of the curve (i. e. increases the rate of 

 fall in E.M.F. according as the current-density increases), the 

 substitution of cadmium for zinc in a Daniell cell does not 

 materially alter the position of the curve ; thirdly, the curves 

 with the zinc-silver and copper-silver cells overlie all the 

 others, whilst the copper-silver curve (VIII.) is not widely 

 different from the zinc-silver curves (V., VI., and VII.) — 

 indicating that, whilst the substitution of silver for copper in a 



