196 



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



of 2*5 and 5*0 square centimetres). The results were similar 

 in character to those obtained with the Daniell cells, no 

 appreciable falling-off in E.M.F. occurring with a current- 

 density of less than some 5 to 10 microamperes per square 

 centimetre of plate-surface, but very considerable amounts 

 being observed with stronger currents. 



Thus the following table exhibits the values obtained in four 

 experiments — the first three with zinc-cadmium plates, the 

 fourth with cadmium-copper plates, solutions of sulphates of 

 the respective metals employed being used throughout: — 





Amalgamated. 

 Electro [ 



Amalgamated. 



Amalgamated. 



Fluid amalgam. 



Amalgamated. 

 Amalgamated. 

 Solid amalgam. 



| Bright. 

 Electro. 



Cadmium plates . . . 

 Copperplates 







Sp. gr. of zinc sul- "1 

 phate solution... J 



Sp. gr. of cadmium 1 

 sulphate solution J 



Sp. gr. of copper 1 

 sulphate solution J 



117 

 1-25 



1-17 

 1-32 



117 

 1-32 



1-32 

 117 



Resistance of cell, "1 



in ohms J 



MaximumE.M.F., 1 



95 

 •366 



105 



•418 



110 

 •395 



7-4 

 •741 





Current-density, in 

 microamperes per 

 square centimetre. 



Observed amounts of Fall in E.M.F. 



10 



20 



40 



100 



200 



400 



1000 



2000 



4000 









 •001 

 •002 

 •004 

 •012 

 •026 

 049 

 •088 





 •001 

 •002 

 •004 

 •007 

 •013 

 •030 

 •059 

 •099 





 •001 

 •003 

 •007 

 Oil 

 •017 

 •030 

 •055 

 •094 



•001 

 •004 

 •008 

 •014 

 •020 

 030 

 •049 

 •077 

 128 



The values are represented graphically by the curves marked 

 I., II., III., and IV. respectively in the annexed figure. 



A number of experiments were made with cells containing 

 solutions not of equal molecular strengths (like those described 

 in § 110), for the purpose of rinding how much of the dimi- 

 nutions observed with the larger current-densities might pos- 

 sibly be due to the strengthening of the solution round the 

 dissolved plate, and the weakening of the liquid round the 

 other plate, which takes place whilst the cell is in action. 

 The general result was that the maximum possible diminution 

 due to these causes could not exceed about *04 volt. The 



