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



those corresponding with the thermal values by amounts ma- 

 terially outside the experimental errors. As with the copper- 

 cadmium cells, however, the observed difference in E.M.F. 

 between electro-cadmium (crystalline) and amalgamated cad- 

 mium (liquid) is notably greater than that corresponding with 

 the heat of solution of precipitated crystalline cadmium in 

 mercury, being '407 — "3595 = '0475 as compared with "0135 

 volt. 



Voltcis Law of Summation of Electromotive Forces. 



122. The foregoing experiments clearly show that, as far as 

 cells containing zinc, cadmium, and copper plates are concerned, 

 Volta's law of summation holds, at any rate when the plates 

 are immersed in solutions of their respective sulphates, the 

 solutions being of equal molecular strength ; that is, the sum 

 of the electromotive forces generated with a given pair of zinc 

 and cadmium plates, and with that same cadmium plate and a 

 given copper plate, is equal to the E.M.F. generated with the 

 given zinc and copper plates; or, otherwise, 



/Zn /Cd /Zn 



\Cd + \Cu ~ \Cu 



where the symbol -! pj represents the E.M.F. generated with 



a given kind of zinc plate opposed to a given kind of cadmium 

 plate, each plate being immersed in a solution of its sulphate 

 of constant molecular strength. 



Thus the average results for Daniell cells quoted in PartV. 

 and the above figures give the following comparisons: — 



Nature of Plate-surfaces. 



Electromotive Force 

 developed. 



Normal 

 Daniell. 



Zinc. 



Cadmium. 



Copper. 



Zinc- 

 Cadmium. 



Cadmium- 

 copper. 



Sum. 



Amalgamated. 

 ■ « 



Electro. 

 Brigbt. 

 Amalgamated 



(fluid). 



Amalgamated 



(solid). 



Electro. 



•3595 



•364 



•407 



•380 



•7525 

 •7485 

 •707 



•7335 



Mean ... 



1112 



1-1125 



1-114 



1-1135 



Amalga- 

 mated zinc 

 and electro- 

 copperllll 

 to 1116, 

 averaging 

 1-114. 



1-1130 



Amalgamated. 



Electro. 



Brigbt, 

 Amalgamated 



(fluid). 

 Amalgamated 



(solid). 



Amalgamated. 



•3595 



•364 



•407 



•380 



•7515 

 •7475 

 •706 



•7325 



Mean ... 



1-111 



11115 



1113 



11125 



Amalga- 

 mated zinc 

 and amalga- 

 mated cop- 

 per 1110 

 to 1-115, 

 averaging 

 1113. 



11120 



