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



there does not seem to be any evident reason why the same 

 state of things should not exist in the case of cells containing 

 silver plates. Thomsen's thermo-chemical valuations, how- 

 ever, indicate that the electromotive forces corresponding to 

 the three equations 



ZnS0 4 , 

 CdS0 4 , 



Zn 



+ Ag 2 S0 4 = 2Ag 



+ 



Cd 



+ Ag 2 S0 4 = 2Ag 



+ 



Cu 



+ Ag 4 S0 4 = 2Ag 



+ 



CuS0 4 , 

 are considerably higher than those actually observed and 



Zinc-silver. 

 Zn, O, S0 3 aq. = 106090 

 Ag 2 , 0, SO, aq. = 20390 



Diff., per gramme- 1 i9R m 



equivalent f i26M 



Corresponding to volt 1*890 



Cadmium-silver. 

 Cd, O, S0 3 aq. = 89500 

 Ag 2 , O, S0 3 aq. = 20390 



69110 



34555 

 1-524 



Copper-silver. 

 Cu, O, S0 3 aq. = 55960 

 Ag a , O, S0 3 aq. = 20390 



35570 



17785 



•784 



In each of the three cases the calculated E.M.F. is from *34 

 to *37 volt above the observed values when silver plates not 

 amalgamated are used, indicating that even when only infi- 

 nitesimal currents are generated a large amount of energy is 

 nonadjuvant. It will be shown in a future paper that this 

 behaviour is more or less marked in other kinds of cells con- 

 taining silver plates and silver compounds, although the mini- 

 mum amount of nonadjuvancy observed in any given case is 

 variable with the nature of the saline compounds in the cell *. 

 In order to see whether the rise in E.M.F. produced by amalga- 

 mating the silver plate is due simply to the heat of formation of 

 silver sulphate being less when the silver is dissolved in mer- 

 cury than when it is free, determinations of the heat of solution 

 of silver (precipitated from the nitrate by copper, crystalline) 

 were made. It was found a little difficult to get every trace 

 of silver used dissolved in mercury when 20 grams of silver 

 and 600 of mercury were employed, even though the surface 

 of the former was washed with dilute nitric acid. With 

 smaller amounts of mercury only incomplete solution was 



* Raoult lias already obtained numbers {Ann. Chim. et Phys. [4] ii. 

 317 and iv. 392) indicating tbat tbe "galvanic heat" (§ 17) of a cell con- 

 taining copper, silver, and the nitrates of their metals is sensibly below the 

 value due to the net chemical action taking place. These and other similar 

 observations will be discussed in a future paper. 



