Chemical Affinity in terms of Electromotive Force. 199 
Zinc-Silver. | Copper-Silver. 
PPD nc ccascuc es - 1501 404 
J 1°486 389 
PPE RRO 205 vse van 1-490 397 
Probable error ......... +0024 +-0021 
From these figures the following concordant valuations 
are deduced for the voltaic constant of electro-silver immersed 
in saturated silver-acetate solution :— 
Zinc-silver . . bia eA OO 
*Zinc-copper ee inc, . f 108 091 =1°488 
Weare soo = YES O9 
The heat of formation of silver acetate not being known, 
the value of Ey cannot be calculated. Admitting that this 
value is the same as in the case of nitrate cells of the same 
molecular solution-strength, viz. near to 1°890, the value of 
E—Eg would be —:°401 ; whence it is at least evident that 
the thermovoltaic constant for electro-silver in acetate solution 
is a large negative quantity, comparable in magnitude with 
the corresponding constants found for sulphate and nitrate 
solutions. 
It is noteworthy that the E.M.F. of lead-silver-acetate cells 
deduced from the foregoing experiments is 1:489 —°607 = -882 
volt. On setting up a number of such cells, however, fluctu- 
ating and inconstant figures were obtained, usually averaging 
during the first half-hour after setting up vale from ‘02 to 
-12 volt below this amount; these cells therefore resembled 
in this respect the lead-copper- chloride cells above described 
(§ 184). 
HK. Voltaic and Thermovoltaic Constants of Metals immersed 
in Solutions of their Bromides. 
197. The experiments above described indicate that the 
sign and magnitude of the thermovoltaic constant for a given 
metal does not vary widely, whether the metal be in contact 
with its sulphate, nitrate, or acetate, whereas the values obtained 
under these circumstances are often considerably different from 
those obtained when in contact with its chloride. In order to 
* Assumed to be the same as the value found for solution-strength 
25 M(C,H,0,), 100 H,0. 
