Chemical Affinity in terms of Electromotive Force. 107 
on each side. The probable error is in all cases below 
+°003. 
The thermovoltaic constants for electro-silver thus immersed 
are calculated from the heat of displacement of silver from 
silver chloride by zine forming mZnCl, 100 H,O, viz. :— 
112840 —58760—h=54080—A; 
where 
112840= Zn, Cl,, aq. (m='25), 
58760=Ag,, Cl,, 
h =heat of dilution of mZnCl, 100 H,O to 
°25 ZnCl, 100 H,O (§ 160). 
| m. h, | 54080—%.| Eq. | og E—Eg. 
"25 0 54080 17192 1-080 — 112 
5 400 53680 1184 1:068 —'116 
1-0 1250 52830 1-165 1-049 —'116 
30 3800 50280 1-109 | 1:026 —°083 
| 6-0 | 5300 | 48780 | 1076 | 1-014 —-062 
Hence it results that both the voltaic and thermovoltaic 
constants diminish in value as the solutions become stronger; 
and that whilst the thermovoltaic value of silver in contact 
with silver chloride (suspended in zinc-chloride solution) is 
negative in sign as with the sulphate, its numerical value is 
considerably less than in that instance. 
Some cells were next examined, containing on the one side 
electro-silver plates immersed in a magma of silver chloride 
suspended in zinc-chloride solution, and on the other side 
electro-copper or electro-cadmium in their respective chloride 
solutions, the solution-strength being *25MC1,100H,0 through- 
out. The following values were obtained, sensibly agreeing 
with the value —*112 for the thermovoltaic constant above 
obtained with zinc-silver-chloride cells for this molecular 
strength. It is to be noticed that the values of Hy with these 
two kinds of cells respectively are °827 and °154, correspond- 
ing with the heat-evolutions 96250—58760=37490, and 
65750 —58760=6990. In the former case Hy+(k,—4,) is 
positive in sign, in the latter case negative ; so that the copper- 
silver cells are analogous to the zinc-cadmium-sulphate and 
12 
