Chemical Affinity in terms of Electromotive Force. 1138 
Zinc-Mercury. | Cadmium-Mercury. 
Maximum #.M.F., observed...... 1-144 815 
Minimum se, 2) Were 1-137 °808 
Average om RRM Th wats os 1140 "812 
PREREADIGIOETOR icocccccaesncceseeses + :0013 +0014 
From these figures the following values result as the thermo- 
voltaic constant for mercury in contact with calomel suspended 
in ‘25 CdCl, 100H O, :— 
E. Eu. E—Eg. 
Zine-mercury ... . 1°140 668 +°472 
Cadmium-mercury . ae 1°142 668 + °474 
Wear <=) 'i-T4t +°473 
From the values of the heats of formation of silver chloride 
and mercurous chloride respectively, it might, a priori, be 
expected that an H.M.F. of +°525 should result (correspond- 
ing with 82550—58760=23790 gramme-degrees) in silver- 
mercury-chloride cells, silver acquiring the higher potential. 
On the other hand, whether the silver chloride be suspended 
in zine or cadmium-chloride solutions, and whether the mer- 
curous chloride be similarly suspended, in all four cases the 
value of ki—k, is not only negative, but is numerically 
greater than Hy=*525; so that, in fine, the current flows in 
the opposite direction to that @ priors predicable, the mercury 
acquiring the higher potential. Then the H.M.F. of the four 
kinds of silver-mercury-chloride cells are as follows :— 
Calculated from formula E=E,,+4,—4,. Ghsetead: | 
S| 
AgCl Hg, Ol, Maxi- | Mini-| Ave- | 
suspended } suspended mum, | mum.| rage. | 
in ZnCl, ...| in ZnCl, ...| *525-+(—"112)—-458= —-045 |—-040|—-051 | —-046 | 
Ditto ...|in CdCl, ...} *525+(—-112)—-473= —-060 |—-055 |—-062|—-058 | 
in CaCl, ...|in ZnCl, ...| 5254+(—-103)—458=—-036 |—-034|—-041 |—-038 | 
Ditto ...|in CdCl,...| -525+(—-103)—-473 = —-051 |—-047 |—-053 |—-050 | 
Considerably larger negative values were obtained with 
analogous cells in which mercurous chloride was suspended 
in mercuric-chloride solution instead of zine or cadmium- 
chloride solution, as would naturally be inferred from the 
larger values of the thermovoltaic constant in this case. The 
