Chemical Affinity in terms of Electromotive Force. 105 
Whence the thermovoltaic constant for electro-copper in con- 
tact with cuprous chloride suspended in cupric-chloride solu- 
tion of strength :25 CuCl, 100 H,O is 1:099—1:038= +:061. 
The experiments detailed in § 174 indicated that when lead- 
sulphate was suspended in cadmium-sulphate solution a higher 
H.M.F. was observed, cvteris paribus, with zinc-lead-sulphate 
cells than when zinc-sulphate solution was employed ; from 
which it would seem probable that, if cuprous chloride be sus- 
pended in zine-, cadmium-, and copper-chloride solutions in 
three zinc-copper-chloride cells otherwise alike, the E.M.F. 
will be smallest in the first case and greatest in the last. This 
is in fact the case. The following values were obtained in a 
number of experiments on the point, indicating that the use 
of cadmium-chloride solution gives values intermediate be- 
tween those obtained with zinc- and copper-chloride solutions 
respectively. The solutions were in all cases of strength 
‘25 MCI, 100 HO. 
! 
Cu,Cl, suspended in | Cu,Cl, suspended in 
zine chloride. | cadmium chloride. 
| ee | 
| Maximum E.M-F. ... 993 | 1-011 
| Minimum ,,... 980 993 
| Average “- ae ‘988 1:001 
| Probable error ...... +°0028 + -0035 
| | 
Hence the thermovoltaic constants for electro-copper in 
contact with cuprous chloride suspended in zinc- or cadmium- 
chloride solutions of strength °25 MCI, 100 H,O are negative 
in sign, Viz. :— 
Suspended in zinc-chloride solution . *988—1:038=—-050 
Fe cadmium ,, i . 1:001 —1°088= —:037 
Tt should hence result that cells set up with electro-cadmium 
immersed in ‘25 CdCl, 100 H,O on the one side, and on the 
other side electro-copper immersed in a magma of cuprous 
chloride suspended in zine-chloride solution of the same 
strength, will have an H.M.F. of 672 —-050 —(— 036) =°658 ; 
and, similarly, that analogous cells set up with cuprous chlo- 
ride suspended in cadmium-chloride solution will have an 
E.M.F. of :672—:037—(—:‘036)=°671 (672 being the 
H.M.F. corresponding with the heat of displacement of copper 
Phil. Mag. 8. 5. Vol. 19. No. 117. Feb. 1885. I 
