Chemical Affinity in terms of Electromotive Force. 117 
throughout. As with the magnesium cells, the values fluc- 
tuated considerably, so that the final averages had much larger 
probable errors than usual. 
Zinc-Aluminium. Algcainice Onan 
PATHE cscs. <2 00 — 239 +:091 
Riraiaige ~ +. -.5.......: —*352 — ‘022 
DEVORE cade vencsnsosoess —°280 +:050 
Probable error ......... | +011 +011 
Hach of these averages leads to the same value, +°280, for 
this voltaic constant. 
mere Ft eile a kee. pw po anerhe280 
Zinc-cadmium — Aluminium-cadmium | i rh \ +. +280 
Mean) y «40-nth B22 80 
This constant being of + sign, since aluminium was found to 
acquire the higher and zinc the lower potential (as with the 
sulphate-cells, § 178); whilst, on the other hand, the readings 
observed with the zinc-aluminium cells are marked — above 
because this cell is another example of the case where 
Ey+h,—k, has a negative value, the current actually set up 
passing in the direction opposite to that predicable from the 
heats of formation of the electrolytes. 
Julius Thomsen finds Alz, Cl, aq.=158550, whence Hy= 
—1:008; consequently 
H—Hy= +'280—(—1:008)= +1:288; 
2. é. the thermovoltaic constant for bright aluminium in contact 
with its chloride solution is a large positive quantity, as with 
the sulphate. 
VILL. Lron. 
187. Cells were set up containing plates of nearly pure 
sheet-iron (bright) opposed to amalgamated zinc and electro- 
cadmium in solution of constant strength -25 MCI, 100H, O; 
also to electro-silver immersed in a magma of precipitated 
silver-chloride suspended in zinc-chloride solution of this same 
strength. The following numbers were obtained as the 
average readings during the first half-hour after setting up. 
