Chemical Affinity in terms of Electromotive Force. 27 
VI. Magnesium. 
177. Two sets of cells were examined containing bright 
magnesium (wire) immersed in magnesium-sulphate solution 
opposed to amalgamated zinc and electro-copper in their sul- 
phate solutions respectively, the solution-strength being 1:0 
MSO, 100 H,0 throughout. 
The galvanometer-readings showed a slight increase in each 
case as time elapsed after first setting up; the following figures 
represent the mean readings of each cell during the first half 
hour after setting up, reduced to volts :— 
Magnesium-Zine. | Magnesium-Copper. 
= —— 
Maximum mean reading ... “740 1-854 
Minimum ,, ‘5 oy fale 1-827 
Average ,, a ai "724 1:840 
IPEODAME CLLOL «2... ccasceoeee. +:0042 +:0041 
Hence the following valuations of the voltaic constant result; 
these values are negative, since zinc acquires the higher, and 
magnesium the lower potential :— 
Manis Miaemesiam Cell 025. .c6c.s cei ecececsscscsetessese —°724 
Magnesium-Copper + Zinc-Copper... ‘ a —-796 
—— 
Mean = —°725 
Julius Thomsen finds Mg, O, SO; aq. =180180 for -25 
MgSO, 100 H,O, whence for this strength Hyg=—1°634. 
Moreover, he finds practically no difference between the heats 
of dilution of magnesium and zinc-sulphate solutions of strength 
1:0 MSO, 100 H,0, so for this strength also Hy sensibly 
=—1'634. Hence the thermovoltaic constant for bright 
magnesium in 1:0 MgSO, 100 H,0 is 
—°725 —(—1°634)= +:909. 
VII. Aluminium. 
178. Two sets of cells were examined, containing bright 
aluminium plates opposed to amalgamated zine and electro- 
copper respectively, immersed in sulphate solutions of strength 
‘-5 MSO, 100 H,O (instead of using aluminium sulphate, pure 
-potash alum was employed, the potassium sulphate present 
