124 On the Determination of Chemical Affinity. 
nitrate solutions is a considerable + number, as found in the 
chloride-cells. 
It hence follows that the H.M.F. actually set up in zinc- 
mercury, copper-mercury, and lead-mercury nitrate-cells is in 
excess of that corresponding with the difference between the 
heats of formation of the electrolytes in each case respectively, 
the excess amounts being +°297, +:°297—(—-039) = 4+ *336, 
and +:298—(—'179)=+°477 respectively. 
VI. Magnesium. 
193. Two sets of cells were examined containing bright 
magnesium (wire), opposed to amalgamated zinc and electro- 
cadmium respectively, in solutions of constant strength 
25 M(NO;), 100 H,O. The following values were obtained, 
the readings exhibiting the same kinds of fluctuations as 
those previously found with magnesium sulphate and chloride 
cells. 
Magnesium-Zinc. Magnesium-Oopper. 
Mia xa Nes ecto ictersne "570 1636 
AM itronbooqb tone payapeepodoodéae 503 1569 
PAWEL AMO nmaseneitoeesces ‘531 1-595 
Probable error ......... +:011 +:011 
These two sets of readings lead to sensibly the same values 
for the voltaic constant, which is negative (as with the sul- 
phate and chloride cells), since zine now acquires the higher 
potential. 
Zinc-magnesium . Spo ss “athe gt, eee em 
Copper-magnesium eee — 529 
Pere ae e066 : 
—— 
Mean... 2 == 530 
From Julius Thomsen’s figures, the heat of formation of 
magnesium-nitrate solution, *25 Mg(NO;), 100 H,O, is 
176480, whence Ey=—1°631. Hence the thermovoltaic 
constant 1s 
—°5380—(—1°630)= +1101, 
or positive toa great extent, as with the other magnesium-cells. 
[To be continued. | 
