The _hot_
solution, when exposed to the action of the current, deposits the cobalt
as a closely adhering gray film. By the aid of two Bunsen's elements,
0.2 gramme cobalt can be separated in an hour's time. When the reduction
has been completed, and this is best determined by testing a small
sample (removed by a pipette) with ammonium sulphide, the positive
electrode[1] is removed from the solution, and the liquid poured off.
The dish is immediately rinsed several times with water, and the excess
of water removed at first with alcohol, and then with absolute ether.
The cobalt in the dish is dried in the air bath at 100 deg. C., and in the
course of a few minutes a constant weight is obtained.
[Footnote 1: A piece of platinum foil, 4.5 cm. in diameter, is used
for the positive electrode, and a deep platinum dish as the negative
electrode.--_Vide_ "Classen's Quantitative Analysis," 3d Edition, p.
46.]
DETERMINATION OF NICKEL.
This process is precisely identical with the previously described method
for cobalt. The ammonium oxalate is added in excess to the solution,
which is then heated, and four more grammes of the solid salt added. The
separation of the nickel is as rapid as that of the cobalt. The nickel
is precipitated as a gray, compact mass, tightly adhering to the
electrode.
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