DETERMINATION OF IRON.
For this estimation, solutions of the chloride as well as those of the
sulphate (ammonium, iron, alum) may be used in the manner previously
described. The electrolysis is best effected in the presence of a
sufficient quantity of ammonium oxalate; no separation of any iron
compound takes place. The iron is deposited in the form of a bright,
steel gray, firmly-adhering mass on the platinum dish. The iron may be
exposed to the air for several days without any noticeable oxidation
taking place.
DETERMINATION OF ZINC.
Zinc may be separated from a solution of the double salt fully as easily
and rapidly as the previously mentioned metals were. The reduced zinc
has a dark gray color, and adheres very firmly to the electrode. The
separated metal is dissolved by using dilute acids and heating. It is
only removed with difficulty, and generally leaves a dark coating on the
dish, which is separated by repeated ignitions and treatment with acid.
DETERMINATION OF MANGANESE.
It is already known that manganese may be separated as the peroxide from
its nitric acid solution. We find, however, that the precipitation is
only completely effected when the quantity present is small; the amount
of nitric acid must also be slight, and it is necessary to wash the dish
without interrupting the current.
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