If the manganese is converted into
the soluble double salt, prepared by adding an excess of potassium, and
submitted to the electric current, the whole of the manganese will be
deposited at the positive electrode. When ammonium oxalate is used, the
complete precipitation does not take place. As the separated peroxide
does not adhere firmly to the electrode, it is necessary to filter it
and convert it, by ignition, into the trimangano-tetroxide (Mn_3O_4).
DETERMINATION OF BISMUTH.
This separation presents considerable difficulty, because the metal
is not precipitated as a compact mass on the platinum. The bismuth is
always obtained in the same form, no matter whether it is precipitated
from an acid solution, or from the double ammonium oxalate, or, finally,
from a solution to which potassium tartrate has been added. As large a
surface as possible must be used, and the dish piled to the rim; then,
if the quantity of bismuth is small, the washing with water, alcohol,
and ether may be effected without any loss of the element. If small
quantities of the metal separate from the dish, they must be collected
on a tared filter, and determined separately. In our experiments, an
excess of ammonium oxalate was added to a nitric acid solution of
bismuth. During the electrolytic decomposition, a separation of the
peroxide was observed at the positive electrode, which, however, slowly
disappeared.
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