WET METHODS.
Strong hydrochloric acid is the best solvent for ores of manganese; but
where the proportion of dioxide (MnO_{2}) is required, the solution is
effected during the assay. The ore should be in a very fine state of
division before treatment with acids.
The separation of manganese from other metals is thus effected: Ignite,
in order to destroy any organic matter which may be present; dissolve in
hydrochloric acid, and evaporate to dryness, to separate silica. Take up
with hydrochloric acid, dilute, pass sulphuretted hydrogen, and filter.
Boil off the excess of gas, peroxidise the iron with a drop or two of
nitric acid, and separate the iron as basic acetate (as described under
_Iron_).[81] If the iron precipitate is bulky, it is dissolved in a
little hydrochloric acid, reprecipitated, and the filtrate added to the
original one. Neutralise with soda, and add bromine in excess; heat
gradually to boiling, allow to settle, and filter. The precipitate is
impure dioxide of manganese (containing alkalies and, possibly, cobalt
or nickel).
GRAVIMETRIC DETERMINATION.
Dissolve the precipitate in hydrochloric acid, and boil; add a slight
excess of carbonate of soda, warm, and filter. Wash with hot water, dry,
carefully ignite in an open Berlin crucible, and weigh. The substance is
the brown oxide (Mn_{3}O_{4}), and contains 72.
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