This reaction
proceeds according to the formula,
3MnCO_{3} + 2KMnO_{4} + H_{2}O = 2KHCO_{3} + 5MnO_{2} + CO_{2}
and it may be employed for estimating the content of manganese by
titration. As follows from the formula two equivalents of permanganate
of potash are required for the titration of three equivalents of
protoxide of manganese, which has also been established by direct
experiments, as well as that the escape of carbonic acid indicated
by the formula actually takes place. The precipitate of manganese is
dissolved either in water to which 0.5 per cent. of hydrochloric acid
has been added, or in boiling nitric acid. When manganese occurs along
with iron, which in general is the case, we must take care that the iron
in the solution is in the state of peroxide, which is precipitated on
the addition of the bicarbonate of soda, and is allowed to remain as a
precipitate, because it does not affect the titration injuriously. The
removal of this precipitate by filtering would be more loss than gain,
partly because there would be a risk of losing manganese in this way,
partly because the precipitate of manganese, which occurs immediately on
the addition of the chameleon solution, proceeds both more rapidly and
with greater completeness in the presence of the iron precipitate than
otherwise.
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