It is
calculated to MnO. It may contain, and should be tested for oxide of
zinc, which, if present, must be deducted. If the dish becomes stained
during evaporation, take up with a few drops of hydrochloric and
sulphurous acids, evaporate, and then treat with carbonate of soda.
~Lime, &c.~--The filtrate from the manganese sulphide is boiled, and
without cooling, treated with ammonium oxalate in solution, which also
should be heated to boiling. The liquid is filtered off and reserved for
magnesia. The precipitate is dissolved in very little hydrochloric acid
and reprecipitated by adding ammonium oxalate and ammonia to the boiling
solution. The filtrate and washings from this are reserved for magnesia.
The precipitate is either dissolved in dilute sulphuric and titrated
with permanganate of potash as described under Lime (p. 322); or it is
ignited and weighed as oxide. In this last case it may be examined for
barium and strontium, the former of which will rarely be present.
~Magnesia.~--The filtrate from the first lime precipitate is treated
with sodium phosphate and ammonia, and allowed to stand overnight. It is
then filtered. The precipitate is dissolved in hydrochloric acid; the
solution is filtered into the beaker containing the solution from the
second lime precipitate. Ammonia and sodium phosphate are again added,
and the precipitate, after standing, is filtered off, washed with water
containing ammonia; it is then dried, ignited and weighed as magnesium
pyrophosphate.
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