Dry in the water-oven for an hour.
Brush the precipitate into a weighed dish, and weigh it. It is potassium
platino-chloride (K_{2}PtCl_{6}), and contains 16.03 per cent. of
potassium, or 30.56 per cent. of potassium chloride (KCl), which is
equivalent to 19.3 per cent. of potash (K_{2}O).
If the filter-paper is not free from precipitate, burn it and weigh
separately. The excess of weight over that of the ash will be due to
platinum and potassic chloride (Pt and 2KCl). This multiplied by 1.413
will give the weight of the potassic platino-chloride from which it was
formed. It must be added to the weight of the main precipitate.
The mixed alkaline chlorides obtained in the usual course of analysis
are treated in this manner; the quantity of platinum added must be about
three times as much as the mixed chlorides weigh.
VOLUMETRIC METHODS.
These are the same as with soda.
~Examination of Commercial Carbonate of Potash.~--The impurities to be
determined are moisture, silica, and insoluble matter, chlorine,
sulphuric oxide, and oxide of iron. These determinations are made in the
ways described under the examination of common salt.
The ~potassium~ is determined by converting it into chloride and
precipitating with platinum chloride, &c., as just described.
~Available Alkali.~--Weigh up 23.
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