The precipitate is allowed to settle for a
few minutes, decanted through a filter, and washed with hot water; and,
afterwards, dried, transferred to a porcelain crucible, and strongly
ignited in the muffle or over the blowpipe for a few minutes. It is then
cooled, and weighed as sulphate of baryta (BaSO_{4}). It contains 65.67
per cent. of baryta (BaO).
In determining the baryta in minerals which are soluble in acid, it is
precipitated direct from the hydrochloric acid solution (nearly
neutralised with ammonia) by means of sulphuric acid. The precipitated
baric sulphate is digested with a solution of ammonic acetate; and
filtered, washed, ignited, and weighed.
VOLUMETRIC DETERMINATION.
The principle and mode of working of this is the same as that given
under the Sulphur Assay; but using a standard solution of sulphuric acid
instead of one of barium chloride. The standard solution of sulphuric
acid is made to contain 32.02 grams of sulphuric acid (H_{2}SO_{4}), or
an equivalent of a soluble alkaline sulphate, per litre. 100 c.c. will
be equal to 5 grams of baryta.
Five grams of the substance are taken, and the baryta they contain
converted into carbonate (if necessary). The carbonate is dissolved in
dilute hydrochloric acid. Ten grams of sodium acetate are added, and the
solution, diluted to 500 c.
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