The latter method is hardly practicable, and
I never have time to use it, as the titration and all together yields a
value of 99.80 in most cases, if accurately executed.
From the bases of groups V. and VI. these are separated by hydrogen
sulphide, from iron in alloys, ores, etc., and in general the iron is
separated as basic acetate, and the manganese afterward precipitated
with chlorine. Bromine is generally used in place of chlorine, the use
of which chemists claim as troublesome; but in a number of examinations
I have found it to yield more satisfactory results than bromine, which
is much more expensive.
From the acids in insoluble and a few other compounds, chromic, arsenic,
and arsenious acids, by fusion with carbonate of soda in presence of
carbonic acid gas; borate of manganese is readily decomposed when the
boracic acid is to be determined by boiling with solution of potassa,
dissolving the residue in hydrochloric acid and precipitating the
manganese as binoxide. This boiling, however, is seldom needed, as the
borate is soluble in HCl.
From phosphoric acid I always use Girard's method of treatment with
tin, using it rasped, and it yields much more accurate results with but
little manipulation.
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