The basic acetate precipitate obtained on boiling is
filtered off and washed. Reserve the filtrate. The precipitate is
dissolved off the filter with hot dilute hydrochloric acid; and the
solution thus formed is treated with a slight excess of ammonia, and
boiled. The precipitate is filtered off, washed with hot water, dried,
ignited, and weighed as mixed ferric oxide and alumina. The ignited
precipitate is then dissolved with sulphuric and hydrochloric acids; and
the iron determined in the solution by titration with the solution of
stannous chloride. The iron found is calculated to and reported as
ferrous oxide, FeO (factor = 1.286). To find the alumina, which is best
estimated by difference, multiply the iron by 1.428 to get the weight of
ferric oxide, and deduct this from the weight of alumina and ferric
oxide found. This, of course, gives the alumina. A direct determination
may be made by removing the tin from the titrated solution with
sulphuretted hydrogen, filtering, nearly neutralising with ammonia, and
boiling with a few grams of hyposulphite of soda. The precipitate,
filtered, washed, and ignited, is the alumina, which is weighed. The
direct determination gives a slightly low result.
~Oxides of Zinc and Manganese.~--These are determined in the filtrate
from the basic acetate precipitate by rendering alkaline with ammonia,
and passing a current of sulphuretted hydrogen.
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