The dissolving of the fused mass in hydrochloric acid does not need to
be carried to dryness for the separation of the soluble silica, but the
boiling, after the addition of a little nitric acid, is only kept
up until the iron passes into perchloride and the manganese into
protochloride. The quantity, which ought to be taken for the test,
depends on the accuracy with which it is desired to have the manganese
estimated.
Of ferromanganese and other very manganiferous substances, in which the
manganese need not be determined with greater exactness than to 0.1 per
cent., only 0.01 gram. is taken for a test; but of common pig, wrought
iron, steel, iron ore, slags, etc., there is taken 0.5 to 1 gramme
according to the supposed content of manganese and the desired exactness
of the estimation. For instance one gramme iron, which has passed
through a metal sieve with holes half a millimeter in diameter, is
placed in a beaker 125 mm. in height and 60 mm. in diameter, and has
added to it twenty cubic centimeters of hydrochloric acid of 1.12
specific gravity, which, with a well-fitting glass cover, is boiled for
half an hour, in order that the combined carbon may be driven off in the
shape of gas.
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