Iron itself, when
soft, is easily soluble in dilute hydrochloric, or sulphuric, acid.
Pyrites, mispickel, &c., are insoluble in hydrochloric acid, but they
are readily attacked by nitric acid. Certain minerals, such as chrome
iron ore, titaniferous iron ore, and some silicates containing iron,
remain in the residue insoluble in acids. Some of these yield their iron
when attacked with strong sulphuric acid, or when fused with the acid
sulphate of potash. Generally, however, it is better in such stubborn
cases to fuse with carbonate of soda, and then attack the "melt" with
hydrochloric acid.
When nitric acid, or the fusion method, has been used, the metal will be
in solution in the ferric state, no matter in what condition it existed
in the ore. But with dilute hydrochloric or sulphuric acid it will
retain its former degree of oxidation. Hydrochloric acid, for example,
with chalybite (ferrous carbonate) will give a solution of _ferrous_
chloride; with h?matite (ferric oxide) it will yield _ferric_ chloride;
and with magnetite (ferrous and ferric oxides) a mixture of ferrous and
ferric chlorides. Metallic iron yields solutions of _ferrous_ salts. It
is convenient to speak of the iron in a ferrous salt as ferrous iron,
and when in the ferric state as ferric iron. Frequently it is required
to determine how much of the iron exists in an ore in each condition.
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