It occurs in granite,
basalt, and other igneous rocks in quantities up to as much as 1 per
cent. It is also met with in clays and iron ores, and in river sands, in
which it is often associated with stream tin. The proper minerals of
titanium are rutile (TiO_{2}), titaniferous iron (titanate of iron), and
sphene (titanate and silicate of lime).
The oxide of titanium (like cassiterite and quartz) is undecomposed by
hydrochloric or nitric acid; so that it is generally found in the
residue insoluble in acids. The titanates, however, are attacked, and a
portion of the titanium dissolves; so that it must be looked for in both
the filtrate and residue. Oxide of titanium in its native form, or after
ignition, may be made soluble by fusing the finely-divided substance
with fusion mixture in a platinum dish. The resulting titanate is
dissolved out of the "melt" by cold hydrochloric acid.
The method most commonly used is fusion with bisulphate of potash. This
renders the oxide of titanium soluble in cold water. The process is as
follows:--The substance is extracted with hydrochloric and nitric acids,
and the solution reserved for further treatment; the residue is dried,
moistened with sulphuric acid, and evaporated once or twice to dryness
with hydrofluoric acid. It is then fused with bisulphate of potash, and
the "melt" extracted with cold water until all soluble matter is
removed.
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