It is best detected in acid solutions by the deep brown or iodine
colour developed on adding hydroxyl. A solution of this can be prepared
by pouring peroxide of barium (BaO_{2}) diffused in water into dilute
hydrochloric acid (a little at a time), and keeping the acid in excess.
~Separation.~--In the usual course of an analytical separation the
hydrate of titanium will be thrown down with ferric hydrate, &c., on the
addition of ammonic chloride and ammonia. It is best separated from this
precipitate by fusion with bisulphate of potash, as already described,
but it must be remembered that the presence of much mineral acid
prevents complete precipitation when the solution is boiled. Further, if
phosphates are present, the precipitate will contain phosphoric oxide;
it may be freed from this by fusion with sodium carbonate. A very good
method of separating titanium from iron is to add tartaric acid and
ammonia to the solution, and then precipitate the iron (as sulphide)
with sulphuretted hydrogen. The filtrate contains the titanium, which is
recovered by evaporating and igniting. It may be separated from zirconia
by the action of sodium carbonate, which precipitates both; but when
concentrated, redissolves the zirconia. The separation from large
quantities of silica is best effected by evaporating with hydrofluoric
acid, which volatilises the silicon; but sulphuric acid must be present,
otherwise some titanium also will be lost, as may be seen from the
following experiments,[77] in which oxide of titanium (pure, ignited)
was evaporated to dryness with a quantity of hydrofluoric acid known by
experiment to be sufficient to volatilise 1 gram of silica.
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