_Without sulphuric acid_, 0.0466 gram of titanic oxide left 0.0340 gram,
showing a loss of about 25 per cent.
_With sulphuric acid_ the following results were obtained:--
Oxide taken. Left after Evaporation
and Ignition.
0.0340 gram 0.0340 gram
0.0414 " 0.0413 "
0.0520 " 0.0520 "
0.0352 " 0.0352 "
GRAVIMETRIC DETERMINATION.
The titanic hydrate thrown down by ammonia (or on boiling the solution
from the bisulphate) is collected, washed, dried, ignited strongly with
the addition of a little ammonic carbonate, and weighed. The substance
is titanic oxide (TiO_{2}), and is generally reported as such. It
contains 60.98 per cent. of titanium. It should be white, if pure
(Holland), white, yellow, or brown (Fresenius), or black (Tidy).
VOLUMETRIC METHOD.
A method has been proposed based on the reduction of titanic oxide by
zinc in hydrochloric acid solutions to the sesquioxide. The reduction is
marked by the development of a violet or green colour, the former with
chlorides and the latter when fluorides are present. The quantity of
titanium reduced is measured by titrating with permanganate of potassium
solution. The water used must be free from dissolved oxygen.
TUNGSTEN AND TUNGSTATES.
Tungsten occurs in nature only in the oxidised state, or as tungstic
acid (WO_{3}), either free, as in wolframine, or combined with oxides of
manganese and iron, as in wolfram, or with lime, as in scheelite.
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