2. _Hydrate of Baryta_ (BaO, HO).--This salt is used sometimes for the
detection of alkalies in silicates. Mix one part of the substance with
about four parts of the hydrate of baryta, and expose it to the
blowpipe flame. The hydrate of baryta combines with the silicic acid,
and forms the super-basic silicate of baryta, while the oxides become
free. The fused mass must be dissolved in hydrochloric acid, which
converts the oxides into chlorides. Evaporate to dryness, and dissolve
the residue in water. The silicic acid remains insoluble.

The hydrate of baryta is prepared by mixing six parts of finely
powdered heavy-spar (BaO, SO_{3}) with one part of charcoal and one
and a half parts of wheat flour, and exposing this mixture in a
Hessian crucible with a cover to a strong and continuous red heat. The
cooled chocolate-brown mass must be boiled with twenty parts of water,
and, while boiling, there must be added the oxide of copper in
sufficient quantity, or until the liquid will not impart a black color
to a solution of acetate of lead (PbO, [=]A). The liquid must be
filtered while hot, and as it cools the hydrate of baryta appears in
crystals. These crystals must be washed with a little cold water, and
then heated at a low temperature in a porcelain dish until the crystal
water is expelled. The hydrate of baryta melts by a low red heat
without losing its water of hydration.


3. _Bisulphate of Potassa_ (KO, 2SO^{3}).--At a red heat the half of
the sulphuric acid of this salt becomes free, and thus separates and
expels volatile substances, by which we can recognize lithium, boracic
acid, nitric acid, fluoric acid, bromine, iodine, chlorine; or it
decomposes and reveals some other compounds, as, for instance, the
salts of the titanic, tantalic and tungstic acids. The bisulphate of