ed 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
potash is also used for the purpose of converting a substance into
sulphate, or to free it at once from certain constituents. These
sulphates are dissolved in water, by which we are enabled to effect
the separation of its various constituents.

PREPARATION.--Two parts of coarsely powdered sulphate of potash are
placed in a porcelain crucible, and one part of pure sulphuric acid is
poured over it. Expose this to heat over the spirit-lamp, until the
whole becomes a clear liquid. The cooled mass must be of a pure white
color, and may be got out of the crucible by inverting it. It must be
kept in a fine powder.

4. _Oxalate of Potassa_ (KO, [=]O).--Dissolve bioxalate of potash in
water, and neutralize with carbonate of potash. Evaporate the solution
at a low heat to dryness, stirring constantly towards the close of the
operation. The dry residue is to be kept in the form of a powder.

The oxalate of potash, at a low red heat, eliminates a considerable
quantity of carbonic oxide, which, having a strong affinity for
oxygen, with which it forms carbonic acid, it is therefore a powerful
agent of reduction. It is in many cases preferable to carbonate of
soda.

5. _Cyanide of Potassium_ (Cy, K).--In the dry method of analysis,
this salt is one of t