alysis, we use it particularly to convert
sulphides (as those of arsenic, antimony, &c.) into oxides and acids.
We furthermore use saltpetre for the purpose of producing a complete
oxidation of small quantities of metallic oxides, which oxidize with
difficulty in the oxidation flame, so that the color of the bead, in
its highest state of oxidation, shall be visible, as for instance,
manganese dissolved in the microcosmic salt.

7. _Biborate of soda, borax_--(NaO + 2BO^{3}).--Commercial borax is
seldom pure enough for a reagent. A solution of borax must not give a
precipitate with carbonate of potassa; or, after the addition of
dilute nitric acid, it must remain clear upon the addition of nitrate
of silver, or nitrate of baryta. Or a small piece of the dry salt,
fused upon a platinum wire, must give a clear and uncolored glass, as
well in the oxidation flame as in the reduction flame. If these tests
indicate a foreign admixture, the borax must be purified by
re-crystallization. These crystals are washed upon a filter, dried,
and heated, to expel the crystal water, or until the mass ceases to
swell up, and it is reduced to powder.

Boracic acid is incombustible, and has a strong affinity for oxides
when fused with them; therefore, it not only directly combines with
oxides, but it expels, by fusion, all other volatile acids from their
salts. Furthermore, boracic acid promotes the oxidation of metals and
sulphur, and induces haloid compounds, in the oxidation flame, to
combine with the rising oxides. Borates thus made, melt generally by
themselves; but admixed with borate of soda, they fuse much more
readily, give a clear bead. Borax acts either as a flux, or through
the formation of double salts.

In borax, we have the action of free boracic acid, as well as borate
of soda, and for that reason it is an excellent reagent for blowpipe
analysis.

All experiments in which borax is employed should be effected upon
platinum wire. The hook of the wire should be heated red hot, and then
dipped into the powdered borax. This should be exposed to the
oxidation flame, when it will be fused to a bead, which adheres to the
hook. This should be then dipped into the powdered substance, which
will adhere to it if it is hot; but if the bead is cool, it must be
previously moistened. Expose this bead to the oxidation flame until it
ceases to change, then allow it to cool, when it should be exposed to
the reduction flame. Look for the f