mmonia. When it is
ignited it passes into the biphosphate of soda, the ammonia being
driven off. This biphosphate of soda possesses an excess of phosphoric
acid, and thus has the property of dissolving a great number of
substances, in fact almost any one, with the exception of silica. If
the substances treated with this salt consist of sulphides or
arsenides, the bead must be heated on charcoal. But if the substance
experimented upon consists of earthly ingredients or metallic oxides,
the platinum wire is the best. If the latter is used a few additional
turns should be given to the wire in consequence of the greater
fluidity of the bead over that of borax. The microcosmic salt bead
possesses the advantage over that of borax, that the colors of many
substances are better discerned in it, and that it separates the
acids, the more volatile ones being dissipated, while the fixed ones
combine with a portion of the base equally with the phosphoric acid,
or else do not combine at all, but float about in the bead, as is the
case particularly with silicic acid. Many of the silicates give with
borax a clear bead, while they form with microcosmic salt an
opalescent one.

It frequently happens, that if a metallic oxide will not give its
peculiar color in one of the flames, that it will in the other, as the
difference in degree with which the metal is oxidized often determines
the color. If the bead is heated in the reducing flame, it is well
that it should be cooled rapidly to prevent a reoxidation. Reduction
is much facilitated by the employment of metallic tin, whereby the
protoxide or the reduced metal may be obtained in a comparatively
brief time.

The following tables, taken from Plattner and Sherer, will present the
reactions of the metallic oxides, and some of the metallic acids, in
such a clear light, that the student cannot very easily be led astray,
if he gives the least attention to them. It frequently happens that a
tabular statement of reactions will impress facts upon the memory when
long detailed descriptions will fail to do so. It is for this purpose
that we subjoin the following excellent tables.

* * * * *

TABLE I.

A. BORAX.
1. Oxydizing flame.
2. Reducing "

B. MICROCOSMIC SALT.
1. Oxydizing flame.
2. Reducing "

A. BORAX

1. Oxydizing flame

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Color of Bead.