ascertained, by heating the
assay; when, if it be present, the characteristic horse-radish odor
will reveal the fact.

Sulphuric acid may be detected by fusing the substance with two parts
of soda, and one part of borax, on charcoal, in the flame of
reduction; the mass must now be wetted with water, and placed in
contact with a surface of bright silver; when, if sulphuric acid be
present, the silver will become blackened.

Or the substance may be fused with silicate of soda in the flame of
reduction. In this case, the soda combines with a portion of the
sulphuric acid, which is then reduced to the sulphide, while the bead
becomes of an orange or red color, depending upon the amount of the
sulphuric acid present. If the assay should, however, be colored, then
the previous treatment should be resorted to.

(6.) _Boron, Boracic Acid_ (BO^{3}).--This acid occurs in nature in
several minerals combined with various bases, such as magnesia, lime,
soda, alumina, etc. Combined with water, this acid exists in nature as
the native boracic acid; this acid gives with test paper prepared from
Brazil wood, when moistened with water, a characteristic reaction, for
the paper becomes completely bleached. An alcohol solution turns
curcuma test paper brown. Heated on charcoal, it fuses to a clear
bead; but, if the sulphate of lime be present, the bead becomes opaque
upon cooling.

The following reaction is a certain one: the substance is pulverized
and mixed with a flux of four and a half parts of bisulphate of
potassa, and one part of pulverized fluoride of calcium. The whole is
made into a paste with water, and the assay is placed on the platinum
wire, and submitted to the point of the blue flame. While the assay is
melting, fluoboric gas is disengaged, which tinges the outer flame
green. If but a small portion of boracic acid is present, the color
will be quite evanescent.

(7.) _Silica, Silicic Acid_ (SiO^{3}).--This acid exists in the
greatest plenty, forming no inconsiderable portion of the solid part
of this earth. It exists nearly pure in crystallized quartz,
chalcedony, cornelian, flint, etc., the coloring ingredients of these
minerals being generally iron or manganese.

With _microcosmic salt_, silica forms a bead in the flame of oxidation
which, while hot, is clear, while the separated silica floats in it. A
platinum wire is generally used for the purpose, the end of it being
first dipped in the salt which is fused