the selenide, and with copper as the selenide of copper. It exists
also combined with cobalt and lead, as the selenide of these metals;
also as the selenide of lead and mercury.

The smallest trace of selenium may be detected by igniting a small
piece of charcoal in the flame of oxidation, when the peculiar and
unmistakable odor of decayed horse-radish will indicate the presence
of that element. An orange vapor is eliminated if the selenium be
present in any quantity, while there is an incrustation around the
assay of a grey color, with a metallic lustre. This incrustation
frequently presents a reddish-violet color at its exterior edges,
often running into a deep blue. If a substance containing selenium be
placed in a glass tube, closed at one end, and submitted to heat, the
selenium is sublimed, with an orange-colored vapor, and with the
characteristic odor of that substance. Upon the cool portions of the
tube a steel-grey sublimate is deposited, and, beyond that, can be
discerned small crystals of selenic acid. If the mineral be the
seleniferous lead glance, sulphurous acid gas will be given off, and
may be detected by the smell, or by a strip of moistened litmus paper.

If arsenic is present, heating upon charcoal will quickly lead to the
determination of the one from the other.

* * * * *

TABULAR STATEMENT OF THE REACTIONS OF MINERALS BEFORE THE BLOWPIPE.

In PART THIRD of this work, commencing at page 109, the student will
find a sufficiently explicit description of the blowpipe reactions of
those principal substances that would be likely to come beneath his
attention. The following tabular statement of those reactions--which
we take from Scheerer and Blanford's excellent little work upon the
blowpipe--will be of great benefit, as a vehicle for consultation,
when the want of time--or during the hurry of an examination--precludes
the attentive perusal of the more lengthy descriptions in the text.

In the examination of minerals, before the student avails himself of
the aid of the blowpipe, he should not neglect to examine the specimen
rigidly in relation to its physical characters, such as its hardness,
lustre, color, and peculiar crystallization. It is where the
difference of two minerals cannot be distinguished by their physical
appearance, that the aid of the blowpipe comes in most significantly
as an auxiliary. For instance, the two minerals molybdenite and
graphite