, it should be pushed down with a roll of clean paper, or
the clean cotton rag referred to above.

In submitting the tube to the flame, it should be heated at first very
gently, the heat being increased until the glass begins to soften,
when the observations of what is ensuing within it may be made.

If the substance be of an organic nature, a peculiar empyreumatic odor
will be given off. If the substance chars, then it may be inferred
that it is of an organic nature. The matters which are given off and
cause the empyreumatic odor, are a peculiar oil, ammonia, carbonic
acid, acetic acid, water, cyanogen, and frequently other compounds. If
a piece of paper is heated in the bulb, a dark colored oil condenses
upon the sides of the tube, which has a strong empyreumatic odor. A
piece of litmus paper indicates that this oil is acid, as it is
quickly changed to red by contact with it. A black residue is now left
in the tube, and upon examination we will find that it is charcoal.
If, instead of the paper, a piece of animal substance is placed in
the bulb, the reddened litmus paper will be converted into its
original blue color, while charcoal will be left at the bottom of the
tube.

A changing of the substance, however, to a dark color, should not be
accepted as an invariable indication of charcoal, as some inorganic
bodies thus change color, but the dark substance will not be likely to
be mistaken for charcoal. By igniting the suspected substance with
nitrate of potassa, it can quickly be ascertained whether it is
organic or not, for if the latter, the vivid deflagration will
indicate it.

If the substance contains water, it will condense upon the cold
portion of the tube, and may be there examined as to whether it is
acid or alkaline. If the former, the matter under examination is,
perhaps, vegetable; if the latter, it is of an animal nature. The
water may be that fluid absorbed, or it may form a portion of its
constitution,

If the substance contain _sulphur_, the sublimate upon the cold part
of the tube may be recognized by its characteristic appearance,
especially if the substance should be a sulphide of tin, copper,
antimony, or iron. The hyposulphites, and several other sulphides,
also give off sulphur when heated. The volatile metals, mercury and
arsenic, will, however, sublime without undergoing decomposition. As
the sulphide of arsenic may be mistaken, from its color and
appearance, for sulphur, it must be exam