arsenic. Besides, this kind of glass is easily fusible in the
oxidating flame of the blowpipe, while, in the reducing flame, its
ready decomposition would preclude its use entirely. The tube should
be composed of the potash or hard Bohemian glass, should be perfectly
white, and very thin, or the heat will crack it.

The tube should be perfectly clean, which can be easily attained by
wrapping a clean cotton rag around a small stick, and inserting it in
the tube. Before using the tube, see also that it is perfectly dry.

The quantity of the substance put into the tube for examination should
be small. From one to three grains is quite sufficient, as a general
rule, but circumstances vary the quantity. The sides of the tube
should not catch any of the substance as it is being placed at the
bottom of the tube, or into the bulb. If any of the powder, however,
should adhere, 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