isagreeable taste. To avoid this, the top
of the tube must be supplied with a mouthpiece of ivory or horn C. The
blowpipe here represented is the one used by Ghan, and approved by
Berzelius. The trumpet mouthpiece was adopted by Plattner; it is
pressed upon the lips while blowing, which is less tiresome than
holding the mouthpiece between the lips, although many prefer the
latter mode.

[Illustration: Fig. 1]

Dr. Black's blowpipe is as good an instrument and cheaper. It
consists of two tubes, soldered at a right angle; the larger one, into
which the air is blown, is of sufficient capacity to serve as a
reservoir.

A chemist can, with a blowpipe and a piece of charcoal, determine many
substances without any reagents, thus enabling him, even when
travelling, to make useful investigations with means which are always
at his disposal. There are pocket blowpipes as portable as a pencil
case, such as Wollaston's and Mitscherlich's; these are objectionable
for continued use as their construction requires the use of a metallic
mouthpiece. Mr. Casamajor, of New York, has made one lately which has
an ivory mouthpiece, and which, when in use, is like Dr. Black's.

[Illustration: Fig. 2]

The length of the blowpipe is generally seven or eight inches, but
this depends very much upon the visual angle of the operators. A
short-sighted person, of course, would require an instrument of less
length than would suit a far-sighted person.

The purpose required of the blowpipe is to introduce a fine current of
air into the flame of a candle or lamp, by which a higher degree of
heat is induced, and consequently combustion is more rapidly
accomplished.

By inspecting the flame of a candle burning under usual circumstances,
we perceive at the bottom of the flame a portion which is of a light
blue color (_a b_), _Fig._ 2, which gradually diminishes in size
as it recedes from the wick, and disappears when it reaches the
perpendicular side of the flame. In the midst of the flame there is a
dark nucleus with a conical form (_c_). This is enveloped by the
illuminating portion of the flame (_d_). At the exterior edge of the
part _d_ we perceive a thin, scarcely visible veil, _a, e, e_, which
is broader near the apex of the flame. The action of the burning
candle may be thus explained. The radiant heat from the flame melts
the tallow or wax, which then passes up into the texture of the wick
by capillary attraction until it reaches the glowin