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 glowing wick, where the
heat decomposes the combustible matter into carbonated hydrogen
(C^{4}H^{4}), and into carbonic oxide (CO).

While these gases are rising in hot condition, the air comes in
contact with them and effects their combustion. The dark portion, _c_,
of the flame is where the carbon and gases have not a sufficiency of
air for their thorough combustion; but gradually they become mixed