muscles of the cheeks, while he continues to breathe without
interruption through the nostrils. Having become acquainted with this
process, it only requires some practice to produce a steady jet of
flame. A defect in the nature of the combustible used, as bad oil,
such as fish oil, or oil thickened by long standing or by dirt, dirty
cotton wick, or an untrimmed one, or a dirty wickholder, or a want of
steadiness of the hand that holds the blowpipe, will prevent a steady
jet of flame. But frequently the fault lies in the orifice of the jet,
or too small a hole, or its partial stoppage by dirt, which will
prevent a steady jet of air, and lead to difficulty. With a good
blowpipe the air projects the entire flame, forming a horizontal, blue
cone of flame, which converges to a point at about an inch from the
wick, with a larger, longer, and more luminous flame enveloping it,
and terminating to a point beyond that of the blue flame.

To produce an efficient flame of oxidation, put the point of the
blowpipe into the flame about one third the diameter of the wick, and
about one twelfth of an inch above it. This, however, depends upon
the size of the flame used. Blow strong enough to keep the flame
straight and horizontal, using the largest orifice for the purpose.
Upon examining the flame thus produced, we will observe a long, blue
flame, _a b_, Fig. 3, which letters correspond with the same letters
in Fig. 2. But this flame has changed its form, and contains all the
combustible gases. It forms now a thin, blue cone, which converges to
a point about an inch from the wick. This point of the flame possesses
the highest intensity of temperature, for there the combustion of the
gases is the most complete. In the original flame, the hottest part
forms the external envelope, but here it is compressed more into a
point, forming the cone of the blue flame, and likewise an envelope of
flame surrounding the blue one, extending beyond it from _a_ to _c_,