e inserted in the edge of the flame close
over the level of the wick, and blown into gently and evenly. A conical
jet is thus produced, consisting of an inner cone, with an outer one
commencing near its apex--the former, corresponding to (a) in the free
flame, blue and well defined; the latter corresponding to (d), pale blue
and vague. The heat is greatest just beyond the point of the inner cone,
combustion being there most complete. Oxidation is better effected (if a
very high temperature be not required) the farther the substance is from
the apex of the inner cone, for the air has thus freer access. To obtain
a good _reducing flame_ (in which the combustible matter, very hot, but
not yet burned, is disposed to take oxygen from any compound containing
it), the nozzle, with smaller orifice, should just touch the flame at a
point higher above the wick, and a somewhat weaker current of air should
be blown. The flame then appears as a long, narrow, luminous cone, the
end being enveloped by a dimly visible portion of flame corresponding to
that which surrounds the free flame, while there is also a dark nucleus
about the wick. The substance to be reduced is brought into the luminous
portion, where the reducing power is strongest.

Various materials are used as supports for substances in the blowpipe
flame; the principal are charcoal, platinum and glass or porcelain.
Charcoal is valuable for its infusibility and low conductivity for heat
(allowing substances to be strongly heated upon it), and for its
powerful reducing properties; so that it is chiefly employed in testing
the fusibility of minerals and in reduction. The best kind of charcoal
is that of close-grained pine or alder; it is cut in short prisms,
having a flat smooth surface at right angles to the rings of growth. In
this a shallow hole is made for receiving the substance to be held in
the flame. Gas-carbon is sometimes used, since it is more permanent in
the flame than wood charcoal. _Platinum_ is employed in oxidizing
processes, and in the fusion of substances with fluxes; also in
observing the colouring effect of substances on the blowpipe flame
(which effect is apt to be somewhat masked by charcoal). Most commonly
it is used in the form of wire, with a small bend or loop at the end.

The mouth blowpipe is unsuitable for the production of a large flame,
and cannot be used for any lengthy operations; hence recourse must be
made to types in which the air-blast is