g 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
with air, although not then sufficient for complete combustion. The
hydrogen is first oxidized or burnt, and then the carbon is attacked
by the air, although particles of carbon are separated, and it is
these, in a state of intense ignition, which produce the illumination.
By bringing any oxidizable substance into this portion of the flame,
it oxidizes very quickly in consequence of the high temperature and
the free access of air. For that reason this part of the flame is
termed the oxidizing flame, while the illuminating portion, by its
tendency to abstract oxygen for the purpose of complete combustion,
easily reduces oxidated substances brought into it, and it is,
therefore, called the flame of reduction. In the oxidizing flame, on
the contrary, all the carbon which exists in the interior of the flame
is oxidized into carbonic acid (CO^{2}) and carbonic oxide (CO), while
the blue color of the cone of the flame is caused by the complete
combustion of the carbonic oxide. These two portions of the flame--the
oxidizing and the reducing--are the principal agents of blowpipe
analysis.

If we introduce a fine current of air into a flame, we notice the
following: The air strikes first the dark nucleus, and forcing the
gases beyond it, mixes with them, by which oxygen is mingled freely
with them. This effects the complete combustion of the gases at a
certain distance from the point of the blowpipe. At this place the
flame has the highest temperature, forming there the point of a blue
cone. The illuminated or reducing portion of the flame is enveloped
outside and inside by a very hot flame, whereby its own temperature is
so much increased that in this reduction-flame many substances will
undergo fusion which would prove perfectly refractory in a common
flame. The exterior scarcely visible part loses its form, is
diminished, and pressed more to a point, by which its heating power is
greatly increased.

_The Blast of Air._--By using the blowpipe for chemical purposes, the
effect intended to be produced is an uninterrupted steady stream