Every cubic foot of atmospheric air, driven into a furnace,
consists of two gases.(2*) about one-fifth being oxygen, and
four-fifths azote.
According to the present state of chemical knowledge, the
oxygen alone is effective in producing heat; and the operation of
blowing a furnace may be thus analysed.
1. The air is forced into the furnace in a condensed state,
and, immediately expanding, abstracts heat from the surrounding
bodies.
2. Being itself of moderate temperature, it would, even
without expansion, still require heat to raise it to the
temperature of the hot substances to which it is to be applied.
3. On coming into contact with the ignited substances in the
furnace, the oxygen unites with them, parting at the same moment
with a large portion of its latent heat, and forming compounds
which have less specific heat than their separate constituents.
Some of these pass up the chimney in a gaseous state, whilst
others remain in the form of melted slags, floating on the
surface of the iron, which is fused by the heat thus set at
liberty.
4. The effects of the azote are precisely similar to the
first and second of those above described; it seems to form no
combinations, and contributes nothing, in any stage, to augment
the heat.
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