The plan, therefore, of heating the air before driving it
into the furnace saves, obviously, the whole of that heat which
the fuel must have supplied in raising it from the temperature
of the external air up to that of 600 degrees Fahrenheit; thus
rendering the fire more intense, and the glassy slags more
fusible, and perhaps also more effectually decomposing the iron
ore. The same quantity of fuel, applied at once to the furnace,
would only prolong the duration of its heat, not augment its
intensity.
290. The circumstance of so large a portion of the air(3*)
driven into furnaces being not merely useless, but acting really
as a cooling, instead of a heating, cause, added to so great a
waste of mechanical power in condensing it, amounting, in fact,
to four-fifths of the whole, clearly shews the defects of the
present method, and the want of some better mode of exciting
combustion on a large scale. The following suggestions are thrown
out as likely to lead to valuable results, even though they
should prove ineffectual for their professed object.
291. The great difficulty appears to be to separate the
oxygen, which aids combustion, from the azote which impedes it.
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