Page:On the economy of machinery and manufactures - Babbage - 1846.djvu/271

Rh tense, 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 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. If either of those gases becomes liquid at a lower pressure than the other, and if those pressures are within the limits of our present powers of compression, the object might be accomplished.

Let us assume, for example, that oxygen becomes liquid under a pressure of 200 atmospheres, whilst azote requires a pressure of 250. Then if atmospheric air be condensed to the two hundredth part of its bulk, the oxygen will be found in a liquid state at