Comparative view of the quantity of materials required at the Clyde iron works to smelt a ton of foundry pig-iron, and of the quantity of foundry pig-iron smelted from each furnace weekly

Fuel in tons of 20 cwt each cwt 112 lbs; Iron-stone; Lime-stone Cwt; Weekly produce in pig-iron Tons

1.  With air not heated and coke; 7;3 1/4; 15; 45 2.  With air heated and coke; 4 3/4; 3 1/4; 10; 60 3.  With air heated and coals not coked; 2 1/4; 3 1/4; 7 1/2; 65

Notes. 1.  To the coals stated in the second and third lines, must be added 5 cwt of small coals, required to heat the air.

2.  The expense of the apparatus for applying the heated air will be from L200 to L300 per furnace.

3.  No coals are now coked at the Clyde iron works; at all the three furnaces the iron is smelted with coals.

4.  The three furnaces are blown by a double-powered steam-engine, with a steam cylinder 40 inches in diameter, and a blowing cylinder 80 inches in diameter, which compresses the air so as to carry 2 1/2 lbs per square inch.  There are two tuyeres to each furnace.  The muzzles of the blowpipes are 3 inches in diameter.

5.  The air heated to upwards of 600 degrees of Fahrenheit.  It will melt lead at the distance of three inches from the orifice through which it issues from the pipe.

289.  The increased effect produced by thus heating the air is by no means an obvious result; and an analysis of its action will lead to some curious views respecting the future application of machinery for blowing furnaces.

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.

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.