Perhaps the manufacture of iron(1*) would furnish the best illustration of this subject; because, by having the actual price of pig and bar iron at the same place and at the same time, the effect of a change in the value of currency, as well as several other sources of irregularity, would be removed.
288. At the present moment, whilst the manufacturers of iron are complaining of the ruinously low price of their produce, a new mode of smelting iron is coming into use, which, if it realizes the statement of the patentees, promises to reduce greatly the cost of production.
The improvement consists in heating the air previously to employing it for blowing the furnace. One of the results is, that coal may be used instead of coke; and this, in its turn, diminishes the quantity of limestone which is required for the fusion of the iron stone.
The following statement by the proprietors of the patent is extracted from Brewster's Journal, 1832, p. 349:
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.