66 
Iron 
coals to the lower stratum, which by degrees ignite the 
whole mass. The breadth of the pile at the bottom 
varies from 10 to 16 feet, the usual height is about five 
feet, and the length varies from 30 feet to 60 yards. When 
the coals are consumed the pile gradually cools, and in 
eight or ten days may be wheeled away to the furnace. 
The ore if well roasted will now be of a reddish brown 
colour, of diminished specific gravity, and will have be- 
come magnetical : the sulphur, water, inflammable matter, 
and carbonic acid that it originally contained, will have 
been dissipated, and it is now ready to be smelted. 
The following remarks and experiments by Mr. Mush- 
et, throw great light on the theory of roasting, or toirefac- 
tion. 3 Phil. Mag. 200. 
The burning or torrefying of iron-stones, known in the 
large way by the rather improper term of calcination , con- 
sists in exposing the stone to a certain degree of heat in 
contact with air, in order to dispel those substances which 
it contains, capable of assuming the aeriform state by the 
combination of caloric. This operation ought to be per- 
formed in a progressive heat, always short of fusion. The 
water is then slowly evaporated without being decompo- 
sed ; the caloric unites to the carbonic acid, which soon 
assumes the gaseous state ; and lastly, the sulphur, if 
any, sublimes. 
This process is essentially necessary to be performed be- 
fore the iron-stone is introduced into the blast-furnace. 
Were raw iron-stone, or ore, precipitated in the violent 
heat of the smelting, .furnace, the water and acid would in- 
stantly be decomposed ; the oxygen w ould partly unite to 
the iron in addition to the fixed quantity peculiar to each 
ore, and part of it would oxygenate the sulphur, either of 
the ore, or of the pit-coal, a portion of which is always 
present in the furnace. The whole mass would then be 
precipitated in fusion, and a dark porous lava obtained. 
