72 Iron. 
seldom exceeding 2 inches in thickness* Upon this is 
reared the subsequent building, always gradually narrow* 
ing itself till it has assumed the shape of a stout wedge, 
with its base resting upon the ground. After this is ef- 
fected, the whole of the external surface receives a com- 
plete covering of the smallest sort of coals. The pile is 
kindled by applying burning coals to the ground stratum. 
This creeps slowly along ; heats the stone upwards ; kin* 
dies the second layer of small coals, and ultimately inflames 
the whole mass from top to bottom. 
When the coals are consumed, the pile gradually cools, 
and in 8 or 10 days may be wheeled away to the furnace. 
The quantity of iron-stone burnt at one time is various 
at different and even at the same places ; some kinds re- 
quire to be burnt in smaller heaps, owing to their nature 
and fusibility. At some works the fires extend from 50 
to 60 yards ; and it is not uncommon to see skilful work* 
men, at one end, adding fresh materials to the burning 
pile; while others, at the opposite end, are employed 
wheeling away that which the fire has left sufficiently 
burned for the purpose of the furnace. Fires that extend 
from 30 to 60 feet in length are more common ; from 10 
to 16 feet wide, and about 5 feet high. 
At most iron- works a local opinion exists, to what de- 
gree of heat iron-stone ought to be exposed before it is 
properly fit for the blast-furnace. All, however, agree that 
burning is necessary ; though few give an accurate rea- 
son why. The only one I have heard adduced is, that 
iron-stone is calcined in order to burn out the sulphur and 
other heterogeneous mixtures. Hence arise a diversity of 
opinions, chiefly founded upon individual notions of the 
fixity or volatility of sulphur. Some contend that sul- 
phur is easily displaced, and that therefore the iron-stone 
should be moderately calcined ; lest the sulphur from the 
coal used in burning it should enter, and again hurt the 
