Iron . 
103 
being considerably dependent upon the quantity of air 
used for reduction, it is now so well understood, that at 
some works the blowing-machine is calculated to pro- 
duce frequently 40 tons of melting pig-iron per week at 
each furnace. At some iron- works in Wales, where oxy- 
genated crude iron is manufactured purposely for con- 
verting into bar- iron, there are several instances of a fur- 
nace producing 70, 71, and 72 tons of metal weekly. 
This astonishing quantity forms a most striking contrast 
with the early exertions of Dudley, who conceived three 
tons a profitable produce, and whose greatest exertions 
never exceeded 7 tons of pig-iron weekly. 
After this slight sketch of the progress of manufactur- 
ing pig-iron with pit-coal, it may be gratifying to make a 
few observations upon the process conducted with the 
charcoal of w r ood. The superior purity of the carbona- 
ceous matter in wood, and its greater degree of inflam- 
mability, render this operation more simple than that 
performed with pit-coal. The former properly admitted 
of a small furnace being used ; and also required a much 
less degree of blast to purify the ore, and give out sa- 
tisfactory results both in the quantity and quality of the 
metal. Few charcoal furnaces exceeded the height of .20 
feet, and many of them were from 12 to 15. A very small 
column of blast was necessary to excite ignition, and pro- 
duce the reduction of the materials. Lancashire and Cum- 
berland ores were chiefly in use ; their superior richness 
in iron rendering them soon metallised when in contact 
with ignited charcoal of wood : 12 to 24 hours were suf- 
ficient for this purpose, according to the size of the fur- 
nace and the quality of the pig-iron wished. Not so in 
the manufacturing of coak pig-iron at present : the infe- 
rior quantity of iron which is contained in iron-stones, the 
impurity of the carbonaceous matter in pit-coal, establish- 
es a much less degree of affinity betwixt the metal and 
