The most inferior quality of air used in the blast-furnace 
"is that thrown into the air- vault, and afterwards expressed 
from thence by its own elasticity and the successive strokes 
of the engine. The capacity of such a building is from 
60 to 70,000 cubical feet ; this, when filled, generates a 
much superior degree of heat to that sensible in the 
blowing-cylinder. As this heat is produced many feet 
distant from any mechanical motion, it is most evident 
that it is extricated from the air, and will readily unite 
with the moisture which penetrates the building : the 
quality of the air introduced into the furnace will there- 
fore be in proportion to the quantity of moisture taken up ; 
this will be much more in summer than in winter, as the 
temperature of the former exceeds that of the latter. The 
sensation, on entering the air- vault in the coldest months, 
immediately after stopping the engine, is exactly similar 
to that experienced upon entering a crowded room in the 
hottest summer day ; the walls are covered with damp, 
and the superior regions of the vault readily obscure the 
llame of a candle. The feeling, upon remaining in the 
air- vault when the engine is at work, is less marked than 
would be expected where so great a compression of air 
I existed ; the sense of hearing, owing to the moisture in 
the conducting medium, is considerably impaired, and 
respiration is performed with some difficulty ; the light of 
a candle is faint, and not visible at the distance of a few 
feet. 
I have explained the necessity of just proportions ex- 
isting betwixt the area of the interior of the blast-furnace, 
the quantity of air thrown in per minute, and the quality 
®f coal. The various modes of blowing, and their res- 
pective effects, deduced from strict observation, were also 
attended to. We have now, 3d, to adduce examples 
where the various changes of the atmosphere, as to lit at 
and pressure, occasion the most sensible difference in the 
