380 Dr Cxiarx on the Application of the Hot Blast 
cal feet to be the quantity; a number that I adopt for the sake 
. of simplicity, inasmuch as, calculated at an avoirdupois ounce 
and a quarter, which is the weight of a cubical foot of air at 50° 
Fahrenheit, these feet correspond precisely with 2 cwt. of air 
a minute, or siv tons an hour. 'Two tons of solid material an 
hour, put in at the top of the furnace, can scarce hurtfully affect 
the temperature of the furnace, at least in the hottest part of it, 
which must be far down, and where the iron, besides being re- 
duced to the state of metal, is melted, and the slag too produced. 
When the fuel put in at the top is coal, I have no doubt that, 
before it comes to this far-down part of the furnace—the place of 
its useful activity—the coal has been entirely coked ; so that, in 
regard to the fuel, the new process differs from the old much 
more in appearance than in essence and reality. But if two tons 
of solid material an hour, put in at the top, are not likely to af- 
fect the temperature of the hottest part of the furnace, can we 
say the same of six tons of air an hour, forced in at the bottom 
near that hottest part ? The air supplied is intended, no doubt, 
and answers to support the combustion ; but this beneficial effect 
is, in the case of the cold blast, incidentally counteracted by the 
cooling power of six tons of air an hour, or two cwt. a minute, 
which, when forced in at the ordinary temperature of the air, 
cannot be conceived otherwise than as a prodigious refrigeratory 
passing through the hottest part of the furnace, and repressing 
its temperature. The expedient of previously heating the blast 
obviously removes this refrigeratory, leaving the air to act in pro- 
moting combustion, without robbing the combustion of any por- 
tion of the heat it produces. 
Such, I conceive, is the palpable, the adequate, and very 
simple explanation of the extraordinary advantages derived in 
the manufacture of cast-iron, from heating the air in its passage 
from the blowing apparatus to the furnace. 
Mariscuat CoLLecr, 
Aberdeen, Jan. 10. 1835. 
