182 Miscellanies. 
Dr. Clark gives what we conceive to be the obvious explanation 
of the mode in which the hot air acts.—Berthier, it is true, has 
broached another.—(See “ Records,” ii. 151.) But it is far-fetched, 
and superseded by the more simple explanation presented by our 
author. He observes: 
* As nearly as may be, a furnace, as wrought at Clyde sreinssacolen 
in 1 1833, had two tons of solid materials an hour put in at the top, 
and this supply of two tons an hour was continued for 23 hours a 
day, one half hour every morning, and another every evening, being 
consumed in letting off the iron made. But the gaseous material, 
the hot air—what might be the weight of it? ‘This can easily be 
ascertained thus: I find by comparing the quantities of air consumed 
at Clyde iron-works, and at Calder iron-works, that one furnace re- 
quires of hot air from 2500 to 3000 cubical feet ina minute. I 
shall here assume 2867 cubical feet to be the quantitity ; 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 six tons an hour. ‘Two tons of solid mate- 
rial an hour, put in at the top of the furnace, can scarce hurtfully af- 
fect the temperature of the furnace, at least in the hottest part of it, 
which must be far down, and where the iron, besides being reduced 
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 affect 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 com- 
bustion ; but this beneficial effect j 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 pei 
temperature of the air, cannot be conceived otherwise than a p 
gious refrigeratory passing through the hottest part of the ‘aie, 
and repressing its temperature. The expedient of previously heat- 
ing the blast, obviously removes this refrigeratory, leaving the air to 
act in promoting combustion, without robbing the combustion of any 
portion of the heat it produces.” 
