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 and superseded by the more simple explanation presented by our 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 maybe, a furnace, as wrought at Clyde iron-works 

 in 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 in a minute. I 

 shall here assume 2867 cubical feet to be the quantitity ; a number 

 that 1 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 

 activit}'', 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 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 a prodi- 

 gious refrigeratory passing through the hottest part of the furnace, 

 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." 



