in the Smelting of Iron. 185 



the one case than the other, but from the greater intensity of 

 temperature that prevails when the heated air is employed, in- 

 suring the more steady and certain action of the charcoal on the 

 calcined ironstone, less or none being exhausted without any 

 adequate return, i. e. consumed at an inferior temperature, with- 

 out affecting the ore in contact with it. It is possible, however, 

 that the absolute quantity of heat evolved may differ according 

 to the temperature at which an inflammable substance is con- 

 sumed, though no precise experiments have been made to de- 

 termine this. 



If we consider the quantity of air required for the combustion 

 of common inflammable matter, we shall be better able to ap- 

 preciate the important effects which must arise from the use of 

 heated air. Let us suppose that coke alone is used in the 

 smelting furnace, and that carbonic oxide is the sole product of 

 the combustion in that part of the furnace where the blast takes 

 effect upon the fuel, then, even according to this calculation, 

 every six parts of charcoal require no less than thirty-six of at- 

 mospheric air for their combustion, this quantity containing on- 

 ly eight parts of oxygen. Accordingly, though the air may be 

 so thin and attenuated that we are apt to overlook its cooling 

 influence, every portion of combustible matter mixes with six 

 times its weight of cold air (air at natural temperatures), all of 

 which must be heated to a certain extent at the expense of the 

 fuel already in a state of combustion, before it can give out any 

 heat by its action on the inflammable matter of the coal. If, 

 again, carbonic acid be the product of the combustion when the 

 heat is most powerful, twice as much fur (seventy-two parts) will 

 be necessary for every six of charcoal, or each portion will require 

 twelve times its weight of air. The first effect of the introduction 

 of this large quantity of cold air, must be to diminish the actual 

 temperature of the furnace, however much it may add to it im- 

 mediately afterwards as it is consumed. If, then, the air be heated 

 before it passes to the furnace, its temperature must be higher 

 than when air is supplied in the usual manner, just in propor- 

 tion to the degree of heat previously communicated to it. 



The high temperature of the furnace not only enables the 

 iron-ore to be smelted with less fuel than would otherwise be 

 necessary, but by effecting a complete separation of the scoriae 



