392 SECTION MECHANICS. 



In cupolas, for the simple melting of cast iron, less alteration has 

 been made, during recent years, than in blast furnaces. 



Considerable savings in fuel have, however, been effected, by melting 

 more rapidly, so as to diminish the loss of heat by radiation from the 

 outer surface, and by making the cupola considerably smaller in area 

 at the tuyeres than in the rest of the shaft, in order to obtain a more 

 concentrated heat at the point of fusion. Larger cupolas have also 

 been employed, as, for instance, to melt the metal for the Bessemer 

 process, than were generally in use before ; and the plan has become 

 common of providing these and other large cupolas with fore hearths, 

 or receptacles for the melted metal, of a capacity of five or ten tons, 

 which are kept warm by allowing a part of the flame to escape 

 through them, and into which the metal flows at once, as it melts, 

 instead of accumulating in the bottom of the cupola in contact with 

 the coke. 



An arrangement that presents some points of interest is the " flame- 

 less" cupola of M. Voisin. The principle of this is to admit a second 

 and carefully moderated supply of air to the upper part of the shaft, 

 sufficient to burn the carbonic oxide contained in the escaping gases, 

 without wasting any sensible quantity of coke, or producing suffi- 

 cient heat to transform the CO 2 , that has been produced by the 

 burning of the gas, again at the expense of the coke to CO. 



It is claimed that in this way the CO in the gases may be burned, 

 without wasting coke, and that the top of the cupola is thus maintained 

 cool and flameless ; while as the metal and fuel are heated to redness, 

 by the combustion of the, waste gas, a smaller proportion of coke 

 is required. Thus, in foundry cupolas, to which the plan has been 

 chiefly applied, a saving is effected by it, according to some state- 

 ments, equal to 40 Ibs. of coke per ton of metal melted ; the con- 

 sumption per ton having been reduced from 200 to 160 Ibs. ; and in 

 other cases the coke consumption of foundry cupolas on Voisin's 

 plan, exclusive of the first charge, is stated at as little as 140 or even 

 134 Ibs. per ton. 



That when the coke used in a cupola is fairly hard, the materials 

 of the charge may be thus raised to a red heat, by the combustion of 

 the gases, with little or no loss of coke, is shown by one of the experi- 

 ments made by Mr. Bell, in the course of his investigations of the 



