HAMILTON SCIENTIFIC ASSOCIATION 49 



quality superior to that laid down in the foregoing require- 

 ments. 



Turning now to the methods of production, we have the 

 three main subdivisions of melting, casting and annealing, 

 but as the second has the least effect upon the quality of the 

 metal, we will omit it from consideration, and will deal only 

 with the processes of melting and annealing. 



Melting may be carried out in the Cupola, the Open 

 Hearth Furnace or the Reverberatory Air Furnace, and each 

 of these is in actual use in present day foundries. Owing, 

 however, to the somewhat poorer quality of the material 

 turned out by the Cupola, and the difficulty of economical 

 manipulation of the Open Hearth Furnace in malleable work, 

 by far the largest toimage is melted in the Air Furnace, to 

 which alone we will make reference. 



The special form of the air furnace varies according to 

 the conditions of the foundry, but there is a general agree- 

 ment with regard to the main features of construction. The 

 hearth of the furnace is separated from the fire box at one 

 end and the entrance to the stack at the other by bridgewalls 

 of suitable height. The roof of the furnace is usually made 

 up of detachable bungs, which may be readily removed for 

 repair, or to permit of charging the furnace from above. 

 There is usually a forced draft below the grate of the 

 firebox, and means for distributing a blast of air into the 

 flame just as it enters the hearth over the front bridgewall. 

 Long flame bituminous coal of low sulpliur content is the fuel 

 usually employed, and by suitable stoking and air regulation 

 the furnace may be filled with flame of either an oxidizing or 

 reducing nature. The regulation of the flame is one of the 

 most important matters in connection with air furnace 

 practice, since upon it depends both the economy of the melt- 

 ing and the quality of the metal produced. 



The charge for each melt varies in amount within fairly 

 wide limits, but 8 to lo tons represents perhaps the average 

 practice. The making up of the charge is a matter requiring 

 experience and care, as disastrous results may attend the use 



