398 SECTION MECHANICS. 



connected with each furnace, and is led into a jet of air, from a fan, at a 

 pressure equal to three or four inches of water column, by which it is 

 carried forward into the furnace. In this, the jet of mixed coal dust and air 

 takes fire, and burns like a jet of combustible gas, except that the flame 

 is solid, not hollow like a gas flame burning in air. The revolving 

 puddling furnace is in form a short cylinder, closed at one end and 

 slightly narrowed at the other, and consists of a double casing, of thin 

 boiler plate, kept cool by a current of water flowing through it, and 

 lined with a " fettling," of oxide of iron, five or six inches thick. The 

 air and coal dust are blown in through the line-piece, that fits against 

 the open end of the revolving puddling chamber, and the waste flame 

 escapes to the chimney by the same opening, round the entering jet. 

 The combustion of the fuel is thus effected in the working chamber, 

 itself, and as the coal and air are mixed intimately throughout the 

 flame, it is very complete. The consumption of coal, in puddling ten- 

 hundredweight charges of pig iron, run liquid into the furnace, is stated 

 to be nine hundredweight per ton of puddled bar produced. 



This system of furnace, though in most respects remarkably perfect, 

 and giving every promise of success as applied to revolving puddling 

 furnaces, is not found to be suited for use in those more ordinary ar- 

 rangements, in which the working chamber is built of brickwork or other 

 siliceous material, as the fluxing action of the ash of the coal destroys, 

 very rapidly, any such work that is in contact with the flame and ex- 

 posed to its full heat. 



Among the directions in which improvements have been effected in 

 flame furnaces of the ordinary type, are the use of the waste heat to 

 raise steam, a system now carried out, to a greater or less extent, in all 

 iron works where such furnaces are used ; the employment of a blast 

 or forced draught under the fire-grate, (the air forced in being frequently 

 more or less heated,) in order to allow of burning cheaper small coal, 

 and to give a command, such as that possessed by the regenerative 

 gas furnace, over the pressure in the working chamber ; and, lastly, 

 arrangements for preventing the cooling down of the fire, each time 

 that fresh fuel is put on, and the rush of cold air into the furnace, 

 through the opened fire-door, when a pressure is not maintained in it 

 by blast. 



