CONSTRUCTION OF BLAST FURNACES. 37
eight tuyeres are evenly divided around the circumference and project from 6 to 10 inches beyond the lining. These are for the purpose of aiding the blast to reach the center, and also protecting the lining. A tuyere protruding no farther than the face of the lining would rapidly cut out the brick-work at that point. These furnace tuyeres are made of an alloy chiefly composed of copper, so as to approach a bronze metal. This class of metal has been found good to prevent the melted iron, as it drops down, from adhering to or clogging around the tuyeres, which, if it should occur, would be very troublesome and liable to cause much damage.
To prevent these tuyeres from melting or burning away from exposure to the heat of the fuel and hot blast, a constant stream of cold water flows through them, going in at H and coming out at P. Often through irregular workings, tuyeres may become bunged up as in cupola practice, and the method gen-erally followed to open them is to shut off the blast and endeavor to knock a hole through the chilled material, after which the hot blast (of about 1,000 degrees heat) with its high pressure, which ranges from 6 to 24 pounds, instead of 6 to 20 ounces, as in cupola practice, will assist to cut or burn away the chilled material fronting the tuyeres. Should this fail, the blast is shut off and the tuyeres are pulled out, thereby leaving a big hole to work through, and by means of sledges and steel bars an opening is cut into the furnace and the cold, chilled debris pulled backward out of it. In replacing such a tuyere, a large lump of clay is pushed forward into the face of the hole to prevent the heat melting* the tuyere, and then the tuyere isin ordersent in the ore. Both these manganese metals are jf|V