BLAST FURNACE

a furnace in which in ores are melted in contact with the fuel, to the combustion of the latter being accelerated by air being pumped into the furnace through the bottom under heavy a pre ure. Furnaces range from a few feet in height to over 100, the big ones being for iron ore. The interior of the furnace is usually round, like the inside of a cannon, tapering gradually toward the top. At the bottom is the hearth, where the air is introduced by means of pipes. The fuel and the ore are dumped in from the top, in alternate layers, combustion going on meanwhile. As of these layers expand from heat they sink the wider portions of the furnace. Finally the molten metal reaches the hearth at the bottom of the furnace, the consumed fuel, in the form of slag, floating on top. Through a hole near bottom the molten metal is tapped, usually twice a day. In the large iron reducing furnaces it usually takes the from a day to a day and a half to reach the bottom in a molten state. A modern furnace will treat from 400 to tons of ore in a day. Formerly there was great danger to the workers attending the blast furnace from ‘breakouts,’ the intense heat of the fire crumbling the brickwork and causing an outburst of molten metal, enough to flood the whole floor of the foundry, sometimes killing a dozen men at a time. modern blast furnace has reduced danger to a minimum, by having wound around it, within the brickwork, coils of pipe through which cold water is Be-|constantly circulating. The structure is encased in a steel jacket, heavily banded on the outside. A modern blast furnace, with all its equipment, may cost from $500,000 to $1,000,000. There about 500 in the country, most of them being in Pennsylvania and around eee in the steel manufacturing