The active agent, which produces the chemical or fluxing action in the blast furnaces, is carbonate of calcium (lime) of which limestone contains about 98 per cent. Dolomite is a mixture of carbonates of lime and magnesium, about 53 per cent of the former and 45 per cent of the latter, and is sometimes used in place of limestone. Fluor spar, a rock composed of calcium and fluorine, is used in small quantities in some of the metallurgical processes. It is a very powerful flux. CHAPTER IV THE BLAST FURNACE Up the dark tower shoots the elevator with its “buggy” of coke. Its speed is not conditioned to the comfort of man, who is not supposed to be a passenger, except the occasional laborer whose duty as buggy-pusher requires his presence on twelve-hour shifts at the top. So we, whose exploratory proclivities have led us at the office to sign away our lives for grant of a pass to the blast furnace, find our breath about taken from us with the first mad dash into the darkness of the climb. That stone tower had looked much more innocent from below. But now the rickety elevator has as suddenly emerged into the light again and stopped abruptly at the charging floor which extends across the chasm to the top of the furnace. As the smoke-begrimed buggy-pushers rush the buggy of coke across to the furnace bell, we have opportunity to notice that we are a full hundred feet above ground. Just here, seemingly so close that we can put our hands on them, in a row, are the round steel tops of the four stoves which are for the purpose of preheating the blast. The huge pipes, dust arresters, tanks, and buildings, all so necessary to the plant, look almost like a tangled mass from our high station, while the charging floor upon which we stand, the shoulder-high steel fence around it, the furnace top, the adjacent stoves and in fact everything for a half mile around us, is colored yellow-red with iron dust. We understand the reason for this when the buggies of ore which have succeeded the coke are dumped into the funnel-shaped depression around the conical bell at the center. As the huge bell is lowered and the charge slides in there is considerable blowing out of the fine ore dust, which, in fact, continually “oozes” out of all crevices under the heavy pressure of the blast inside. [Illustration: HAND-FED BLAST FURNACE ] Day and night, month in and month out, during the life of the fire-brick lining of the furnace, this routine of charging, first coke, next the theoretically correct charge of analyzed iron ores, then limestone, in rotation goes on. From 6 A.M. to 6 P.M. and from 6 P.M. to 6 A.M. on twelve-hour shifts, alternating gangs of laborers push the buggies across to the furnace top, dump and return them to the elevator already up with another load.