“The hot gases which are led from the upper part of the furnace through that brick-lined ‘downcomer’ are burning in three of those ‘stoves’ to heat them, while cold, clean air from the blowing engines is coming through the other stove, which, ten minutes ago, when it was put on blast, was the hottest of the four. It is now giving up part of its accumulated heat to the blast on its way to the furnace. Switching the cold incoming air every little while from a partially cooled stove through a hotter one while allowing the former to reheat, provides continuous blast of a temperature of 800° to 1400° F. The ‘hot blast’ idea originated about 1830 with James Neilson, a gas engineer of England, and its introduction revolutionized the blast furnace industry and made the highly efficient modern practice possible. [Illustration: FURNACE AND SAND BED READY FOR IRON ] “This big pipe above our heads which encircles the furnace is the ‘bustle pipe.’ It also has to be lined with fire bricks. The hot blast is distributed by this ‘bustle pipe’ to the tuyères here—these L-shaped pipes—which shoot it directly into the furnace. Through the peep-holes in the tuyères you can get a glimpse of the dazzling interior of the furnace. The blast of heated air is causing the coke to burn fiercely there so that it melts the iron, which farther up in the furnace has been forced to part from the oxygen, as I explained to you.” [Illustration: LAYOUT OF BLAST FURNACE PLANT ] But now six men with a long steel bar are starting to break through the two or three feet of clay with which the “tap hole” of the monster furnace is plugged, and our informant hurries away. [Illustration: SKIP HOIST AT WORK. SKIP DUMPING INTO HOPPER ] For ten minutes with strong sledge blows the tappers struggle to break through the plug of burned clay. Meanwhile the monotonous whistle of the heavy blast into and through the bustle pipe and tuyères goes on and the discharge pipes of the water-cooling plates empty into the gutter around the furnace bottom the water which has been circulating to keep the inner bricks from fusing. [Illustration: SECTION OF BLAST FURNACE SHOWING FILLING ARRANGEMENT, BINS AND ORE BRIDGE ]