English: Fig. 614 shows a ground plan of the furnace; fig. 615 an elevation; and fig. 616 the form of the fire itself and the position of the metal within it. The fire, d, is 24 inches long and 24 inches wide ; a, a, a are metal plates, surrounding the furnace.

Fig. 615 shows the elevation, usually built of stone, and braced with iron bars. The fire, o, is 16 inches deep and 24 inches wide ; before the tuyfere, at b, a space is left under the fire, to allow the damp to escape, and thus keep the bottom dry and hot.

In fig. 614 there are two tuyeres, but only one tuyere iron, which receives both the blast nozzles, which are so laid and directed that the currents of air cross each other, as shown by the dotted lines ; the blast is kept as regular as possible, so that the fire may be of one uniform heat, whatever intensity may be required.

Fig. 615 shows the fire itself, with the metal, charcoal, and blast, a is a bottom of charcoal, rammed down very close and hard, b is another bottom, but not so closely beaten down ; this bed of charcoal protects the under one, and serves also to give out carbon to the loop of steel during its production, c is a thin stratum of metal, which is kept in the fire to surround the loop. D shows the loop itself in progress.

When the fire is hot, the first operation is to melt down a portion of pig iron, say 50 to 70 pounds according as the pig contains more or less carbon ; the charcoal is pushed back from the upper part of the fire, and the blast, which is then reduced, is allowed to play upon the surface of the metal, adding from time to time some hammer slack, or rich cinder, the result of the previous loop. All these operations tend to decarbonize the metal to a certain extent ; the mass begins to thicken, and at length becomes solid. The workman then draws together the charcoal and melts down another portion of metal upon the cake ; this operation renders the face of the cake again fluid, but the operation of decarbonization being repeated in the second charge, it also thickens, incorporates itself with the previous cake, and the whole becomes hard ; metal is again added until the loop is completed. During these successive operations,, the loop is never raised before the blast, as it is in making iron, but it is drawn from the fire and hammered into a large bloom, which is cut into several pieces, the ends being kept separated from, the middle or more solid parts, which are the best.

This operation, apparently so simple in itself, requires both skill and care ; the workman has to judge, as the operation proceeds, of the amount of carbon which lie has retained from the pig iron ; if too much, the result is a very raw, crude, untreatable steel ; if too little, he obtains only a steelified iron ; he has also to keep the cinder at a proper degree of fluidity, which is modified from time to time by the addition of quartz, old slags, etc. It is usual to keep from two to three inches of cinder on the face of the metal, to protect it from the direct action of the blast. The fire itself is formed of iron plates, and the two charcoal bottoms rise to within nine inches of the tuyere, which is laid flatter than when iron is being made. This position of the tuyere causes the fire to work more slowly, but it insures a better result.

The quantity of blast required is about 180 cubic feet per minute. Good workmen make 7 cwt. of steel in 17 hours. The waste of the pig iron is from 20 to 25 per cent., and the quantity of charcoal consumed is 240 bushels per ton. The inclination of the tuyere is 12 to 15 degrees. The flame of the fire is the best guide for the workmen. During its working it should be a bluish color. When it becomes white the fire is working too hot.