SMELTING IN THE SLAG HEARTH.
The slags picked out of the brouse during the process of ore hearth smelting are subjected to another operation, in what is called a slag hearth. A view of this hearth, in perspective and section, is shewn Plate II. Figs. 2 and 3. It is simply a square furnace, open towards the bottom of the front side. Its dimensions are various, but a common size is 26 inches from back to front, 22 inches broad, and 36 inches deep, inside measure. The blast enters through the back wall, about 12 or 14 inches from the top, and below this, as the heat is inconsiderable, the sides of the furnace are usually made of cast iron (at working smelting-houses old bearers, or other worn parts of ore hearths, are economically used), but above the blast, where the heat is intense, the sides are formed of the most refractory firestone, or firebrick. A cast-iron plate, 2 inches thick, placed at a slight slope outwards, forms the bottom of the hearth. A cast-iron pan, Plate II. Fig. 7. of a peculiar form, is placed opposite to the opening in front, Plate II. Fig. 2, one lip of which is made to project inwards towards the furnace, and to extend a little below the sloping bottom of the hearth, as shewn in the section a, Plate II. Fig. 4. This pan is divided with two compartments, by an iron partition, b, reaching nearly to its bottom, and is kept hot by a small fire underneath, which is not represented in the figures, but a section of the flue is shewn at c, Plate II. Fig. 4. Below the front of this pan, a square pit, 6 or 8 feet long, and 4 or 6 feet broad and deep, is dug; shewn at A, Plate II. Fig 2. Pipes to convey water are laid to this pit, by which it can be kept constantly filled to within a few inches of the top, when the hearth is at work.
The only fuel used at the slag hearth is coke, and the method of working it is as follows:—
The larger division of the iron pan, and the whole space of the hearth below the orifice through which the blast enters, is filled with cinders of a moderate size, generally obtained from below the grate of an adjacent reverberatory furnace. Upon the top of these cinders, and opposite to the nozzle of the bellows, a kindled peat is placed, and the
