_Bottom Hearth._—Cooler, dark red (about 650° C.). The doors on this floor are left open. The charge is guided towards openings at the outer edge to discharge chutes whilst still red hot, and it is fed from here whilst hot into the reverberatory furnace-bins. Efficient dust catchers and settlers are essential on the roasting plant. The gases escaping at a temperature of about 315° C. contain 2 per cent. of SO_{2} by volume, 5 per cent. by weight. The ore takes 2¼ hours to pass through the furnace. Practically no fuel is required except to warm up the roaster on commencing work. _Labour._—The requirements are small. There is one general foreman for the plant, and two helpers for each set of four furnaces. The conditions are rather trying, especially during the discharge of the calcines into the reverberatory charge cars. ROASTING ORES POORER IN SULPHUR, IN MACDOUGAL ROASTERS.—The Anaconda concentrates carry sufficient sulphur (33 per cent.) to supply all the heat necessary for carrying out the roasting operations. When the sulphur is below this requisite quantity, some extra heating may be required, though, on the other hand, the reduction which is necessary in the sulphur contents is lessened, depending, of course, on the proportions of copper and iron in the charge. At Garfield, Utah, where the concentrate only contains 20 per cent. of sulphur, the fuel required for all roaster purposes is equivalent to 0·2 per cent. of the charge, one of the calcines’ outlets being converted into a fireplace. Here the output per furnace per day approaches 55 tons, roasting the sulphur from 20 per cent. down to 10 to 11 per cent. The flue-dust losses at this plant are 6 per cent., so efficient dust catching appliances are essential. =The Costs of Roasting in the MacDougal Furnace.=—Ricketts has recently published a valuable analysis of the costs of the roasting operations at the Cananea Smelter. The figures must, however, be understood to apply strictly to the conditions prevailing at this particular camp. The roaster plant consists of 32 improved MacDougal furnaces. The charge supplied to the roasters assays— Copper, 5·2 per cent. Iron, 28·4 " Sulphur, 29·9 " Silica, 23·6 " Alumina, 3·7 " whilst the product (“calcines”) has an average composition of Copper, 6·3 per cent. Iron, 34·5 " Sulphur, 7·7 " Silica, 28·6 " Alumina, 4·4 " The plant operated on the following quantities of material, from February to July, 1911, inclusive:—