(=b=) =The Roasting of Fines.=—Fines (and particularly fine concentrates) are the usual materials subjected to roasting. The finer the particles, the more rapid and complete is the oxidation, but the losses by dust are heavier. The size limit is thus liable to some variation, but often the material roasted is that under ⅜-inch in size. _Roasting Furnaces—Requirements._—For the roasting of fines there is simply required a place where the material can be gently heated in the presence of a constantly renewed air supply. The fuel has itself a reducing action, it must therefore be separated from the charge, and hence the furnace employed is of the reverberatory type. Muffles are never used for the oxidising roasting of copper ores. Since only a moderate temperature is necessary for the operation, the furnace needs but a small fireplace, and it is provided with a large hearth area. The fuel used is one yielding the fairly long oxidising flame required. _Developments of Roasting Practice._—The main objects sought in roasting practice have been— (1) To have as large a surface of material exposed to heat and air as possible. (_a_) By elongating and multiplying the beds of the furnace. (_b_) By furrowing and rabbling the charge. (2) Continually to expose fresh surfaces of ore to oxidation. (_a_) First by hand-rabbling. (_b_) Later by movable furnace hearths. (_c_) By mechanical rabbling. (3) To obtain a continuous output— (_a_) By mechanical charging, rabbling, and discharging. The Development of the Roasting Furnace. A. FIXED HEARTH.—In Great Britain from 1583 onward, roasting in _small reverberatory furnaces_ seems to have been the usual method, and up to 1850 the furnaces appear to have been only of moderate dimensions, with a single hearth, 16 feet × 13 feet 6 inches, constructed of firebricks set on end, and with a fire-box 7 feet × 2 feet 3 inches × 18 inches. Rabbling was done by a long rake, the material being charged and worked through one door. This method of working wasted time, made the process intermittent, and caused continual cooling down of the furnace, involving large fuel costs and much labour. The first improvements were to lengthen the hearth, to add more working doors, and to put the charge into the furnace by a hopper passing through the roof. It was next found best to elongate the hearth still further, and to drop the level of the bed in stages by about 2 inches at a time, thus ensuring better control of working. By this means the best type of _hand-calciner_ was arrived at, consisting of four beds, each 16 feet × 16 feet, the whole charge being moved forward from one bed to the next at each stage of the process.