TORY, &C.
The reduction of an ore requires fre quently previous roasting, to expel the sulphur and other volatile ingredients ; or this may be effected by mixing the powdered ore with nitre, and projecting the mixture into a crucible. The sul phate of potash, thus formed, may be washed off, and the oxide must be served for subsequent experiments. As many of the metals retain their oxygen so forcibly, that the application of heat is incapable of expelling it, the addition of inflammable matter becomes expe dient. And, to enable the reduced par ticles of metal to agglutinate and form a collected mass, instead of scattered grains, which would otherwise happen, some fu sible ingredient must be added, through' which, when in fusion, the reduced me tal may descend, and be collected at the bottom of the crucible. Substances that answer both these purposes are called' fluxes. The alkaline and earthy part of fluxes serve also another end, viz. that of combining with any acid which may be attached to a metal, and which would prevent its reduction, if not separated.
The ores of different metals, and differ ent ores of the same metal, require dif ferent fluxes. See FLux. The ore, after. being roasted, if necessary, is to be Well mixed with three or four times its weight of the flux, and put into a crucible, with a little powdered charcoal over the sur face. A cover must be luted on, and the crucible exposed to the necessary heat in a wind-furnace. Ores of iron, as being difficultly reduced, require a very intense fire. Those of silver and lead are me tallized a lower heat. The metal is found at the bottom of the crucible, in the form of a round button. The volatile metals, as mercury, zinc, arsenic, tellu rium, and osmium, it is obvious, ought not to be treated in the above manner, and require to be distilled with inflam mable matters in an earthen retort. See Kirwan's Mineralogy.