CALCINA′TION

The operation of burning or roasting any solid body to expel its more volatile parts, as the conversion of chalk into lime by the expulsion of carbonic anhydride. The roasting of the ores in the first stage of the Welsh proce of copper smelting and in the Silesian mode of extracting zinc is technically termed CALCINATION . The method of conducting the proce of calcination depends on the nature of the body operated on. Many substances, for delicate experiments, are calcined over a spirit lamp in a platinum spoon or crucible; others, in iron ve els or earthen crucibles, placed in a common furnace. When the action of the air proves injurious, as in the manufacture of charcoal, the proce is performed in close ve els or chambers. In some cases the fuel is mixed with the articles, and they are both burnt together, as in the manufacture of lime, the roasting of ores, . The proce of drying salts, or driving off their water of crystallisation by heat, is also frequently called CALCINATION ; thus we have calcined copperas, alum, .