CALCINATION. Solids, when heated to a high temperature for the purpose of removjng volatile substances, for the purpose of oxidizing a portion of the mass, or to render them friable, are said to be calcined. Calcination, therefore, is sometimes con sidered a process of purification. A typical example is the manu facture of lime from limestone. In this process the limestone, usually admixed with coke or other fuel to maintain the high temperature but sometimes treated in rotary kilns heated by gas or powdered fuel, is brought to a temperature high enough to expel the carbon dioxide, producing the lime of commerce in a highly friable or easily powdered condition. Calcination in special cases may be carried on in furnaces designed to exclude air, for which an inert gas may be substituted.