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Refractory Materials

All such substances as melt only at the highest temperatures that can be produced are classed as refractory. Amongst these are included some natural rocks, as sandstones, quartzites, granites, etc.; but it is not customary to use these alone for metallurgical purposes, on account of their liability to split apart at high temperatures. The principal substances employed, in varying proportions, as mixtures for furnace-linings, crucibles, retorts, fire-bricks, etc., are silica, magnesia, bauxite, steatite, clays, carbon, gannister, coke, etc. Nearly all clays require to be mixed with other materials, to counteract the tendency to shrink and crack. If it were not for these admixtures, the bricks made from some of the clays would soften and melt away when subjected to very high temperatures. A description of the materials mentioned, and numerous other refractory substances, will be found at their respective places.