FIRE-CLAY. A variety of clay capable of withstanding a high degree of heat. This is because it contains such a low percentage of fluxing impurities such as iron, lime, magnesia, and alkalies. A good fire-clay should resist a temperature of 2900° F., and some will resist 3500° ; hut, unfortunately, many clays are called fire-clays which are not really refractory. Fire clays are often plastic, hut in the United States especially there exists a non-plastic variety known as 'flint clay.' Fire-clay is found in many geological formations, and in the Carboniferous rocks is often associated with coal. In the United States it is found in large quantities in the Carboniferous rocks of Pennsylvania. Ohio, Mis souri, and Kentucky, and in the Cretaceous of New Jersey and other States, especially Colo rado. Large quantities are obtained in Germany, England, France. Belgium. Austria, and Russia. Some of the German and Belgian clay is exported to the United States.
The following analyses give the composition of sonic American and European fire-elays: Fire-elays are used in the manufacture of fire bricks, gas-retorts, glass-pots, assayers' furnaces, crucibles, and other objects which in their use are subjected to a high degree of heat.
Among (lie varieties recognized are: Flint clay, a hard form, resembling flint in appearance and lacking plasticity. found in the same bed with plastic clay; farnixter, a refractory clay having high percentage of silica ; put-clay, a fire-clay burning dense at a low red heat, but otherwise refractory. used in the manufaeture of glass.pilts; fire-snorter, a sandy lire-clay used for making mortar to set fire-bricks; retort-clay, a very plastic refractory clay used in the manufacture of gas-retorts. Consult: Bisehof, feuerfestrn Thone (Leipzig, 1395) ; Ries, article on "Clay," in The Mineral Industry, vol. ix. (New York, 1001). See CLAY; CoAl..