Fluor-spar Flux
Fluor-spar or calcium fluoride is a brittle, transparent to sub-translucent mineral with a perfect octahedral cleavage, a vitreous, sometimes splendent lustre, and specific gravity of 3.12. It decrepitates, tinges the flame dull red, and fuses into an enamel before the blowpipe. Fluor-spar is used for the production of hydrofluoric acid in etching on seals and glass, and it is extensively used in the smelting of lead and copper as a flux. It is found in metalliferous veins, also in granite, slate, limestone, etc.
A very small quantity of fluor-spar in the cupola makes the slag more thinly liquid and poorer in iron than does limestone. It saves labor, preserves the cupola, and keeps it clean. To some extent fuel is saved by a judicious use of this flux, and at the same time it facilitates the separation of phosphorus and sulphur from the iron. While limestone is to some extent a dephosphorizing agent and active flux, and is cheap also, it must be admitted that it is also dirty and difficult to get along with in the cupola. For a heat of five tons, ten pounds of fluor-spar to the ton would be sufficient; for ten tons, fifteen pounds to the ton; and for twenty-five tons, twenty pounds to the ton. When dirty iron is being melted and aided by this flux, it is absolutely necessary to employ a slag-hole to allow the contaminating accumulations to run off. See FLUX; CUPOLA; CHARGING THE COMMON CUPOLA.
Flux is a general term given to the substances employed in the arts which cause or facilitate the reduction of a metallic ore and the fusion of the metal. White flux is an intimate mixture of 10 parts dry carbonate of soda and 13 parts dry carbonate of potash, and is used for withdrawing the silica or combined sand from mineral bodies.
Black flux is prepared by heating in close vessels ordinary cream of tartar, with an intimate mixture of finely divided charcoal, by which means the carbonate of potash is obtained.
Limestone is employed as the flux in the smelting of iron ore. Fluor-spar, borax, protoxide of lead, are also fluxes. See ALLOY; SOLDER; CAST IRON; FLUOR-SPAR FLUX; SLAG.