CARBIDE, in chemistry, a binary com pound of carbon with a metallic element, or with certain of the non-metallic elements. Of the known carbides those of iron and calcium are most important. Carbide of iron occurs in steel, and is undoubtedly concerned in some manner, with the hardening of that metal, al though the authorities are not agreed as to the precise role that it plays. The best-known car bide of iron is the one having the formula CFe,; but Campbell has shown (American Chemical Journal, XVIII, 836) that a series of iron carbides probably exists, having the gen eral formula C.Fes., and corresponding in a certain sense to the hydrocarbon series C.H2.; so that when any one of the carbides of iron is treated with an acid, the corresponding hydro carbon is set free. Calcium carbide is formed by the action of carbon upon lime at the tem perature of the electric furnace. It has the formula CaC,, and its commercial value de pends mainly upon the fact that it is readily de composed by water, with the copious liberation of acetylene gas (q.v.). Carbide of magnesium is not formed at the temperature of the electric furnace, probably because it is not stable at that temperature. It may be prepared, how ever, by the action of calcium carbide upon magnesium fluoride, in accordance with the equation CaCi MgF3=-CaF, MgC,. Like calcium carbide it is decomposed by water with evolution of acetylene gas, the yield being 50 per cent greater, per pound of the carbide, in the case of magnesium carbide. It is not un likely that magnesium carbide will one day replace calcium carbide for the production of acetylenegas, on account of the larger yield; but this substitution cannot be made on a com mercial scale until some cheaper mode of.manu facture is found. The chemistry of the car bides is still in its infancy, but within the past few years, and largely owing to the splendid work of Moissan, many new bodies belonging to this class have been discovered. Gold, bis muth, lead and tin do not form carbides at the temperature of the electric furnace, nor do they dissolve carbon at that temperature.
Platinum and iridium dissolve carbon freely, but deposit it again, upon cooling, in the form of graphite. Aluminum absorbs carbon freely, with the formation of Al4C, and similar re sults are obtained with many other metals and metallic oxides. The carbides of chromium, molybdenum, titanium, tungsten and zirconium do not decompose water. Those of calcium, strontium, barium and lithium decompose it with liberation of pure acetylene; but the car bides of aluminum and beryllium yield pure methane, and carbide of manganese gives a mixture of equal parts of methane and hydro gen. Other carbides decompose water with more complex results. Thus the carbides of the rare metals of the cerium group yield com plicated mixtures of hydrogen, acetylene, methane and ethylene, and the carbide of ura nium gives all these products (except, perhaps, acetylene), and, in addition, copious quantities of various liquid and solid hydrocarbons. The carbides of sodium and potassium, which are best prepared by passing dry acetylene gas over the corresponding metals at a temperature of about 450° F., decompose water with liberation of acetylene. The carbides of titanium and of silicon are characterized by extreme hard ness, and it is said that they will even cut the diamond with facility. Carbide of silicon is an exceedingly stable substance, and is now largely used under the trade name of "carborundum,* as an abrasive material in the manufacture of grinding-wheels, whet-stones and polishing cloth.
Moissan's researches with the electric fur nace are reported chiefly in the Annales de Chimie et de Physique, and useful reviews of them have been printed at frequent intervals in Nature. Moissan claims to have been the discoverer of the crystalline carbide of calcium that is now commercially familiar; but in the United States this honor is usually accorded to Mr. Willson, whose labors were certainly quite independent of those of Moissan. See CALCIUM CARBIDE; CARBORUN DU M ; ELECTRCl- CH EM ICAL INDUSTRIES.