UNTIL about three years ago, the only definite compounds of carbon with metals whose existence had been proved with certainty were the acetylides of some of the metals of the alkalis and alkaline earths, and these were only known in an amorphous and impure state. The construction of the electric furnace by M. Moissan in 1893, in which the heating power of the electric arc was directly utilised, by extending the upper limit of working temperatures, added a powerful instrument of research to the laboratory. Among the many new fields of work thus opened up, the preparation of the difficultly reducible metals, such as tungsten, molybdenum, manganese and chromium, was attacked with much success by M. Moissan. These reductions being necessarily effected in the presence of carbon, the formation of definite metallic carbides of great stability soon became apparent, the properties of which proved to be of such interest that their preparation was systematically attempted. Certain metals, such as gold, bismuth, lead, and tin, do not form carbides at the temperature of the electric furnace, neither do they dissolve any carbon. The metals of the platinum group dissolve carbon with facility, but deposit the whole of it on cooling in the form of graphite, the metals being unchanged. Copper, silver and iron take up carbon in quantities that, although small, are sufficient to cause marked changes in the physical properties of the metals; it is noteworthy that no definite crystalline compound could be obtained with iron. On the other hand, fused aluminium takes up carbon readily with formation of the crystalline carbide Al4C3, and the oxides of many other metals furnish similar crystalline compounds when heated in the electric furnace with an excess of carbon. The behaviour of these substances with water furnishes the most convenient mode of classification. The carbides of molybdenum, Mo2C, of tungsten, W2C, of titanium, TiC, of zirconium, ZrC and ZrC2, and of chromium, Cr4C and Cr3C., do not decompose water at the ordinary temperature. Of those reacting with water, the carbides of lithium, Li2C2, calcium, CaC2, strontium, SrC2, and barium, BaC2, furnish pure acetylene; of aluminium, Al4C3, and of beryllium, Be2C, pure methane; of manganese, Mn3C, a mixture of equal volumes of hydrogen and methane; whilst the metals of the cerite group give crystalline carbides of the type RC2 (CeC2, LaC2, YC2, and ThC2), all of which react with cold water, forming a complicated gas mixture containing hydrogen, acetylene, ethylene, and methane. But the most complex reaction is that furnished by uranium carbide, U2C3, with water. In this case, in addition to a gaseous mixture containing methane, ethylene, and hydrogen, liquid and solid hydrocarbons are produced in abundance, more than 100 grams of liquid hydrocarbons being obtained in one experiment from four kilograms of carbide. Cerium and lanthanum carbides have also furnished small quantities of solid and liquid hydrocarbons.