[38] Aluminium, when heated to the high temperature of the electric furnace, dissolves carbon and forms an alloy which, according to Moissan, when rapidly treated with _cold_ hydrochloric acid leaves a compound C_{3}Al_{4} in the form of a yellow crystalline transparent powder, sp. gr. 2·36 (_see_ Chapter VIII. Note 12 bis). This _carbide of aluminium_ C_{3}Al_{4} corresponds to methane CH_{4}, for Al replaces H_{3} and carbon O_{2} or H_{4}, that is, it is equal to three molecules of CH_{4} with the substitution of twelve atoms of H in it by four of Al, or, what is the same thing, it is the duplicated molecule of Al_{2}O_{3} with the substitution of O_{6} by C_{3}. And indeed C_{3}Al_{4} under the action of water forms marsh gas and hydrate of alumina: C_{3}Al_{4} + 12H_{2}O = 3CH_{4} + 4Al(OH)_{3}. This decomposition gives a new aspect of the synthesis of hydrocarbons, and quite agrees with what should follow from the action of water upon the metallic carbides as applied by me for explaining the origin of naphtha (Chapter VIII., Notes 57, 58, and 59). Frank (1894) by heating Al with carbon obtained a similar although not quite pure compound, which (like CaC_{2}) evolves acetylene with hydrochloric acid _i.e._ probably has the composition AlC_{3}. Aluminium forms alloys with different metals with great ease. Among them the copper alloy is of practical use. It is called _aluminium bronze_. This alloy is prepared by dissolving 11 p.c. by weight of metallic aluminium in molten copper at a white heat. The formation of the alloy is accompanied by the development of a considerable quantity of heat, so that it glows to a bright white heat. This alloy, which corresponds with the formula AlCu_{3}, presents an exceedingly homogeneous mass, especially if perfectly pure copper be taken. It is distinguished for its capacity to fill up the most minute impressions of the mould into which it may be cast, and by its extraordinary elasticity and toughness, so that objects cast from it may be hammered, drawn, &c., and at the same time it is fine-grained and exceedingly hard, takes an excellent polish, and, what is most important, its surface then remains almost unchangeable in the air, and has a colour and lustre which may be compared to that of gold alloys. Hence aluminium bronze is much used in the arts for making spoons, watches, vessels, forks, knives, and for ornaments, &c. No less important is the fact that the admixture of one-thousandth part of aluminium with steel renders its castings homogeneous (free from cavities) to an extent that could not be arrived at by other means, nor does the quality of the steel in any respect deteriorate by this admixture, but rather is it improved. In a pure state, aluminium is only employed for such objects as require the hardness of metals with