Note 38 — Chapter XVII · BORON, ALUMINIUM, AND THE ANALOGOUS METALS OF THE THIRD GROUP

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 C3Al4 in the form of a yellow crystalline transparent powder, sp. gr. 2·36 (see Chapter VIII. Note 12 bis). This carbide of aluminium C3Al4 corresponds to methane CH4, for Al replaces H3 and carbon O2 or H4, that is, it is equal to three molecules of CH4 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 Al2O3 with the substitution of O6 by C3. And indeed C3Al4 under the action of water forms marsh gas and hydrate of alumina: C3Al4 + 12H2O = 3CH4 + 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 CaC2) evolves acetylene with hydrochloric acid i.e. probably has the composition AlC3.