[L. acetum, vinegar.] A substance composed of carbon and hydrogen and of remark-able powers. It is not a new discovery but has only lately been produced in large quantities from carbide of calcium, a product of the electric furnace. When water is thrown on this sub-stance it gives off acetylene gas. It was found about 1895, that this gas, when burned in a suit able burner, would give the brightest light of any known gas. When placed under strong pressure acetylene becomes a liquid, and the gas which arises from this is burned in suitable lamps, yielding a light twelvetimes as bright as that of ordinary coal gas. But this new light has not come into much use, for there is danger of explosion. Acetylene has other uses, for a great many chemical substances can be made from it, belonging to what are called the hydrocarbons.