methane

methane , CH ₄ , colorless, odorless, gaseous saturated hydrocarbon; the simplest alkane . It is less dense than air, melts at -184°C, and boils at -161.4°C. It is combustible and can form explosive mixtures with air. Methane occurs naturally as the principal component of natural gas ; it is formed by the decomposition of plant and animal matter. When this decomposition occurs underwater in swamps and marshes, marsh gas is released. The firedamp of coal mines is chiefly methane. In the atmosphere methane is a greenhouse gas, helping to trap infrared radiation and warm the earth (see also global warming ).

Methane can be prepared in the laboratory by heating sodium acetate with sodium hydroxide, by the reaction of aluminum carbide with water, by the direct combination of carbon and hydrogen, or by the destructive distillation of coal or wood. As natural gas, methane is widely used for fuel. It is also used for carbonizing steel. It is unaffected by many common chemical reagents but reacts violently with chlorine or fluorine in the presence of light and is therefore important as a starting material for the synthesis of solvents, e.g., methylene chloride, chloroform, and carbon tetrachloride, and of some of the Freon refrigerants.

methane XIX. f. METH(YL) + -ANE.

methane(CH₄) The simplest hydrocarbon compound, which is released as a gaseous by-product of the metabolic activity of certain bacteria. The principal sources of atmospheric methane are swamps, marshes, and natural wetlands (which may also be nature reserves), paddy-rice fields, and cellulose-digesting bacteria in the guts of termites and ruminant cattle. Methane is an important greenhouse gas, absorbing long-wave radiation at wavelengths of about 10 μm.