methane (mĕthˈān) [key], CH4, 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, in the form of icelike methane hydrate
(composed of methane and frozen water), also is stored in seabed
sediments at ocean depths where sufficiently low temperatures
and high pressures prevail. 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 t