MARSH

See also:

• GAS

GAS (methane),

See also:

• CH4

CH4  , the first member of the series of paraffin hydrocarbons . It occurs as a constituent of the " fire-damp " of coal-mines, in the gases evolved from volcanoes, and in the gases which arise in marshy districts (due to the decomposition of vegetable matter under the surface of water) . It is found associated with petroleum and also in human intestinal gases . It is a product of the destructive distillation of complex organic matter (wood, coal, bituminous shale, &c.), forming in this way from 3o to 40% of ordinary illuminating gas . It may be, synthetically obtained by passing a mixture of the vapour of carbon bisulphide with sulphuretted hydrogen over red-hot copper (M . Berthelot, Comptes rendus, 1856, 43, p . 236), CS2 + 2H2S + 8Cu = 4Cu2S + CH4; by passing a mixture of hydrogen and carbon monoxide over reduced nickel at 200—250° C., or hydrogen and carbon dioxide at 230—300° C . (P . Sabatier and J . B . Senderens, Comptes rendus, 1902, 134, pp . 514, 689); by the decomposition of aluminium carbide with water [H .

Moissan, Bull . Soc . Chim., 1894, (3) II, p . 1012]; and by heating phosphonium iodide with carbon bisulphide in a sealed tube to 120-140 C . (H . Jahn, Ber., 1880, 13, p . 127) . It is also obtained by the reduction of many methyl compounds with nascent hydrogen; thus methyl iodide dissolved in methyl alcohol readily yields methane when acted on by the zinc-copper couple (J . H . Gladstone and A . Tribe, Jour . Chem .

Soc., 1884, 45, p . 156) or by the aluminium-

mercury couple . It may be obtained in an indirect manner from methyl iodide by conversion of this compound into zinc methyl, or into magnesium methyl iodide (formed by the action of magnesium on methyl iodide dissolved in anhydrous ether), and decomposing these latter substances with water (E . Frankland, 1856; V . Grignard, 1900), Zn(CH3)2+H2O=2CH4+ZnO; 2CH3MgI +H2O=2CH4+MgI2+ MgO . In the laboratory it is usually prepared by J . B . A . Dumas' method (Ann., 1840, 33, p . 181), which consists in heating an-hydrous sodium acetate with soda lime, CH3CO2Na + NaOH= Na2CO3 + CH4 . The product obtained by this method is not pure, containing generally more or less ethylene and hydrogen . Methane is a colourless gas of specific gravity 0.559 (air = I) .

It may be condensed to a colourless liquid at -155° to -16o° C. under atmospheric pressure (S . Wroblewsky, Comptes rendus, 1884, 99, p . 136) . It boils at -162° C. and freezes at -186°C . Its

critical temperature is -99.5° C . (J . Dewar) . The gas is almost insoluble in water, but is slightly soluble in alcohol . It decomposes into its constituents when passed through a red-hot tube, small quantities of other hydrocarbons (ethane, ethylene, acetylene, benzene, &c.) being formed at the same time . It burns with a pale flame, and when mixed with air or oxygen forms a highly explosive mixture . W . A .

Bone (Jour . Chem . Soc., 1902, 81, p . 535; 1903, 83, p . 1074) has shown that in the oxidation of methane by oxygen at 450—500° C. formaldehyde (or possibly methyl alcohol) is formed as an intermediate product, and is ultimately oxidized to carbon dioxide . Methane is an exceedingly stable gas, being unaffected by the action of chromic acid, nitric acid, or a mixture of nitric and sulphuric acids . Chlorine and bromine, however, react with methane, gradually replacing hydrogen and forming chlor- and brom- substitution products .