MARSH-GAS, or METHANE, also called light carbureted hydrogen and fire-damp. It is generated in muddy bottoms of pools in which water-plants grow. When the mud is stirred bubbles of gas rise to the surface, and are easily collected in an inverted bottle. This gas is a mixture of methane and carbonic acid; the latter is readily removed by agitation with limewater or caustic potash or soda. It is also often disengaged in coal mines, sometimes issuino. in streams from fissures, having been pent up in the coal. It is •one of the products of tlie distillation of coal in making illuminating gas. Its formula is .CIL, and it contains 12 parts of carbon and 4 parts of hydrogen, by weig:ht. Its specific gravity is 0.'559, having a little more than half the density of common air. Containing, as it does, a large proportion of hydrogen, it forms, when mixed with oxygen, a highly •explOsive compound. Mixed with common air it is also very explosive, as the terrible -accidents in coal mines have unhappily demonstrated. It was a long time before marsh
gas could be obtained pure by artificial means. That contained in coal gas and rnade by passinm alcohol through a red-hot tube is exceedingly difficult of separation. Dumas, however,%as discovered a method by which it can be readily procured in large quanti ties, perfectly pure. A mixture is made of 40 parts of crystallized acetate of soda, 40 parts of caustic soda, and 60 parts of quicklime in powder, strongly heated in a retort. The gas is given off in great abundance and may be collected over water. The reaction is as follows: NaC,11808-FNaHO=CH.+Na,CO3. It will be perceived that lime does not enter as an element in this calculation. It is introduced only to prevent the soda froni attacking the glass of the retort.