Carburetted Hydrogen, the name of two compounds of carbon and hydrogen, one distinguished as light carburetted hydrogen, and the other as olefiant gas. The former is the fire damp of miners, also called marsh gas, etc. It was observed in coal mines as early as 1640. Dr. Franklin in 1774 called the attention of Priestley to an inflammable gas obtained in this country by stirring stagnant pools. It was first accurately described by Drs. Dalton and Thomson in 1811. It is a colorless gas, without taste or smell, and neither of acid nor alkaline properties. Its composition is: carbon 1 atom, hydrogen 4 atoms, CH4; or per cent., C=75, H=25. Its weight, compared with that of air, is 0.555. Burning bodies immersed in it are extinguished, and it does not support respiration. It is highly inflammable, burning with a yellow flame; but it requires a high heat to ignite it. United with oxygen or atmospheric air in due proportion, a compound is produced which explodes with the electric spark or the approach of flame. The mixture of air to produce an explosion may be from 7 to 14 times that of the gas. Water and carbonic acid gas result from the chemical change. In mines of bituminous coal this gas is generated abundantly, and it also issues from the earth in various parts of the world.

The burning springs of Baku have already been noticed in the description of that place. Similar springs are met with in western New York, Pennsylvania, and Virginia; and the gas from some of these is used for illuminating purposes. The principal interest that attaches to this gas is owing to the terrible explosions it has caused in the English coal mines, which led Sir Humphry Davy and George Stephenson to investigate its properties with a view of discovering some method of protecting the miners. Thus the safety lamp was discovered, which still continues to be the most valuable guard next to thorough ventilation. - Olefiant gas, the other variety of carburetted hydrogen, was discovered by some Dutch chemists in 1796, who gave it this name in consequence of its forming an oil-like liquid with chlorine. It consists of 85.71 per cent, of carbon and 14.29 of hydrogen, and is properly represented by the symbol C2H4. Its specific gravity is very near that of atmospheric air, being estimated at 0.967. The gas possesses an odor slightly ethereal. Burning bodies are extinguished and animals cease to breathe in it. It burns with a dense white light. Mixed with three or four volumes of oxygen or 10 or 12 of air, it violently explodes by the electric spark or flame.

Exposed to red heat in a porcelain tube, it is decomposed, charcoal is deposited, and light carburetted hydrogen or hydrogen remains. A succession of electric sparks convert it into charcoal and hydrogen, the latter occupying twice the original bulk of the gas. It is liquefied under the pressure of 40 atmospheres, when exposed to the low temperatures attained by solid carbonic acid and ether in a vacuum. In this form it is a clear, colorless, transparent fluid. Several methods are given for obtaining it. It results from distilling coal or fat substances in close vessels. Alcohol distilled with four to seven times as much sulphuric acid yields it, and the gas is purified by passing it through lime water.