GAS 635 they rush into a vacuum through an aperture in a thin plate, still they do not strictly act as vacua to each other ; for the diffusion of one gas into another is vastly slower than its pas- sage into a vacuum. III. ILLUMINATING GAS. This is to a limited extent obtained from natural sources, but the great supplies are made from the following substances: 1, coal; 2, wood; 3, peat; 4, resin; 5, petroleum; 6, oils and fats ; 7, water and coke. There are many lo- calities where combustible gases have long been known to issue from the earth. Gas has been used in China for centuries, conveyed in bam- boo tubes from fissures in salt mines in exca- vations from 1,200 to 1,600 ft. in depth. Near the Caspian sea in Asia there are several so- called eternal fires caused by gas issuing from the soil. In the Szalatna salt mine in Hun- gary illuminating gas constantly issues from a muddy clay contained between rock-salt strata. The village of Fredonia, N". Y., is lighted by gas which issues from bituminous limestone in- terspersed among the slates and sandstones of the Portage group. This gas consists of a mix- ture of marsli gas, CEU, and hydride of ethyl, CaHe. A flow of natural gas issued from a well which was sunk in 1865 at West Bloom- field, Ontario co., N. Y., for the purpose of ob- taining petroleum. Its composition, according to Profs. Silliman and "Wurtz, is: marsh gas, 82'41 ; carbonic acid, lO'll ; nitrogen, 4'31 ; oxygen, 0'23 ; illuminating hydrocarbon, 2'94. It was carried in a wooden main to the city of Rochester, a distance of 24 miles, in 1870, for the purpose of illuminating the city, but the experiment was a failure. Such gas has also been known to issue from beneath peat bogs, as that of Chatmoss, near the Manchester and Liverpool railway in England. These natural gases are of variable composition, light car- buretted hydrogen or marsh gas being usual- ly the principal constituent. Coal Gas. The first artificial production of illuminating gas from coal is due to Dr. Hales or the Rev. John Clayton, rector of Crofton, Wakefield, Yorkshire, England. Dr. Hales describes in a book published in 1727, called " Vegetable Statics," an experiment by which he obtained 180 cubic inches of inflammable air from 158 grains of Newcastle coal. In 1659 Mr. Thomas Shirley communicated a paper to the royal so- ciety on an inflammable gas which issued from a well near Wigan in Lancashire ; and the Rev. John Clayton nearly a century later, in examining the locality, found that the gas is- sued from a bed of coal. The experiment of subjecting the coal to heat was made, with the result of obtaining an illuminating gas, which, being collected in bladders, could be burned in jets. An account of these experi- ments was communicated to the royal society in 1739. Dr. Rick el, professor of chemistry at Wurzburg, in 1786 lighted his laboratory with gas made by the dry distillation of bones ; and in the same year Earl Dundonald of Scotland, in obtaining tar from the distillation of coals, also collected an illuminating gas, with which he lighted Culross abbey by way of experi- ment. The first practical attempt at gas light- ing is however generally accredited to William Murdoch, who in 1792 used coal gas for light- ing his workshops at Redruth in Cornwall. His invention remained unknown till about 1802, when it was introduced at the Soho foundery of Boulton and Watt, near Birming- ham. In the mean time Lebon, a Frenchman, used gas made from wood for lighting his house, and was therefore considered by the French as the inventor of gas lighting. In 1804 Mr. Mur- doch lighted the mills of Phillips and Lee at Manchester with gas which yielded an amount of light equal to that of 3,000 sperm candles. In 1813 London bridge was lighted with gas, and about the same time it was introduced into the streets in that part of the city ; but it was not introduced into Paris till 1820. Bituminous coals, such as English cannel and boghead coals, Ohio cannel, and the caking coals of Pennsyl- vania, Maryland, and Virginia, are used in this manufacture. The following may be consid- ered as the average composition of caking and cannel coals : CONSTITUENTS. Caking. Cannel. Carbon 87 '752 75 -25 Hydrogen 5 "239 5*50 Nitrogen 1-702 1-61 Oxygen 3-806 13'83 Ash 1-898 2'81 There are also small quantities of sulphur and iron, mostly in the form of iron pyrites. The nitrogen has its origin in the organic matter from which the coal is derived. When bitu- minous coal is heated to redness in the presence of air, it is principally converted into gases which unite with oxygen ; but if air is excluded, as when the coal is confined in retorts, the gas- eous products, unable to unite with oxygen, may be collected in receivers and burned in tubes. The products of the destructive dis- tillation of bituminous coal consist of a great number of gases, liquids, and solids, which may be conveniently included under the following heads, according to an analysis by Bunsen : Coke 68-93 Tar 12-23 Water 7'40 Marsh gas 7'04 Carbonic oxide 1 18 Carbonic acid... . 1*07 Olefiant gas 0*78 Sulphuretted hydro- gen 0-75 Hydrogen 0'50 Ammonia 0*17 Nitrogen 0'03 The olefiant gas here represents not pure heavy carburetted hydrogen or elayl, but a mixture, in variable quantities, of acetylene, C 2 H 2 , elayl, C 2 H 4 , trityl, C 3 H, ditetryl, C 4 H 8 , and several hydrocarbon vapors. There are also small quantities of cyanogen and sulpho- cyanogen. (See DISTILLATION, DESTRUCTIVE.) Upon the temperature to which the coal is subjected depend the products of distillation, which are formed by a rearrangement of the elements of the coal. The lower the heat>
