GAS distillation were volatilized by passing through a range of red-liot pipes; but now it is found that ordinary retorts, properly heated and fed with small charges, answer perfectly well for the operation. Wood-gas, owing to its high specific gravity and the proportion of carbonic oxide it contains, must be burned at considerable pressure, in specially con- structed burners with a large orifice. It is largely used in Germany, Switzerland, and Russia, where wood is more easily obtained than coal. It was used at Philadelphia gas- works in 1856, where it was affirmed to be cheaper and of greater luminosity than coal-gas. Peat-Gas is evolved under circumstances the same as occur in connexion with the wood—gas manufacture, but the amount of moisture contained in peat is a serious obstacle to its successful use in this as in most other directions. Earnest and persistent efforts have been made to use peat as a source of gas, but these have met but little commercial success. To a limited extent it is used in various German factories which happen to be situated in the immediate iieiglibourhood of extensive peat deposits. Carbiu'etlecl G'as.—U1ider this head may be embraced all the methods for impregnating gaseous bodies with vapours of fluid or solid hydrocarbons. The objects aimed at in the carburetting processes are—(1) to increase the illuminat- ing power of ordinary coal-gas; (2) to render iion-luminous combustible gases, such as water—gas, luiiiiniferous; and (3) so to load iion—conibustible gases with hydrocarbon vapour as to make the combination at once luminiferous and a supporter of combustion. The plans which have been proposed, and the patents which have been secured for processes of carburetting, coming under one or other of these heads, have been almost endless ; and while the greater part of them have failed to obtain commercial suc- cess, they are sufficient to indicate that there is still a pos- sibility of doing much to increase the effect and cheapen the cost of production of gas. Further, although for ex- tensive use none of the gas-making plans can compete with coal—gas nianufacture, some of them are of much value for private establishments, country houses, factories, and similar places, where connexion with coal—gas works cannot be obtained. The carburetting of common coal—gas with the vapour of benzol obtained by the distillation of gas-tar was originally suggested by Lowe as early as 1832, and subsequently by the late Charles Mansfield, who showed that by passing gas over sponge saturated with benzol a very great addition was made to the illuminating power ; and he introduced an apparatus by which cominoii gas could thus be benzolized at a point very near the burner. The facts, however, that benzol is a highly inflammable liquid, that the benzolized gas varied in richness owing to the gas taking up much more benzol when the carburetter was newly charged than it did afterwards, and consequently that it often produced a smoky flame, and that sulphur compounds accumulated in the carburetter, as well as the trouble connected with charging the apparatus, all combined to prevent the extensive intro- duction of the process. In later times the value of benzol for aniline manufacture and other purposes would have been a serious bar to its use. Mr Bowditch introduced the use of a heavier hydrocarbon—a mixture of naphthalin with cymol—which he called carbolin, and which possesses the advantage of giving off no inflammable vapour at ordinary temperatures, and is, moreover, a substance for which no commercial demand exists. The carburetting appliance had to be placed in immediate proximity to the burners, and either heated by them direct, or by a small subsidiary jet, as the vapour of naphthalin solidifies on a very small fall of temperature and chokes up pipes. Carburetting by means of a solid block of naphthalin introduced into a gas-tight box, and partly volatilized by a strip of copper passing from 101 the burner flame into the box, has recently been proposed, and is now being carried into efi'ect with every prospect of great increase of illuminating power, and consequent economy, by the Albo-Carbon Light Company. The efforts to introduce carburetted water-gas have been numerous and persistent; and the sanguine statements of the various inventors have led to the loss of much capital through experiments undertaken on a great scale which have always resulted unfavourably. The whole of the proposed processes depended on the decomposition of water by passing it over highly-heated surfaces in pre- sence of glowing charcoal, whereby free hydrogen, carbonic oxide, and carbonic acid gases are produced, the carbonic acid being eliminated by a subsequent process of purifi- cation. The combustible gas so obtained was in earlier experiments charged with luniiiiiferous hydrocarbons by being passed into a retort in which coal, resin, or oil was being distilled, as in Selligue’s and other processes; or, as in Wliite’s hydrocarbon process, both steam and coal were treated together in a special form of retort. Since the introduction of American petroleum, however, most methods of carburetting water—gas have been by impregnat- ing it with the vapour of gasolin, the highly volatile portion of petroleum which comes over first in its distilla- tion for the preparation of “kerosene” lamp oil. VVater-gas has been proposed, not only as an illuminating agent, but at least as much as a source of heat; but the heat expended in the decomposition of water is much greater than can in practice be given out by the resulting gases. Several of the processes introduced for rendering ordinary atmospheric air at once combustible and luminiferous, by saturating it with the vapour of gasolin, have been so satis- factory that this air-gas is now largely used both in America and Europe for lighting mansions, churches, factories, and small rural districts. The general principle of the air- machines will be understood from the following description of the “ sun auto-pneumatic ” apparatus (Hearson’s patent), which is in extensive use throughout Great Britain. will mil ,|lgi1l , ll‘; /- yfl ‘in p A will "l l” 1. a nus»; ; iliilmis 11"‘ ll“! W 1| WW .. -|‘ I I,» ..-'. FIG. 23.—Sun Auto-Pneumatic Apparatus. t&x' surmounted by two turrets. Internally the cylinder is divided into two compartments by a transverse portion, one being occupied by a rotary blower, an apparatus similar in construction to the drum of a water-meter, and the other by an elevator or dipper wheel, the function of which is to raise gasolin into the blower chamber, where the gasohn
must be maintained at a constant level. The blower and