To obtain carburetted hidrogen, or coal-gas, from common pit-coal, and to apply it for the purposes of illumination, the coal is introduced into large iron cylinders, called retorts, to the apertures of which iron pipes are adapted, terminating in a vessel, or vessels, destined to purify and collect the gas. The retorts charged with coals and made air-tight, are placed upon the fire, the action of which extricates the gazeous products from the coals, together with an aqueous ammoniacal vapour, and a tenaceous bituminous fluid, or tar, &c. The liquid substances are conveyed into proper vessels, and the gazeous products are conducted, by means of pipes, under the gasometer, where the gas is again washed, and remains ready for use. There are also other pipes leading from the gasometer, which branch out into smaller ramifications, until they terminate at the places where the lights are wanted. The extremities of the pipes have small apertures, out of which the gas issues, and the streams of gas being lighted at those apertures burn with a clear and steady flame as long as the supply of gas continues. All the pipes which come from the gasometer are furnished at their extremities with stop-cocks to regulate the admission of the gas. The burners are formed in various ways, either a tube ending with a simple orifice, at which the gas issues in a stream, and if once lighted will continue to burn with the most steady and regular light imaginable, as long as the gas is supplied; or two concentric tubes of brass, or sheet-iron, are placed at a distance of a small fraction of an inch from each other, and closed at the bottom. The gas which enters between these cylinders, when lighted, forms an Argand lamp, which is supplied by an internal and external current of air in the usual manner. Or the two concentric tubes are closed at the top with a ring having small perforations, out of which the gas alone can issue, thus forming small distinct streams of light. [Illustration] The gas-apparatus, plate 2, will be found very convenient for exhibiting, in the small way, the general nature of this new art of illumination, whilst at the same time it may serve to ascertain, at a trifling expence, the comparative value of different kinds of coals intended to be employed for the production of this species of light, as well as other occasional purposes connected with the gas-light system of illumination.