It consists of three distinct apparatus:--namely, a portable furnace, fig. 1, plate 2, by means of which the gas is prepared--fig. 2, a purifyer, or condenser, which separates and purifies the products obtained from the coal, so as to render the gas fit for the purpose of illumination--fig. 3, a gasometer, or reservoir for receiving and preserving the purified stock of gas, and from which it may be transferred and distributed as occasion may require. The following statement will explain more fully the general nature of this portable chamber apparatus:--_a_, represents a cast iron retort, such as is used for chemical operations in the small way. This retort rests upon a tripod of hammered iron, placed upon the bars of the grate of the chemical furnace. Into this retort the coals are put for furnishing the gas. It is provided with a solid iron stopper ground air-tight into the mouth of the retort, and the stopper is secured in its place by an iron wedge passing over it in the centre; by means of which the mouth of the retort when charged with coal is readily made air-tight, and the stopper may easily be removed by knocking out the iron wedge. _b._ is a metal pipe which conveys all the distillatory products from the retort into the purifier fig. 2. This tube is bent at right angles at the extremity where it enters the intermediate vessel fig. 2. The purifier fig. 2, is divided into three compartments marked _c._ _d._ _e._ The first compartment is filled with water, and by means of it an air-tight communication is established with the retort which furnishes the gas. The second compartment, _d_, contains a solution of caustic pot-ash composed of about 2 parts of caustic pot-ash and 16 of water, or a mixture of quick-lime and water of the consistence of very thin cream. The object of this compartment is to separate the non-inflammable gases and other products evolved during the distillation of the coal, from the carburetted hidrogen or coal-gas, so as to render it fit for use. The third compartment _e_ is left empty to receive the tar and other liquid products. Into the first compartment _c_, all the gazeous and liquid products are delivered, as they become evolved during the distillation, by means of the pipe _b_. The compartment _d_, of the purifier, or alcali vessel, is furnished with a wide perpendicular pipe, which serves to make an air-tight communication with the retort, by allowing the tube _b_, to pass readily through it. From the chamber _c_, the liquid and gazeous products pass to the tar-chamber, or compartment _e_, by means of the descending pipe _f_. The tar and other condensible substances are therefore deposited at _e_, whilst the gazeous products alone ascend from the tar-chamber _e_, by the pipe _g_, and down again the pipe _h_, (which is closed at the top) into the compartment _d_, of the vessel or purifier, fig. 2. The gas being thus made to pass from the compartment