Theoretically one kilogramme of coal should develop 5·26 cubic metres of gas, having a heat of combustion at 0° C., and atmospheric pressure of 1360 calories. These figures enable us to calculate the efficiency of a gas-producing plant and the value of the gas obtained. Very good results have been obtained by gas generated by the latest Lencauchez process, with improvements added by the firm of Buire of Lyons, who construct the apparatus. The chief point to be noticed in these plants is the suppression of the steam boiler, which requires constant attention and stoking. The hearth of the generator is made of refractory bricks surrounded by a layer of sand to keep in the heat. The fuel enters through a hopper, which by means of a bascule and counterpoise never allows any direct communication between the interior of the retort and the surrounding atmosphere. The fuel is either coke or anthracite, and is spread over a grate situated over an ash-pit. This ash-pit forms an important part of the apparatus, for it is fed with water which evaporates from the heat striking down on to it from the incandescent coke. The steam generated by this novel process passes together with air up through the heated mass of fuel, forming a mixture of producer and water gases in the generator above. The supply of air is regulated by a centrifugal fan driven by the gas engine which the plant is supplying. The necessity of having to use this fan very often more than destroys the advantage gained by the absence of a boiler. The gases produced pass by a pipe into the scrubbers after first surmounting the pressure of a water valve, which prevents them from returning to the generator. The scrubbers are filled with coke, with a continual stream of water flowing down over it. The gases in passing up are therefore thoroughly cleansed, so much so that they are fit to pass straight to the gasometer. When the gasometer is full and has reached its top position, it acts on a lever connected by a wire rope with a tap regulating the air supply of the generator. The centrifugal fan ceases to act, and the coke in the generator soon cools down, and the production of gas ceases. As the gasometer falls again the process is re-started, but not before the coke or anthracite in the generator has been re-lit automatically. The whole plant, therefore, only produces gas in proportion to the demand made on it, which is a necessary condition when driving gas engines. The coke is automatically re-lit by a small jet at the side of the generator, and fed by gas from the gasometer. A plant producing gas sufficient for 60 horse-power, or about 200 cubic metres per hour, uses up about 100 litres of water for vaporization, and about 500 for cooling the scrubbers. The water used for cooling the cylinder of the engine which the plant is supplying may be used for vaporizing purposes, and requires the addition of a small pump. Matter et Cie. of Rouen uses the Buire-Lencauchez gasogene