_Bénier gasogene._—Since the 1889 Exhibition, where a Simplex engine was to be seen working with poor gas generated on the Dowson system, engineers and others have fully recognized the advantages of this cheap motive power. In the last few years a very large number of these plants have been erected, and the experience gained by practice has shown, that in spite of the extreme cheapness there are serious faults to be found with this class of apparatus. The gases are produced under pressure and are of an exceedingly poisonous nature, carbon monoxide being the same gas which is principally evolved from burning charcoal. Great care has therefore to be taken that there are no leaks, which might have fatal results if inhaled by the persons attending to the plant. The chemical operation of the production of the gas is a very delicate one, and requires skilled attendants if constancy in the quality of the gas is required. The Bénier gasogene has been designed to eradicate or circumvent these grave drawbacks. It presents many novel features, the most interesting of which is the device for absolutely ensuring no leaks. This is done by generating the gas below the pressure of the atmosphere. This low pressure is maintained throughout the plant right up to the valve which admits the explosive mixture to the motor cylinder. The only places in which the pressure is raised are surrounded by vacuum jackets leading to the gas reservoir. The gas-producing plant can therefore be installed anywhere, even in dwelling-houses or cellars, without running any risk of poisoning the inmates. The irregularity of the qualities of the gas produced by other generators is due to the difficulty of always admitting the air and steam in the same proportions to the generator. This difficulty is got over in the Bénier gasogene, indirectly as the result of the low pressure in the interior: the air and steam enter under atmospheric and therefore constant pressure, and their proportions can be regulated to a fine degree of accuracy by varying the size of the orifices through which they are admitted. So regular is the production of the gas in quality that diagrams taken from an engine at intervals of several hours showed no appreciable difference. The functions of attendant can be thoroughly fulfilled by an unskilled labourer or boy, the operation of emptying a quantity of coke once every half-hour being sufficient to keep the plant working steadily. This apparatus is also an economic one, partly because of the invariable qualities of the gas produced, but chiefly owing to air and steam being heated before entering the hearth. A rotating grate is also provided, so that the generation of gas is in no way interfered with by the clearing out of ash and clinkers. A special engine is constructed for use with this plant, which we shall describe in the next chapter.