Their latest achievement in this direction is the erection of a 320 horse-power engine supplied by two Buire-Lencauchez gasogenes with poor gas. This is the largest single-cylinder gas engine in the world. The Simplex engine was the pioneer of motors using poor gas. The machine we described was for use with coal gas, and some modification has to be made in the parts when the motor is required to use gases of the Dowson type. The economy is very good, only 580 litres of coal gas or 550 grammes of anthracite being used per horse-power hour. [Illustration: FIG. 48.—Combined Simplex Engine and Buire-Lencauchez Gas-Producer.] _Gardie motor._—We have shown how poor gases are, beyond a shadow of a doubt, cheaper than coal gas for the production of power. Many makers have therefore attempted to use it by simply adding a gas-producing plant to existing engines. Sometimes these motors were totally unsuited for these cheaply produced gases, and the result has been failure from miss-fire or irregular speed. The Crossley, Niel, and Andrews motors are exceptions, and a few others have also given fairly good results. We described in the previous chapter the ingenious gasogene devised by M. Gardie of Nantes; the motor which is constructed for use with it is rather novel. It has two cylinders placed side by side, a compressing pump and reservoir for compressed air. The gaseous mixture arriving at a high temperature from the gasogene passes into the cylinders, and is mixed with a volume of air coming from the reservoir; these gases are compressed to about 100 lbs. on the square inch. At the entrance to the cylinders are placed two igniters of platinum heated to a white heat by an electric current at starting, but the temperature is afterwards maintained by the combustion. During the admission the gaseous mixture burns without any explosion and without raising the pressure, but considerably increasing in volume. At the commencement of the stroke the pressure in the cylinder is therefore the same as in the compressor, but it soon decreases by virtue of the expansion and driving forward of the piston. After having exhausted themselves in doing work the gases pass out into a regenerator, which communicates their heat to the air for admission. The valves are actuated by a horizontal shaft placed above the cylinders; the cams are three in number corresponding to three valves, of which two regulate the admission of gas and air to a chamber in which they are mixed. The third valve opens the exhaust. This arrangement is not unlike that adopted by MM. Forest and Gallice for their marine oil engines.