In this country the engine is made for the trade in three sizes, from two to seven horse-power, but those of larger power are built when desired. The English makers furnish it from one up to forty horse, and as wide a range is given it on the Continent. The engine, as shown in the engraving (Fig. 12), is of the form constructed by the American makers. The cylinder is placed horizontal and overhangs the substantial bed-block of the machine. It is open to the atmosphere at the end toward the fly-wheel, and is closed at the other by a head-piece in which are the appliances for introducing and igniting the gaseous mixture, the construction of which is shown in the sectional cut Fig. 13. The head-plate A closes the cylinder entirely except at l, where there is a passage for the admission of the combustible charge. Between this plate and an outer one, C, is a slide-valve, B. The outer plate is pressed against the valve by the spiral springs shown in Fig. 12. The
Fig. 13.
pipe supplying the gas opens in its inner face at c, and at m there is a small jet constantly lit while the engine is in operation. The slide-valve B has two channels, i and n, the former placing the air and gas in communication with the cylinder, and the latter serving to ignite the mixture. The piston being at the beginning of its stroke, the valve B is in such a position that the air-inlet a and the gas-inlet c are in communication with the passage l through the port i. The piston then moves outward, drawing in a charge of air and gas which it compresses on its return, the valve B having moved so as to close the opening l. By this movement the channel n becomes filled with gas from the small supply-pipe o, which is ignited at the jet m. Just as the piston has completed the compression of the gaseous mixture, n arrives opposite l and ignites it, the valve continuing its motion so as to close the opening. The piston is driven outward by the expansion of the gases, and on its return they are expelled through the valve q in the side of the cylinder operated by the mechanism of the engine. The slide valve is reciprocated by a crank on the end of the lay-shaft, shown running lengthwise of the cylinder, which revolves but half as fast as the main shaft. The combustible mixture can therefore be drawn in only once
