_Niel petroleum engine._—In these motors, the general arrangement of whose parts is similar to that of the gas engines constructed by the same firm, the principal part is the vaporizer. It consists of a small cast-iron chamber, provided with radiating ribs in its interior so as to increase the surface; the petroleum, coming from a reservoir placed at a height of about six feet, passes through a regulating valve, and is dispersed in fine drops over the surface of the radiating ribs; the vaporization is consequently very steady. An automatic valve allows air to pass into this chamber from the outside, forming an explosive mixture with the vaporized oil. A special tube coming from the reservoir supplies a lamp with oil for heating the ignition tube and also the vaporizer at the same time. A methylated spirit lamp is used for warming them up to the right temperature before starting the engine. The governor acts on both the admission and the exhaust, and the supply of oil is indirectly regulated by the closing of the exhaust valve. The whole mechanism is ingenious, giving excellent results; the speed is very constant, and the consumption of oil is within wide limits proportional to the demand for power. About a pound of oil is consumed per horse-power hour, including that necessary for the lamp. Two patterns of this engine are built, one vertical and the other horizontal. In the latter, called the Atlas engine, the consumption per hour is slightly greater. The governor is also different. The compression in the cylinder rises to about two atmospheres, and the quantity of water necessary for the water jacket varies from seven to ten gallons per horse-power hour, according to the size of the motor. CHAPTER VI GAS GENERATING PLANT