small amounts at a time. In the steam-engine, large or small, the whole body of water is exposed to the action of the fire, and a considerable quantity of steam is constantly generated. In this, small quantities of water are successively forced from a reservoir through coils of highly heated tubing, and there flashed into steam. A force-pump driven by the engine continually supplies water to the reservoir. The relation of the different parts of the apparatus to each other, and the working of the system, are clearly shown in Fig. 6. The long tubing, in which the water is converted into steam, leads from the air-chamber to the steam-chest of the engine. It is coiled first in a receptacle through which the exhaust steam passes, and then in the generator, where it is as completely as possible exposed to the action of the fire. In starting the engine, the fly-wheel is turned by hand, so as to produce a pressure in
Fig. 7.
the air-chamber. This forces the water into the coil, where it is rapidly converted into steam, and delivered in the steam-chest at the pressure furnished by the pump. When the engine begins running, it drives the pump and maintains the pressure. If the engine is stopped
