574 MACHINES, WORK, AND ENERGY 



the cylinder and allow the steam in the right end of the 

 cylinder to escape through the exhaust. 



684. The Boiler. The boiler in which the steam is generated 

 may be any one of several different types. The more common 

 types are the tubular upright (Figs. 358 and 359) and the 

 tubular horizontal (Fig. 360) boilers. But with any form of 

 boiler three safety devices must be supplied: A water gauge, 

 a steam pressure gauge, and a safety valve. Review Arts. 

 158, 159, and 160. 



THE GAS ENGINE 



685. The Internal Combustion Engine. We have seen 

 that in the case of the steam engine the fuel is burned be- 

 neath the boiler, producing steam which is then conveyed to 

 the engine. It is evident that the boiler may be located 

 some distance from the engine. In gas engines, however, 

 the fuel is burned within the cylinder of the engine. Such 

 engines are, therefore, called INTERNAL COMBUSTION ENGINES. 



686. The Fuel of Internal Combustion Engines. Such 

 engines may burn almost any kind of combustible gases. 

 Everybody is somewhat familiar with such engines burning 

 gasoline and used in automobiles or on farms. But in- 

 ternal combustion engines, or gas engines as they are com- 

 monly called, may also use as fuel natural gas, coal gas, water 

 gas, producer gas, kerosene, crude petroleum, alcohol-, or 

 even finely powdered coal. 



687. The Earliest Gas Engines. The first really successful 

 internal combustion engines burned gasoline. They were 

 made in France and Germany in 1861 and 1862. The first 

 successful gas engines made in the United States were made 

 in 1873. 



688. Importance of the Gas Engine. For many years 

 these engines were not of great importance. They were then 

 used only where small amounts of power were needed oc- 

 casionally and in places where other power was not easily 

 obtainable. In recent years, however, engines burning 



