BOILERS AND GENERATION OF STEAM 325 



When the steam is taken directly from the boiler to the 

 engine, it is termed saturated steam and is generated in con- 

 tact with its water of generation. 



When the boiler is overworked, the steam, due to the vio- 

 lent action of its generation, takes with it particles of water. 

 Such steam is called wet steam. Dry steam contains no 

 watery moisture; it may be saturated or supersaturated. 



Steam from the boiler, heated to a higher temperature by 

 passing it through a vessel or coils of pipe separated from the 

 boiler, called a superheater, is termed superheated steam. 

 Steam loses heat as quickly as it acquires it, and so every 

 passage conveying superheated steam should be well covered 

 with non-conducting material. 



366. Terms Used in Calculations. One should be famil- 

 iar with a number of terms which are frequently used in 

 calculations. 



Heating surface means all surface having water on one side 

 and fire or heated gases on the other. 



Grate surface means the surface of the grate bars, or the 

 area of the surface which supports the burning fuel. 



Steam room is the space above the water line, or all the 

 space in a boiler not occupied by water. 



Horse-power. There is no such thing as the horse-power 

 of a boiler. The term horse-power refers to the measure- 

 ment of power or energy produced in a given time. A boiler 

 does not produce energy; therefore, the work of a boiler 

 cannot be measured by horse-power. Energy is the product 

 of a given force in pounds multiplied by the distance in feet 

 through which it moves; horse-power is obtained by dividing 

 the energy thus obtained in one second by 550 ; in one minute, 

 by 33,000; and in one hour by 1,980,000. A boiler contains 



