CHAPTER XXV 

 BOILERS AND THE GENERATION OF STEAM 



343. Source and Characteristics of Steam. The source 

 of energy used in driving many forms of machinery is the oil 

 or coal consumed usually in the boiler-room of the power 

 plant. When this oil or coal is burned it gives off heat. The 

 heat converts water into steam, and the expansion of the 



steam drives the engine. The steam 

 that issues from a steam locomotive 

 or from an open pipe of a power plant, 

 like the steam that is given off from 

 a kettle on the stove, is a watery 



FIG. 157 .Heating Water (aqueous) vapor and is always found 

 by Steam. The arrow V . . 



represents the passage when water is heated. Steam resem- 



the he water. Ste Th I e "at- bleS common air and other S ases in 

 tachment is screwed many of its properties. It differs 

 onto the steam pipe. r ., . .. , , . 



irom gases in that it does not retain 



permanently its gaseous condition. For this reason it is not 

 called a gas but an aqueous vapor. The white cloud of vapor 

 noticed when steam is liberated is due to water particles in 

 suspension in the air. 



The chief property or characteristic of steam is its elas- 

 ticity which makes it capable of enormous expansion. 



344. The Boiler of the Steam Engine. The principal 

 parts of a steam engine are the boiler and the engine. The 

 boiler is a cylindrical steel vessel located over a fireplace. 



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