366 FARM MOTORS 



temperature, but steam forms and the piston gradually 

 rises. Since the water is passing into steam, it must be 

 disappearing. During formation the steam and the water 

 remain at the same temperature as the water was when 

 steam commenced to form. The heat which has been 

 continually added has been used to convert the water 

 into steam and is known as latent heat. 



3. After all the water has been evaporated, if heat be 

 still applied the temperature of the steam will commence 

 to rise and the piston will also continue to rise. Since 

 the steam is not now in contact with the water and is 

 hotter than the steam was when formed and in contact 

 with the water, we have superheated steam; in other 

 words, steam which is heated above the temperature of 

 the boiling point of water, which corresponds to the 

 pressure at which it is generated. 



508. Saturated steam is steam at its greatest possible 

 density for its pressure. It is invisible and must con- 

 tain no water in suspension ; in other words, it must be 

 dry and still not be superheated. The temperature of 

 saturated steam in the presence of water is the same as 

 that of the water, and for steam of a given temperature 

 there is only one pressure. If the temperature increases 

 and the volume remains constant, the pressure does like- 

 wise, for as the temperature increases more water is evap- 

 orated, or if the temperature decreases the pressure does 

 also and some of the water is condensed. 



509. Total heat of steam is made up of two com- 

 ponents, heat of the liquid and latent heat. 



Heat of the liquid is the amount of heat there is in water 

 at the temperature of the steam. 



Latent heat is the amount of heat required to evaporate 

 I pound of water at a given temperature into steam at 

 the same temperature. It is made up of two components. 



