STEAM ENGINES 365 



The classes of engines generally used in agricultural 

 pursuits would be known as high-speed, non-condensing, 

 either simple, single or double, or compound tandem or 

 cross, throttling governed, either stationary or loco- 

 motive traction and double-acting. 



507. Generation of steam. Enclose I pound of water 

 at a temperature of 32 F. in a cylinder under a movable 

 frictioriless piston. Suppose the piston to have an area 

 of I square foot, but no weight other than the atmos- 

 pheric pressure. Apply heat to the water and the follow- 

 ing results will be noted : 



A, one pound of water at 62 F. ; #, one pound of water at 212 P., but lacks 

 heat enough to turn it into steam ; C, is saturated steam in contact with the 

 water ; D, one pound of steam at 212 F. ; E, one pound of superheated 

 steam. 



1. The temperature rises, but the piston remains in the 

 same position until a certain temperature is reached. 

 When the piston commences to rise the degree of tem- 

 perature is known as the boiling point. This point varies 

 with the pressure. If the pressure bearing on the piston 

 had been 10 pounds to the square inch instead of 14.7, the 

 boiling point would have been reached at a lower tem- 

 perature, and if the pressure had been 20 pounds to the 

 square inch, the boiling point would have had a higher 

 temperature. 



2. As soon as the water has reached the boiling point, 

 though heat still be applied, there is no further rise in 



