192 



ON SUPERHEATED STEAM. 



Tig. 21. 



steam or steam-boiler? Why, that 230° of in- 

 creased temperature gives or causes an expansion 

 of force equal to twenty-five atmospheres, or 

 360 lbs. to the square inch ! 



A further illustration of the 

 formation of sub-saturated steam 

 will be shown on reference to the 

 diagram, Fig. 21. 



In it let it be supposed that 

 one cubic inch of water is gene- 

 rated into one cubic foot, or 1,700 

 cubic inches under the ordinary pressure of the 

 atmosphere; if heat be applied, it is the next 

 EiG. 22. moment sub-saturated, as it 



would take up more water if 

 present; if 15 lbs. pressure be 

 added, as in Fig. 22, it will evap- 

 orate one cubic inch more water 

 with heat in the same space ; if 

 another 15 lbs. pressure be added, 

 another cubic inch of water will 

 be evaporated ; if a fourth cubic inch of water, and 

 about 45 lbs. pressure, it also will be evaporated 

 into the same space of a cubic 

 foot; or, further, the cubic foot 

 of steam could be compressed by 

 15 lbs. weight into half its space, 

 or 850 cubic inches, as shown in 

 Fig. 23. 

 And if the heat be continued, it immediately be- 





Fig. 23. 



