120 CALORIFIC POWER OF FUELS. 



proportional weight of water which the thermal value of the 

 superheating would evaporate into dry steam from and at the 

 temperature due to the pressure. "The factor of correction 

 for quality of steam " in a boiler-test differs from the * ' quality " 

 itself, from the fact that the temperature of the feed-water 

 is lower than that of the steam. 

 Let 



Q = quality of moist steam as described above ; 

 Q i = the quality of superheated steam as described above ; 

 P the proportion of moisture in the steam ; 

 k the number of degrees of superheating; 

 F= the factor of correction for the quality of the steam 



when the steam is moist 

 FI = the factor of correction for the quality of the steam 



when the steam is superheated ; 



H = the total heat of the steam due to the steam-pressure ; 

 L = the latent heat of the steam due to the steam-pressure ; 

 T= the temperature of the steam due to the steam-pressure ; 

 T^ = the total heat in the water at the temperature due to 



the steam-pressure;* 

 J = the temperature of the feed- water; 

 Ji the total heat in the feed- water due to the temperature.* 



Therefore, for moist steam, 



Q=i-P, . . . . . . (i) 



P=i-Q, (2) 



<2 + ^=i ' . (3) 



See also equation (6). 



* Most tables of the properties of steam and of water are based on the 

 total heat of steam and water above 32 degrees Fahr. For such tables the 

 total heat in the water at a given temperature is equal approximately to 

 the corresponding temperature minus 32 degrees. Exact values should, 

 however, be taken from the tables. 



