CHAPTER XII. 

 CALCULATION OF THE HEAT UNITS. 



HEAT OF THE AQUEOUS VAPOR. 



THE quantity of heat contained in a kilogram or pound of 

 steam at any temperature is 



Q =z 606.5 + -35^ calories, 

 or Q' = 1091.7+0.3050- 32) B. T. U., 



allowing the specific heat of water to be constant. The 

 number of heat units is considered the same as the tem- 

 perature. 



So that, allowing the average temperature of aqueous 

 vapor to be; 150 C., each kilogram at o has absorbed a quan- 

 tity of heat equal to 



606.5 + -35 X 150 = 652.25 calories 



or one pound has absorbed 1 174 B. T. U. 



There is a correction to this, since we do not wish the 

 units existing in the steam, but only those added to it from 

 the fuel. We must then deduct that already existing in the 

 water at its entrance to the boiler. If the feed-water be 20 

 (68 F.) the formula becomes 



652.25 20 632.25 calories, 

 or 1174 (68 - 32) = 1138 B. T. U. 



159 



