CALCULATION OF THE HEAT UNITS. 163 



is determined by multiplying the weight of hydrogen by 9. 

 This is added to the hygroscopic water, and the formula 



(606.5 -|- 0.305*) t' 



applied ; t being the temperature of the vapor in the gases 

 (equal to that of the gases), and t' being that of the external 

 air. Besides this, however, we must consider the specific 

 heat of the aqueous vapor, 0.475. Each kilogram still 

 absorbs 0.475 multiplied by the number of degrees of tem- 

 perature above 100, and the formula becomes 



.4(606.5 + 0.305*) - t' + o. 4 75(* - ioo)], 



x being the quantity of water, in kilograms, furnished by the 

 coal. 



Suppose a coal contains 1 5 grams per kilogram of hygro- 

 scopic water and 45 grams of hydrogen, as follows: 



Hygroscopic water 15 



Carbon 735 



Hydrogen 45 



Nitrogen and oxygen 50 



Ash.. 1 60 



1000 



Hydrogen 45 produces 9 X 45 = 45 grams, to which 

 add the 15 grams of hygroscopic water, 405 -f- 15 = 420 

 grams. The heat necessary to vaporize this, increased by 

 that corresponding to the temperature of the gases passing up 

 the chimney, represents the heat lost. 



If the flue temperature is 145 = *, and the external air 

 17.5 = *', we have 



0.420^606.5 + 0.305 X 145) 17-5 + 0-475(i45 ioo) 



= 274.9(494.8 B T.U.). 



