CALCULATION OF THE HEAT UNITS. 165 



The weight and heat of combustion of carbon vapor are 

 given, as most of the time we do not know the molecular 

 condensation of the hydrocarbons ; usually the ultimate com- 

 position is all that is known. Hence the hydrogen and car- 

 bon must be given their heat values as though free. Fortu- 

 nately they occur in only small percentages, and the error 

 introduced by so doing is small. 



Suppose a gas to analyze 



Carbonic oxide i.o 



Carbonic acid 13.0 



Methane I .o 



Oxygen 6.0 



Nitrogen . . 79.0 



100.0 



Assuming that the air has been fed at the rate of 10 cubic 

 metres per kilogram (160.5 cubic feet per pound), and that 

 the coal has a heat value of 8000 calories (14400 B. T. U.), 

 we will have, for 10 cubic metres, 



Carbonic oxide o. I cubic metres. 



Carbonic acid 1.3 " " 



Methane o. i " 



Oxygen 0.6 " lt 



Nitrogen 7.9 " " 



10. o 

 Then 



CH t , o.i cub. m. @ 0.715 = 0.0715 kilogram; 

 CO, o.i " " @ 1.251 = 0.1251 



and 0.0715 X 13343 = 933-7 calories; 



0.1251 X 2435 = 305.0 



Total 1238.7 " 



