CHAPTER II. 

 METHODS OF DETERMINING HEAT OF COMBUSTION. 



THERE are two methods for determining tne heat of com- 

 bustion of substances one by calculation based on the 

 chemical composition, and the other by actual combustion in 

 a calorimeter. The first method may be considered under 

 two heads: that in which the units are calculated directly from 

 the composition, and that in which they are calculated from 

 the quantity of oxygen consumed during combustion in a 

 crucible. 



CALCULATION FROM CHEMICAL COMPOSITION. 



Dulong stated that the heat generated by a fuel during 

 combustion was equal to the sum of the possible heats gener- 

 ated by its component elements, less that portion of the hy- 

 drogen which might form water with the oxygen of the fuel. 



His formula was 



x = 8o8oC + 34500 H - -, 



v 



or expressed in B. T. U.'s, 



x = I4500C + 62 100 ( H -), 



x o ' 



in which 



x = the heat of combustion sought ; 

 8080 = the heat of combustion of carbon in calories ; 

 14500 = " " " " " " " B. T. U. ; 



34500= " " " " " hydrogen in calories; 



62100= " < u *< n " B. T. U. ; 



7 



