METHODS OF DETERMINING HEAT OF COMBUSTION. 9 



Mahler formulated one based on the results of calorimetric 

 determination of the heat of combustion of 44 different kinds 

 of fuel. It is 



8i4oC + 345QQH 3000(04- N) 

 100 



or simplified, 



x = 111.40 + 37$H 3000; 

 or in B. T. U.'s, 



x = 200. 5 C + 675 H 5400. 



With the coals he examined he found a very close agree- 

 ment between the results calculated by this formula and 

 those observed. A similar but not equally close concordance 

 was found using the Dulong formula. With wood and lig. 

 nites the difference amounted to 2 per cent. His formula 

 applies also to other substances whose constituents are accu- 

 rately known. Cellulose, the heat of combustion of which 

 according to Berthelot is 4200 calories, by Mahler's formula 

 is 4264. 



In summing up he says: '* From a scientific point of 

 view, in the present state of our knowledge on the subject, 

 we cannot give a general formula depending strictly on the 

 chemical composition which will give the calorific power of 

 combustibles, substances so complex and varied." 



Lord and Haas in a paper read before the American Insti- 

 tute of Mining Engineers, Feb. 1897, state that in a series of 

 forty Pennsylvania and Ohio coals they found differences 

 varying from -f- 2.0 to 1.8 per cent between the calculated 

 and the observed results, and an average difference of 0.12 

 per cent. 



In 1896 Bunte published some analyses and calorimetric 

 tests of gas-cokes, showing a difference of from -f- 0.04 to 

 1.2 per cent. 



