174 cox. 



Dollfus (1868-1875)" has long been considered the moot reliable ever accomplished 

 on European coal and has done much to further the determination of tlie heating 

 power of coal and the substantiation of Dulong's formula. Beginning in 188.5" 

 these authors continued their earlier investigations and made a number of deter- 

 minations in order to fi.x; a fair average for all coals. They found the heating 

 power of many coals to be greater than that calculated from the elements ; the 

 Russian coal gave results which were very much nearer, in fact, fell slightly below 

 the calculated value; therefore, indicating that the calculated value was a fair 

 approximation to the truth. Mahler " has also done much careful work on 

 European coal. He modified Dulong's formula by using the value 8140 for the 

 heating power of carbon as determined by Berthelot and Petit" instead of 

 8080 as determined by Favre and Silbermann " and also so as to take into ac- 

 count the nitrogen content as follows: 



Calorific value=-| j8140C-f-34500 (h — 10+|>=1\ 1 



=ji^r8140C+34500H— 4312.5((0+N)— 1)1 



Mahler emphasized the fact that Dulong's formula generally gave results 

 which were below the actual, corroborating the observations of Scheurer-Kestner 

 and Meunier-Dollfus, and proposed the adoption of the formula modified to read: 



„ , .„ , 8140C—34500H— 3000(C)— N) 

 Caloritic value= r-r^r ^ 



The application of this to a large number of coals gave vari;xtions of about 

 the same magnitude from the actual value as that of Dulong, but in the opposite 

 direction. 



Dulong's formula has stood the test through many years of discussion and 

 suggested substitutions. The formula has no scientific value, but in 1891, Bunte,'" 

 as the result of a series of investigations in Munich, showed it to be sufficiently 

 accurate for all practical purposes; and in 1899 the report of the Committee on 

 Coal Analysis '' appointed by the American Chemical Society gave it in the 

 following form as the most reliable formula for the calculation of the heating 

 effect of a coal bunied to liquid water : 



"Calorific power=80S0C-f 34,460 (H— JO) +2250S" 



"Scheurer-Kestner, A., and Meunier C. Compt. rend. Acad. sol. (1868), 66, 

 1220; 67, 659, 1002; (1869), 68, 608; 69, 412; (1871), 73. 1061: (18731, 

 77, 1385; Ann. chim. et phys. (1874), V, 2, 325; BuU. Soc. chim. Paris (1874), 

 n. s. II, 21, 402. Scheurer-Kestner, A. Compt. rend. Acad. sci. (1868), 66, 

 1047. 



■- Scheurer-Kestner, A., and Meunier-Dollfus, C. Compt. rend. Acad. sci. 

 (1885), 100, 908; Ann. chim. et phys. (1886), VI, 8, 267. 



"Mahler, P. Btill. Soc. encourag. ind. nat. (1892), 91, 358. 



^^ Ann. chim. et phys. (1889), VI, 18, 80. 



«/6id (1852), III, 34, 403. 



^^Journ. f. Casbeleuchtung (1891), 34, 21 and 41. 

 -^Wourn. Am. Chem. Soc. (1899), 21, 1130. 



