32 COALFIELDS AND COLLIKiIUKS OF AUSTRALIA. 



determination of the heat units developed by carbon, hydrogen 

 and sulphur when completely burnt ; also the results of dif- 

 ferent formulae vary. The difference between the calorific 

 power calculated from Dulong's formula and that obtained by 

 Mahler's calorimeter in careful hands is not so great as is 

 generally thought. "N. W. Lord and F. Haas* made several 

 tests, and the results were so uniform that they could not be 

 credited to accident. "The maximum difference between the 

 heat calculated from the elementary- analysis and the heat 

 developed in the bomb is 2 per cent, of the total calculated 

 heat, the minimum difference 0.1 per cent. The posible error 

 of an ultimate analysis may be placed at 0.5 per cent, on car- 

 bon, and 0.2 per cent, on hydrogen, especially with coals as 

 high in ash and sulphur as are many of the samples included 

 in our tests. This would lead to an error of about 108 units, 

 or nearly 1.4 per cent, on the calculated heat value." 



The ultimate analysis of a coal is much more difficult to 

 make than the calorimetric determination, so attempts have 

 been made to ascertain the relation between the fixed carbon 

 obtained by the more rapid proximate analysis and calori- 

 metric tests. These are naturally not so correct as when cal- 

 culated from the ultimate analysis. W. Keiitt states: 

 "Knowing the percentage of fixed carbon in the dry coal free 

 from ash, we may in the ca-se of all coals containing over 58 

 per cent, of fixed carbon predict their heating value within 

 a limit of errors of about 3 per cent. . . Below 50 per cent, 

 of fixed carbon the law apparently does not hold good, as 

 shown by the tests of some lignites." He then gives the fol- 

 lowing table of approximate heating-values of coals, which 

 was constructed from the average curve from Mahler's tests 

 on European coals : 



Per Cent, of Fixed Heating Value. 



Carbon in Coal. Dry British 



und Free from Ash. Calories. Thermal 



Units. 

 14,760 

 15,120 

 15,480 

 15,660 

 15,840 



*The Calorific Value of Certain Coals as Determined by 

 the Mahler Calorimeter (T. Am. I.M.E., Vol. XXVII., p. 259) 



t Tests of the Heating Power of Coals. Mineral Industry, 

 Vol. 1 (1892), p. 97. 



