CLASSIFICATION OF COALS. 15 



fixed carbon to volatile hydrocarbons, and from this they 

 adopted the following ratios: 



Anthracite fuel ratio from 100 to 12 



Semi-anthracite- . . . . fuel ratio from 12 to 8 



Semi-bituminous .... fuel ratio from 8 to 5 



Bituminous fuel ratio from 5 to 



This scheme classified all the bituminous coals together, 

 good and bad, but made no provision for lignites. Carbon is 

 the prominent element in coals, but its value depends on 

 whether it occurs as fixed or volatile hydrocarbon. A classi- 

 fication according to fixed carbon is fairly satisfactory when 

 the amount of hydrocarbon is small, but lignites and low grade 

 bituminous coals are apt to become confused lower down the 

 scale. 



A classification according to the calorific value is fairly 

 satisfactory so far as the lower part of the scale is concerned, 

 but there is still some uncertainty about the division between 

 lignites and bituminous coals. Lignites are noted for their 

 large percentage of moisture, so Collin proposed (Bulletin No. 

 218. U.S.A. Govt. Surv. 19(W a moisture content of 10 per 

 cent, as a basis of separation between lignite and bituminous 

 coals; but it was found that certain bituminous coals contain 

 more than 10 per cent., while some lignite contained less. If 

 we turn to ultimate analysis and recalculate, excluding ash and 

 sulphur, there are hydrogen and carbon to consider. If hy- 

 drogen is taken as a basis there is still a difficulty in distin- 

 guishing between coal and lignites. If carbon is taken, the 

 classification is satisfactory generally, but not in certain de- 

 tails where some coals appear to be misplaced. As neither of 

 these fuel elements alone appear to fit all cases, a classification 

 has been provisionally proposed by Mr. B. Campbell, based on 

 the carbon-hydrogen ratio. When taking these into con- 

 sideration they should not be added or multiplied, as these 

 processes would tend to equalise the results, but they should 

 be subtracted or divided, preferably the latter. Mr. Campbell 

 writes* "So far as I am acquainted with the character and 

 fuel value of the coals tested, the classification of coal accord- 

 ing to carbon-hydrogen ratio seems to be almost ideal. It is 

 not only correct in a general way, but in detail it seems to fit 

 almost every case. True, the separation between bituminous 

 coal and lignite is not sharp and distinct, but it is highly prob- 

 able that there is no sharp distinction between these two 

 classes, and that the facts are best represented by a merging of 



*"The Classification of Coals." Trans. Am. Inst. Min. 

 Eng., XXXVI., 338 (New York, 1906). 



