ON THE ASSAYING OF COALS BY THE BLOWPIPE. 211 



popular name of " gas coals." They soil very slightly, or not at all. 

 The coke obtained from them is sometimes fritted, and partially agglu- 

 tinated, but never fused into globular, mamillated masses, like that 

 obtained from the caking coals. It varies in amount from 30 to 60, 

 or, in typical specimens, from 55 to 58 per cent. Mean composition 

 (normal cannel) : Carbon 80-85, Hydrogen 5.5, Oxygen (with nitro- 

 gen) 9-12.5. 



5. Lignites or Bi^own Coals. — These coals of Tertiary age, differ 

 greatly from one another in external aspect. Some of the so-called 

 jets — passing into the cannel coals — are black, lustrous, and non-soil- 

 ing ; whilst other varieties are brown, and of a ligniform or stratified 

 structure ; or, otherwise, earthy and loosely coherent. All, however, 

 are partially soluble in caustic potash, communicating to it a dark 

 brown colour. The coke — usually of a dull charcoal-like aspect, or 

 in sharp-edged fragments retaining their original form — varies from 

 25 to 50 per cent. Its separate fragments are rarely agglutinated, ex- 

 cept in the case of certain varieties (as the lignites of Cuba, and those 

 from the fresh-water deposits of the Basse Alpes in France) which 

 contain asphaltum. All the typical varieties of lignite, as pointed out 

 by Cordier, continue to burn for some time, in the manner of " braise" 

 or ignited wood, after the cessation of the flame occasioned by the 

 combustion of their more volatile constituents ; whereas with ordinary 

 coal, ignition ceases on the flame going out. The mean composition 

 of lignite may be represented by — Carbon 65-75 ; Hydrogen 5, Oxy- 

 gen (with nitrogen) 20-30. 



All the different kinds of coal, enumerated above, contain a variable 

 amount of moisture, and of inorganic matter or "ash." The mois- 

 ture rarely exceeds 3 or 4 per cent., although in some samples of coal 

 it is as high as 6 or 7, and even reaches 15 or 20 per cent, in certain 

 lignites. The amount of ash is also necessarily a variable element. In 

 good coals it is under 5, frequently indeed, under 2 per cent. On the 

 other hand, it sometimes exceeds 8 or 10, and in bad samples even 15 

 or 20 per cent. The ash may be either argillaceous, argillo-ferruginous, 

 calcareous, or calcareo-ferruginous. The ferruginous ashes are always 

 more or less red or tawny in color from the presence of sesqui-oxide of 

 iron, derived from the iron pyrites (Fe S^) originally present in the 

 coal. If much pyrites be present, the coal is not available for furnace 

 operations, gas making, engine use, &c., owing to the injurious effects 

 of the disengaged sulphur. Calcareous ashes are more common in 

 Secondary and Tertiary coals than in those of the Palaeozoic Age. For 



