436 Prof. Chapman on the Assmjing vf Coals by the Blowpipe. 



4. Cannel or Gas Coals. — These coals, at least in normal spe- 

 cimens, do not fuse or " cake " in the fire. They give off a large 

 amount of volatile matter, frequently more than half their weight; 

 hence their popular name of " gas coals." They soil very slightly, 

 or not at all. The coke obtained from them is sometimes fritted, 

 and partially agglutinated, but never fused into globular, mammil- 

 lated masses, like that obtamed 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 to 

 85 ; Hydrogen, 5-5 ; Oxygen (with nitrogen), 9 to 12-5. 



5. Lignites or Brown 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-soiling ; 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, communica- 

 ting 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 frag- 

 ments are rarely agglutinated, except in the case of certain 

 varieties (as the lignites of Cuba, and those from the freshwater 

 deposits of the Basses 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, 67 to 75 ; 

 Hydrogen, 5 ; Oxygen (with nitrogen), 20 to 30. 



All the different kinds of coal enumerated above contain a 

 variable amount of moisture, and of inorganic matter or "ash." 

 The moisture 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 ne- 

 cessarily a variable element. In good coals it is under 5, fre- 

 quently indeed under 2 per cent. On the other hand, it some- 

 . times 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 coloui', from the presence of 

 sesquioxide of iron, derived from the iron pyrites (FeS^j 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. Cal- 

 careous ashes are more common in secondary and tertiary coals 

 than in those of the palaeozoic age. For methods of ascertain- 



