292 M. Karsten's Observations and 



ferent kinds of coal have in comporting themselves, exercises 

 over their use. They have remarked, that the coals which 

 swell cannot always be substituted by those which do not, and 

 the reverse. But, between the one and the other, common opinion 

 establishes no other difference than the following : — The coals, 

 it is said, which swell, are only distinguished by a greater quan- 

 tity of constituent parts, which are not carbonaceous, parts 

 which have been designated by the name of Bitumen ; in other 

 words, it is the quantity of charcoal which decides Whether a 

 coal possesses the property of swelling or not. 



This opinion is incorrect ; and, so far from this being the 

 case, it is most commonly observed, that the quantity of charcoal 

 is greater in those coals whichf swell, than in others. There are 

 coals of the first and second classes (with pulverulent and con- 

 glutinated coke), which, on being carbonised, do not yield more 

 than about 50 per cent, of coke, and very few coals of the third 

 class (with intumesced coke) yield so little. On the contrary, a 

 great number of these coals with intumesced coke, furnish up- 

 wards of 80 per cent-^ of a very loose and swollen coke. Such 

 a coal cannot contain so many constituent parts, which are not 

 charcoal, as a coal with pulverulent or conglutinated coke, from 

 which there is only obtained about 50 per cent, of coke. 



The products of the distillation of coal in the dry way are 

 well known. The greater the quantity of charcoal, the thicker 

 is the consistence of the oil which is formed. All the varieties 

 of coal, without exception, on being subjected to dry distillation, 

 give feeble traces of ammonia. The coals with pulverulent 

 coke, when they have a small proportion of charcoal, present 

 traces of an acid. In all the varieties of coal belonging to this 

 first class, the proportion which the aqueous fluid bears to the 

 oily fluid, is greater than in those of the second class ; and, in 

 these latter, the proportion is greater than in the coals of the 

 third class (those with intumesced coke). The quantity of gaseous 

 substances, and of fluids or vapours which is formed, is in the 

 inverse ratio of the contents in charcoal. A smaller quantity of 

 gas is disengaged by the varieties of black coal, than by most of the 

 brown coals ; but, in the former, the combinations of carburetted 

 hydrogen are more predominant. Sulphuretted hydrogen gas is 

 only formed when the coal is mixed with iron pyrites, which it 



