332 M. Karsten's Observations and Experiments 



Pitch-coal, or piciform-coal, having tke lustre of pitch (Pech- 

 Jcolile) ; Slate-coal (Schieferkohle) ; compact or cannel-coal 

 {Kennelhohle) ; Foliated coal (Blaetterkohle) ; Columnar coal 

 (Stangenkhole) ; Coarse coal {GrohTcohle). 



An alternation of beds of coal, some richer, others poorer in 

 carbon, with frequent interpositions either of fissures or of par- 

 titions, or even a frequently repeated alternation of very thin 

 beds of mineral charcoal, dividing the mass of combustible, — 

 such are the circumstances which afford proof, sometimes that 

 a coal is slaty, sometimes foliated, sometimes passes from slaty 

 to foliated coal, according as such effects are more or less nu- 

 merous. If the arrangement of the combustible substance in 

 thicker beds appears to the eye to remain constant, a coal rich in 

 carbon, which therefore exhibits the lustre of pitch together 

 with the conch oidal fracture, is named Pitchcoal ; while a coal 

 poorer in carbon, and of a dull appearance, is named Cannel 

 Coal. These two kinds of coal, the one richer in carbon, and 

 the other poorer, when they are intimately united with one an- 

 other, and not disposed in alternating beds, occur in mineralogi- 

 cal systems under the denomination of Coarse Coal. 



If sufficient importance be attached to the separations of the 

 mass of combustible to make it the basis of a classification of 

 coals, then, without doubt, matters may be allowed to continue 

 so ; but, in that case, it cannot be hoped that the name given 

 to the body which it is to designate, should present an accurate 

 image of it to the eye. A slaty coal may differ as much from a 

 coal of the same name, as two pitch coals, or two cannel coals, 

 may differ from each other ; and these manifest a mutual accor- 

 dance only in certain respects, while in other respects they are 

 much more widely separated from each other than a foliated 

 coal is from a pitch coal, or a slate coal from a compact coal. 

 The colour^ lustre^ cohesion, and hardness of the combustible, 

 are in general the only properties from which the external and 

 distinctive characters of coals are derived ; for the specific gra- 

 vity is an uncertain guide in this respect, on account of acci- 

 dental mixtures. But these properties themselves do not seem 

 to be sufficient, if it be required that, with the external charac- 

 ters, the intimate nature and composition of coals be at the 

 same time determined. The true difficulty, however, lies solely 



