COAL. 615 



series, cannel coal, with some interruption in com- 

 position, and a considerable one in texture, com- 

 mences that of the coals. From this variety, 

 down to the most perfect anthracite, there is a 

 similarly indefinite range of composition ; the 

 hydrogen gradually diminishing as the coal be- 

 comes less inflammable, as it is less capable of 

 being separated into bitumen and charcoal by 

 distillation, and as it yields a smaller comparative 

 proportion of the former. Thus the composition 

 of the bitumens illustrates that of the several 

 varieties of coal. This gradation is, however, 

 only noticed in a general manner in the Synop- 

 sis, where the several popular and received varie- 

 ties, are distinguished as if they were all definite. 

 The most perfect anthracite appears to yield 

 no bitumen, yet it still contains hydrogen, per- 

 haps in every case ; as that element is present 

 even in common charcoal, which is itself a com- 

 pound substance. Where anthracite passes to 

 plumbago, which may in fact be considered as 

 the true end of this series, the hydrogen seems 

 to have disappeared ; and, if this substance be 

 not mere carbon, as it probably is not, from the 



