the different kinds of Coal. 69 



On glancing over this table, we observe the preponderating pro- 

 portion of oxygen and hydrogen to the carbon, in the unaltered 

 vegetable fibres ; whereas, in brown coal or lignite and black coal, 

 the proportion of these two gases to the carbon diminishes ; — 

 but we also see that this diminution does not take place in a re- 

 lation which remains the same between the oxygen and hydro- 

 gen. We come ultimately to conclude, from the facts detailed, 

 that, in coals, the property of intumescing more or less depends 

 solely upon the relation of the hydrogen to the oxygen, and that 

 the contents in carbon have no influence in this respect. 



Thus the appearance and quantity of the charcoal, which is 

 obtained as the residuum of the distillation of coals in the dry 

 way, will enable one to guess with sufficient certainty what must 

 be the composition of these combustibles; but, on the other 

 hand, experience teaches us how much these charcoals or cokes 

 furnished by distillation, vary as to quantity and appearance. 

 Employing the same degree of heat for all, as nearly as possible, 

 we obtain sometimes 50 and sometimes 90 per cent, of charcoal. 

 Sometimes these carbonaceous residuums are in the state of the 

 finest powder. Most commonly gradations without number are 

 observed in them, from the state of a conglutinated matter to 

 the inflation of a vesicular matter, and almost to the appearance 

 of a blackish foam. It may therefore be regarded as certain, 

 that scarcely two carbonaceous residuums will be found the com- 

 position of which is exactly the same, and that all, in the miu 

 tual relations [of their atoms, approach more or less to those 

 which formed the object of the above mentioned analyses, while, 

 at the same time, we can never expect to find a perfect agree- 

 ment of constituent parts. 



From this extreme variation in the composition of coals, it is 

 easy to see that all the charcoals or cokes do not answer equally 

 for all purposes, and that some particular kinds are preferable. 

 If it be asked, what charcoal or coke deserves the preference in 

 general, this question cannot receive a positive answer. But 

 if one wishes to know for what determinate object a particular 

 charcoal or coke 4s better adapted than another, this may be de- 

 termined by the proportion of its constituent parts. 



The richer the coal is in carbon, the more heat will it de- 

 velope in burning; for^ the more carbon it contains, the more 



