on the different Mnds of Coal, 323 



useless, for such a coal in burning falls into small pieces, which, 

 far from agglutinating themselves together so as to form a loose 

 and light mass, on the contrary, apply themselves so closely to 

 one another, that the affluent air finds no passage through 

 them. 



Is the object in view the production of coke ? Then several 

 circumstances are to be considered, which may make the coke of 

 one coal be preferred to that of another, although each may be 

 a perfectly pure charcoal ; that is to say, although the purity 

 of both may only be altered by a small quantity of ashes. In 

 the first place, regard ought to be had to the more or less loose 

 or light state in which the cokes, obtained from different coals, 

 present themselves. Matters, however, go on differently here, 

 from what they do in those wood-charcoals which are obtained 

 from the hardest or the softest woods, or in those charcoals 

 which are produced from straw or other vegetable fibres, — from 

 substances, in short, which, in their original and undisturbed 

 state, were very loose and very light. In coals, the loose and 

 light aspect of the charcoal is occasioned by the manner in which 

 the coals comport themselves, whether they be coals with intu- 

 mesced, or coals with conglutinated, coke ; whereas, in unaltered 

 fibres of wood, this aspect is^ only the effect of the original den- 

 sity of the fibres. 



Thus, a comparison between the different degrees of lightness 

 of the cokes obtained from coals, and those of the charcoals pro- 

 cured from still unaltered vegetable fibres, could only take place 

 with regard to coals with pulverulent coke. But the intumesced 

 cokes are in reality a charcoal in a state of partial fusion, which 

 the almost silvery colour of several of these cokes already indi- 

 cates. The large proportion of hydrogen which coals with in- 

 tumesced coke contain, and, at the same time, the small propor- 

 tion which the oxygen bears to the hydrogen, produce the follow- 

 ing effect : the coal, at the moment when the decomposition of 

 that combustible is effected, passes into a state of partial fusion. 

 There results from this, that the mass, which is softened through- 

 out, and of which a part has become adhesive, is often intumesced 

 by the vapours and gases which are developed. It then extends 

 in all directions, and frequently swells out like an agglomeration 

 of vesicles. 



x2 



