Experiments on the different Kinds of Coal. 291 



These three denominations sufficiently indicate the aspect and 

 mode of existence of each of the three sorts of coke, as well as 

 the transition which may take place from one kind to the other. 



In all these kinds of coal, as in unaltered vegetable fibres, 

 the quantity of charcoal obtained, differs according as a slow or 

 quick heat is employed during distillation. In general, this dif- 

 ference of product is so much the greater, that the coals contain 

 less charcoal. The coals with intumesced coke, however, form 

 an exception. These often, with a greater quantity of charcoal, 

 present greater differences of product in the two modes of car- 

 bonization, than with a less quantity of charcoal the coals with 

 pulverulent coke do, and especially than those with conglutinated' 

 coke. At the most, these differences of product, in all the va- 

 rieties of coal examined by M. Karsten, do not exceed 6 per 

 cent., and even this maximum of difference was only observed in 

 a coal with an intumesced coke, which presented a mean quan- 

 tity of charcoal. The produce in coke of coals of this class, 

 when they possess a greater quantity of charcoal, does not vary 

 more than 4 per cent, in the two modes of carbonization. 



Another remarkable fact is, that the application of a low 

 heat, raised very slowly to the strongest red heat, diminished in 

 coals the property of furnishing either a conglutinated or an in- 

 tumesced coke. A coal which, on being subjected to a rapid 

 incandescence, announces itself as belonging to the second class 

 (coal with conglutinated coke), may, by means of a heat raised 

 very slowly, present the aspect of a coal of the first class (that 

 with pulverulent coke). It is chiefly in the transitions from the 

 one to the other class, that this fact is observed. In like man- 

 ner, by means of a slow heat, a coal of the third class presents 

 the aspect of the second, and especially if the coal in question 

 possesses only in a feeble degree the property of furnishing an 

 intumesced coke. In every case, if the heat be produced but 

 slowly, the swelling of the coals with vesicular coke is diminish- 

 ed. They then form a less loose, less bulky, and less light mass, 

 than if an ardent heat had been rapidly applied. 



A distinction between the coals which swell, and those which 

 do not, has long been established in the arts, because these two 

 kinds of combustibles act very differently. Manufacturers have 

 readilv observed the «:reat influence which the manner that dif- 



