290 M . Karsteirs Observations and 



and magnesia, are the substances which are found in the resi- 

 dua of the combustion of fossil wood and brown coal. They 

 present themselves in very different and very variable propor- 

 tions, which depend upon the local circumstances under the in- 

 fluence of which the deposition of matter has been effected in 

 the natural beds of these combustibles. 



In black coal, the quantity of charcoal which may be obtain- 

 ed, by means of distillation in the dry v^'ay, varies still more 

 than in the different sorts of brown coal, comprising also fossil 

 wood. M. Karsten has not met with any black coal, which, on 

 being distilled, has furnished less than 48 per cent, of charcoal. 

 From this number, the quantity of residuum in charcoal rises 

 to 90 per cent. Between these two limits there is scarcely a 

 number to be found that would not answer for the produce in 

 charcoal, or coke, of some kind of coal. Striking differences, 

 however, are remarked in the external form of the carbonized 

 coals called cokes. 



In some the form of the coal remains unchanged, the volume 

 only being diminished, as in charcoal from fresh vegetable fibre, 

 fossil wood, and brown coal. Others remain unchanged in form 

 and volume, while some swell and expand more or less. In or- 

 der to observe correctly these different relations, it is necessary 

 to use the coal we intend submitting to dry distillation in the 

 state of powder. Coal of the first kind affords a coke in a dus- 

 ty pulverulent state, without the least cohesion, just as in brown 

 coal. In coal of the second kind, the powder is conglutinated 

 into a cake, often very solid and tough, but without any swel- 

 ling or intumescence. The fine powder, in coal of the third 

 kind, melts, and forms a homogeneous mass, which takes the 

 form of the retort in which it is distilled, and frequently swells 

 so much as to choke up the retort. 



Here the author divides coals into three classes, which he es- 

 tablishes from the external appearance of the charcoals or 

 cokes which are produced by them. For the object which he 

 proposes to himself, M. Karsten distinguishes, 



1*^, The coals with pulverulent coke, (Sand KoJden) ; 

 9.dly, Those with conglutinated coke, (Sinter Kohlen) ; and, 

 ^dly^ Those with an intumesced coke, (Bade Kohlen). 



