334 M. Karsten's Observations and Experiments 



The coals in which the proportion of oxygen is much superior 

 to that of the hydrogen, act differently : they do not soften 

 either before or during their decomposition. What did not ad- 

 here together previous to carbonization, because it was inter- 

 mixed with foreign matters, or had only thin walls interposed 

 between its parts, still remains in the same state after carboniza- 

 tion ; and each isolated fragment, which in such a coal does not 

 immediately adhere to the mass, is carbonized separately, and 

 on its own account. There results from this, that, according to 

 the proportion which the hydrogen bears to the oxygen, the 

 state of the cokes obtained will differ very much. From those 

 which swell to such a degree as to present the aspect of a light 

 slag, to those which preserve the external appearance of the coal 

 while they diminish in bulk, there exists an uninterrupted series 

 of transitions. 



In the good coals with conglutinated coke, the proportion of 

 the hydrogen to the oxygen is still favourable enough for the 

 fragments of combustible, which previously were not in imme- 

 diate contact, but were separated by surfaces or partitions, be- 

 coming soft during the process of carbonization, uniting them- 

 selves to the mass, and forming together a single body. This 

 effect of the process of carbonization becomes particularly strik- 

 ing, when, after destroying the aggregation of the mass of coal 

 by pulverizing it, its powder is submitted to distillation. 



On the other hand, a coal which has passed into the state of 

 a more or less complete fusion, ought, on account of its smooth, 

 and, as it were, semi vitrified surfaces, to kindle with more dif- 

 ficulty than an unmelted coal, which presents uneven surfaces. 

 This is actually what is observed in the incineration of cokes ; 

 for the intumesced cokes, being placed under the muffle of an 

 assay furnace, require for their complete combustion a higher 

 temperature, or more time at the same temperature than th^ 

 conglutinated cokes, and still more than the pulverulent cokes. 

 For the same reason, also, the coke obtained from mineral char- 

 coal is more readily reduced to ashes under the muffle than 

 the intumesced coke of a coal of the third class. But the case is 

 quite different, when a mass of coke, formed into a heap, is made 

 to burn with the aid of a current of air, whether natural or ar- 

 tificial, and not to be consumed gradually by the action of the 



