S96 M. Karsten's Observations and Experiments 



mesced coke, which are not too much swelled, are the best of all 

 for this object. A coal with conglutinated coke must hot have 

 too many natural joints, because, in the carbonization, it is re- 

 duced to too small fragments. Lastly, a coal with pulverulent 

 coke cannot be employed, if it does not present itself in large 

 masses, which keep together, and, in the process of carboniza- 

 tion, form large pieces of coke. 



A coal which intumesces a little, is therefore always prefer- 

 able to that which only conglutinates, and still more to that 

 which furnishes a pulverulent coke ; for, if the first presents 

 natural fissures, its property of intumescing destroys their bad 

 effect ; and even in this coal, the solutions of continuity, the 

 partitions of mineral charcoal and of foreign mixtures, which the 

 mass may present, cease in ia great measure to be hurtful, on 

 account of the intumescing. 



In the coals with conglutinated coke, and especially in those 

 with pulverulent coke, the frequency of fissures, which, even 

 without the existence of real joints, may result from the mere 

 want of uniformity of substance, is an inconvenience which of 

 itself suffices to render these combustibles altogether incapable 

 of being converted into coke. 



An excessive quantity of ashes may also become an obstacle 

 in the way of employing cokes for fourneaux a cuve ; and the 

 lighter the cokes are, or the more they fall into fragments in the 

 furnace, the greater obstacle will the ashes yield ; the reason of 

 which is, that they increase the difficulty of combustion, and en- 

 velope the surface of the coke before they have been brought to 

 a state of melting. This difficulty of fusion, which results from 

 too great a quantity of ashes, makes the melted mass remain in 

 the state of a paste. There follows from this, not only that the 

 air traverses such a mass with difficulty, but also that a part of 

 the effect of the incandescent coke must be employed to melt the 

 ashes. • 



For obtaining coke, as this is practised, by means of the small 

 debris furnished by the breaking up of the beds of combustible 

 in mining, it is obviously only coals with vesicular coke that can 

 be used. Such cokes are sometimes very liable to fall into 

 crumbs, whether on account of the nature of the mass itself, or 

 on account of an accidental admixture of slate, clay, or other 



