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but without any sulphurous smell, is observed; undoubtedly from 

 the decomposition of water. Exposed to a porcelain heat for 

 several hours, in a closed crucible, it entirely or almost entirely, 

 evaporates like diamond. Under a muffle it is nearly consumed. 

 Distilled, it yields a small quantity of water; but no air, oil, 

 acid, nor alkali. Mixed with sulphate of pot-ash, it yields a liver 

 of sulphur ; and projected on red-hot melting nitre, it deflagrates 

 and alkalizes it : hence, Mr. Kirwan remarks, there is no doubt 

 but it is a combustible substance, possessing both the external and 

 internal characters of mere coal, or charcoal. 



The Kilkenny coal is of this species ; its fracture being foliated, 

 and its fragments often coated with whitish illinitions. The culm 

 of Wales seems to be a variety of this species ; but less pure, 

 differing from it, chiefly, in being more brittle, and emitting, when 

 ignited, a disagreeable smell. 



This substance yielded to Dr. Hutton, and the French chemists, 

 a strong corroboration of the opinion they had formed, respecting 

 the changes which bituminous substances, and particularly coal, 

 underwent from the influence of subterranean heat*. Knowing 

 that besides the common pit-coal, rich in bitumen, there existed 

 this substance also, in which no bitumen was discoverable, they con- 

 sidered the former kind, as abounding in the oily matter which had 

 been contained in the various organized bodies, from which it had 

 derived its origin : and concluded, the latter to have been exposed 

 to a considerable degree of subterranean heat, in consequence of 

 which, it had suffered a deprivation, by distillation, of its bitumen; 

 it being thereby left a caput mortuum, or perfect coal. The exist- 

 ence of the purer bitumens, in separate situations, has been also 

 reckoned in evidence of the propriety of this theory. Thus Dr. 

 Hutton mentions, as an instance of the separate existence of these 



* Theory of the Earth, with Proofs and Illustrations, by James Hutton, M.D. 1795. 

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