Mr, Hatchett'j Obfervations on Bituminous Subfiancet. 133 



THE divifion which comprehends the fimple bituminous fub- 

 fiances derived from naptha, may therefore be confidered as termi- 

 nating in afphaltum ; but Nature appears to have glided on by air 

 uninterrupted chain which Connects the fimple bitumens with 

 thofe which we have called compound; and this effect is produced 

 by the gradual increafe of the carbonic principle, and the introduc- 

 tion of extraneous matter, the different quantity of which, toge- 

 ther with the greater or lefs degree of mixture or of chemical union, 

 occanon confiderable changes in thefe fubftances, lb that they are 

 gradually removed from thofe characters which diftinguifh tha 

 pure bitumens* 



To form an accurate table of thefe gradations, it would be ne- 

 cefTary to have comparative analyfes of the different bituminous 

 fubftanceSj and alfo to contrail the analyfes with the properties cf 

 thefe bodies. But at prefent thefe analyfes, for the greater part, 

 are wanting; and although at fome future time I intend to attempt 

 a feries of fuch experiments, 1 muft now content myfelf with the- 

 obfervations and facts which 1 have been able to collect* From 

 thefe I am of opinion, that the molt immediate gradation from 

 afphaltum (which is the laft of the fimple bitumens) into thofe 

 which are compound, takes place in the lubftance called - 



I would be underftood however to mean that the carbon is only relatively incTeafed, 

 in refpea to the other ingredients, in a given quantity of 'thefe bitumens, and that it pre- 

 dominates in proportion to the diffipation, of a certain portion of the hydrogen, which 

 was originally .neceffary to the forming of the bitumen in conjunction with the carbon. 



* This paper was written and read before I had feen the ingenious experiments which 

 the celebrated Mr. Kirwan has publilhed, in the laft edition cf his Llecwnts of Mine- • 



ralogy.— Vide vol. ii- p. 5*4- 



J P 1 • 



