102 D'tvijion of Bitumlnou} Subfianctfi 



The bituminous fubftances are : ~ 



Naptha, Jet, 



Petroleum, Pit Coal, 



Mineral Tar, Bituminous Wood, 



Mineral Pitch, . Turf, 



jAfphaltum, Peat, and 



thofe combinations of the oxides of certain metals with bitumen called Bituminous Ores*. 



Thofe who are acquainted with the nature of thefe fubftances will immediately perceive, 

 that they may be formed into two divifions : the firft of which confifts of fimple fpecies, or- 

 unadulterated bitumens : and the fecond is compofed of bitumen mixed or combined with 

 the earths, vegetable matter, and metallic oxides ; fo that thefe appear to merit the name of 

 compound fpecies. 



I {hall now firft confider how the fimple fpecies are connedted with each other. 



SECT. II. 



IT has been the opinion of fome eminent Naturalifts and Chemifts, that naptha is an 

 ethereal oil produced from the more compa£t and folid bitumens by a fort of natural diftilla- 

 tion. This however appears to be an hypothefis founded upon analogy, and fupported only 

 by a few local fadls, which may often be queftioned. But many fa6ls and obfervations con-.- 

 Cur to prove that the contrary moft frequently happens, and that the compaft bitumens arc 

 often, if not always, formed from naptha and petroleum by infpilTation. I will not however, 

 now infift upon theproofe of this, as the varieties of the elaftic bitumen, which I. {hall foon 

 defcribe, will be fuiEcient for the purpofe t« 



NAPTHA. 



Naptha is a fubftance well known to Mineralogifts, as a light, thin, often colourlefs oif, 

 highly odoriferous and inflammable, which is fometimes found on the furface of the waters 

 ©f fprings, and at other times ilfuing from certain ftrata. 



When expofed to the air, it becomes at firft yellow, afterwards brown, and in the like 

 proportion it thickens, and pafles into 



PETROL OR PETROLEUM. 



This has a greafy feel, is thicker than the preceding fubftance, is tranfparent or femi- 

 tranfparent, and of a reddifh or blackilh brown colour. By air it becomes like tar, and 

 then is called 



• As I intend only here to notice the modifications of naptha and petroleum, I have not mentioned ambei" 

 and the honey-ftone. 



•f- Bergman was of opinion, that the liquid bitumens were ofteir, if notalways, formed from thofe which are 

 folid, by the means of fubterraneous lieat; and exprclTcs himfelf thus: " Caeterum ad fidem pronum eft, 

 naptham, petroleum, bituminofofque liquores, quibus abundat Afia, plures harum materierum exhibens noa 

 tantum fcaturigines, fed rivulos quoque, quibus etiam, parcius licet diftributis, Auflralis Europa non caret : 

 probabiie, inquam, eft, has pinguedines liquidas variis antea terris inhsefifle exficcatas, et mediante calore 

 fubterraneo, fi non fempcr, fajpe tamcn fluiditatem recuperSfle. Novimus ignem in alto baud raro agere, 

 quamvis in fuperficie vix obfcura ejufdem indicia iiiveftigare liceat: novimus practerea e ficco aluminari fchifto 

 petroleum cxtorqueri jufto calorii gradu, cui arte exponitur.— Bergman de Produftis Vuicaniis Opufcula, 

 torn. Ui. p. ajS. 



MOUN- 



