Mr. Harcuertt’s Obfervations.on Bituminous Subfiances. 131 
‘tics of the elaftic bitumen, which I fhall foon defcribe, will be 
fufficient for:the purpofe*. |. 
NAPTHA, 
; 
Naprtua isa fubftance well known to Mineralogifts as a light, 
‘thin, often colourlefs oil, highly odoriferous and inflammable, 
which is fometimes found on the furface of the waters of fprings, 
and at other times iffuing from certain ftrata. 
When expofed to the air, it becomes at firft yellow, afterwards 
brown, and in the like proportion it thickens, and paffes into 
PETROL or PETROLEUM. 
“Ths has a greafy feel, is thicker than the preceding fubftance, 
is tranfparent or femitranfparent, and of a reddifh or blackifh brown 
colour. By air it becomes like tar, and then i is called _ 
midi yhisl eee OR MINERAL TAR, Brrumen PeTRoLEuM 
' “TARDE FLUENS. 
Tus fubftance is vifcid, and of a reddifh or blackith brown. fi 
black. When burned, it emits a difagreeable bituminous {mell, and 
by expofure to the air it paffes into 
* Bergman was of opinion, that the liquid bitumens were often, ifnot always, formed 
from thofe which are folid, by the means of fubterraneous heat ; and exprefles himfelf thus : 
“ Cxterum ad fidem pronum eft, naptham, petroleum, bituminofofque liquores, quibus 
abundat Afia, plures harum materierum exhibens non tantum {caturigines, fed rivulos 
quoque, quibus etiam, parcius licet diftributis, Auftralis Europa non caret 3 probaile, 
inquam, eft, has pinguedines liquidas variis antea terris inhzfifle exficcatas,, et, mediante 
calore fubterraneo, fi non femper, fepe tamen fluiditatem recuperafle. Novimus ignem 
in alto haud raro agere, quamvis in fuperficie vix obfcura ejufdem. indicia, inveftigare 
liceat: novimus preeterea e ficco aluminari {chifto petroleum extorqueri jufto caloris 
gradu, cui arte exponitur.— Bergman de Producis Vulcaniis Opufcula, tom. iii. p. 238. 
$2 MOUN- 
