s6z A SYSTEM OF 
the fire, become firft yellowifh green, 
and afterwards reddifh brown, when, 
befides iron, they then alfo difcover 
fome marks of copper ; it has how- 
ever not been pofTible to extradl ariy 
metallic fubftance from them, the 
effe(5ls of the loadfione, and the co- 
lour communicated to the glafs of 
borax, having only given occafion t@ 
this fufpicion (conf. Se6t. cl. & cliv.). 
SECT. CLXII. 
Observation on the Bitumens. 
That fubftance which the chemifts call Phlo- 
gifton, or an inflammable principle, exifts in moft 
of the mineral bodies, though often in fo fmall a 
quantity as not to be perceived ; and therefore I 
have here only enumerated thofe kinds in which 
it exifts as a principal character j for inftance, in 
the foetid fpar or fwine-ftone, &c. 
I do not myfelf know the iubftance in its fimple 
ftate which I call a mineral phlogifton, fince the 
ambergrife and the rock-oil can be nothing elfe 
than compofitions which cannot be perfedlly de- 
compounded j and befides, they are not to be ex- 
traded from coal, fulphur, &c. w'hich yet con- 
tain an inflammable fubftance. It feems as if a 
great part of this dais were originally generated 
from the animal and vegetable kingdoms; fo that 
they fiift have been an humus ater or mould, whth 
which a vitriolic acid has afterv/ards been mixed j 
and that they have been beft able to retain this 
phlogifton, when they have been covered and 
Joined together by another earth : the coal, coal ore, 
and pitch turif, (Sed. ccxciii,) give feme hints or 
reafons 
