i6z A SYSTEM OF 



the fire, become firft yellowiih preen, 

 and afterwards reddifh brown, when, 

 befides iron, they then alfo difcover 

 ibme marks of copper ; it has how- 

 ever not been poffible to extract any 

 metallic fubflance from them, the 

 effects of the loadftone, and the co- 

 lour communicated to the glafs of 

 borax, having only given occafion to 

 this fufpicion (conf. Seel. cl. & cliv.). 



SECT. CLXIL 



Observation on the Bitumens. 



That fubflance which the chemifls call Phlo- 

 giilon, 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 •, for inflance, in 

 the foetid fpar Gr fwine-flone, &c. 



I do not myfelf know the fubflance in its fimple 

 Hate which I call a mineral phlogiflon, fince the 

 ambergrife and the rock-oil can be nothing elfe 

 than compofitions which cannot be perfectly de- 

 compounded; and befides, they are not to be ex- 

 tracted from coal, fulphur, &c. which yet con- 

 tain an inflammable fubflance. It feems as if a 

 great part of this clafs were originally generated 

 from the animal and vegetable kingdoms ; fo that 

 they firft have been an humus ater or mould, with 

 which a vitriolic acid has afterwards been mixed \ 

 and that they have been belt able to retain this 

 pnldgifton, when they have been covered and 

 coined together by another earth : the coal, coal ore, 

 and pitch turjf* (Sect, cexciii.) give ibmc hints or 



reaions 



