[ T3 ] 
As the fulphureous matter, in the intire metals, 
ads ftrongly on the rays of light, it is neceffary to 
calcine, or to divide them into extremely minute 
particles, in order to examine feparately the adion 
of the calx, or fixed matter, on the rays of light. 
In order to examine all the metals in like cir- 
cumftances, by reducing them into the fmallefi: 
particles, and depriving them of their fulphur as far 
as was pradicable, I expofed each of them, united 
with a proper quantity of the pureft glafs, without 
any additional ingredient, to the greateji degree of 
fire they are capable of bearing, without having all 
colour whatever dejiroyed. 
In this flate it appears, from a variety of experi- 
ments and fads, that they adually do, without any 
exception, exhibit colours in the order of their 
denfities, as follows. 
Gold Red. 
Lead — — — Orange. 
Silver Yellow. 
Copper — — Green. 
Iron — — — Blue. 
GOLD. 
