r?8o ) 
To tills fame greedinefs alfo, with which the vitriolick 
Salt of Iron abforbs the oily part of the Coal, we may 
attribute the eallnefs with which Ircnconfumes the Coal 
for there is no other Metal* that fo foon wafts the Coal 
In the Focus of the Glafs, as Iron does. 
An other Obfervation upon Iron is, that it is the only 
one of the four imperfedf Metals, on which vitrified 
Drops arife while it is in fufion upon the Coal ; The rea- 
son of which I have not yet been able to difcover. 
Of Copper, 
Copper cxpofed to the Focus of the Burning-glafs, at 
firft turns white on its furface, and afterwards grows 
black, and is covered with a kind of Skin, or black, fur- 
row’d, and uneven Scales, till at lafc it quite melts. 
I have withdra wn this Metal out of the Focus as foon 
as this white colour has appear’d, and after it has been 
cold, found nothing extraordinary on its furface, which 
has again by little and little recover’d very near the fame 
Colour as it had before. 
I have not been able to difcover from whence this w^hite 
Colour proceeds ^ unlefs we may attribute it to fome Vo- 
latile Arfenical Salt contain’d in the Copper, and driven 
by extreami:y of Heat to the furface of the Metal ^ or whe- 
ther it purely proceeds from the alteration that is made in 
the grofter parts of the furface of the Metal when it be- 
gins to melt. The black colour that Copper afterwards 
takes, feems to be caufed by the fulphurous Matter that 
melts firft in this Metal as well as Iron, and is raifed to 
its furface by the extream Heat. 
I placed a piece of Copper in the Focus upon Char- 
coal : It melted, and emitted a very thin Fume, and by 
Ettlc and little diminiftied till it was all evaporated. 
I 
