[ 68 3 ] 
that the gravity of pure zinc turned out 7. oyo, and 
that of bifmuth p. 733. 
Hitherto we have confidered the mifcibility of pla- 
tina with metallic bodies, and the alterations, which 
different proportions of it produce in their appear- 
ance and qualities : employing the neceffary pre- 
cautions for preventing the fcorification and diffipa- 
tion, which mod; of the metals fuffer in the fire ; 
and which fome remarkably promote in thofe, which 
by themfelves are more difficultly, or not at all, de- 
ftrudtible. We {hall now examine the relation of 
platina, in this refpeCt, to thofe metallic fubftances, 
which are the moft deftruCtive. 
1. Cupellation and Scorijication of Lead with 
Platina. 
1. A mixture of platina and lead was cupelled, 
under a muffle, in an affay-furnace. For fome time 
the procefs went on well ; the lead gradually chang- 
ing into fcorias, which were thrown of to the fides, 
and abforbed by the cupel, or diffipated in fume. 
In proportion as the lead worked off, the matter re- 
quired a fflronger fire to keep it fluid ; and at length, 
collecting into a dull flat lump, could no longer be 
made to flow in the greatefl: degree of heat, which 
the furnace was capable of giving. The lump broke 
very eafily, appeared of a dull grey colour both in- 
ternally and externally, and of a porous texture. It 
weighed about one-fifth more than the quantity of 
platina employed. 
2. This experiment was many times repeated and 
varied : the lead attempted to be worked off on 
bone-afh, preffed into the bottoms of crucibles, fco- 
4 R 2 rified 
