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weight ; fome metallic com 
their weight. 
Platina appears in general to have no remarkable 
affinity with one metal more than with another. Lead 
and iron, which do not mingle together, and of 
which the former will take up fome bodies from the 
latter, and the latter fome from the former, feem 
both indifferent to platina ; which, if combined with 
either, is not feparated by the other. 
Neverthelefs fome fubftances have greater or lefs 
degrees of affinity with platina than with other me- 
tallic bodies. Thus, from aqua regia, in certain cir- 
cumfiances, it throws out gold ; and is itfelf preci- 
pitated by the other metals, which diffolve in that 
menftruum. From quickfilver it throws out lead j 
and is itfelf thrown out by gold. 
The changes, which platina occafions in the per- 
fed metals, were examined in a former paper : Its 
effeds on the femi-metals are lefs remarkable. The 
principal are, that it increafes the hardnefs of zinc, 
and the antimonial femi-metal, but not of bifmuth ; 
and difpoles this lad to change its colour in the air, 
but not the others. 
Its effeds on the compound metals are fimilar to 
thole, which it produces on the fimple ones. Brafs 
it renders white, hard, brittle, fufceptible of a fine 
polifh, and not liable to tarnifh in the air, as it does 
the copper, and in fome degree the zinc, of which 
this metal is compofed. Mixtures of it with copper 
and tin are more apt to tarnifh than with copper only, 
and lefs than with tin only. 
All metallic fubllances, except gold, are exeded 
from platina by the fimple acids : Mercury is the only 
one 
pofitions more than twice 
