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glafs of lead ; and when the calx is increafed more 
in weight, fo that it’s gravity is become greater 
than that of the lead originally^ it paffes into red, 
the next colour in order. 
Thefe three colours fucceeding each other in 
proportion as the gravity of the metal increafes, 
, feem to prove that, in this cafe, the greater denfity 
produces the lefs refrangible colours : and as orange 
is the colour of this calx, when in a middle degree 
of weight, between that which is lighter and that 
which is heavier than the original metal, it appears 
that orange is the colour natural to lead when it’s 
weight is neither much increafed nor diminidied. 
SILVER. 
THE only preparation of fiver, which is of 
any primary colour (except the yellow it im- 
parts to glafs, and other vitreous fubftances, as 
earths or falts) is luna cornea, which Mr. Boyle 
fays is of a J air yellow, Shaw’s Boyle, vol. i. p. 255. 
Phyfical EjSays, Edinburgh, 1754, vol. i. p.310 [yj. 
[y] Art. 10. Remarks on chemical folutions and precipita- 
tions, by A. Plummet, M. D. 
When either a muria of fea fait, a folution of fait ammoniac, 
or fpirit of fea fait (for thefe three have nearly the fame efFedls) 
is put into a folution of ftlver \ it becomes milky, and, as it were, 
crudled, and at length a white powder fubfides to the bottom : 
this powder, being wafhed with warm water and dried, is foftand 
impalpable j it’s weight exceeds that of the filver diflolved by 
COPPER 
