[ 32 ] 
COPPER and I R O N. 
I T appears then that all the preparations of 
goldj lead, and fiher, invariably retain the colours 
peculiar to the order of their denjities, and that they 
are the fame ^uoith thofe njohich they co7nmunicate to 
glafs. 
The two mod: imperfect metals, copper and 
iron, being very ealily adled on by almoft all men- 
Itrua, the colours of their folutions, &c. viz. green 
and blue, are apt to change into each other’s order; 
the copper in lome folvents becoming blue and the 
iron green, and in other folvents vice verfa ; this 
probably depending on the increafe or diminution 
of their denfities. 
The folutions of copper, in the acids of nitre and 
fea flit, and in the vegetable acids, are green. But 
if copper be attenuated, by folution in volatile 
alcalies, it becomes blue. Theophraftus and others 
have obferved, that emeralds are frequently found in 
copper mines ; and it is probable that they obtain 
their tinge from that metal. 
I melted fome emeralds with twice their weight 
of falts, and found that they had formed a fine 
geren glafs, fuch as would have been produced from 
the fame quantity of a vitrifiable earth, and about 
a hundredth part of its weight of copper. 
t 
more the one fixth part. This powder comes much fooner to 
fufion than filver, but does not recover the appearance or pro- 
perties of that metal ; for it looks like a piece of yellowijh glafs, 
femiopaque and brittle, yet bending or yielding a little, whence 
it gets the name of luna cornea. 
Iron 
