ctjfaying Copper Ores. 39 
in vapour; or vapours produced by the decompofition of 
this oil occafion an effervefcence. 
All the calces of copper I have tried are combined 
with gas, refpirable air, or other vapours, excepting one, 
which is of a light green colour, brittle, ana which breaks 
fmooth like glafs; a fpecimen of it is contained in Dr. 
hunter’s, mufeum: this diflblves without effervefcence, 
the others all effervefce. A boiling heat is neceffary to 
render the folution compleat, of which great care is to 
to be taken. 
If there be any fulphur in the ore, it appears quite 
clear in lumps; a fmall portion of it, however, is de- 
ftroyed by the nitrous acid. Earthy matters infoluble in 
acids, if any, and arfenic, appear in a powder at the bot- 
tom. If there be any filver it is mixed with this powder, 
and is to be extradted by melting it with black flux and 
litharge, and cupelling in the common way. If there be 
any gold it may be taken out of the folution by aether. 
When the copper is combined with nitrous and muri- 
atic acids, it might be thought fuflicient to apply the iron 
immediately; but it is much more convenient to preci- 
pitate it from them, and combine it with vitriolic acid, 
on account of the convenience of wafhing the precipi- 
tate, which is in a more compacted mafs. 
If 
