37 
ajjaying Copper Ores. 
with chemiftry, fo that an proprietor of an eftate, n 
his fervant, may determi ne if an ore be of cc ; *per, ' m 
value ; fecondiy, as affording an aifay-tnafter a u 
perfect manner of determining the vuiue c f a copper 
ore; and, laftlv, as a procefs by which the naturaiift may 
inveftigate not only the copper in an ore, but its various 
other contents. 
There is but one known fpecies of copper ore in 
which the copper is not capable of being combined with 
aqua regia , which is blue vitriol, which is fometimes 
found folid, but more frequently in mineral waters; from 
this the copper may be precipitated by iron immediately. 
We have lately had many opinions publilhed of me- 
tals being found in mineral waters combined with various 
fubftances. I never examined any mineral water in 
which I found the metals combined with any other fub- 
ftance but vitriolic acid ; and am certain, many authors 
have been milled by not knowing this property of me- 
tallic falts, viz. that if we diffplve them in a fmali pro- 
portion of water, or if there be fuperfluous acid, the fo- 
lution will remain perfect when expofed to the air; but 
if the acid be perfectly faturated with the metal, and the 
proportion of water to the metallic fait be very great, on 
expofure to the air it is decompofed, the metal .precipi- 
tating in the form of a calx, and the acid being loft. 
This 
