aflaying Copper Ores. 33 
found at the bottom, it is to be wafhed and added to the 
reft. 
The copper is now to be dried and weighed, and 
gives the proportion contained in the ore. 
Obfervations on the above procefs. 
It is about twenty years ago that I contrived fome me- 
thods of aflaying ores, which might avoid tedious and 
troublefome roaftings and fufions in great degrees of 
heat, which require a dexterity which is only to be ac- 
quired by great practice, and which after all form a pro- 
cefs that is often various in the refult, and feldom fhews 
the fubftances contained in the ore, excepting the metal. 
The principles on which thefe procefles depend, as far as 
regards copper ores, are, 
Firft, Metals are attracted more ftrongly by acids than 
by fulphur, with which they are often combined in their 
ores. In confequence, if a metal be combined with ful- 
phur in an ore, it may be feparated by applying an acid, 
which will unite with the metal, and feparate the ful- 
phur. The metal may generally be feparated from the 
acid in its metallic form by m,eans of another metal, 
which attracts the acid more ftrongly. 
Vo l. LXX. F 
Secondly, 
