ajfaying Copper Ores. 35 
ore be diffolved in an acid, fo as to form a compound i'o- 
luble in water, the folution of the metal may be poured 
oft^ leaving fuch earthy matters behind. 
Fifthly, If the earthy matter Ihould diflolve in the 
acid, it is feldom to be precipitated by a metal : therefore 
if both earth and metal be diflolved, on the application 
of another metal, which attracts the acid more ftrongly, 
that which was combined with the acid will be precipi- 
tated, and the earth left in the folution. 
Sixthly, Acids attract the metals with different powers : 
therefore, if two metals be combined with an acid, if 
we apply to the folution a mafs of that which attracts 
the acid ftrongeft, the other will be precipitated. The 
mafs being weighed before and after the precipitation, 
the difference will be the quantity of additional metal 
diffolved ; if, therefore, we pour off the liquid from the 
precipitate, and apply another metal, which attracts the 
acid ftill more ftrongly, the fecond metal will be precipi- 
tated, which being weighed, and the weight loft from 
the mafs deducted, gives the weight of the fecond metal. 
As this principle is of great ufe in inveftigating the ele- 
ments of mixed metals, we fhall give an example. Sup- 
pofe copper and filver mixed; diffolve the whole in pure 
nitrous acid, properly diluted with water; apply to the 
folution a mafs of copper, the filver will be precipitated. 
F a Pour 
