36 Dr. fokdyce’s Method of 
Pour off the folution, and wafh the filver and undiflolved 
copper with water; pour the wafhings into the folution; 
weigh the mafs of copper left, and mark what it has loft ; 
apply to the folution a mafs of iron, the whole copper 
will be precipitated. Pour off the fluid, and wafh the 
precipitate carefully, dry it, and weigh it, deduct the 
weight loft from the mafs of copper, what remains is the 
weight of the copper in the mixture; if this weight, 
together with that of the filver, be the weight of the 
metal originally expofed to examination, there is no rea- 
fon to fufpet any mixture of another metal. 
If the metals mixed are unknown, if we can find an 
acid which will diffolve them, we may try to make a 
precipitation with the metal which is lowed; but one in 
the order of eletive attractions, and fo proceed to the 
next above it, until we come to the higheft ; and by this 
means we fhall obtain all the metals in the mafs. 
There are other principles on which I have founded 
various precedes for affaying; but thefe are diffident for 
copper ores, all the different known fpecies of which I 
have actually allayed, and therefore have ventured to 
offer this procefs to the confederation of the Society; 
firft, as only requiring an apparatus which can be 
bought at any apothecary’s or chemifts, and as capable 
of being performed by a perfon totally unacquainted 
with 
