40 Dr. fordyce’s Method of 
If there be any calcareous earth diffolved, the vitriolic 
acid will combine with it, and form a white pow'der, 
which will be left after the copper is re-diffolved, and 
muft be feparated carefully from the folution. 
After the precipitation of the copper, it is neceflary to 
get rid of the falts perfectly before we apply the vitriolic 
acid, otherwife part of the copper would be re-dif- 
folved. 
Vitriolic acid will not diffolve copper in its metallic 
form, and may be applied to diiiolve any iron that may 
be mixed with the precipitate, as well as to loofen cop- 
per, which fometimes adheres to the iron. 
The folution of the iron muft be carefully waflied off 
from the copper. 
There is a criterion by which we may judge certainly 
if any of the copper be loft. Let all the w'afhings and 
every thing, except the copper, be put into a vefiel toge- 
ther; pour in folution of fixed alkali till no further pre- 
cipitation takes place ; let the precipitate fubfide, and 
pour off the liquor ; apply to the precipitate folution of 
volatile alkali, fold by the name of fpirit of fal ammoniac ; 
fhake them together, and let them ftand for an hour ; if 
the folution of the alkali acquires a purplifh blue co- 
lour, the procefs is imperfedt, if it does not, it is perfedt. 
If 
3 
