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SILVER. 227

tist's laboratory. The specimen to l)e treated is heated with
from twelve to thirty times its weight of granulated lead,
in a bone-ash cupel, which is placed in a muffle so arranged
that a current of atmospheric air may pass freely over the
vessel and oxidize the lead. This oxid of lead, being quite
fusible, combines w'ith any base metal present and oxidizes
it, uniting subsecjuently with the oxid as a fusible slag,
while the gold or silver wdll be held by the unoxidized por-
tion of the lead. In the treatment of specimens of alloy,
such as plate or coins, a cjuantity of the specimen is ac-
curately w^eighed and mixed with from four to five times
its weight of pure granulated lead. It is then placed in
the cupel and exposed to heat, as above described, until all
the lead is oxidized or converted into litharge, when the
remaining button assumes the brilliant appearance of sur-
face to which allusion has been previously made, denoting
that the base metals or oxidizable constituents have been
oxidized and taken up by the lead oxid. This button is
then to be weighed by means of a delicate assay balance, and
the loss of w-eight denotes the amount of alloy that was
present.
—
Wet Method. " Pure silver, wdiich is reckoned as 1000
fine, may be obtained from standard or other grades of
silver by dissolving them in nitric acid slightly diluted wdth
water, the solution being much facilitated by exposure to
gentle heat. If gold be associated wdth the alloy it wdll be
found at the bottom of the vessel, in which case it will be
necessary to use a siphon to remove the argentic nitrate solu-
tion. The silver is now to be precipitated in the form of
chlorid by the addition of an excess of common salt. When
all has subsided the liquid is carefully poured off, and the
chloric! thoroughly w^ashed, to remove all traces of acid.
The chlorid is then placed in water acidulated with hydro-
chloric acid (an ounce of chlorid recjuiring six to eight