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COT.l). 219

may be poured or hulled off. As some of the gold will
remain with the residue, more silver must be melted with it,
the operation being repeated several times until nearly all
the gold is removed." The gold and siher alloy may then
be separated as directed above.
When Platinum is Present.—If, after treating the
allov with the reagents enumerated, it should be found
malleable, but stiff or elastic and of a rather dull color, it is
due to the presence of platinum, and any further attempts
to reduce it by the " dry process " w'ill prove unavailing.
It must then be subjected to what will hereafter be described
as the " humid, or wet method."
The Humid Method.—When it is desired to reduce the
alloy to pure gold, wdiich is generally advisable whenever
the gold to be refined consists of very coarse filings, frag-
ments of plate containing large quantities of solder, linings
with platinum pins attached, particles of base metals, etc.,
the " humid, or wet method," as it is called, should be em-
ployed. The solvents in common use for this purpose are
nitric, sulphuric, and nitro-muriatic or hydrochloric acid,
but as the desired results can be more conveniently and
directly obtained by the use of the latter, or hydrochloric
acid, this most available method alone will be given. The
following practical remarks on the subject are from an
article on the " JManagement of Gold," by Professor George
Watt :—
" When the alloy is composed of metals differing but
little in their afifinities for oxygen, chlorin, etc., we resort
to one of the ' wet methods.' And, in this connection,
w'e will only describe the one wdiich we consider the most
convenient and eft'ectual for the practical dentist. It is
effectual in all cases, as it always gives us pure gold.
" Let us. then, suppose that our gold alloy has become
contaminated with platinum to such an extent that the color