Page 229 - My FlipBook
P. 229
—
GOLD. 217
I'iKST xMKLT Till-: ALLOY AT A lUClI TEMPERATURE. tO
oxidize the base metals; the rehnini;" ag'cnts may then he
added in small qnantities from time to time, and the heat
continued from half an hour to an hour, according to the
coarseness of the allow The agents first employed are
l)orax and potassium nitrate (KNO;,). The latter assists
the oxidation by parting with its oxygen, when the foreign
metals will generally become entirely oxidized and dissolved
in the slag.
The crucible should be removed from the fire, and the
metals allowed to cool gradually. The crucible may now
be broken and the button of gold' at the bottom removed
and sepai'ated from the slag that covers it with a hammer.
The gold should then be put into a fresh crucible and re-
melted for pouring into ingot-molds, which should be pre-
viously warmed and oiled. This treatment, with nitrate
of potassa and borax, will usually be sufficient, as most
metals are oxidizable. If, however, after hammering, an-
nealing, and rolling the ingot, it should still be found brittle,
it must be remelted, and some other refining agent employed
to remove the traces of the base metals. If it is known
what foreign metal is present, the particular reagent which
will most readily attack it should be used. But if, as is
often the case, the alloy is of uncertain composition, or con-
tains several metals having distinct affinities, the process
becomes to some extent experimental, making it necessary
to use first one refining agent and then another, until from
the appearance and the manipulation of the gold, it is
found to be free from alloy. The special reagents em-
ployed are as follows :
When tin or lead is present, add mercuric chlorid,
HgCU (corrosive sublimate), and zinc chlorid, ZnCU, or
lead chlorid, PbClg, are formed and with the mercury
^-olatilized by the heat.
19
GOLD. 217
I'iKST xMKLT Till-: ALLOY AT A lUClI TEMPERATURE. tO
oxidize the base metals; the rehnini;" ag'cnts may then he
added in small qnantities from time to time, and the heat
continued from half an hour to an hour, according to the
coarseness of the allow The agents first employed are
l)orax and potassium nitrate (KNO;,). The latter assists
the oxidation by parting with its oxygen, when the foreign
metals will generally become entirely oxidized and dissolved
in the slag.
The crucible should be removed from the fire, and the
metals allowed to cool gradually. The crucible may now
be broken and the button of gold' at the bottom removed
and sepai'ated from the slag that covers it with a hammer.
The gold should then be put into a fresh crucible and re-
melted for pouring into ingot-molds, which should be pre-
viously warmed and oiled. This treatment, with nitrate
of potassa and borax, will usually be sufficient, as most
metals are oxidizable. If, however, after hammering, an-
nealing, and rolling the ingot, it should still be found brittle,
it must be remelted, and some other refining agent employed
to remove the traces of the base metals. If it is known
what foreign metal is present, the particular reagent which
will most readily attack it should be used. But if, as is
often the case, the alloy is of uncertain composition, or con-
tains several metals having distinct affinities, the process
becomes to some extent experimental, making it necessary
to use first one refining agent and then another, until from
the appearance and the manipulation of the gold, it is
found to be free from alloy. The special reagents em-
ployed are as follows :
When tin or lead is present, add mercuric chlorid,
HgCU (corrosive sublimate), and zinc chlorid, ZnCU, or
lead chlorid, PbClg, are formed and with the mercury
^-olatilized by the heat.
19
