Barrow, John [Hrsg.]: Dictionarium Polygraphicum: Or, The Whole Body of Arts Regularly Digested: Illustrated with Fifty-six Copper-Plates. In Two Volumes (Band 2) (London, 1758)

220

R E F

the operation is over, leaves the gold of eighteen or twenty carat3s

according as it was in finenefs before.

When they have done this, they raiie it by fire, as follows:
Having put the broken fublimate into a crucible, with the

melted gold, they cover the crucible immediately to fmother the

mineral ; and then furnifh the furnace with charcoal, and put

on the capital.

Then a quarter of an hour after they take off the capital, lay-
ing the crucible bare, and give it the cool air, i. e. blow off all
the afhes and other impurities that may be floating on the li-
quid gold, with a pair of bellows, the nozzle of which is crook-
ed.

This is repeated again and again, till all the impurities of the
eold are cairied off, by virtue of the fublimate; and that they
find it of a bright glittering colour ; after which, it is taken out
of the crucible, and the gold is caff, into an ingot

This method of Refining by fublimate is both cheaper and
more complete than that by antimony; but they are both ex-
ceedingly dangerous, by realbn of their fulphureous and arfenical
exhalations ; the only difference in their malignity confifts in
this, that the poifon of the antimony is flower than that of the
fublimate.

For the method of Refining gold by aqua-fortis, fee DE-
PART.

Gold may alfo be refined with lead and afhes; but this me-
thod is feldom ufed, excepting in effays.

The method <?/~ReF1ning fiber. There are two ways of do-
ing this ; the one is with lead, and the other is with faltpetre.

That performed with lead is both the beft and cheapen:; al-
though that with faltpetre ftill obtains in many places, for want
of workmen who underffand the method of the operation of the
former. The method of Refining with faltpetre is as follows:

This operation is performed in a wind-furnace. They firff.
reduce the filver, to be refined into grains, about the fize of a
fmall pea; which is done by firff. melting it, and then throwing
it into a tub of common water, and then heating it over again in
a boiler.

This being dene, they put it into a crucible ; putting to every
eight ounces of filver two of faltpetre.

Then they cover the crucible with an earthen lid, in the form
of a dome, exactly luted ; which lid muff have a fmall aperture
in the middle.

The crucible being fet into the furnace, and covered with
charcoal, which is only to be lighted by degrees; at length thev
give it the full force of the fire, to put the metu! into a perfect

fuiion.