side
of the lid, whereby one clamp is only necessary instead of two, if that
pipe was as usual screwed in at the centre. Then, again, the lower end
of the syphon pipe is let into a sheet-iron cylinder, 5 inches in
diameter by 2 feet long, perfectly watertight at the joints; on top of
this cylinder a funnel is riveted leading into the cylinder; also on
the top a syphon fixed the same way, taking care that the lower or
outlet pipe is at least 1 inch lower in level than the inlet funnel.
Water is turned into the funnel preferably by means of a "main," when,
after filling the cylinder, the syphon retort pipe supplied with water
through the funnel to be constantly removed by the lower syphon at this
" cooler," will always remain cool for the purposes of condensation of
the vaporised mercury.
In
mines where the yields are large, and where consequently a
proportionately greater quantity of amalgam (gold or silver) has to be
retorted, the above or ordinary method is too tedious, and consequently
these mines, like some at Clunes, have retort furnaces specially
constructed for the purpose of dealing with their amalgam, and it has
been found that these furnaces are more economical, healthy, and almost
self-working.
At
the Comstock lode, Nevada, the retort house, with a number of furnaces
in it belonging to the Virginia Consolidated and California United
companies, is quite a fine and substantial structure, where retorting
is carried on every day.
The
retorts (Plate VIII.), eight in number, are built in fire-brick and
connected by furnaces with the flue and stack, care having been taken
to construct the fireplaces so as to allow full play and access to the
retorts by the flames. They are made of cast iron, cylindrical in form (a), in
order to permit their being turned round should one side be burnt too
much. The most convenient and approved size is 5 feet in length; the
inside cylindrical portion of 1-1/2-inch cast iron being 3 feet in
length by a clear foot in diameter. The neck i gradually contracts to 2-1/2 inches diameter for a length of 2 feet and over; this end of the neck i is furnished with a flange to which the condensing pipe c is
bolted. This condensing pipe does not sit horizontally like the main
body of the retort, but it is bent downwards, similar to that of the
ordinary portable retorts; and it then passes through a body of water b contained in a vessel constructed of boiler-iron, which water is being continually (during retorting) added to through the pipe e, whence it escapes at k, for the eventual discharge at d. The
amalgam is placed in the retorts, in cast-iron trays fitting the inner
sphere of the lower parts of same, and in three hours retorting with
eight retorts at the above quoted mines not less than 13,000 lbs. of
dry amalgam were treated simultaneously every day. (1877.)
Section VI.—Reduction of Pyrites.
(a.) COMMON BOASTING AND GRINDING.
The
treatment of sulphurets containing gold or silver in reverberatory
furnaces to drive off the sulphur, and subsequently the grinding or
milling in Chilian mills, Wheeler's, or other pans, and Berdan's
basins, with mereury, in order to amalgamate with the thus liberated
gold or silver, has become quite obsolete in California these twelve
years past or more, and for gold ores specially, a process has been
generally adopted by means of which as much as upwards of 97 per cent,
of the gold contents of the calcined pyrites, as previously ascertained
by careful assays, have been obtained.
F
