Treating the Amalgam.—The
quicksilver and amalgam obtained is well stirred in buckets, and the
coarse sand, nails, and other foreign substances which float on the
surface are skimmed off. This residue (which holds considerable
amalgam) is concentrated by washing in pans or rockers, and the
concentrations ground in iron mortars and treated with more
quicksilver. Any base material which floats on the surface of the bath
is melted by itself to a base bullion. The remainder is added to the
fine amalgam. The amalgam is strained from the quicksilver through
drilling, and the dry amalgam is retorted in iron retorts.
Retorting.—Where
the amount of amalgam obtained is small the hand retort is used, but at
large gravel-mines the cast-iron retorts are made stationary, similar
to those used at gold and silver quartz mills, only that they are
smaller. Where large quantities of amalgam are retorted and the
furnaces when fired are left unattended, as is frequently the case, the
retort, which is set immediately above the fire, becomes overheated.
The weight of the metal which it contains then causes the retort to "
belly," which ruins it. To overcome this difficulty the retort should
be set with supports and arranged with the fire to one side, that the
heat may be evenly distributed over it. Retorts thus set are found to
work well in practice. (See Figs. 70, 71.)
Before
the amalgam is put in the retort the interior is coated with a thin
wash of clay, which prevents the amalgam adhering to the iron.
The
amalgam should be carefully introduced and evenly spread. The iron pipe
which connects the back end of the retort with the condenser must be
clear of all obstructions, and under no circumstances should the
amalgam be spread so that the pipe can possibly become choked, as in
that case an explosion would probably ensue.
To avoid any danger arising from this source, after the cover has been put on, luted with either clay or a
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