purington.] CLEANING, RETORTING, AND MELTING. 205 
accumulates in the sluices or tables in an} r considerable amount, it 
should be sampled and assayed to ascertain the amount of finely 
divided gold which still remains in it. 
CLEANING, RETORTING, AND MELTING. 
If amalgam is to be treated, it should be well stirred, either in 
buckets or large porcelain mortars, and the base material — sand, scraps 
of iron, etc. — which comes to the surface should be skimmed off. 
This residue (which holds considerable amalgam) is concentrated by washing in 
pans or rockers, and the concentrations ground in iron (or porcelain) 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 amal- 
gam. The amalgam is strained from the quicksilver through drilling, and the dry 
amalgam is retorted in iron retorts. « 
In cleaning the placer gold, when no quicksilver is used, a magnet 
inside a cotton sack passed through the dust will remove all the mag- 
netite. Minerals of high specific gravity not attractable by the mag- 
net are not easil}' removed by mechanical means. Rutile, garnets, and 
ilmenite are examples of these occurring in Alaska. In small opera- 
tions the gold dust is roughly cleaned from these minerals by blowing 
and dry-panning. Where the amount of gold is considerable, a melt- 
ing plant is advisable. In retorting amalgam, small hand retorts will 
in general be found adequate. 
Before the amalgam is put in the retort the interior is coated with a thin wash of 
clay, which prevents the amalgam from 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, lined 
with either clay or a mixture of clay and wood ashes, and securely clamped, the fire 
is lighted and the heat gradually raised, a dark-red heat being all that is necessary 
to thoroughly volatilize the quicksilver. Toward the end of the operation the heat 
is raised to a cherry-red color, at which it is kept until distillation ceases. The 
retort is allowed gradually to cool, and when cold is opened.'' 
A stream of cold water should be always flowing through the jacket 
which incloses the condensing pipe, so that by no possibility can mer- 
curial vapor pass into the receiving vessel in which the lower end of 
the pipe terminates. The discharge end of the pipe should be kept 
under water during the retorting operation. 
When gold accumulates in sufficient quantities to make the shipment 
of the dust inconvenient, the metal may be melted on the ground and 
molded into bricks. Both for convenience of shipment and facility 
in guarding against losses, this practice is to be recommended. A 
brief description of the essential features of this work follows. 
a Bowie, op. cit., p. 249. & Bowie, op. cit. 
