gold, which it protects from amalgamation. This
separation of the pyrites from the pulverized rock is called
"concentrating the tailings," and the material collected is called
"concentrated tailings." In the sluices of some quartz-mills cast iron
riffle-bars are used; cast in sections about fifteen inches square, and
about an inch deep. Much study has been devoted to the subject of
making these riffle-bars in such a manner that the dirt will not pack
in them, but will always remain loose, and keep in constant motion
under the influence of the water running over them; but the object has
never been fully attained. Quicksilver is used in nearly all
quartz-mill sluices.

The raw hide used in separating gold from the pulverized quartz is a
common cow hide, laid down in a trough with the hairy side up, and the
grain of the hair against the course of the water. The gold is then
caught in the hair. Sheep hides have been used in the same manner,
recalling to mind the Golden Fleece. The hides, however, are inferior
to the blankets for this purpose, and are never used in the best mills.

The methods of amalgamating are numerous. Among them are amalgamation
in the battery, amalgamation with the copper plate, amalgamating bowls,
and patent amalgamation of many kinds.

In many mills quicksilver is placed in the battery, two ounces of
quicksilver for one of gold; and about two-thirds of the gold is caught
thus. The copper plate in quartz-mills is made in the same manner as in
placer-sluices, under which head a description of the plate may be
found. Some amalgamating bowls or basins are little Chilean mills and
arastras, made of cast iron. One plan of amalgamation is to use a cast
iron bowl about four feet in diameter and a foot deep. Near the bottom
are horizontal iron arms, which revolve and stir the quicksilver and
pulverized quartz together. Four or five of these bowls sit in a row
but at different levels: the bottom of the first bowl being level with
the top of the second, and so on. The pulverized quartz passes through
them all. Under each bowl a fire is kept up, because heat forms the
action of amalgamation. If there be any pyrites in the quartz, some
common salt is thrown in to assist in releasing the gold from the
embraces of the sulphurates, and preparing it to be seized by the
mercury. Another amalgamating bowl revolves on an axis that stands at
an angle of about seventy-five degrees to the horizon, so that the
material i