40 MINING IN CALIFORNIA AND NEVADA.
prototype
is on the same principle as a revolving and endless blanket, only, the
materials used are of greater durability, and some additional
improve-mets in working have aided in the perfection of the machine.
Two principal rollers at each end of the machine carry the " belt," or
endless blanket. These rollers are made of galvanized sheet iron
riveted together, 13 inches in diameter, and 51 inches in length; and a
larger roller, 24 inches diameter, is fixed midways and a few inches
below the line of the lower periphery of the two end rollers, so that
the belt travels on top of the end and beneath the
intermediate roller. A fourth roller is provided, made of hard wood,
which is geared to a movable plummer-block by a screw. This screw is
also used to take up any slack on the belt caused by the weight of the
stuff and water, thus preventing the " bagging " of the belt. This belt
is 4 feet wide by 27^ feet long, and it travels on a number of
intermediate wooden rollers, so as to keep an even surface; it is made
of vulcanized rubber, A1 3-plynavy canvas, and it has two rims at the
sides, raised to 1^ inches, thus forming an even narrow -channel. The
sands (crushed or otherwise) are run through a distributor upon this
revolving belt in this way, that the belt travels towards the feed, and
at the same time an additional supply of water, arranged in irregular
drops or jets, is thrown in, so as to prevent the sand from forming
ridges or grooves. When working, not less than half an inch of sand
should cover the belt; and in order to improve the action of the belt
as a concentrator still further, three flat steel springs are provided,
which are worked by cranks off the rollers. These springs communicate a
quick lateral action—about 190 per minute—to the belt, thus inducing a
kind of wavy motion, which results in bringing the lighter sands on the
belt to the surface to be washed away. As the belt travels along,
carrying the sands, the result is as follows :—The concentration takes
place just beneath the feed, where the metalliferous and concentrated
parts of same are carried in the opposite direction of the feed,
whereas the wastes remain on the belt until they fall into a launder at
the opposite end. The concentrated pyrites on the belt are immersed in
the vessel provided below, in order to be collected. These machines
work very easily, and one lad can attend to more than half a dozen of
them, the only thing that wants regulation being the additional supply
of pure water during the process. They may be placed immediately
beneath the tailings-shoots, where they can treat from 6 to 10 tons per
day. Some kindred concentrators require an inordinate amount of
motive-power, in some cases up to three or more horse-power each; but,
in this instance, from a quarter to half horse-power is quite ample for
the purpose. The results of samples of raw sands washed in my presence
at San Francisco for concentration were most satisfactory. Both
tailings and black sand as thrown up by the Pacific Ocean were tested
with equally convincing results as to the capability of this
concentrator. As regards the black sand, as mixed with titaniferous
iron-sand, and more difficult to separate than free gold and pyrites
from tailings, systematic tests were made and average samples obtained
for assay, which gave 8-27 dollars per ton of unconeentrated sand as found in situ at
the coast. This sand, after treatment in the Frue's concentrator, had
been enriched to 1,935*43 dollars per ton, with but a slight trace of
gold in the tailings. This is a machine eminently suited for re-working
old tailings.
RETORTING.
The
Californian gold retorts are in some districts similar to ours, only
that when the old retorts are used the usual syphon pipe is placed at
one
