Sifting, riddling, and screening are treated of under Section 72. For
concentrating ores many methods are in use, of which the water processes
are the most important.
=475. Circular revolving concentrating table.= The lightest particles
are discharged over the edge, and the heaviest remain in the centre.
The ordinary magneting machine, for separating particles of iron or
steel from mixed borings, &c., consists of a series of magnets drawn
through the material, and then through fixed brushes, which brush off
the iron particles adhering to the magnets.
[Illustration: 465.-479.]
=476. Separating dust from grain,= &c., by a current of air driven
through the stream of material as it falls from hopper to hopper. See
also Nos. 1268, 1270.
=477. Ore concentrator;= consists of an endless rubber belt with flanges
(see No. 1082), having a slow longitudinal motion, and a rapid shaking
motion, either sideways, as in the “Frue Vanner,” or endwise, as in the
“Embrey” concentrator; a stream of water runs over the ore, the heavy
particles settle on the belt, and the mud is washed off.
=478. Jig= for separating ores by motion of a piston in water, the heavy
parts settle to the bottom and the light parts are removed at the top.
Filtration through various substances--as sand, charcoal, calcined
ores, &c., is employed to separate suspended matter from liquids.
Separation by subsidence in a tank, similar to No. 1571, is employed
for lime, &c.
Chemical deposition and evaporation are necessary in many cases.