SEPARATION. Having the ore erushed. the suc ceeding process is to separate the valuable ore from the waste. Sorge of the principal apparatus and methods for performing this operation are as follow,: Palimingry are used to dis integrate and float adhering clay or fine stuff from the coarse particles. which is done by using running water aided by some stirring device. and .screens are used for separating the coarse from the fine of the ore: they may be classified as: (I) stationary screen-. (a) grizzlies or bar screens. lb I gravel screens of wire cloth, (c) perforated plate screens; and (2) moving screens, (a ) oscillating bar screens. (b) plain shaking screen- or and (e) re volving screen; or trommels. are de vices for obtaining a series of of dimin ishing size by means of currents of water. The most common form consist, of a channel connect ing a series of pockets. Water is supplied to each pocket so as to form an current. the force of the current in each pocket after the fir-t hieing less than that in the pocket. The effect produced is that grains which are heavy enough to settle against the upward cur rent in each pocket can do so, while the lighter grains are carried on to succeeding pockets until they strike one where the current is mild enough to permit them to settle.
Hand picking is the process of separating the waste from the valuable ore by picking it out by hand. This work i, usually done on `tables.' There are five classes of picking tables in use: (1) stationary horizontal tables; (2) stationary sloping chutes; (3) shaking tables; (4) belt, rope, or plate conveyors: and (51 revolving cir cular tables. Hydraulic jigs operate through the action of two currents of water, an upward and downward, alternating with each other in quick succession, upon a bed of sand supported by a screen. The screen may be pushed up and down in a tank of water to bring about the necessary current action: or it may be stationary while a reciprocating motion is given to the water. In
either ease the effect is to separate the crushed material in layers according to the specific gravity of the TR consist essentially of an endless belt which is shaken rapidly either sidewise or end wise and which has a continuous slow motion up-hill. The ore is fed onto the belt in the form of wet pulp. The agitation makes the ore bed so loose that particles of higher speeific gravity rise to the upper layer. The travel of the belt draws the heavy minerals to the head end. while the water washes the light minerals down to the tail. Bumping tables operate much as do van ners, the bumping action separating the particle: according* to specific gravity and the heavier particles to one side of the table while the water current carries the lighter particles to the other side. Film sizing tables depend upon the relative power of a Olin of water flow on a quiet surface to net the 110W lb red ore. As is well known, a filln of water (lowing over a quiet surface has an upper current which moves faster than the lower curnmt. whose water is re tarded by friction; the heavier grains remain at rest in the slow bottom current, while the lighter grains aiv carried away by the id: top current. May,,, tie scpurators utilize the action of an air current to separate particles of hni• siweific gravity from those of higher slavilie gravity. For a comprehensive discussion of the methods and machinery used in crushing and sep arating ores, see Richard, ()re I1rcssin9 (New York, I900; ; and for an annual record of cur rent progress in this art, see the annual volumes of the ral Industry (Nevi York).