The Clifton clarion., 1889-05-22
CONCENTRATION OF ORES A Series of Descriptive Articles Showing the Various Methods Employed.
 BY ANDREW WALLACE.

1 To get the best results from any se- ries of screens, they must be 80 arrang- ed that the crushed rock is first deliv- cred to that screen which has the largest holes, ending with that one which has the smallest holes. The cf- feet of this arrangement on the series adopted in these papers, would be like this: The crushed rock entering the screen with 1-2 inch holes, the revolv. ing motion of the screen constantly brings new holes under the mass of rock and permits those pieces which are small enough, to pass through them. while the larger pieces are kept moving toward the lower or outer end of the screen. As it is necessary that all the rock should pass through the holes in the first screen, those pieces which are too large collect in 8 spout and are conveyed by gravitation to a pair of rolls, set closer together than those which did the first crushing; hay ing been re-crushed it then falls to the elevator and is carried up and again delivered to the screen.
 Placed under each screen, there is a large iron hood or apron, made with sloping sides and terminating in an inclined spout, forming the bottom of the apron. The purpose of this apron is to catch all the rock which comes through the holes, and deliver it to that screen which has the 3-S inch holes. The action of all the screens in the series is precisely the same as the first one; the finely crushed rock goes through the holes, is collected in the apron below, and is delivered to the next or IA inch screen; that which goes through the 1-4 inch holes is sent on to the Is inch screen, and what goes through the Is inch holes goes to the hydraulic classifler.
 As the crushed rock in passing from screen to screen is successively met by holes which are smaller in diameter than those last passed, the result is that each screen receives portion of the rock which is too large to go through its holes. What then happens is this. 1 the 3-8 inch screen retains all rocks larger than 3-S, but which are still smaller than 1-2 inch; the 1-4 inch screen retains all sizes between IA inch and 3-S; while in its turn, the 1-S inch retains all between Is and 1-4 inch. Having now obtained three different sizes, l-2, 3-S, and 1-4 inch, each size as it leaves the lower end of the screen which produces it is col lected in separate spout and is con- veyed by gravitation to the concel : trating machine prepared for it.
 The hydraulic classifier, to which all the finer crushed rock is conveyed, is made in an endless variety of styles, some being very costly and intricate. The action of the classitier is very sim- pie, and the object aimed at by its use is the same in all: as rule, the less contraptions there are about classi- fer the better it will work. Describ- ing it generally, it consists of an ob- long box divided by partitions into four or five compartments, the top of each partition being one or two inches lower than the partition immediately before it. Each compartment has . hopper shaped bottom, with an outlet for the escape of sands, and is provid- ed with suitable pipe to admit a stream of clear water, which must be projected in an upward direction. The different compartments being fill ed with water, and the upward stream flowing from each pipe, the fine rock or sands can now be fed to that com partment having the highest partition As the sand continues to flow into this compartment it naturally has ten dency to sink to the bottom, and ii would certainly do 30 were it not met by the upward stream ofwater. When the force of the upward current ii properly regulated, the result is that only the heaviest particles of sand car sink through it to be delivered at the opening in the hopper bottom, while the lighter particles are carried ovcl the partition into the hopper next 1T succession; here the sand is again me
 by an upward current, regulated, as il the first case, to allow only the heav jest particles to sink. This process ii
 continued in each hopper in success