The Clifton clarion., 1889-06-26
ccNcENqRArroN OF oREs
\ Series of Descriptive Article. showing
 thc Various Methods Employed.
BY ANDREW WALLACE.

uid-HtaIAlhS bbiN lONCSt J"H VI '%' "9 nearly as possible the same thickness it will be apparent that to do this in a proper and of course cheap man. ner. the discharge must be regulated automatically.
 It is known that column of quick silver inches high will balance in equilibrium a column of water ? feet high. the quicksilver being so much heavier than water. In the same wey, Q column of any ore which is heavier than its gangue, will support column of that gangue so much higher in proportion to the difference between their specific grayities. For instance. take a gaiena ore contained in lime rock. The specific gravity of gaicna is "a, whilst that of the lime rock gangue is 2.75. The column of ore necessary to balance the column of gangue in this case would be in the proportion of inches of ore column | to , inches on the seive.
 On this principle all the patented and unpatented automatic discharges are based. and theIr action is shortly described thus Tn that portion of the jig allotted to the screen. and close to the outside of the jig frame, a small space is walled off, generally by q piece of short iron bent in thesform of square with finch sides, the short iron making three sides of the square, the fourth being made by the front side of the jig. This short iron is so fastened to the jig that all around is lower edge there is Jeff q space be- tween itself and the screen sufficient ly high to allow of the free passage of ali properly sized particles. The jig being ROW started to work, as al- ready explained. the heaviest particles going to the bottom layer, the effect of having such discharge column as above described is this: as the ore particles accumulate on the screen, and the mixed column of ore and gangue rises until the gangue at tains the height set for the overflow, the increase in weight of the column in the screen space has the tendency to spread the heavy ore particles next the screen, and there being no outlet fot them otherwise than through the discharge column are forced through the space between the short iron and the screen and so into the discharge
 As the ore is forced into the dis charge column at every stroke given by the plunger as fast a5 it accumu- lates on the screen, it stands to reason that if the crushed rock is at all rich in ore the column will soon reach the theoretical height whereby it can bal ance the column in the screen space when this height is reachedt the pressure on both columns Icing equal, no more ore will be forced into the discharge, and here is where the automatic comes in. The heigth ol the ore column being known, an open ing is made i'll the side otthe jig frame in that space occupied by the column at the exact heigth required to main tain the proper depth of ore on the screen and balance the column ot gangue. Any increase in the deptl of ore js at once met by the tendency of the ore to spread on the screen
 and ar increase of pressure on the dis
 charge is the result. causing some O
 the ore to flow from the opening al
 the top of the column and give plac,
 to that ore which is being continual! formed on the screen. This action i, repeated at each down stroke of tn, plunger, and if the heigth of the dis charge column and opening is proper ly regulated, the machine require , very little attention outside of seein: : that the ore and water supply is kcp
 regular, the speed of the machiner.
 steady, and the machine itself kep oiled and in repair.
 It must be remembered that the or which is thus discharged, is that or : which collects on the jig screens, ant only on the screens of those jigs whicI are treating ore particles which vii not pass l-16 inch holes. As a gencr al thing, the ore which leaves the dis charge from the first screen whel two or three screens are used is fiji fo l smelting or other treatment directly 2 and when four screens are used, tn : discharges from the first and second i = .bo eor;os ora o.oo1. but o, ;u tb