DRESSING OF ORES 149 



vances so much further under the cam of the driving shaft t ; in the second, it goes 

 so much less forwards ; thus the adjustment is produced. 



The water for washing the ores is sometimes spread in slender streamlets, some- 

 times in a full body, so as to let two cubic feet escape per minute. The number of 

 shocks communicated per minute, varies from 15 to 36 ; and the table may bo pushed 

 out of its settled position at one time three quarters of an inch, at another nearly 8 

 inches. The coarse ore sand requires in general more water, and greater slope of 

 table, than the fine and pasty sand. 



The following remarks on the Freiberg Shaking Table, are by Mr. Upfield Green, 

 formerly of the Wildberg Mines, Prussia. The bed of the table is about fourteen feet 

 long, by six feet wide, and is formed of double one-inch boards, fastened to a stout 

 frame. The table is hung by four chains, the two hindermost are generally two feet 

 long with an inclination of 2 to 4 inches. The two front ones, which are attached 

 to a roller for the purpose of altering the inclination of the table, are five feet six 

 inches long, and hang perpendicularly when the table is at rest. 



The tables receives its action from cams inserted in the axle of a water wheel, 

 acting on the knee of a bent lever. The slimes after being thoroughly stirred up by 

 a tormentor, are conveyed by a launder in a box, where they are still further diluted 

 trith clean water, and passing through a sieve with apertures corresponding to the 

 size of the grain to be dressed, flow upon an inclined plane furnished with diffusing 

 buttons, and from thence drip on to the shaking table. 



In treating rough slimes the two hindermost chains are set at an inclination of 5 to 

 6 inches, and the table with an inclination of 4 to 6 inches on its length, makes 36 to 

 39 pulsations of 5 to 6 inches in length per minute. About 2| cubic feet of diluted 

 slimes, twelve of clean to one of slime-water, enter the table per minute. 



Before commencing the percussive action, the table is covered with a thin layer of 

 rough slimes, and during the first few minutes only clean water is admitted. In 

 consequence of the quantity of water and violent motion employed, the smaller and 

 lighter particles of ore are likely to drift down the table, and a rake is therefore em- 

 ployed at intervals to reconvey such particles towards the head of the table. Care 

 must, however, be taken not to allow the water to wear furrows in the deposit. From 

 two to three hours are usually required for the roughest sand-slimes to deposit four 

 to five inches on the head of the table. The crops are twice more passed over the 

 shaking table, and afterwards dollyed. The rapidity of movement and quantity of 

 clean water increase with each operation. The tails of the first operation, which are 

 considerably poorer than the original stuff, may be either thrown away, or once more 

 passed over the table, when the crop will be fit for treatment along with a fresh quan- 

 tity of original slime. The treatment of fine slimes is similar to that of the rough, 

 with the exception that the inclination of the table, quantity of slime-water, proportion 

 of clean water, and length of stroke, constantly decrease with the degree of fineness of 

 the slime ; and the number of strokes increase in proportion. In fact, for the finest 

 slimes, the table has no greater inclination than one inch on its whole length, while 

 the stroke, of which 35 to 45 per minute are made, is no longer than to | an inch. 

 The time required for dressing varies with the nature of the slime operated on, five 

 tons of rough slimes occupies sixty-eight hours, whilst the same quantity of very fine 

 slimes requires no less than four times that period. 



Eittenger's Percussion Tables. The primary object intended to be accomplished by 

 these tables, is the extraction of gold, silver, and other valuable ores from the vein- 

 stuff with which they may be associated. 



Figs. 750, 751, represent front elevation and plan of two tables in one frame, 

 divided by the strip s ; these tables are suspended by rods from the points o, in such 

 manner that they represent an inclined plane, the upper or higher end being at M ar. 



The sand and water, after passing through the sizing trommel x, is supplied to the 

 tables at 1 1, the other places z l and z* being for the admission of water only. As the 

 tables are suspended from four points, they are free to oscillate in one direction, that 

 is, at right angles to the direction of their inclination. The oscillation is produced 

 by a cam wheel acting upon the end of the beam A, upon which the table is mounted, 

 the cam pushing it in one direction, and a spring bringing it back with a sharp blow, 

 when the cam catches it, and a quick succession of blows is the result. It will thus 

 be seen that the stuff under treatment is subjected to two forces, the one being the 

 stream of water tending to wash the particles to the bottom of the table, the other 

 being the blow, to bring the ores over to the ridges s s'. The effect of these com- 

 bined forces is to induce the heavier or metallic particles to describe in their descent 

 curvilinear lines, the light materials suspended in the water reaching the bottom 

 of the table much quicker, and being less acted upon by the side blows, describe the 

 shorter line r r 1 , and leave the table almost in a straight line from the feeding plane 

 I and I. 



