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stamp-mill, and at this point the most important features of the Luhrig system commence. The crushed material is allowed to flow through a system of sizing-drums of about mesh. This is done in order to size off any particle of ore which may not have been stamped to sufficient fineness owing to bad workmanship Or wear in the rolls and stamps ; anything over Am. is then concentrated on continuous and automatic jigs. Concentration of the finer particles now takes place. They are firstly graded according to specific gravity in hydraulic graders, which are placed on a higher level than the concentrators and vanners to allow for gravitation. These hydraulic appliances have several sets of compartments, say four, and clean w-ater is supplied to each compartment by a pipe, and the flow is regulated by taps, which are fitted with graduated discs. The following action then takes place : The material is fed into the first compartment, and the water carries on the lighter particles into the second set, the still lighter into the third set, and so on. Thus the fine minerals suspended in the water are graded according to their relative weights, and sink to the bottom in each compartment, their respective weights overcoming the upward stream of clean water. The grader is narrow at the inlet, and widens towards the outlet. This is done in order that the whole mass may gradually attain a very low velocity, thus insuring the overflow of only very light particles. The apparatus described gives products which consist of partially concentrated ore, and only the lightest material or tailings pass away with the waste water. "Products. " The products are : Ist, classified pulp, partially concentrated, containing a high percentage of mineral; 2nd, classified pulp containing a less percentage ; 3rd, classified fine pulp or slimes ; 4th, slimes containing a very low percentage of minerals. " The product from the first is generally concentrated to a higher degree on continuous jigs constructed to treat fine ores, and the results obtained on the five-compartment jigs at Freiberg are generally as follow : First compartment, galena of 65 per cent, to 75 per cent., and a middle product of arsenical lead ; second compartment, arsenical pyrites, with about 40 per cent, of arsenic; third compartment, arsenical pyrites, with from 20 per cent, to 25 per cent, of arsenic ; fourth compartment, clean iron-pyrites; fifth compartment, zinc-blende and tailings. The middle products are again treated on concentrating machinery. " The first product from the grader generally contains only about— 0-0208 Ag. 5-32 Pb. 2-7 As. 20-4 FeS. 10-9 Zn. " The concentrates from the five jigs contain— 0-045 per cent. Ag. 15- „ Pb. 4- „ As. 25- „ FeS. 14- „ Zn. " This is now led into Ltihrig's compound vanner or percussion-table on which the minerals are concentrated and separated from one another. " Tailings from the bottom vanner seldom contain more than— 0-005 per cent. Ag. 00 „ Pb. 0-25 „ FeS. 0-5 „ Zn. " Luhrig's patent compound vanner is a recent invention, and is employed in separating the various minerals after they have been concentrated and classified according to relative weight. The pulp from the various compartments of the grader is fed on to a band through a feeder, which is attached to a movable frame. The band is suspended on the frame, and whilst continually moving also receives an end-shake ; this causes the several minerals contained in the pulp to separate according to their respective weights. The pulp flows over a distributer on to the continuous band, which is of rubber. The band is retained in position on the roller by strips of wood which travel along a groove. Free passage of water on the table enables the band to move without friction. The end-shake is imparted in the usual way. The lightest materials are washed off into a hopper; the first product is washed off by two jets of water into a second hopper, and the second product by jets into a third hopper. These vanners are used in the Luhrig system compounded, the lower machine working up the products of the upper without manual labour. " Thus, the materials fed on to the upper tables are firstly separated according to specific gravity, Class 1 going to the lower table on the right, Class 2 to that on the left, while Class 3 can go to the No. 4, and so on. In this manner a high degree of concentration is obtained without manual labour. In this compounded treatment of the pulp the only true solution of close and good concentration is to be found. And this close treatment, being automatic, has made Luhrig's compound vanner the most successful ore-concentrator and separator in use. " The products of the top vanners at Freiberg are —galena with 70 to 75 per cent, lead and arsenical lead-ore ; pyrites, with 40 per cent, sulphur; and middle products which are worked up on the lower ones. One compound vanner will treat over 12 tons in ten hours, giving clean tailings. These machines are in sets of three and six, and are driven by tappets. " The whole of the washwater used in Luhrig's plant is run into a tank at the lower end of the plant, where it is filtered so as to use it again. The sludge or very fine tailings are collected by Luhrig's sludge-recovering apparatus, and elevated by a perforated bucket elevator into hoppers;