US2058713A - Apparatus for washing coal and the like - Google Patents

Description

Oct. 27, 1936. w. NEEDHAM 2,058,713

APPARATUS FOR WASHING COAL AND THE LIKE Filed April 18, 193.5, 3 Sheets-Sheet l 9 L. w. NEEDHAM Y 6 2,058,713

APPARATUS .FOR WASHING COAL' AND THE LIKE Filed April 18, 1955 3 Sheets-Sheet 2 Oct. 27, 1936. L. w. NEEDHAM v 2,058,713

APPARATUS FOR WASHING COAL AND THE-LIKE Filed April 18, 1935 3 Sheets-Sheet 3 Patented Oct. 27, 1936' 2,058,713

UNiTED STATES PATENT ()FFIQE APPARATUS FOR WASHING COAL AND THE LIKE Leonard William Needham, Selly Oak, Birmingham, England, assigncr to Colliery Engineering Limited, Shefiield, England, a company of Great Britain Application April 18, 1935, Serial No. 17,101 In Great Britain November 15, 1933 8 Claims. I (Cl. 209-441) This invention comprises improvements in or bed is composedpredominantly of solid materelating to the washing of coal and other solid rials, and separately discharging upper and lower divided materials of different specific gravities, strata of the bed. The expression viscous-fluidand has for its principal object to provide an like condition is intended to refer to a thick improved Stratification process of treatment and agitated bed of materials, composed of a comapparatus for carrying out such process, whereparatively dense mass in which free flowing liqby highly efficient separation of the clean coal uid currents are absent. The bed of the presor concentrates from the impurities of the raw ent process is in the form of a deep layer which material is achieved in simple and economical may be three or four inches thick and the dense manner. mass is obtained by distributing restricted quan- 10 A further object of the invention is to protities of liquid uniformly over the bed in such vide improvements in the construction and opmanner that flooding of the bed or excess of eration of known concentrating tables so as thereliquid at any local zone or zones is avoided. Thus by to increase their capacity while maintaining assuming the solid materials to be packed into or improving the efficiency of theseparation. a stationary vessel, the liquid is just sufficient 5 In the majority of washing processes at presto fill the voids between the solid particles. For ent in commercial operation, the stratification of example the amount of solid materials may be the dense and less dense fractions of the feed about 60% by volume of the bed composed of is brought about in a comparatively deep bed solids and liquid. In this connection it is to in a stationary apparatus either by the wellbe noted that the invention is sharply distinknown effects of alluviation set up by a stream guished from the well known trough washers, of water in a trough, or by the action of vertiupward current classifiers and rifiled tables in cal water currents which may be steady or conwhich a quantity of water which is large in relatinuous as in upward current classifiers or of tion to the solid materials, is employed as a pulsating nature as in jigs. In trough washers swiftly moving stream, for separating the solid and upward current classifiers, the stream of materials by the fluid currents set up by the solid materials and water is loose and swiftly stream. The agitation of the bed in the presflowing while in jigs the bed of material is slow ent process is obtained by vibration imparted to moving and alternately dense and loose as the the vessel containing the bed so that a relatively alternations of vertical water flow occur. high-frequency order of agitation is attainable.

In other processes carried out on well-known The agitation imparted to the bed thus induces rifiied concentrating tables, mechanical vibraa condition in which relative movement between tion of the tables is imposed upon the stream the particles is facilitated, high frequency of the action of the Water so that the materials which vibrations enhancing the desired conditions. In are fed on to the tables with water in the neighthis connection it is to be noted that the inbourhood of one corner, are caused to be spread vention is sharply distinguished from the wellout in a thin layer. In such processes, the sepknown jig washers in which separation is ob aration is brought about principally by the stream tained by fluid currents in the bed, such currents action of the water, the less dense materials bebeing produced by relatively slow cycles of puling floated over the riilles by the stream while sations of the liquid for the bed. In jig washers the denser materials sink behind them. The vialso the ratio of solid materials to liquid varies, bration doubtless assists the separation to a certhe bed being tight with a low percentage of tain extent but it is well-known that its main liquid at the end of the suction stroke and being function is to spread the materials out over the flooded with a high percentage of liquid at the tables and propel settled denser materials beend of the pressure stroke. In the present inhind the riflies along the tables to their disvention the proportion of solid materials to liqcharge point. uid is as nearly as possible maintained constant,

According to the present invention, a process the combined effect of the restricted and confor the wet separation of solid materials of diftrolled supply of liquid, its distribution and the ferent specific gravities, comprises producing and vibration inducing a state of semi-equilibrium or maintaining a thick bed of the materials, impartial suspension of the materials without the parting to and maintaining in such bed a visuse of fluid currents in or above the surface of cous-fluid-like condition, as hereinafter defined, the bed. Thus the denser material tends to disby agitation thereof and distribution thereupon place the less dense material which rides over of liquid in such restricted quantities that the it and Stratification ensues. Careful choice of the nature of the vibration is necessary and it has been found that the desired effect is achieved by the use of a motion comprising horizontal and vertical components combined with a bumping or jerking action on the forward stroke. Under these conditions an effect is obtained in which the state of the bed may be likened to a viscous fluid and this state is what is to be understood in this specification when referring to the fluidity of the bed.

In regard to the liquid distribution it is to be understood that there should, as nearly as possible, be a uniform amount of liquid at all points. Therefore the main part of the liquid supply is distributed upon the bed and only sufficient liquid for Wetting the raw material is admitted at the feed, so that the minimum disturbance of the bed occurs due to the introduction of the feed material. This desired condition would not be realized if a surplus of water were fed in with the materials and if local excesses of water were present at different places in the bed.

From the foregoing statement it will be understood that the invention is not concerned with prior proposals for concentrating apparatus in which liquids or gases were to be forced upwardly through a porous support for separating the materials thereon due to the fluid currents and motion imparted to the support. The invention is also not concerned with prior proposals in which a thin layer of material was to be drowned or submerged in a pond or tray, the currents of flowing water carrying off a fraction of the material; neither is it concerned with a prior proposal in which material flowed in a thin stream on a steeply inclined riflled deck submerged in liquid and arranged in a tank to which water was to be admitted through a diffusion box to avoid currents.

The present invention does not rely on the employment of fluid currents, and the material is not drowned or submerged in an excess of liquid. Only enough liquid is added to a thick bed of materials to produce a dense viscous mass, the liquid being carefully distributed upon the materials to avoid local excesses of liquid and surface currents. The distribution of liquid upon the materials avoids liquid currents produced by forcing liquid upwardly through the bed. The bed thus consists of a thick layer in which the proportion of the solid material predominates, the natural buoyancy effect of the water combined with the vibration causing stratification to take place, the admission of materials to the vessel being able to cause spillage of the upper layer of the stratifled material over a discharge edge of the vessel as hereinafter more particularly described.

By the operation of the several conditions prescribed in accordance with this invention, the dense and less dense components of the bed are able to move with facility to their respective layers, and the stratification obtained in a short distance has been found to be remarkably good. It is probable that the stratification takes place according to density independently of the size of the particles and an important advantage is that a considerable range of sizes of particles can be treated in one and the same operation. It is mainly due to the absence of water current effects in the bed that this result is achieved, as currents are selective in their action both as regards size as Well as density.

An apparatus or so-called table for use in carrying out the process suitably comprises an elongated box or trough having sides sufficiently deep to retain a thick bed of materials, one or both of the longitudinal sides providing a spillage edge or edges for less dense materials extending from the rear side of the box or trough, a hopper or other suitable means for feeding raw material into the box or trough at its rear end and at a point spaced inwardly from the aforesaid spillage edge or edges, means for distributing liquid substantially uniformly over the whole area of the bed and in such restricted quantities that free-flowing currents are absent, means for vibrating the box or trough, and a dam constituting the front end of the box for controlling the movement of the bed in such manner that the materials progress slowly along and across the bed and less dense materials overflow the spillage edge or edges while the dense materials discharge at the forward end of the box.

The box or trough is disposed approximately horizontal so that discharge of less dense materials will be by simple overflow and not by gravity as when a whole stream moves at a uniform rate down a slope. Thus, the bed may be of constant thickness determined by the height of the overflow or spillage edge, and greater or less feed merely causes corresponding variation of overflow discharge as in a tank of liquid.

It is advantageous to provide deflectors at suitable points alongthe bed to assist distribution of overflow of upper layers to desired points along the spillage edge or edges. These deflectors have a forwardly directed angular setting in plan and the angle may be adjustable. The bottom edges of these deflectors are disposed at a higher level than the spillage edge of the table so that they only just cut into the top layers. If they penetrated too deeply into the bed they would be liable to cause packing, unevenness or variable denseness of the bed.

The box or trough may be of substantially rectangular shape in plan with the feed device for the raw material in the far rear corner remote from a spillage edge at one longitudinal side, but it is preferred to make the trough narrower at the forward end than at the rear end so as to concentrate the denser materials into a thicker layer or stratum after the main bulk of the less dense materials has been removed. In a modified form of table, the box or trough is relatively wide at the rear end and has the feed for raw material disposed at the middle of the width and a spillage edge at each longitudinal side. As before, this form of box or trough may be narrowed towards the forward end.

The process and apparatus described are of advantageous application in conjunction with other types of concentrating table, particularly the well-known riffied tables, as they provide a means whereby a preliminary stratification may take place in a relatively thick bed of the materials before separation is allowed to proceed on such other concentrating tables. Rifiled tables are very effective in practice in treating small coal but a disadvantage which has tended to restrict their application is the relatively small amount of coal which may be washed by them in any given time and the present improvements enable this disadvantage to be overcome, or, at any rate, considerably reduced. In this arrangement, an upper stratum of coal is discharged from the box or trough over a spillage edge or edges near the feed end without further treatment. The fractions of ,coal and middlings of different values are successively deflected off along the box at points further along the spillage edge or edges and are diverted to a riiile table or tables for further treatment thereon. The stone is discharged from the box or trough at the, forward end. Thus the box or trough removes a certain proportion of clean coal and a quantity of stone, leaving the rifiled table or tables to perform a refining treatment on the middle and most mixed portion of the raw material.

The box or trough might replace part of the known concentrating tables or be applied separately thereto.

In order to enable the invention to be readily understood reference is directed to the accompanying drawings illustrating in more or less diagrammatic manner suitable constructions of coal washing apparatus in accordance .with the invention. In these drawings:-

Figure l is a plan showing one form of apparatus.

Figure 2 is a side elevation of Figure 1 with parts omitted.

Figure 3 is a transverse section of the box or trough taken on the line III-III of Figure 1.

Figures 4 and 5 are longitudinal and transverse sectional diagrams respectively, illustrative of the operation of the apparatus shown in Figures 1 to 3.

Figure 6 is a plan of a modified form of apparatus.

Figure 7 is a plan of a further modification and Figure 8 is an elevation of Figure 7 omitting the rifiled deck tables.

Figure 9 is a view of the feed end portion of the box of modified construction.

Figure 10 is a diagrammatic transverse sectional view of the embodiment of Figure 9.

In the drawings, the improved construction of apparatus is illustrated in conjunction with riffled concentrating tables but each example is capable of independent application as will be described.

According to Figures 1 to- 3, a portion of the riflied deck a of an ordinary rifiled coal concentrating table 7), including the corner 0 at which the raw coal is introduced is replaced by a box or trough d into which.the raw coal is fed at e mixed with a suitable quantity of water. In plan, the box is of rectangular form for a part of its length at the rear or feed end and then it narrows forwardly by inward inclination of its outer longitudinal side al which corresponds in position with the back of the riffled table. The inner longitudinal side :2 of the box is straight and lies parallel or about parallel with the front edge of the riiiled table. This inner longitudinal side is made of less height than the other sides to provide a spillage edge for overflow of the purified coal and middlings. The height of the other sides is such as to prevent the upper layer from spilling over so that the clean coal and middlings discharge only over the spillage edge The forward side of the box is constituted by a gate or dam or, stationary or vertically adjustable, which provides an outlet h beneath it for the stone or dirt. If desired, there may be a further gate or darn it beyond the first one g to provide space for further treatment of the stone but the forward end of the bed proper is defined by the gate g. Obviously other equivalent means, such as weighted flaps, may be employed in place of the gates shown to allow stone or refuse collecting on the floor of the box d to escape from the forward end of the box while retaining the desired thickness of the bed.

From Figures 2 and 4 it will be seen that the floor of the box (1 may be slightly inclined downwardly and forwardly to the gate g. Between the gates there may be a horizontal floor portion while beyond the forward gate is is a stone-delivery chute Z which has an upwardly and forwardly inclined floor. If desired, the chute may be mounted on a hinge at n so as to provide an advantageous means for adjustably controlling the speed of outflow of the stone. The region between the gates g and k may have a spillage edge 0 which, however, is of less height than the spillage edge f because the layer of materials here is of much less thickness than the bed proper. There may also be a short spillage edge at p in the near side of the stone chute Z. The floor of the stone chute I may have shallow rifiies m, normally submerged, to keep the layer of stone even. The floor of the box d, however, is plain. All floor parts are impervious and may be covered with linoleum.

Apart from the supply of water with the raw coal feed at e, a supply of water for the remainder of the bed is provided for by spray pipes r. These pipes extend longitudinally over the box at and are spaced laterally apart so that altogether liquid is distributed substantially uniformly upon the bed. There is also a water spray pipe s for the region between the gates g and k and another spray pipe t for the stone chute Z.

The box (1 is mounted on the same understructure u as the riflied deck a. It is mounted horizontally though there may be the slight forward inclination of the floor as already described. The horizontal mounting includes horizontaldisposition of the floor as regarded transversely as seen in Figure 3.

The understructure u is mounted for vibration upon rearwardly inclined springy flexible legs 1) secured to a base w. The vibrating or driving mechanism comprises a rotating unbalanced pulley v mounted on the understructure u and a bumper a: mounted on the base w. This is a known type of mounting and driving mechanism in riiiied concentrating tables and it is advantageous for the purposes of the present invention as it provides appropriate motion of the box d for imparting the desired fluidity to the bed and assists the travel of the denser material, but any other suitable form of mechanism which will produce the described eifects such as mechanisms incorporating eccentrics or cams may be employed as will be understood. Under the impulse of the unbalanced pulley v and the inclined disposition of the flexible legs 21 the box (with the table b) receives a motion in the rearward direction comprising horizontal and vertical components and on the forward stroke the cross-bar y of the under-structure frame comes against the bumper imparting a bumping or jerking action to the box and table. A pad 2 of leather or canvas may be operative between the cross-bar y and the bumper and a spring I may be provided to control the forward stroke.

Obviously, the separate mountings and driving mechanism may be provided for the box 12 and the riffied table b if so desired.

The rear corner of the box d adjacent to the spillage edge I, is preferably cut off by sloping the rear side of the box as at 2 in order to avoid poor viscosity which might otherwise exist in this region. The slope is approximately parallel to deflectors 3 which are advantageously fitted over the box to assist travel of the upper layer to discharge.

The level of the lower edge of these deflectors is above the level of the spillage edge 1 for the purpose already described. The position in plan of the deflectors is determined by trial and they may be placed in such positions that clean coal may be obtained from the portion of the spillage edge extending from the rear to the first deflector, coal and a small proportion of middlings between the first and second deflectors and coal and a greater proportion of middlings, possibly mixed with a little dirt, between the second and third deflectors.

In operation, the raw coal is fed into the box and, owing to the provision of the upstanding sides and forward dam g for such box and the appropriately regulated feed, a bed of substantial thickness is formed (see Figures 4 and 5). This bed of materials is made to simulate a slowly moving viscous fluid by reason of the restricted and uniform liquid distribution and the agitation produced by the mechanical vibration of the box or trough and the absence of water currents in the bed. As a result the bed stratifies, a stratum of coal rapidly occupying the top layer of the bed. This rapid stratification occurs in what may be termed the primary region A between the feed 6 and the longitudinal spillage side d and first deflector 3. Thus clean coal can be removed from the part of the spillage edge lying between its rear end and the first deflector without further treatment. The remainder of the material passes forwardly along the box which narrows in order to preserve the thickness of the bed. The slight downward and forward inclination of the floor of the box prevents sluggishness of the denser lower layer. As the material progresses in its travel forwardly of the box, appropriate fractions are discharged over the spillage edge 1 their discharge being assisted by the deflectors 3. Thus in the secondary regions Band C between the first and second and the second and third deflectors, coal and middlings and possibly some dirt are discharged over the spillage edge 1 to the launder l and thence to the riffled deck a for further treatment. refuse and a low proportion of coal and middles being passed forwardly from these regions to the region D between the gates or dams g, k. In this region D, the coal and middles are freed and spilled over the edge 0. The refuse which passes beneath the gate 7c to the stone chute Z is nearly clean stone and the last vestiges of coal and middles may be removed over the spillage edge 21.

The clean stone is discharged at the end of the chute I.

It is important that the chute Z should be upwardly inclined to provide an uphill portion which prevents unduly quick discharge of the dense material and consequent upsetting of the conditions in the bed.

If the box or trough d were used alone the several fractions of discharged materials would be taken away by suitable chutes. The mixed coal and middlings may be returned to the feed for re-treatment or otherwise further treated.

When the box is used in conjunction with another type of concentrating table as shown, the rifiies a may end at a and the deck area a be left plain. The water passing over the spillage edge with the clean coal from the region A is thus able to carry this coal relatively quickly across the deck a. to the head end of the discharge edge of such deck. Thus the capacity of the concentrating table, as compared with the known tables, is increased owing to the facility with which the clean coal can be removed. It is also an advantage not to have to pass the stone, discharging from the chute Z, over the rifiled deck because in effect, this means that the ordinary table is treating a cleaner coal than it would be doing if the box or trough d and its associated parts were not used. It will be readily understood that the extent of the riffled portion of the deck a may be varied according to the amount of material which it is desired to treat further.

The materials passing into the launder 4 would feed along the sloping bottom of the launder to the far corner 5 of the riflied deck a, for treatment on the latter. As an alternative, the launder may be dispensed with and the materials be allowed to pass across the deck a from the locations where they are discharged over the spillage edges. In the latter case, the distribution of the products of different qualities to different points along the feed edge of the rifiied deck a, corresponding to the degree of primary separation in the box 11, lessens the distance the materials have to travel over the deck a and makes better use of the rifiled table area so increasing the capacity of the table in that way. Naturally any portion of product from box d may be fed to any point along the deck a, by launders suitably disposed, to secure the most efficacious treatment.

The further or secondary cleaning operation on the rifiied deck a is in accordance with known practice and therefore needs no description. However, the arrangement of the riffles a on this deck may be modified and the water supply, as by spray pipe 6, adjusted as may be necessary to secure maximum benefit from the invention.

If desired, and as shown in Figures 9 and 10, a platform 1 may be fitted in the box (1 at the feed end between the feed device e and the spillage edge and sloping upwardly to the spillage side. This improves the fluidity of the bed in this region. It may be of advantage, for example, in preventing too great an accumulation of denser products against the spillage side (1 when treating a raw material containing a large proportion of denser constituents.

Experiments have shown that the clean coal delivered over the first part of the spillage edge 1 may amount to at least 50 to 60 per cent of the feed of raw material in average cases.

Figure 6 shows a smaller and simplified form of the primary separating apparatus adapted to be applied to an existing rifiled table I) with minimum of alteration. The box d has only one gate or dam g and the stone chute Z is fixed, its floor being constituted by a fixed upward and forward slope. The material from this chute discharges on to the rifiled deck a and being more or less free from less dense particles it is easily purified in travelling the comparatively short distance along the deck to the refuse discharge edge 8 of the table 22. This smaller form of box if. is of advantageous use with certain classes of raw materials. However, the size of the box will in any case depend on the properties of the materials to be treated and can be fixed definitely only after a complete examination of such material. Parts in Figure 6 which are not specifically referred to but are similar to those shown in Figures 1 to 3 are similarly lettered or numbered.

In the construction shown in Figures 7 and 8, the box (2 is of forwardly tapering form in plan with the feed 6 in the middle of its width and a spillage edge 1 at each longitudinal side. A parallel-sided portion 9 extends forwardly from the tapering part and this may be fitted with gates or dams g and is similar to those before described and terminate in a fixedly or adjustably inclined stone chute l. The water spray pipes 1" are disposed over the middle of the box 03 and over each side. There is also a spray pipe .9 placed centrally over the region between the gates g and It. The deflectors 3 extend to each side of the box and the latter is again cornered off at 2 though rather more extensively than in the other constructions. The vibrating mechanism and the mounting of the box are similar to those already described but in this case they are applied directly to the box instead of through a riffied table as in Figures 1 and 2.

In Figure 7 a rifiled concentrating table b is shown on each side of the box or trough d to take up and treat middlings passing over the spillage edges 1, Clean coal passing over the spillage edge 1 from the rear end to the second deflector is led directly away as by a chute (not shown). The rifiled tables may be mounted on the same understructure u as the box at or they may have independent mounting and mechanical vibrating means.

When the boxes are used independently of a known type of concentrating table, the clean coal is rejected from the main stratifying region and stone or shale from the forward end. For refining the middle fraction which is not sufIiciently stratified in the box, small riiiled areas may be mounted on the box at each side as shown in Figure 7, or, as already indicated, this fraction could be passed back to the feed for further treatment.

I claim:-

1. Apparatus for the wet separation of solid materials of different specific gravities, comprising a box-like vessel having sides sufliciently deep to retain a thick bed of materials, one of the longitudinal sides of said vessel providing a spillage edge for the upper stratum of the bed, the bottom of said vessel being substantially level, means for feeding raw materials into the vessel at its rear end, means disposed over the vessel for distributing restricted quantities of divided liquid uniformly upon the bed, means for vibrating the vessel, and a dam at the front end of the vessel for the discharge of the lower stratum of the bed.

2. Apparatus for the wet separation of solid materials of different specific gravities, comprising a box-like vessel having sides sufficiently deep to retain a thick bed of materials, the bottom of said vessel being substantially level, one of the longitudinal sides of said vessel providing a spillage edge for less dense materials, means for feeding raw materials into the vessel at its rear end, liquid spray means disposed over the vessel for uniformly distributing restricted quantities of liquid to the bed, means for vibrating the vessel, transversely disposed deflectors located above the vessel for assisting the travel of the upper stratum of the materials towards the said spillage edge, and a dam at the front end of the vessel for the discharge of the lower stratum of the bed.

3. Apparatus for the wet separation of solid materials of different specific gravities, comprising a box-like vessel having deep sides and a substantially level bottom, means for feeding raw materials into the vessel at its rear end and at a point spaced inwardly from one of its longitudinal sides, liquid spray means disposed over the substantially level bottom, a feed hopper at the rear end of said vessel, the longitudinal sides of said vessel converging towards the forward end, transverse deflectors disposed over the vessel for assisting the travel of the upper stratum of materials towards the longitudinal sides, a parallelsided portion constituting a cell for the discharge of dense material extending forwardly from the converged sides, a dam under which the lower stratum of denser material passes into the cell, a hinged delivery chute on the forward end of said cell, liquid-spray means disposed over the said vessel for uniformly distributing restricted quantities of liquid over the material and means for vibrating said vessel.

5. Apparatus for the wet separation of solid materials of different specific gravities, comprising a box-like vessel mounted on a riiiled concentrating table, a hopper for feeding materials to the rear end of said vessel, the latter having deep sides for producing a thick bed of materials and a substantially level bottom, one longitudinal side being of less height than the remaining sides to provide a spillage edge for spillage of the upper stratum of materials from the vessel to the table while the other longitudinal side converges towards the forward end of the vessel to maintain the thickness of the bed, transverse deflectors disposed over the vessel for assisting the travel of the upper stratum towards said spillage edge, a cell for the lower stratum extending forwardly from the converging part of the vessel, a hinged delivery chute at the end of said cell, dams for controlling the passage of material to the cell and the chute, liquid spray devices disposed over the vessel for uniformly distributing restricted quantities of liquid upon the bed, and means for vibrating the vessel and said table.

6. Apparatus for the wet separation of solid materials of different specific gravities, comprising a forwardly tapering box-like vessel having a substantially level bottom, means for feeding materials disposed between the sides of said vessel at its rear end, transverse deflectors disposed above the vessel for assisting travel of the upper stratum of material towards the converging sides of said vessel, a dam at the forward end of the vessel for the discharge of the lower stratum of material, means disposed over the vessel for uniformly distributing restricted quantities of liquid upon said bed, and means for vibrating said vessel.

7. Apparatus for the wet separation of solid materials of different specific gravities, comprising a riflied concentrator table having plain unrifileol portions at its rear and upper portions, a box-like vessel mounted on said plain upper portion and having deep sides to maintain a thick bed and a substantially level bottom, means for feeding material to the rear end of the vessel, liquid spray means disposed over the vessel for uniformly supplying restricted quantities of liquid onto the bed, means for vibrating the concentrator table and vessel, a transverse deflector for assisting travel of the upper stratum of materials at the rear of the vessel to discharge on to the plain unriflled portion at the rear of the concentrator table, a further transverse deflector positioned above the bed for discharging portions of the upper stratum of the bed towards the forward end on to the rifiled portion of the concentrator table for further treatment, and discharge means at the forward end of the vessel for the lower stratum of the bed.

8. Apparatus for the wet separation of solid materials of different specific gravities, comprising a box-like vessel having sides sufficiently deep to retain a thick bed of materials, one of the longitudinal sides of the vessel providing a spillage edge for the upper stratum of the bed, the bottom of said vessel being substantially level, means for feeding raw materials into the vessel at its rear end, means for supplying restricted quantities of divided liquid uniformly to the material of the bed, a platform in the feed end of the box between the feeding means and the spillage edge, said platform sloping upwardly toward the spillage edge, means for vibrating the vessel, and a dam at the front end of the vessel for the discharge of the lower stratum of the bed.

LEONARD WILLIAM NEEDHAM.

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