574,527. Washing granular materials. NORTON, R. M., and NORTON, G. B. Dec. 23, 1943, Nos. 21547/43 and 11236/44. [Class 82 (ii)] The separation of raw coal into clean and reject fractions by stratification in a washing jig is effected at a specific .gravity which varies with the relative depth of two or more strata contained in the clean fraction so that as the depth of a light stratum relatively to a heavier stratum in this fraction increases, the specific gravity of the separation increases also and vice versa. The separation is controlled by two or more floats, each adjusted to a different specific gravity and each responsive to any change in the stratum of the coal, at least one of the floats always working in that part of the bed which is discharged as the clean fraction and all of them operative directly or indirectly to vary the rate of discharge of the clean fraction and in doing so to effect the separation at sucha specific gravity as to reduce the variations in the ash. content of the clean fraction that would occur if only one float were used. In a jig in which the coal is stratified on a perforated plate by pulsating water reject material being passed through an outlet 2 over a plate 3, the end of which is controlled by a gate connected by a rod 5 to a pivoted rod 6 having a weight 7 on one end and connected at the other end to the rod 10 of a piston 11, working in a cylinder 12 to which compressed air is supplied by a pipe 13, the supply of air is controlled by a relay valve 14 to which is connected floats 36, 37, the float 36 being carried by the vertical arm 38 of a linkage comprising upper arms 39 and lower arms 44 pivoted on a bracket 44 fixed to a girder 45, a shaft 42 passing through the linkage and being keyed to arms 39, 40, the arm 39 being extended to carry weights 43. A sleeve 46 is keyed to the shaft 42 and is integral with a calliper bar 47 having arms 48, 49 through which pass screws 50, 51 so as to present an adjustable gap into which projects the nose 52 of a rod 53 secured to an extension 54 of the part 1'8 of the valve 14. The float 37 .is mounted in similar fashion on a shaft 421 integral with the shaft 44 and carrying a calliper bar 47<1>. The valve, Figs. 5, 6 and 7, comprises a casing 15 provided with control openings in which are fixed the arms 16, 17 for a rotatable member 18 which is moved by a pivoted sleeve 19. The casing 15 is also provided with an inlet port 20 connected by a, pipe 21 to a supply of compressed air, a port 22 connected to the pipe 13 and a port 23 open to the atmosphere. Ports in the sleeve 19 are formed by the slots 24, 25, 26 adapted to register with the ports 20, 22, 23. The flow of compressed air is controlled by the member 18 which has two circular ends 27, 28, a starshaped body portion and forming recesses 29, 30, 31, 32 with the sleeve 19 and having two bosses 33, 34 at right angles to each other, the member 18 being rocked by the movement of the float 36 and the member 19 by the float 37. In operation, the float 36 moves up and down with the pulsating water, but so long as it only moves about a stationary mean position its movement has no effect on the valve 18 due to lost motion between the calliper arms and the nose 52. If, however, the float rises in consequence of an increase in the depth of the bed of reject material, the bar 47 will rock anticlockwise, bringing the end of the screw 50 into engagement with the nose 52 and thus rocking the valve member 18. Downward movement of the float will bring about reverse movement of the member 18 by the engagement of the screw 51 with the nose 52. If the float 36 rises and the float 37 is stationary, the arm 35 is moved anti-clockwise to uncover the port 25 and if the float 36 falls, the arm moves clockwise and puts the space 29 into communication with the port 25 so that air blows out of the cylinder 12 into the space 29, through the bore 33 into the space 31 and so to the atmosphere through the ports 26, 23. If the float 37 rises while the parts are in the position shown in Fig. 6, sleeve 19 is rocked in a clockwise direction, putting the space 32 into communication with the port 25 so that compressed air can pass to the port 22 and so to the cylinder 12 ; if the float 37 falls, the sleeve 19 will rotate anti-clockwise and allow air to escape to the atmosphere by the port 25 and space 29. Before the jig is put into operation, the coal is analysed and the float 36 weighted to sink through the stratified bed to the stratum at which separation is to take place, the float 37 being also weighted to sink through the pure coal stratum to rest on a, lighter stratum in the middlings than the float 36. In practice, the total depth of the stratified material remains substantially constant and, since the position of the float 36 varies with the depth of the reject fraction, the difference in level between the two floats is an approximate measure of the ratio of middlings to coal in the cleaner fraction. In the apparatus described above, changes in the difference of the levels of the two floats are used to vary the specific gravity at which the float 36 affects 'the separation. This operation may also be effected by varying the specific gravity of the float, e.g. as described in Specification 570,845. In another form of the apparatus, Fig. 12, the relay valve 60 is a slide valve with an open-ended cylindrical casing 61 and a cylindrical valve member 62 which is hollow, open-ended and reduced in diameter 50 as to leave annular spaces 63, 64. Ports 66 are formed in the wall of the member 62 and the casing 61 is recessed at 67 to provide an annular space 6-8 which, in the position shown, is shut off from the spaces 63, 64 by the central part of the member 62, a port 69 leading from the space 68 to the pipe 13. Air is admitted into a passage 65 and passes into the space 63. If the member 62 is moved to the left as shown, air passes from the space 63 through the port 69 and pipe 13 to the cylinder 12 and if the valve is moved to the right, air in the cylinder 12 is exhausted back through the pipe 13, spaces 68, 69 and ports 66 to the atmosphere. The member 62 carries a pin 62 having a square shank projecting through a slot 71 in the casing 61 so that the valve can slide but not rotate, the pin terminating in a cylindrical part 72 which enters a cylindrical opening 73 in a transverse lever 74, the ends of which lie between the calliper bars 75, 76 connected to the primary and secondary floats. If three floats are used, the second end of the lever 74 is connected to a second lever, the two ends of which may then be rocked by the other floats and if four. floats are used, three levers are used, one a primary lever connected to the relay valve and two secondary levers, one pivoted to one end and the other to the other end of the primary lever, and the floats may act on the ends of the secondary levers. The floats are preferably arranged alongside one another.