736,313. Centrifugal separators; washing granular materials. RAKOWSKY, V. Aug. 7, 1952 [Aug. 14, 1951; Aug. 14, 1951; Aug. 14, 1951 ; Aug. 14, 1951 ; Aug. 14, 1951], No. 19904/52. Classes 23 and 82 (2). The invention relates to the classification and separation of solid mixtures, and to the thickening of slurries. As shown in Fig. 1, apparatus for separating solids (which may be used for classifying solids) comprises an open-topped cylinder 1 having a tangential inlet 3 for carrier liquid, an axial outlet 8 for light solids, a peripheral outlet 10 for heavy solids, and a shoot 4 delivering the solids to be separated onto or just below the surface of the vortex 17 formed by the carrier liquid. The separation is controlled by adjusting the flow through the inlet 3, by adjusting the flow through the outlet 10 by varying the flow of air through a pipe 14, and by adjusting the flow through the outlet 8 by adding or removing rings such as 9 or by substituting rings having varying internal diameters or by axially sliding the pipe 8 to vary the distance it projects into the cylinder 1. In a modification the flow through the outlet 10 may be adjusted by means of an adjustable syphon. In a further modification (Fig. 3, not shown) the top of the cylinder is closed and provided with vents, the shoot passes through the top plate of the separator and is curved so that particles enter the vortex with circumferential movement, and a vented cylindrical baffle is arranged so that its lower edge touches the surface of the vortex. In another modification (Fig. 4, not shown) the axial outlet is replaced by two concentric outlets to permit the collection of particles of middle density. In the embodiment shown in Fig. 6 the carrier liquid fills the annulus below a top plate 29 and outside a baffle 28, and the vortex 17 rises within the baffle. The solids are supplied through a pipe 4 but in modifications the solids supply pipe is located within the baffle 28 which may flare outwardly within the separator. In the apparatus shown in Fig. 13, slurry to be thickened is supplied through a tangential inlet 2, a vortex 69 forming below a baffle 57. Thickened slurry is discharged through the outlet 63 and liquid is discharged through an outlet 8, liquid entrained in the thickened slurry being drawn up through a pipe 70 to discharge through the outlet 8. The pipe 70 may be disposed outside the separator, and may be provided with a control valve or means for supplementing the suction. In the thickener shown in Fig. 17 the baffle is dispensed with and the liquid outlet 86 has a lower tubular appendage through which liquid is removed from the thickened slurry passing to the outlet 63. In the separating plant shown in Fig. 21 crushed ore from a bin 92 is supplied to a preliminary separator 93 which discharges lighter solids to draining and washing screens 151, 152. The heavier solids discharged from the separator 93 at 150 are separated in a separator 94 which discharges heavier solids to draining and washing screens 98, 101, and lighter solids to draining and washing screens 106, 107, the washed solids from the screens 101, 107 comprising the required separated fractions. Liquids draining from the screens 98, 106 together with water from a pipe 115 and thickened liquid from the washing screens 152, 101, 107 form the bulk of the carrier liquid for the separator 94. The liquid from the washing screens is first thickened in a thickener 123, which may be of conventional construction, and then passed through a thickener 130. After passing through a magnetic cleaner 140 and a demagnetizer 146 the light fraction from the thickener 130 is used as the carrier liquid for the separator 93, and part of the carrier liquid for the separator 94. In modifications the separator 93, the thickener 123 and the demagnetizer may be dispensed with. Dimensions and performance figures for the apparatus are given in the Specification.