CONTINUOUS CENTRIFUGAL SEPARATION AND CLASSIFICATION 169 Figure Scroll Discharge (Fig. 7) Another interesting centrifugal filter utilises a fully continuous scroll discharge. It therefore resembles the decanting type centrifuge described Figure

170 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS previously, with the exception that the bowl is perforate instead of solid. The bowl is conical in section, and fitted with perforated or slotted screens. The solid moves continuously through the machine and is controlled by the differential speed of the internal scroll. The mother liquor is discharged under centrifugal pressure through the perforate bowl. The machine has the advantage of low cost per unit of capacity and is of great value when large crystals or fibres are to be de-watered. Its use on fine crystals is limited since there will be a loss of solid in the flitrate. Since the machine does not use cyclic operation it cannot give the same degree of washing as the centrifugal filter previously described. (Received: 8th March 1962) Oh NOTATION E ,-- pe Fc•,' Effective force acting on a particle in a centrifugal field. F• Viscous drag force on a particle. g Gravitational constant. n Number of spaces between discs in a stack. 0 Disc half angle. p Density of a particle. p• Density of a liquid. •, Density of light phase liquid. •h Density of heavy phase liquid. Ap ! Sigma value. o• Angular velocity of cylinder or rotor about its axis of rotation. DISCUSSION MR. tt. I5. H•ATH: (1) In a liquid/liquid separation of say an oil and weak alcohol, is it always necessary to prime the centrifuge with water, as added water will alter the concentration of the aqueous phase which is the product ? (2) One frequently gets air entrainment in a diluted alcoholic product which can lead to alcohol loss. Can this be avoided ? THe: L•,:CT[mER: (1) When carrying out a two-phase liquid separation it is necessary on start-up to prime the bowl with some heavy phase liquid in order to achieve a hydrostatic seal. On many occasions, water is the heavy phase and therefore on those occasions water would be used for priming. Where the heavy phase is a weak alcohol it would be perfectly in order to prime the bowl using some of the weak alcohol which had previously been