It is a subject of great practical interest, which has been examined in various ways. ... radius r, being emptied at suction p. p is a mean suction value defined by the capillary equation: 2 cos e P = . in which y is surface tension and 6 is contact angle. P is the ... hr. installation is working at Ferranti Ltd. Manufacturers are John C. Carlson Ltd. colloidal. The use of synthetic organic coagulants for sludge filtration is described by Bargman et a/., 29 who give also a comprehensive reference list.