1376905 Mixing powder and liquid MONO PUMPS (ENG) Ltd 7 July 1972 [25 Aug 1971] 39851/71 Heading B1C Apparatus for adding powdered lime to a vortex of sewage sludge comprises a closed chamber 1 having a liquid inlet 8, a powder inlet 5 and an outlet 3 from which the mixture is sucked to induce a vortex in the outlet. The inlet 8 may as shown, be downwardly inclined and may intersect the chamber axis, or be tangential (see Figs. 3 and 4, not shown). There may be a removable window 10 also providing access to the chamber, and a point 9 for a water spray nozzle, a probe, or a vacuum gauge. The outlet 3 may be connected to an eccentric rotor pump to provide the suction.