Abstract: An apparatus for reducing, dispersing, wetting and mixing pumpable, non-magnetic multiphase mixtures comprises a sealed annular-gap chamber having an annular gap which forms a working chamber, into which the material to be worked flows in from the bottom and flows out from the top. This annular-gap chamber is formed by a double tube, the outer tube of which is surrounded by an outer exciter system and the inner tube of which is surrounded by an inner exciter system. In the working chamber there are, apart from the material to be worked, freely mobile magnetic working media, which move in the direction of the rotating electromagnetic fields within the multiphase mixture flowing through the annular-gap chamber and perform translatory transverse motions and tumbling motions. Within the working chamber or the annular gap there exist an inflow zone and an outflow zone, which are in each case free from working media.