Abstract: An apparatus for mixing plural flowable materials, for example liquids, is disclosed having a disk-shaped rotor connected to a rotating drive shaft and housed in a cylindrical chamber. The rotor has engraved on one or both faces a spiral-shaped groove to provide sufficient mixing turbulence and prevent unmixed solute from exiting the chamber. The chamber is defined by walls of two stationary end plates separated by an outer cylindrical barrel. When configured in multiple stages having a plurality of rotors connected with a single rotating drive shaft and housed in a plurality of axially arranged such chambers, a centrally-drilled passage intervening between chambers connects adjacent chambers. Additional solvent liquid is introduced at each mixing stage through a radially drilled passage. The materials to be mixed are confined to a narrow interstice between the rotor, adjacent walls and barrel, and pass in sequence from one chamber to the next.