of a funnel shaped mixing beaker 1a integral with a cylindrical stirrer housing 1b a cruxiform shaped flexible mixing fin 2 is mounted within the beaker 1a to depend within the stirrer housing 1b the fin 2 is formed of a pair of crossed flat parts 2a in one of which parts a permanent magnet 3 is embedded at its lower end at its upper end the mixing fin 2 is broadened into two rigid ears 4 which extend radially into and are hung in slit shaped recesses 5 formed in the wall of the mixing beaker 1a the slits are tapered and flare open into the upper edge 9 of the mixing beaker 1a so that the mixing fin may be inserted into the slots allowing the flat parts 2a to removably enter into the stirrer housing along the axis of the housing in fig5 a and 5b which develop this embodiment it will be seen that a permanent magnet 3 of cylindrical disk shape is provided with its poles on its flat faces so that for example the north pole shown hatched and the south pole shown without hatching lie in vertical planes about the axis of the rotation in certain cases it may be preferable to provide in the center of the mixing fin transverse ridges perpendicular to its plane so as to reinforce the magnet an electromagnet consisting of an armature 8 provided with a wire coil 7 having its ends 7a and 7b connected to an alternating current source not shown is provided as the driving source for the stirrer the coil 7 is wrapped about the transverse beam of the armature 8 which is formed of a stack of u shaped soft iron sheets providing at the free ends of the arms.