Abstract: For the uniform treatment of bulk material by means of a gas the bulk material is fluidized in a rotating container (101) in order to be mixed by the rotation thereof. In the case of heating the bulk material the rotation of the container is expediently interrupted at periodic intervals. A transport device is preferably provided in the interior of this container, in particular in the form of a worm or screw flight (20) of irregular pitch--related to one rotation in order to be able to precisely determine the dwell time through the mechanical transport. This screw (20) is preferably constructed as a two-start screw (FIG. 6).