Abstract: An arrangement for mixing and treating powdered and granular material by introducing compressed gas into a mechanically driven mixing device with an upright cylindrical mixing tank. The tank has an intake for the material to be mixed, and an outlet for the mixed material. Above the flat bottom of the tank, is a rotating hub to which stirring paddles are fastened. A vacant space is left between the flat bottom of the tank and the wall panels of the stirring paddle, and extends from the hub to the cylindrical outside wall of the tank. Supply channels introduce the compressed gas through the hub and into the vacant space. A slit is provided between the hub and the wall panels of the stirring paddle and the adjacent tank wall section for the exit passage of compressed gas into the mixing tank along the entire stirring paddle from the hub to the outside cylindrical wall of the tank.