from fig5 that the height of the paddles 44 is less than the radial thickness of the passage 31 so as to leave spaces between the drum 12 and the inner longitudinal edges 44a of the paddles 44 in order to mix as well as to move material in the passage 31 the opposite outer longitudinal edges 44b of the paddles 44 in turn closely abutting the wall 30 by using paddles 44 of different heights or by joining the paddles 44 end to end in some of the flights or even by altering the angle of pitch of the paddles 44 or by doing all or some of these various combinations of rate of movement versus degree of mixing of the material can be achieved spacing the paddles 44 of one or more flights apart or decreasing the height of the paddles 44 or decreasing the pitch of the paddles 44 or again doing all or some of these will slow movement of the material but increase its mixing and vice versa at what then becomes the downstream end of the passage 31 the exterior of the drum 12 is fitted with a circle of radially extending discharge blades 46 parallel to the axis of the drum 12 which urge the material into the alternate discharge port 36 and down the chute 37 the exterior of the bottom wall 30 is provided with a number of hat section channels 47 see fig2 and 3 secured thereto to form ducts 48 for the circulation of hot oil in order to bring the wall 30 up to proper temperature when the plant is started up and to help maintain the temperature of the material as it proceeds through the passage 31 an opening 49 see fig4 closely adjacent.