the device shown in the fig1 to 5 comprises a cylindrical chamber 2 with a horizontal axis provided with a feeding hopper 4 placed in an upper position and a discharge well 5 a rotor 6 mounted co axially inside the chamber 2 is operated by means of an electric motor 7 the walls of the chamber 2 consist of an assembly 10 formed by uniting two semi cylindrical shells 11 and 12 assembled together by means of a hinge along one lateral edge 13 and a safety closing device 14 is disposed along the edge 15 opposite the edge 14 the upper shell 12 is connected to a pneumatic device 16 of a type known per se which makes possible its opening by pivoting around the hinge 13 the driving motion of the rotor 6 by the motor 7 is transmitted by means of a pneumatically controlled clutch 18 the rotation of rotor 6 can be interrupted at will by means of a braking device 21 also pneumatically controlled the rotor 6 is supported at each of its ends by a bearing 22 fastened on a pillar 23 a threaded joint 24 makes it possible to pass each end of the shaft of the rotor 6 tightly through the wall of the chamber 2 a protective cover 26.