1. PNEUMATIC CONVEYING APPARATUS FOR CONVEYING PARTICULATE MATERIAL COMPRISING A GENERALLY VERTICALLY ALIGNED CONDUIT HAVING A SLOT EXTENDING ABOUT THE PERIPHERY THEREOF, MEANS FOR PRODUCING AN UPWARD FLOW OF CONVEYING GAS THROUGH THE CONDUIT, MEANS DEFINING A CHAMBER SURROUNDING THE CONDUIT WITH ITS LOWER END DISPOSED ADJACENT THE SLOT AND IN COMMUNICATION THEREWITH, MEANS FOR FEEDING PARTICULATE MATERIAL INTO THE CHAMBER, A POROUS MEMBER DISPOSED ABOVE THE LOWER END OF THE CHAMBER AND CLOSELY ADJACENT THE CONDUIT SLOT, MEANS FOR INTRODUCING A GAS INTO THE CHAMBER BELOW THE POROUS MEMBER, WHEREBY THE GAS DIFFUSES THROUGH THE MEMBER AND FLOWS UPWARDLY THERETHROUGH TO PRODUCE A FLUIDIZED BED OF PARTICULATE MATERIAL THEREIN, AND A SLEEVE SURROUNDING THE CONDUIT, THE SLEEVE HAVING AN EDGE OVERLYING AND CLOSELY ADJACENT THE SLOT AND SPACED A PREDETERMINED DISTANCE FROM THE POROUS MEMBER AND FROM AN EDGE OF THE CONDUIT SLOT SO AS TO PROVIDE A PASSAGE OF PREDETERMINED DIMENSION FOR CONDUCTING THE FLUIDIZED PARTICULATE MATERIAL THERETHROUGH AT A PREDETERMINED RATE RADIALLY INWARD INTO THE CONVEYING GAS FLOW WITH A SUBSTANTIAL COMPONENT OF VELOCITY PERPENDICULAR TO THE DIRECTION OF THE CONVEYING GAS FLOW.