be angled about the axis of the pivotal connection to support 18 it will be apparent that such angular adjustment produces the least movement at the upper end of the inclined drum while its lower end traverses the greater distance at the upper end of the drum platform structures is a collector or plenum 20 which is separated by a partition 22 fig9 into two separate chambers 24 and 24a partition 22 extends down from the top of the plenum 20 with its lower end terminating well above the bottom of the plenum so that there is provided a single compartment which is shared by both chambers 24 and 24a at the bottom of the plenum means such as a screw conveyor not shown is provided in the extreme lower end of the plenum for removing material deposited therein as will be described the two drums 10 and 10a communciate at their upper ends with the respect chambers 24 and 24a through air seals 26 and 26a which are designed to allow tilting movement of the upper ends of the drums without escape of substantial amounts of air such an air seal is shown and described in u s pat no 4 052 797 christensen assigned to the same assignee as the present invention the volume of each chamber 24 and 24a can be varied by a vertically extending movable baffle or partition 28 and 28a respectively for reasons to be fully explained hereinafter movement of the baffles may be accomplished by any suitable manual mechanical or electrical means shown in fig1 and 2 as being cables 30 and 30a which are attached to the respective baffles 28 and 28a and which ride in pulleys 32 and 32a cables 30 and 30a are.