A dispensing apparatus is provided for a pulverulent material entrained in a stream of a transporting gas or mixture of gases. The apparatus includes a first member and a second member. The first member includes an interior into which the stream flows and a perimetral discharge edge. The second member includes a side facing the interior and a perimetral discharge edge. A discharge opening is defined between the discharge edges of the first and second members. A dimension of the discharge opening is determined by one or more third members. Each third member has a first end adjacent the first member and a second end adjacent the second member. The third members have non-uniform transverse sections. A transverse section of each third member between its first and second ends has a smaller area than the transverse section of each third member at one its first and second ends.