which enter at two jets 11 12 material is fed into the mill at an inlet 13 the entering material is carried by the air stream from one jet 11 to an impact chamber 14 where particle size is reduced the particles then travel through an upstack 15 to a centrifugal classification chamber 16 where the fine particles 17 collect in the center and exit the mill at an outlet 18 the larger heavier particles 19 at the periphery of the classification chamber 16 return to the impact chamber 14 via a downstack 20 and their size is further reduced by impact with entering new material the mill illustrated in fig2 is a commercially available micronizer u00ae mill this mill has a shallow cylindrical grinding chamber 31 eight feed inlets 32 are spaced around the periphery of the chamber these inlets provide communication between the chamber and a feed manifold 33 a series of twelve air jets 34 which are supplied with air by an air manifold 35 are also spaced around the periphery of the grinding chamber the air jets cause entering particles to move in high speed rotation so that they violently impact each other larger particles are kept at the periphery of the grinding chamber where most of the grinding occurs smaller particles are carried to the centrally located collector 36 air escapes through a centrally located outlet 37 fig3 illustrates an arrangement of equipment.