Abstract: A first stage chamber has upwardly diverging walls so that an upward airstream has different air velocities at different heights in the chamber. When particles such as seeds are fed homogeneously along the chamber top length, they reach equilibrium at different heights depending on their weights and volatilities. The particles suspended and classified at different heights are conveyed by a horizontal airstream in parallel horizontal channels toward a chamber side wall, where they are removed by suction. Ribbed sections adjacent to the channels divide the chamber into deviating cascaded pathways, where the upward air velocity is homogenized and an opposite horizontal airstream conveys falling particles toward the side wall opposite to that on which the particles are removed, to thereby homogenize the spread of particles in the chamber. Light trash is removed through a convergent top section toward a cyclone. Heavy particles not suspended in the chamber are collected and removed at the chamber bottom.