Abstract: An apparatus for providing a fluidized bed to effect the separation of a mixture of articles having at least a first density and a second density that is greater than the first density into separate groups. The apparatus includes an inclined trough which is supplied at an input end with either a fluidization medium, such as sand, or a mixture of articles from which a fluidized bed is formed by forcing gas upwardly through the bottom of the trough and through the fluidization medium or the mixture. In the case where a fluidization medium such as sand is used, the mixture of articles is introduced into the fluidized bed medium so as to be entrained therewith to effect separation as the articles travel in the direction of flow of the fluidized bed medium. Vertical oscillatory movement is imparted to the inclined trough to improve the separation and layering where the mixture of articles is fluidized, or to improve the density uniformity where a fluidization medium such as sand is fluidized as the bed.