The following conclusion was obtained by comparative studies on 1) behaviors of natural air bubbles around flat-plates and curved-plates placed in water-flow channel, 2) behaviors of ore-particles on the model impeller and of natural air bubbles and 3) Wearing conditions of impeller employed at the field work in practice. (1) Behaviors of air bubbles in the water flow around flat and curved plates are different from those around columns in the point where air cavity is not formed in the wake

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... to displacement of separation point, but as to other conditions they can be inferred from those of columns. (2) Some of recomminution of air bubbles on the impeller, involving diffusing vanes of food plate, of F. W. type flotator are like those observed in the studies using columns, flat and curved-plates, and they are working effectively coexisting with other actions. (3) Wearing conditions are consequently helpful in acknowledging patterns of pulp-flow. Flow of coarse and heavy ore-particles being deflected to the front side of blade in the impeller, flow of air bubbles is influenced by this variation of pulp density.