It was found that the flow of light Φr scattered by a dispersion at the angle of 900, integrated along the optical path of the incoming beam, exhibits an extremum in dependence on the dispersion concentration; its concentration coordinate is a linear function on the dimension of the dispersed particles. This linear dependence is also valid for the concentration corresponding to the selected transparence level on the dependence of the flow Φt of light transmitted by the dispersion. A physical model was constructed and the derived equations of the Φr(C) and Φt(C) dependences are in very good agreement with experiments in a concentration range of roughly three orders. The method can be practically applied in determinations of dispersed particle size.