Theoretical values on the specific turbidity of colloidal spheres within the range of diameters of 1 to 2 microns are given. It is shown how an unambiguous particle size can be determined within this range in spite of a turbidity maximum. The latter can be determined for almost any refractive index by means of an empirical equation. An alternate turbidity maximum can be used for determining the refractive index of the light scattering material provided the diameter is known.