Dispersion of depolarisation of light-scattering in colloids

Summary

Measurements of the depolarisation factorsρ _u ,ρ _v andρ _h and the extinction coefficients of iodine, graphite, stearic acid, vanadium pentoxide, arsenic trisulphide and ferric hydroxide sols are made for different wavelengths from 2500 A.U. to 7000 A.U. All these sols except the iodine sol do not possess any region of specific absorption. As in the case of gold and silver sols so also in the case of the iodine sol the depolarisation values attain their maximum value in the region of the characteristic absorption,i.e., at 4500 A.U. In stearic acid, vanadium pentoxide and ferric hydroxide sols the depolarisation factors exhibit normal dispersion. The observed dispersion in these cases is a size effect. The behaviour of the graphite sol is slightly different from that of the sols mentioned above, for in this case,ρ _v andρ _h both diminish with decrease of wave-length. Unlike all the other sols up till now studied, the depolarisation factors in the arsenic trisulphide sol increasepari passu with wave-length. The depolarisation measurements indicate that the particles in the sols of iodine and arsenic trisulphide are spherical in shape, while, those in vanadium pentoxide, stearic acid, ferric hydroxide and graphite sols are non-spherical in shape.