Measurement of the complex refractive index of pulverised coal by light scattering: an attempt and some comments

An experiment was performed to measure the refractive indices of pulverised coal and its products, both cold and in a flame. The chosen method was based on the Fresnel reflection equations which suggest that the ratio of scattered intensities for two orthogonal polarisations is independent of size. This method proved entirely unsuccessful. The polarisation ratios were smaller than expected, the root cause being a high degree of depolarisation in the scattered light. It is conjectured that the main source of this is multiple scattering by constituents within the coal particles and by the edge irregularities.