The Molecular Scattering of Light in Benzene, Vapor and Liquid

Scattering of sunlight by benzene, vapor and liquid, from 35° to 283° C.—The intensity of the light scattered at right angles was determined relative to that scattered by liquid ether at 35° C, by photometric comparison with the aid of reflecting prisms and a sectored disc. The relative intensity increased with the temperature at an accelerated rate; for the liquid, from 3.2 at 35° to 102 at 283° and, for the saturated vapor, from 0.95 at 182° to 11.9 at 267°. The scattered light is not completely polarized. The imperfection of polarization was measured by use of a double-image prism and a nicol. The ratio of the weaker to the stronger component, $r$, was found to decrease from 7.2 to 0.9 per cent for the vapor and from 43 to 2.8 per cent for the liquid as the temperature was raised from 35° to 280°. Comparison with theories. This imperfection has been attributed to the anisotropy of the molecules by Rayleigh, Born and others. The theory as extended by Raman to the general case of fluids leads to the relation $\frac{\mathrm{Sr}}{\rho }\mathrm{}(1+r)=\mathrm{const}.\mathrm{}$, where $S$ is the intensity and $\rho$ the density. This is found to agree satisfactorily with the observations for both vapor and liquid. Since for the vapor, the intensity $S$ increases with the temperature much more rapidly than the density, the Rayleigh law is not valid. The Einstein-Smoluchowski formula shows much better agreement, although, when calculated values of the refractive index and compressibility are inserted, it gives for the scattering in the vapor values which are 20 per cent or more too high.