Light Scattering in the Critical Region. I. Ethylene

Abstract

1. In the neighborhood of the critical point, light scattering reveals the presence of four regions: a. A region where the light scattering depends on the inverse fourth power of the wave‐length. b. A region of increasing scattering and decreasing dependence on wave‐length, beginning about a degree above the critical temperature, and extending about a degree. The maximum scattering in this region is of the order of 100 times the initial value. c. An abrupt decrease in scattering, accompanied by absorption which sets in at a higher temperature for the shorter wave‐length. d. A large and erratic increase in scattering, apparently resulting from condensation. 2. The scattering observed upon cooling and heating are identical, provided the temperature does not drop below the temperature for zero scattering or condensation. 3. The wave‐length dependence of light scattering is not completely described by any existing theory. 4. Applying the Ornstein‐Zernike equation where it is possible, one calculates clusters of about 20 molecular diameters more than a degree above the critical temperature. These clusters increase rapidly with decreasing temperature.