Coexistence Phenomena in the Critical Region: I. The Gravity Effect in Ethane From Light Scattering

A method of measuring density gradients caused by gravitational compression in gases near the critical region is described. Relative light scattering coefficients of ethane in bombs 40 cm. long increase, remain constant, or decrease in the downward direction, depending upon the mean filling density. These observations have been correlated with the variation of scattering coefficient with density, and show that appreciable density gradients exist. These observations are confirmed by parallel studies of condensation, and serve to explain the flat portion of the liquid–vapor coexistence curve found with a carefully purified system.