Coexistence Phenomena in the Critical Region: Iii. Compressibility of Ethylene and Xenon From Light Scattering

Abstract

Turbidity measurements in the region immediately above the critical temperature are used t o calculate values of ( a p l a u )~. These results show that ( a p l a v )~ is a continuously variable function of the density t o within 0.02"C. above the critical temperature. The experiments indicate that there esists no region above T, throughout which (ap/av)T = 0 in ethylene or xenon.

Coexistence Phenomena in the Critical Region: V. The Gravity Effect in the Binary Liquid System Aniline-Cyclohexane From Light Scattering

“…In previous publications (3,4), the authors reported large vertical gradients in density near the liquid-vapor critical point in one-component systems. These gradients, due t o gravitational compression, were anticipated owing to the large compressibility of a fluid in the critical region.…”

“…I t was, however, shown by Yvon (9) that such concentration gradients are predicted theoretically. Since Rice and Rowden (6) reported a flat apex on the coexistence curve for aniline-cyclohexane, it was of interest to see if this flat top could be ascribed t o concentration gradients by analogy to the gravity effect in one-component systems (3,4,7,8).…”

“…By combining Equations [2] and [3] the variation of concentration with height becomes B' is a constant for any given concentration, temperature, and wave length of the incident light. Equation [4] is analogous to the relationship between turbidity ant1 density gradient in a one-component system near the gas/liquid critical point.…”

“…Equation [4] predicts that the magnitude of these gradients, a t any height in the fluid column, will be directly proportional to the turbidity.…”

“…I t was, however, shown by Yvon (9) that such concentration gradients are predicted theoretically. Since Rice and Rowden (6) reported a flat apex on the coexistence curve for aniline-cyclohexane, it was of interest to see if this flat top could be ascribed t o concentration gradients by analogy to the gravity effect in one-component systems (3,4,7,8).The critical solution point for a binary liquid system is defined by the conditions where p1 ancl cl are respectively the chemical potential and mole fraction of component 1 in the solution.For the variation of concentration with height in a binary liquid mixture, Yvon (9) obtained an expressioil which may be simplified to the form where x is distance measured positive downward and G(x) is a finite function of x. From Equation [2], Yvon concluded that when the solution approaches the critical state, i.e.…”