The solubility of inert gases and methane in H2O and D2O has been measured between room temperature and 600 K. The calculation of Henry’s constants kH, from the solubility data is analyzed in detail; if due account is taken of the nonideality in the gas phase, they can be determined unambiguously up to 520 K. Above this temperature, the ambiguity in kH increases sharply as contributions of third and higher order virial coefficients to the equation of state of the gaseous mixture become more important. The differences of gas solubilities in light and heavy water essentially disappear above the temperature of minimum solubility of the gases. The characteristic thermodynamic features of the aqueous solutions of gases (i.e., large values of −ΔS02 and of ΔC0p2) are still present at 520 K. It is shown that mean-field theories can account for the

It has been experimentally observed, for water and nonaqueous solvents alike, that Henry's constant passes through a maximum and then declines as the temperature is raised from the triple point to the critical point. From classical and nonclassical models, we derive exact relations for the value of Henry's constant and its temperature dependence at the solvent's critical point, showing that the decline of this constant is a universal phenomenon. We demonstrate that the limiting temperature dependence of Henry's constant can be predicted from the thermodynamic properties of the pure solvent and the initial slope of the critical line. The validity of our prediction is tested by comparing it with experimental solubility data for several gases in high-temperature water and benzene. Our predictive model appears valid over a temperature range of at least 15% in temperature below the critical point of the solvent.

A high pressure autoclave equipped with sapphire windows is described. With water‐nitrogen mixtures of thirteen different concentrations (x) determinations were made of liquid‐gas phase equilibria conditions along “isopleths” between 523 and 673 K and 20 to 270 MPa. Molar volumes of the mixtures were measured at the three‐dimensional (PTx) phase equilibria surface and in the supercritical homogeneous region at 673 K. The critical curve, an envelope of the isopleths, begins at the critical point of water (647 K), has a temperature minimum (639 K) at about 75 MPa and proceeds to 250 MPa at 659 K. Phase equilibria and critical curve data are given. Values for the Henry‐constant to 647 K for mixtures dilute in nitrogen and for the nitrogen solubility from 300 to 600 K and from 10 to 200 MPa are presented. Excess volume, VE, values have been calculated for 673 K from 30 to 250 MPa. All VE values are positive. The maximum is 57 cm3 mol−1 at 70 mol per cent of H2O at 30 MPa and about 2 cm3 mol−1 at 40 mol per cent H2O and 250 MPa. Excess Gibbs energy‐values and activity coefficients are presented.

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Critical Phenomena / Fluid Mixtures 1 Gases / High Pressure / Liquids 1 ThermodynamicsA high pressure autoclave with sapphire windows, auxiliary equipment and means and precautions needed for experiments with high pressure, high temperature oxygen are described. With water-oxygen mixtures of different mole fractions, x, determinations were made of liquid-gas phase equilibria conditions along "isopleths" between 500 and 660 K to 250 MPa. Molar volumes of the mixtures were measured at the three-dimensional ( P T x ) phase equilibria surface and in the supercritical region at 673 K. The critical curve, an envelope for the isopleths, begins at the critical point of water (647 K), has a temperature minimum (640 K) at about 75 MPa and proceeds to 250 MPa at 663 K. Phase equilibria and critical curve data are given. The H 2 0 -0 2 critical PT curve is very close to the critical curve recently (10) determined for H20-N2. Values for the Henry-constant from 300 K to 647 K for mixtures dilute in oxygen are presented. The Henry constant at room temperature has only about half the value of the Henry constant for nitrogen in water. At the critical temperature of water (647 K), however, both constants do not differ by more than the uncertainty of the determinations. The excess volume was calculated at 673 K from 30 to 250 MPa. All values are positive. The excess Gibbs energy and activity coefficients are presented. One isopleth for H'O-air with x(H,O) = 0.80 was measured and molar volume values for this composition at 673 K between 33 and 280 MPa are given.

from considering the asymmetry of the molecule and the presence of three chiral centers. However, for a particular methylene segment, not all chiral centers are effective to produce inequivalence of the two deuterons.We have found that the molecular packing of AOT in surfactant layers is similar to what is found in phospholipid bilayers-with a preferred bending of one of the chains close to the headgroup Acknowledgment. We are grateful to HAkan Wennerstrom for clarifying discussions and to Erick J. Duforc for allowing us to use his computer simulation program. T.C.W. thanks the University of Missouri for granting a research leave. This work was supported by the Swedish Natural Science Research Council.Registry No. AOT, 127399-06-8. -. region. This particular packing of AOT and phospholipids is due to the asymmetry of the molecules. It is interesting to note that, in the case of AOT? this particular packing is found not only in a bilayer (the lamellar phase) but also in a monolayer where the mean curvature of the polar-apolar interface is toward the polar solvent (the reversed hexagonal phase).We note, finally, that the system AOT-H20, strictly speaking, should be recognized as a nine-component system. Stereoisomers (35) Stewart, M. V.; Arnett, E. M. In Topics in Stereochemistry; Eliel, N. L., Wilen, S. H., Eds.; Wiley: New York, 1982; Vol. 13, p 195, and (36) Arnett, E. M.; Gold, J. M. J . Am. Chem. SOC. 1982, 104, 636. (37) Wisner, D. A.; Rosario-Jansen, T.; Tsai, M.-D. J . Am. Chem. SOC. (38) Sarvis, H. E.; Loffredo, W.; Dluhy, R. A,; Hernqvist, L.; Wisner, D. references therein. 1986, 108, 8064. A.; Tsai, M.-D.Measurements are reported of the coexistence curve and electrical conductivity of the partially miscible aqueous solution of tetra-n-pentylammonium bromide near its consolute point, which was located at T, = 404.90 * 0.01 K and approximately 0.03 in mole fraction. The compositions of coexisting phases were measured over three decades of temperature, from 21 to 0.01 K from the consolute point. The conductivity was measured in the supercritical regime, from high dilution to compositions exceeding the critical. The degree of dissociation was estimated to be higher than 20% at the critical composition. In the data analysis, attention was given to the assessment of experimental error and proper weight assignment, and also to asymptotic range and choice of order parameter. No evidence of classical behavior was found. This finding is in contrast to several recent reports of effectively classical critical behavior in ionic solutions similar to ours; but it is in accordance with earlier measurements in very weak electrolytes. We present reasons why our conclusion differs from these recent results; an explanation is given why nonclassical behavior might be expected in systems of this type.

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The density ρ of coexisting phases of the ternary system water+1,4-dioxane+potassium chloride was investigated along the liquid–liquid–solid coexistence curve near the critical end-point using a vibrating tube densimeter. By visual determination, this lower critical end-point was located at 311.026±0.010 K with a mole ratio dioxane (D) to water (W) rc=nD/nW=0.418±0.004. Density measurements were carried out in the range 0.01 K<(T−Tc)<31.5 K (i.e., 3×10−5<t=(T−Tc)/Tc<0.1). The obtained coexistence curve displays an apparent sharp crossover at reduced temperatures t≃10−2 from a nonclassical (Ising) to a classical (mean field) exponent. In ancillary experiments, the critical salt concentration was determined. Reduced critical values were calculated and compared with those predicted by the simplest ionic model (RPM, Restricted Primitive Model). The relation between critical behavior and reduced critical parameters in the present and other non-Coulombic systems is discussed.