The virial equation approach for description the thermodynamic properties of aqueous non electrolytes is proposed. It is based on the precise equation of state for the solvent (H20) given by Hill (1990) and requires only three empirical parameters that are independent on temperature and pressure. The standard state chemical potential of the dissolved species at given pressure P and temperature T can be expressed as: p~ = p~ + RT(-ln(55.51) + ln~l + 2p~ where g~ is the chemical potential of the associated pure gaseous component at standard pressure (1 bar), R is the gaseous constant, ~11 and

New values of the dissociation constants of HCl degrees referring to low density supercritical solutions and near-critical temperatures of water (350-500 degrees C and 500-2500 bars) have been obtained based on comparison of AgCl(s) solubility in NaCl or KCl solutions with Ag-(s) solubility in HCl + NaCl or KCl solutions at controlled hydrogen fugacities. During the course of this study the thermodynamic properties of AgCls- were refined with the aid of the revised HKF equation of state (Tanger and Helgeson, 1988). The dissociation constants of HCl degrees obtained in the present work are higher than that found from electrical conductance measurements (Frantz and Marshall, 1984) by more than an order of magnitude at pressures of about 500 bars, but the difference becomes smaller as the pressure increases. Both sets of dissociation constants agree well at high pressures where the isothermal compressibility of water is less than about 1.42.10(-4) bar(-1).To reliably compare experimental data obtained by different methods, the Redlikh-Kwong equation of state was applied to available literature data as well as to the results of this study. Finally, the standard state thermodynamic properties and HKF parameters for HCl degrees((aq)) were established. These results allow extrapolation of the thermodynamic properties of HCl degrees((aq)) and consequently the HCl dissociation constant up to 700 degrees C and 5000 bars. Copyright (C) 1997 Elsevier Science Ltd.

Summary Based on a synthetic fluid inclusion study we present a new phase diagram for the bulk composition 21.01 mol% CO2 + 77.47 mol% H2O + 1.52 mol% NaCl, displaying the position of the miscibility boundary (solvus) and a set of isochores through the homogeneous fluid field. We also present new diagrams and a computer code that allow the bulk composition and molar volume of individual fluid inclusions to be determined from low-temperature microthermometry combined with phase volume-ratios measured at room temperature.