Experimental results are reported for fluid‐fluid phase equilibria of the ternary system H2OCO2NaCl. Measurements were extended to 773 K and pressures to 300 MPa. A “synthetic” method was used: Known quantities of the three components were filled into an autoclave at room temperature. The autoclave with a sapphire window and variable volume is described. Transition points to homogeneous one‐phase conditions could be determined from recorded p—T‐curves at constant volumes and from visual observation. From the transition points p—T‐curves on the three‐dimensional phase equilibrium boundary surface at constant compositions, “isopleths”, were obtained. Data for 20 isopleths with CO2‐concentrations between 0.2 and 85 mol% and with 6 weight YO of NaCl are presented together with a few additional results for higher salt concentrations. Molar volumes were measured at the phase boundary surface and within the one‐phase region. Excess molar volumes are given. In comparison with the binary H2O‐CO2 system, the addition of NaCl shifts the range of partial immiscibility to higher temperatures by up to 100 K; for example from 573 to 673 K at 100 MPa for 48 mol% CO2. Results are in agreement with earlier data of Takenouchi and Kennedy. Considerations of the ternary phase diagram H2OCO2NaCl within a wide range of conditions are given.

The specific volume of aqueous sodium chloride solutions with 6, 10, and 20 weight percent salt was measured from 200°C to 600°C and from 100 bar to 3000 bar. The uncertainty of the data is below 0.5%. Data are given of temperature, pressure, volume and composition at 24 points on the two-phase boundary surface. About 230 values for the one-phase region are presented. The critical curve for the binary system runs from 374°C and 220 bar for pure water to 500°C and nearly 600 bar for a solution with 12% salt. The specific volume at this point is 2.0 cm3 g-'. At 600"C, 3000 bar and 20% salt a volume of 1.163 cm3 g-' was found. The apparatus and procedure, which uses an autoclave with variable volume and sapphire window is described.

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