ISOTHERMAL DIFFUSION-COEFFICIENTS OF NACL-MGCL2-H2O AT 25-DEGREES-C .5. SOLUTE CONCENTRATION RATIO OF 1/1 AND SOME RAYLEIGH RESULTS

Isothermal interdiffusion coefficients have been obtained by Gouy interferometry for the ternary system NaCl-MgCl2-H2O at 25.00-degrees-C and a 1:1 mole ratio of NaCl to MgCl2. Data are reported for total molar concentrations of 0.5, 1.0, 2.0, 3.0, and 3.72 M. Diffusion coefficients at mole ratios of 1:1 (0.5 and 1.0 M), 1:3 (1.0 and 3.0 M), and 3:1 (1.0 M) were also obtained by Rayleigh interferometry during the corresponding Gouy experiments by switching the two optical systems back and forth. As expected, good agreement is found between Gouy and Rayleigh results. Diffusion coefficients at the 1:1 ratio are intermediate between the results for 1:3 and 3:1 ratios, with D12 becoming large with increasing concentration but always less than D11 and D22, and with D11 and D22 crossing at 2.8 M. Densities were measured for all solutions. Rayleigh experimental and data analysis techniques are described.