An optical technique for in situ density determination in electrolyte solutions under hydrothermal conditions

We report on a technique which determines the density of hydrothermaI solutions tlarough the relationship between density and refractive index given by the Lorentz Lorenz equation. An optical cell is described which allows the refractive index of Iluids to be measured at temperatures up to 823 K and pressures up to 1200 bar. The validity of the Lorentz Lorenz equation is demonstrated for pure water and water/NaCI solutions. New experimental results are preseInted Ibr the density of water/NaNO~ solutions at high temperature and pressure. The use of density data to derive other properties such as compressibility, thermal expansion coefficient, and apparent molar volume is demonstrated