Effects of isotopic composition, temperature, pressure, and dissolved gases on the density of liquid water

Abstract

A review is made of measurements of the effect of temperature, pressure, isotopic composition, and dissolved atmospheric gases on the density of liquid water at temperatures to 100°C. The molar volume is expanded as a multiple power series in the variables, and the coefficients determined. A number of gaps become evident in our knowledge of properties that are within the capacity of current measurements. For example, there appears to be no measurement of the effect of oxygen isotopes on the compressibility. Data on the thermal expansion of D₂O are strikingly inconsistent. The partial molar volumes of dissolved gases are only sketchily known. At O°C, equilibration with the oxygen, nitrogen, and argon of the atmosphere lowers the density about 3 p.p.m., while atmospheric carbon dioxide raises it about 0.3 p.p.m. Appendix I discusses the care needed to obtain various degrees of precision in practical density measurements, and the effect of isotopic uncertainties on them. Appendix II treats the representation of the equation of state of water at slightly higher pressures.