The Vapor Pressures of the Isotopic Forms of Water

Abstract

The ratio of vapor pressures of H₂O¹⁶ and HDO¹⁶ and of H₂O¹⁶ and H₂O¹⁸ have been determined at four temperatures between 11.25°C and 46.35°C. The ratio of vapor pressures of HDO¹⁶ are very nearly the geometric mean of the vapor pressure of H₂O¹⁶ and D₂O¹⁶. The vapor pressure of H₂O¹⁸ varies from approximately 0.8 to 1.2 percent less than the vapor pressures of H₂O¹⁶ for temperatures between 46.35°C and 11.25°C. The application of these to the separation of the hydrogen and oxygen isotopes by distillation is discussed. It seems possible that the hydrogen isotopes can be separated by the fractional distillation of water, but that the separation of the oxygen isotopes by this method will be considerably more difficult.