Vapour Pressure of H₂¹⁸O Ice

Abstract

WE have measured the vapour pressure of H₂¹⁸O ice in the temperature range −5° to −20° C in order to determine the fractionation factor of ¹⁸O between ice and vapour. Water enriched with ¹⁸O was supplied by the Research and Development Co. Ltd, of the Weizmann Institute of Science, Israel, in the form of D₂¹⁸O with an ¹⁸O content of 97 per cent. To convert D₂¹⁸O into H₂¹⁸O, D₂¹⁸O was vaporized in vacuo and reacted with metallic iron at 500° C. The evolved D₂ gas was removed through a palladium-leak. When the reaction was complete, the iron oxide containing ¹⁸O was reduced by circulating ordinary H₂ gas at 500° C to produce H₂¹⁸O which was trapped by cooling with dry ice. As much as 96 per cent of deuterium was replaced with protium by one run (deuterium analysis was carried out by Showa Denko Co. Ltd), and the process was repeated twice to secure complete replacement.