The pressure differences between H2O and the equimolar H2O-D2O mixture were measured between 5 and 90°C and the experimental data can be represented by the equation (formula presented) where T is the absolute temperature. For comparison the vapour-pressure differences between pure H2O and D2O were also determined. The results show that the H2O-HDO-D2O liquid mixture does not deviate from the ideal behaviour within the limits of the experimental data. The present investigation supports the earlier conclusion that the law of the geometric mean for the vapour-pressure isotope effect in the series H2O, HDO and D2O is not obeyed.
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