2015read, as was the difference in levels of the legs of the differential manometer. The procedure was then repeated at a higher temperature. RESULTSThe data are given in Table I. The per cent relative humidity was calculated from the aqueous tension by dividing by the vapor pressure of water at the same temperature, as given in International Critical Tables (6). Clausius-Clapeyron plots (log p vs. 1/T) were linear over the temperature ranges studied, and existence of phase transitions was characterized on such plots by abrupt changes of slope. Such transitions are discussed below.