June 5, 1952 REACTION OF BERYLLIUM OXIDE WITH WATER VAPOR 2701 tions and experimental results from different laboratories. The Committee plans to maintain this set of recommended values of the fundamental constants for physical chemistry up-to-date by revision a t appropriate intervals and will appreciate being advised Of any new information and data which may affect the values.At high temperatures the volatility of beryllium oxide is greatly increased by the presence of water vapor. Measurements of the effect of temperature and partial pressure of water on the rate of volatilization of beryllium oxide indicate that the increased volatility results from the reaction BeO(s) + HzO(g) -+ Be(0H)dg) for which log,@ Kp = 1.63 -9060/T'.
Previous experimental determinations of the
E°
of formation of fused metal halides have depended largely on the equilibrium cell method rather than the simpler, but less precise, decomposition potential method. This report describes a modification of the latter method, the electronic commutator method, which provides some improvements. This technique, with its simple cell and electrodes, was used to evaluate
E°
of formation for fused
normalAgCl
in the temperature range 500°–907°C in direct comparison with the equilibrium cell method. The results agree well with equilibrium cell values obtained both in this study and by other investigators.
The vapor pressure of beryllium oxide has been measured by a modification of the Knudsen effusion method, utilizing radioactive 4Be7 as tracer. In the experimental temperature range of 1950° to 2150°C the vapor pressure is given by the equation log10pnormalmm=18.50−34,230T−2 log10T The boiling point of liquid beryllium oxide is estimated to be 4120 ± 170°C with a molar entropy of vaporization at the boiling point of 25.6 plusmn; 2.7 cal/deg.
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