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Equilibrium phase relations in the system sodium oxide-uranium trioxide-water at 50 and 75' have been investigated by phase rule methods. In addition to the terminal solids of NaOH.HZ0 (I) and UOs.2HzO (VI), there are at 50' four intervening solid combinations of the two oxides, all incongruently soluble, the concentration of uranium trioxide in the liquids throughout being of the order of 10-20 milligrams per liter. For solutions almost saturated with sodium hydroxide, containing!rom 42.8 to 45.2% NazO (the solubility of NaOH.HzO), the saturating solid is a pink hydrated compound, solid 11, with a hlgh ratio of sodium oxide, probably 5 or 6 NazO per UO,. The next solid phase, solid 111, for liquid concentrations extending down to 0.0106% NazO, is a solid solution of considerable range in composition and ranging in color from bright orange to plain yellow. If it is anhydrous its upper sodium oxide limit is a t 43Na~O.llUOs, while if it is slightly hydrated it may just include the formula NasUO,.H20; its lower limit is very nearly Naz0.3U0,. The familiar diuranate formula, Na2U207, is therefore simply a point in the continuous range of this principal solid solution. This phase is followed, for liquid conce?trations down to 0.00058% NazO, by the compound Na20.6UO3, solid IV, which shows little, if any, tendency to take up adjacent solids in solid solution. There follows finally another solid solution, V, ranging approximately from Na20.12UOs to Na~0.18UO~, and saturation with both this solid and UOa.2H20 (VI) occurs a t 0.00012% NazO in the liquid. The 75' isotherm was studied only for liquid concentrations below 30% NazO, showing in this region the same sequence, nature and compositions of solid phases as at 50'. The NazO concentrations of the three isothermally invariant liquids covered, each saturated with two solids, are lower than at 50".

NotesVol. 61 less than 0.001. It would be expected that the contribution of hydrogen bonding to the heat of vaporization of methanol would become smaller and eventually negligible as the methanol concentration is decreased, and that the heat of vaporization of methanol would not increase again but rather approach a low constant value.Method II.-The behavior of the equilibria systems in the foregoing experiments was most unusual, and it appeared worthwhile subsequently to check the results. A more sensitive method of analysis employing C14-tagged methanol was used10 to extend the measurements into a more dilute concentration region. Cyclohexane was substituted for carbon tetrachloride because of potential difficulties in the purification of the latter. A similar glass, high-vacuum system was employed. The solvents, Eastman Kodak Spectro-Grade stored in glass flasks attached to the vacuum system, were dried in situ with calcium hydride and were thoroughly deaerated.

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