The new technique will be used extensively in the development of alloys for nuclear reactors and gas turbines as well as for many other purposes. The program will be carried forward in cooperation with Battelle.

Using the resonant frequency of a coaxial cavity excited in TEM modes at frequencies between 50 and 480 mgcy./sec., the dielectric constant of water was determined at 5°intervals between 0 and 70°, and at 100 bar intervals between 1 and 1000 bars. The results are expressed as a set of isothermal and isobaris equations whose parameters were evaluated by the method of least squares. The dielectric constant of water and its temperature and pressure derivatives at 1 atmosphere are tabulated at 5°intervals from 0 to 70°.

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with the dicalcium silicate hillebrandite shows, on the other hand, a complete saturation of the reactive silica.The results of earlier investjgations' have established a recrystallization of the phase B starting just below 180" within about 2 4 4 8 hr. and leading to the formation of the phases mentioned above. The reactions and the equilibria described in the present paper must therefore also be of a similar kind within the whole temperature range 180-220".The results described above are illustrated by Fig. 4. The stages of the formation of the phases and of their existence range are elucidated when the compounds are or are not in equilibrium, within the temperature range 180-220".Acknowledgment.-The author wishes to express his gratitude to the International Ytong Co. of Stockholm for a grant which made possible this investigation.The velocity of sound in dilute aqueous solutions of sodium chloride and potassium chloride is reported a t 25", and a t frequencies of 2.5, 5 and 10 megcy./sec. The velocity in pure water (saturated with air) is reported as 1496.7 m./sec. The complete calculation of isothermal partial molal compressibilities a t infinite dilution] KzO, from these data is illustrated. By suitable equations and numerical exkmples it is shown that the neglect of the correctionoof adiabatic to isothermal compressibilities causes an error of 7.5% in K# for sodium chloride and potassium chloride a t 25 . IntroductionThe partial molal compressibilities required for the calculation3 of the effects of pressure upon ionic equilibria have been derived from two kinds of data, bulk compressions and sound velocities. Compression nieasurements are well suited for "srmining compressibilities as a function of presabove two or three hundred atmospheres, but .essibilities a t one atmosphere, which are of ,-at practical importance, require a long extrapolation in their evaluation. This extrapolation, usually based upon some modification of the Tait e q~a t i o n ,~!~ is not completely satisfactory. Compressibilities calculated from sound velocities a t one atmosphere avoid extrapolation by the Tait equation, but are, of course, adiabatic compressibilities,

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