No abstract

An improved technique has been developed for the determination of the electrical conductivity of reactive molten salts and has been applied to cryolite. The method employs a platinum cell with two concentric hemispherical electrodes. This cell is maintained a fixed distance below the surface of the molten salt which is held in a larger platinum container. Errors from lead resistance have been eliminated by measuring with a Kelvin double bridge (Thomson bridge) and polarization difficulties have been minimized by extrapolation of the nearly linear plot of resistance vs. frequency−1/2 to infinite frequency. Conductivities of molten potassium chloride, sodium chloride, and lithium cloride were determined with a quartz dip‐cell. Best values for the conductivities (ohm−1cm−1) at 1000°C were: cryolite 2.80; potassium chloride 2.65; sodium chloride 4.17; and lithium chloride at 700°C, 6.14. Densities (g/ml), measured by a platinum sinker, were found to follow these equations from the melting points to 1080°C : potassium chloride 1.964–0.574ċ10−3 t; sodium chloride 1.969–0.524ċ10−3 t; cryolite 3.032–0.937ċ10−3 t. The logarithm of equivalent conductance (A) changed linearly with reciprocal absolute temperature (T). Best values for the activation energy for conductance (kcal/mole) (calculated as 2.303 times 1.986 cal/mole deg times slope of log A vs. 1/T) were: cryolite 4.48; potassium chloride 3.32; sodium chloride 3.04; lithium chloride 1.70. Maintaining the fused cryolite in contact with an atmosphere of argon as compared with room air had a negligible effect upon the measured conductivity values for cryolite.

The electrical conductivities at 1000°C, expressed as per cent of the cryolite value, for cryolite containing 10 weight per cent of the following substances are: sodium fluoride 112, calcium fluoride 96, aluminum fluoride 91, and alumina 83. For pure sodium fluoride at 1000°C, conductivity is 5.52 ohm−1cm−1, compared to 2.80 ohm−1cm−1 for cryolite. Molar conductance decreases linearly with mole per cent sodium fluoride, aluminum fluoride, alumina, or calcium fluoride addition to cryolite. The activation energy for conductance, calculated from a plot of the Arrhenius equation, is about 4.3 kcal/mole for the systems of cryolite with sodium fluoride, aluminum fluoride, and alumina, as well as for pure sodium fluoride, but is slightly higher for the cryolite‐calcium fluoride system. This value agrees reasonably with the 4.48 kcal/mole for pure chryolite. Densities in these systems change linearly with temperature, that for pure sodium fluoride following the equation 2.567–0.610×10−3 t . The stability of the complex normalNaF·×Na3AlF6 is indicated by a density maximum.

Vapor Pressure of Ammonia ammonia is equivalent to a change in the vapor pressm-e of about 2 mm, 12 mm, and 40 mm of mercury at -50^,0°, and +5o°C, respectively, or a percentage change in pressure of about 0.7, 0.4, and 0.25, respectively. The aim in the present experiments was to maintain temperatures constant to 0.01°C, or better, for very long time intervals. Platinum resistance thermometers were employed for the temperature measurements and temperatures were read to thousandths of a degree. II. PREVIOUS MEASUREMENTSThe measurements of various observers are given in Table i, which also includes for comparison, in the columns designated p calc. the final results obtained in the present investigation. Various determinations of the normal boiling point of ammonia are given in Table 2.

VAPOR PRESSURE OF AMMONU.