The electrical conductivities of molten BiClg, BiBr3, and Bil3 were measured at temperatures up to 886°at a pressure of 5.4 kbars. At this elevated pressure the specific conductivity ( ) varies exponentially with l/T, i.e., k = e~EVRT. This is in contrast to the behavior of these molten salts at low pressures (P < 0.1 kbar) where Grantham and Yosim (1963) found a maximum in k vs. T curves.The isothermal electrical conductivity of molten BiCl3, BiBrs, and Bil3 was examined at pressures from 3 to 14 kbars. At temperatures above the temperature of maximum conductivity at ordinary pressures, n increases with increasing pressure. It is concluded that pressure inhibits the association of these salts at high temperature. This effect is predominant over the decreased conductivity expected from the lower ionic mobility in liquids at these elevated pressures.

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The vapor pressure of solid thorium was determined over the temperature interval 1757 to 1956°K. by the vacuum evaporation method of Langmuir. Special purification of the thorium was necessary since traces of Th02 react with thorium to give ThO(g). Thorium also reacts with residual gaseous oxygen in the vacuum system to form ThO(g). The latter effect was found to be negligible at residual oxygen pressures of less than 2 X 10 ~* mm. The vapor pressure equation for Th(s) -Th(g) is log Patm = -28,780 =fc 620/7' . + 5.991 ± 0.333. These results yield values of Aff°298(subi> of 137.3 ± 2.8 keal./ mole and 136.6 ± 0.5 kcal./mole from a slope and third law determination, respectively. From an estimate of the pressure of ThO(g) over Th(s) containing ThO^s), Í)0°(ThO) = 196 kcal./mole.(1) This work was supported by the Atomic Energy Commission• This paper has been presented in part before the Division of Physical Chemistry at the 135th National Meeting of the American Chemical Society in April, 1959. (2) S. Dushman, "Scientific Foundations of Vacuum Technique,"

The fusion curves of HgC!, and HgI2 were measured to a pressure of 22 kbar. The melting temperature can be represented as a function of pressure by tp=to+bl P+b2P2, where tp is the melting temperature in degrees Centigrade at a pressure P in kilobars; bl and b, are constants. Values for to (deg) , bl (deg kbac l ), and b2 (deg kbac') are 276, 259; 19.8, 17.1, and -0.26, -0.41, respectively. The electrical conductivities (K) of molten HgCI, and HgI2 were measured to 805 and 620°C, respectively, at a pressure of 5.4 kbar. The electrical conductivity of HgCI,(l) was also measured from 557 to 634°C at P=20.5 kbar. At these elevated pressures K varies exponentially with liT, i.e., K~A exp-(Ek/ RT). At 5.4 kbar, A =2.13 and 0.36 (g·cm)-l; Ek=8.46±0.14 and 2.53±0.12 kcal/mole, respectively, for molten HgClz and HgI,. The behavior of HgC!,(l) and HgI 2 (l) at this elevated pressure is now typical for a strong electrolyte. This is in contrast to their behavior at ordinary pressures where HgCI, shows a maximum in its K vs T curve and HgI 2 has a negative temperature coefficient of K from the onset of melting. The conductivities of molten HgCl, and HgI2 were also examined from 3 to 20 kbar at constant T. At 600 o K, Kp~20 kbarlK P-3 kbar for HgCI, = 12.4; at 555°K this ratio for HgI2 is 1.66. Thus pressure increases the conductivity of these salts. This is attributed to a greater degree of ionic dissociation at elevated pressures.