April, 1958 COMPLEX IONS IN FUSED SALTS 417 value. At a temperature of 25' the values of k'and k" have been determined and the values of lcl are known with a precision of *2%; hence, by a trial and error procedure extreme values which E / and E" can have were found. From these calculations it has been possible t o show that E' = 15.8 f 0.5 kcal. The uncertainty in the value of E" is considerably larger; the value obtained was 16.0 f 2.5 kcal. From expressions of the transition state theoryjB values of the heat, free energy and entropy of activation were computed for the reaction between plutonyl ion and trivalent vana-(6) S. Glasstone, K. Laidler and H. Eyring, "The Theory of Rate Processes," MoGraw-Hill Book Co., Inc., New York, N. Y., 1941, p. 417. dium ion in terms of the principal species, i.e., P U O~+~ + V+3 + (activated complex) + H+. These quantities are AF* = 17.03 f 0.01 kcal./mole, AH* = 15.5 f 0.4 kcal./mole and AS* = -5* 2 cal./deg. The magnitudes of the rate constants k' and k" show the relative importance of the two paths which appear to be indicated in the reaction between plutonyl ion and vanadium(II1). Thus a t 25' about 90% of the over-all reaction occurs through the path in which a single hydrogen ion is liberated.Acknowledgment.-The author wishes to express his appreciation t o Drs.

E.m.f. measurements on cells of the type, Na|iq/Na+(glass)/Na-Hgnq have been made on sodium amalgams (mainly in the 1 to 20 atom % sodium region) at 350°to 400°C. The determined activity coefficient on Na can be expressed by the equation, log7n= = -yn®-+ ya.4¿ xNo+('4.7-0.027T) X Na This equation can be used for calculating thermodynamic properties from 5°to 400°C. for liquid sodium amalgams containing up to 40 atom % sodium.ThE THERMODYNAMIC properties of the sodiummercury system have been investigated by several methods in the past, both at room temperature and at elevated temperatures. The data at the lower temperature were from e.m.f. measurements of liquid amalgams containing up to 0.05 mole fraction sodium (2, 5, 6). At higher temperatures, the data were obtained from e.m.f. and vapor pressure measurements. The e.m.f. data were obtained at 300°and 375°C. on amalgams ranging from 0.34 to 0.91 mole fraction Na, while the vapor pressure data were obtained at 300°, 335°, and 375°C. on amalgams ranging from 0.038 to 0.489 mole fraction Na. At the higher temperature, Hauffe (3) has combined his e.m.f. data of amalgams in the sodium-rich region with the vapor pressure data of Bent and Hildebrand (1) on more dilute amalgams to obtain the activity of sodium over the entire composition range at 375°C. The vapor pressure data at 375°C. were represented by only one experimental observation in the dilute concentration region. Thus, accurate temperature coefficients could not be calculated, and the data could not be used for calculating entropies and other thermodynamic functions in the dilute region. To obtain data necessary for these calculations, the e.m.f. method was applied to a study on the sodium-mercury system in the mercury-rich region at elevated temperatures. Cells of the type Na^/borosilicate glass (Na+)/Na-Hgliq were used.

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