The thermodynamic behavior of electrolytes in aqueous solutions up to high concentrations is described on a uniform theoretical basis. I n addition to the electrostatic interaction of the ions two properties of the electrolyte prove to be especially characteristic of the thermodynamic behavior: lst, the space requirement of hydrated ions in the ionic atmosphere; 2nd, an incomplete dissociation appearing for a large number of electrolytes a t higher concentrations. The quantity characteristic for the space requirement of the hydrated ions and for the formation of undissociated molecules is the hydration radius "a," which is approximately known from values of the apparent molar functions a t infinite dilution. By introduction of new distribution formulas for the ionic atmosphere in the theory of Debye and Hiickel, which follow from statistical and thermodynamical considerations analogous t o adsorption statistics or to Eucken's treatment of hydration shells, the properties of some completely dissociated electrolytes such as Li halides, MgCl?, and others are calculated and found to be in good agreement with experimental data. Other applications of the distribution formula-especially with respect to colloid ionsare indicated. I n the general case one has to consider the additional effect of incomplete dissociation. Then t,he calculstions of mean activity coefficient's, heats of dilution, and apparent molar heat capacities from the expression for the free energy are i n fair agreement with experimental data for 1-1, 2-2, 1-2, and 1-3 electrolytes up to conceritrations of about 1 to 4 molar. The effect of incomplete dissociation appears most obviously, separated from other effects, in sound absorption results of some electrolytic solut,ions. In addition, the relaxation effects of the hydration shells of the ionic atmosphere, and of the dissocia.tion equilibrium are discussed with respect to heat conductivity, electrical conductivit.y, and sound absorption data of electrolytic solutions. The last mentioned quantity gives information about the kinetics of extremely fast ionic reactions in aqueous solutions.

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The limits nαmax and nβmin of the two‐phase region of PdHn can only roughly be estimated from the shape of the equilibrium isotherms pH2(n). Other methods applied so far do not yield more accurate results. More precise values can be obtained, however, from measurements of the magnetic susceptibility x as a function of the hydrogen content n at various temperatures. Such x(n) isotherms have been measured at temperatures between 20 and 300°C and H2 pressures up to 140 atm (0 · n · 0.8), using samples of Pd wire (1 mm) and Pd foil (33 μm). In the homogeneity range isotherms for adsorption and desorption were identical, in the two‐phase region, however, hysteresis was always observed. Here the desorption curve was taken as the equilibrium isotherm, and was applied to determine the values of nαmax and nβmin by extrapolation. Measurements on Pd black in the same region of pressure and temperature showed a number of peculiarities, for instance smaller values of susceptibility and smaller hysteresis loops as compared with bulk Pd. These can be attributed to the large specific surface area of Pd black as well as to its strongly distorted lattice structure. By means of the measurements on bulk Pd the position of the critical point of the palladium‐hydrogen system could be redetermined with rather high precision: Tc = 291 ± 2°C; nc = 0.250 ± 0.005 mol H/mol Pd; Pc = 19.7 ± 0.2 atm H2. The measurements on Pd‐black yielded within the limits of error the same values for the critical temperature and the critical pressure, whereas the value of the H/Pd ratio, properly corrected, was found to be a bit higher, namely nc = 0.260 ± 0.005.

Mit Hilfe von Übertragungskatalysatoren (UH3‐, UD3‐, Cu‐Pulver) wurden an kompaktem Pd (0,3 und 0,15 mm Folien) Aufbau‐ und Abbauisothermen mit H2 und D2 gemessen; Temperaturen + 75 bis −78 °C, Drucke 760 bis 10−3 Torr, Atomzahlverhältnisse n (= H/Pd bzw. D/Pd) von 0,001 bis 0,83. Aus den Messungen im Bereich der α‐Phase wurden die chemischen Potentiale des gelösten H bzw. D im Grenzzustand n → 0 und ihre auf eine Attraktionswechselwirkung zurückgehenden, der Konzentration proportionalen Zusatzanteile berechnet. Im Bereich der β‐Phase wurden die entsprechenden Zusatzanteile ermittelt. Sie treten hier formal als Repulsionswechselwirkung auf; die Desorptionsenthalpien nehmen linear mit n ab. extrapoliert auf n → 1 bis nahezu auf 0. – Eine eingehende Diskussion der im Bereich des Zweiphasengebietes auftretenden Hysterese führt zu dem Schluß, daß die Zersetzungsdrucke nahezu den Gleichgewichtsdrucken entsprechen. Aus ihrer Temperaturabhängigkeit ergaben sich die Zersetzungsenthalpien zu ΔHH2 = 9,32 ± 0,1; ΔHD2 = 8,88 ± 0,1 (kcal/mol), die Zersetzungsentropien zu ΔSH20 = 21,8 ± 0,2, ΔSD20 = 23,4 ± 0,2 (cal/grd.mol). Messungen an Pd‐Mohr lieferten innerhalb der Fehlergrenzen dieselben Werte. ‐ Für die Trennfaktoren von H2/D2‐Gemischen 1/1 an Pd‐Mohr wurde α = 2,25 (50 °C) bis 3,7 (−78 °C) gefunden.

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