The ultrasonic absorption in aqueous solutions of a number of 2–2 electrolytes including the sulfates of the bivalent transition metal ions has been measured in the frequency range 105–109 Hz at temperatures between 5 and 50°C. Generally, three relaxations can be separated in this frequency range if the structural absorption of the electrolytic solution is properly taken into account. Relaxation times and corresponding maximum absorption per wavelength are allocated to the normal coordinates of a three-step association or dissociation mechanism. In order to be applicable to the new experimental results, the existing theory of the stepwise association had to be extended to a more general form. By means of suitable transformations the normal coordinates can then be expressed in terms of kinetic and thermodynamic parameters of the individual reaction steps. Values of the rate constants, equilibrium constants, reaction volumes, and activation energies calculated on the basis of the extended theory are presented for the individual reaction steps.

The complex ac conductivity of a 0.1 MPM lithium-ammonia solution has been measured in the frequency range 1.2-70 GHz at temperatures between 198 and 293 K. Two theories for the ac conductivity, random range hopping and random barrier hopping in disordered systems, are used to analyze the experimental data. It is found that random barrier hopping with a distribution of electron relaxation times peaked around 10"10 sec gives good agreement between experimental and theoretical results.

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The properties of metal‐ammonia solutions in the concentration range of the metal‐nonmetal transition between 0.1 and 10 mol percent metal (MPM) are discussed. The high‐frequency electrical properties show a number of characteristic features in this intermediate concentration range, such as additional dielectric relaxations at about 0.1 MPM and 0.7 MPM for LiNH3 and NaNH3, respectively, and a resonance‐like behavior at about 1.0 MPM and 1.5 MPM for LiNH3 and NaNH3, respectively. For both LiNH3 and NaNH3 the real part of the high‐frequency dielectric function changes to large negative values around 2.5 MPM, indicating a transition to metallic behavior at high frequencies. The high‐frequency properties, which are also discussed in terms of electron conductivity, are explained quantitatively as a function of concentration, temperature, and frequency using a model of polaron hopping. The metal‐nonmetal transition is related to structural changes in the solutions which lead to phase separations in LiNH3 and NaNH3 at lower temperatures. The structural properties of the solutions are investigated using sound velocity and ultrasonic attenuation data. Concentration and temperature dependence of the ultrasonic attenuation in LiNH3 and NaNH3 can be described quantitatively in terms of structural fluctuation.