Effect of Pressure on Ultrasonic Relaxation in Electrolytes

Measurements of the pressure dependence of the ultrasonic absorption were made on aqueous solutions of manganous sulfate and ammonium hydroxide. Absorption data were obtained for manganous sulfate at frequencies from 9 to 75 mc/sec, up to pressures of 3930 kg/cm2 and at a temperature of 60°C. The relaxation frequency increased from 19.1 mc/sec at atmospheric pressure to 30.7 mc/sec at 3930 kg/cm2. Absorption measurements in ammonium hydroxide were obtained at frequencies from 15 to 75 mc/sec, up to pressures of 2030 kg/cm2 and at a temperature of 45°C. The relaxation frequency increased from 21.2 mc/sec at atmospheric pressure to 52.0 mc/sec at 2030 kg/cm2. The results in both electrolytes can be explained on the basis of a chemical dissociation. In both electrolytes a decrease in the volume difference between the products and reactants with pressure is necessary in order to account for the pressure dependence of the sound absorption.