Velocity of Ultrasound in Potassium–Ammonia Solutions: Concentrated Solutions

The velocity of 10-MHz sound waves in potassium–ammounia solutions has been determined using a new apparatus for 35 different metal concentrations between 1.5 and 15.5 MPM (mole percent metal) over the temperature range 200° to 240°K. The adiabatic compressibility of these solutions has been determined by combining this data with the available density data. The concentration dependence of the sound velocity changed abruptly at a concentration of 3.2 MPM. This change is quite similar to the one previously observed in the lithium–ammonia solutions although it occurs at a lower concentration. Comparison of the sound velocities in Li–NH3 solutions and K–NH3 solutions shows that the sound velocity is solute independent for concentrations less than about 4 MPM and that the Mott transition is not solute independent but apparently depends on the radius of the solute ion.