Ultrasonic Dispersion in Methyl Alcohol Vapor

Ultrasonic velocities have been measured at temperatures of 32°C in the vapor of methyl alcohol, at pressures from 1.12 to 16 cm Hg, and at frequencies from 0.2 to 2.0 Mc sec—1. A systematic variation with pressure of several percent in the measured values of velocity at the lower frequencies is attributed in large part to dimerization of the vapor. Previously determined constants in state equations for methanol have not been found adequate to reconcile the values of velocity at the higher pressures, but empirical values not far from those found by Weltner and Pitzer are satisfactory. There remains evidence of a thermal dispersion of velocity, attributed to internal rotation with a relaxation frequency of 100 Mc sec—1 atmos—1, corresponding to a relaxation time of 2.27×10—9 sec.