Acoustic Velocity with Relation to Chemical Constitution in Alcohols

The results of this investigation extend and confirm conclusions given in the literature deduced from sound velocity and auxiliary data concerning alcohols. Acoustic velocities at 500 kcps were measured in a large number of alcohols and in three series of alcoholic binary solutions with a precision ultrasonic interferometer within the temperature range of 0°–80°C. Viscosities were determined at 25°C and densities within the range 14°–37°C. At fixed temperature, increase in sound velocity with increase in number of carbon atoms in primary alcohols follows a simple exponential law. The square root of the viscosity varies inversely as the molecular sound velocity. Secondary alcohols have lower sound velocities than the corresponding primary isomers because of lower densities. The increment in van der Waals' b per CH2 group is about 20 cm3 per mol. This holds true for all the homologous series studied. Fluorinated alcohols have much lower sound velocities than the alcohols from which they were derived. Rao's constant (molecular sound velocity) drifts somewhat with temperature, which is to be expected for associated liquids. The three series of binary solutions studied were n-propanol and isopropanol, n-propanol and n-octadecanol, and aqueous solutions of a propane diol derivative. Apparent molal adiabatic compressibilities for the component taken to be the solute vary as the square root of the molality at fixed temperatures.