Velocity of Sound in a Liquid Containing Gas Bubbles

At low frequencies consideration of the quasi-static elastic moduli and densities of the gas and liquid parts of the mixture yields a value of sound velocity which is much lower than the velocity in either constituent. The computation has been confirmed experimentally in the concentration regions of 1 to 60% air by volume. The sound velocity was found from the change of phase in a plane progressive wave as a function of distance. Concentrations were determined from a measure of the hydrostatic pressure of the mixture. The “froth” was made by pumping the water rapidly past a porous glass filter through which the air was forced. A trace of detergent retarded the coalescence of bubbles. Minimum sound velocity in a water air mixture occurs at 50% concentration where the velocity is approximately 22 mps.