process for the determination of the interfacial area in a container containing a two - phase mixture incorporating a liquid phase and a gaseous phase flowing in the liquid phase in the form of bubbles . for a same path of a sequence of ultrasonic sound wave trains emitted at constant amplitudes in said container , the ratio of the mean values of the maximum amplitudes of the wave trains received after passing through the two - phase mixture and after passing through the liquid phase only is determined and the thus determined ratio is plotted on a calibration curve giving the interfacial area value as a function of this ratio .