Ultrasonic technique is one of the methods for determination of dispersed phase hold-up which does not disturb the operating system. This technique was developed for systems of two components that the extraction does not take place. For the extraction process, the system has at least three components. The concept of traversing time of ultrasonic waves through different components or through mixtures with different hold-up should be applicable with ternary system as well as with binary system. However, the detail phenomenon might be differed, especially the relative velocity in each media. In this research we studied the ternary system : acetone-toluene-water, which acetone is the solute. The concentration of acetone might cause different ultrasonic velocity in the mixture. The hold-up calculated from this technique was compared with the sampling method. The flow rates of dispersed phase and continuous phase, and the rotating disc speed have influence on the hold-up. the hold-up was increased by increasing the flow rate of dispersed phase. In contrast, the hold-up was decreased by increasing the flow rae of continuous phase. The rotating disc speed has sightly effect on the hold-up. the hold-up measurements by the ultrasonic technique and by the sampling method were very close and reliable
