Coagulation of colloidal particles in hydrosols is of considerable industrial concern. It is employed, for example, in industries that have occasion to handle slurries containing valuable solid matter of colloidal and near colloidal dimensions and where separation of the solids from the suspension medium is desired. Another important application is the treatment of domestic and industrial wastes in which separation of solids from the liquid suspension medium must be accomplished before discharge of the liquid into streams. Methods employed to accomplish coagulation include treatment of colloidal systems with chemical, mechanical, electrical, thermal, radiant, or ultrasonic energy. Two factors that govern coagulation in hydrosols are (1) probability or collision and (2) adhesion of the colloidal particles. In order to coalesce, particles must first collide. The intensity of collision determines the degree to which the particles will adhere, provided they are at or near their isoelectric point. It has been demonstrated previously that ultrasonic energy will increase the intensity as well as the number of collisions of colloidal and near colloidal particles and consequently hasten their rate of coagulation. However, since this type of coagulation has only been reported in batchwise operations, it is believed that if ultrasonic energy is applied to a continuously flowing hydrosol, an evaluation may be made leading to its industrial utilization. The purpose of this investigation was to design, construct, and evaluate a continuous-flow, ultrasonic coagulation unit, employing a ball-clay hydrosol for experimental tests. / Master of Science