This is the third work in a series of monographs* written by a col­ lective group of authors and is devoted to the physical mechanisms of specific ultrasonic technological processes that have already come into general use, as well as those which have just begun to enjoy practical applications. The problems covered in the book are exceedingly important insofar as the understanding of the phys­ ical mechanisms of ultrasonic processes forms the solitary basis of an intelligent approach to the design of industrial equipment and proper choice of optimum working conditions. The purely em­ pirical approach to the solution of these problems does not afford satisfactory results, because the state of affairs in a high-inten­ sity acoustic field is complex and diversified. Many papers in the Soviet Union and abroad have been con­ cerned with the practical utilization of ultrasound, but the over­ whelming majority is limited to the solution of highly individual­ ized practical problems, usually under conditions that are not amenable to comparison. Systematic studies have been initiated in the Ultrasonics Section of the Acoustics Institute of the Academy of Sciences of the USSR on the physics of high-intensity ultrasonic waves and their effects on matter; the results of these studies form the basis of the present book.