One of the important new research methods involves the use of ultrasonics during crystallization or dis­ solution. Ul trasound has become extensively used in many branches of science' and technology in recent years, as we may see from the number of papers' published. The total up to 1939 was about 700, but by 1960 it was well over 5000. Applications in physics, crystallography, chemistry, and so on provide a powerful means of discover­ ing new effects, although such studies tend to be very complicated and demand an acquaintance with a wide range of topics. The main effect of ultrasound on matter is to change the energy state considerably; an ultra­ 6 2 sound flux as low as 10 W/cm at 3 x 10 cis produces a pressure wave whose amplitude is 5 atm, while the 5 maximum acceleration may exceed 10 times that of gravity, the maximum particle speed being 40 m/sec and 2 the radiation pressure 1300 dynes/cm [I, 2]. 2 Recent ultrasonic emitters, even without focusing systems, can give steady fluxes up to 300 W/cm . The kinematic and dynamic parameters of ultrasonic fileds are such that they can cause effects at the level of atoms and molecules, quite apart from macroscopic effects.

I. Methods and Apparatus for Studying Crystallization and Dissolution in Ultrasonic Fields.- 1. General.- 2. Choice of Material for Observing Crystallization.- 3. Ultrasonic Waveguides and Radiators.- II. A Brief Review of Work on the Interaction of Ultrasonic Energy with Recrystallizing or Dissolving Material.- 1. Crystallization of Various Materials in an Ultrasonic Field.- 2. Effects of Ultrasonic Energy on Solids.- III. Crystallization Processes of Organic Compounds.- 1. Thin Films.- 2. Crystallization in Bulk Material.- 3. Structure of Castings. Mechanical Properties.- 4. Effects of Ultrasonic Frequency on Crystallization.- 5. Effects of Ultrasonics on Columnar Crystallization.- 6. Crystallization of Mixtures of Eutectic Type.- 7. Production of Zoned Structures.- 8. Effects of Vibration of the Walls of the Vessel.- IV. Effects of Various Agents on Nucleation in an Ultrasonic Field.- 1. Nucleation in Purified Materials.- 2. Nucleation at Impurities.- 3. Nucleation in Amorphous Materials.- V. Growth and Dissolution of Monocrystals.- 1. Effects of High-Frequency Ultrasound on Crystallization and Dissolution.- 2. Effects of Low-Frequency Ultrasound on the Growth of Monocrystals of Potash Alum.- 3. Avalanche Crystallization of Potash Alum from Solution as Influenced by Ultrasound.- 4. Properties of Metal Monocrystals Grown in an Ultrasonic Field.- 5. Dissolution of Crystals in an Ultrasonic Field.- 6. Production of Etch Figures in the Presence of Ultrasound.- 7. Detection of Dislocations in Crystals with Ultrasonics.- 8. Effects of Ultrasound on Liquid Crystals.- Literature Cited.