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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.
