296 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS system with the tubular crystal installed in a line and driven by a generator. Some equipme. nt, designed for dispersion use, has employed this type of transducer assembly. MAGNETOSTRICTION GENERATORS In the presence of an alternating magnetic field certain metals such as nickel and its alloys will be periodically elongated and contracted, thus setting up vibrations. This is the principle of the magnetostriction gen- erator. The alternating magnetic field is adjusted to the natural frequency of the metal rod, which can be laminated to reduce eddy currents. This type of transducer assembly can be so constructed that the vibrating rod Figure 5.--Minisonic Mark II homogenizer, Sonic Engineering Co., Stamford, Conn. is placed directly in the liquid to be treated, so that there is no energy loss due to absorption or reflection by the treatment container. Many types are available for commercial cleaning applications or for the processing of small amounts of material in the laboratory. Figure 3 shows a laboratory unit of this type designed for research in the area of disintegration, emulsification, acceleration of chemical reactions, etc.

SONIC EMULSIFICATION 297 HYDRODYNAMIC GENERATORS This type of generator, referred to as the "liquid whistle," operates on the principle of the organ pipe except that a high pressure jet of liquid is forced through a narrow slit and impinges on a blade edge, which is forced into vibration at its resonant frequency. Intense sound waves are prop- agated into the liquid from this resonator (blade) and continuous cavitation results as the liquid rushes past the blade. Complex vibrations are pro- duced by the resonating blade with a mixture of frequencies resulting. A resonant bell contains the jet-blade assembly as shown in Fig. 4. The Rapisonic, Minisonic (Fig. 5), Dispersonic and Sanisonic Homog- enizers (c) are examples of this type. With the recent commercial production of ultrasonic generators operating on the "liquid whistle" principle ultrasonic emulsification in production 4.00 3.50 3.00 2.50 2.00 1.50 1.00 I I [ I • 0 15 3O 45 60 Days Figure 6.--Varations in the mean globule size of stored mineral oil-Fluronic F-68-Span 80 emulsions made with various apparatus. Emulsifying apparatus: O--Eppen- bach colloid mill X--"Sonogen" ultrasonic generator /x-- "Minisonic" ultrasonic generator.