298 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 3.50 .• 2.50 .=• •2.00 1.50 1.00 0.50 , I I 0 15 I I 30 45 6O Days Figure 7.--Variations in the mean globule size of stored peanut oil-Tween 40-Span 80 emulsions made with vari- ous apparatus. Emulsifying apparatus: O--Eppen- bach colloid mill [2--G. E. ultrasonic generator X--"Sono- gen" ultrasonic generator A--"Minisonic" ultrasonic gen- erator. quantities is a reality. Two studies of the efficacy of this equipment in emulsification have been completed in our laboratories (3, 4). In the first investigation emulsions were prepared with the aid of three ultrasonic units and a colloid mill. Analysis of the emulsions was conducted as a size-frequency analysis using a photographic technique. The first generator used (a) was a piezoelectric type with a quartz crystal operating at 300 kc. A laboratory experimental model, this generator can process a sample of about 20 mi. The second unit (b), a piezoelectric generator with barium titanate crystals driven at 39.1 kc., is a unit primarily designed for cleaning and degreasing operations. The exposure chamber consists of a two-gallon stainless steel tank. The third unit (c) was of the hydrodynamic type, able to pass 4 to 5 gallons of liquid per minute. The fourth unit (d), a colloid mill, was used to represent

SONIC EMULSIFICATION 299 4.50 4.00 3.00 2.50 2.00 1.50 15 30 45 60 Days Figure 8.--Variations in the mean globule size of stored cod liver oil acacia emulsion made with various apparatus. Key: []--"Minisonic" ultrasonic generator (room tempera- ture) A--Charlotte colloid mill (room temperature) 1- "Minisonic" ultrasonic generator (40øC.) A--Charlotte colloid mill (40øC.) conventional dispersion equipment, with which to compare the ultrasonic generators. (a) Model G-3, General Electric Co., Schenectady, N.Y. (b) Sonogen AP-25-B with T-52 Transducer, Branson Ultrasonic Corp., Stamford, Conn. SIZE FREQUENCY ANALYSIS The major goal of this research was to determine the relative efficacy of the Minisonic unit with a colloid mill, often used in liquid dis- persions. It was felt that this could be best determined by a size-fre- quency analysis of emulsions stored over a period of time. The emulsions were diluted with a propylene glycol solution, placed in a haemocytometer cell, examined under the 43 X high power lens and photographed at 0, 15, 30, 45, and 60 days. Projected on a screen, approximately 1000 globules were placed in 1 micron class limits and the mean glolSule diameter,