A novel method is suggested for accelerating the physical changes in suspensions. The suspension is stirred in a jacketed vessel and is alternately heated and cooled. Results indicate a rectilinear relationship between the median particle size of sulphathiazole in suspension and the number of temperature cycles. Crystal growth is measured by the Coulter counter and growth rates are compared arithmetically to indicate which additives (surface‐active agents) may be used to inhibit crystal growth.

An automatic control unit, activating electrically operated solenoid valves, is used to regulate the flow of “hot” and “cold” water from two thermostated baths to the jacket of a reaction vessel so that the temperature of a liquid sample within the vessel follows a highly reproducible programmed cycle. A comparison is made of the temperature hysteresis between 23–33° during a 16 min cycle, when the flow rates to the vessel are changed and when the valves are operated manually. The adjustment of temperature hysteresis to effect the accelerated storage testing of liquid preparations is described.