120 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS serious separation from the system. Another possibility is the adsorption of antifoam onto other available surfaces this is especially significant in systems where suspended solids are present. All the above conditions will lead to a net decrease in availability of antifoam during the course of the test and result in an apparent decrease in •q. Yet, on the other hand, in some instances an increase in antifoam efficiency as a function of test time is possible. This is true in those systems where antifoams become better dispersed, so causing a change in the number of droplets present in the system. Figure 6 depicts a typical plot of efficiency versus antifoam (AF-1) concentration in a protein foaming system. The relationship can be expressed as log •/= AC d- log B or •/ = Be ^c, where A and B are constants related to the effectiveness of the antifoam in the given medium and C is the concentration of added antifoam. This relationship is valid unless the concentration of antifoam becomes excessive, as would be the case if it reaches and exceeds the point where no foam is formed. For a given antifoam the value of A changes with the quality of its dispersion and A will be constant as long as the degree of dispersion remains unchanged. A nonlinear plot of log •/versus C can reflect an increasing tendency of the antifoam to aggregate with increase in concentra- tion. 1000 100 10 I I I 0.5% PALMOLIVE DISHWASHING LIQUID 23øC TEMPERATURE A f-1 O ' o\ TAf-1 o I [ 20 40 AGING TIME, hrs. Figure 7, Demonstration of transient nature of TAF-1 antifoam.

ANTIFOAMS 121 The practical factors affecting the performance of silicone antifoams, in general, have been given (8-10) and will be elaborated upon elsewhere. Certain experimental aspects of the behavior of transient antifoams are now presented. SPECIALTY ANTIFOAMS: THE "TRANSIENT" ANTIFOAM Over the past 20 years, several specialty antifoams have evolved. They have been developed both on an ad-hoc basis, i.e., for specific foaming systems, or as generic specialty types. The most recent example of the latter type is the transient antifoam which is in contrast to practically all the antifoams described thus far which, in general, I I lOOO •ß 0.5% PALMOLIVE DISHWASHING LIQUID 2300 TEMPERATURE 100 - u ¸ 10 - TAf-1 300 ppm o• , TAr-l, 200 ppm 1 - - I I I 0 20 40 60 AGING TIME, hrs. Figure 8. ]•ffect of transient antifoam concentration on its performance in 0.5% Palmolive dishwashing liquid.