118 .JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 10o0 800 CONTROL Af-1 0 ppm Af-1 ANTIFOAM 250 ml SOLUTION 10 sec. AGITATION o o 4oo 20 ppm 30 ppm 2OO •© 40ppm 80epPm 0 100 200 300 400 500 600 TIME, seconds 5. Foaming behavior of protein-based foaming system in the presence of varying concentr of antifoam, AF-1. Figure more satisfactory and it also provides quantitative information. The test involves bubbling nitrogen through the foaming liquid under controlled our version of the test, nitrogen is supplied at a constant flow rate through glass frit (20•50•tm pore size) immersed in 250 ml of test foaming solution a 1000-ml graduated cylinder. The rise of foam is noted as a function of a linear increase in foam volume with time is obtained (see Figure 5). solution is tested alone and with increasing concentrations of antifoam chosen so that the foaming is only partially inhibited. The "antifoam efficiencyisare(r/)arefoamintypicallincoarseInandasimplewhichKcontaineisconditionThetimeand calculated for each dosage of antifoam, as r/• Ko/K, where Ko the

ANTIFOAMS 119 foaming rates without and with antifoam present. In well dispersed antifoam systems the foaming rates are generally constant for at least the first 15 min, allowing determination of a single r/ value which is representative of the performance of the antifoam at the particular dosage employed. Mechanistically, r/represents the degree to which the foaming rate has been reduced by the antifoaming action. Thus a value of r/ equal to unity means either the absence or total ineffectiveness of an antifoam r/= 10, for example, means that one would obtain only one tenth of the normal foam volume in a given time. It should be noted that the comparison of various antifoams by the above test procedure will be valid only if foam production is strictly reproducible in terms of bubble size and size distribution. In this connection it is extremely important to standardize the glass frit and maintain it scrupulously clean so that the pores are always well wetted by the foaming solution and are completely unblocked. In certain cases, especially in the presence of antifoams, a linear increase in foam volume with time may not be obtained. Such deviation from normal behavior is typical of systems in which the antifoam is either lost from the solution or changes its effectiveness during the course of the test. For example, a poorly dispersed antifoam will tend to "cream" and/or coalesce, eventually growing large enough to suffer 1000 I I I -- : 100 - - • 10 - 1 • • I , 0 100 200 300 ANTIFOAM CONCENTRATION, ppm Figure 6. Antifoam efiCiciency of antifoam, AF-1, in a protein-based foaming system.