758 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the initial wetness of the skin during the test may be the cause. It is surprising how long it takes to dry wet skin even with a very dry gas stream. Capillary creepage of liquid moisture from the wet side to the dry side under the edge of the separation in the cup may be another cause. If this is so, then any method utilizing absorption cups will be subject to this error. Applying grease to the cup can possibly eliminate Figure 8 Heating chamber this creepage, but great care must be used not to smear the test area with it or the results will be compromised. The additive error becomes considerably more serious as the test period is reduced or as the rate of perspiration utilized for the test is de- creased. However, if the test period is lengthened, one loses the ability to follow the relative change in product effectiveness with time. If heavy perspiration rates are used, a washing away of the active material renders the test inaccurate. Since the procedure to be described can separate the error from the desired data, a short test period does not im- pair the results. Consequently, this procedure can both follow a product effect with time and measure, if any, a wash-out effect as well.

EVALUATION OF ANTIPERSPIRANT ACTIVITY 759 Figure 9. Temperature controller EXPERIMENTAL PROCEDURE The block diagram in Fig. 4 illustrates the test equipment assembled for this procedure. All gas connections are of 3.2 mm Teflon tubing to minimize the permeation of moisture through the walls of these connec- tions. The gas supply system is shown in Fig. 5. Dry nitrogen from the cylinder flows through a sensitive regulator to reduce the pressure to approximately 1000-1500 ram. The wet and dry gas values may be balanced against each other to adjust the delivery of moisture to the main gas stream and to calibrate the operation of the system. The manometer need not be accurate. It is used only to insure that the pressure from test to test remains the same or as a cue to a leaking cup. The mixing chamber assures the thorough distribution of added moisture before the gas stream is diverted to the rest of the system. Clear plastic is used in fabricating the absorption cups (Fig. 6). The importance of relocating them precisely in the identical area for a test