610 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS After an interval o.f one hour, the screw cap was slowly tightened un- til the jar was airtight and leakproof. The jar was then weighed every 24 hours over a period of 96 hours in order to determine the weight loss as a result of permeation of the water vapor through the exposed area the film. Under these conditions, the relative humidity above the sur- face of the film would be zero and would be 100% below the surface of film. Therefore, the pressure differential, /xp, responsible for diffusion would be the vapor pressure of water a't the test .temperature. The loss in weight over a specified period was noted in milligrams and the flux value was calculated. Tables I and II indicate these results. Flux was plotted as a function of time and from the straight line which was produced the slope was calculated by linear least square treatment of the data using a library program.* From the slope value, the permeabil- ity coefficient of each film was calculated. These results are shown in Figs. 2 and 3 and Table III. * STAT 9A, available on the Control Data Multi-Access Computer (System 420), C.E.I.R. Inc., Multi-Access Computer Service, Washington, D.C. Table I Water Vapor Transmission of Films Prepared from Ethyl Cellulose at 37øC Flux (F) Time Plasticizer• (hours) I (mg) II (mg) Mean Unplasticized 24 151.3 151.5 151.4 48 275.9 277.6 276.8 72 410.9 412.0 411.4 96 537.0 547.8 542.4 Tributyl citrate, 10 PHR 24 84.0 84.9 84.4 48 162.7 162.4 162.5 72 220.0 221.4 220.7 96 281.0 279.5 280.3 Tributyl citrate, 20 PHR 24 120.2 121.1 120.6 48 269.6 270.6 270.1 72 450.2 451.8 450.5 96 645.8 647.4 646 6 Tributyl citrate, 10 PHR 24 254.5 253.7 254.1 hexadecyl alcohol, 10 48 572.1 573.9 573.0 PHR 72 869.5 871.6 870.6 96 1177.0 1179.6 1178.3 Tributyl citrate, 15 PHR 24 110.0 93.4 101.7 hexadecyl alcohol, 15 48 219.6 176.4 198.0 PHR 72 3½3.5 270.7 307.1 96 473.5 338.0 405.7 • PHR indicates parts plasticizer per 100 parts polymer.

WATER VAPOR TRANSMISSION OF FILM-FORMING AGENTS Table II Water Vapor Transmission of Fihns Prepared from Polyamid Resin at 37øC 611 Flux (F) Time Plasticizer" (hours) I (mg) II (mg) Mean (rag) Unplasticized 24 4.91 4.74 4.83 48 10.95 11.00 10.96 72 14.81 14.86 14.79 96 20.06 19.90 19.90 Tributyl citrate, 10 PHR 24 8.94 9.09 9.02 48 17.36 17.49 17.37 72 29.21 28.60 28.90 96 41.90 42.17 41.98 Tributyl citrate, 20 PHR 24 8.03 8.23 8.13 48 16.88 17.09 16.86 72 27.64 27.85 27.45 96 35.84 36.25 36.04 Hexadecyl alcohol, 24 7.39 6.46 6.88 20 PHR 48 15.66 14.87 15.23 72 22.09 22.02 22.05 96 32.37 32.11 32.19 Tributyl citrate, 10 PHR 24 12.17 12.28 12.22 hexadecyl alcohol, 48 24.19 24.38 24.28 10 PHR 72 37.97 38.18 38.03 96 50.06 50.22 50.14 "PHR indicates parts plasticizer per 100 parts polymer. Table III Permeability Coefficient of Ethyl Cellulose and Polyamid Resin Films at 37 øC Film Composition• Slope of Flux vs. t 48 slope X 24 Ethyl cellulose, unplasticized Ethyl cellulose tributyl citrate, 10 PHR Ethyl cellulose tributyl citrate, 20 PHR Ethyl cellulose hexadecyl alcohol, 10 PHR Ethyl cellulose, hexadecyl alcohol, 20 PHR Ethyl cellulose tributyl citrate, 10 PHR hexadecyl alcohol, 10 PHR Ethyl cellulose tributyl citrate, 15 PHR hexadecyl alcohol, 15 PHR Polyamid resin, unplasticized Polyamid resin tributyl citrate, 10 PHR Polyamid resin tributyl citrate, 20 PHR Polyamid resin hexadecyl alcohol, 20 PHR Polyamid resin tributyl citrate, 10 PHR hexadecyl alcohol, 10 PHR 5. 449 2.691 7. 326 2. 541 2.517 12.795 .255 ß 204 ß 460 .393 .417 .531 2 724 1 346 3 663 1 271 1 259 6 396 2 128 0 103 0 230 0.196 o. 209 0.266 "PHR indicates parts plasticizer per 100 parts polymer.