HYGROSCOPIC AGENTS AND THEIR USE IN COSMETICS 23 over a Scott Tester, using a pen- dulum weight that swings in an arc to apply the required force to the member that penetrates the cream. The jar of cream is placed on a plat- form that is raised at a steady, slow rate. The movement of the pene- trating member is slight so as to de- form the cream at a steady rate ac- cording to the advancement of the platform carrying the sample. Pre- liminary tests indicated the desira- bility of using a blade to penetrate the cream rather than a solid plunger, since when either a large or small plunger was used quantities of the sample were extruded from beneath the plunger as it was forced into the cream. A circular blade was finally adopted, a thin wall brass tube. Our results with this equipment agreed with appearance and feel of the creams. The creams, when subjected to the tester, produced loading curves of four general types as seen in Fig. 15. The type "A" curve un- doubt,edly results where no crust is present and the cream is of suffi- ciently low consistency so that the cream is immediately penetrated by the brass tube as it advances. As the consistency of the cream in- creases the slope of this curve in- creases. The type "B" curve also results where there is apparently no crust however, for the most part, the type "B" curves obtained showed a definite change of slope as the creams continued to be pene- trated, apparently indicating a heavy consistency. The type "C" curve is produced by a cream that possesses a hard, thin crust. A large force is required to break through the crust, but when this has been penetrated, the inertia carries the brass tube down into the cream a distance depending on the consistency at which point the curve rises slightly or levels off. The type "D" curve is also produced by a cream having a crust however, the break-through is not so sharp which would seem to indicate a thicker crust. After the crust has been penetrated the curve again levels off or rises. In testing the unexposed soap- type creams, some rather interesting results were obtained. With no humectant present an "A" type curve of 0 slope was obtained. At 2% humectant glycerin gave an "A" type curve of 0 slope, propylene glycol an "A" type curve of 0.4 slope and sorbitol an "A" type curve of 0.9 slope indicating that TYPIGAL LOADING OURVES O•FA/NEO WIFtt ORUST MEASURING APPARATUS SNOWING EXAMPLE BAR GRAPH B k oR 1 INCneA SiNG PeNe rnA rio,v-• Figure 15

24 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the creams containing these hu- mectants increased in consistency in that order. As the concentration of humectant was increased, the con- sistency of the creams increased until "B" type curves were pro- duced. In examining the shapes of these curves, it appeared that the consistency of the sorbitol creams leveled off at 5%, whereas the glycerin and propylene glycol creams remained lower in consistency until 10% glycerin and 20% propylene glycol were added. At 10% and 20% the sorbitol and glycerin creams had apparently the same consistency as those at lower per- centages of the polyols while at 20% propylene glycol the consistency was markedly greater. On the basis of the above results it appears that as little as a 2% sorbitol addition will increase the consistency of a soap-type cream appreciably however, with increas- ing concentration the consistency is not increased excessively. With the addition of glycerin the consistency increases less sharply, but at 10% the consistency is equal to that of sorbitol creams. With propylene glycol additions, the rise in consist- CRUST FORMATION OF SOAP TYPE CREAM AT 30% RELATIVE HUMIDITY 2c I ,,vo •' 5 I0 2O •' 5 I0 2O 2 5 I0 20 PROPYLENE •Ot.•'OL SOEBITO• •/• GLYOERIN • GLyOOL CRUST FORMATION OF NON-IONIC TYPE CREAM AT 30% RELATIVE HUMIDITY 2C UNOXPOSED I0 • • • • r• rn n n 20 EXPOSED •,l HOUR5 • 15 oeXPOS• 4G HOUR • •0 NO 2 5 I0 20 2 5 I0 20 2 5 I0 20 PROP}•LENE ß EXGEECEO CAPACITY OF MACHINE Figure 16 CRUST FORMATION OF SOAP TYPE CREAM AT 50% RELATIVE HUMIDITY Iõ No 2 5 I0 20 2 5 I0 20 2 5 I0 •RUST FORMATION OF NON-IONIC TYPE CREAM AT 50% RELATIVE HUMIDITY 2c I UNOXPOSED 15 • 15 EXPOSED 24 HOURS • ,o • 15 ExPo•O • •OUR• •0 0 •OLYOL SORBI•OL • GLYGERI• • GLYCOL • -,• EXCEEDED CAPACITY OF MACHINE Figure 17