24 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS foams. These two uses are considered together by Pickthall' in one of his recent authoritative essays on aerosol formulation. Drawing attention to the general utility of this trihydric alcohol in aerosol-packaged products, he adds that it is in emulsified foam-type products that glycerin really comes into its own. "The most important single factor," he states, in the develop- ment of adequate spreading power, body and foam stability "is glycerin." He goes on to quote a formula for a shaving cream containing 20 per cent of glycerin. Much more could be written on this subject. In tooth pastes and mouth washes glycerin finds application as a sweetening agent, humectant and "throat-conditioner." As Pepper observes, '• it has a subsidiary advantage in vanishing creams intended for sale to very cold countries, in that its freezing point-lowering property prevents emulsion breakdown at low temperatures. Glycerin also reduces the stickiness of gum mucilage and gelatinous films (a property that, with its lubricating action, is used to special advantage in jellies for cosmetic, pharmaceutical and gynaecological use). From the dermatological point of view, little need be said, having regard to this material's known lack of toxicity and freedom from any tendency to provoke harmful skin reactions under normal conditions of use. There is ample evidence in fayour of this view and little but vague and unsubstanti- ated rumours against it. This does not mean to imply that glycerin should be used quite indiscriminately or without intelligent appreciation of all the concomitant factors involved. • Significant, perhaps, among recently published work is that of H. Chino, '• who, in biochemical studies of the Bombyx silkworm, has revealed for the first time the presence in animal tissues of both glycerol and sorbitol as normal products of metabolism. Also noteworthy is the use of glycerin in the preservation of corneal grafts and bull's semen.•' By way of conclusion, I would like once again to second E.G. McDonough's plea for further fundamental work on the physical chemistry of glycerin. This would be of great value, he pointed out to American glycerin producers in 1954, in determining whether many of its interesting, yet varied, properties could be integrated and explained more simply. "For example (he added) is the strong hydrogen bonding property of glycerin a basis and an explanation for such terms now used as the hygroscopic nature of glycerin, the humectant character of glycerin, the strong solvent action of glycerin, the high viscosity of glycerin, and the plasticising action of glycerin on such widely divergent matehals as proteins (e.g., gelatin, casein, zein and gluten), methyl and carboxymethyl celluloses, amylose and starches, polyvinyl alcohols, alginates and pectates ?" The subject is important enough to deserve the lucid and elegant inter- pretation of an A. E. Alexander or tl•e subtle analysis of a Linus Pauling.

GLYCERIN AS A CONSTITUENT OF COSMETICS 25 REFERENCES Wells, F. V., "Glycerin in Cosmetics and Toilet Preparations," Sort], Perfumery • Cosmetics, Feb., March, June, August, 1957. Kalish, J., "Glycerin and Cosmetics," Druoa •, Cosmetic Industry, August, 1957. Pickthall, J., "Glycerol in Aerosols," .Mrtnufrt•t•ring Chemist, December, 1957. Reckless, F., "Glycerine in Adhesives," 3//fg. C/win., August, 1957 "Glycerin in Household Products," S.P.C., October, 1957. Bragg, H. J., "Pharmaceutical Application of Glycerin," Retrtil Chemist, November, 1957. Stetson, R. A., "Glycerine in Hair Preparations," •'tmeri•rtn Perf•mer, April, 1953. Chadwick, E., and Pears, G., "Solvents, Humectants and Blending Agents in Cos- metics," Journal of the Society of Cosmetic Chemists, November, 1951. Harry, R. G., Modern Cosmeticology, Vol. 1 (revised 1955), Leonard Hill Ltd., London. Leffingwell, G., and Lesser, M., Glycerin: Its Industrial and Commercial Applications, 1945, Chemical Publicity Co., New York. Lawrie, J. W., Glycerin and the Glycols, A.C.S. Monograph, No. 44, 1928, Reinhold, New York. Griffin, W. C., Behrens, E. W., and Cross, S. T., "Hygroscopic Agents and their Use in Cosmetics," J.S.C.C., March, 1952. Velon, P., "Interpretation of Constants in Cosmetic Analysis," S..P.C., September, 1951. See ReL 8, p. 754. Blank, Irvin H., "Mechanism of the Action o• Agents Used for the l•elie• o• Dry Skin," .proceedings of the Scientific Section o• the T.G.A., May, 1955. • Wall, Florence E., The .principles and .Practice of •eauty Culture, 1950, Keystone, New York. •6 See Ref. 1, Feb. 1957 (also issued in reyrint form by U.K. Glycerine Producers Association). Boner, C. J., Manufacture and Application of oe•bricating Greases," 1954, Reinhold, New York. •8 Segur, J. t3., and Miner, C. S., _Proceedings Sc. Sect. T.G.A., No. 19, May, 1953. Fisher, W. J. W., "Shaving Soaps and Creams," S..P.C., September, 1936. Singer, David B., "How Glycerin Aids Research," Industrial Laboratories, U.S.A., August, 1957. Pepper, W. P., "Face Creams," .perfumery • Essential Oil l•ecord, February, 1952. Chino, H., Nature, September 21, 1957. Strianse, S.J. Chapter 6, Cosmetics: Science and Technology, New York and London, 1957. Wells, F. V., "Glycerin Rediscovered," Drug and Chemical Exports, December, 1957. SELECTED PHYSICAL PROPERTIES OF GLYCERoL-WATER SOLUTIONS Boiling Per Cent Glycerol Point Specific Viscosity Freezing Relative % wt. o C. at Gravity Centipoises Point Humidity 760 mm. 20/20 ø C. 20 ø C. ø C. at Equilibrium. _ 100 290 1-26362 1410 18.0 0 99 239 1.26105 1150 15'9 4 98 208 1.25845 939 13'9 9 95 164 1.25075 523 7'7 20 90 138 1.23755 219 1.6 32 70 114 1.18355 22.5 38'9 65 66.7* 112 1.17448 17-5 46'5 67 50 106'7 1'12845 6.00 23'0 82 30 102.9 1'07470 2'50 9.5 92 10 100-7 1.02395 1'31 1.6 98 0 100.0 1.00000 1.005 0'0 100 * Eutectic mixture, minimum freezing point. (Table reproduced from "Glycerine Properties and Uses," issued by the Glycerine Producers' Association, U.S.A.)