SILICONES IN THE COSMETIC INDUSTRY 29 n• 0 I Mean Those polymers are similar to the previously described alcohol esters in the bonding of the silicone to the non-silicone portion of the molecule via carbon-oxygen-silicon linkages. Ethylene and polyethylene glycol copolymers have been produced at varying dimethyl siloxane concentrations. Generally, the glycol-siloxane copolymers are clear, water-white liquids with a slightly oily feel. The viscosity of such copolymers remains relatively constant whilst the poly- ethylene glycol copolymers increase in viscosity as the dimethyl siloxane content increases. The copolymers have low surface tension and spread easily. On hydrolysis of the fairly easily ruptured Si--O--C bond, the glycol and a dimethyl siloxane polymer are produced. This brief survey of the part which silicones may play in the cosmetics industry in this country shows that the chemist in the silicone industry is amenable to synthesising special silicones to meet particular requirements, and is intended to suggest that the evaluation of silicones by cosmetics chemists will be amply repaid. REFERENCES • Rowe, V. K., Spencer, H. C., and Bass, S. L., "Toxicological Studies on Certain Commercial Silicones." Journal Industrial Hygiene, November, 1948, 30, 332-352. 2 Largent, E., Blackstone, M., and Roth, J., Report on the Immediate Toxicity of Dow Corning 200 Silicone Oil Given Orally to Rats. U.S. Air Force Medical Service (1950). a Schoog, M., "Significance of Silicones for Dermatology." Arzneirnittel-Forschung, 1951, I, 167-169. 4 The Results of Range Finding Toxicological Tests on Certain Dow Corning Fluids. Private Communication of March 5th, 1954, from M. A. Wolf and H. C. Spencer, Biochemical Research Department, The Dow Chemical Company, Midland, Michigan. 5 Repeated Insult Patch Test Study (Shelanski Method) with Dow Corning 555 Fluid. Private Communication of May 21st, 1954, from Morris V. Shelanski, M.D., C.M. 6Schoog, M., "The Importance of Silicones for Dermatology." Arzneimittel- J•orschung, 1951, I, 167-169. ? Morris, G. E., "Silicone Protective Creams--a Clinical Study." Archives of Industrial Hygiene and Occupational Medicine, 1954, 9, 194. 6 Piein, J. B., and Piein, E. M., "A Preliminary Study of Silicone Oils as Derma- tological Vehicles." J. Amer. tharm. Assn., Scientific Ed., 1953, 42, 79. g Smith, C. C., Thomas, M.D., Day, L., and Zimmerman, E. H., "Studies of a Nitrocellulose Silicone Cream as a Skin Protectant Against Eczemtogenous Contact Allergens." Journal of Investigative Dermatology, August 1953, page 111. •0 Susskind, R., "Industry and Laboratory Valuation of a Silicone Protective Cream." Archives of Industrial Hygiene and Occupational Medicine, 1954, 9, 121. n Talbot et al., "The Use of Silicone as a Skin Protectant." J. Invest. Derre., September 1951, 125. •2 Bateman, F. J. A., "Silicone Barrier Cream in Prevention of Bedsores." British Medical Journal, March 10th, 1956, 1, p. 554. •a Currie, C. C., and Gergle, R. C., "New Silicones for the Cosmetic Industry." Journal Socy. Cosmetic Chemists, lrli, No. 3, 1956.

30 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS NIPA-ESTER COMBINATIONS AS PRESERVATIVES AND ANTISEPTICS By ERICH BOEHM, Ph.D., F.R.I.C., •,•D ELIZABETH JONES, B.Sc. I•TRO•)UCTtO• AS FAR back as thirty years ago, when one of us, in conjunction with Th. Sabalitschka, discovered the inhibitory action of the aliphatic esters of •-hydroxybenzoic acid upon fungi and investigated in great detail their suitability for the preservation of foods, medicaments, cosmetics and a number of technical products, it occurred to us that the simultaneous use of two such esters had a favourable effect. This effect could be explained when different types of micro-organisms are present in the material to be preserved (as is usually the case), by the differing ability of different classes of organisms to resist a particular ester. In other words, there is a difference of degree in the capacity of the individual esters to harm the different types of organisms. The behaviour of the individual esters against the different kinds of bacteria in the maximum concentrations obtainable in water does, in fact, vary considerably, although in general the bactericidal effect of the esters increases with the size of the ester alkyl group. An example of the above generalisations is afforded by the study of the preservation of sugar solutions. The lowest member of the ester series, the methyl ester--Nipagin M--successfully prevents mould growth in concentrated sugar solutions, but fails to suppress fermentation by yeasts even in weak sugar solutions. For the latter, the propyl ester--Nipasol M-- proves considerably more effective. The combined use of the two esters will accordingly afford to a substance protection against attack and spoilage by both moulds and yeasts. But a combination of two esters frequently shows a stronger harmful effect upon a pure culture of one type of micro-organisms than one ester alone in the corresponding concentration. How can this be explained ? The esters of •b-hydroxybenzoic acid, indeed, differ from each other only in the size of the alkyl group introduced into their carboxyl group, and consequently the mechanism of their action on bacteria should be qualita- tively the same they should become concentrated in the same position in the bacterial cell and react in the same way with the cell contents. A genuine synergism of two esters is therefore hardly conceivable, i.e., that the two esters of the mixture should attack different regions of the cell, or the same region by a different mechanism. Nevertheless, the different activity of individual esters, in the same concentration on the same species of bacterium, can be due to their differing physico-chemical properties. * From the Research Department of Nipa Laboratories Ltd., Treforest Industrial Estate, Pontypridd, Glam.