370 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (about 100 grams) of white or albino negroid hair that is highly kinked, and, preferably, it should be from a single human head. QU•.STION: What relationship does this work have to the recent studies of Pauling and Corey, which show that many proteins have an a-helical configuration that is, the protein molecule is a rather tightly packed coil? /lnswer: Perhaps none, since the ortho-para behavior appears to be related to an assembly of protein molecules rather than to single molecules. A major difference between the two cortex fractions is the cystine content. If the cystinc disulfide bonds serve to cross-link a-helices of the type pro- proposed by Pauling and Corey, it may be that the cystinc difference would affect the way the a-helices are twisted together. Pauling envisions that a-helices (single molecules) to be twisted together to form a still larger, and still helical, assembly of molecules. In this connection, it would be useful to make structural studies with kid mohair (ortho) and human hair (para), if possible, of the sort that Pauling and Corey have made. QUESTION: Wouldn't it be a good idea to make amino acid analyses of your kid mohair and human hair samples to check on the amino acid analysis work of Golden, et al.? alnswer: It certainly would, and we would be delighted to have another graduate student (Golden was one) sent to us who would be interested in doing such work. If he can gain admission to Princeton's Graduate School, please send us his name and address. (Laughter.) J. H. DUSENBU•¾ FOAM TRANSITIONS AND FOAM PERSISTENCE* By M. B. EPSTEIN Onyx Oil & Chemical Co., .Tersey City, N. yt. THE COSMETIC INDUSTRY has a special interest in the persistence of foam. In the development of shampoos, shaving preparations, bubble baths and other toilet articles considerable effort has been expended in finding materials and formulations which can produce long lasting foams. The requirements of the cosmetic industry in these respects differ from other important applications of surface-active agents. Thus with respect to detergents for laundering, high sudsing is not at the moment regarded in some circles as essential for technical or marketing purposes and in some situations is unnecessary and undesirable. * Presented at the May 13, 1955, Meeting, New York City.

FOAM TRANSITIONS AND FOAM PERSISTENCE 371 There has been a certain divergence between the classes of materials in common use for cosmetic purposes and those finding wide outlet as house- hold detergents. Those surface-active materials which at the present time comprise by far the greatest portion of the cosmetic market include soaps, fatty alcohol sulfates, sulfated monoglycerides, sarcosinates and certain other materials of more restricted use such as the fatty acid derivatives of taurine and isethionic acid. Among household detergents there has been a diminishing importance of soaps, which have given way to the alkyl- benzene sulfonates. These in turn are being supplanted to some extent by various nonionic detergents, principally the condensation products of ethylene oxide and some hydrophobic or water-insoluble group. It is striking that the alkylbenzene sulfonates of present manufacture have found limited use in shampoos and this must be attributed at least in part to their characteristic lacy, dry foams. For many cosmetic purposes, in addition to persistent foams, there have also been the requirements of body, feel or gross viscosity, sometimes referred to as creaminess, which are best met by fine bubbled and high density (wet) foams. Such foams are characteristic of soaps, fatty alcohol sulfates and related materials. In the description of a foam its persistence or its lifetime is perhaps its most important characteristic. When gas is passed through a liquid, the volume of foam formed must be equal to the volume of gas that is passed through the solution plus the volume of liquid in the films. After formation, all foams undergo a period of continuing drainage and of decay. Foams vary all the way from those which collapse immediately to those which last indefinitely, until ended by some outside destructive force. A pure liquid, when shaken violently, forms a foam that collapses the moment the shaking stops. At the other extreme is whipped cream, which loses liquid through drainage very slowly and lasts a long time. The carefully shielded bubbles of Dewar survived for years. It is the relative persistence which distinguishes one group of foams and their stabilizing agents from another. There are materials which are associated with a low order of persistence. Ginger ale and solutions of sodium octyl sulfate give foams which drain rapidly and then sponta- neously collapse. They appear to have no means whereby the individual films overcome the forces producing drainage. In contrast solutions of the common alkylbenzene sulfonates or highly purified sodium lauryl sulfate give foams which drain rapidly without spontaneous collapse. The drainage can proceed until the films are astonishingly thin, of the order of a few tens of Angsttoms, but nevertheless can last indefinitely if properly protected from air currents, heat gradients, mechanical shock or outside destructive forces. Among these foams it appears that forces come into play between the opposing surfaces of the films which resist further drainage and spontaneous collapse.