GAS BUBBLE FORMATION 337 will minimize the problem but frequently a reformulation will be re- quired to solve the proble•n completely. CONCLUSIONS Control of gas bubbles in cosmetic preparations is a difficult but ex- tremely important problem in making stable and aesthetically pleasing products. Although there is deaeration equipment * designed to remove gas bubbles from the products, it is generally best to prevent the gas from getting into the products in the first place. As has been shown, once the mechanisms and sources of bubble formation are correctly identified, it is generally possible to prescribe solutions which will prevent or minimize the problem. (Received October 21, 1970) REFERENCES (l) Martin, A. N., and Banker, G. S., Rheology, in Bean, H. S., Beckett, A. H., and Carless, j.E., A•'dvanc•s in Pharmd•euticM Sciences, Vol. 1, Academic Prfiss, New York, 1964, p. 58. (2) SterbJcek, Z., and Tausk, P., Mixing in the Chemical Industry, Pergamon Press, Oxford, 1965, pp. 278-82. (3) Lin, T. J., Rheology Fundamentals and Applications in Cosmetic Industry, in deNavarre, M. G., Chemistry and Manufacture of Cosmetics, Vol. 1, Van Nostrand, Princeton, N.J., 1962, pp. 332-6. (4) Lin, T. J., and Donnelly, It. G., Gas bubble entrainment by plunging laminar liquid jets, AIChE ]., 12, 563-71 (1966). (5) Lin, T. J., Ph.D. dissertation, Wayne State University, Detroit (1963) Univ. Microfilms, N. 64-9539, Ann Arbor, Mich. (6) Lin, T. J., Bubble formation in hydroalcoholic gels, ]. Soc. Cosmet. Chem., 20, 795-805 (1969). • Examples, Versatot© from Cornell Machine Co., Springfield, N.J., or Sontrifuge© from Teknika Inc., Dayton, Ohio.

1. Soc. Cosmet. Chem., 22, 339-348 (May 27, 1971) Chemical Aspects Human Hair of Bleaching CLARENCE ROBBINS, Ph.D.-* $ynopsis--A review of HAIR BLEACHING, which describes reactions of bleaching agents with hair proteins and with hair pigments, is presented. The major emphasis is on the CHEMICAL ASPECTS of bleaching with special attention given to the oxidative degradation of the DISULFIDE BONDS in hair. [NTRODUCTION During the past 20 years a great deal of progress has been made in determining the composition of amino acid residues (1-5) and hydrol- yzates (6, 7) of oxidized keratin fibers, and in the isolation and analysis of fragments formed from the chemical degradation of natural pigments (8-12). Although many aspects are still controversial, general features of the structures of hair and of hair pigments, and of the reactions occur- ring during bleaching, may be described in terms of chemical structures and reaction mechanisms. The objective of this paper is to review and to describe some of this work in the language of physical-organic chemistry. Thus, the following discussion contains a brief description of current bleaching compositions followed by a review of the chemistry concerned with the oxidative degradation of hair proteins and hair pigments. REAGENTS USED IN HAm BLEACHING Modern bleaching preparations contain hydrogen peroxide as the primary oxidizing agent with salts of persulfate added as "accelerators" (13). The pH of these systems is generally in the range of 9.0 to 11.0, and stabilizers (e.g., sequestrants) are generally added to minimize decom- * Colgate-Palmolive Research Center, 909 River Road, Piscataway, N. J. 08854. 339