24 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS mechanism of skin colour inheritance which enables two coloured (half- bred) persons to produce an occasional pure white or pure black child. (Slide 23) It has been possible in this lecture to deal with only a very few aspects, and those only briefly, of skin structure and function, but it is hoped that all those present have been able to find something in this discourse which has been of interest to them. Acknowledgement I am indebted to Prof. W. Montagna and the Academic Press of New York for permission to reproduce Slides 2, 3, 4, !1, !2, !3, 14, 15, !6, 18 19, 20 and 21, from the book "The Structure and Function of Skin." Similarly, my thanks are due to Dr. Stephen Rothman and the University of Chicago Press for permission to reproduce Slides 1, 5, 6, 7, 9, 10, 17, 22 and 23, from their book "Physiology and Biochemistry of Skin."

SILICONES IN THE COSMETIC INDUSTRY 25 SILICONES IN THE COSMETIC INDUSTRY T. W. WATSON, B.Sc.* A lecture delivered to the Society on Friday, 2rid November, 1956 IT WAS near the end of the nineteenth century that Professor Kipping began his classical research on organo-silicon compounds at Nottingham. Seeking to establish that organo-silicon compounds were capable of optical asymmetry in the same manner as their carbon analognos, Kipping, in fact, laid the foundation stone of what was to become a new branch of polymer chemistry and a thriving chemical industry. Kipping, who did succeed in preparing, purifying and identifying organo-silicon stcreoisomcrs, made a further vital contribution to the manufacturing processes involved in silicone preparation by modifying the Grignard reaction so that silicone intermediates could be prepared by this method. Present-day manufacture of silicone intermediates follows closely Kipping's method. Silicones are organo-silicon compounds having a structure of alternate silicon and oxygen atoms, organic radicals such as phenyl and methyl being attached to the silicon atoms. There are two main manufacturing methods used in the production of the intermediates from which silicones are obtained. Those are the Grignard reaction and the later "Direct method." Diagrammatically those reactions are shown below. heat Chlorosilanes Direct process :--Si + R C1 R SiCI• catalyst R aSiC1, mainly R •SiC1 Grignard :-- SIC14 + Mg + RC1/• The Grignard is the more elegant method since, by its use, the degree of substitution of the silicon atom can be more carefully controlled. For many purposes, however, the direct method is more economic, since it yields mainly the dichlorosilane without the necessity to convert elementary silicon into silicon tetrachloride. Whichever method is used, however, a certain amount of disproportionation takes place so that a variety of by-products are encountered. * Technical Service Department, Midland Silicones Limited, Barry, Glamorgan.