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A m o n o l a y e r of h e x a d e c a n o l s p r e a d o n L o c h L a g g a n , S c o t l a n d . S u c h a c o n d e n s e d m o n o l a y e r c a n c o n s i d e r a b l y r e d u c e e v a p o r a t i o n of t h e w a t e r (Chapter 7) a n d also effectively d a m p s o u t t h e ripples (Chapter 5). R e p r o d u c e d b y p e r m i s s i o n of Price's (Bromborough) Limited. [ Frontispiece Interfacial Phenomena J . T. DAVIES Professor of Chemical Engineering and Director the Department, University of Birmingham of Ε. K. RIDEAL Former Professor of Colloid Science, University Cambridge (>4K) Χ^,^χ Academic Press New York and London of ACADEMIC PRESS INC. Ill NEW FIFTH YORK, AVENUE U.S.A. 3, N.Y., United Kingdom Edition Published by ACADEMIC PRESS INC. ( L O N D O N ) L T D . 17 O L D Q U E E N S T R E E T , L O N D O N S.W.I. Copyright ©, 1961, by Academic Press Inc. ALL NO PART BY OF THIS LIBRARY PRINTED IN BOOK PHOTOSTAT, WITHOUT GREAT MAY BE MICROFILM, WRITTEN OF RIGHTS RESERVED REPRODUCED OR PERMISSION CONGRESS BRITAIN CATALOG BY ANY FROM CARD WILLMER IN OTHER THE ANY FORM, MEANS, PUBLISHERS 61-8494 NUMBER BROTHERS & HARAM LTD. Preface Since the first edition of "Surface Chemistry" in 1926, the subject matter embraced by this title has grown both in importance and in complexity. There has appeared during the intervening years a number of excellent books on the subject, but with each new development the volumes become more compendious. The stage has now been reached when the adsorption of gases on to solids has merited special treatment, and specialized works have appeared on physical adsorption, chemisorption and heterogeneous catalysis. It seems to us that while these properties of the solid-gas interface have received much attention, there has been a tendency for treatments of the various interfaces involving liquids to be confined to the more technical aspects of such subjects as detergency, flotation, foams and emulsions. In this volume we therefore examine particularly some of the more fundamental properties of the various liquid interfaces: we include a systematic presenta tion of the results of our studies together over a period of ten years, first at the Royal Institution and subsequently at King's College, London. In Chapter 8 we discuss the more important characteristics of disperse systems and of adhesion, especially in so far as these follow from the fundamental interfacial properties described in the preceding chapters. We wish to express our indebtedness to many friends and colleagues for stimulating discussions over the years. This book was written while J.T.D. was a lecturer at the Department of Chemical Engineering, University of Cambridge, and while E.K.R. was at Imperial College, University of London. It will, we hope, be useful to chemists, chemical engineers and biologists, and prove stimulating in both industrial and academic laboratories. J.T.D. E.K.R. ν Chapter I The Physics of Surfaces CONDITIONS AT A PHASE BOUNDARY The boundary between two homogeneous phases is not to be regarded as a simple geometrical plane, upon either side of which extend the homogeneous phases, but rather as a lamina or film of a characteristic thickness: the material in this "surface phase" shows properties differing from those of the materials in the contiguous homogeneous phases. I t is with the properties of matter in the surface