AN INTRODUCTION TO SURFACE CHEMISTRY By ERIC KEIGHTLEY RIDBAL HUMPHREY OWEN JONES LECTURER IN PHYSICAL CHEMISTRY CAMBRIDGE UNIVERSITY CAMBRIDGE AT THE UNIVERSITY PRESS 1926 Wilt Thou not ope the heart to know What rainbows teach and sunsets ahow EMERSON. c IN GREAT BBITAIN PREFACE By Professor F. G. DONNAN THE importance of an accurate study of the actions, equilibria, and structures which occur at . the interfaces between homo geneous phases of matter is widely recognised at the present time. Thus a knowledge of these matters is required for a proper under standing of adsorption, the formation and stability of disperse or micro-heterogeneous systems colloid sols and gels, catalysis, enzyme actions, etc., whilst the progress of research shows more and more clearly that the phenomena of life, i. e. the behaviour of cells and tissues, are intimately concerned with the actions occurring at surfaces, and that the effects produced by drugs, disinfectants, and other substances which profoundly affect the operation of cells and micro-organisms are largely due to surface actions. From the general statistical and thermodynamic point of view, the scientific theory of surface phenomena was placed on a satisfactory basis by the researches of J. Willard Gibbs, Sir J. J. Thomson, and J. I, van der Waals. In comparatively recent times the more in timate molecular study of the structures and kinetics of surfaces has advanced very rapidly, thanks, more especially to the pioneer work of Lord Eayleigh, Andre . Marcelin, Sir W. B. Hardy and Irving Langmuir. Our knowledge of this subject has been greatly increased during the last few years by the excellent work of N. Adam and of E. K. Rideal. The combined effect of these researches has been to reveal the existence of a newly recognised so-called two dimensional molecular world, the dynamics of which is analogous to that of the ordinary three dimensional molecular world of homogeneous phases in bulk, whilst the structure of this surface world presents new phenomena of molecular orientation of the highest importance for the understanding of great regions of natural phenomena. The great merit of Dr E. K. Rideals book lies in the fact that the author, whilst in no wise neglecting the thermodynamic treatment and its results, gives a very admirable account of this more recent and extremely important field of study. VI PREFACE Since this is also the most promising line of advance in the in vestigation of disperse systems, Dr Kideals book can be most warmly recommended to all who are interested in colloid physics and chemistry. In the last two chapters the author gives a good introduction to the principal facts and theories of what is usually understood to-day as colloid chemistry, so that the reader is fully supplied with everything that is necessary for a thorough under standing of this subject. Every student and investigator of surface and colloid phenomena owes Dr Rideal a warm debt of gratitude for his admirable survey and presentation of a great and rapidly advancing field of physico-chemical science. F. G. D. UNIVERSITY COLLEGE, LONDON. April, 1926. INTEODUOTION essential differences between the properties of matter when JL in bulk and in the colloidal state were first described by Thomas Graham. The study of colloid chemistry involves a consideration of the form and behaviour of a new phase, the interfacial phase, possessing unique properties. In many systems reactions both physical and chemical are observed which may be attributed to both bulk and interfacial phases. Thus for a proper understanding of colloidal behaviour a knowledge of the properties of surfaces and reactions at interfaces is evidently desirable. Whilst the conditions of equilibrium for such systems were clearly enunciated by J. Willard Gibbs and Sir J. J...