118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. I08 REVIEWS OF BOOKS REVIEWS OF BOOKS. Practical Physics. By T. G. BEDFORD, M.A., F.1nst.P. (London, 1926: Longmans, Green 8z Co. Pp. x + 425 with 2 2 j figures. 10s. 6d. net.) Teachers of physics will be greatly indebted to Mr. Bedford for the care he has taken in writing up the course in practical physics arranged at the Cavendish Laboratory for Part I. of the Natural Sciences Tripos. Taking the book as a whole the standard is about that of a pass degree ; but certain essential experi- ments are missing while others, of quite an elementary character, find a place. Apparently students taking physics at Cambridge start at once on the practical course described in Mr.Bedford’s book and, for the benefit of those who have done no practical work at school, a number of very simple experiments are set out in the laboratory. Such experiments include the verification of Boyle’s law, the roller and pointer method for linear expansion and the verification of the laws of reflexion of light with pins and a plane mirror. These inclusions would not matter to the general reader if they did not take the place of more important material. Here, however, the omission of any experiments on thick lenses or on the measurement of inductance makes us regret the space devoted to work which really belongs to a more elementary course. Two aspects of the author’s treatment of the subject are particularly good ; the excellent judgment he has shown in his selection of theoretical matter and the close attention he has given to experimental technique.The principles underlying the experiments are assumed to be known, but the theory peculiar to each of them is given, except in a few cases where there is good reason for a more extensive treatment. This is no doubt the obvious course to adopt ; but the decisions involved are sometimes quite difficult, and practical text-books have been written in which the principles are, on occasion, treated in some detail and the experimental procedure omitted altogether. As for experimental technique the operations to be performed are described to the smallest detail and students using the book will not be able to plead ignorance as an excuse for bad or faulty practice.The subject is treated under five headings: Mechanics and Properties of Matter, Heat, Light, Sound, Magnetism, and Electricity. The first section in-REVIEWS OF BOOKS IOg cludes experiments on the comparison of masses with the ballistic balance, on moments of inertia, on friction, etc., in addition to those on the subjects always dealt with in a general physics course. The only omission of consequence would appear to be the determination of viscosity by the application of Stoke’s formula for falling spheres. This experiment is included in a list of additional exercises at the end of the section, but no student would carry it out properly without de- tailed instructions. The section on Heat is quite orthodox, although an exercise involving the measurement of temperature with a thermocouple might have been added with advantage.(It is a pity, however, that on p. 105 the author has per- mitted himself to characterise a thermometer as deZicate.) Part 111. on Light includes, in addition to the usual experiments in geometrical optics, an account of Searle’s flare spot method for the refractive index of glass and a number of ex- periments on interference. The description of the air cell method for finding the refractive index of a liquid by total internal reflection is particularly good. The chapter on Sound is notable for a number of experiments with resonators of various kinds. Part V., on Magnetism and Electricity, includes an unusually large number of experiments with magnets and an account of the theory of the damped ballistic galvanometer, whose application to the measurement of capacity, high resistance, and hysteresis is described.The outlook of the book is rather elementary. There are no references (except perhaps half a dozen to Searle’s papers and two or three others), and the student receives no special encourage- ment to read or think about his work. Further, he is not instructed to estimate the errors of his measurements or to assess their influence on the final result. It is true that the introductory chapter discusses the question of the relative accuracy with which the several measurements involved in an experiment should be made, but, unfortunately, most students omit that chapter and, in any case, the matter is one which needs and will bear continual emphasis.In spite of these defects Mr. Bedford has produced the most useful laboratory text-book of pass standard available to students in this country. It is obvious that he will have to prepare many future editions, and it is to be hoped that, in the next, he will add twenty or thirty pages dealing with the above-mentioned omissions. D. 0. W. A little adverse criticism is necessary. Catalysis in Theory and Practice. Pp. xv + 516. By E. K. RIDEAL and H. S. TAYLOR. (London : Macmillan & Co., Ltd., 1926. Second Edition. Price 20s. net.) Seven years have elapsed since the first edition of Rideal and Taylor’s monograph on Catalytic Action was published; during that time many new experimental facts on the fundamental processes of catalysis have been brought to light, with the consequence that some of the views of the older generation of physical chemists have been definitely abandoned, whilst others have been drastically modified in order to satisfy the requirements of the recent data.The most arresting outcome of the researches of the past decade is the realisation that (at least so far as actions at solid surfaces are concerned) we are dealing not with the average properties of a crowd of molecules but with the behaviour and functions of a select few-a numerically insignificant proportion-of the total number of atoms which are present in the solid aggregate. In the present edition this trend of affairs is admirably reflected in Chapters IV., V., and VI., which deal respectively with the theory of heterogeneous catalytic action, promoted and protected catalysts, and poisoning or inhibition of catalytic activity. The many recent investigations relevant to this theory of the1 I 0 REVIEWS OF BOOKS catalytic surface are surveyed thoroughly and critically, with the result that on the whole it is readily seen to what extent our present conception of catalytic action is more or less complete and satisfactory ; whilst the treatment given also throws into relief the numerous points which are still not clear and which are either receiving study at the moment in one or other laboratory or are in need of further research.These chapters, and indeed most of the book, go a long way in the direction of realising the authors’ hope that the volume will be a further incentive to research and development in this field.It is perhaps unfortunate that the authors? have not included in the discussion on pages 75-79, a more detailed account of Taylor‘s theoretical paper in which he has developed a particularly vivid picture of the surface of a nickel catalyst. It may be granted that these pages include this conception in effect, but it is pre- sented with peculiar clarity in the communication in question and in a manner which, in the experience of the writer, is exceptionally readily grasped by the student. When the present edition is compared with its predecessor, one realises that during the past few years the necessity for consideration of the association of aZZ interactants and products with a catalyst has become far better recognised. This is particularly noticeable in catalytic actions into which organic compounds enter, of which class a very complete and readable account is given.Yet the most striking and also one of the earliest proofs of this kind-the formation of a mixture of the cis- and trans-forms of oleic or elaidic esters when either of the latter individuals are hydrogenated--is not mentioned ; that which seems convincing to the organic chemist will probably always not necessarily seem equally important to his physical confrhe. The selectivity of hydrogenation processes is discussed at some length, but the exceedingly delicate susceptibility of such actions to slight modifications in structure, as indicated by the general results of Lebedev, and of other investi- gators, is not developed fully ; quite possibly, however, the communications referred to appeared too late for review in this edition.Two minor slips which have been noticed may be mentioned here : on page 288 the case of ether formation from diphenyl carbinol in presence of copper at 280’ is one of dehydration, not dehydrogenation (as the equation given implies), and on page 302, lines I I and 12 from bottom should read “ transformed cyclo- hexanol and methyd cinnnmate by the action of nickel into cyclohexanone and methyl phenylpropionate.” The whole field of catalysis, from both theoretical and practical standpoints, is certainly more completely surveyed in this volume than in any other single work on the subject known to the writer. As is natural (since this edition is only twenty pages longer than the earlier one), the proportion of “theory” has increased at the expense of 6‘ practice,” so many fresh experimental results having been published in the interim between the two editions. Presumably this tendency will continue for some considerable time and, if the volume is to be kept within its present convenient limits of size, it seems doubtful whether it will continue to be possible adequately to treat both sides of the subject.Already it is noticeable that the sections on Hydrogen and Hydrogenation Dehydrogenation, and the Fixation of Nitrogen have been shortened considerably, although the technical modifications of these processes continue to be multiplied. The descriptive matter in the concluding chapters of the book, all of which is interesting but much of which deals with reactions of relatively minor importance, inight possibly have been sacrificed to some extent in order to set the more important technical phases of catalysis in better perspective.P ~ o c . ROY. SOC. 1925, I ~ A , 105.REVIEWS OF BOOKS I 1 1 These criticisms are not directed to deprecation in any way of the theoretical discussion of catalysis ; indeed, it is to be hoped that the authors will be able in future editions to develop and extend this aspect as the results of fresh researches become available. The writer would like to suggest, in this connection, that that highly important group of catalysts, the natural enzymes, should be still more fully dealt with from the theoretical and experimental standpoint. The authors have rendered a great service to chemists in collecting together and correlating critically the results of recent work on catalytic action in the two editions of this book ; it is to be hoped that they will pursue the same course by similar thorough revision of the volume as opportunity offers.On the whole, they survey the field from a broad and modern standpoint, free from the over- dependence on mathematical symbols and preconceived dogma which marred the outlook of a passing generation of physical chemists. Ostwald’s ‘‘ criteria of catalysis ” still act as a kind of ghostly curtain-raiser early in the book-perhaps these may make way for more relevant matter in a subsequent edition ? The members of this Society may ascribe credit to Rideal and Taylor for insisting once again on the priority and clarity of Faraday in this province : “ The student of catalysis no less than, for other reasons, the student of electro- chemistry is deeply indebted to Faraday for this early orientation ” ( I 834) ‘‘ into the mechanism of catalytic action.” The authors are to be congratulated on having produced a volume which is a worthy successor to their first edition ; the book is well set up, clearly printed and eminently readable in both senses of the word.T. P. H. . Indicators. Their Use in Quantitative Analysis and in the Colorimetric Determination of Hydrogen-Ion Concentration. By DR, I. M. KOLTHOFF. An authorised translation based on the Second German Edition, revised and enlarged by N. HOWELL FURMAN, Ph.D. (New York : John Wiley & Sons, Inc.; London: Chapman and Hall, Ltd.Pp. 269 + xii. Price 17s. 6d. net.) The popularity of Dr. Kolthoff’s book in its two German editions is ample justification for an edition in English, and it is a happy choice that Dr. Furman should have been asked to undertake the revision and translation of the second German edition. The present work differs considerably from the German issue. A new chapter has been added dealing with amphoteric compounds from the viewpoint of the modern conceptions of Bjerrum ; the valuable results of recent investigations of Kolthoff, Michaelis, and others, have been included. Among these additions is a method of preparing a set of buffer mixtures without the use of standard solutions of acid or base. The measurement of hydrogen-ion concentration has grown to be of such importance, for all branches of chemistry, biochemistry and bacteriology, that the importance of a work such as the present cannot be ignored.It ranks equally with the well-known works of Clarke and Prideaux; in some respects it is of more value than these from the practical point of view. The theoretical aspects receive adequate consideration and modern theories have been applied to the explanation of the action of certain indicators. The considerable difficulty which is met in the use of indicators for measuring the #H of protein solutions makes the use of the electrometric method with the hydrogen electrode a necessity in practice. Although this ‘‘ protein error ” is dealt with in the present work, it is of such practical importance as to warrant fuller consideration.I12 REVIEWS OF BOOKS The only serious error noticed is on page 142, where Sorensen’s primary and secondary phosphate buffer should be prepared from I / I 5 mol.solutions of both salts and not with 1 / 1 0 secondary phosphate as stated. On page 186, in reference 2, the first year given should be 1909 and not 1919. Taken on the whole, the work is perhaps the best all-round book on the subject we have and should prove of use to those interested in the theoretical side of the measurement of hydrogen-ion concentration, as well as, pre-eminently, to those engaged in its practical measurement. An important feature is the wealth of bibliographical references. w. c. The Corrosion of Metals. By ULICK R. EVANS, M.A. (London: E.Arnold & Co. Pp. 284. 15s. net.) The second edition of this book is particularly welcome in view of the rapid development of knowledge in this field. During the last two or three years considerable advances have been made, both in the production and application of materials and, also, as regards a proper understanding of the under-lying principles of corrosion. Although only a short time has elapsed since the publica- tion of the first edition, it is quite clear that considerable effort has been needed on the part of the author to bring the book successfully up to date and to keep it within the relatively small compass intended. Considering the wide interest of the subject, there are relatively few satisfactory books dealing with it. The present volume can safely be recommended to those engaged in works practice who are concerned either with the production or utilisation of corrosion resisting materials, or to those engaged in further research.To the student the book will be found a very complete and reliable guide. In the early pages,< the author deals in a useful manner with the electro-chemical aspects of the matter and, also, makes a successful attempt to correlate the numerous facts, many of them apparently small and insignificant, but each having their place in the complete picture necessary for an intelligent appreciation of the problems involved. Naturally, the author has given considerable space to his own experimental work, but the merit of his researches justifies this, particularly as such work was undertaken in those regions which needed more complete exploration. As regards the metals and alloys now available, it must be conceded that the book contains an adequate account of them; some of the essential outstanding problems of corrosion in the industrial world are ably dealt with. The author bases his theoretical consideration of the subject largely upon a conception of the mechanism of corrosion based upon electro-chemical phenomena -using ‘‘ electro-chemistry ” in its broadest sense-and upon a study of protective films. Particularly in the latter respect does one feel that he is on right lines and that we are now arriving at some workable theory, which is useful in advancing our knowledge in this field. The chapter on the corrosion of metals in the presence of dissolved oxygen is an outstanding one. The book is well produced and particularly free from printers’ errors, W. H. H. ABERDEEN : THE UNIVERSITY PRESS