REVIEWS OF BOOKS. Valence and the Structure of Atoms and Molecules. By GILBERT NEWTON LEWIS, Professor of Chemistry in the University of California. (American Chemical Society. Monograph Series. New York, I923 : The Chemical Catalogue Company, Inc. Pp. 172. Price 3 dollars.) Professor G. N. Lewis has in this monograph broken a silence that had already lasted for seven years, since he himself has made no important pro- nouncement on the subject of valency since the appearance of his epoch-making paper on “The Atom and the Molecule,” in 1916, although some of his colleagues, e.g. Latimer, Rodebush, and Eastman, have made some minor con- tributions to the development of Lewis’ theory. Professor Lewis has “devoted several of the earlier chapters to an attempt to bring to the better acquaintance of chemists some of the astounding accom- plishments of modem physics.” In this he has achieved remarkable success, since his account of the progressive development of the atomic theory, under the influence first of the periodic law and then of the study of spectral series, is brilliant in its simplicity, especially in the very difficult sections which depend on the application of the quantum theory to problems of atomic structure.In the section which follows Lewis deals somewhat fully with the magnetic properties of the elements, and uses the ring-electron of Parson as a bridge to bring together the static conceptions of the chemist and the dynamic models of the physicist. The reconciliation of these views has been made much easier since physicists have supplemented the classical laws of mechanics by the rigid limitations of the quantum theory.Thus the persistence of molecular structure (eg. in isomers, or in molecules which are undergoing substitution, etc.), is funda- mentalIy opposed to the extreme flexibility of any planetary system of the old- fashioned kind, but is much more concordant with the later view that an electron has to seek permission to move to a new orbit and that under normal conditions this permission is almost invariably refused ! In his sixth chapter Professor Lewis develops somewhat fully the theory of electron-sharing as the principal means of producing a bond between adjacent atoms. This theory is Lewis’ own, and is one of the main features which make his 1916 paper so much more valuble than the paper which Kossel published in the same year, and which is often spoken of as if it covered the same ground.Lewis lays great stress on the tendency of electrons to unite in pairs and quotes, as evidence of this, the electrical conductivity of fused iodine (which must there- fore contain even numbers of electrons in the ions I and I) of triphenylmethyi (C Ph3 and C Ph3) in sulphur dioxide, and of liquid nitrogen peroxide (which must therefore contain the ions NO, and NO,). He regards the loss of colour when NO, polymenses to NIOI as showing that the loose odd electron of NO, suddenly 935 + - - + - +936 REVIEWS OF BOOKS loses its freedom when it is paired with a similar electron and thus becomes rigidly clamped in the even-numbered electronic system of N,04.The chapter on the chemical bond is followed naturally by chapters on double and triple bonds and on co-ordination-compounds, and by a chapter de- voted to the peculiarities of elements such as boron which have such a small atomic number that the K as well as the L electrons appear to share in the development of valency. The book closes with a fascinating chapter on “The Discontinuity of Physico-Chemical Processes,’’ in which the two conceptions of numbering and measuring, the abstract theory of number, and the eminently practical science of geometry, are contrasted, and the inquiiy is made whether in the future only the former may be regarded as rigidly applicable to scientific problems. The con- tinuous fluid of hydrodynamics is clearly a fiction, and so is the ‘L fluid ” concep- tion of an electric current.Since these ideas have gone, is there any phenomenon that suggests a real continuum? Professor Lewis thinks that probably there is not, and that all the sciences which appear to depend on continuous properties will have to be re-organised on a statistical basis, as branches of the universal science of numbers. T. M. L. A Comprehensive Treatise on Inorganic and Theoretical Chemistry. By J. W. MELLOR, D.Sc. (London, 1923: Longmans, Green & Co. Vol. 111. : Cu, Ag, Au, Ca, Sr, Ba. Pp. 927. Vol. IV. : Ra and Ac Families, Be, Mg, Zn, Cd, Hg. Pp. 1049, Price 3 guineas net each volume.) The first two volumes of this notable work were reviewed in Vol. XVI I I . (p. 274) of the Transactions and its general character was there described. The present volumes have followed in a remarkably short space of time considering the magnitude of the work.It is very unsatisfactory when the early portions of a big work become out-of-date before the work is even completed. It may be appropriate to indicate here the general mode of treatment Dr. Mellor has adopted in dealing with the chemistry of the metallic elements. First the history, occurrence, preparation from its compounds and extraction of the metals are dealt with. Then follow accounts of its physical and chemical properties, with a section on atomic weight, crowded with numerical data. Finally, the principal compounds of the metals are dealt with, far more attention being paid to their physical properties than is usual in books on chemistry.The unimportant or more complex compounds, when not of special interest, are referred to incidentally and briefly. The treatment throughout is predominantly physico-chemical. The vast field covered has necessitated many sections being little more than catalogues of numerical data and we are tempted to think that perhaps the author has overstrained his desire for completeness. Many facts of historical interest only might have been dispensed with, but on the other hand all such facts are very fully referenced and this will render the book a most con- venient starting-point for detailed investigation of the history of any particular product, process, or hypothesis. The lists of references at the end of each section are bewildering in their range and completeness, Volume 111.deals with Copper, Gold and Silver, and with the alkaline earths Calcium, Strontium, and Barium. No useful purpose would be served in criticis- ing this arrangement from the standpoint of the periodic classification ; probably That is as it should be.REVIEWS OF BOOKS 93 7 the author was guided by reasons of practical convenience. Unlike in Volumes I. and 11. the present gives few opportunities for excursus on matters of general chemical interest. One such opportunity is, of course, afforded in the chapter on Silver, and here Dr. Mellor introduces an admirable summary of photo- graphic theory which is as up-tc-date as possible. It is interesting to note that the author-who generally endeavours to observe an objective standpoint in matters of theory-favours the solid solution theory of the latent image.The paragraph on sensitisers is not very good and the word is not to be found in the index. The subject of the properties of colloidal solutions is appropriately introduced in the chapter on Gold. Volume IV. deals with the Radium and Actinium metals, and with Beryllium, Magnesium, Zinc and Cadmium, and Mercury. Here again the arrangement is open to criticism from the strict systematic point of view. Consideration of radio- activity gives the author an opportunity to introduce important chapters on ‘( The Structure of Matter,” and ‘( The Architecture of the Atom.” The treat- ment of the subject in the former is properly based on spectrum analysis and the phenomena of electric discharge.Description of the photo-electric effect is followed by an excellent summary of the radiation theory of chemical action, which appears to be based on the Faraday Society’s general discussion, although there is no reference to the report of that discussion. A curious and characteristic section on alchemy forms a link between the treatment of radioactivity and atomic structure. The latter subject, so difficult to condense satisfactorily, is on the whole well developed, although rather unbalanced in parts, but the field is adequately covered. The simple derivation of the Bohr orbits, given on pp. 167 and 168, will be found extremely useful by readers who want the essence of the matter without its mathematical difficulties. It is really astonish- ing how the author has managed to incorporate the most recent work available when the separate volumes were printed.Thus, in the chapter on Mercury we find reference to the most recent experimental work on the separation of the isotopes of that element. A curious omission-unless the fault is that of the reviewer-is that the cyanides are not dealt with. Are these regarded as organic compounds? The cyanides of many metals are of some importance in the arts and the omission is regrettable. We wish the author had not adopted the practice of adding the initials to proper names. It may be defended in the case of living workers of minor rank, but it is surely a little absurd to give initials to immortals like Newton, Laplace or Faraday. It is the very magnitude of this remarkable treatise which perhaps tempts one to criticise it in unimportant details. We cannot refrain from ending once again on a note of wonder, how one man could have collected together and presented in so attractive a fashion such a vast quantity of material and of admiration for his learning, skill, and industry. Theoretical Chemistry from the Standpolnt of Avogadro’s Rule and Thermodynamics. By Professor WALTER NERNST, Ph.D.Fifth English Edition revised in accordance with the Eighth-Tenth German Edition by L. W. CODD, M.A. (London, 1923: Macmillan & Co., Ltd. Pp. 922. Price 28s.) Few books have done more to spread the modern doctrines of physical chemistry than Nernst’s famous treatise, and although a whole library of works938 REVIEWS OF BOOKS on this aspect of chemistry has been written since the first Nernst was published in 1893, the book still, in many respects, stands in a class apart.We, therefore, heartily welcome the appearance, after an interval of eight years, of a new English edition. Professor Nernst has his own conception of what constitutes physical chemistry, and his book is an elaboration of that conception. To him physical chemistry is not a new science, it is the uniting of two sciences hitherto somewhat independent of each other. If that was true thirty years ago its truth is more than ever evident now, when so much advance in chemistry is being made by physicists and when so much chemical knowledge is being utilised in laying afresh the foundations of physical knowledge. Consistent with his principle the author has, therefore, included in his book all that the chemist must know of physics and all that the physicist must know of chemistry.The general plan and contents of the book are so well known to every student of physical chemistry that we need only comment upon the special features of the edition before us. In Book I. “The General Properties of Matter,” few additions have been made, although we notice that the translator has introduced several references to important work (for example, that of Berkeley and Hartley on semi-permeable membranes) not noticed in the text. Book 11. is on “Atom and Molecule,” and here the results of modern experi- mental work and theory are naturally drawn upon. The essential difference between the classic and quantum method of treating atomic problems is de- veloped with commendable clearness and simplicity (pp. 199 and 272 ff.and again on p. 512) and the application of the quantum idea to the molecular theory of the solid state, a subject which the author has made his own, deserves special mention. Brief reference only is made to modern developments in X-ray spectroscopy. The German edition on which this translation is based was written in 1920, and there is, consequently, no attempt to utilise electronic theory to clear up some of the difficulties referred to in the older theory of valency. For the same reason the latest work on isotopes is not referred to, although the brief chapter on radioactivity has been largely rewritten. The chapter on colloidal solutions is disappointing in a book designed to give special attention to the states of matter.In Book 111.-“The Transformation of Matter”-few important changes have been made. The author accepts, with some reserva- tion, the dissociation theory of strong electrolytes put forward by Ghosh, although this has since been subject to some severe criticism. In Book IV.--“The Transformations of Energy ”-reference is made to the observations of Smits on retardation phenomena in the determination of transition points, but the author is not prepared, as yet, to found thereon a general theory of allotropy. In the chapter on electrochemistry the author maintains his older views on the origin of electromotive force in a galvanic cell ; he does not refer directly to the sup- port given to the old contact theory by modern electronic conceptions of the photo-electric effect.Nernst’s ‘‘ Theoretical Chemistry,” incomplete though it be in some respects, will always possess an interest and importance of its own. Students of physical chemistry may find other text-books more useful for examination purposes, but they cannot afford to neglect Nernst if they wish for a philosophical understanding of their science, for here they will follow its development, from his own particular standpoint, at the hands of a master, one of its creators. F. S . S .REVIEWS OF BOOKS 939 The Chemical Elements. By F, H. LORING. (London, 1923: Methuen & Co. Ltd. Pp. 172 with 14 tables and 4 diagrams. Price 8s. 6d). Mr. Loring has published during the past 14 years a series of papers, mainly speculative in character, in the Chemical New, and has already written a book on Atomic Theories. The present volume is largely based upon his articles in the ChemicaC News. It has probably been compiled on account of the current demand for books dealing with the fundamental problems of atomic and molecular structure ; but the author is not a specially skilled ex- positor, and has not himself contributed substantially to the amazing progress which this subject has made in recent years. The serious student would therefore be well advised to derive his information from original sources, or at least from an author who can handIe the documents with the authority that can only be acquired by direct contact with experimental work Moreover, in view of the fact that attractive monographs have recently been written by Lewis, Aston and Bohr, there is no argument which would justify him in reading books which are obviously of a lower order of merit.The Properties of Matter. BY B. C. MCEWAN. (London, 1923 : Longmans, Green & Co. Pp. 316. Price 10s. 6d.) The volume before us deals, in a very competent manner, and with a wealth of experimental illustration, with the subject viewed from an angle which is not quite the customary one. Exactly one half of the book is occupied with a discussion of the first Law of Thermodynamics, the Kinetic Theory of Matter, Isothermal and Adiabatic Transformations and the Specific Heats of Gases, Elasticity of Gases and the Continuity of the Liquid and Gaseous States, Thermal Expansion Diffusion and Solubility of Gases, and Equations of State.It is clear that many of the doctrines here expounded are usually relegated to a treatise on Heat, and their inclusion in a volume bearing the title of Properties of Matter is to be decided as well by considerations of expediency as by the taste of the author. Admirably as they are treated here, it seems to the reviewer preferable to preserve the traditional classification, for the space allotted to these topics necessitates the discussion, in some hundred and fifty pages, of such important subjects as the general properties of liquids, capillarity, elasticity torsion and flexure, and the determination of the constant of gravitation, and of the acceleration due to gravity. This leads inevitably to a huddled mode of presentation which is agreeably absent from the first part of the work.Much water has flowed under the bridges since the days when the treatises of Tait and of Poynting and Thomson first saw the light, and it is with some surprise that one notes, in the section dealing with compressibility, no reference to the very important work of Bridgman. As usual, the distinction between free and total surface energy is not clearly brought out, and the conditions under which it is legitimate to apply the simple formulz for the depth of a sessile drop are wrongly quoted. Considerations of space presumably have led to the omission of the simple but beautiful argument of Boys concerning the relation between the sensitiveness and dimensions of a torsion balance.And it is surprising to find, in a volume published under the date 1923, no more than a passing allusion to the Brownian movement. These lacunae notwithstanding, the book is well suited to the needs of pass and junior honours students reading for a science degree. A. F.940 REVIEWS OF BOOKS Theoretical and Applied Colloid Chemistry. By Professor WOLFGANG Second and Enlarged American Edition translated from the (London, 1922 : OSTWALD. Eighth German Edition by Dr. MARTIN H. FISCHER. Chapman & Hall, Ltd. Pp. 266. Price 12s 6d. net.) This book is described on the title-page as an introduction to the world of neglected dimensions. It is not intended to be a text-book but a stimulus to the study of colloidal phenomena, addressed to the general scientific reader.It is based on a series of lectures delivered in 1913 and 1914 at various universities and colleges in America given with the object of drawing attention to the im- portance of colloid chemistry, its great possibilities of scientific and technological application and the fascinating interest attaching to its study. In Dr. Ostwald’s own words the volume is a ‘( propaganda sheet for colloid chemistry.’’ It is divided into five lectures. The first deals with the fundamental properties of the colloidal state and methods of preparing colloidal solutions ; the second with the classification of colloids and their ph ysico-chemical properties ; the third with their changes in state ; and the last two with some scientific and technical applications of colloid chemistry. In the last chapter we observe the very necessary reminder that although conscious application of colloid chemistry to technology has not as yet been made in anything like the degree possible or probable, yet colloids constitute the most universal and the commonest of all things we know.The author further insists, that in industries based on materials of a colloid nature the details of technical procedure need to be rewritten in terms of colloid chemistry. The unrivalled knowledge of the subject possessed by Dr. Ostwald is sufficient guarantee of the range and accuracy of his treatment, while its attractive and pointed style is a reflection of his enthusiasm for this branch of science, so peculiarly his own, and of his faith in its unlimited possibilities. We have sufficiently indicated the purpose of the book.Clouds and Smokes. By WILLIAM E. GIBBS, I).Sc. Churchill. Pp. xiii + 240. Price 10s. 6d. net). (London, 1924 : J. & A. The sub-title of this work : ‘‘ The properties of disperse systems in gases and their practical applications ” indicates the point of view from which the author has arranged and presented a vast amount of scattered and-in part- inaccessible material. After a short introduction on heterogeneous systems and the effect of curvature of the interface, the formation of aerosols (a convenient title introduced by Svedberg) by dispersion and by condensation processes is discussed and their various physical properties are described. A good account of the Brownian movement and of the optical and thermal properties, as well as of the electrical behaviour is given, and even such familiar phenomena as the deposition of dust in interiors heated by different methods are mentioned and explained.The chapter on the stability of aerosols contains a great deal not to be found in existing text-books, and includes some very interesting photo- graphs of a (‘ coagulating ” zinc oxide smoke. The second part of the book is devoted to “The industrial treatment of fumes and dusty gases.” The principal methods used for removing disperse matter from gases, such as settling, centrifuging, washing and electrostatic separation, are briefly described and illustrated. Although a good deal has been published regarding the last named process, the scale on which it is used may surprise some readers.REVIEWS OF BOOKS 941 The book fills a distinct gap in the literature of disperse systems and its value is enhanced by a very full bibliography.Printing and illustrations are very good, and proof reading seems to have been done with care, though it has failed to detect a particularly unfortunate error both on p. I and on p. 41, where the average velocity of a gas molecule is given as being of the order of IO-‘ ” instead of 104 cm. The reviewer knows the difficulty of persuading compositors that both positive and negative exponents have their raison &&re, but has generally found that it could be overcome by firmness in demanding revises. E. H. Light and Colour. By R. A. HOUSTON, M.A., Ph.D., D.Sc. (London, 1923 : Longmans, Green 81 Co.Pp. 179. Price 7s. 6d.) While intended chiefly for amateurs and, more particularly, that large and often very intelligent section of the public interested in photography, colour printing and so forth, this interesting book contains much that the student of physics will like to have in a simple, readable form. The popularity of the treatment is in this instance by no means synonymous with looseness of expres- sion or vagueness of argument. The first few chapters deal with the nature of light and radiation, and colour. A section on X-ray spectrometry leads to a brief account of atomic structure and stellar magnitude. The treatment of colour is very clear and should prove helpful to many people who have been confused by much loose writing on this subject ; it is based on the colour triangle method of exhibiting the relations of primary and derived colours.I)r. Houston holds an even balance between the classical three-colour theory of vision and the non- elemental theory associated with the name of Edridge-Green, and his words deserve to be quoted seeing that the controversy still rages : ‘‘ . . . the mathe- matical development of Helmholtz’s modified theory does equally well for the non-elementary theory, so that there is no serious difference between the two standpoints.” The account given of colour photography is commendedly simple, brief though it be. There are chapters on The Light of the Future, Photo- chemistry (in which a photoelectric explanation of the photographic process is indicated) and Phototherapy. The last chapter describes some of the remark- able, little-known and, at present, inexplicable phenomena, summarised under the name of The Psychology of Colour, but we think the subject is more far reaching than the author‘s treatment indicates.It is doubtful whether the theory -apart from the facts-can be adequately discussed without reference to the whole big subject of aesthetics. A very useful and interesting book, which can be strongly recommended. The Metallurgy of Steel. By F. W. HARBORD, A.R.S.M., F.I.C. and J. W. (London, 1923 : C. Griffin & Co., 32s. net each volume.) HALL, A.M.1nst.C. Eng. Ltd. Vol. I. xii + 545 pp. Vol. 11. xv+ 553 pp. 7th edition. ‘‘ Harbord and Hall,” ever since the appearance of the first edition in 1904, has been looked upon as the standard work in the English language on the metallurgy of steel.The treatment of the subject is intended to be exhaustive in character and with succeeding editions it has grown from a single volume of about 750 pages till in the present edition it consists of two bulky volumes (totalling some I 100 pages) which for convenience are being sold separately. In the preface to this new edition, it is stated that the volumes have been942 REVIEWS OF BOOKS thoroughly revised, and hence one looks with considerable interest to see how this revision has been carried out. Dealing first with Volume I., which is devoted to the purely metallurgical side, one is bound to experience a considerable amount of disappointment at the unsatisfactory nature of the revision. From a survey of the whole of this volume it would appear that, with the possible exception of the chapter on Electric Furnaces, the revision has taken the form of interpolating short para- graphs giving references to recent work or improvements.Owing to this, the plan of the work remains largely as it was in the first edition published twenty years ago. In the descriptions of the Open Hearth and Bessemer steelmaking processes and furnaces, the effect of this may be fairly satisfactory though it leads to somewhat of a patchwork effect. In these chapters however, one is struck with several notable omissions. Thus in those devoted to the open hearth furnace, descriptions are given of new types of ports and other details of construction, but apparently no reference is made to Clements’ work on British Siemens Furnace Practice.Again, in view of the fundamental importance of casting conditions on the properties of the steel and the impossibility of removing by any subsequent process, short of remelting, some of the characteristics im- pressed in the metal at this stage, it would have been expected that an adequate account would have been given of the mechanism of solidification and of the influence of the shape of mould on the extent and position of the pipe, with some reference to the important work of Brearley and others on this subject. On the contrary, the influence of mould design on the pipe is dismissed in a few h e s , and the only reference to Brearley’s work which the reviewer has been able to discover occurs in Volume 11.devoted to the Mechanical Treatment of Steel ! When one considers, however, the part of Volume I. dealing with the metallography, constitution, and heat treatment of steel and the properties and uses of alloy steels, the effect of the unsatisfactory nature of the revision becomes very obvious. These subjects have been developed to a relatively enormous extent during the past two decades. In the period just preceding the publica- tion of the first edition, the subject of the constitution of steel was the battle- ground of several opposing theories ; the basic principles underlying the heat treatment of steel were not thoroughly appreciated or even understood, and the knowledge of alloy steels was to a considerable extent confused, largely as a result of the fact that the necessity for their correct heat treatment was not realised.This state of affairs has changed considerably during the last twenty years ; thus heat treatment has acquired to a great extent a scientific basis, while careful experimental work has taught us much concerning the constitution of steel and the properties of alloy steels. On turning to the chapters in Volume I. dealing with these subjects, one finds that in dealing with Heat Treatment, for example, a great deal of space is taken up with accounts of investigations which were carried out before the principles underlying the subject were understood. While such investigations are of interest to a student who wishes to trace the gradual development of the science of steel metallurgy, they are of doubtful value to the engineer who wishes to know how steel should be treated and why ; incidentally if he knows anything about the subject at all he will recognise that some of the conclusions then reached are quite opposed to fact, and yet these conclusions are still printed in full without any comment I In the same way, in the metallographical portions, there are detailed accounts given of how several pioneers in the subject prepared theirREVIEWS OF BOOKS 943 microsections at a time when the commercial production of polishing materials had not commenced, while on the other hand such matters, surely of greater importance, as sulphur prints, Humphrey’s method of macroetching and contact printing and Howe’s acid etching to develop the macrostructure are apparently ignored. Again there are several pages given to expositions of the older theories on the constitution of steel, theories now either abandoned or very con- siderably modified, while the more recent developments, as for example X-ray investigations and the effect of such on the theoretical side, are practically ignored. With regard to alloy steels, the busy engineer who is interested in such steels for motor or zero purposes will find pages of matter dealing with early investigations, much of which is only of slight interest to him, but he will not find much information to guide him in the selection of different steels for specific purposes ; such informatior as, for example, would help him to decide whether under given conditions a 3 per cent.nickel steel or a similar steel containing in addition about I per cent.of chromium is the more suitable, or whether he should choose a chrome-vanadium steel in preference to either. ‘‘ Harbord and Hall ” has been such an institution in British ferrous metallurgy that one expects the very best from it, and is therefore the more critical of any shortcomings it may possess. In order that it may retain its premier position, the first volume requires thorough revision in the sense that a number of the chapters should be completely redrafted and rewritten in the light of modern experience and not merely patched up. In this respect the present revision of Volume II., dealing with the Mechanical Treatment of Steel is much more satisfactory than that of its companion volume. A considerable amount of new matter has been incorporated and much of the old redrafted or rewritten.In addition an interesting chapter has been added dealing with the origin and progress of steel manufacture in the principal steelmaking countries together with some ideas as to what is likely to occur in the immediate future. J. H. G. M. Materials and their Application to Engineering Design. By E. A. ALLCUT M.Sc. (Eng.), and E. MILLER. (London, 1924 : C. Griffin & Co., Ltd. Pp. xiii + 519. In the present volume, the authors have endeavoured to deal in a practical manner, for the benefit of the busy engineer who cannot spare time to consult metallurgical papers or treatises, with the variety of metals-both ferrous and non-ferrous-available for engineering use, with their chemical composition and constitution, with the effect on the latter of varying casting conditions, mechanical work and heat-treatment, with the effect of such variations on their mechanical properties and also with the methods used in measuring these properties. A general perusal of the book suggests that the authors have been very successful in their efforts.Their treatment of the subject is clear and logical and there is no doubt that it will be a useful and valuable book to many engineers. A number of minor criticisms could be levelled at some of the details given, for example, some of the temperatures recommended for the heat-treatment of certain grades of steel would not be regarded as the best possible by many steel metallurgists while the authors are likely to confuse the non-metallurgical reader by suggesting that the normal change from austenite to pearlite at the Arl point in steel takes place via martensite, troostite, and sorbite-an idea quite opposed to fact.As a whole, however, such faults as the book exhibits are of a minor character and do not detract to any great extent from its general good qualities. 32s. net.)944 REVIEWS OF BOOKS The Micro-organisms of the Soil. (London, 1923 : Longmans, Green & Co. 17 tables. Price 7s. 6d.) By Sir JOHN RUSSELL, F.R.S., and others. Pp. 188 with 24 diagrams and The subject matter of this work is based on a series of lectures delivered in the Botanical Department at University College, London, and is indeed in the nature of a series of essays characterised by diversity of treatment rather than continuity of narrative : a feature which has the virtues of its defects.As one in the series of Rothamsted Agricultural Monographs the text con- cerns itself chiefly with the investigations there carried out, the work on soil biology elsewhere being for the most part dealt with only in so far as is necessary to a proper appreciation of the Rothamsted results. In the first chapter Sir John Russell gives a brief summary of the develop- ment of the concept of a soil population which concludes with an approximate estimate of the different groups as represented at Kothamsted. From this it would appear that, of the total organic matter in the soil, the soil organisms account for about one quarter per cent., although of this only about a third part is to be attributed to the microscopic flora and fauna.As Sir John justly remarks such numerical data give no idea of the relative importance of the various groups, which depends on their respective demands on the energy supply of the soil and the character and magnitude of the physical and chemical changes they effect. The physico-chemical changes constitute, however, just that aspect concern- ing which least is known but to the elucidation of which Rotharnsted is contribut- ing in no small degree. Mr. Thornton in two admirable chapters on the soil bacteria emphasises this importdnt aspect. Beginning with the dead remains of autotrophic organisms the carbohydrates and nitrogenous compounds respectively form the starting-point of a series of exothermic reactions, mostly oxidations, by which a whole sequence of bacteria derive their energy and a variety of chemical substances are produced.The amount of energy liberated may be small, as in the oxidation of nitrite to nitrate, or large, as in the oxidation of methane to water and carbondioxide.. Not, however, until our knowledge is much more extensive can we hope to estimate the relative importance of the different species as energy transformers. On the more chemical side the problems are sufficiently complex since there must be maintained a delicate balance in a chain of reactions due to different organisms of which the optimal activity is dependent upon conversion of the pro- ducts of their metabolism. Thus the efficiency of azotobacter is dependent on the presence of adequate bases in the soil and, as shown by Mr.Cutler in the chapter on soil protozoa, the frequency of this organism in common with other bacteria is dependent on the infrequency of protozoa. This inter-relation is further illustrated by the increased nitrogen fixation which bacteria exhibit in the presence of soil algae which form the subject of a chapter by Dr. Bristol. Increased acidity of the soil apparently has a depressing influence, alike on bacteria and protozoa, but Dr. Brierly, dealing with the soil fungi, quotes data showing that an increase in acidity of the plating medium from pH5 to pH4-3-4 resulted in the development of nearly double the number of colonies. The general effect of habitat factors is again emphasised by Dr.Imms, who summarises the nature and distribution of the invertebrate soil fauna of manured and unmanured plots at Rothamsted. Both plots show the usual vertical gradient which is so marked a feature of undisturbed soils, in this and otherREVIEWS OF BOOKS 945 respects, but the number of invertebrates in nearly all groups is considerably higher in the manured ground. In the concluding chapter Sir John gives a suggestive outline of the physico- chemical equilibrium of the soil which stresses the need for invest:gations on the r6le of particular organisms and in general their importance in determining soil fertility. When one recalls the disastrous results that have often attended interference by man with the balance of nature amongst the higher organisms, it is scarcely to be wondered at that progress in the control of the soil population is as yet in its infancy.The wonder, when we recall the delicacy and complexity of the balance, merely adumbrated in these pages, is not that we can do so little but that we can do so much, and it is probably no exaggeration to state that this is mainly the outcome of a happy combination of the methods of pure science and technological research. The student who has perused these chapters will find that the (‘ idea of the soil population ’’ has taken definite shape, and it is no small tribute to the various contributors that the impression which they leave is more of the vast field that awaits exploration than of that small part already surveyed. We may add that there are short bibliographies appended to the different sections, that the printing is clear and that the misprints are few.We would, however, express the hope that in future volumes of the series a combined author and subject index will replace the separate indices. The latter practice can only be justified where the number of citations of each class is exceptionally large. E. J. S. Lead : its occurrence in nature, the modes of its extraction, its properties and By J. A. SMYTHE, M0i:ographs on Industrial Chemistry, Edited by Sir EDWARD (London, 1923 : Longmans, Green & Co. uses, with some account of its principal compounds. Ph.D., D.Sc. THORPE, C.B., LL.D., F.R.S. Pp. 343. Price 16s. net.) Dr. Smythe has done a real service in collecting the essential facts regarding the chemistry, metallurgy and technology of lead, and presenting them in a form much more readable than is usually found in books of this kind.Although the treatment of the subject is exceedingly thorough, the author has avoided the common mistake of burying the really valuable truths beneath a dust of worthless details. The book opens with a brief history of the metal, followed by a chapter devoted to the principal ores. It is the third chapter which will most interest the physical ‘chemist. Here the existing knowledge of the chemistry of roasting and smelting is brought together in a compact manner. Although, as the author points out in the preface, our knowledge is far from complete, yet the satisfactory presentation of the information now available is the first step towards the investigation of the points which are still uncertain.Particulars of the equilibrium conditions of the various reversible reactions involved are given, so far as they are known, and the mechanism of the roasting and smelting processes is discussed in a sensible fashion. For instance, in considering the function of lime in lime-roasting, the reader is not encouraged to accept the somewhat fanciful view that calcium plumbate-or perhaps calcium peroxide-acts as an intermediary in the passage of oxygen to the galena. The more probable VOL. XIX-T34946 REVIEWS OF BOOKS explanation suggested is that the lime serves to absorb sulphur dioxide, the pro- duct of the reaction, as well as to prevent the charge from clotting. The description of the metallurgical processes, as well as that of the manufacture of the compounds, is very clear, and is illustrated by good diagrams.Although obsolescent methods are mentioned, more modern processes receive full attention. Numerous tables, showing the composition of the various products at different stages, add to the value of the work as a book of reference, whilst there are numerous references to scientific literature, including recent papers. The only serious omission in the book is the absence of any description of the intricate methods of concentration which serve to separate the lead- minerals of the ores from the accompanying zinc-minerals and gangue. These concentration processes have undergone much more rapid changes during recent years than the smelting proper, and in a new book on lead it is a descrip- tion of the earlier treatment of the ore that is likely to be looked for most eagerly.Perhaps, however, the absence of such a description from the present volume may indicate that Dr. Smythe has in view a separate work on this subject, which would be greatly welcomed. U. R. E. The Genesis of Petroleum. By P. E. SPIELMANN. (London : Ernest Benn, Ltd., 1923. Pp. 72. 5s.) The steadily growing economic importance of petroleum has aroused an increasing interest in the speculations and theories formulated to explain its probable origin and mode of formation. Dr. Spielmann presents in this little volume a summary of Ithe literature published on the subject during the last decade. His critical examination of the material leads him to conclude that there is overwhelming, though not completely unquestioned evidence in favour of the organic and against the inorganic origin of petroleum.He discusses the question of a sufficiency of vegetable and animal matter having been available to account for the existing oil deposits, laying stress on the differences of raw material and conditions of chemical and physical changes, both in sitzr and during migration by which the final composition of the oil, as found in any particular field, is determined. The summary will be found useful by every student of this important subject. R. L. Biomathematics, being the Principles of Mathematics for Students of Biological By W. M. FELDMAN, M.D , B.S., F.R.S.E., with an Introduction (London, 1923 : Charles Griffin & Science.by Sir WILLIAM M. BAYLISS, F.R.S. Co., Ltd. Pp. 398. Price 21s. net.) We have long had text-books in mathematics written specially for physicists, engineers and chemists, but in this book a course of mathematics has for the first time been designed to meet the special needs of biologists and medical men. Both the author and the publishers are to be warmly commended for their enterprise in producing so novel a work. Purists may say that mathematics should be studied as such, without regard to the particular use to which it is to be put. The argument may have some force when addressed to physicists and engineers, for mathematics is the very foundation of their sciences. It is, how- ever, quite irrelevant as applied to the biological sciences, which are only now beginning to emerge from the (6 descriptive ” stage and to become ‘‘ exact,” forREVIEWS OF BOOKS 947 in these days of extreme specialisation it is essential so to shap the mathematical weapon that it may be used by the student of biology with the minimum of effort.Although the book covers almost the whole range of applied mathematics, Dr. Feldman has very wisely begun at the beginning, assuming in his reader only the simplest school-knowledge of arithmetic and algebra. The biological examples adduced under such headings as Simplified Methods in Arithmetic and A Few Points in Algebra and Elementary Trigonometry convince one of the soundness of his method, which may be illustrated by reference to some of his ingenious applications. For example, the use of simple trigonometry is illustrated by calculations on the work performed by muscles ; mensuration by examples dealing with the numbers and surfaces of air cells and bacteria and the mechanism of the tubules of the kidneys ; the compound interest law by the rate of cicatrisation of a wound, the hydrolysis of cane sugar and so forth.The chapter on Functions includes a clearer account of nomography than one usually finds in books on applied mathematics. Some striking biological applications in the chapter on Maxima and Minima are calculations on the growth of infants, the ionisation of protein and the form of blood vessels. The biologist must be something of a physical chemist nowadays ; he cannot understand reaction so important to him as the dissociation of oxyhoemoglobin without a general knowledge of the law of mass action and for that simple calculus is indispensable (In his Introduction Sir William Bayliss points out that the data on which this dissociation formula is based can also be fitted by an adsorption formula.) The last and longest, and in many respects the most complete, chapter in the book is that on Biometrics, or the application of statistical methods to the measurements of variable biological quantities.We have described the book sufficiently to indicate its scope and usefulness. It needs to be added that the exposition throughout is clear and concise and the careful choice of type has made it easy to read. It is a book that no modern student of biology or medicine can afford to ignore, if he wishes to be able to follow the best work of his day. It may here be recalled that the most eminent of our younger physiologists was trained as a mathematician and a physicist. Notes on the Composition of Scientlflc Papers. By the Rt. Hon. Sir T. CLIFFORD ALLBUTT, P.C., K.C.B., M.A., M.D., F.R.S., etc. (Third Edition, London, 1923. Pp. 192. Price 6s.) This is a book which the harassed editor of learned Tramactions would like to be able to present to every author before his paper, having been accepted by a publication committee, has to be put into a form fit for printing. It is gratifying to note that the book has passed into its third edition since it first appeared in 1904, but loose writing and crude, involved modes of expression are still painfully common in scientific papers and, speaking with some personal feeling, we sincerely hope that this book will eventually reach the hands of every worker in science whose ideas or results are intrinsically worthy of publi- cation. Although the author addresses himself primarily to writers of medical papers his advice is of quite general application ; indeed it is not the scientific writer only who can profit by his ripe experience and sage counsel. Lucidity, simplicity, precision, force, are far more fundamental than, although they are inextricably connected with, what is usually understood by ‘‘ style ” ; but whereas style can be attained only by the girted few, these fundamental qualities can be948 REVIEWS OF BOOKS acquired by everybody who has thoughts or knowledge worthy of translating into words. The book is divided into two chapters ; the first dealing with some general principles to be observed in planning and writing a scientific paper, and the second with some detailed rules of word-choosing and sentence-building (that is ‘‘ coinposition ”), the neglect of which tends to obscure and ugly writing. For the rest the reader is advised to ‘‘ converse with great authors, in poetry as well as prose ’’ ; no sounder advice could be given.