Bibliography

B. V. Il’in. The Nature of Adsorption Forces, Gostekhizdat, 1952, p. 124, price 4 rubles 70 kopecks.

The theory of adsorption constitutes one of the important chapters of the modern science of the structure of matter. Adsorption phenomena are of interest to the physicist both in themselves and because in them the character of the molecular forces acting between the surface of the adsorbent and the adsorbed substance is manifested very clearly; thus the study of adsorption forces opens the way to the investigation of molecular forces in general. Adsorption phenomena are of interest to the chemist, for adsorption of foreign gases on crystals affects the properties of the latter, and adsorption of reacting molecules on the surface of a catalyst is an inevitable stage in many, if not all, heterogeneous reactions. Finally, adsorption phenomena are of interest to the engineer concerned with various kinds of disperse systems. Thus, in the theory of adsorption the interests of representatives of the most diverse specialties are interwoven.

At the present time the problem of adsorption forces has acquired special urgency in connection with the investigation of elementary processes occurring on the surface of a solid body (the work of A. N. Terenin, V. E. Lashkarev, F. F. Volkenshtein, and others). Understanding the nature of these processes proves necessary for the successful development of a number of branches of physics and chemistry (the theory of heterogeneous catalysis, the physics of semiconductor rectifiers, the theory of corrosion, etc.). At the same time, up to now our literature has not had a fully modern and sufficiently complete exposition of the microscopic theory of adsorption forces. Yet the need for such a review is very great. Therefore the publication of B. V. Il’in’s book The Nature of Adsorption Forces should be regarded as very timely. The appearance of this work is all the more gratifying because it belongs to a scholar who himself has made a major contribution to the science of adsorption. Unfortunately, the author confines himself only to physical adsorption on nonporous adsorbent dielectrics, leaving aside the large and important field of chemisorption, the study of which has recently aroused considerable interest. Thus the coverage of adsorption problems in the book under review cannot be considered sufficiently complete. However, what it does contain is presented with great clarity and precision and deserves the most serious attention.

The first chapter of the book is devoted to a general characterization of the problem. In its first paragraph the problem of investigating the nature of molecular (in particular, adsorption) forces is clearly posed as one of the central tasks of modern physics and chemistry; a definition of the term “adsorption” itself is then given; finally, attention is drawn to a number of sometimes very varied—

related phenomena, the investigation of which in the final analysis inevitably reduces to the problem of adsorption forces.

The next paragraph gives a survey of the historical development of the theory of adsorption forces in connection with the development of the doctrine of intermolecular forces in general. Having subjected to convincing criticism the attempts to reduce adsorption forces solely to the effect of electrical images (thereby completely excluding the influence of the specificity of the adsorbent), the author proceeds to a consideration of the electronic theory of adsorption of B. V. Il’in, V. K. Semenchenko, and V. V. Tarasov, in which the nature of the adsorbent is taken into account to a proper degree. The basic ideas of the modern theory of intermolecular forces (in particular, adsorption forces) are then briefly formulated. Despite the extreme brevity (the whole paragraph occupies only 20 pages of small format), the clarity of the exposition suffers not at all, and this entire chapter should be considered quite successful.

In the second chapter, in detail and with all computational particulars, the modern views on the nature of the forces of physical adsorption are considered. After an exposition of the basic results of investigations of the electrical properties of molecules (which is necessary for understanding what follows), all three components of the adsorption energy are examined successively: electrostatic, repulsive, and dispersion. No special objections can be raised to the quality of the exposition. Particularly valuable, in the reviewer’s opinion, is the fact that the author does not for a moment lose sight of the connection between the questions under consideration and the general problem of molecular forces. This makes the book under review useful not only for persons engaged specifically in adsorption problems, but also, in general, for all who, for one reason or another, are interested in the present state of the question of the forces acting between molecules. It is also pleasant to note the “physical” character of the exposition, which favorably distinguishes B. V. Il’in’s work from a number of foreign works in which, behind the mathematical “forest,” the essence of the matter is not always visible. The only serious critical remark that may be made is the following: it is very probable that the division of the total adsorption energy into three components, each of which has an independent physical meaning, is possible only in a certain (though, apparently, rather good) approximation and therefore does not exactly reflect the true state of things. This circumstance is not given due elucidation in the book. It is true that it should be borne in mind that the present state of the question is not yet such that any definite concrete judgments on this matter could be expressed.

The last, third chapter contains an application of the developed general theory to various concrete problems of adsorption and wetting. Here, first of all, the basic thermodynamic relations between the various quantities characterizing an adsorption system are presented; these relations must always be taken into account when comparing the results of theory with experiment. The basic methods for measuring heats and isotherms of adsorption are then briefly described.

The next paragraph is devoted to the adsorption of polar molecules on ionic crystals, and also to the wetting of ionic crystals by polar liquids. As the author shows, “classical” electrostatic forces play the principal role in this case. This paragraph, based to a considerable extent on the results of the author’s own investigations and those of his collaborators, is, in the reviewer’s opinion, of the greatest interest in the book. Here both the theoretical questions concerning the calculation of the adsorption energy and the methods of comparison with experiment are examined in sufficient detail and clarity. The quite convincing considerations, expressed as early as 1934, by the author concerning the significance of the porosity of the adsorbent and the uncertainty in the велич-

…of the adsorbent surface introduced by this factor. The paragraph contains extensive experimental material which, on the whole, agrees well with the theoretical predictions (to the extent that the approximate theoretical formulas used have any quantitative meaning at all; in this connection it should be noted that the book always specifies the assumptions under which a given relation is derived). All the questions touched upon are considered by the author not as a set of particular, mutually unrelated problems, but in connection with a new direction in crystal physics—crystal-physicochemical aspects.

In the last paragraph, adsorption of nonpolar gases on ionic crystals is considered, where the main role is played by dispersion forces. Here Opp’s calculations concerning the computation of the various components of the adsorption energy are set forth clearly and in detail (the results are carried through to specific numerical values). As the author indicates, he set himself the task of illustrating carefully the approximations used here by calculation methods. This aim should undoubtedly be regarded as achieved. However, perhaps it would have been worthwhile to emphasize more sharply the crude physical assumptions used in Opp’s work, which to a considerable degree render pointless the scrupulous calculations he carried out (the mathematical method itself, of course, is not under discussion).

Of great interest is the “Conclusion,” in which an instructive comparison is made between the history of the doctrine of adsorption and the development of crystallography, and a number of urgent problems in the physics of adsorption processes are also posed.

In assessing the book as a whole, one should first of all say that its content is at once broader and narrower than its title. Broader—because, having studied it, the reader will gain an idea not only of the theory of adsorption forces, but also of the nature of intermolecular forces in general. Narrower—because only the field of physical adsorption is examined, whereas the study of chemisorption is now apparently no less topical. This circumstance, however, in no way prevents the book under review from being a valuable contribution to Soviet scientific literature, useful to all who are engaged, or will be engaged, in this range of questions. At the same time, the question of compiling a comprehensive manual that would fully and thoroughly encompass all the problems connected with the theory of adsorption forces and reflect the contemporary state of affairs is by no means removed. One would hope that the book under review will serve merely as an excellent outline of this large and necessary work.

V. Bonch-Bruevich