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quality may be obtained. The present monograph, in which twenty workers of several countries have collaborated, does more than this, as it includes under each metal a full account of such physical and mechanical properties as have been determined with sufficient accuracy, although not always on material of identical purity. This part of the work has been exceedingly well done, and will be found invaluable by metallurgists and by physicists who are working o p the properties of metals. The monograph is weaker on the chemical side. When a preparation is described by an author as, say, 99.97 per cent pure, the statement cannot be accepted without close examination. It is necessary to know the methods of analysis which were used, and the degree of care which was taken to ensure that no impurities were overlooked. With products of such a degree of purity, a direct analytical determination of the principal metal is of no value. It must always be estimated by difference, and any omission to determine an impurity which is actually present leads to a fictitiously high value for the purity. It is only rarely that a satisfactorily full analysis is made. The task has been greatly aided by the recent development of quantitative spectrographic analysis, but even this is limited by the difficulty of preparing standards containing known small quantities of impurities. Also, some of the non-metallic impurities are overlooked by this method, while hydrogen, nitrogen, and oxygen, which may profoundly influence the properties of a metal, are rarely looked for. The problem of “blanks” is the most important factor in such analyses. This side of the subject is rather scantily treated in the present work, in which the statements of authors as to the purity of their metals are accepted rather a t their face value, and the difficulties of analysis are not fully treated. A most interesting, and a t first sight surprising, fact is the very high degree of purity of certain metals now produced industrially. It would be quite impracticable to prepare aluminum in the laboratory of such high purity as the metal electrolytically refined by the A.F.C. process, described here by Gadeau, which contains less than 0.01 per cent of foreign elements. The cost of such a metal is not greatly above that of the commercial product, which has itself steadily risen in quality in recent years. Several other metals, including magnesium, zinc, and cadmium, have reached a similar stage in their industrial preparation. The situation is different in regard to metals of high melting point. No industrial variety of iron is pure enough for exact research, and tedious laboratory methods have t o be used for its purification. The editor of this book, who is now Professor a t Leyden, has been particularly associated with a method for the preparation of the more refractory metals, such as tungsten, thorium, and zirconium, by the thermal dissociation of their halogen compounds; this process has been found t o be widely applicable, and to lend itself well to the production of single crystals. The physical properties of tungsten, in spite of its refractory character, are better known than those of almost any other metal, its importance to the electric lamp industry, with its many well-equipped physical laboratories, being responsible for this. There are still some metals which are hardly obtainable in a satisfactory state for modern research, and in some instances, such as that of beryllium, minute traces of difficultyremovable impurities hamper the investigator. The accounts written and collected by Dr. van Arkel are of the highest value, and this well-printed volume should receive a cordial welcome. C. H. D ~ S C H . Principles of Mineral Dressing. By A. M. GAUDIN. First edition. 554 pp. New York: McGraw-Hill Book Company, Inc., 1939. Price: $5.00.
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This is an excellent classroom text, thoroughly modern, which lays emphasis on principles and minimizes machine descriptions, details of practice, and discussion of auxiliary operations. It comes from the pen of the Professor of Mineral Dressing of the Massachusetts Institute of Technology, who has had some years of experience in teaching this rapidly growing subject. A number of the author’s own sketches and drawings add to the clarity of the expositim. The unique chapter on liberation is illustrated with some of the finest drawings and photographs ever assembled on this important and often neglected subject. Many types of locked particles are pictured. A fine set of flow sheets appears in the very first chapter, serving to tie the whole subject together as an introduction and to create a desire to study the individual unit processes mentioned in the flow sheets. Gravity concentration on tables has been very happily called ‘‘flowing 6lm concentration,” thus creating an immediate picture of the mechanism of the process. Scientific principles are well described, and the mathematics is within easy reach of students. Excellent bibliographies a t the end of each chapter lead one to the more professional papers and to further detail. The very name of the book shows that dressing of ores is only a part of its subject matter and that both coal washing and the dressing of other industrial minerals are included. The book is useful. OLIVERC. RALSTON.
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Lectures o n Osmosis. By F. A. H. SCHREINEMAKEBS. 16 x 25 cm.; 45 figures; x 266 pp. New York: Nordemann Publishing Company, 1938. Price: $7.00. This book presents a summary of the extensive theoretical and practical researches on osmosis carried out in the University of Leyden by Dr. Schreinemakers and his associates. The treatment embraces a great diversity of systems, ranging from simple syetems of binary liquids and a single membrane to highly complex liquid systems involving two or more membranes. Paths representing possible diffusion behavior of each of the components were developed for each of the systems. The various types of concentration changes which might occur during diffusion are given detailed treatment, but no consideration is given to the mechanism of osmosis or to osmotic pressures which might attend the process of diffusion. experimental systems treated include those with aqueous solutions of salts such as sodium chloride, ammonium chloride, or sodium carbonate, of acids such as oxalic, tartaric, succinic, salicylic, phthalic or boric, with membranes such as cellophane, parchment paper, pigs’ bladder, or pigs’ omentum. In addition to these systems for which data are given a large number of imaginary systems were treated in detail. Included in the factors considered were the number and the concentration of the components in the liquids, the presence of hydrous or anhydrous solid phases, the pressure and volume variability, the elasticity of the walls, and the selectivity of the membranes. Each of the different factors was treated as an “osmotic complex,” and the different diffusion possibilities were referred to as “diffusion types.” The justification for such an extensive and detailed treatment of such a diversity of imaginary systems can come only through the fact that the osmotic systems were considered to have permeable, not semipermeable, membranes. Equilibrium conditions would not exist a t any stage of the process of diffusion, and hence thermodynamic treatment could not be employed in the prediction of the diffusion paths of these systems. The main value of the book is that it depicts the multitudinous variety of conditions which may prevail in experiments on diffusion through membranes. I t serves to impress upon one the various changes which may occur in an osmotic system during the process of osmosis. One can, however, have no assurance that any designated “diffusion type” will apply to a given experimental osmotic system.
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