text for such students would discuss these topics fully and simply; such a text has in effect been incorporated into West and Todd's "Textbook of Biochemistry" but there would appear to be a need for some independent textbooks of the same general nature. The present book, by attempting to cover too muoh in too little Bpace, has made much of the coverage rather thin. Less than one page, for example, is devoted to the Joule-Thomson effect; everyone knows that the sverage student requires much careful explanation, repeated severel times, before he understands this phenomenon. The attempt to "close pack" the material has also made the treatment episodic and unexciting. The author mentions the fact that large crystals grow a t the expense of small ones when both are in contact with the mother liquor; when this behavior is explained in terms of solubilities and equilibrium the student is always intrigued, but the author bas no space for this. Many features of the book are excellent. The observation that the capacity of a buffer is not necessarily the same toward both acids and bases is a step in the right direction, as is the paragraph on buffering action provided by the escape of CO* in the titration of bicarbonate. The composite neutralization curve (Fig. 38, p. 238) is valuable. One must applaud the author's statement in the preface that "physical chemistry is concerned with explaining. the attitude of the student should be one of seeking to understand. . . ." I t is unfortunate that this hook is not a greater help in achieving that goal.
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PETER OESPER H*HNEMANN MEDICAL COLLEGE PHIL*DELP"I*, PENNBYLV*",*
ORGANO-METALLIC COMPOUNDS
G. E. Coates, Professor of Chemistry, University of Durham. Methuen & Co., Ltd., London; John Wiley & Sons, Inc., 197 pp. 7 New York, 1956. viii figs. 10 tables. 13 X 19 cm. $2.50.
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WITH the increasingly rapid growth of the chemical literature, the practicing chemist is more and more dependent upon reviews of specific areas of hisscianee to keep abreast of developmente and, mare particularly, to utilize developments outside his o m area of major interest to help him advance his own investigations. I t is most pleasing to find a. small book writ ten by an active investigator which summarizes so well the present state of knowledge in a. wide area of ohemistry, leads the uninitiated easily into the literature of that ares, and, a t the same time, presents the material so effectively that the reader finds himself adapting many items to his own needs or contemplating how a gap in the literature may be filled. Further, if such a book is made available a t such aprice that nu oneinterestedin the subject can afford to be without it, the net result is near perfection. Professor Coates is to be heartily congratulated for the excellent quality of his book.
teachers as it should be. Most of the molyhdenum used in the past has been as an alloying agent in steel. An important, hut tonnage-wise minor role, has been played by molybdenum in the metallic components of electronic tubes. Now molybdenum has possibilities of use in other high temperature applications. Pure molybdenum is brittle a t room temperature. When it is heated to about 250°F. it can be "warm-rolled" into sheet or d r a m into wire. Molybdenum bas a very high melting point (2622-C.) and has high strength and rigidity at elevated temperatures. For this reason, it has been used for s. long time for heating elements in furnaces that are capable of operating at 2000' to 2200°C. Induction furnaces, in which a cylinder of molybdenum serves as the susceptor, may reach even higher temperatures. Such heating elements, of course, must be protected by vacuum or inert atmospheres and must be kept out of contact with ceramic parts with which a reaction might occur. In the past molyhdenum has usually been worked by powder metallurgical techniques. Westinghouse has evolved a low temperature sintering process, utilizing an atmosphere of moist hydrogen, which effects consolidation of a ton of molybdenum powder to a solid mass which may be swaged, forged, rolled, and d r a m into wire or sheet having large dimensions. Arc melting has also permitted the production of massive molybdenum bar stock. Methods of joining molybdenum have also been evolved. In the technology of molybdenum, thus, many difficulties have been overcome, and the hope that this very promising metal will be able to meet the demands for engineering materials for high temperature service are based upon increasingly reliable information. Unfortunately, molybedenurn still suf fers from two serious defects. I t is readily embrittled and it has low oxidation resistance. A great deal of money has been spent since World War I1 on research to circumvent these defects by one way or another. Protective coating materials, like molybdenum disilicide (MoSid (formed by heating Mo wire while emW. CONARD FERNELIUS bedded in metallic silicon in & flowing I.vonc*arc C n r ~ m ~ n L r~ s o ~ ~ ~ o n r atmosphere of hydrogen saturated with Oxrono. E a o ~ m o hydrogen chloride), afford some protection to temperatures as high as 1700°C. For example, such a coating 0.025 mm. thick completely ~rotecteda molybdenum METALLURGY OF THE RARER METALS. wire for over 4000 hours in sir at 100O0C., NUMBER 5: MOLYBDENUM snd far over 30 hours at 1700°C. Several other coatings have been investigated and L. Northcott, Fort Halstead, England. some are so promising that there is hope of Academic Press, Inc., New York, and producing a coating that will make it Buttarworths Scientific Publications, Lonpossible to use molybednum as an en222 pp. 104 figs. don, 1956. xii gineering material for high temperature and tables. 14.5 X 22 om. $6.80. applications. Molybdenum alloys of promPREVIOUSvolumes in this series have ise have also been developed. been reviewed earlier in THIS JOURNAL The present volume revie~vsall these (31, 670 (1954); 32, 651 (1955); 33, developments in an honest and forthright A340 (1956)). Esch volume has been manner. The greatest emphasis is on written by an expert in his subject and is physical metallurgy. There is little inas completely up to date s t the time of formation about the chemistry of molybpublication as it is possible to be; in this denum, except as it affects its mechanical instance, as late as 1055. As with the behavior and ultimate high temperature elements covered in previous volumes applications. Pievertheless, like the rest (Cr, Zr, Mn, and Ti), the element molybdenum is not so familiar to chemistry The nature af the book is adequately expressed in the Preface. "So far as this hook is concerned, organo-metallic compounds are substances containing metalcarbon bonds; these are generally eavtllent but may occasionally be ionic as in some of the alkali metal compounds. This definition excludes metal alkoxidrs and many other interesting compounds in which metal atoms are bonded to organic systems via oxygen, nitrogen or sulfur; thus classes of coordination and chelate compounds and the large number of organic eompounds so useful for analytical purposes are also escluded." A d e scription of the very extensive organic chemistry of sulfur, phosphorus, and arsenic is omitted since they are hardly metallic elements. "Organa-metallic compounds are often of great value for s,ynthetic purposes, and they hsve frequently provided problems of interest in connection with valence theory. Indeed, it is probable that the study of organo-metallic compounds, together with that of aromatic systems and the boron hydrides, has provided some of the major stimuli for recent developments in valence theory. This book, however, has neen written with particular attention to prepamtive aspects and, although there has been no at,tempt to make references exhaustive, tho reader is likely to find reference to recent and satisfactory preparative metbods for many of the compounds described. Although the lend may soon he lost, preparat,ive chemistry still appears to be ahead of theoretical chemistry; for example, the remarkable q&pentadienyls were prepared before predicted." Suffice it to say that, in this reviewer's opinion, the high quality of the baok amply justifies the limitations which Professor Coates placed upon himself. The product gives every indication of sound scholarship and high quality workmanship. Only one typographical error came to light on a complete reading of the book and only one omission which should hsve been included: i.e., no mention of the B-diketone derivatives of the dialkyltin radical. The baok is recommended highly.
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JOURNAL OF CHEMICAL EDUCATION
