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tions. This is indeed a sound and escellent textbook of chemical engineering thermodynamics. CHARLES A . ~ I A N N . T’alency, Clnssical and 3 f o d e r n . By IT. G . P.II.AII~;R. 1 2 x 2 2 cm.; xf 2-42 pp. Cambridge (England) : Cambridge L-niversity Prcss, 1944. Price : 10!/6. There is undoubtedly scope a t the present time for another book on valency. The substantial advances which have been made in the last ten years already have an iniportaiit hearing on many branches of chemistry, and, although the subject has by no means reached a “stationary state”-it is, of course, still developing steadily-many chemists, industrial and academic, undergraduate and postgraduate, nil1 mlcome the opportunity of taking stock of the present state of knoir-ledge. Dr. Palmer’s monograph, which is of medium size, will therefore meet a wide demand. It differs from the Tvell-knon-n pioneering testbooks of Sidgvick anti l’auling on the one hand and from elementary introductions such as Speakman’s small book on the other, in being essentially a concise review of the n-hole field of valency theory a t its present stage. The treatment is original. The first two chapters deal n.itli the early history of the valency concept and the development of the periodic classification. (’liapter 111, which o+ cupies nearly a third of the entire book, consists of a summary of the valency behavior of the elements as revealed by direct chemical and physical evidence. I n this section no theories are used except the siniple “classical” ideas of single and double bonds, steric arrangement, and ionic and covalent binding, but the full weight of modern experimental methods (x-ray crystallography, electron diffraction, dipole monients, spectroscopy, et?.) is brought t o bear on the problem. The chapter is therefore a notable survey of recent, drvelopments in pure inorganic chemistry, and would be valuable on that account alone. Chapter IV introduces-unfortunately, in a rather superficial manner--the electronic spin theory of valency. the idea of resonance hybrids, and the isoelectronic principle. With this basis, the probable valency structure of a number of compounds forincd betxveen firstrow elements is then deduced, and the chapter concludes v i t h a short section o n the stereochemistry of the light elements. (“hapters V and VI are of an advanced standard. In the fornicr the s11iiitheory is cstcnded t o the Periodic Table generally, and the latter deals briefiy n-it’hsonic spcc.i:il topics including coordination compounds, the method of molecular orbitals, aromatic suhstitution, single-electron bonds, and “proton” bonds. The book thus provides a very useful, though sonie\vhat uncritical, summary of the modern developments. It Tvould form an excellent outlinc for a postgraduate coursc, but is not very suitable for a beginner n h o needs a lucid exposition of the subject, because it is too highly concentrated in style and matter t o be either easy t o read, o r , by itself, wholly comprehensible. To quote but one example : the rboncept of rf’sonanee hybrids, which is sucli a characteristic and significant feature of thc nen-cr electronic theory as contrasted t o the old, is explained sketchily in little more than b o short p : i g ~ s - .surely too hrief a treatineiit t o give the student any r e d understanding of reson:inrc. In f a r t , the t)ook needs supplementing a t evcry stage by \vide reading. l’erhaps I his \\’:is the aiit,hor’s intention, as he has provided ainple referenres to testbooks and original papers throughout. S e v e r t,heless, i n the reviewer’s opinion, the book \voultl be vastly improvcd if, in a future cditiori when paper shortage is past, the supersaturated t e s t could be diluted with an equal volume of explanatory matter. The successful production of a textbook of this ltind under difficult war-time conditions is a remarkable achievement on the part of both the author and the puhlishers. The quality is very good for the present time and the price reasonably low. J. .I. KITCFIENER.
