information is available on ternary mixtures; insufficient for practical needs even in the case of axygen-nitrogen-argon. The reviewer regrets that no reference is made to the fundamental contributions made by M. Ponchon (Tech. Modeme, 13, 20 (1921)) and by R. Sevarit (A1-ts et Metiws, 65, 142, 168, 241, 266, 307 (1922)) introducing the use of the enthalpy-concentrs- tion diagram for the exact and complete treatment of the problem of separation by distillation of binary mixtures. The use of Ponchon's diagram is presented, however, for the case of nitrogeu- oxygen mixtures.

The treatment of irreversible processes as related to air sepa- ration has been modified and extended. This notoriously in- efficient process well deserves continued consideration.

While the author oonfmes his presentation by intention to an exposition of theory and principles, it is gratiiying to find in the section on heat-e&an&rs a brief sketch pertaining to the modern theory of heat transfer, a subject a t the heart of plant desien for distillation orocesses. Sustained advance in this fieldhas taken place in the United States during the past twenty years although the theoretical foundations were laid in England and Germany.

Rare gas separation, a subject of importance in view of the expanding uses ta which these gases are being put, is treated in more detail in the new edition.

The separation of "cracker" gas advanced under the stimulus of war requirements and Chapters XI and XI1 have been ex- panded and rewritten to cover the separation of gases from coal as well a s oil. Descriotions of the newer olant desims are - included.

The author is to be congratulated for a revised edition of a very useful and needed book.

FREDERICK G. KEYES

0 AN INTRODUCTION TO MOLECULAR SPECTRA

R. C. lohnson, Master of Queen's College, University of Mel- bourne. Pitman Publishing Corp., New York, 1949. (Printed in Great Britain by Richard Clay and Co., Ltd., Bungay, Suffolk.) xiii + 296 pp. 8 plates. 151 figs. 14.5 X 22.5 cm. $7.50.

IT IS difficult to judge a text written for student use in another country without su understanding of the pedagogical problems in- volved there. The present introduction to molecular spectra attempts "to provide a textbook for the student who has gradu- ated in physics or chemistry or who is approaching graduation and desires an understanding of the subject with the limits of ordinary msthematical equipment a t that stage."

The suhieot is "introduced" bv an examination of exoerimental ~~~~ ~~~ .~~~ ~

spwm of eonsidrrnblr vomplexity, inrluding rases of &in and uf _\ douLliug (pagc 2;). It suuld appcnr bcrrrr ro intn~duvr the subject nith rhr m:lrerinl of Chapter \'I, pagc SO, whvra qu;rnturu numbers, electronic configuration and states, and dection rules are considered.

The major part of the text is concerned with the experimental details of selected band soectra. The details are rather com- pletely reproduced from ohgina~ sources, and are shown in many excellent tables and figures. The selected cases are well chosen. The empirical analysis of the spectra by fitting to formulas and curves is emphasized.

There appears throughout the text, however, a tendency to avoid not only mathematics (as the author apparently intended), but also discussion of the fundamental physical principles in- volved. I t would not take much mechanics, and very little group theory, to make clear the meaning of quantum uum- hers, symmetry properties, and selection rules. I t is indeed diffi- cult to believe that the suhject can be understood at all without this, and instead the subject will continue to appear to the stu- dent as a oollection of empirical facts and the spectra as compli-

This lack of physical theory is especially felt in the treatment of polyatomic molecules, which occupies the last third of the text. Some complex subjects are discussed here such as the rotational levels of the asymmetric top and the Raman effect, which again can hardly be understood by a student without more theoretical background than is presented in the text.

The principal utility of this book appears to lie in the numerous and well-chosen examples of data, which may save trips to a li- brary. It may also stimulate s thoughtful student to acquire a proper background in theory, after which he msy return to a more profitable study of the material of this text.

0 THE HFTFROCYCLIC DERIVATIVES OF PHOS PHORUS. ARSENIC. ANTIMONY. BISMUTH. AND

Frederick George Monn, Cambridge University. England. Arnold Weisissberger, Consulting Editor of the series, The Chemis- try of Heterocyclic Compounds. Interscience Publishers, New York, 1950. ix + 180 pp. 16 X 23.5 cm. $4.20 for sub- scribers to series; $5.25 for nonsubscribers.

Tms is the first volume in a. series of monographs whidh are to be devoted to the presentation of heterocyclic chemistry. Each volume will be prepared by an expert and there are now olanned some 28 monoeraohs in all. .~ ~

~ ~ ~- ~.~ .\lthough the authors lhopc t l~e series will Ire i w & r ~ r aud wm-

prclwnsive, no attempt ir being rltade to list hl. cuntpuull and their derivatives bur ruher 111 : h m importunt fur tla-ir chemis- try or use.

This the first of the series treats of P, As, Sb, Bi, and Si; each chapter giving the chemistry, properties, and brief preparation description of the most important ring structures of each ele- ment. onlv those rine structures includine carbon are considered.

physiological and industrial applications

ELASTOMERS AND PLASTOMERS. VOL. I

Edited by R Houwink, External Lecturer, Technical University, Delft, Netherlands. Elsevier Publishing Co., Inc., 1950. xiv + 495 pp. 318 figs. 93 tables. 18 X 26 cm. $7.

TKIS book is the third sectional volume of major volume No. 3 in a Polymer Series of eight, and is the third one of the three to be published. The other two have already been reviewed in these columns (Vol. 26,,p. 624; Vol. 27, p. 109). Like its predecessors it is an intcrnet~onal undertaking, but i t is predominantly a Netherlands book since 58.5 per cent of the pages are by authors in the Netherlands, 22.6 per cent by American authors, 9.6 by English authors, and 9.2 by a French author. Each of the three volumes is written by a different group of authors.

The previous (second) volume covers 'LManufacture, Proper- ties and Applications," but contains a considerable amount of theoretical discussion, and this volume, although on "general theory," contains a fair amount of preotioal material, one chapter being on Mechanical Properties and another on Mechanical Operations. The additional material of an opposite nature in each case is, however, helpful because it makes that particular volume more complete in its treatment, even though not in arcord with the title.

The theoretical treatment of the subiect varies. of course. with the authors. hut it is eenerallv cornole& and nd<done. here is . ~ ~~ ~~~~~

tm nI,unhuee of wivrrrrcp< wI.i< h :m xdvnnrngeously plncod 3t the eud ofexlt ch:tptvr. 110 n w 4 caves t b ~ s r~rm.1 mro 1948; in ested arrangements of lines