The electric dipole moments of cis-and trans-azobenzene, two cis-and three trans-azopyridines, and of five azoquinolines have been calculated from measurements of the dielectric constants, specific volumes, and refractive indices of their solutions in pure benzene a t 25.00'. Of the azoquinolines, only the 6,6'-isomer showed any change in its dipole moment after exposure to ultraviolet light. The conformations of the various molecules in solution are discussed.THE electric dipole moments of azobenzene and of the azopyridines have been measured previously. That reported for 4,4'-azopyridine (2.0 D) seems exceptionally high, and merits further investigation, but in any case the results have only been employed in discussing cis-trans isomerism. Equally interesting are the conformations of these molecules, as it is unlikely that either the cis-or the trans-forms are planar in solution. The dipole moments of five azoquinolines have also been measured. Only with the 6,6'isomer did irradiation with ultraviolet (u.v.) light change the dipole moment, indicating a very small conversion of the stable trans-into the less stable cis-form. The U.V. spectra of the compounds in pure ethanol were measured and agreed with published results.3 EXPERIMENTAL AND RESULTSPreparation and Purification of the Azo-compounds.-The dipole moment of each compound Azobenzene. Purified nitrobenzene in methanol was reduced by refluxing with sodiumThe mixture was neutralised, filtered, most of the It was then filtered off, washed The into the cis-isomer by irradiation in glacial acetic acid A Hanovia mercury vapour lamp, placed 25 cm. from the Most of the residual trans-isomer was precipitated with water and filtered The remaining azobenzene was extracted with cold chloroform, washed rapidly with was measured immediately it had been purified.hydroxide and powdered zinc for 12 hr. methanol distilled off, and the compound allowed to crystallise. well with water, and warmed with dilute hydrochloric acid to remove occluded zinc salts. trans-azobenzene was washed, dried, and recrystallised from ethanol to constant m. p. (69"). solution with U.V. light for 6 hr. solution, was used. off. trans-Azobenzene was converted

The electric dipole moments of eight nitrophenylpyridines have been calculated from measurements of the dielectric constants, specific volumes, and refractive indices of their solutions in pure benzene a t 25-00'. In the para-and meta-isomers the planes of the pyridine and benzene rings are probably inclined a t about 40', but this angle is greater in o-nitrophenylpyridines. The 2-m-, 3-m-, and 3-o-nitrophenylpyridines favour a transconformation but in the 2-o-isomer a cis-configuration is preferred.THE electric dipole moments of phenylpyridines and of some phenyl-substituted 2-phenylpyridines have been considered previously. These molecules are not planar, and in many phenyl-substituted phenylpyridines the substituent can have a cis-or a trans-configuration with respect to the pyridine nitrogen atom. Information concerning conjugation between the pyridine and benzene rings in nitrophenylpyridines, analysed in relation to nitrobenzene and pyridine, is provided by the dipole moments; further information on the extent of conjugation is furnished by the ultraviolet (u.v.) spectra of these compounds.EXPERIMENTAL AND RESULTSPreparation and PuriBcation of Nitropheny1pyridines.-The dipole moment of each compound was measured immediately it had been purified and its infrared (i.r.) and U.V. spectra recorded.The compounds were prepared by the method of Haworth, Heilbron, and Hey,3 in which a diazotised nitroaniline is decomposed in the presence of pyridjne.

Like the author's previous book, "Rapid Methods of Trace Analysis for Geochemical Application," the present work is intended as a practical handbook for those engaged in the analysis of geochemical exploration samples. Its contents reflect the extensive replacement of colorimetric by instrumental methods that has taken place over the 10 years between the publication dates of the two works. Thus, chapters on atomic-absorption spectrophotometry, X-ray fluorescence spectrometry and emission spectrography haw: been included, while colorimetric methods are retained only for bismuth, boron, molybdenum, palladium, platinum, thorium, tin, tungsten and vanadium. Further sections deal with the statistical control of analysis, reagents and coldextraction methods.Presumably the new work is not intended to be read in conjunction with the old, yet some important omissions might lead one to conclude that this was so. In the first chapter, the statistical control of analysis using the statistical series approach is presented in a concise and updated form, yet in the second chapter, on reagents, the list is so brief and selective as to appear complementary to that in the 1966 book. Furither, in the volume under review, no methods of any kind are offered for the important elements chromium, phosphorus, niobium and uranium, save for a mention of a spectrographic detection limit for chromium.The third chapter, on colorimetric methods, includes procedures for the determination of boron, palladium and platinum combined, and thorium, which did not appear in the earlier work, and the other methods have been updated. In view of discussion in the literature of the inadequacy of potassium hydrogen sulphate fusion for the dissolution of molybdenum in certain mineralogical forms, an alkaline fusion procedure might profitably have been included here. Cold-extraction methods are dealt with in the fourth chapter arid here the "handbook" style appears somewhat restrictive. The section would have been improved by some discussion of the particular mineral species dissolved by the recommended reagents.The selection of elements is sound and no exaggerated claims are made. In contrast to the chapter on colorimetric methods, the choice of suitable concentrations for calibration solutions is left to the user. Methods of analysis by X-ray fluorescence for arsenic, selenium, tellurium, bismuth, gold, palladium and platinum are outlined in Chapter 6. Chemical pre-concentration procedures are used in every instance so that a simple instrumental procedure can be used. This approach has certain advantages, although the potential multi-element capability of the technique is sacrificed.It is doubtful whether the final chapter, in which an attempt is made to deal with emission spectrography and direct-reading spectrometry in less than 6 pages, should have been included in such an essentially practical work, Certainly the claim on the back cover that "a technician with no detailed knowledge of the analytical processes involved can readily follow the directions" ...

This book is an interesting combination of chemistry and microbiology and is published a t a time when chemical techniques are being used more and more in the biological sciences. Sufficient microbiology is included to allow the chemist to appreciate the inherent difficulties of analysing biological materials, and sufficient chemistry is included to allow the microbiologist to appreciate and understand the principles of gas chromatography. Thus, the volume will serve as a practical guide for the microbiologist using this chemical technique and for the chemist confronted with biological samples.The book is logically written, beginning with a detailed account of the theory of gas chromatography. Descriptions of the various components of gas chromatographs are included, together with details of the most appropriate system to use for particular types of applications. The author then concentrates on the applications of the technique, with chapters on the analysis of fermentation products, the detection of microorganisms and the analysis of metabolites. The growth and metabolism of microorganisms is described with detailed methods for the analysis of neutral, basic and acidic fermentation end-products together with headspace gas analysis and the identification of anaerobes. The advantages of gas chromatography over the classical microbiological procedures for the detection of microbes are promulgated and the development of the methods used in lunar and planetary exploration described. Methods are then detailed for the analysis of food samples and clinical specimens such as cerebrospinal fluid, urine, blood, serum, pleural effusions and pus. The fourth chapter describes the chemistry of microbial cells, the fractionation of cells and the subsequent analysis of cellular components such as lipids, proteins, nucleic acids, polysaccharides, teichoic acids and peptidoglycans. Methods for the analysis of specific metabolites, intermediates and specific enzymes are also described, together with applications particularly appropriate to industry. The latter include the analysis of alcoholic beverages such as beer and wine, various dairy products, fish, vaccines, antibiotics and mycotoxins.

The first of the above booklets contains four methods. Determination of alkalinity in the range 20-1 000 mg 1-1 as CaCO, by titration with standard acid to p H 8 . 3 and 4.5 using visual or instrumental end-point detection. Phenolphthalein is retained for the first end-point but a bromocresol greenmethyl red mixed indicator is recommended, after statistical evaluation of alternatives, for the pH 4.5 end-point. A continuous-flow automated method is also given that uses methyl orange as indicator. For alkalinities between 0.47 and 20 mg 1-1 as CaCO,, an instrumental method is given that involves titration with standard acid successively to p H 4.5 and 4.2 and determination of the true equivalence point using a Gran plot type procedure. A method for the determination of acidity in polluted waters and certain trade effluents is given in a fourth procedure, which involves titration with standard sodium hydroxide solution to p H 4.5 using instrumental end-point detection. A spectrophotometric method for hydrazine is described in the second booklet. The reagent used is p-dimethylaminobenzaldehyde and the method is intended for the determination of 1.0-100 pg 1-1 of hydrazine in clean waters such as boiler water. As usual, both of these publications are extremely informative and well prepared and will be essential for routine water laboratories involved in the relevant determinations. J. M. OTTAWAY EDUCATION AND TEACHING IN ANALYTICAL CHEMISTRY. By G. E . BAIULESCU, C. PATROESCU and R. A. CHALMERS. Ellis Hvvwood Sevies in Analytical Chemistry. Pp. 190. Ellis Horwood (distributed by J . Wiley). 1982. Price L15. ISUX 0 85312 384 5 (Ellis Horwood); ISBN 0 470 27283 X (Halsted Press).