686 SCIENCE PROGRESS 



omissions may be referred to. In dealing with the valency of the mercurous atom, 

 no mention is made of Ogg's well-known electro-chemical method. Further, in 

 connection with subvalent atoms Bose's name is omitted, and in the chapter on 

 electro-chemical theories no place is found for Stark's views on the electro- 

 dynamics of the atom. In general the treatment of the subject, especially the 

 electro-chemical aspect, suffers from too brief presentation. It must be recognised 

 that valency has become essentially a physical problem inseparably bound up with 

 the electro-dynamics of the atom. In the reviewer's opinion, therefore, consider- 

 ably more space ought to have been devoted to Rutherford's atom-model and 

 Bohr's extension of it, not because we have yet reached a clear idea of valency on 

 these lines— for as the author very truly remarks, our ideas about valency are in the 

 melting-pot— but because it seems probable that along these lines the ultimate 



explanation of valency is to be found. 



W. C. McC. Lewis. 



The Fixation of Atmospheric Nitrogen. By Joseph Knox, D.Sc, Lecturer 

 on Inorganic Chemistry, Aberdeen University. Chemical Monographs, 

 No. 4, edited by A. C. Cumming, D.Sc. [Pp. vii+ 112, with 7 Illustrations.] 

 (London : Gurney & Jackson, 1914. Price 2s. net.) 



Dr. Cumming has performed a very useful work in undertaking the editorship 

 of the series of Chemical Monographs to which this volume belongs. Each of these 

 monographs deals with one specific theme in a fairly complete manner, and as 

 the volumes are small and inexpensive, they can easily be kept up-to-date by the 

 frequent issue of new editions. 



This plan has everything to commend it from the point of view of professional 

 chemists generally, and especially of technological chemists. 



For advanced and honours students the volumes will save a large amount of 

 time which might otherwise have to be spent in looking up numbers of papers, 

 and, as copious references are included, they will serve as a good groundwork for 

 those engaged in research work. 



The present volume deals with the more important technological processes for 

 the fixation of atmospheric nitrogen, and more especially with the theory on which 

 they are based. The author has rightly confined himself to those processes which 

 are in actual operation, or which show promise of assuming technical importance 

 in the near future. 



Chapter I. deals with fixation through nitric oxide, and gives a very clear 

 explanation of the relative importance of electrical and thermal effects in such 

 processes. The important work of the Haber school in this connection receives 

 the attention which it merits. The Birkland-Eyde, Pauling, and Schronherr 

 processes are described in some detail. Attention is paid to important points, 

 such as the oxidation to nitrogen peroxide, the absorption of the oxides by water 

 and by alkalies, and the yields. In the following chapter, syntheses of atmospheric 

 nitrogen to ammonia and ammonium compounds receive treatment, and here, 

 necessarily, there is extended reference to the brilliant work of Haber. In the 

 final chapter, the author introduces the methods based on the production of 

 metallic cyanides, cyanamides and nitrides, especially Serpek's aluminium nitride 

 process. 



The book is thoroughly interesting, and the author has done full justice to the 

 subject in the space at his disposal. We do not, however, agree with his indis- 

 criminate use of chemical formulas in the text to designate substances. Fig. 2, 





