September 15, 192 1] 



NATURE. 



77 



familiar to the student of medicine. In a brief 

 article on dentistry Dr. William Guy pointedly 

 refers to the anatomist Goodsir for his early work 

 on the development of the teeth. 



Section 13, on political economy, is contributed 

 by Prof. Nicholson, who leads up through the 

 labours of Adam Smith's predecessors to Adam 

 Smith himself, the great economic genius of all 

 time, and then discusses the work of later econ- 

 omists, such as Macpherson and M'Culloch. Dr. 

 Drever supplies the articles on psychology and 

 education, sections 14 and 15 respectively, in 

 which David Hume, Dugald Stewart, the brothers 

 Combe, Laurie, and Melville Bell find their appro- 

 priate places. Finally, in section 16, Miss Nora 

 . Milnes describes the social aspects of Sir Robert 

 Philip's anti-tuberculosis dispensary movement 

 and the important part played by Edinburgh 

 authorities in child welfare schemes. 



The whole record of scientific work as presented 

 in these contributions to "Edinburgh's Place in 

 Scientific Progress" is one of which any city 

 may well be proud. The work done in Edinburgh 

 and by Edinburgh men does not stand alone, but 

 is closely linked with the labours of men of science 

 in other lands, and it is one of the merits of the 

 book that these international relations are skilfully 

 touched upon by the several writers. 



The book is illustrated by portraits of Napier, 

 Black, Hutton, Nasmyth, Edward Forbes, 

 Simpson, Lister, Adam Smith, and David Hume. 

 Intended originally as a handbook for the 

 members of the British Association meeting in 

 Edinburgh, it is being published for general circu- 

 lation by Messrs. W. and R. Chambers at the 

 price of 65. net. 



An Electronic Theory of Valency. 



The Electronic Conception of Valence and the 

 Constitution of Benzene. By Prof. H. Shipley 

 Fry. (Monographs on Inorganic and Physical 

 Chemistry.) Pp. xviii-i-300. (London: Long- 

 mans, Green, and Co., 192 1.) 165. net. 

 PROF. FRY bases his conception of valency 

 on Sir J. J. Thomson's interpretation of the 

 bond (without reference to the nature of chemical 

 affinity or to the structure of the atom) as a unit 

 Faraday tube. Such a bond is produced by the 

 transference of an electron from one atom to 

 another. Furthermore, each atom can both lose 

 and gain electrons, or, in other words, can func- 

 tion as possessing positive and negative valency. 



Thus a univalent hydrogen atom may function in 



-t- 

 two ways, as H or H ; a bivalent oxygen atom in 



NO. 2707, VOL. 108] 



+ + -(-- -- 

 three ways, O, O, O; a tervalent atom in four 



ways ; and a quadrivalent atom, such as carbon, 



in five ways. nx' 



On this simple foundation an elaborate s^ysitfeRi >: 



of valency has been built up. It follows from^. 



the above assumption that by the combination of • 



two substances X and Y two compounds may be 



4- - - + 



formed — namely, X — Y and X — Y. These are 



called electronic isomers, or electromers, and may 

 form an equilibrium mixture. How are they dis- 

 tinguished? The author suggests that if water 



is composed of H— OH (though there appears to 



- + 

 be no reason why it should not be H — OH) a 



neg'ative atom or group will attach itself to 



hydrogen, and a positive atom or group to OH. 



In this way the valency of atoms and groups 

 is determined. 



Passing on to part 2 of the work, which deals 

 w'ith aromatic compounds, the electronic formula 

 for benzene is represented as follows : — 



H- 



c- 



HC 

 HC 



CH 



4- - 



CH 



c- 



H- 



Upon this formula the various reactions of 



benzene, its physical and chemical properties, as 



well as those of its homologues and congeners, 



are based. 



It would take up too much space to discuss 



part 2 in detail, and one or two examples must 



suffice. It is clear that where substitution takes 



place a negative atom or group will replace a 



negative H atom. Here a difficulty appears to 



arise, for in the case of substitution by chlorine 



there are two competing atoms in the molecule 

 -t- - 

 CI. CI. This is met by formulating two elec- 



- + -f- - 



tromers, CgHjCl and CgHjCl. The author 



assumes that CI enters the nucleus. It follows, 



then, that CI has to be satisfied with H, in which 



case it is to be presumed that the electromer of 



- + _ 

 hydrogen chloride, HCl, is formed. Similarly 



with nitric acid, which may exist in equilibrium 



as 



HO.NOo" 



HO.NO., 



Here the author gives preference to the first 

 formula, whereby NOo replaces electropositive 

 hydrogen in the nucleus. After making these vari- 

 ous, though not very convincing, assumptions, 



