820 



NATURE 



[Deckmber 8, 192 



suspect that Sir Joseph Thonwm has abandoned an 

 earlier intention of assigning to the molecule of this 

 element a confiirtiration not unlike that of the atom of 

 an inert gas. 



The method 01 posilivi- ray analysis, whi( h originally 

 we owe to the author's giiiius, lias given many results 

 which scarcely admit of misinterpretation, a virtue 

 not always conspicuous in the conclusions derived from 

 other metliods of investigation of atoms and molecules. 

 Chemists will therefore turn eagerly to those pages 

 in which Sir Joseph Thomson explains how positive 

 i.i\> throw light upon the chemical propcrtii > ct the 

 elements. 



Highly interesting and suggestive, too, are those 

 sections of the work which treat of polar molecules 

 and their importance in connexion with chemical re- 

 activity, as, for example, the explosiveness of certain 

 gas mixtures and the inertness of certain carefully 

 dried systems such as those included in the classical 

 experiments of H. B. Dixon and of H. B. Baker. These 

 ideas on polarity are extended to explain electrolytic 

 dissociation in solutions, the formation of the double 

 layer, and the principle of the Armstrong hydroelectric 

 machine, to mention only a few applications. 



The conditions which give rise to the development 

 of electrical polarity in a molecule are treated from an 

 elementar)- point of view, and the principles are used 

 to explain the varying acidness of hydroxylic com- 

 pounds and substitution in hydrocarbons and their 

 halogen derivatives. 



Residual affinity, active molecules, Werner's co- 

 ordination numbers, production of light during chemical 

 change, magnetic characters of elements and com- 

 pounds, and of oxygen in particular, are also considered. 

 Nor does Sir Joseph Thomson omit discussion of Thiele's 

 theory of conjugation and related questions ; but the 

 applications of his views to organic chemistry have 

 undergone some modification since the book was 

 written, as comparison with his recent contribution 

 to the Philosophical Magazine will show. 



The electronic theory of solids occupies the last 

 chapter of the work, and as this involves the treatment 

 of crystal structure, compressibilities of metals and 

 other elements, surface tension, intermetallic com- 

 pounds and mixed crystals, it will make a special appeal 

 to chemists and metallurgists who can think in three 

 dimensions, and there is much of interest for others. 



The text is freely interspersed with mathematical 

 symbols, but there is little that cannot be compre- 

 hended by those who have a knowledge of algebra and 

 elementar\- physics. Chemists owe to Sir Joseph 

 Thomson grateful thanks for a work which illuminates 

 many of the dark comers of their science with the glow 

 of his rich knowledge and experience. 

 NO. 2823, VOL. I 12] 



(3) The current of orthodox opinion on electror 

 theories of valency has changed its course so of 

 that the permanence of any one aspect of the 8ubj< 

 cannot be assumed. Nevertlielcss, the adjective 

 " ephemeral," which Prof. Lewis suggests in i 

 to his monograph as a whole, should properly l>< 

 only to the latter half of the work. The earlier cIm;. 

 ters, which deal with the pageant of discoveries and 

 ideas which led up to the present position of our 

 knowledge of the atom, could scarcely be bettered as an 

 initiation to the subject, and are distinguished by an 

 ingenious arrangement of the material and by the 

 graphic way in which it is descrilx^d. 



Beginning with Dalton's conceptions of the .i.^. wi,- 

 tinuity of matter, the author leads, by several con- 

 verging paths in turn, to the ionic dissociation thcor . . 

 to the discovery by J. J. Thomson of the electron, and 

 to the electronic conception of the atom. The ideas 

 of Abegg, Thomson, Kossel, and others in relation to 

 the octet theory are explained, while an interesting 

 reproduction of some of his own lecture notes of 1902 

 throws light on the embryology' of the cubic atom. 



Later in the book, Ramsay is credited with the first 

 idea of electrons shared by two atoms (1908). Stark > 

 conception of valency electrons attracting simultan< - 

 ously the positive parts of two different atoms is gi\ m 

 great prominence and illustrated with four diagrams. 

 Parson and Kossel are not forgotten in this connexion . 

 and the author generously makes out the best case 1 "r 

 every possible claimant to a share in the development 

 of the notion of co-valency. 



The history of the Bohr atom is also expounded in lii 

 introductory chapters, and thus spectral series, radiant 

 heat, specific heats at low temperatures, Planck's os< il- 

 lators, the quantum theory-, and Einstein's photoelectric 

 equation come forward in turn for exposition, tl a 

 significance of each being made clear. Bohr's theor\ 

 of the hydrogen atom and some of its more striking' 

 applications to the theory of emission and X-ra\ 

 spectra, ionisation and resonance potentials, are ex- 

 plained in a simple way. 



Werner's theory of co-ordinated comfK)unds, or at 

 least that part of it now accepted as a permanently 

 useful generalisation, might with advantage have been 

 included in these earlier chapters, lea\nng its inter- 

 pretation in terms of the electronic theories to be dealt 

 with in the later and highly controversial sections of 

 the work, where Prof, Lewis develops his own \'iews 

 with the aid of numerous applications both in organic 

 and inorganic chemistry. Some of the electronic for- 

 mulae suggested are already well-known and provision- 

 ally accepted ; others, including many which are novel. 

 will be received with var^-ing grades of satisfaction. 

 As was to be expected, the electron duplet is in this 



