May II, 1916] 



NATURE 



219 



attempt in the present volume any full discussion 

 of the latest views, and merely indicates the main 

 lines alongf which progress is being- made. This is 

 a wise decision. 



The chapter on "Exceptions to the Periodic 

 Law " has been enlarged by a brief consideration 

 of the valency of the metals of the rare earths, 

 and their position in the periodic table, as well as 

 by a short discussion of the radio-elements and the 

 existence of isotopes. The exposition of Werner's 

 theory given in the first edition has been ampli- 

 fied by an account of Ephraim's work, the results 

 of which have shown that on the whole the 

 strength of the auxiliary valencies falls as the 

 atomic volume of the metal concerned increases. 

 In this connection reference is made to Werner's 

 recent conclusion that there is no essential differ- 

 ence between principal and auxiliary valencies. 



Some theories of valency, such as those of 

 Werner, and of Barlow and Pope, postulate the 

 existence of certain forces, and on this basis 

 attempt to formulate the constitution of the mole- 

 cule. Others, more definitely physical in char- 

 acter, deal with the origin of the forces postu- 

 lated by the chemist, and are therefore affected 

 by any alteration in the views held as to the struc- 

 ture of the atom. These considerations have led 

 the author to devote a few additional pages to 

 the electronic theor}^ of valency, as this has de- 

 veloped in the light of modern work by Ruther- 

 ford, Bohr, van den Broek, Moseley, Falk, and 

 Thomson. It will be interesting to see how far 

 the conclusions based on this work, as, for ex- 

 ample, the assigning of a valency of two to hydro- 

 gen and the consequent doubling of the valency 

 numbers of all other elements, will command 

 general acceptance. 



(2) The compilation of tests and the tabulation 

 of methods for qualitative inorganic analysis 

 which mainly constitute the first part of this 

 •volume are sound enough, but except for slight 

 differences in the arrangement of the matter and 

 in the general get-up, the thing has been done 

 scores of times already. True, the reactions of 

 some of the less common metals and acids are 

 also described, but this scarcely constitutes such 

 a claim to originality as would justify publication. 



The second part contains quite a useful selec- 

 tion of exercises in volumetric analysis, and the 

 explanations and directions given are on the whole 

 satisfactory. The relation, however, between the 

 general definition of a ngrmal solution and its 

 interpretation in the case of oxidisers might be 

 put more clearly. Further, in connection with the 

 use of potassium dichromate, the student might 

 legitimately be puzzled by the statement on p. 74 

 that "a standard solution is made by dissolving a 

 known weight of pure dry KoCr^Oy in distilled 

 water, and its exact strength can be determined 

 by titrating it against a known weight of pure 

 iron in the ferrous state." The author himself, on 

 the following page, points out that the strength 

 of a solution of potassium dichromate, prepared 

 by dissolving a known weight of the pure dry 

 salt and then making up to one litre, is known 

 exactly. 



NO. 2428, VOL. 97] 



(3) The authors of this first year college labora- 

 tory manual, almost conscious that some apology 

 is required for an addition to the large number 

 of such books already on the market, state in the 

 preface that the volume lays no claim to origin- 

 ality, either in method or in content. All that 

 has been done is to select the exercises which the 

 beginner should undertake. It is really time to 

 protest against this unlimited production of ele- 

 mentary laboratory guides, and to point out again 

 the absurdity of the implied claim that slight dif- 

 ferences in the character of the experiments 

 proposed and in the order of their arrangement 

 are of such paramount importance. Why not 

 leave something to the judgment and initiative of 

 the teacher? 



The arrangement of the experiments suggested 

 by the authors invites criticism. For example, 

 the most elementary examination of the character- 

 istics of acids, bases, and salts is preceded by a 

 chapter in which work is proposed on fractional 

 distillation, protective colloids, and the colour of 

 ions and molecules. Again, the student's atten- 

 tion is not specifically directed to the production 

 and properties of carbon dioxide until more than 

 half the course has been covered. 



Even the hints given in the appendix for the 

 benefit of the instructor are not entirely satisfac- 

 tory. The direction to prepare dilute sulphuric 

 acid by diluting- the concentrated acid in the ratio 

 I : 4 is a case in point : a 30 per cent, solution of 

 this acid should not be erhployed as a dilute 

 reagent. 



Altogether, it may be said that in a badly-man- 

 aged or poorly staffed laboratory the volume under 

 review might be useful as a guide, but that for 

 the student in an institution where competent 

 teaching is available the best hint is that given on 

 p. 75 — "report to the instructor for quiz on the 

 methods." 



{4) The views expressed above as to the scant 

 justification for adding to the number of intro- 

 ductory laboratory manuals are in some measure 

 applicable to this case also. If the " Rugby " 

 variety of elementary chemistry course is to be 

 put before us, why not many others as well, which 

 may have quite as good a claim to publicity? At 

 the same' time it may be admitted that this volume, 

 which is Intended to cover a period of two school 

 years, contains evidences of originality in the way 

 of suggestive experiments and in the devising of 

 simple apparatus for carrying them out. The 

 course on which the book is based is clearly char- 

 acterised by thought and initiative on the part of 

 the author and his associates. J. C. P. 



OUR BOOKSHELF. 

 Colour: a Handbook of the Theory of Colour. 



By G. H. Hurst- Second edition revised. 



pp. vii+i6o. (London: Scott, Greenwood and 



Son, 1916.) Price 7s. 6d. net. 

 Those who are interested in colour effects, 

 esp>ecially, perhaps, dyers, calico-printers, decora- 

 tors, students, and, to a lesser degree, artists, 

 will find much useful information in this very 



