NA TURE 



241 



THURSDAY, NOVEMBER 28, 1918. 



[BSORPTION SPECTR I I Xl> CHEMICAL 



1 1 INSTITUTION. 

 Colour in Relation to Chemical ('(institution. By 

 E. K. Watson. I'p. xn I '97- ' ' 

 Longmans, Green, and Co., (918.) Price 

 !-'.•.. i«l. net. 



IT is justifiable to ask whether this boo] has 

 been written to help those engaged in research 

 on synthetic dyestuffs or as a text-book for those 

 investigating the problems of absorption spectra. 

 On one hand ii contains scarcel) anything oi suffi- 

 < ient definiteness for the colour chemist to pin his 

 faith to, .Hid*, on the other, the information is 

 not complete enough to justify its use as a 

 bext-book on absorption spectra. The author, 

 however, 1 in scarcely be blamed for the lack- of 

 definiteness in establishing even one article of 

 faith for the colour chemist to accept, because it 

 is progressively becoming more evident that there 

 is no definite relation between colour and chemical 

 constitution in the generally accepted sense. Every 

 one "t the theories connecting the two that from 

 time to time have been proposed is shown by 

 the author to fail in one way or another. Even 

 his own theory of oscillation within a conjugated 

 system of double bonds is of limited application, 

 for it entirely fails to explain his own test case 

 of the blue nitroso-derivatives of the paraffins, not 

 to mention the numerous examples of colour 

 changes shown by the same compound in different 

 solvents. The time has surely come when it were 

 wiser frankly to let the colour chemist into tin- 

 secret and tell him that the usual conception of 

 correlation between colour and constitution has 

 n found to be unsound. Let us be brave and 

 state that the real connection between them is far 

 deeper than any of the theories of Witt, Xietzki, 

 Armstrong, von Baeyer, or Hantzsch would lead 

 us to beliet e. 



Criticism must be made of some statements in 

 this book, statements which cannot be allowed to 

 pass unchallenged. For example. Beer's law can- 

 not be said to be true within a wide range. The 

 substances which conform to this law are rela- 

 tively few, and, indeed, the law is more honoured 

 in the breach than in the observance. Then, again, 

 it would seem that the author has confused the 

 numbei ol absorption bands shown by sub-, 

 Man ition bands exhibil a number of sub- 



groups, and great care must be taken to guard 

 against looking upon these sub-groups as separate 

 absorption bands. Some of the author's criticisms 

 are based on this error and lose their point when 

 it is ed that different sub-groups ol one 



band and not different absorption bands are under 

 discussion. 



1 again, the persistence of a band is 

 wrongly defined as the ordinate passing through 

 the head of an absorption band; ibis ordinate is, 

 of course, a measure of the absorptive power, 

 while the persistence is the difference between the 

 •extreme ordinates over which the band persists. 

 2561, VOL. I02] 



Although this is a minor point, it directs attention 

 to the fact mentioned i> he author of the remark- 

 able differences shown by substances in the persist- 

 1 he reason for this 

 is that in the case ol those compounds which 

 .liibit relativel) shallow bands very few mole- 

 ules exist in the absorbing condition, the 

 remainder not exerting any selective absorption 

 in the Spectral region under examination. It will 

 once be seen how dangerous it becomes to 

 gmatise or even postulate any theory as to the 

 constitutional origin of a band when such is due 

 to a \er\ small fraction of the- molecules present. 



The boo].: is well put together and excellently 

 illustrated with absorption curves of a variety of 

 compounds. The chapters dealing with the earlier 

 theories on colour and constitution are well 

 written, and although the discussion of each of 

 these is necessarily restricted, the author has suc- 

 1 eeded in presenting their salient points well. 

 Chapters are devoted to infra-red absorption and 

 to fluorescence, and finally there is a good account 

 of the work on the colour of inorganic compounds. 

 In some ways this book may be recommended, 

 but the impression will remain that the author 

 loses conviction by reason of having stepped too 

 delicately. E. C. C. B. 



SYNTHETIC AND ANALYTIC PHYSICS. 



(1) Cours dc Physique Gendrale. By H. Ollivier. 

 Tome Troisieme. I'p. 632. (Paris : A. Hermann 

 et Fils, 1918.) Price 30 francs. 



(2) Electrical Experiments. By A. Risdon Palmer. 

 Pp. xii+115. (London: Thomas Murby and 

 Co., 1918.) Price is. 6d. net. 



(",) Magnetic Measurements and Experiments 

 (with Answers). By A. Risdon Palmer. Pp. r -4- 

 (London: Thomas Murby and Co., 1918.) Price 

 is. 6d. net. 



IN the discussion on the teaching of physics in 

 schools which took place recently at a meet- 

 ing of the Physical Society two methods of teach- 

 ing phvsies were contrasted. The first, which 

 may be called the synthetic method, starts from 

 certain general principles and develops the con- 

 sequences of those principles. The second, or 

 analytic method, dissects out the principles 

 from some more or less complicated piece of 

 mechanism. Thus the first method starts with 

 Boyle's law- and ends with the steam-engine, 

 whilst in the second method the order is reversed. 

 Kach method has its advantages and its draw- 

 backs, and makes its appeal to a particular type 

 of mind or at a particular stage of development. 

 The volumes under discussion may be regarded 

 amples of the two methods of presentation. 

 (1) The subject of vibrations and their trans- 

 mission forms the groundwork of the third part 

 of M. Ollivier's text-book, and it is developed 

 from first principles with the lucidity which seems 

 to be innate in French scientific writers. The first 

 six chapters may be regarded as introductory; 

 they contain a concise and interesting summary 

 of the main features of periodic functions, of 



