74 



NATURE 



[May 24, 1906 



wearied with indigo that he was quite unable to con- 

 tinue experimenting on the subject, and had to allow 

 the various problems connected with the commercial 

 development of his discoveries to pass into other 

 hands. In search of fresh fields for investigation, 

 Baeyer commenced an inquiry with the object of dis- 

 covering whether carbon atoms, uncombined with 

 hydrogen, are capable of uniting to form long chains, 

 and, in order to determine this, he synthesised a number 

 of poly-acetylene compounds, including tetracetylene- 

 dicarboxylic acid 



C02H.C=C— C=C— C=C-C=C.CO,,H. 

 This remarkable acid is quite colourless, but is 

 readily blackened by the action of light, and compounds 

 of this type were found to be so explosive that their 

 further investigation had to be abandoned. One of 

 th-3 fruits of the consideration of the properties of 

 these compounds was the enunciation of the well- 

 known " Spannung's Theorie," which has given rise 

 to so much discussion, and proved to be of such value 

 in suggesting new lines for experimental inquiry. 



Section viii., which Baeyer has placed directly 

 after the phthalcins, deals with the chemistry of the 

 hydroaromatic compounds and the constitution ot 

 benzol. These researches date from the year 1866 

 when, in conjunction with Graebe, Born, Mohs and 

 others, he first investigated the behaviour of phthalic 

 acid and terephthalic acid towards sodium amalgam. 



Baeyer repeatedly returned to this subject in later 

 years, but it was not until 18S8 that the epoch-making 

 series of papers " Ueber die Constitution des 

 Benzols " began with the exhaustive study of the 

 products which are formed when terephthalic acid is 

 reduced with sodium amalgam. These researches on 

 the reduction products of the phthalic acids and of 

 benzene itself are well known, but they have perhaps 

 hardly received the close attention which they merit, 

 owing partly, no doubt, to their difficult and intricate 

 nature. The careful study of these papers will, how- 

 ever, more than repay the time spent, and to the 

 young investigator they may well serve as an example 

 of the patience and endurance which he must be pre- 

 pared to face if he wishes to attempt the solution of a 

 problem of really first-rate importance. 



It is perhaps a consequence of the study of these 

 artificially prepared reduction derivatives of benzene 

 that Baeyer was led to investigate that wonderful 

 series of naturally occurring reduced benzene deriva- 

 tives — the terpenes — the constitution of which has 

 offered one of the most difficult problems to the 

 modern organic chemist. During the course of his 

 experiments on the oxidation of substances which, 

 like the terpenes, contain unsaturated closed chains, 

 Baeyer commenced to experiment with Caro's acid, 

 and, among many other interesting results, showed 

 that this acid was a most valuable reagent for the 

 conversion of ketones into lactones. Further experi- 

 ments resulted in the discovery of the remarkable 

 series of peroxidised substances of which benzovl- 

 hyperoxide and diethylperoxide may be taken as 

 types, and led to a dei'elopment of Collie and Tickle's 

 important work on the tetravalent nature of oxygen 

 and the oxonium theory. 



NO. 1908, VOL. 74] 



Baeyer's latest publications deal with the vexed 

 question of the relation of colour to constitution, and 

 are concerned especially with the reason for the 

 coloured nature of certain salts derived from dibenzal- 

 acetone and from triphenylcarbinol. One of the 

 most remarkable results of this investigation is the 

 proof that the coloured salts of triphenylcarbinol are 

 in reality esters possessing the properties of salts, 

 and that they cannot be regarded as quinoid com- 

 pounds. 



Baeyer is, at the present time, occupied with the 

 further development of this important matter. 



It is impossible to close the volumes before us with- 

 out marvelling at the immense amount of work which 

 it is possible for one man to carry out, and without a 

 deep impression of the enormous influence which the 

 work of Baeyer has had on the development of 

 modern chemistry. The list of papers published from 

 Baeyer's laboratory occupies no less than sixtv-three 

 pages of closely-printed matter, and when we look at 

 the names attached to these papers we are able to 

 form some idea of the magnitude of the school which 

 he has founded, and of the extent to which many of 

 the greatest chemists of the day owe their training in 

 research to Baeyer. W. H. Perkin, Jun. 



.4 STANDARD TREATISE ON ELASTICITY. 



A Treatise on the Mathematical Theory of Elasticity. 



By A. E. H. Love. Second edition. Pp. xviii + 



552. (Cambridge : University Press, 1906.) Price 



18s. net. 



JNSTE.\D of nierelv revising his former treatise, 

 Prof. Love has written a new one ; the result 

 is that we have two works by the same author, in some 

 ways contrasting, in others complementary. And as 

 in the similar cases of Maxwell's " Electricity," and 

 Thomson and Tait's " Natural Philosophy," the 

 prudent will buy the new book without parting with 

 the old. 



Naturally one feature in the new edition is the in- 

 clusion of important or interesting results obtained 

 since the appearance of the earlier one. In some 

 branches of mathematics the proportion of English 

 workers is distressingly small ; but in elasticity this is 

 happily not the case, and the recent researches of 

 Michell, Filon, Dougall, and others, besides those of 

 veterans that need not be named, receive in these pages 

 their due recognition. So also do those of their 

 Continental confreres, more particularly Voigt ; but 

 it is hard to avoid the impression that the deaths of 

 Kirchhoff and Hertz have left vacancies which have 

 yet to be worthily filled. 



It is interesting to compare the historical introduc- 

 tion in its old form with its successor. The former was 

 in some places controversial, and the author seems to 

 have thought some of the statements too dogmatic, at 

 any rate in form. However this may be, the new 

 introduction is strictly impersonal, and shows clearly 

 enough how recent physical theories and discoveries 

 affect the subject of elasticity. A great deal of the 

 polemic about the number of elastic constants was as 

 illogical as the quarrel about vis -viva. As an abstract 



