Notices respecting New Books. 441) 



compounds described also have at present no technical value, but 

 are introduced in illustration of general methods of formation or 

 on account of their historical interest. 



The volume is in its way a model of conciseness, extending to 

 little more than 300 pages and comprising fifteen chapters, an 

 introduction, an appendix, and a remarkably complete list of 

 references occupying about fifteen pages. The reader who masters 

 the contents of the work will, in spite of the conciseuess referred 

 to, find that he has obtained an accurate and comprehensive grasp 

 of the chemistry of the coal-tar colouring-matters, and this is 

 perhaps the very best tribute that can be paid to the merits of 

 Dr. Nietzki's production. A brief analysis of the contents will 

 suffice to show what extent of ground is covered. 



The introductory chapter deals with tbe general question of 

 colour and the relation between chemical constitution and tiuctorial 

 power. In this connexion Witt's theory of the Chromophor and 

 Chromogen is explained. It is of interest to note also in this 

 chapter the acceptance of the view as to the probable existence of 

 trivalent phenyl, C 6 H 5 '", in aromatic compounds as first suggested 

 in the pages of this Magazine by Meklola in 1887 (vol. xxiii. p. 513). 

 Among other subjects touched upon is that of the theory of dyeing, 

 the action of mordants, the formation of lakes, the testing of 

 dyestuffs for tinctorial value ; and the chapter concludes with a 

 brief historical summary which is fair on the whole, although open 

 to correction on one or two points. In fact, this particular 

 section is hardly as complete to date as the author might have 

 made it for this English edition of his work. There is an error 

 on p. 7 which confuses the meaning of the whole paragraph in 

 which it occurs, viz. " a valent chromophor " for a " polyvalent 

 chromophor " as it stands in the original. Also we object to 

 the adoption in Euglish of the literal translation " methane rest " 

 on p. 9. 



The fifteen chapters following the introduction are devoted to 

 the various groups of colouring-matters arranged according to a 

 very convenient system of classification introduced originally by 

 Dr. Nietzki and now generally adopted. The first chapter deals 

 with nitro-compounds and comprises such well-known dyestuffs as 

 picric acid, dinitronaphthol, acid naphthol yellow, &c. The large 

 and important class of azo-dyes form the subject of the second 

 chapter. With respect to the much-discussed question of the 

 constitution of theamido and oxyazo-compounds the author prefers 

 to retain the old formulae, because, as he says, there is just as much 

 evidence for the view which regards these compounds as containing 

 KH 2 and HO as for the later theory of Zincke, Groldschrnidt, &c. 

 according to which the groups C=0 and C=NH are present. 

 The probability is that both views are correct and that the com- 

 pounds can behave in one way or the other according to the nature 

 of the reagent which acts upon them. In this chapter there is a 

 slight error, present also in the German edition. One of the 



