REVIEWS 359 



properties of the oils characteristic of the plants. And it must be recorded that 

 the species thus defined are found to be practically constant in botanical and 

 chemical features under all conditions of geographical range. 



Finally, no claim is made for the anatomical method that it supersedes that 

 based on external characters. "The anatomical method is only an auxiliary one, 

 although it is of great importance. Properly employed ... it is of the greatest 

 value both as a means of confirmation of results already obtained, and for the 

 further elaboration of the Natural System." 



S. E. Chandler. 



The Chemistry of the Diazo Compounds. By John Cannell Cain, [x + 

 170 pp.] (London, Edward Arnold, 1908.) 



This monograph on the chemistry of the diazo-compounds is an excellent 

 example of a type of work too rarely seen in English chemical literature. The 

 author, who is fully conversant with the technical as well as the purely scientific 

 applications of the diazo-compounds, has succeeded in imparting a considerable 

 amount of first-hand information, together with a comprehensive survey of the 

 investigations of all the other workers in this field. The work appears in the 

 jubilee year of the diazo-compounds, for it is now fifty years since Johann Peter 

 Griess prepared the first diazo-derivative, by treating picramic acid with cold 

 nitrous acid. It is therefore a fitting and convenient time for taking stock of 

 the data which have accumulated during half a century of steady progress. 



Two-thirds of the treatise deals with matters of fact, the remaining third being 

 devoted to a concise exposition of the various views which have been held in 

 regard to the constitution of diazo-compounds. Throughout both these sections 

 the author has given so full a bibliography that practically all important statements 

 are accompanied by references (in footnotes) to the original sources of information. 



As the chief scientific value of the diazo-compounds is their employment in 

 the synthesis of derivatives of aromatic hydrocarbons, the chapters relating to the 

 preparation and reactions of these substances are a mine of information to the 

 chemist who proposes to use the diazo reaction. Some of the recipes are given in 

 full with all necessary working details. 



The chapters devoted to the consideration of the theoretical speculations will 

 be read with special interest by all students of the subject, for, with the exception 

 of the reviewer's Brit. Assoc, report on the aromatic diazo-compounds (1902), 

 no other resume of these extremely intricate and controversial matters has yet 

 appeared in English. In this connection it should be stated that the treatise now 

 under review deals with aliphatic as well as aromatic diazo-derivatives. 



The German monographs on diazo-compounds, which have been written by 

 Hantzsch and his pupil Eibner, are somewhat biassed in favour of the stereo- 

 chemical theories of diazo-configuration advocated by the former. The author, 

 while doing justice to the ingenuity and persistency displayed by Hantzsch in 

 elaborating and defending his views, has endeavoured to present the case for 

 those who, like Bamberger, prefer an explanation based on structural differences 

 of constitution. The author has himself put forward a theory of the constitution 

 of diazonium salts, which has elucidated certain obscure phenomena, and has 

 served as a stimulus for fresh researches. 



The value of this very readable hookas a work of reference is increased by the 

 inclusion of both name and subject indexes. 



G. T. Morgan, 



