S7o SCIENCE PROGRESS 



account of the method of combustion, introduced by Walker and Blackadder, 

 which has generally replaced the older methods wherever it has been tried. The 

 last section is a clear account of the determination of molecular weights. The 

 appendix contains data and useful tables concerning reagents, also a table of 

 logarithms. Finally, the book is judiciously illustrated in a helpful manner. 



Altogether, the authors are to be congratulated on having produced a book 

 which cannot be too highly recommended for its purpose, and whose worth has 

 already been discovered both by teachers and by students in more than one 

 laboratory. j jyj 



Organic Chemistry for Advanced Students. Vol. II. By Julius B. Cohen, 

 F.R.S., etc. [Pp. vii + 427.] (London : Arnold, 1913. Price 16^. net.) 



To write a book dealing generally with any one of the three main branches of 

 chemistry is a task which becomes yearly more difficult ; and this is particularly 

 true in the case of the organic branch. Physical chemistry has reached the 

 quantitative stage, and, guided by mathematics, it keeps on a fairly straight 

 path ; inorganic chemistry is now semi-quantitative as a result of the affiliation 

 with physical chemistry of which Abegg's Handbuch is a visible sign. In the 

 eyes of many followers of these two branches, their organic colleagues are 

 simply wallowing in the mire of qualitative thought ; and yet it was from the 

 study of organic compounds that some of the fundamental principles of general 

 chemistry arose, and the inorganic worker is often apt to overlook the very 

 important contributions which his own branch is continually receiving from the 

 organic side. 



Nevertheless, organic chemistry is certainly in a less advanced state, and it 

 is deficient as yet in quantitative laws. Failing these, classification of the vast 

 masses of fact must be resorted to ; and after classification comes theorising. 

 The regrettable fact is that frequently theories are propounded before classification 

 is properly begun ; and, in addition, what are in reality tentative schemes of 

 classification are often mistaken for explanatory theories. 



It is here that the teacher enters the field ; and the chief purposes of an 

 advanced course of organic chemistry should be to direct the student's steps away 

 from these two pitfalls, and at the same time to criticise, both destructively and 

 constructively, actual theories. Viewed from this standpoint, Prof. Cohen's 

 second volume is curiously patchy. Impartiality in a teacher is a very necessary 

 virtue, but it can be practised to excess ; and this is the chief fault of an otherwise 

 interesting book. 



The five chapters which compose the volume under review naturally dovetail 

 into the earlier parts of the first volume, which has been widely used during 

 the last five years. With the author, we may hope that in later editions a 

 re-arrangement may be effected ; but in the meantime, these five chapters in 

 themselves form on the whole a fairly natural sequence. The theme around 

 which they chiefly centre may be said to be the perturbations of atoms and of 

 interatomic forces within the molecule ; in other words, the central problems 

 of present-day organic chemistry. It follows that many of the subjects dealt 

 with are of a physico-chemical character, and thus the value of the completed 

 work is much enhanced. 



The first two chapters ("The Valency of Carbon" and "The Nature of 

 Organic Reactions "), which occupy some 200 pages, are undoubtedly the most 

 interesting of the five. Theories of valency may be said to deal with one or 



