REVIEWS 333 



If written in a more critical spirit, the book under notice mignt easily have 

 been much shortened — perhaps to half its length ; the effect would have been at 

 least to double its value — to make it really worth fourteen silver shillings, which it 

 is not in its present form. 



Almost every page of the book affords a subject for discussion. Perhaps one 

 of its most striking features is the evidence it affords of the slowness with which 

 ideas penetrate, of the difficulty we have in putting two and two together, of 

 our unwillingness to draw general conclusions. The fact that, speaking generally, 

 there are no such things as physical constants — that physical constants are 

 usually dependent variables — should have been insisted upon ; and the improbability 

 that we shall ever arrive at true atomic constants should have been made clear. 

 Far too little attention is drawn to the effect of the extra-molecular unions con- 

 ditioned by residual affinity ; the complexity of the phenomena to be analysed is 

 in no way made sufficiently obvious. These are matters to which the attention 

 of students should be directed from the outset, so as to guard them from the 

 belief that it is likely that we shall ever be in the position to arrive at final 

 conclusions. 



It is stated in the introduction that the distinctive feature of the past twenty- 

 five years has been the growth of dynamical theories of structure and the student 

 is left to believe that such theories have been more or less justified. The exact 

 contrary is the case. The fact is we are becoming daily more and more con- 

 vinced of the structural stability of compounds if only they are in a pure condition ; 

 and the conversion of isodynamic compounds into one another has been clearly 

 proved to depend on their inclusion within a complex system. Even those who 

 of late years have been most prominent advocates of " wobble '' admit that their 

 arguments have broken down — although they have not had the courage to with- 

 draw their contentions publicly. Much of the difficulty arises from the fact that 

 chemists are in the habit of interpreting "structural formulae" too literally. Such 

 formulje are very largely symbolic of function rather than of absolute mole- 

 cular structure. The objection to be taken to Kekule's formula of benzene, for 

 example, is that it does not picture the chemical behaviour of benzene, inasmuch 

 as it represents it as an eminently unsaturated compound — which it is not. The 

 centric formula is preferable from this point of view. The real reason why Kekule's 

 formula has been and still is popular is that it is the formula proposed by Kekule ; 

 chemists are human in respecting authority. The existence of two isodynamic 

 forms of benzene was postulated to save the formula, not to satisfy the facts. Again 

 it is absurd to say that " there are many substances which cannot be satisfactorily 

 represented by the ordinary structural formulae, since they react sometimes accord- 

 ing to one structure and sometimes according to another." Such is not the fact. 

 Nothing is easier than to represent the alternative behaviour of a compound such 

 as ethylic acetoacetate, for example, if only it be recognised that — as pointed out 

 above — interaction occurs in a complex system and that the passage from the 

 one form into the other takes place with utmost facility, given the determining 

 agent. These are matters which should have been discussed more carefully, as 

 they are fundamental. 



As another illustration of the manner in which the student may be misled, 

 reference may be made to the section on the Nature of Colour. Exception is 

 taken to the term " colour " as inexact. This is an illustration of the manner in which, 

 at the present day, we are attempting to improve on ordinary speech and by so 

 doing introducing confusion. Colour is something visible to the normal eye and 

 no word has a more definite connotation. In discussing the "origin of colour," the 



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