TRANSACTIONS OF SECTION B. 643 



methods of determining ' constitution/ and is endeavouring: to furnish us with new 

 weapons for attaclfiiig this same problem. The chemist who is seeking to unravel 

 the architecture of molecules is dependent at the outset upon physical methods of 

 determining the relative weights of his molecules. The worker who is bringing 

 about new atomic groupings is furnishing material for the farther development of 

 generalisations from which new methods applicable to the problem of chemical 

 structure may again be evolved. The physical chemist sometimes from the broad- 

 ness of his view is apt to overlook or to minimise the importance of chemical 

 individuality. On the other hand the chemist who is studying the numberless 

 potentialities of combination resident in the atoms, and who has grasped to the full 

 extent their marvellous individualities, is equally liable to forget that there are 

 connecting relationships as well as specific dltferences in the properties of elements 

 and compounds. These are but the mental traits — the unconscious bias engendered 

 by the necessary specialisation of work to which I have referred, and which is 

 observable in every department of scientific labour. 



The Peesext State of Structiteal Chemistry. 



The success attending the application of the doctrine of valency to the com- 

 pounds of carbon has helped its extension to all compounds formed by other 

 elements, and the student of the present day is taught to use structural formulre as 

 the A B of his science. It is, I think, generally recognised among chemists that 

 this doctrine in its present state is empirical, but it does not appear to me that this 

 point is sulliciently insisted upon in chemical teaching. I do not mean to assert 

 that for the last thirty years chemists have been pursuing a phantom ; neither do 

 I think that we should be justified in applying to this doctrine the words applied 

 to its forerunner, the ' types ' of Gerhardt, by Lothar Meyer, who says that these 

 ^have rendered great service in the development of the science, but they can only 

 be regarded as a part of the scafi'olding which was removed when the erection of 

 the system of organic chemistry had made suificient progress to be able to dispense 

 wdth'it.' ' It appears to me, on the contrary, that there is a physical reality under- 

 lying the conception of valency, if for no other reason because of the con form- 

 ability of this property of the atoms to the periodic law. But the doctrine as it 

 stands is empirical in so far that it is only representative and not explanatory. 

 Frankland and Kekule have given us a great truth, but its very success is now 

 making it more and more obvious that it is a truth which is pressing for further 

 development from the physical side. If we are asked why CO exists, and why 

 CH,, and CCl, do not, together with innumerable similar questions which the in- 

 quisitive mind will raise, we get no light from this doctrine. If any over-sanguine 

 disciple goes so far as to assert that all the possible compounds of the elements indi- 

 cated by their valency are capable of existence, and will sooner or later be prepared, 

 he will, I imagine, find himself rapidly travelling away from the region of fact. 



There is something to be reckoned with besides valency. The one great desi- 

 deratum of modern chemistry is unquestionably a physical or mechanical interpre- 

 tation of the combining capacities of the atoms. Attempts at the construction of 

 such theories have been made, but thus far only in a tentative way, and these 

 views cannot be said to have yet come within the domain of practical chemical 

 politics. I have in mind, among other suggestions, the dj'uamical theory of van 

 't Hoff published in 1881,'- the theory of electric charges on the atoms broached 

 by Johnstone Stoney in 1874, and so ably advocated by the late Professor v. 

 Helmholtz in his Faraday lecture in 1881, and the electric polar theory of Victor 

 Meyer and Riecke, published in 1888.^ 



Pending the rationalisation of the doctrine of valency its promulgation must 

 continue in its present form. Its services in the construction of rational formuhe, 



' Modern Theories of Chemistry, p. 194. 

 - Ansichten ilher die orf/anisohe C'hemie. 



" 'Einige Bemerkungen iiber den KohlenstofEatom und die Valenz," £er.,2\, 

 pp. 946, 1620 



T T 2 



