ABSTRACTS 331 



A Simple Method of Constructing Models for Demonstrating the Structure 



of Organic Crystals 



By A. Norman Shaw, D.Sc. 



Presented by Dr. A. S. Eve, F.R.S., F.R.S.C. 



(Read May Meeting, 1922) 



Abstract 



A model constructed with rubber balls and needles was exhibited 

 to the Society. It embodied the results of the important work of 

 Sir William Bragg on the structure of naphthalene crystals,^ showing 

 clearly the arrangement of the atoms and the relative dimensions of 

 the various spacings. 



The value of such a model can only be indicated in part by a 

 photograph, but it will be quite evident from the illustration that a 

 model of this type should greatly facilitate the teaching and the full 

 appreciation of these recent results about the structure of complex 

 organic crystals. 



The black balls represent the carbon atoms and the white balls 

 the hydrogen. The scale of the model is such that the length of one 

 molecule corresponds to 8 . 69 A.U. A single molecule (not quite on 

 the same scale) is shown separately in the front of the photograph, 

 and it will be seen that it can be identified at once from its similarity 

 to the diagram for the conventional method of representing the double 

 benzene ring with a and jS hydrogen atoms attached. Ten mole- 

 cules {i.e., 180 balls) are required to represent the unit parallelepiped 

 cell in this model, although obviously these are shared by neighbouring 

 cells and there are really only two molecules per cell in any given 

 crystal of naphthalene. 



A brief review of Sir William Bragg's experimental work was 

 given, and other models were shown to illustrate the relation between 

 the structures of diamond and of graphite, with special reference to 

 the identification and spacing of the carbon rings which appear in 

 each case. The persistent appearance of these rings constituted the 

 main clue in the deduction of a structure which was entirely compatible 

 with the results of X-ray analyses. 



iSir William Bragg, Proc. Phys. Soc. Lon., Vol. 34, p. 33 (Dec, 1921). 



