viii Proceedings. {October 16th, 1906. 



The communication standing in the name of Mr. R. L. 

 Taylor, F.C.S., F.I.C., having been withdrawn, an account was 

 given of the following paper: "A Development of the Atomic 

 Theory which correlates Chemical and Crystalline 

 Structure and leads to a Demonstration of the Nature 

 of Valency," by William Barlow, F.G.S., F.C.S., and Prof. 

 W. J. Pope, F.R.S. 



The primary object of the work now described was to derive 

 an explanation of the numerous crystallographic relationships 

 which exist between chemically related substances and which 

 have not hitherto been embraced by any theoretical scheme. 

 It was found, however, on formulating and developing the very 

 simple fundamental conception stated below concerning the 

 environment of the atoms composing a chemical molecule, that, 

 not only is the relation between the chemical constitution and 

 crystalline form of any compound quantitatively indicated, but 

 chemical valency is clearly demonstrated to be a simple volume 

 relationship. The fundamental conception is the following : — 



Each chemical atom present in a compound occupies a 

 distinct portion of space by virtue of an influence which it exerts 

 uniformly in every direction. The domain of the chemical 

 molecule is the space-unit, consisting of one or more of these 

 distinct portions of space, obtained by homogeneously sub- 

 dividing into units a homogeneous structure built up of the 

 spheres of influence of a number of associated atoms. The 

 form of aggregation of the spheres of influence of the atoms thus 

 associated in a molecule constitutes the stereometric arrange- 

 ment of these atoms, and thus the chemical molecule acquires a 

 definite shape. A crystal is the homogeneous structure derived 

 by the symmetrical arrangement in space of an indefinitely large 

 number of spheres of atomic influence. 



In order to embody this conception and its developments in 

 a concrete form, balls of definite sizes are employed to represent 

 the spheres of influence of the different atoms, and close-packing 

 of these balls in various symmetrical arrangements is resorted to. 

 For the purpose of making models which accurately express the 



