JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. 9 NOVEMBER 19, 1919 No. 19 



PHYSICAL CHEMISTRY.— 7/^^ nature of the forces between 

 atoms in solids.''- Ralph W. G. Wyckoff, Geophysical 

 Laboratory, Carnegie Institution of Washington. 



The study of the arrangement of the atoms within a crystal- 

 line body and especially of variations in these arrangements 

 with changes in the physical conditions of the soHd, such as tem- 

 perature and pressure, when taken in connection with the 

 knowledge which has been accumulating concerning the nature 

 of the atom, should give considerable information concerning 

 the kinds of forces operating between atoms and between molecules. 

 With this in mind the determination of the structures of a number 

 of typical compounds was undertaken by the author about two 

 years ago in the chemical laboratory of Cornell University. 



It seems possible to arrange all crystalline solids in a number 

 of groups according to the nature of the forces between their 

 atoms. The general outhne of such a classification is presented 

 in this discussion. Because of the numerous speculations which 

 have been introduced into recent discussions of the structure of 

 the atom, it has seemed advisable to present the point of view 

 which has served as a basis for this classification. The first 

 part of this paper is given up to such a presentation. 



J. J. Thomson,^ G. N. Lewis, ^ and W. Kossel'* have applied the 

 present knowledge of the structure of the atom to a consideration 

 of the nature of the forces of chemical combination. In develop- 

 ing the following discussion extensive use was made of the first 



' This paper was written in February, 1919, but was still in manuscript when 

 Langmuir's paper on a similar subject appeared (June, 1919). 



2 J. J. Thomson, The forces between atoms and chemical affinity. Phil. Mag. 

 (6) 27: 757-789. 1914- 



3 G. N. Lewis, The atom and the molecule. Journ. Amer. Chem. Soc. 38: 762- 

 785. 1916. 



* W. KossEL, Ueber Molekiilbildung als Frage des Atombaus. Ann. d. Physik 

 (4) 49: 229-362. 1916. 



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