198 R. W. G. Wyckoff — Sodium Hydrogen Acetate. 



positions of the special case 24e. It is of course impos- 

 sible now to determine the positions of any of these 

 atoms. The coordinates of both of these arrangements 

 are given in the book by the writer entitled ' ' The Analy- 

 tical Representation of the Theory of Space Groups'' 

 which is shortly to be published by the Carnegie Institu- 

 tion of Washington. 



When it is considered that such a relatively simple sub- 

 stance as this sodium acid acetate has such a very compli- 

 cated structure as it has here been shown to possess, it 

 scarcely needs to be emphasized that any studies of the 

 structures of organic compounds should be made with 

 extreme care and in order to be of any value should make 

 use of the most powerful diffraction methods now at our 

 disposal. 



Summary. 



It is shown that the unit cell of sodium hydrogen 

 acetate must contain 24 chemical molecules. The length 

 of the side of this unit cube is found to be 15.98 A.U. 

 The determination of the underlying space group as 

 probably T h 7 defines the general manner of the arrange- 

 ment of the atoms of this crystal, though it is impossible 

 to obtain the positions of these atoms. A graphical 

 method is outlined for identifying the planes causing the 

 secondary spectra upon a reflection spectrum photo- 

 graph. 



Pasadena, California. 

 May, 1922. 



