Structure of Sodium Hydrogen Acetate. 195 



molecules was not only possible on the grounds of symme- 

 try but was chemically plausible, that it seemed worth 

 while to obtain a direct spectrum observation of a reflec- 

 tion in the first order from this larger unit. This could 

 be done by studying the secondary spectra from a cube 

 face reflection. If a spectrum is taken from a crystal 

 face in the usual manner, not only is the reflection from 



Figure 1. 



this face observed upon the photographic plate, but reflec- 

 tions from various other faces which are brought into 

 position by the continuous rotation of the crystal during 

 the course of the experiment will be registered at the 

 same time at various angles to the principal spectrum. 

 Such a composite spectrum was prepared by passing the 

 X-rays through a section of a crystal of NaH(C 2 H 3 2 ) 2 

 mounted so that one of the cubic axes was coincident 

 with the axis of its rotation and hence lay in the plane of 

 the slit of the spectrograph. A reproduction of this 

 spectrum is shown in fig. 1. 



