\ 



WycJtoff — Crystal Structure of Ammonium Chloride. 471 



by urea would presumably lower the index about 0.001 

 for each per cent. ' ' 



Passage of a beam of X-rays in a direction roughly 

 normal to a cube (100) face of several of these crystals 

 yielded a series of very beautiful Laue photographs. 

 A reproduction of one of these is given in figure 1 ; the 



Fig. 2. 



1 ■ 1 1 1 11/ 



iii i __- f— — r ' 



— -- — 1 — / ^ ' ' / ' 



' ' 



j_ a— ^ — t — -f — r"T — ; 



/ / / ; ° ; ° j ° ; ; 



/ ' / '/•••. \ — Q P — 



— _i ]__ 



- ; / ' o / / •••••. \ ~ 



— — f—^a— ^J '/ • •••••••• . \ 



l -« / / ' — -.J '01 



ill: r\ 



■-r f— 



i i 

 / i 



7 ^_K 



; i - 

 / , 

 / i 

 I i 



/ 1 -— - 



; 



' "^~~~. 1 



1 ~--^ 



Figure 2. A gnomonic projection of a Laue photograph of ammonium 

 chloride which had very nearly the orientation of the photograph of 

 Figure 1. With the aid of Table I (which refers to the photograph 

 of Figure 2) and an enlargement of this projection it is possible to 

 reconstruct the original data. 



gnomonic projection of a photograph having an orienta- 

 tion very close to that of figure 1 is shown in figure 2. 

 With the aid of these two figures and the plate distances 

 of typical spots which have been recorded in Table I, it 

 is possible to reproduce approximately the original data 

 found upon this second photograph. 



From the powder photographic data the length of 



6 G. Bartlett and I. Langmuir, op. cit. 



