194 



potassium- f err ocyanide, apophyllite, sodium-chlorate, benitoite, racemic 

 triethylenediamine-cobaltibromide, benzile, brucite, etc., were studied, 

 and also some crystals endowed with rotatory power, like quartz, 

 cinnabar, strychnine-sulphate, etc. Although in the last mentioned 

 cases faultless patterns were obtained (fig. 156), --a fact which 



demonstrates to what 

 high degree of per- 

 fection this supposed 

 lamellar intercalation 

 can go, - - we obser- 

 ved in the case of 

 apophyllite , pot assium- 

 ferrocyanide, benzile, 

 benitoite, and the 

 complex cobalti-di\t 

 just mentioned, that 

 even from apparent- 

 ly homogeneous and 

 faultless plates, pat- 

 terns of a lower sym- 

 metry were obtained, 



Fig. 156. 



Stereographical Projection of the Ron t gen-pattern 

 of pseudo-tetragonal Strychnine-sulphate. 



than should be the 

 case with respect to 

 their proper symme- 

 try. 



In particular, images were obtained which posessed only a single 

 plane of symmetry, as is quite normal for monoclinic crystals cut 

 parallel to the faces (100) or (001), or to any other face of the 

 orthodiagonal-zone 1 ). As an instance of this in fig. 757 the Ron t gen- 

 pattern, as it was obtained with racemic triethylenediamine-cobalti- 

 bromide is reproduced in Stereographical projection. 



Here, the natural' crystals parallel to 001} were used in the 

 experiment 2 ) in the shape of very thin, splendidly developed pseudo- 

 hexagonal plates, which showed an exactly central and almost 

 undisturbed axial image in convergent polarised light; a slight 

 deformity of the axial interference-image, because of an apparent 

 biaxiality of the substance, was the only abnormality observed. 



!) F. M. Jaeger, Proceed. Kon. Akad. van Wet. Amsterdam, 18, 51, (1915). 

 2 ) H. Haga and F. M. Jaeger, ibid., 18, 1201, (1915). 



