195 



Analogous phenomena were met with in the case of the perfectly 

 transparent benzile-p\a.tes cut parallel to 001}, and of cleavage- 

 lamellae of apophyllite l ) . Potassium-ferrocyanide once gave an almost 

 tetragonal-symmetrical pattern, but in most cases abnormal images 

 showing only a single plane of symmetry. Obviously this is a fact 

 which supports the 

 lamellar theory; for 

 it proves that local 

 disturbances of the 

 structure may occur, 

 which cannot but 

 consist of a slight 

 rotation of a part 

 of the basal plate 

 round an axis ha- 

 ving the direction 

 of the perpendicular 

 to the plane of sym- 

 metry visible in the 

 obtained pattern. If 

 such a crystal be 



Fig. 157. 



Stereographical Projection of an abnormal Ron t gen 



pattern of pseudo-tetragonal 

 rac.-Tnethylenediamine-Cobalti-bromide. 



composed of lamel- 

 lae, it is easily con- 

 ceivable that such 

 dislocations may oc- 

 cur, if a pile of 

 lamellae is slightly rotated, e.g. round its longer direction. The effect 

 will depend on the accidental choice of the place where the pencil 

 of Rontgen-rays pierces the crystal-plate, as was in fact stated in 

 some cases 2 ). As stress or tension produced in the plate by slightly 

 compressing it, has no appreciable effect as long as the crystal is 

 not internally dislocated by the force applied, the phenomenon 

 mentioned here can only be caused by a local disarrangement of some 

 of the component lamellae. In a recent investigation, the author 3 ) 



!) H. Haga and F. M. Jaeger, ibid., 17, 438, (1914). 



2 ) H. Haga und F. M. Jaeger, loco cit.; e.g. in the case of d-sodium- 

 ammonium-tartrate, parallel to 010} . 



3 ) F. M. Jaeger, Proceed. Ron. Acad. v. Wet. Amsterdam, Vol. 22, 

 May, (1920). 



