STUDY OF ORES AND METALS. 



439 



Methods Based on the Detection of a Ro- 

 tation OF the Plane of Polarization 

 (Position of Extinction). 



These methods have been long in use by 

 petrologists and the principles underlying the 

 construction of the different devices need not 

 be repeated here." 



Kocnigsberger's Method}'^ — In this method 

 Koenigsberger adopted the arrangement shown 

 in Fig. 12. The incident light passes first 

 through the polarization prism (vibration 

 plane horizontal or vertical) P, and the total 

 reflecting prism R to the crystal plate whence 

 it travels through the Biot quartz plate A (cut 

 normal to the axis and of such thickness, 3.75 

 mm., that it gives the sensitive tint between 

 crossed nicols), the eyepiece E, the cap nicol 

 A^ to the eye of the observer. The rotation of 

 the plane of polarization on reflection is de- 

 tected by the change in interference hue on 

 rotating the crystal plate. Koenigsberger 

 emphasizes the fact that this method is not so 

 sensitive as his first method and is only quali- 

 tative in nature. 



H an emann's Method. — In 1913 Hanemann^- 

 improved Kocnigsberger's method by substi- 

 tuting a Soleil-Biot plate (two adjacent Biot 

 quartz plates, 3.75 mm. thick, cut normal to 

 the axis, the one of right-handed, the second 

 of left-handed quartz) for the single 

 Biot plate. This arrangement introduces the 



n A 



Fig. 12. Diagram 

 showing general ar- 

 rangement for the 

 detection of the rota- 

 tion of the plane of 

 polarization of nor- 

 mally incident plane- 

 polarized light waves 

 on reflection from a 

 birefracting and bi- 

 absorbing plate. 



feature of color con- 



10 These are treated at length in " The Methods of Petrographic Micro- 

 scopic Research," Carnegie Institution of Washington Publication 75^, pp. 

 115-148, 1911. 



'^^ Centralhlatt fiir Mineralogie, etc., 1909, 245-250; 1910, 712-713; Metal- 

 lurgie 4, 605-608, 1909. 



12 K. Endell and H. Hanemann, Stahl und Risen, 1913, p. 40; Zeitschrift 

 fiir anorganische Chetnie, 83, 267-274; 88, 265-268, 1914. 



