( 195 ) 



twin-plane with a twin-axis nomially standing on it. On the 

 pkne of p may be often observed a delicate line parallel ^; : c; 

 in this vertical zone tlie most important geometrical anomalies are 

 fonnd. 



The following arc the calcidated and observed angulai- values. 



Observed: 

 -m : m = (110) : (lIO) = 54° 567,' 

 >n : a = (110) : (100) = 27 287, 

 m : r = (110) : (fOl) = 43 20 

 *c:r i=(001):(IOJ)=:59 39 

 r:a= (lOl) : (TOO) = 35 20 

 c:a= (001) : (100) = 85 15 

 *c : m = (001) : (110) = 85 447, 

 c-.j, = (001) : (120) = 86 40 

 c:n = (001) : (130) = 87 30 

 c:b=z (001) : (010) = 89 58 

 p : n = (120) : (130) = 11 12 

 m : p = (110) : (120) = 18 35 

 p:r =(120): (101) = 55 25 

 c:t = (001) : (Ï04) = 21 12 



C:0= (001) : (Ï12) = 41 527, 



CIS =z (001) : (Ï32) = 55 49 

 m : s = (1Ï0) : (132) = 47 367, 



A distinct cleavability was not observed. 



On c, r, and a the position of the optical elasticity -axis is orien- 

 tated perpend icnlarly to the direction of the orthodiagonal ; the 

 symmetrical angle of extinction on m amounts to 23° with regard 

 to the vertical axis. An axial image could not be observed. 



The sp. gr. of the crystals is 2,456 at 15°; the equivalent volume 

 is, therefore : 170,6. 



The topical axes are; 



: ip : CO = 3,9087 : 7,4921 : 5,8461. 



b, l-2-3-5-t7nbromo-4:-Q-dinitrotohieiie. 



C, . Br . Br . Br . (NO,) . (NO,) . (CH,); melting point: 210^ C. 



(5) (3) (2) (6) (4) (1) 



