( 796 ) 



No distinct cJeavage was found. 



Tlie optical axial plane is |0Ü1|, with the a-axis as a first bisectrix 

 of positive character. Weak dispersion : Q ^ v. The apparent axial 

 angle in olive oil amounts to about 55°. 



The sp. gr. of the crystals is: 1,423; the equivalent volume 255,44. 

 Topic parameters . / -. xp -. to = 4,5516 : 7,5748 : 7,4089. 



A comparison with tii-p-chïoroinplienylmethane 

 shows that the moi'photropic relations of both 

 compounds are of such a nature that they bor- 

 der on isomorphism. In fact, both compounds 

 form mixed crystals with each other. 



§ 5. Tri-p-Bromo-Triphenylcarbinol. 



(C, H, Br)3:C.0H; m.p. 133° 0. 



Crystallises from ethylalcohol in small colour- 

 less, clear crystals possessing a high lustre and 

 a good geometrical construction. 



Rhombic-bipyramidal. 

 rt:^:C== 0,8407: 1 : 0,8081. 



Forms observed: m = |110|, predominant and 

 yielding sharp reflexes; a = \iOO\ narrow but 

 easily measurable; q =z \011\, gixes excellent 

 reflexes and is well developed ; r =z jlOlj small 

 and somewhat dull. The crystals from alcohol 

 are shown in fig. 4. 



Calculated : 



Fig. 4. 



Tri-p-Bromo-Triplienyl- 



carbinol. 



Angular Values : Measured : 



m: «:z=(110):(iOO) = MO^ 37/ 



m: ^z:=(TfO):(011) = -66^ 8V; 



q : q = {Oil) : {On) = 77° 



7>i:m = (110):(110)= 80° 



m: r = (110): (101)= 57^ 



r : q = (101) : ^011) = 55° 



r : r=: (101): (101)= 87° 



r : a = (lOlj : (100) = 46° 



No distinct cleavage. 

 ■ The optical axial plane is |001|; the ^>-axis is the first bisectrix 

 and of a negative character. The apparent axial angle in olive-oil 

 is about 65°. No strong dispersion : o > v. 



The sp. gr. of the crystals is 1,847; the equivalent volume 269,08. 



Topic parameters : x.^^-.to^ 6,1739 : 7,3439 : 5,9346. 



