( 797 ) 



In contrast to what was found with both chloroderivatives, tri- 

 broinocai'binol shows no distinct form-relationship with tribromo- 

 triplienybnethane ^). The substitution of H by — OH, however, 

 appears (o exert an influence on the equivalent volume which is of 

 a nature opposite to that which causes the same substitution in the 

 chloro-derivati\'e. 



§ 6. Tri-p-Iodo-Triphenylcarbinol. 

 {C, H, J\ : C—OH; m.p. : 155° a 

 Crj'stallises from ethylalcohol in fairly large yellowish crystals 

 which, however, contain either no terminal planes at all or else 

 strongly curved ones. 



In any case the isomorphism with the pre\'ious compound may 

 be easily proved. 



Rhombic-bipyramidal, 

 a:b:c = 0,85^3:1 : 0,817. 



Forms observed: 7?i := jllOj, predominant and highly lustrous; 

 a = \100\ narrow and generally absent but always giving a good 

 reflexion; q = \011\ distinctly developed but in most cases curved 

 and only approximately measurable; r = [10i\ was observed once 

 or twice. 



Measured : Calculated : 



m : m = (110) : (110) = *81° 1' — 



q : q = (Oil) : (Oil) = *-78 29 — 



a : m = (100) : (110) = 40° 36\/, 40° 307; 

 m: q = (110) : (Oil) = 66 3\/, 65 447, 

 m: r = {110):{i01)= 58 10 58 18 

 No distinct cleavage. 



The optical axial plane is jOOlj with the 6-axis as first bisectrix. 

 Particularly large dispersion : q^v. The apparent axial angle in 

 olive-oil amounts to about 80°. 



The compound crystallises from benzene in combination with the 

 solvent. 



B. Tri-p-Iodo-Triphenylcarbinol -|- Benzene. 



This occurs in large, yellowish needles having a strong lustre but 

 generally possessing no terminal planes. In the case of one single 

 individual however a few angles were measured. No trace of efflo- 

 rescence was noticed in the crystals. 



1) There is no question of a direct isomorphism. By exchanging the a- and ö-axis 

 we can find a' : b' : c' 1,189:1:0,9612; which (with double a-axis) somewhat 

 resembles the values for the bromoderivative. 



54 



Proceedings Royal Acad. Amsterdam. Vol. X. 



