( 792 ) 



The symmetry is triclmo-pinacoïdai. Axial ratio: 

 a : b :c = 0,5719:l : 1,4298. 



A = torn' rc = uw 8' 



7?=J23^15' /?=:J26°21' 



C= 98^ 5' 7 = 107° 32' 



Forms observed: b = {0W\, very predominant and lustrous; 



c = \0(n\ and a = \iOO\, well developed and yielding sharp reflexes i 



q=\On\, also rather largely outgrown; r = |T02|, narrow but 



readily measurable. 



The habit is flattened towards lOlOj but elongated along the «-axis. 

 Perfect cleavage parallel jOlOj. 



Angular values: Measured: Calculated: 



a:b = (100) : (010) = -98° 5' _ 



c:b = (001) : (010) =: *78' 48' — 



c:a = (001) : (J 00) = *56° 45' — 



a : r = (100) : (lOÏÏj = *50° 10' — 



b:q = (010) : (Oil) =: -44° 4' — 



a:q=z (100) : (Oil) = 106^ 8\/; 

 The ratio of the axes a and b in the two derivatives is quite analogous. 

 In accordance with the supposition of a varying benzene percentage 

 the angular values of the individual crystals vary rather considerably. 

 § 3. When we compare the three ;;^zra-substituted trihalogen- 

 compounds of triphenylmethane with each other, there can be no 

 doubt as to the analogous molecnlai- structure of the derivatives 

 in the solid condition. Only in optical orientation the chioro-componnd 

 distinctly ditFers: 



Tri-j)- Chloro-compound : 

 Rhombic-bipy ramidal . 

 Forms : 



|110|;|011|;|010|;|130;;|OJ2|;|102j 

 a :/;:C=n 0,5904: 1 : 0,9261. 



Cleavable towards 1110,'. 



Thick-prismatic towards the c-axis. 



(110):(irO)z=61° 7' 

 (110): (Oil) = 69^ 47V; 

 (Oil): (01!) = 85° 36' 

 Sp. Gr. = 1,435; 

 Equiv. Vol. 242,16. 



Tri-p-Bromo-compound -. 

 Rhombic-bipyraniidal. 

 Forms : 



ril0j:|0rii;|010|;|102| 

 rt:/>:c' = 0,5896: 1:0,9003. 1 



Cleavable towards |110|. j 



Short-prism, tow. tlie c-axis' 



(110) : (110) = 61° 3' 

 (110): (Oil) =70° 8' 

 (Oil) : (Oil) = 83° 59 v; 

 Sp. Gr. = 1,752; 

 Equiv. Vol. 274,54. 



I Tri-p-Jodo-compound : 

 I Rhombic-bipyramidal. 

 Forms : 



lllOj ; jOllj ; |130| 

 a :6:t' = 0,5765:1:0,8798. 



Probably cleavable to- 

 wards jllÓj. 



Elongated prisms towards 

 the c-axis 



(110):(irO) = 59°55V; 



(110) :(0J1) = 70^47,' 



(Oil): (Oil) = 82' 41' 



Sp. Gr. = 2,141 ; 



Equiv. Vol. : 290,64. 



