( 791 ) 



The optical axial plane for all rays is jOOlj ; the a-axis is the 

 first bisectrix with positive character. Average strong, rhombic dis- 

 persion, with q'^v, the apparent axial angle in cedar-oil (1,54) is 

 about 68°. 



The sp. gr. of the crystals is 2,141 at J 5°; the equivalent volume 

 290,64. 



Topic parameters : x : V' • ^'^ = 4,7883 : 8,3061 : 7,3077. 

 B. Tri-p-Jodotripheiiylmethane -{- 1 Benzeiie. 

 Large, very lustrous and transparent crystals. 



^:^ 



Fig. 2. 

 Tri-p-Jodo-Triphenylmethane + 1 Benzene. 



When taken out of the motherliquor they keep transparent for a 



fairly long time but after a few hours they lose all their benzene 



vi^hile retaining their form; sometimes there is only a partial loss. 



It is not improbable that the amount of benzene varies with the 



temperature and pressure. 



