( 197 ) 



symmetrical vertical lines on the prism p, willi regard lo the twin- 

 section. The sp. gi'. of a perfectly homogenous fragment of a crystal 

 was found to be 2,465 at 15°; the equivalent-volume is therefore 

 169,98 and the lopical axes become: 



X : If, : to = 4,028G : 7,4713 : 5,G580. 



I ha\e tried, of course, to gain some insight into the progressive 

 course of the binary meltingpoint-lijie of these two isomorj)hous 

 derivatives, although the want of sufficient supply of material i)roved 

 a great obstacle. 



Tliis investigation had, however, soon to be abandoned because the 

 mixlures of the two substances assuming a much darker colour are 

 decomposed at their melting point with violent evolution of gas ; the 

 temperatures are situated between 210^ and 220^. The more the mixture 

 contains of the compound with the higher melting point, the more 

 readily the decomposition takes place, and therefore the only mixtures 

 of which I could sharply determine the melting point, were those 

 containing from 07o lo 4472V0 of Hie derivative with the higher 

 melting point ; this melted at 214^ the others between 210° and 214°. 

 I, therefore, suspect that we have here a continuous melting curve; 

 whether an absolute maximum occurs in the meltingpoint-line, such 

 as happens with the two non-nitrated initial products, could not 

 be decided. The mutual behaviour of these two isomorphous deri- 

 vatives probably corresponds entirely with that of the two tribro- 

 motoluenes. 



From mixed solutions of the two nitro-derivatives in benzene we 

 obtain large curve-planed and badly formed mixed crystals which 

 exhibit the same typical twin formation as the two components, but 

 which generally, possess only jllOj, |120| and jOOlj. They are unsuitable 

 for measuring purposes. 



c. l-S-4:-54ribromo-2-Q-di7iitrO'toluene. 

 C, . Br . Br . Br . (NO,) . (NO,) . (CH3) ; melting point : 216= C. 



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



When recrystallised from benzene, in \vhich this compound, which 

 was prepared in the same manner as the preceding ones, is less 

 soluble at the ordinary temperature than the two other isomers, the 

 substance is obtained in thick, quadratically-bounded, crystalline 

 plates, which at first sight appear tetragonal, an occurrence to be 

 expected, when taking into account the slight morphotropical force 

 of the (N05)-group, and the previously found tetragonal symmetry 

 of the corresponding tribromotoluene. 



