OF ARTS AND SCIENCES. 147 



These analyses and the melting point 224° prove that the substance 

 is the tetrabromdinitrobenzol melting point 227-228°, discovered by 

 Von Richter.* 



The following experiments were tried to throw light upon the 

 manner in which the tetrabromdinitrobenzol was formed. In the 

 first place, to prove that it was not formed from an impurity (tetrabrom- 

 henzol) in our tribrombenzol, we have prepared it from an analyzed 

 sample of tribromdinitrobenzol. This experiment was hardly neces- 

 sary, as the tribrombenzol and tribromdinitrobenzol used by us in 

 working on the large scale showed the correct melting points within 

 two degrees ; but we felt that absolute certainty on this point was im- 

 portant, and accordingly prepared some perfectly pure tribromdinitro- 

 benzol, melting point 190° (Von Richterf gives 191°, Koerner}: 192°), 

 which gave on analysis the following result. 



0.1658 grm. of the substance gave, according to the method of Carius, 

 0.2314 grm. of argentic bromide. 



Calculated for _ , 



C Br 3 (NO,),H. bound. 



Bromine 59.26 59.39 



This was treated with a mixture of nitric acid and fuming sulphu- 

 ric acid, precisely as in the preparation of tribromtrinitrobenzol, and 

 yielded a product which, after removing the unattacked tribromdinitro- 

 benzol, consisted of tribromtrinitrobenzol and tetrabromdinitrobenzol 

 in about equal parts, thus proving that the tetrabromdinitrobenzol is 

 not derived from an impurity, but is formed during the process. 



A second experiment had for its object to determine whether the 

 conversion of the tribromdinitrobenzol into tetrabromdinitrobenzol 

 was due to the fuming sulphuric acid, which might well be the case, 

 since Bassmann § has observed that symmetrical tribrombenzol is con- 

 verted in part into pentabrombenzol, when heated with fuming sul- 

 phuric acid to 100° from a week to a fortnight. We accordingly 

 heated another quantity of the pure tribromdinitrobenzol with an 

 excess of fuming sulphuric acid in a sealed tube to 100° for twelve 

 hours, but no tetrabromdinitrobenzol was formed, and, as the tempera- 

 ture of our mixture during the manufacture of the tribromtrinitroben- 

 zol could have been little, if at all, above 100°, and that process was 

 carried on for only five hours, we are inclined to ascribe the formation 

 of the tetrabrom compound to the nitric rather than the sulphuric acid. 



* Ber. d. ch. G., 1875, p. 1427. } Gazz. China., 1874, p 425. 



t Ber. d. ch. G., 1875, p. 1426. § Ann. Chem., cxci. 208. 



