148 PROCEEDINGS OF THE AMERICAN ACADEMY 



In a third experiment the mixture of tribromdinitro benzol with 

 nitric and fuming sulphuric acids was boiled for only a quarter of an 

 hour, instead of for the usual five hours, and the proportion of tetra- 

 bromdinitrobenzol formed was comparatively small, it would seem, 

 therefore, that it is formed chiefly in the later part of the boiling; but 

 it is not advantageous in preparing tribromtriuitrobenzol to diminish 

 the length of the hoiling, as the superior purity of the product does 

 not compensate for the much smaller yield. We may add, that 

 another experiment showed that it was impossible to convert tribrom- 

 triuitrobenzol into tetrabromdinitrobenzol by boiling it with the mix- 

 ture of nitric acid and fuming sulphuric acid. 



Von Richter, the discoverer of tetrabromdinitrobenzol, gave the 

 melting point 227-228°, whereas our substance showed a constant 

 melting point of 224°. We are of the opinion, however, that Von 

 Richter's melting point is more correct than ours, as it might well be 

 that a small quantity of tribromtrinitrobenzol, sufficient to lower the 

 melting-point 4°, could not be removed by crystallization, and in fact 

 our analysis seems to indicate the presence of such an impurity ; but 

 as our object was to identify the substance rather than study its prop- 

 erties, we did not think it worth while to sacrifice the large amount of 

 time and labor which would undoubtedly have been necessary to 

 settle this point thoroughly. Von Richter also states that it is soluble 

 in alcohol or benzol, and Bodewig* has published a thorough descrip- 

 tion of its crystalline form. The following properties, which we have 

 had occasion to study, have not been published heretofore, so far as we 

 can find. It begins to sublime at about 175°, and is soluble in me- 

 thylalcohol, ether, acetone, glacial acetic acid, or carbonic disulphide ; 

 the best solvent for it is a mixture of alcohol and benzol, in the 

 former of which it is but sparingly soluble. It dissolves in cold sul- 

 phuric acid, but is precipitated unchanged on dilution. When heated 

 over a free flame with sulphuric acid, it is destroyed. The bromine 

 in it is much more firmly attached to the molecule than in the tri- 

 bromtrinitrobenzol, as it is not removed when the substance is boiled 

 with alcoholic ammonia in open vessels. It is also very hard to effect 

 its complete decomposition in its analysis according to Carius. 



Finally, we may remark that it is highly probable that the substanre 

 melting above 200° obtained by Wurster and Beran by heating tri- 

 bromdinitrobenzol to 220° in a sealed tube with a mixture of fuming 

 nitric and sulphuric acids was the tetrabromdinitrobenzol. 



* Zeitschr. Kryst., iii. 398. 



