374 PROCEEDINGS OP THE AMERICAN ACADEMY 



which had acted on trichlorbenzol in the way already described, and 

 found that this acid converted the tribrombenzol, even when the mixture 

 was carefully cooled, direct into tribromdiuitrobenzol, no mononitro 

 compound being formed ; and further, that by the action of a mixture 

 of this nitric acid with fuming sulphuric acid on tribromdiuitrobenzol 

 the tribromtrinitrobenzol, melting point 285°, was formed without 

 difficulty in open vessels. We therefore confirm completely the 

 results of Koerner, so far as they a2)ply to the di and trinitro com- 

 pounds, in opposition to those obtained by one of us, and by Wurster 

 and Beran ; and, to make the comparison more striking, we have used 

 for these experiments tribrombenzol made from some tribromaniline 

 prepared in Berlin by one of us during his previous experiments. 

 To sum up the whole case in a few words, it appears that our nitric 

 acid of specific gravity 1,505-1.51 is much more efficient in its action 

 than the commercial fuming nitric acid used in the laboratories of 

 St. Petersburg* (1.52), Berlin,t and Munich $ (1.534) ; and we are 

 inclined to ascribe the high specific gravities of these commercial acids 

 in part to the presence of lower oxides of nitrogen, while the specific 

 gravity of our acid was due probably exclusively to HNOg, since it 

 was prepared in our laboratory directly from nitre and sulphuric acid, 

 not pushing the reaction beyond the formation of acid potassic sul- 

 phate. This explanation is based upon the observation of Kolb,§ 

 that the specific gravity of nitric acid is raised by the solution of 

 nitric dioxide in it ; and although we cannot submit it to direct 

 experimental proof, since commercial fuming nitric acid is not to be 

 had in this country, yet the following examination of a nitric acid 

 similar to that used in foreign laboratories makes it exceedingly 

 probable that this explanation is correct. This acid was prepared by 

 distilling common nitric acid twice with an excess of sulphuric acid ; 

 it had a decided yellow color, and a specific gravity of 1.535 at 15° 

 (the temperature at which all our determinations were made), but 

 converted tribrombenzol into tribrommononitrobenzol only, when act- 

 ing in the cold, although it gave the dinitro compound when boiled 

 with it. It was therefore less efficient than our acid of specific 

 gravity 1.51, but more so than the foreign acids mentioned above. 

 The analyses of this acid and of our acid of 1.51 specific gravity 

 yielded the following results, which are given in tabular form to 

 facilitate comparison. 



* Beilstein and Kurbatow. t Jackson. 



i Wurster and Beran. § Ann. China. Phys., ser. 4, x. 137. 



