OF ARTS AND SCIENCES. 875 



The nitric dioxide was determined in the usual way by treatment of 

 the diluted acid with a standard solution of potassic permanganate. 

 The results are not absolutely accurate, as observed by Feldhaus.f 

 because of the loss of nitric dioxide in transferring the acid from the 

 weighing or measuring tube to the beaker, but are nearly enough so 

 for our purpose. The nitric acid was determined by neutralization 

 with ammonic hydrate, and weighing the ammonic nitrate dried at 

 120°. It contained no ammonic nitrite. The estimated amount of 

 nitric acid corresponding to the nitric dioxide found has been subtracted, 

 so that the number given represents the percentage of free HNO3 in 

 the acid. These results show that the acid with the higher specific 

 gravity contains the smaller amount of HNO„, and therefore that the 

 determination of the specific gravity is not a trustworthy way of 

 finding the strength of nitric acid, unless the sample examined is free 

 from lower oxides of nitrogen. 



After the foregoing account of our work was already written we 

 received a paper by Nietzki and Hagenbach,J in which a similar ex- 

 perience is described ; for they found that with commercial fuming 

 nitric acid a mononitro compound alone could be obtained from di- 

 acetylmetaphenylenediamine, whereas they obtained the dinitro com- 

 pound by using "pure monohydrate," which, they say, can be prepared 

 most easily by distilling fuming nitric acid with twice the quantity of 

 sulphuric acid, and which had a specific gravity of 1.533 at 15°. It 

 is to be observed, however, that our experiment with an acid prepared 

 in a similar way shows that even this acid is not so pure as that made 

 direct from nitre and sulphuric acid. 



Preparation of Symmetrical Trichlorhenzol. 



"We have tried all of the three different processes known for making 

 trichloraniline, viz. : 1 st. By the direct action of chlorine on aniline 



* This number is higher than that given by Kolb as corresponding to this 

 specific gravity (1.51), which is 94 per cent. The difference may be due to the 

 presence of amines in the ammonia used by usi; but we have not studied this 

 point more carefully, as we are not interested in the absolute determination of 

 tlie amount of HNO3 in this acid, but only in the relative amounts of HNO3 in 

 these two nitric acids, which are given accurately by our numbers, since they 

 were obtained under exactly parallel conditions. 



t Zeitschr. Anal. Cliem , 1. 426. % Ber. d. ch. G., 1887, p. 333. 



