126 PROCEEDINGS OF THE AMERICAN ACADEMY. 



We are not, however, inclined to be too sure of the general occurrence 

 of this restriction of reactions to a single trimeta zone, since the excep- 

 tional action just mentioned, in which the second trimeta zone was in- 

 vaded, was accompanied by the formation of much tarry matter, and 

 therefore it is possible that the tarry products so frequent in these reac- 

 tions may have been formed by similar invasions of the second trimeta 

 zone. The bearing of these observations on the benzol formula of J. N. 

 Collie* is obvious. 



Preparation of Symmetrical Tribromdinitrobenzol. 



The description of the preparation of tribromdinitrobenzol is scattered 

 through a number of papers from this Laboratory, so that it would be 

 a matter of some difficulty to find it, and there would be danger that any- 

 one looking it up might not find the latest and best form of the process ; 

 we have thouglit it well, therefore, to give here a connected account of 

 this process. 



To make tribromaniline, 60 grams of aniline were treated with dilute 

 hydrochloric acid, and dissolved in four litres of water. Then a rapid 

 stream of air saturated with bromine vapor was drawn through the 

 liquid by means of a Bunsen pump, until it assumed a distinct yellow 

 color, which did not change for several minutes. The amount of bro- 

 mine required was about 320 grams. The precipitate of tribromaniline 

 was filtered out through cheese-cloth, washed until free from acid, and 

 dried by pressing with a screw press, followed by iieating to about 60° 

 over a steam radiator. 



To convert this tribromaniline into tribrombenzol, 100 grams of it 

 were dissolved in 600 c.c. of alcohol and 150 c.c. of benzol by the aid of 

 heat ; 40 c.c. of common strong sulphuric acid were then added to the 

 hot solution from a pipette, and any precipitate formed was dissolved by 

 longer heating, or even adding more of the solvents. Forty grams of 

 finely powdered sodic nitrite were next sifted into the hot solution as 

 rapidly as the violence of the reaction permitted, and the product heated, 

 until there was no more effervescence, after which it was allowed to stand 

 at ordinary temperatures over night, and then filtered and dried. 



The tribrombenzol was converted into tribromdinitrobenzol as fol- 

 lows. The perfectly dry tribrombenzol was mixed with four or five 

 times its weight of fuming nitric acid of specific gravity 1.51, and gently 

 heated over a low flame for two hours in a flask closed with a porcelain 



* 2 Proc. Chem. Soc, 1896-1897, p. 143. 



