WHICH NITROGEN IS SUBSTITUTED EOE HYDROGEN. 
697 
almost as violently as the corresponding nitrate. By treating an aqueous solution with 
freshly precipitated chloride of silver, the hydrobromate is converted into the hydro- 
chlorate of diazobenzol. 
0-5315 grin, of substance, precipitated with nitrate of silver, gave 0-379 grm. of 
bromide of silver. 
Calculated. 
, ^ s 
G 6 H 3 Br N 2 69-32 
Round. 
HBr 30-68 
30-72 
100-00 
Perbromide of Diazobromobenzol, G 6 H 3 BrN 2 , HBr, Br 2 . 
By treating an aqueous solution* of any one of the previously-described diazobromo- 
benzol-compounds with excess of bromine-water, a crystalline orange precipitate speedily 
falls, increasing rapidly till all the diazobromobenzol has been precipitated. If too 
much bromine has been added the precipitate becomes generally of an oily consistency, 
solidifying, however, to a yellow crystalline mass as soon as the mother-liquor has been 
removed and the excess of bromine allowed to evaporate spontaneously. In order to 
obtain the perbromide, thus prepared, in fine crystals, it is dissolved in the smallest 
possible quantity of warm, not boiling, alcohol, from which it separates on cooling in 
yellow monoclinic prisms. A small portion only remains in the alcoholic mother-liquor, 
from which evaporation rarely recovers it, since it usually undergoes decomposition. It 
will, however, be seldom necessary to run this risk of losing part of the substance by 
recrystallization, for the compound is almost perfectly pure from the very first, and at 
all events quite fit to be employed for the experiments to be described further on. 
Under certain circumstances this perbromide is formed during the preparation of 
hydrobromate of diazobromobenzol from diazo-amidobromobenzol, in which case the 
two compounds are readily separated from one another by washing with cold water. 
Perbromide of diazobromobenzol crystallizes, as has been already remarked, in orange 
monoclinic prisms, insoluble in water, freely soluble in warm, difficultly so in cold 
alcohol, and very difficultly soluble in cold ether. 
On boiling an alcoholic solution decomposition ensues, and on heating the crystals 
alone they explode feebly, with disengagement of bromine vapour and nitrogen gas. 
Analysis gave the following results : — 
0-558 grm. of substance gave 0-304 grm. of carbonic acid and 0-054 grm. of water. 
0 4551 grm., ignited with caustic lime, gave with nitrate of silver 0-8135 grm. of 
bromide of silver. 
These numbers lead to the formula 
G 6 H 3 BrN 2 HBr 3 . 
* The crude aqueous solution obtained by the action of nitrous acid upon the nitrate of bromaniline may 
conveniently be employed. 
