r
hydrazoates). All the salts are explosive and readily interact with the
alkyl iodides. In its properties it shows some analogy to the halogen
acids, since it forms difficultly soluble lead, silver and mercurous salts.
The metallic salts all crystallize in the anhydrous condition and decompose
on heating, leaving a residue of the pure metal. The acid is a "weak" acid,
being ionized only to a very slight extent in dilute aqueous solution.

E. Noelting and E. Grandmougin (_Berichte_, 1891, 24, p. 2546) obtained
azoimide from dinitraniline, C_6H_3(NO_2)_2.NH_2, by diazotization and
conversion of the diazo compound into the perbromide,
(NO_2)_2C_6H_3.N_2.Br_3. This compound is then decomposed by ammonia,
dinitrophenylhydrazoate being formed, which on hydrolysis with alcoholic
potash gives potassium hydrazoate (azide) and dinitrophenol. The solution
is then acidified and distilled, when azoimide passes over. Somewhat later,
they found that it could be prepared from diazobenzene imide, provided a
nitro group were present in the ortho or para position to the diazo group.
The para-nitro compound is dropped slowly into a cold solution of one part
of caustic potash in ten parts of absolute alcohol; the solution becomes
dark red in colour and is then warmed for two days on the water bath. After
the greater portion of the alcohol has distilled off, the solution is
acidified with sulphuric acid and the azoimide distilled over. The yield
obtained is only about 40% of that required by theory, on account of
secondary reactions taking place. Ortho-nitro-diazobenzene imide only
yields 30%.

W. Wislicenus (_Berichte_, 1892, 25, p. 2084) has prepared the sodium salt
by passing nitrous oxide over sodamide at high temperatures. The acid can
also be obtained by the action of nitrous acid on hydrazine sulphate; by
the oxidation of hydrazine by hydrogen peroxide and sulphuric acid (A. W.
Browne, _J. Amer. Chem. Soc._, 1905, 25, p. 251), or by ammonium
metavanadate (A. W. Browne and F. F. Shetterly, _Abst. J.C.S._, 1907, ii.
p. 863).

_Ammonium azoimide_, N_3.NH_4, may be prepared by boiling diazohippuramide
with alcoholic ammonia, until no more ammonia escapes, the following
reaction taking place:

C_6H_5CO.NHCH_2CONH.N_2.OH + 2NH_3 = N_3.NH_4 + H_2O +
C_6H_5CO.NH.CH_2.CO.NH_2.

The liquid is then allowed to stand for twelve hours, and the clear
alcoholic solution is decanted from the precipitat