WHICH NITROGEN IS SUBSTITUTED EOR HYDROGEN. 
719 
PART III. 
All the diazo-compounds which have formed the subject of Parts I. and II. of this 
inquiry are derived from monoamido-compounds. If the composition of the latter be 
again expressed by the general formula H (y _ 2) (NH 3 )"0 z (see page 667), it is at once 
perceived that the process of formation of the diazo-compounds is similar to the reaction 
which takes place by the action of nitrous acid on ammonia : 
I. G x H (j ,_ 2) (NH 3 )" 0 z + NHG 2 = G x H (y _ 2) (N 2 )"O z +2H 2 0 *. 
^ yy ' '' ■ V * 
Monoamido-compound. Diazo-eompound. 
II. (NH 3 )" + NH0 2 =(N 2 )" + 2H 2 0. 
Ammonia. Nitrogen. 
By viewing the diamido-compounds in like manner as represented by the general 
formula G x H (y _ 4) (NH 3 ) 2 ", 0 z , it is evident that the action of nitrous acid may give rise 
to two decompositions : 
I- G x H (y _ 4) (NH 3 )- 0 2 +NH & 2 =G x H (y _ 4 ; (NH 3 )" (N 2 )" 0 2 +2H 2 0. 
II. G. H ( y- 4 ) (NH 3 )- 0,+2NH0 2 =<3, H (y _ 4) (N 4 f0 z + 4H 2 0. 
The hydrogen contained in one atom of ammonia can thus be replaced by nitrogen, 
or both atoms of ammonia present in the original compound may be replaced by nitro- 
gen, giving rise to a tetrazo-compound. 
Although this theory has not been fully confirmed by the action (presently to be 
described) that nitrous acid exerts on benzidine, since an intermediate compound 
according to equation I. could not be obtained, it is nevertheless highly probable that 
nitrogenous compounds in accordance with equation I. exist, and that further experi- 
ments with other diamido-compounds will confirm this view. 
Action of Nitrous Acid upon Benzidine. 
Benzidine, which Zinin, its original discoverer, expressed by the formula 
G 6 H 6 N, 
has been found, on further investigation by P. W. Hofmann, to have double the atomic 
weight first assigned to it, and to be a base capable of combining with two molecules of 
acid. Very recently Fittig has shown that it must be viewed as the diamido-compound 
of his newly discovered hydrocarbon-phenyl, and that it ought to be expressed by the 
rational formula G 12 H 8 (NH 2 ) 2 , or G 12 H 6 (NH 3 )" 2 . I entirely abide by Fittig’s view, 
but find it necessary to select for both compounds a somewhat modified nomenclature, 
in order to avoid the use of the same names for some derivatives of these bodies (which 
I shall have occasion to describe) already employed for several long-known derivatives 
* It must be borne in mind that nitrous acid acts upon the nitrates of the amido-compounds ; if otherwise, 
the reactions would frequently give rise to the formation of diazoamido-compounds formerly described by me. 
