148 REPORTS ON THE STATE OF SCIENCE. 
The mechanism of this transformation was investigated by Blanksma,! 
who ascertained (i) that it was apparently a reaction of the first order ; 
(ii) that the speed was proportional to the square of the concentration of 
the hydrochloric acid ; (ii) that in aqueous acetic acid solution the speed 
increased with the concentration of the acetic acid. 
Recently Acree,” since we started work on this subject, has elaborated 
Blanksma’s work, and has brought forward an hypothesis to account for 
the proportionality of the velocity of the change to the square of the 
concentration of the catalyst. He believes that the formation of a salt, 
Ac 
Zl 
Ar. Nop from the chloroamine and the hydrochloric acid is the necessary 
‘H 
intermediate stepin the change. This suggestion was first made by Orton.” 
The complete ionisation of the hydrochloric acid requires that the concen- 
tration of the salt should be proportional to the square of that of the acid. 
It is however difficult to see why on this view hydrochloric acid should 
be the only catalyst. In fact, Acree believes his experiments show that 
other acids (sulphuric acid, &c.) or chlorine or bromine can act as catalysts, 
although in an inferior degree. 
In our experiments we used instead of the unsubstituted chloroamino- 
benzene, acetylchloroamino-p-chlorobenzene, the speed of the transforma- 
tion of which is far less than of the unsubstituted compound. The results 
are summarised in the following :— 
1. Hydrochloric acid is the only catalyst. 
(a) Hydrofluoric, sulphuric acids, &c., have no effect ; hydrochloric 
acid can always be detected when a change begins in the 
presence of these acids. 
(6) Chlorine and bromine are without effect until hydrochloric acid 
is formed. 
(c) Hydrobromic acid reacts with the chloroamines in glacial acetic 
acid quantitatively, thus :— 
Ar.NC].Ac+ HBr=Ar.NH.Ac+ BrCl. 
This primary change is followed by rapid bromination (dimolecular 
reaction). 
The interaction between hydrochloric acid and a bromoamine is similar : 
Ar.NBr.Ac+HCl=Ar.NH.Ac+ BrCl, 
and is followed by an equally rapid bromination. 
In dilute acetic acid, 90 per cent. and less, the reaction is :~-- 
Ar.NCl.Ac+2HBr=Ar.NH.Ac+ HCl+ Br,, 
which is followed by a slow bromination. 
2. Hydrochloric acid reacts with the chloroamine establishing the 
equilibrium : 
Ar.NCLAc+ HCl? Ar.NH.Ac + Cl). 
In glacial acetic acid the reaction is complete from left to right. As the 
acetic acid is diluted the left-hand side of the equation appears; in 90 per 
cent. acetic acid an equilibrium constant can be calculated. 
1 Receuil des Trav. Chim., 1903, 22, 290. 
2 Amer. Chem. Jour., 1907, 38, 258. 3 Proc. Roy. Soc., 1902, 71, 156. 
