ON AQUA-REGIA. 
35 
theory of its formation from the elements of aqua-regia, gave 
no explanation of the simultaneous production of chlorine, 
which was invariably observed by all who have studied this 
acid mixture. 
M. Gay-Lussac has collected the gases evolved from 
aqua-regia at the temperature of boiling water; and, pass- 
ing them through a cooling mixture, has succeeded in con- 
densing a cloudy lemon-coloured liquid, very different in 
appearance from a mixture of nitrous vapour and chlorine, 
while chlorine gas passed oft'. 
This liquid was completely decomposed by water, with- 
out the evolution of any gas, and the solution contained 
hydrochloric acid, but no free chlorine. The amount of 
chlorine in the original gas was ascertained by precipitating 
the aqueous solution with nitrate of silver, and the relation 
which it bore to the other compound of nitrogen and oxy- 
gen was that of 2 equivs. to 1 equiv. 
An analysis of the gas by means of mercury, which ab- 
sorbed the chlorine, led to the same result, and confirmed 
the identity of the nitrogen compound with nitric oxide. 
The composition of the liquid is, therefore, expressed by the 
formula— 
N0 2 CI 2 
and this perfectly explains the simultaneous evolution of 
chlorine ; 3 equivs. of oxygen, separating from an equiva- 
lent of nitric acid, give rise to 3 equivs. of chlorine, 2 of 
which remain in combination with the nitric oxide, and pro- 
duce the new liquid acid, or hypochloronitric acid, while 
the other is liberated. 
Aqua-regia, however, prepared under different circum- 
stances, affords liquid products, which are by no means of 
such constant composition. When the muriatic acid of the 
mixture is replaced by common salt only just covered with 
the ordinary nitric acid of commerce, 2 equivalents of chlo- 
rine to 1.30 equivs., and another case to 1.53 equivs. of ni- 
tric oxide were obtained from the vapour of the liquid. 
