ON AQUA REGIA AND HYPOSULPHURIC ACID. 203 
nitric acids, by mixing water with a solution of chlorine in 
hyponitric acid, is rather in favour of the assertion, that aqua 
regia is the result of a mutual action between the elements 
of the hydracid and those of the oxyacid — (H 2 Cl 2 )-f 
(N 2 4 + 0) = (H 2 +0) + (N 2 4 + C1 2 .) According to 
which, therefore, water and oxychloro-nitric acid are formed, 
the latter of which is little stable, and, like analogous acids, 
is decomposed in the presence of water. The latter hy- 
pothesis having been preferred to the two others, it was 
contemplated to allow an excess of gaseous hydrochloric 
acid to act on concentrated nitric acid. But by the mutual 
action of the said acids water is formed, the quantity of this 
liquid, however, gradually augments and is opposed to the 
complete decomposition of the acids; wherefore, in order 
quantitatively to determine the hydrochloric acid, the ele- 
ments of which combine with those of the nitric acid, it 
was necessary to protect the acids from the influence of 
water during the time of their mutual action — that is, to 
employ a liquid which combines with water the moment it 
is formed, taking care at the same time that this hygro- 
scopical substance be of such a nature as not to exert any 
injurious influence on the reaction, by which the latter 
might be rendered incomplete. 
8. Sulphuric acid may answer this purpose. This combi- 
nation, if present in great excess, possesses, in addition to 
this, the property, at the temperature of the disengagement 
of chlorine, of retaining in solution the hyponitric acid and 
the nitrous acid, a property indispensable for the demon- 
stration, as an excess of hydrochloric acid is necessary to 
replace the whole of the nitric acids employed, and this 
excess, therefore, must be determined. 
9. This determination requires that the influence of the 
chlorine be rendered inefficient, the quantity of which in a 
free state, under these circumstances, cannot be determined, 
as the chlorine in its free state, before it can be completely 
disengaged, under the influence of heat, from its solution in 
