416 KG:NE ON THE NATURE OF 4QUA REGI4, 
mind the observations made by Davy (3.), and take into consi- 
deration the oxidizing power of hyponitric acid, the formation 
of which in the action of nitric oxide on nitric acid precedes 
that of the nitrous acid, we come to the conclusion that hydro- 
chloric acid is capable of reducing nitric only to nitrous acid. 
7. However, the constitution of the oxy-sulpho-sulphurie acid 
and analogous acids, the hypothesis which regards the hyponitric 
acid as a radical, and the formation of hydrochloric acid and 
nitric acid on the addition of water to a solution of chlorine in 
hyponitric acid, lead rather to the view that agua regia is the 
result of a mutual reaction between the elements of the hydracid 
and those of the oxy-acid, 
(H + Cl) + (NO* + O)(H + O) + (NO* + Cl), 
in accordance with which therefore water and oxy-chloro-nitric 
acid are formed, which last is not permanent, but like the analo- 
gous acids, possesses the property of being decomposed by water. 
Since the last hypothesis was preferred to the two others 
(2.4.), it was determined to allow an excess of gaseous hydro- 
chloric acid to act upon concentrated nitric acid. But as in the 
reaction between these acids water is formed, and this liquid, 
whose quantity continually increases, prevents the complete de- 
composition of the acids, it was important for the quantitative 
determination of the hydrochloric acid, whose elements combine 
with those of the nitric acid, that the acids should be allowed to 
act on one another, protected from the influence of the water, 2. e. 
in the presence of a liquid which would combine with the water, 
as it was formed without this hygroscopic fluid having sufficient 
influence on the products of the reaction to prevent the latter 
from being completed. 
8. Sulphuric acid satisfies these conditions, ‘This compound 
moreover possesses, when it is present in great excess, the pro- 
perty of retaining the hyponitric and nitrous acids in solution at 
the temperature of the elimination of the chlorine, a property 
which is absolutely requisite for the decision of the question ; 
because an excess of hydrochloric acid must be used to destroy 
the whole of the nitric acid employed, and it is consequently 
necessary to determine the amount of this excess. 
9. This determination requires that we should be able to pro- 
tect ourselves from the influence of the chlorine, the liberated 
quantity of which cannot be determined under these circum- 
stances, because before the free chlorine has been expelled by 
