202 ON AQUA REGIA AND HYPOSULPHURIC ACID. 
interesting as are the phenomena attending its action, the 
nature of the same is still but incompletely known. 
2. Berthollet attributes the properties of aqua regia to 
the formation of chlorine and nitrous acid. 
3. This hypothesis was adopted by Sir H. Davy, who, 
after having mixed hydrochloric acid with nitrous acid, ob- 
tained a liquid, which did not possess the properties of aqua 
regia. 
But in the days of Davy hyposulphuric acid was not 
known. The English chemist, therefore, may have ope- 
rated with this acid, which seems the more likely, as several 
French chemists, at the instance of Professor Dumas, regard 
this acid as a compound radical, as an oxidising agent less 
powerful than nitric acid, capable of replacing hydrogen in 
some organic substances, which contain more than one 
equivalent of this metalloid (hydrogen.) 
4. Finally, Millon considers nitrous acid as the most 
powerful oxidizing agent of all the stages of oxidation of 
nitrogen — an hypothesis which leads to the assertion that 
the hydrogen of hydrochloric acid may destroy the nitrous 
acid, as the same metalloid may deoxidise nitric acid. 
5. We have, therefore to ascertain whether hydrochloric 
acid reduces nitric acid to hyponitric acid, to nitrous acid, 
or to binoxide of nitrogen. 
6. If it could be proved that nitrous acid, of all the three 
oxyacids of nitrogen, is the most powerful oxidising agent, 
we might give preference to the latter hypothesis. But, 
recollecting the observations made by Davy (3,) and con- 
sidering the oxidising power of the hyponitric acid, the for- 
mation of which, by the reaction of oxide of nitrogen on 
nitric acid, precedes the production of nitrous acid, we ar- 
rive at the conclusion, that hydrochloric acid can reduce 
nitric acid only to the state of nitrous acid. 
7. The constitution, however, of oxysulphuric and analo- 
gous acids leads us to suppose that hyposulphuric acid is a radi- 
cal ; but, on the other hand, the formation of hydrochloric and 
