210 ON AQUA REGIA AND HYPOSULPHURIC ACID. 
We know not, whether in the action of the metal on the 
nitric acid, the formation of a nitrite always precedes that 
of a nitrate ; but it does not appear to me that the production 
of a nitrite by the action of an alkali on a saturated solution 
of oxide of nitrogen in nitric acid, permits us to accede to 
the hypothesis of M. Millon, because the formation of hy- 
ponitric acid precedes that of nitric acid, and because, if the 
nitric acid, as is generally the case, be present in excess, 
only hyponitric acid is formed. Nor do I conceive how 
nitrous acid, one of the most powerful oxidising agents, can 
combine with protoxide of mercury. The presence of ni- 
trite of protoxide of mercury, the circumstances attending 
its formation, the property of the phosphorous acid to resist 
the oxidising power of the nitrous acid, the formation of 
nitrous acid by the action of hydrochloric gas on nitric acid 
and hyponitric acid ; the production of hyponitric acid by 
the action of oxide of nitrogen on an excess of nitric acid, 
the circumstances attending the formation of nitrite of oxide 
of ethyl, and the influence of heat on alkaline nitrates are 
all facts wholly incompatible with the hypothesis of M. 
Millon; and the important observations made by the author 
himself, prove to evidence, that of all the stages of oxidation 
of nitrogen the hyponitric acid is the most powerful oxi- 
dising agent. 
If the reverse were the case, if the hyponitric acid were 
a less powerful oxidising agent than the nitrous acid, an 
anomaly would occur in the oxidising powers of these stages, 
for the greater the amount of oxygen they contain, the more 
powerful oxidising agents they are. In a manner, that 
oxide of nitrogen, which, in the presence of iron, zinc, or 
phosphuretted hydrogen, is converted into protoxide of 
nitrogen, resists the deoxidising power of copper. Nitrous 
acid, which yields one-third of its oxygen to copper, in the 
presence of phosphorus and hydrochloric acids, undergoes 
no change, though either of them may convert the hypo- 
nitric acid into nitrous acid. With reference to the nitric 
