Note 18 — Chapter XI · THE HALOGENS: CHLORINE, BROMINE, IODINE, AND FLUORINE
George Kamensky translation
When left exposed to the air aqua regia disengages chlorine, and afterwards it no longer acts on gold. Gay-Lussac, in explaining the action of aqua regia, showed that when heated it evolves, besides chlorine, the vapours of two chloranhydrides—that of nitric acid, NO2Cl (nitric acid, NO2OH, in which HO is replaced by chlorine; see Chapter on Phosphorus), and that of nitrous acid, NOCl—but these do not act on gold. The formation of aqua regia may therefore be expressed by 4NHO3 + 8HCl = 2NO2Cl + 2NOCl + 6H2O + 2Cl2. The formation of the chlorides NO2Cl and NOCl is explained by the fact that the nitric acid is deoxidised, gives the oxides NO and NO2, and they directly combine with chlorine to form the above anhydrides.