Note 57 — Chapter VI · TTHE COMPOUNDS OF NITROGEN WITH HYDROGEN AND OXYGEN

The action of a solution of potassium permanganate, KMnO4, on nitrous acid in the presence of sulphuric acid is determined by the fact that the higher oxide of manganese, Mn2O7, contained in the permanganate is converted into the lower oxide, MnO, which as a base forms manganese sulphate, MnSO4, and the oxygen serves for the oxidation of the N2O3 into N2O5, or its hydrate. As the solution of the permanganate is of a red colour, whilst that of manganese sulphate is almost colourless, this reaction is clearly seen, and may be employed for the detection and determination of nitrous acid and its salts.