Note 64 — Chapter XX · SULPHUR, SELENIUM, AND TELLURIUM

When an acid of the strength H2SO46H2O is taken, at first only the hydrate of the sulphuric peroxide, S2O7H2O, is formed, but when the concentration at the positive pole reaches H2SO43H2O, a mixture of hydrogen peroxide and the hydrate of sulphuric peroxide begins to be formed. A state of equilibrium is ultimately arrived at when the amounts of these substances correspond to the proportion S2O7 : 2H2O2, which, as it were, answers to a new hydrate, S2O92H2O. But its existence cannot be admitted because the sulphuric peroxide can be easily distinguished from the hydrogen peroxide in the solution owing to the fact that the former does not act on an acid solution of potassium permanganate, whilst the hydrogen peroxide disengages both its own oxygen and that of the permanganic acid, converting it into manganous oxide. Their common property of liberating iodine from an acid solution of the potassium iodide enables the sum of the active oxygen in them both to be determined.