Persulphuric acids

Abstract

Although it was observed by Faraday in 1834 that “if the acid were very strong, a remarkable disappearance of oxygen took place” on electrolysing aqueous solutions of sulphuric acid, it was not until 1878 that its disappearance was at all satisfactorily accounted for by the discovery of persulphuric acid by Berthelot. Only the anhydride, S 2 O 7 , was isolated by Berthelot, but he concluded that the corresponding acid was formed (1) on dissolving the anhydride in water, (2) on electrolysing strong solutions of sulphuric acid, and (3) by the interaction of hydrogen peroxide and ordinary sulphuric acid. The correctness of these conclusions appears to have been regarded as beyond question after Marshall had discovered in 1891 that well-defined salts of "Berthelot's acid" could be prepared by electrolysing solutions of potassium or ammonium hydrogen sulphate.