Method of preparing storage-stable aqueous sodium peroxymonsulfate solutions

A method for preparing aqueous sodium peroxymonosulfate (NaHSO.sub.5) solutions which are storage-stable to the extent that no solid matter is separated and the loss of available oxygen is not more than 1.7% based on the initial value, during storage of 10 days at room temperature, and which have a content of 15% to 35% by weight sodium peroxymonosulfate by means of the partial neutralization of an aqueous solution, which contains Caro's acid and sulfuric acid and which was obtained by means of reacting sulfuric acid or oleum with at least 50% by weight aqueous hydrogen peroxide or by means of the electrolysis of an at least 30% by weight aqueous sulfuric acid with subsequent hydrolysis of the peroxydisulfuric acid formed, with sodium hydroxide or sodium carbonate at a temperature below 50.degree. C.;

• a solution containing Caro's acid (H.sub.2 SO.sub.5) and sulfuric acid being used which contains less than 2 parts by weight hydrogen peroxide per 100 parts by weight Caro's acid (H.sub.2 SO.sub.5) and the partial neutralization being carried out up to an equivalent proportion of total SO.sub.3 to sodium ions in the range of 1 to 1 up to 1 to 1.3, the total SO.sub.3 denoting that molar amount which is bound in said Caro's acid and sulfuric acid containing solution to be partially neutralized in the form of H.sub.2 SO.sub.5, H.sub.2 SO.sub.4 and H.sub.2 S.sub.2 O.sub.8.