Given general knowledge available to those skilled in the art, in particular the above-mentioned equilibrium reaction (1), a suitable mixture of (a) and (b), i..e. a ternary mixture of hydrogen peroxide (H2O2), lower aliphatic carboxylic acid RCO2H and corresponding carboxylic peracid RCO3H is obtainable in having either H2O and RCO3H or H2O2 and RCO2H together in H2O, provided that hydrogen perox