the present invention is concerned with a method of imparting storage stability to aromatic isocyanato sulphonic acids and to the stabilized mixtures so prepared . the aromatic isocyanates are combined with liquids which are non - polar , inert non - solvents having boiling points above 90 ° c . either before or after they are sulphonated to prepare the acids . the stabilized mixtures contain between about 80 to 10 wt . % of the inert liquids and about 20 to 80 wt . % of the acids .