The aromatic sulphonic acids are in general present as salts, in particular the sodium, potassium or lithium salts.The temperature data are in .degree.C.EXAMPLE 146.2 g of H acid=1-amino-8-hydroxy-naphthalene-3,6-disulphonic acid (monosodium salt) are dissolved in 120 ml of water with 30 ml of 11% strength lithium hydroxide solution, as a result of which a pH of 6.0 to 6.5 is set.