. . . "sodium sulfate, (d) carbonates of an alkali metal such as potassium carbonate and sodium carbonate, (e) thiosulfates of an alkali metal such as sodium thiosulfate, (f) sulfates of a metal having an ionic radius of at least 1.30 ??? except an alkali earth metal and having a solubility in water at 25??? C. of at least 10 g/100 ml such as manganese sulfate, aluminum sulfate and magnesium sulfate and" . .