S 1727 (OTTO) Sodium bisulphite, GR Cas 7631-90-5 - used as a urine acidifier to reduce urinary stones in cats. S 1727 (OTTO) Sodium bisulphite, GR Cas 7631-90-5 - used in controlling outbreaks of crown-of-thorns starfish. It is a primary ingredient used in jewelry making to clean the surfaces. In addition to this, it is used as a food additive and serves as a reagent for the decomposition of basic metal oxides by fusion.