Make a paste with 1 g of starch and a small amount of cold distilled water. Add, while
stirring, to 200 mL of boiling water. Stir rapidly for a few seconds and immediately remove from heat. Allow to cool. Place
5 mL of this solution in 100 mL of water and add 0.05 mL of 0.1 N iodine solution. The deep blue color produced must be
discharged by 0.05 mL of 0.1 N sodium thiosulfate. Test daily. Fresh indicator must be prepared when the end point of the
test titration fails to be sharp from blue to colorless. The starch solution should be refrigerated when not being used. Salicylic
acid (1.25 g/L) may be added as a preservative..