Ferroxyl indicator solution
Ferroxyl indicator is a solution containing potassium ferricyanide and phenolphthalein. It turns blue in the presence of Fe2+ ions, pink in the presence of hydroxide ions, and can be used to detect metal oxidation. It is often used to detect rusting in various situations.
It can be prepared by dissolving sodium chloride and potassium hexacyanoferrate(III) in distilled water, and adding the resulting solution to phenolphthalien indicator.[1]