═══════════════════════════════════════════════════*/ Let say, the mixture of potassium hexacyanoferrate(III) and phenolphthalein is the rust indicator. And we use to detect the rusting of the iron nail. And the result is: the idea, head area of the nail appear blue color; the straight location appears pink color. With a few transfer circumstance https://alphonsel544zpf2.wikiexpression.com/user