Fill a small pitcher full of water and dissolve a small amount of ferric ammonium sulfate in the water. Then make up a small amount of sodium salicylate solution. Get two wine glasses, and in the first wine glass do not put anything; in the second wine glass put a few drops of sodium salicylate solution. Then you pour some water from the pitcher into your first wine glass. It will remain clear, but when you pour from the pitcher into the second wine glass it will take on the color of wine.