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The “Blue Bottle” experiment, which uses the indicator methylene blue, has long been used in chemistry to demonstrate oxidation–reduction and kinetics. The solution changes from colorless to blue as oxygen is added with shaking. If indigo carmine is used as an indicator in place of methylene blue, the solution changes from yellow to red–orange to green with shaking, forming a “Stop-’N-Go Light” effect. An interesting variation on this “Stop-’N-Go Light” is to use a Tornado Tube to join two, 2-L soda bottles. When one of the bottles is filled with solution and swirled, the solution first turns yellow, then red–orange, and then green as it falls into the second bottle.