Salt Finger Putting hot salt water on pure water

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Water tank 2 glass cups   Working fluid Upper layer: salt and phenolphthalein dissolved in hot water Lower layer: sodium hydroxide solution   Visualization Where the upper and lower layers mix, the phenolphthalein and sodium hydroxide react and turn red.   Experimental process As if doing a magic trick, place a sheet of paper over the salt water cup turn it upside down, place it on top of the other cup, and pull the paper out with a flick of the wrist.