Ammonia Fountain Demo 

Ammonia fountain demonstration.
Boiling ammonia solution is flipped so that a straw is placed into a large beaker of water with phenolphthalein added. As the flask cools the pressure drops and the constant atmospheric pressure pushes the water up the straw.
Once the water reaches the ammonia, the ammonia gas molecules dissolve in the water further reducing the pressure pushing down the straw causing the still constant pressure of the atmosphere to push the water up the straw even faster. As the ammonia and phenolphthalein mix the pink color becomes evident of the pH rising above 9.