Ammonia fountain. Ammonia solution being drawn into a vacuum created by ammonia easily dissolving in water. The conical flask (bottom) holds water with a chemical indicator. The round-bottomed flask (top) contained ammonia (NH3) gas. Allowing the easily soluble ammonia to contact the water resulted in it dissolving and creating an alkaline ammonia solution (purple due to the chemical indicator). This left a vacuum in the upper flask, which drew the ammonia solution up into the upper flask. This fountain effect is maintained by the upper flask being sealed and the lower flask being open to the atmosphere (tube at centre left).