This demonstration experiment can be used to illustrate the very high solubility in water of ammonia.
Ammonia solution is seen to be alkaline and various indicator colour changes can be demonstrated.
A flask, fitted with a glass jet, is filled with dry ammonia. Injecting water into the flask dissolves the ammonia, reducing the pressure inside the flask and causes a fountain via the jet.
The demonstration itself takes only a few minutes but needs careful advance preparation.