SCENE 1: APPARATUS INTRODUCTION
Step 1: Introduce Flask, 500 cm3 or 1 dm3 which is completely dry and filled with ammonia
Step 2: Introduce Two-holed rubber stopper to fit the flask fitted with a glass jet
Step 3: Introduce Plastic syringe (10 cm3) half filled with water.
Step 4: Introduce Trough or large beaker which can hold more water than the flask and filled with a mixture of water and an acid-alkali indicator (e.g. Universal indicator)
Step 5: White board or sheet of card to act as a background to improve visibility
SCENE 2: APPARATUS SETTING
Step 1: show inverted flask on who’s entrance the two way rubber stopper has been placed and the syringe has been placed inside the 2nd hole of the rubber stopper. The end of the glass jet with the smaller bore is show inside the flask and the one with the bigger bore is kept free for the moment.
Step 2: The end of the jet with the bigger bore is placed dipped inside the liquid in the trough as shown in the diagram and the white background is placed behind this whole arrangement.
SCENE 3: THE DEMONSTRATION
Step 1: Use the syringe to squirt a few cm3 of water into the flask and gently swirl to dissolve some of the ammonia gas.
Step 2: As the gas dissolves, a partial vacuum forms inside the flask and the external air pressure will force water up the tube and through the jet - forming a fountain (see first diagram). The ammonia gas dissolves in the water emerging from the jet and the indicator changes colour.
Step 3: The fountain continues for some minutes, depending on the size of the flask and the width of the jet. When the fountain finishes, a bubble of gas remains. This is air and its volume gives an indication of how well the flask was originally filled.