This demonstration shows the construction of of an eleven foot high barometer made with a concentrated solution of potassium tetraiodomercurate(II).
When water is squeezed into an inverted flask containing ammonia, the ammonia dissolves in the water and the reduced pressure causes a fountain effect.
Comparing the densities of mercury, potassium tetraiodomercurate(II) solution, and water illustrates that barometers made from the three liquids have different heights.
Balloons are placed on the tops of two Erlenmeyer flasks, one containing boiling water and the other containing hot air. As the flasks cool, the balloon on the flask of water is drawn into the flask.