A simple lava lamp .
You can do this at home

You will need the following.

A tall glass.
Vegetable oil
Food dye.

Three quarter fill a tall glass with water. Add enough cooking oil to make a 2cm deep layer.

Pour salt onto the layer for 5 seconds as shown on the left.
Notice how the oil will sink and rise from the bottom. Repeat this by adding more salt. Click to see a 120kb movie.

The oil will sink and rise as shown on the right.

Click to see a 120kb movie..

Using the words density, soluble and buoyant explain how this simple lava lamp works.
Click once to show the solution