Lava lamp -with oil and salt

Salt is poured onto the layer of oil . Salt and oil do not mix . The oil covers the salt and protects it from the water. As the salt is heavier than water it will sink taking with it some of the oil that sticks to its crystals.

Salt is soluble and at the bottom of the glass the salt dissolves and as the oil has a lower density than water it will rise. The salty water provides a buoyant force that lifts the oil quickly to the surface.

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A simple lava lamp . You can do this at home
You will need the following. A tall glass. Vegetable oil Salt 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..
Questions. Using the words density, soluble and buoyant explain how this simple lava lamp works. Click once to show the solution