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Make a lava lamp

Instructions

1. Fill the bottle about 3/4 full of water and add a few drops of food colouring.

2. Fill the rest of the bottle with cooking oil,and allow the components to settle and separate.

3. Screw the lid on tightly and invert the bottle. The oil should rise through the liquid to the top..

4. If you add salt to the floating oil, the oil should sink and then rise again!

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You will need:

A clean, transparent PET bottle
Oil (try different types)
Water
Salt
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Because the oil and water don't mix, you get some nice oily blobs circling around the bottle as you turn it upside down. Water is denser than oil and if left will settle to the bottom of the container.

Adding salt into the floating oil causes it to sink as it makes it more dense. However, once the oil reaches the bottom of the container the salt dissolves in the surrounding water, allowing the oil to rise back up to the top again.

Commercial lava lamps rely on heat from a lamp to expand oil, making it rise to the top of the lava lamp. This oil then eventually cools, contracting and falling down to the heat source to start the process again. This is known as a convection current which is very important in weather systems and ocean currents. Here is an experiment on establishing a convection current

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