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Make your own Lava Lamp
You will need:
- 500ml plastic drinks bottle
- vegetable oil
- water
- food colouring
- an Alka-Seltzer tablet
What to do:
3/4 fill the bottle with the vegetable oil, then fill almost to the top with water. Add about 10 drops of food colouring. Add 1/8 of an Alka-Seltzer tablet and see what happens! Add more Alka-Seltzer when you need to.
The dissolving Alka-Seltzer tablet releases carbon dioxide, which nucleate on the coloured water and cause them to float to the top of the oil. When the bubbles burst at the surface, the coloured water sinks back down.
Although this might look a little like a lava lamp, these usually work with heat. The lamp contains two liquids, one of which is more dense than the other when they are both the same temperature (and so sinks below it) but becomes less dense than the other when it is heated.