Things you need:

• 16 oz plastic soda bottle, empty and clean, or a tall glass jar or vase
• Soda bottle cap
• Vegetable oil
• Food coloring
• An Alka-Seltzer
• Water
• Flashlight (optional)

The Experiment:

Fill the bottle 3/4 full with vegetable oil. Add water to the remainder of the bottle, almost to the top but without overflowing. Drop in 10 drops of food coloring, to make the solution appear fairly dark. Cut the Alka-Seltzer or Airborne tablet into 8 pieces. Drop one of the tiny pieces into the oil and water mixture. The mixture will start to bubble. As the bubbles rise, you’ll see globs of colored water rising as well, just like a lava lamp. Wait until the bubbling stops and add another piece of Alka-Seltzer or Airborne. Continue until there is no more Alka-Seltzer or Airborne left, and the bubbling has completely stopped. If you’re using a soda bottle, screw on the cap of the soda bottle. Tip the bottle back and forth and watch the wave appear. The tiny droplets of liquid join together to make one big lava-like blob. Place a strong flashlight or search light under the bottle. This will illuminate the bubbles for maximum effect.

So that’s how it works…

The Alka Seltzer tablet includes bicarbonate of soda which has the gas carbon-dioxide locked away in it's structure, and a dehydrated acid (such as citric or tartaric acid) this does not behave as an acid until you put it in water, at which point the acid releases the carbon-dioxide which forms bubbles.

The bubbles form a foam which will float in water and also in the oil, however water and oil are immiscible - they won't mix together so the foam stays in large lava-lamp like blobs and floats to the surface, where the bubbles pop and then the remaining water sinks again rejoining the water at the bottom.

How does a real lava lamp work?

A real lava lamp also uses two immiscible (they don’t mix) liquids. When the liquid on the bottom gets heated up by the lamp, it expands and becomes less dense, just enough to make it float the top, where it cools off and gets heavier, then sinks to the bottom again.

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