Try it at home

Steps

1. Pour 3/4 cup of water into the bottle.
2. Use a funnel or measuring cup to slowly pour vegetable oil into the bottle until it’s almost full. It may take a few minutes for the oil and water to separate.
3. Add about 10 drops of food coloring. Any color works (red looks the most like lava). The drops fall through the oil and mix into the water at the bottom.
4. Break a tablet in half and drop one half into the bottle. Watch it sink to the bottom, and then watch the blobs start rising and falling.
5. When the bubbling stops, drop in another piece to start it up again. For a real lava lamp look, turn off the lights and shine a flashlight up through the bottom of the bottle.

To save your lava lamp for later, put the cap back on once it stops bubbling. To bring it back to life, add another piece of tablet.

Why it works

The oil floats on top because it’s less dense than water. The two don’t mix because water molecules stick to other water molecules and oil molecules stick to other oil molecules, but water and oil don’t stick to each other.

When the tablet hits the water, it makes bubbles of carbon dioxide gas. The bubbles carry blobs of colored water up through the oil. At the top, the gas escapes into the air, and the blob of water is heavy again, so it sinks back down.

Make it an experiment

• Does warm water or cold water make the blobs move faster?
• Does a bigger bottle make more blobs?
• Do smaller pieces of tablet make more blobs or fewer?