Salt Volcano


 15 minutesWhat do I need?

  • A glass jar or clear drinking glass
  • Vegetable oil
  • Salt
  • Water
  • Food coloring (if you want)

Don't forget to be careful with glass.
 Mixing Ingredients

What do I do?

1  Pour about 3 inches of water into the jar.

2  Pour about 1/3 cup of vegetable oil into the jar. When everything settles, is the oil on top of the water or underneath it?

3  If you want, add one drop of food coloring to the jar. What happens? Is the drop in the oil or in the water? Does the color spread?


Wow! I didn't know that!

Lava Lites are lamps that were invented by an English man named Craven Walker in 1964. They are basically tall thin glass jars filled with liquid and a special kind of colored wax, set on top of a base with a light bulb. When the bulb is turned on, the lamp glows, the liquid heats up, and the wax begins to melt. Blobs of wax rise to the top of the lamp, then cool and sink back down--over and over again.



Shaking the salt4  Shake salt on top of the oil while you count slowly to 5. Wow! What happens to the food coloring? What happens to the salt?

5  Add more salt to keep the action going for as long as you want.

Six-year-old Nina Gumkowsky shared this activity with the other students in her first-grade class. Everyone loved it! They did it over and over again and kept trying to touch the layers. It was messy, but it was fun!

What's going on?

Why does the oil float on the water?

Oil floats on water because a drop of oil is lighter than a drop of water the same size. Another way of saying this is to say that water is denser than oil. Density is a measurement of how much a given volume of something weighs. Things that are less dense than water will float in water. Things that are more dense than water will sink.

Even though oil and water are both liquids, they are what chemists call immiscible liquids. That's a fancy word that means they don't mix.

What happens when I pour salt on the oil?

Salt is heavier than water, so when you pour salt on the oil, it sinks to the bottom of the mixture, carrying a blob of oil with it. In the water, the salt starts to dissolve. As it dissolves, the salt releases the oil, which floats back up to the top of the water.

Lava LitesThis looks like a Lava Lite. How does a Lava Lite work?

Like your oil and water, the "lava" in a Lava Lite doesn't mix with the liquid that surrounds it. When it's cool, the "lava" is a little bit denser than the liquid surrounding it. When the "lava" rests on the bottom of the Lava Lite, the light bulb in the lamp warms it up. As it warms up, the "lava" expands a little. When it expands, the "lava" stays the same weight but it takes up more space-so it's less dense. When it's warm enough, the "lava" is less dense than the surrounding liquid, and so it rises up to the top to float. At the top of the lamp, it cools down, becomes more dense, and sinks once again. This cycle repeats over and over as the "lava" warms up and rises, then cools down and sinks.

Where did this experiment come from, anyway?

Exploratorium Teacher-in-Residence Eric Muller created this activity while playing with his food in a Chinese restaurant.

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This and dozens of other cool activities are included in the Exploratorium's Science Explorer books, available for purchase from our online store.

About the Books

Published by Owl Books,
Henry Holt & Company, New York,
1996 & 1997

ISBN 0-B050-4536 & ISBN 0-8050-4537-6,
$12.95 each

© 1998 Exploratorium