Lava lamps contain colored liquids. these liquids form globs that rise to the top due to

Liquid motion lamps (which most people know as "lava lamps") have been around for decades. The theory behind a liquid motion lamp goes something like this:

In the lamp you have two liquids which are:

• Very close in density
• Insoluble in one another

Oil and water are insoluble in one another (that's where the expression "oil and water don't mix" comes from), but oil and water have very different densities (a volume of water weighs a lot more than the same volume of oil). They won't work, so you search to find two liquids that are very close in density and are insoluble. This site can help you in that search.

Now you apply heat to the bottom of the mixture. In a liquid motion lamp, the heat usually comes from a light bulb. The heavier liquid absorbs the heat, and as it heats up, it expands. As it expands it becomes less dense. Because the liquids have very similar densities, the formerly heavier liquid is suddenly lighter than the other liquid, so it rises. As it rises, it cools, making it denser and therefore heavier, so it sinks.

This all happens in slow motion because heat absorption and dissipation are fairly slow processes, and the density changes we are discussing here are very slight.

Here are some interesting links:

Originally Published: Apr 1, 2000

1. Fill the flask most of the way with your choice of oil.
2. Fill the rest of the flask with water. The oil floats and the water sinks to the bottom of the jar under the oil and looks like little, clear blobs.
3. Add a few drops of food coloring; your choice of color. The food coloring is water-based, so it will also sink and color the water that is now at the bottom of the flask.
4. Break an Alka-seltzer tablet into a few small pieces, and drop them in the flask one at a time.
5. Watch your lava lamp erupt into activity! As the chemical reaction slows down, simply add more Alka-seltzer.

A lava lamp works because of two different scientific principles: density, and polarity.

• Density is the measurement of how compact a substance is - how much of it fits in a certain amount of space.

(The scientific equation is density = mass/volume.)

If you measure an equal volume of oil and water, you'll find that the water is heavier than the same amount of oil. This is because water molecules are packed more tightly; a cup of water actually has more mass than a cup of oil.

Because water is denser than oil, it will sink to the bottom when the two are put in the same container. Density is affected by temperature—the hotter a liquid is, the less dense it will be.

• Polarity prevents the oil and water from mixing together.

Water molecules are "polar" because they have a lopsided electrical charge that attracts other atoms. The end of the molecule with the two hydrogen atoms is positively charged. The other end, with the oxygen, is negatively charged.

Just like in a magnet, where north poles are attracted to south poles ("opposites attract"), the positive end of the water molecule will connect with the negative end of other molecules.

Oil molecules, however, are non-polar— they don't have a positive or negative charge, so they are not attracted to the water molecules at all. This is why oil and water don't mix!

Real lava lamps use a polar and non-polar liquid just like our homemade one did. In a real one, however, the densities of the liquids are much closer together than vegetable oil and water.

The denser liquid sinks to the bottom, but the lava lamp light heats it up until it expands and becomes less dense, causing it to rise upward. As it gets farther from the light, it cools down, becoming denser again until it sinks; then the cycle starts all over.

Instead of using a light, in our homemade lava lamp, we used Alka-seltzer to power the lamp.

The Alka-seltzer reacts with the water to produce carbon dioxide gas bubbles. These stick to the water droplets. The water/gas combo is less dense than the oil, so they rise to the top of the flask.

At the top, the gas bubbles pop and escape into the air, allowing the dense water to sink back to the bottom again.

Lava lamps powered by heat are trickier to make and can use more hazardous materials. You can experiment fairly safely with things like rubbing alcohol and mineral oil or lamp oil. See if you can make a lamp powered by heat!