How to make a rainbow in a jar

AUSTIN, Texas - This experiment helps to understand the concept of density.

Here’s what you’ll need:

A large, clear glass (I’m using a 24 ounce mason jar)
5 cups
Water
Table salt
Teaspoons
Food coloring
Pieces of foam
A funnel

Fill each of the five cups with ½ cup of water.

In one cup, add 4 tsp. of salt and mix until it’s dissolved. Add two drops of blue food coloring and mix in.

In the next, add 2 ½ tsp. of salt and mix until it’s dissolved. Add two drops of green food coloring and mix in.

In the third cup, add 2 tsp. of salt and mix until it’s dissolved. Add two drops of yellow food coloring and mix in.

In the fourth, add 1 tsp. of salt and mix until it’s dissolved. Add one drop of yellow and one drop of red food coloring. Mix in.

In the final cup, don’t add any salt. Add two drops of red food coloring and mix in.

Cover the bottom of the large, empty glass with a few pieces of foam. This foam will help to keep the colors from mixing.

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Science in Sweatpants: Make a rainbow in a jar

If it’s not disturbed, the rainbow could last for a few days!

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Start by pouring the blue liquid into the large jar. You don’t need to use the funnel here. Next, use the funnel to slowly pour the green liquid in. Pour the yellow liquid in next, followed by the orange, then the red.

At this point, you should see the colors layered on top of each other, creating a rainbow! If it’s not disturbed, the rainbow could last for a few days!

The colors layer, they don’t mix, because they’ve each got different densities.

Density

Each cup has the same volume, ½ cup. What’s different is the mass. We’ve changed that by adding salt to the cups.

The cup that you added the most salt to has the highest density, the cup with no salt has the lowest.

Fluids with higher densities will sink below fluids with lower densities.

The same thing happens with air in the atmosphere. When a cold front moves in, warmer, less dense air is forced upward. This often creates thunderstorms as the warm air cools and condenses as it rises higher in the atmosphere.

Note: You may notice the dry erase board says “sugar” instead of salt. You can use either for the experiment.