Rainbow Density Column

Using a knowledge of liquid density, you can easily "stack" several liquids on top of each other! Use food coloring to make a rainbow of colors.

Materials:

• Liquids of different densities: honey, corn syrup, dish soap, water, vegetable oil, rubbing alcohol
• Graduated cylinder or tall glass or jar
• Pipets (medicine droppers)
• Food coloring

What to do:

1. Pour an inch (or however much you want) of honey into the bottom of the cylinder or glass.
2. Use food coloring to color a little bit of corn syrup (if it's the light kind; just leave it brown if it's the dark kind). Slowly and carefully pour an inch of the corn syrup on top of the honey.
3. Color some liquid dish soap and carefully add an inch on top of the corn syrup. You may find it easier to use a pipet for this one instead of pouring.
4. Next, use a pipet to add an inch of colored water on top of the dish soap.
5. You won't be able to color the vegetable oil, because food coloring is water-based and water and oil don't mix! Go ahead and add an inch of oil on top of the water.
6. Finish it off with an inch of colored rubbing alcohol. (If you have lamp oil, you could also add that to the very top.)
7. Voila - a beautiful rainbow of stacked liquids!

What's happening?

Each of the liquids you used had a different density. You added them to the cylinder in order of most dense (honey) to least dense (rubbing alcohol). Since each new liquid was less dense than the one before it, it floated on top instead of mixing together. You can try other liquids, if you want to! To figure out where your new liquid would fit in the column, you can measure the density of all the liquids. Measure an exactly equal volume of each liquid and weigh it (be sure to subtract the weight of the container). Even though the amount of liquid is the same, the denser ones will be heavier. (Density = mass/volume.)

There are many different things that affect density, such as temperature. Heat causes substances to expand and become less dense, while cold causes them to contract and become more dense. (One exception is water - it becomes more dense with cold until the freezing point, but it freezes in a crystalline structure that makes ice less dense than liquid water.) Adding things to a liquid will also change its density. For example, salt water is more dense than regular water (which is why it's easier to float in salt water than in fresh water!). You can try building a density column using only colored water. Try stacking hot, cold, and room temperature water, or try building a column with salt water, sugar water, and fresh water.

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