Rainbow in a Glass

    Kids, can you imagine drinking a rainbow? In this example of the principle of density, you can! All that you’ll need is four glasses of the same size, sugar, water, and food coloring. 

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    Put three tablespoons of water into each of four of the glasses. Next add one drop of food coloring to each glass, using a different color for each glass. Then mix in one tablespoon of sugar into the first glass, two into the second, three into the third, and four into the fourth.

    Each of the glasses of sugar water will have different densities. The one with the most sugar will be the most dense (thick, or heavy), so use that as your main glass. Slowly and carefully, over the back of a spoon, pour the next-dense liquid (the one with 3 tablespoons of sugar) onto the densest layer. Repeat this careful pouring process until all of the liquids are layered on top of each other, with the least dense layer (one tablespoon of sugar) on top.

    Most experiments do this with liquids such as oil, water, alcohol, and cream, because they are easier to keep separate (see ChemShorts Jan 1999 for examples). As you can see during this experiment, though, just using different densities of sugar water is enough. Eventually, through the random mixing of molecules, and unlike oil and water, the different layers here will easily mix, so you have to pour or drink carefully. Still, this is an easily drinkable rainbow — if you have a fondness for sugar.

    NOTE: While this may seem like a lot of sugar in one glass if actually consumed, consider that a single can of regular soda has the equivalent of about 10 teaspoons of sugar. (


    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    December 2012


    Esther Inglis-Arkell,; she also describes using Skittles as a colored-sugar source. Many thanks also to Milt Levenberg for this idea.