Trading Places – Liquid Magic

    Kids, here is a chance to use the scientific phenomenon of density and make a “magic trick”.  Take two glasses of different-colored liquids and watch the liquids switch places in the glasses! 

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

    For liquid materials, you need water and another liquid with a different density. If the liquids don't mix at all (such as water and oil), you will get a clearly-defined separation. If you use rubbing alcohol (isopropyl alcohol or isopropanol) or an alcoholic beverage (ethanol) with water then there will some mixing and the separation won’t be so clear. You’ll also need two small identical glasses (shot glasses work well) and a thin waterproof card, such as a driver's license or a thick plastic playing card of some type.

    Here is what you do:

    1. Fill one glass completely full with water.
    2. Fill the other glass completely full with the other liquid you selected.
    3. Have an adult partner place the card over the water glass and, while holding the card onto the glass, flip the water glass over and set it and the card on top of the second glass. (Tip, you may want to be near a sink for any spillage).
    4. Line the glasses up so that their rims are aligned and move the card so that there is just a tiny bit of open space at the edge of the glasses.
    5. Over the next few minutes, the liquids will exchange places. The alcohol or oil will rise to the top while the water sinks and fills the bottom glass. You can tint a water or alcohol-based liquid with food coloring to aid in watching this.
    6. If you use an alcohol, the separation isn’t well-defined because both rubbing alcohol and alcoholic drinks are partially diluted with water already.

    How it works:
    You could do this as a magic trick but really it is simple science. The two liquids have different densities and so the lighter liquid will float while the heavier liquid will sink. The result is the same if you remove the card entirely and quickly but this way it is easier to observe the change as it slowly evolves. 


    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    October 2009


    References: Dr. Anne Marie Helmenstine at