Cool Swirling Milk Demo

http://chemistry.about.com/

In a shallow saucer of milk, place some drops of different color food coloring (in the center, or near the outside rim).  The food coloring will just sit there.  Using a cotton swab, or an eye dropper, apply a small amount of dishwashing liquid somewhere close to or far away from the food coloring drops.  Watch as the colors spontaneously move, swirl, and mix.

What's happening?  When the detergent is introduced into the milk, a few things happen simultaneously.  The surface tension of the milk is lowered by the detergent, which allows the food coloring and other components in the milk to flow around more freely.  Additionally, the structure of proteins in the milk is affected by the detergent; they change shape (denature) and move.  Finally, the fat in the milk forms micelles which are pushed around.  All of this movement causes the dyes to swirl and move, remotely from the actual application of the detergent.

For more about this demo, visit chemistry.about.com.  A nice you tube video can also be found here.