bouncing raisins

This is the first time I've done this little "experiment" and it's so cool - even my 2 year-old was fascinated by the raisins.

Materials:
a tall clear glass
enough water to fill the glass about half-way
4 tablespoons of vinegar
3 tablespoons of baking soda
8 or more raisins

Fill the glass about half-way with water. Add the vinegar and baking soda. Make sure you use the given amounts - I just estimated and ended up with a major overflow when the mixture began to fizz. Drop the raisins into the glass, one at a time. They may sink at first, but they will eventually rise to the surface and then sink again. They will continue to "bounce" for about an hour.

What's happening? The combination of vinegar and baking soda creates bubbles of carbon dioxide. The bubbles collect on the raisins and lift them up. Then the bubbles escape at the surface and the raisins sink. The process repeats over and over. Pretty cool, huh?