Touch supercooled water drops with an ice crystal and trigger them to freeze instantly.

During candy making, a single sugar crystal can cause an entire batch of sugar syrup to crystallize, just as a single ice crystal in this activity causes an entire water drop to freeze.

• a timer

1. Stretch the plastic wrap over the mouth of the bowl.

It is possible to cool purified water to temperatures below freezing (32° F) and have the water remain liquid—this is called supercooled water.

The addition of a seed crystal to supercooled water will trigger the formation of ice crystals.

The trick here is that the water must be clean. Any impurities in the water drops, such as dust particles, can trigger ice crystal formation, preventing the water from becoming supercooled. The smaller the drop, the greater the chance it will not have an impurity. The drops that solidified all contained impurities that triggered ice crystal formation. The drops that stayed liquid were all free of impurities.

Experiment with the amount of time you keep the water drops in the freezer before examining them. The exact amount of time depends on the temperature of your freezer and the size of your water drops. You want to find a time so that some of the drops freeze solid and a few remain liquid.