Purpose: To dramatically show the effect of the expansion of water as it freezes.

Completely fill the ice bomb with water and screw the cap on tightly. Completely surround the bomb with dry ice and place the wire cage over the assembly. Go on with your lecture. In 5 to 10 minutes -- long enough for the class to have lost interest in watching it -- the bomb will explode with a loud bang. Note: Anyone within about 2 meters of the explosion might be sprayed with water. The screen should stop any flying pieces of bomb.

You might want to take advantage of the dry ice lying around, by dropping a piece of it into a beaker of water and asking the class to explain what the mist is that rolls out. (Water vapor droplets condensed from the air by the cold gas.)

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