Materials:

• Water
• Rubbing alcohol (poison — never drink this!)
• Clear, narrow-necked plastic bottle (such as a small water bottle)
• Food coloring
• Clear plastic drinking straw
• Modeling clay

Instructions:

1. Pour equal parts of water and rubbing alcohol into the bottle, filling about 1/8 to 1/4 of the bottle.
2. Add a few drops of food coloring and mix.
3. Put the straw in the bottle, but don't let the straw touch the bottom. Don't drink the mixture, either!
4. Use the modeling clay to seal the neck of the bottle, so the straw stays in place
5. Now hold your hands on the bottle and watch what happens to the mixture in the bottle.

Just like in any thermometer, the colored mixture expanded when it was warmed. When it expanded, it no longer fit in the bottom of the bottle and moved up through the straw. If the bottle were to get very hot, the liquid would have come all the way up and out the top of the straw.