Rubbing alcohol can be purchased at your local pharmacy. Don’t drink the mixture once you’ve made it since it’s not safe to consume.
This step is optional if you don’t have any food coloring.
If the straw touches the bottom, the alcohol-water solution won’t be able to travel through it and your thermometer won’t work.
Modeling clay can be purchased at your local arts and crafts store. As an alternative, poke a hole through the bottle’s cap large enough to fit the straw through and twist it onto the bottle. Seal any of the edges with a small amount of clay.
The heat causes the air in the bottle to expand. Since the bottle is airtight and it can only expand through the straw, the water level moves up through it as it expands. The water may come out of the top of the straw if the water is too hot.
The air contracts as it cools down, making the water level drop inside the straw. The mixture inside your thermometer will freeze if it falls below 32 °F (0 °C) and it will not work.
