• 20 mL of bottled water
• A clean, dry plastic cup with a smooth surface
• A flat-bottomed bowl
• Ice cubes
• Table salt
• A tablespoon
• A clean, dry thermometer
1. Gather your materials on a flat surface.
2. Pour the water into the cup and put the cup into the bowl. If you can’t measure out exactly 20 mL of water, use about one and one-third tablespoons of water.
3. Fill the bowl with ice cubes around the cup. Make sure that you don’t drop any ice into the cup of water. Add enough ice so that the level of the ice cubes in the bowl is higher than the level of the water in the cup.
4. Sprinkle 2 tablespoons of salt evenly over the ice cubes. Make sure you don’t get salt in the cup.
5. Put the thermometer into the cup of water. Leave the cup of water to cool. For the rest of the experiment, be careful not to bump the cup of water while it cools.
6. After 10 minutes, carefully add more ice to the bowl like you did in step 3.
7. Repeat step 4.
8. Leave the cup of water to cool for another 10 minutes – or until the temperature of the water is below 0 °C.
9. Once the water is below 0 °C, carefully remove the thermometer.
10. Drop a piece of ice into the cup of water. What happens to the cup of water?