Equipment: Two jars (the same shape and size), aluminum foil, a marker.
1. Fill the two jars about half full of water. Check that the later level is the same in both jars and mark the level on the outside.
2. Make a foil cover for one of the jars.
3. Leave both jars in a warm place for a few days (not the oven). Then check the water levels again. Which jar has less water in it?
picture p. 12
How it works
The heat makes the water evaporate in both jars, but the foil cover stops the water vapor from escaping into the air so the level of water remains higher in this jar.