A cup of ice cubes a cup of crushed ice, or a cup of plain water. Fill one glass with ice cubes. Fill one glass with crushed ice. Fill one glass with water. Let the objects melt, then mark the water levels.
Water expands as it freezes.
Drop an ice cube in each one. Salt increases the buoyancy of the ice cube. The part of the ice cube that is above the surface of the water will take longer to melt. Now place the two filled non-glass jars in the freezer. Check every half hour.