A few weeks ago, Lillie and I tried this science experiment. I found the idea on Pinterest and this site: http://msdsgarden.blogspot.com/search/label/Science%20Experiments
First, We cut a 2 liter bottle in half.
Next, we put about 1" of warm water in the bottom of the bottle and colored it blue with food coloring.
Last, we inverted the other half of the bottle (with the lid on) and put ice in it.