Fill a test tube or beaker will two to three ounces of water. The test tube should be no more than half way full.
Place the test tube or beaker in a ring stand over a Bunsen burner or alcohol stove. If you do not have a ring stand, Bunsen burner or alcohol stove, consider using the double boiler method. To use the double boiler method, place the beaker in a pot and fill the pot with enough water so that the water line of the beaker coincides with the water line of the pot. Place the pot on a stove and bring the water in the pot to a boil. The double boiler method will not work with test tubes due to their rounded bottom.
Blow up three or four party balloons several times each to loosen the plastic. You need only one balloon for the experiment, but it's good to have a back-up in case the first balloon tears during the process.
Bring the water in the test tube or beaker to a boil.
Remove the test tube or beaker from the heat source. If you are using a Bunsen burner or alcohol stove, simply turn off the flame. If you are using a double boiler, remove the beaker from the pot of boiling water, using oven mitts, and set it on a heat resistant surface.
Stretch the opening of a balloon over the mouth of the test tube or beaker. If the opening of the balloon tears, use one of your spare balloons. The seal should be snug.
Sit back and observe what happens to the balloon.