Testing the Skin of Water

Of course, water has no real 'skin' but it does have a tension at the surface that can be readily demonstrated by experiment. For instance, it is possible to overfill an ordinary glass so that the water stands some one-eighth of an inch higher than the edges of the glass. Take a dry glass and fill it almost to the top with water, taking care that none spills down the sides at this stage. Place the glass in the soup plate and then use the eye-dropper to add further water to the glass until the level is well above its edges. It is the surface tension of water which allows you to overfill the glass in this fashion. A further proof of this tension can be obtained by floating a razor blade on water. Place the razor blade on a small piece of tissue paper and float the paper on the surface of the water. After a minute or two the paper will become saturated (i.e., all the air will be driven from the paper and replaced by water) and it will sink to the bottom of the glass leaving the razor blade floating on the surface. You can use a needle in place of the razor blade.