Wettability
Explore further: guide water down a string and dress an egg in silvery camouflage!
Safety
- Perform the experiment on the underlay and use protective gloves to avoid staining your hands.
- Carefully review the general safety advice in the instruction book before starting the experiment.
- Do not eat any eggs used in the experiment!
Step-by-step instructions
* Dress an egg in silvery camouflage!
Please note: this experiment requires adult supervision. Take a boiled egg, a candle from the set, and any transparent cup or glass large enough to accommodate the egg. Fill the glass with water. Light a candle and singe the entire surface of the egg until it turns black. Keep the flame 1 cm (0.5 inches) away from the egg at all times. Put the sooty egg in the water: its surface will acquire a metallic luster.
* Guide water down a string!
For this experiment, you’ll need the piece of yarn from the set and two cups. It’s optimal if one cup has something to tie the yarn to (a measuring cup with a handle and spout would be perfect). Fill this cup with water. The second cup doesn’t need to meet any requirements—it just has to be empty.
Tie the yarn to the handle of the cup with water or hold it in place with your finger. Soak the yarn in the water. When the yarn is soaked through, put the free end in the empty cup.
Raise the cup of water high enough so that the yarn is taut, but don’t hold it directly over the empty cup; the yarn should be connecting the two cups on an incline. Pour some water from one cup to the other—the yarn will work like a pipe. Please note: pour slowly so the water doesn’t drip from the yarn.
Disposal
- Dispose of solid waste together with household garbage.
- Pour liquids down the sink. Wash with an excess of water.
Scientific description
- Dress an egg in silvery camouflage!
When exposed to flame, the egg becomes covered with soot. The soot consists of carbon particles, which are released as the paraffin in the candle burns. As the soot is hydrophobic, the surface of the singed egg becomes hydrophobic as well. Consequently, when the egg is submerged in water, it retains a layer of air on its surface. Some light is reflected on the border between water and air due to total internal reflection. This reflected light creates the metallic luster you see.
- Guide water down a string!
Water wets the fibers in the yarn very well, so it tends to spread along them. Moreover, the water is also in contact with air. The force of attraction between water and air, however, is much weaker than the force of attraction of water to itself, so water strives to lessen its area of contact with air. As a result, the water clings to the yarn, reluctant to form drops. But if you try to pour the water too quickly, gravity will overcome surface tension and some water will drip from the yarn.
