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# Disappearing Ghost Eggs

Call them vanishing, disappearing, or invisible... just know that Ghost Eggs are spooky because you can't see them in water!

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It looks like an ordinary glass of water... crystal clear water. But hiding just below the surface of the water is an amazing collection of large, jelly-like marbles that become invisible when submerged in water. The Jelly Marbles become invisible due to an identical index of refraction with the liquid. In other words, they vanish like ghosts! As you'll see, there's more to this experiment than meets the eye.

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# Experiment

1. Place four plastic cups on a table.  Fill each cup three-fourths full with room-temperature water.
2. Find the package of coloring tablets in your kit.  They’re sort of like food coloring, but won’t stain.
3. Drop a different-colored coloring tablet into each of three cups, leaving the fourth cup plain water.  For the best results, try using two of each color tablet in each cup.  Watch the water bubble and change color
4. After all the colors have stopped bubbling and fizzing, measure approximately one teaspoon of marbles and pour them into each of the three cups.  Pour one teaspoon of marbles into the cup of uncolored water, too.
5. Soak the marbles for at least three hours, checking on them every so often to check on their progress.  Make sure to notice the changes in shape and size; as they grow, the marbles will take some very unique shapes along the way.  Your scientists can point out all the different shapes that they recognize... our marbleologists have noticed everything from brains to the geodesic marble so famous at EPCOT in Disney World!  Your marbles should reach their maximum growth at 5-6 hours, but leaving them overnight is even better!
6. Meanwhile, have your scientists hunt in the bag of marbles for the single marble with the biggest growing potential.  Drop it into a separate clear cup.
7. Fill the cup nearly all the way to the top with water and let it soak for at least six hours or overnight.

#### What Happened to my Marbles?

Wow!  Those tiny, pebble-like balls filled up on water and transformed into tons of gooey, slimy, shimmery Jelly Marbles!

1. If you let your marbles soak overnight, when you come back to them in the morning most of the water should be absorbed.  If there is any extra water hanging around, pour it off.
2. Stick your hand in the cup of Jelly Marbles and grab three.  Lay them out on the table on a piece of paper towel.  Remember, they’re safe to touch!
3. Tell your young scientists that the marbles are now hydrated.  This means they have absorbed as much water as they possibly can.  The little marbles can grow up to 11X their original size when hydrated!
4. Using the ruler, measure the size of the Jelly Marble after it absorbs all that water.  Then, have your assistants draw a picture of a marble before and after it takes the plunge.
5. After you’ve determined how large your marbles have grown, ask your scientists if their predictions about the shape of the marbles were correct.  Let them know that wrong predictions are okay, that’s all part of the learning process!

#### The Ghost Marble

1. Have your young scientists take a look at the single Jelly Marble they left floating in the clear cup.  Hey, where’d it go?
2. Hold the cup up to the light and look at the water very carefully.  Can you see something that faintly looks like a Jelly Marble?
3. Slowly pour off the water until the Jelly Marble mysteriously appears.
4. The marble takes on a ghostly appearance because it’s 99% water.  You can barely see the outline because the light passing through it is refracted (bent) by the edges of the marble.  The more you touch the marble, the more visible it becomes because of the oil and dirt on your fingers.

# How Does It Work?

Ghost Eggs are more commonly known as Jelly Marbles. Jelly Marbles start out as hard crystals, but they are actually made from a superabsorbent polymer that absorbs 300 times its weight in water. These hydrophilic spheres are approximately 99% water. If you look closely, you can barely see the outline of the sphere in the bowl of water.  That’s because light passing through the sphere is only refracted (or bent) by the edge of the sphere. Without this refraction along the edges, the Jelly Marbles would seem to vanish altogether. In other words, the water-filled Jelly Marbles become invisible due to an identical index of refraction with the water in the bowl. The secret is to keep the Jelly Marbles clean and free of oil from your skin. The more you touch the spheres, the less invisible they become because dirt and oil on your fingers are transferred to the surface of the sphere, which also reflects the light to reveal the sphere.