Scientific" Eggshellence"

Dusting off an article I wrote years ago for The Sentinel.

Scientific “Eggshellence”

As a distracted homeschooling mother I’ve had some unforgettable scientific experience with eggs. Do you know what happens when you put a pot of eggs on the stove to boil and then you forget all about them?  Let me save you the trouble of dangerous experimentation. They blow up!  I wasn’t smart that day, but I was brave. It isn’t easy to remove a pot of exploding eggs from the stove without losing an eye.

In honor of eggs, their invitingly economical price this week, and science, here are some seasonal science lessons.  The incredible, edible egg is also the terrific, scientific egg!

*Float an egg.  Put one cup of tap water into a clear glass.  Place a fresh egg in the water.  It will sink.  Remove the egg, then stir ¼ cup of salt into the water, one tablespoon at a time.  Replace the egg and it will float!  (In freshwater the egg is denser than the water, but in saltwater the water is denser than the egg.)  

*How strong are eggs?  Put four raw eggs of the same size in the second and fifth rows of an open, empty egg carton pointed ends down.  Gently stack books on top of the eggs in a balanced pile.  How many books can you stack?  This is a good demonstration of why a mother bird can sit on her eggs without breaking them.  (The egg’s shape of two domes pushed together, make it resistant to compression.  However, this shape is weak in tension, which is why baby birds can easily peck their way out.)

*Dissolve an eggshell. Put an egg in a container and cover it with vinegar. Bubbles will form on the eggs.  Let it sit for 48 hours.  When this is done, you’ll have an egg without a shell!  It’s held together by the membrane and is translucent. (Eggshells are made of calcium carbonate. Vinegar contains acetic acid, which breaks the solid calcium carbonate crystals into their separate parts. The carbonate goes to make carbon dioxide—the bubbles that you see—while the calcium ions float free. This is a good object lesson for showing kids what can happen to their teeth and bones if they don’t take good care of them!)

*Experiment with “naked” eggs.  Dissolve the shells of 2 eggs. Put one shell-less egg into a small container and cover with corn syrup.  Put the other shell-less egg in a small container covered with water.  Put both eggs in the fridge.  After 24 hours, take a look.  The egg that was in the water will be plump. The egg from the corn syrup will be shriveled. (The membrane of the “naked” eggs is selectively permeable. It will allow some molecules to move through it, blocking others. Water moves through the membrane easily, but sugar molecules are much bigger, so they won’t pass through.  In this situation, because egg white is 90% water and corn syrup is 25% water, water molecules from inside the egg will move outside, leaving it limp.)

*What’s the physics behind egg spinning? Take both a hard-boiled egg and a raw egg and spin them on a table.  Stop both eggs then let go of them.  The cooked egg will remain at a standstill while the raw egg will start spinning again! (The liquid inside the raw egg didn’t stop moving when you stopped the shell, so it starts the shell spinning again.) Now set the raw egg aside and spin just the cooked egg. Once it’s going fast enough (faster than 10 revolutions per second), the egg will spontaneously rise up on end! (Friction between the tabletop and the eggshell destabilizes the egg’s spin and causes it to shift position. Kinetic energy is converted to potential energy for a few seconds.)

*It’s magic!  Peel a hard-boiled egg.  Take a glass bottle with an opening slightly smaller than the egg and demonstrate how the egg will not fit through the opening.  Light a couple of matches and drop them into the bottle. Put the egg back into the opening and amaze your kids as the egg gets “sucked” into the bottle. (What’s really happening is that the heat in the jar expanded the air molecules, but then they contracted as they cooled. The air pressure outside of the jar was then greater than inside the jar, so the heavier air pressure outside pushed the egg inside the jar.)

*Try some natural dyes this year. To three cups of water and a teaspoon of vinegar add either one cup strained canned beet juice (pink), one cup purple grape juice (purple), one cup yellow onion skin, (orange), one cup torn red cabbage leaves (blue), or one teaspoon turmeric (yellow). Eggs must soak in the dye for half an hour. Experiment with other edibles to see what colors you can come up with.

*The golden egg. It would take many more pages to list all of the interesting facts about chicken eggs, not to mention all the other eggs in the world. A quick Internet search will give you a wealth of information.  Study the anatomy of an egg. Teach your children why some eggs hatch chicks, and some just make a good breakfast. Compare various bird eggs, learning why some are colored and speckled and how they get their shape. Compare bird eggs to reptile and amphibian eggs.  Learn the science behind heating, beating, and mixing eggs.  

Whatever you do, have an “eggshellent” week and experiment with something!