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Egg Bubbles
This week's experiment is a simple one, but it should make you
think a bit.
You will need:
Be sure to use a clear glass, so you can see what is
happening. Fill the glass with hot water from your kitchen sink. We will put
the egg into the water, so leave enough room so that the water does not
overflow. Your main goal is to have enough hot water so that the egg will be
completely under water.
Let the hot water sit for a few seconds, so that any air bubbles
can float to the top. Carefully place the egg into the hot water. Watch for
a minute. What do you notice? You should see one or more thin streams of
bubbles rising from the egg. The bubbles will continue for quite a long
time. If you listen carefully, you may also hear a tiny squeaking sound that
sounds almost like a baby chick.
What is happening? If you have ever peeled a boiled egg, you
know that there is an air bubble inside the shell. As we have seen in past
experiments, when you heat air, it expands and takes up more space. The air
bubble inside the egg is expanding as it is heated by the water. It is pushing
outwards, and it has to go somewhere.
The streams of bubbles were coming from microscopic holes in the
egg shell. Those holes are too small for the liquid part of the egg to flow
through, but they let air get in, so the developing chick can breathe. As the
air inside the shell expands, it flows out through the tiny holes. If the
water is too hot, then the air will expand faster than it can flow through the
tiny holes, and the shell will crack. That sometimes happens when you are
boiling eggs. To prevent that, start with room temperature water and heat the
water slowly after you add the eggs. That gives time for the air to expand
slowly enough to keep from cracking the shell.
The air forcing its way through the tiny pores sometimes makes a
tiny whistling or chirping sound. I tried several eggs, and it did not happen
with all of them. The eggs might spoil if you put them back in the refrigerator,
so only experiment with eggs that you are ready to eat.
Knowing that the tiny pores were large enough for air to pass
through, I wondered if they were large enough for a bigger molecule, such as
water or food coloring. To test that, I filled a glass with cold water. I
added a couple of drops of green food coloring and moved the egg from the hot
water into the cold, green water. If the pores were large enough for the water
to pass through, then as the air bubble inside the egg cools and shrinks, some
of the colored water should be pushed in through the pores.
I let the egg sit in the cold water for about 10 minutes. Then
I cracked the egg. I was hoping to find green color inside the egg, but at
first I was disappointed. Then I looked carefully at the inside of the
shell. There were quite a few tiny, green dots, showing that the water and
color had indeed been able to fit through the pore.
As a fan of Dr. Seuss
I hoped my eggs would be chartreuse.
Instead, my omelet came out yellow
but I'm an observant fellow.
I know that it came through in spots
because inside there were green dots.
So grab an egg and take a peek.
Be sure to have a wonder filled week.
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