Floating Eggs – Potty Science Club

02/06/202110:0001/06/2021 12:36Leave a Comment

Hello and welcome to the 4th episode of Potty Science Club. We hope you have found our previous experiments interesting and enjoyable! All our experiments are conducted in a home environment, not in a laboratory and will be safe and simple using equipment and items you can find in your own home. The experiments will reflect on an item or exhibit held in the Museum’s collections.

Although it is now illegal to collect bird eggs, our museum has a large collection of eggs that were collected in the past. The Victorians were great collectors of bird’s eggs and found them fascinating.

Eggs have some amazing properties and over the next few sessions we will be finding out a little bit more about them.
In this experiment we will be asking two questions:
1 Do eggs float?
2 What is water density?

Question 1. Do eggs float? What do you think?
Confusingly you may have noticed that some eggs do float in fresh water, while others don’t. Why is this?
Some people say that a floating egg has gone bad and should be thrown away. But a floating egg does not necessarily mean a bad egg.

Fresh eggs don’t float, but all eggs have an air pocket that becomes larger as the egg ages and this acts as a buoyancy sack as it gets larger and fills with more air. So, an egg can float in water when its air sack has enlarged sufficiently to make it buoyant enough. This means the egg is older, but it may still be safe to use. The best way to determine if an egg is still usable is to crack the egg into a bowl and have a sniff. A spoiled egg will give off an unpleasant smell when you break open the shell, either when raw or cooked.

So, we know some eggs will float but not fresh eggs. Unless we help them to! This leads nicely to Question 2.
What is water density?
Have you ever noticed that it is easier to float in the sea than in a swimming pool? The reason for this is the difference in density between pool water and salty sea water which seems to hold you up.
But what does this mean?
The simplest explanation is, density is “the amount of stuff in a given amount of space.” So, if you were to weigh a glass of fresh water and the same amount of salty sea water, you would find that the salty water weighs more because of the salt.

Let’s put it to the test!

If we take 2 fresh eggs and put 1 in fresh water and the other into salt water, What do you think will happen?
Time for an experiment! You will need:

  1. Salt
  2. 2 fresh eggs
  3. 2 jars of the same size
  4. A table spoon
  5. A measuring jug
  6. A towel for mopping up if needed.

Put ¼ Litre of cold tap water into the measuring jug and carefully pour it into the first jar. Refill the measuring jug with ¼ Litre of water again and add 4 table spoons of salt, then stir well until dissolved. Carefully pour into the second jar. Now gently drop an egg into each jar and watch what happens.

So, what’s going on?
An object will sink if its density is greater than the water’s and float if its density is less. When we add the salt, it fills in between the gaps in the water’s molecules, increasing its density.
When enough salt is added to the water, the saltwater solution’s density becomes higher than the egg’s, and the egg will then float!

To confirm the results of your experiment and the freshness of the eggs simply do it again swapping the eggs around.
It’s an EGGCELLENT experiment don’t you think?

See you next time!

By Rob Gagliano, Casual Learning Development Leader and Natural Science Collections Volunteer

Written by museumvolunteers - Modified by Glenn Roadley (Curator, Natural Sciences)

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