Turn on the tap water and run cold water. Fill a glass up halfway to the top.
Place a raw egg with an intact shell into the water. Place it in gently so it won't crack as it sinks to the bottom.
Allow the children to watch the raw egg sink to the bottom of the water glass.
Add 2 tbsp. of salt to the water and stir until the salt dissolves. The salt is dissolved when there is no visible salt at the bottom and the water is cloudy.
Watch the egg slowly float to the top of the glass of water. If it doesn't float with 2 tbsp of salt, continue to add 1 tbsp of salt, and stir until the egg starts to move towards the top.