Action:
Two large, tall cylinders which appear to contain water stand on the demonstration table. You drop an egg in one cylinder. It sinks but remains suspended half way down An egg dropped into the other cylinder falls to the bottom but begins to rise in a few minutes, only to fall again. The process of falling and rising continues indefinitely.

You Need:
Two large cylinders; 400grams salt; dilute HCI solution; two eggs.

Why:
In the first cylinder the egg sinks in ordinary water but remains suspended above the dense salt solution. In the second cylinder, carbon dioxide gas surrounding the egg gives it buoyancy. Loss of gas attached to the egg causes it to lose buoyancy. This occurs when the egg has reached the surface of the solution.

How:
Place the salt in one of the cylinders. With stirring, add water until the cylinder is about one-fourth full. The salt solution should be saturated. Now carefully pour water down the sides of the cylinder until it is nearly full.
To prepare the second cylinder, pour 40 ml. of 6N HCI into it.
Add water until nearly full.

Suggestions:
If the egg fails to float above the salt solution, you probably do not have a saturated solution. More salt is needet.
If after some minutes, the egg in the second demonstion does not rise to the surface, add more acid. If it rises to thesurface and does not sink to the bottom, you probably have added too much acid. Addition of salt until the egg is nearly ready to float makes it necessary to add very little acid.