There is such a popular way to check fresh egg or fouler: put it in the water. a fresh egg will sink, fouler - emerges. Why rotten egg POPs up?
Under the shell of the egg is a two-layer Podkolodnaya shell. She let moisture and air, but does not allow the protein. In the blunt end of the egg the shell splits and forms the air chamber (SLAs). The air chamber of the egg plays a big role in allowing gas exchange of the embryo.
The older the egg, the more the air chamber.
Eggshell freely passes not only the air. Through it in the egg fall and microbes, including putrefactive. Before the egg is demolished, it is a sterile product. But after a few seconds after the demolition, its content is affected by microorganisms to the environment. With the development of putrefactive processes in the egg is the release of gases and odors. Rotten smell of eggs - it's the smell of hydrogen sulfide gas, which is formed by decomposition of egg protein.
The air and gases that accumulate in the old egg lighter than water. Therefore, being lowered into the water, so the egg floats.