Re: An egg shell in vinegar softens. What is happening?

The eggshell does more than soften -- it vanishes!

The shell of an egg is made of calcium carbonate.  If you drop an egg
into vinegar, the shell begins to dissolve slowly.  Eventually, the
shell will dissolve completely, leaving behind the egg's membrane, which
is soft and pliable.  It looks for all the world as though the shell
itself has grown soft, but in reality, what you are seeing is an intact
egg from which the shell has been dissolved away.