Hearing aid batter

[tana at rt66.com]

Hi,

I wear a hearing aid.   I am always curious about hearing aid battery.
Many years ago, I used plain zinc hearing aid battery.
Now, hearing aid uses a different kind of battery:  zinc "air".

The question is about about "air".    On the label, it says:
	* Do not remove tab until ready to use.
	*To activate remove tab.
Could somebody explain to me what does air do?  How come air activates

zinc battery?   

Thanks.

George