If you follow the link and scroll down the right side of the page,
baking911.com has a couple of things to say about the freshness of baking
soda and baking powder.
http://www.baking911.com/pantry/leaveners.htm

"FarmerGirl" > wrote in message
...
>I apologize if this has been discussed before. I only recently joined this
>newsgroup.
>
> How does one tell whether their
> cream of tartar
> baking soda
> and baking powder
> are still fresh? Is there a test you can do? We're about to get ready to
> bake Christmas cookies, and I don't want things to come out flat if my
> ingredients aren't working properly.
>
> Thank you for any insight,
> Bobbett
>