Baker's amonia (ammonium carbonate) is an old fashionned leavener. It gives up a noxius smell while baking, but the odor dissipated by the time baking is complete, leaving extra crisp cookies or crackers.
According to an article at the King Arthur website, staghorn antler, that is a kind of deer antler, has a high amount of that compound, ammonium carbonate. It's an old fashioned leavening, offered at KA, that makes cookies crispier, too.
Every time I have asked someone about it, they look at me like I am looney. Sure glad that you guys have heard of it. I bought it once, but was scared to use it. Weird huh? Well, it is also found in some mennonite recipes I have.
Baker's ammonia is still used as a leavener of choice for certain recipes because of it's ability to make cookies crisper. The chemistry is very interesting. It creates gas when mixed with liquid ingredients but the baker's ammonia removes one extra water (or was it oxygen) molecule than soda so it leaves a dryer crisper product. Some old-fashioned recipes for biscotti and ameretti call for it because of the desired affect.
I've never seen leaveners added to meringues. They crisp up quite well on their own if the whites are whipped up properly (I have trouble judging that when the white are in the hobart). I am also not sure about meringue in napoleons. How do you make them?