I experimented some, and I found calcium carbonate plus cream of tartar works in place of baking powder. For proportions, I experimented with the CaCO3 dissolved in water and then added cream of tartar. For 1 part by volume of powdered pure CaCO3, gradually adding the powdered cream of tartar and then stirring caused fizzing up to 3 parts volume, and then no more with my precise method of hearing the fizzing or not, so when I use this in place of baking powder I'll use a 1:3 ratio. I'm not sure what the equivalent amount would be for professional baking, since I'm not a pro. As a replacement for baking powder I've used a little more of this mixture than I would baking powder, with results that worked for me. As I try it more, I might find that more or less than that works better.
Calcium carbonate is natural limestone, which has been part of people's diet for at least centuries and probably millenia, sometimes in masa harina and also dissolved in naturally occuring water supplies. Think limestone caves and sinkholes, and the springs in those areas.
Cream of tartar naturally forms into tiny crystals as part of the process of making wine and even forms in chilled grape juice.
Edited by OregonYeti - 11/24/13 at 7:42pm