Yesterday when I was making pancakes, I asked myself, how the heck do baking powder and baking soda work? How do their different quantities affect the outcome of the recipe? So I opened up the "Know Your Ingredients" section in the Joy of Cooking and finally found out.
In order for baking powders to work (this includes what we know as "double-acting" baking powder and baking soda), there must be an acid and an alkaline material which react with each other in the presence of moisture to form a gas - carbon dioxide - which forms tiny bubbles that expand with heat and set, resulting in a light-textured crumb.
Double-acting Baking Powder uses a combination of sodium aluminum sulfate and calcium acid for its acids. They start working in cold dough, but the real rising impact happens with the heat of the griddle or the oven.
Baking Soda (Sodium Bicarbonate) has no leavening properties on it's own. However, in the presence of an acid like buttermilk or molasses, it produces one of the most tender crumbs. The proportion of baking soda to buttermilk is usually 1 tsp soda to 1 C buttermilk. The reaction of the soda with the acid is the same as that which occurs when the two acids in baking powder meet moisture, so add your soda to the dry ingredients first.
The acidity in chocolate, honey or corn syrup is not enough to be the only source of acid. In this case, both baking powder and soda are used. The proportions are: 1/2 tsp baking powder + 1/2 tsp soda for every 2 cups of flour. The soda neutralizes the acid and leaves the real leavening power to the baking powder.
These proportions can change at higher altitudes because carbon dioxide expands more quickly in lower barometric pressures. In these cases, the Joy of Cooking has recipes specially designed for mountain folk. Another option is to simply decrease the amount of baking powder and soda. But in those recipes that use buttermilk, don't decrease the amount of soda to more than 1/2 tsp as it is necessary as a neutralizer.
Note that if you don't have any baking powder at home, use 1/2 tsp cream of tartar, 1/3 tsp soda, and 1/8 tsp of salt as a substitute. But get this dough fast into the oven!