Baking Powder is a very fine white powder, similar in appearance to baking soda or corn starch, two ingredients that it is most commonly comprised of. (foodista.com)
This allows wheat to be pulverized into the very fine white powder we know as flour. (idmprogram.com)
Note: For those unfamiliar with cornstarch it is a fine white powder that comes from the inner grain (endosperm) of corn and is used by many as a thickener for gravies and sauces. (joyofbaking.com)