Baking Powder, Double-Acting

Baking powder is a dry chemical leavening agent, a mixture of a carbonate or bicarbonate and a weak acid, and is used for increasing the volume and lightening the texture of baked goods. It is different from baking soda, which is entirely an alkaline (or base) used in cooking to temper an acidic element.

Normally an admixture of baking soda and cream of tartar (a dried acid) and sometimes corn starch to make the two get along in storage. Double acting means that there is an immediate effect when liquid is added to a mix and then a later effect in the bake.

You can substitute baking powder for baking soda in a recipe, but because of the the cream of tartar temper you will need about 2-1/2 times the amount called for.