Baking powder is a dry chemical leavening agent that is used to increase the volume and lighten the texture of baked goods. It works by releasing carbon dioxide gas into a batter or dough through an acid-base reaction, causing bubbles in the wet mixture to expand and thus leavening the mixture. Baking powder is a mixture of a carbonate or bicarbonate and a weak acid, and the base and acid are prevented from reacting prematurely by the inclusion of a buffer such as cornstarch. Baking powder typically contains tartaric acid, also known as cream of tartar, which is a dry acid. When baking powder is used, the acidic ingredient that produces the carbon dioxide bubbles is already included in the mixture. Baking powder is typically used in recipes that do not otherwise have an acidic ingredient, such as molasses or buttermilk. There are two types of baking powder: single action and double action. Single action baking powder creates the carbon dioxide bubbles upon contact with moisture, similar to baking soda. Double action baking powder produces a second round of bubbles when the batter has reached the right temperature in the oven.