Baking powder is a leavening agent that aerates baked goods. It containing sodium bicarbonate (baking soda) cream of tartar and a drying agent, often cornflour. It's rising properties are affected by the type of acid salt used. Most commercial baking powders impart a distinct taste to the ptoduct.
Baking powder can be made by mixing two parts of cream of tartar with one part of sodium bicarbonate. Sieve the mixture six times to ensure even mixing. This mixture leaves no aftertaste but it reacts quickly on contact with liquids so it must be baked off as soon as possible.