Sandra Morley, age 13, of Missoula, Moat., for her question:

JUST WHAT IS BAKING POWDER?

Baking powder 1s a chemical mixture of baking soda, or sodium bicarbonate, and a weak acid. They are mixed with a starch to keep them dry until they are need.

Baking powder makes cakes, biscuits, muffins and other baked foods light and tender when baked. Baking powder works fast. Some bakers use yeast, but yeast takes much longer to do its work of making the batter light.

Three types of baking powder are named for the type of acid they contain: phosphate, tartrate and a combination of phosphate sad sulfate.

When baking powder is added to a cake batter, the chemical reaction starts. The acid reacts with the alkaline soda and produces hundreds of small bubbles of gas. This gas is carbon dioxide. The bubbles rise through the batter and expand when they are heated. This actually lifts the batter. The bubbles form a network of tiny holes that make the final product light and spongy.