April Sargent, age 14, of Danville, Ill., for her question:

WHAT IS BAKING POWDER?

Baking powder is a fine powder that is used to make bread, cakes and biscuits levee or rise. Cooks add baking powder to flour mixtures before baking them.

Chemicals in the baking powder react with air and a liquid to form carbon dioxide gas. The liquid used is usually water or sweet milk.

Bubbles from the gas formed and trapped in the flour mixture, expand when heated and make the mixture rise.

All baking powders contain starch, baking soda (sodium bicarbonate) and acid forming ingredients. Starch keeps the powder dry and prevents it from acting until a liquid is added. Baking soda reacts with the acid forming ingredient to produce carbon dioxide.

Tartrate baking powders contain cream of tartar and tartaric acid as acid forming ingredients. Phosphate powders have calcium dihydrogen phosphate and sulfate powders contain sodium aluminum sulfate, or alum.

Baking powders differ in speed of reaction. Sulfate powder is the slowest while tartrate and phosphate powders are the fastest.

Baking soda and sour milk have the same rising effect on flour mixtures as baking powder and sweet milk.