Trevor Seymour, age 15, of Watertown, N.Y., for his question:

WHAT IS TARTARIC ACID?

Tartaric acid is an important industrial and household chemical that occurs naturally in fruits, both as the acid and as a potassium salt called cream of tartar.

Cream of tartar is used as baking powder. It is also treated with sodium hydroxide to give Rochelle salts. The acid is used in carbonated beverages and as a mordant or dye fixative.

A Swedish chemist named Carl Scheele first isolated the acid from its salt in 1770. Louis Pasteur did some of his pioneer research on the acid.

Most commercial tartaric acid is obtained from the wine industry. As wine ferments, the salt crystallizes on the walls of wine casks.

Tartaric acid forms clear to white crystals, easily soluble in water. They will melt at 338 degrees Fahrenheit.