Cheryl Dean, age 13, of Birmingham, Ala., for her question:

HOW IS IODINE MADE?

Iodine is a nonmetallic chemical element that is never found free in nature. It is always combined with other elements. Iodine is found in seawater and in some vegetable matter, especially seaweed.

The raw material for much of the commercial production of iodine comes from saltpeter beds in Chile. It also comes from the brine of oil wells in California and from seaweed in Japan.

Iodine is made by heating the ash of burned seaweed, containing iodine compounds, with concentrated sulfuric acid and manganese dioxide. It may also be made by heating the iodine compounds with sodium sulfite.

Iodine mixed with alcohol is used as an antiseptic for minor wounds. Farmers use blocks of iodized salt for their cattle and horses.

A small amount of iodine is necessary for health. In man, a common sign of a lack of iodine is a swelling of the throat glands, called a goiter.