Martin Sherrill, age 15, of Albuquerque, N.M., for his question:

WHAT IS ALCHEMY?

Alchemy is a blend of science, magic and religion. It was popular from the time of early Christianity until 1700.

Alchemists tried to change less costly metals into silver and gold. They also tried to find the elixir of life, which was a substance that would cure disease and lengthen life. But these alchemists failed.

Some good came from the alchemists, however. Their work in preparing and studying chemical substances helped the development of the science of chemistry.

Some alchemists were only fakes. Others were learned men who had more philosophical goals. They felt that if they learned how to make gold from lesser metals, they could also perfect other things. They considered gold the perfect metal because of its beautiful luster and its resistance to rusting.

Some alchemy was practiced in China and India before the birth of Christ. But it developed into a major system in Egypt during the next 300 years.

The Greek speaking scholars of Alexandria used it in trying to explain how Egyptian artisans made things. Greek Egyptian alchemy spread through Syria and Persia to the Arabs. It spread to Western Europe during the 1100s and 1200s.

Alchemist believed that all matter was made up of a single formless substance. They thought this substance, when combined with hot or cold and wet of dry, became the four elements: earth, air, fire and water. They thought they could change one substance into another merely by changing the balance of these elements, a process called transmutation.

Alchemists also searched for the philospher's stone which was a magical substance that was supposedly able to make the transmutation process easier. In the early 1500s, a Swiss scientist named Paracelsus tried to substitute sulfur, mercury and salt for earth, air and water.

Gold's lasting quality led many persons to believe that they would find the secret of long life or even immortality if they could discover how to make gold from lesser substances. The Chinese once believed that eating from golden dishes prolonged life.

Alchemy was associated with many religious beliefs. It was believed that the techniques used to make gold were symbolically related to death, corruption, regeneration and resurrection.

Alchemy and astrology became closely related because of the belief that each heavenly body represented and controlled a certain metal. Some thought the sun represented gold; the moon, silver; Mars, iron; Venus, copper; Jupiter, tin; Saturn, lead; and Mercury, the metal mercury, also called quicksilver.

Alchemists believed that the position of these bodies influenced the success of failure of their work.