Jean McCabe, age ll, Of St. Paul, Minn., for her question:

When was oxygen discovered?

The l8th Century was a great age of chemical discoveries. In France the brilliant Antoine Lavoisier looked for chemical properties and relationships while in America Benjamin Franklin probed the secrets of lightning. scientists of different nations began to exchange their ideas. In England, Joseph Priestly became interested in gases and gave up his career as a clergyman to become a chemist. In l772, he discovered the so called laughing gas, Nitrous Oxide.

Two years later he published his discovery of a gas he called dephlogisticated air. Lavoisier put this lively air to chemical tests and promptly named it oxygen, the acid former. But Karl Scheele, working in Sweden, knew nothing of the newly found gas. In l777, three years after Priestly's discovery, Scheele's work led him to the second discovery of oxygen.