Kimberlee Karr, age 11, of Visalia, Calif., for her question:

HOW IS OXYGEN MADE FOR COMMERCIAL USE?

Most commercial oxygen is distilled from liquid air. During the distillation process, the nitrogen boils before the oxygen does because nitrogen has a lower boiling point. As the nitrogen boils away, the liquid air is left with a greater concentration of oxygen.

Commercial oxygen is stored in steel tanks at a pressure of about 2,000 pounds per square inch, more than a hundred times the pressure of the atmosphere.

Small amounts of oxygen can be made by heating potassium chlorate. ,A little manganese dioxide added to the potassium chlorate speeds up oxygen formation.

Oxygen has many uses in industry. A stream of high pressure oxygen, for example, blasts down on melted pig iron and burns out impurities. Welders also use oxygen with fuel. In addition, oxygen is used extensiveely in medicine and in medical procedures.