Jason Burke, age 15, of Hattiesburg, Miss., for his question:

WHERE DO WE GET CADMIUM?

Cadmium is a metallic element that was discovered in 1817 by a German chemist named Friedrich Stromeyer who found it in incrustations in zinc furnaces.

Cadmium occurs as the principal constituent of a mineral only in the rare greenockite. Almost the entire cadmium output of the United States is obtained as a by product in the refining of zinc ores, chiefly from Missouri and Montana. It is also obtained form the zinc ores of Silesia. Fractional distillation or electrolysis is used to separate the cadmium and zinc.

Cadmium may be electrolytically deposited as a coating on metals, chiefly iron or steel, on which it forms a chemically resistant coating. Cadmium lowers the melting point of metals with which it is alloyed; it is used with lead, tin and bismuth in the manufacture of fusible metals for automatic sprinkler systems, fire alarms and electric fuses.

An alloy of cadmium with lead and zinc is used as a solder for iron.

Cadmium salts are used in photography and in the manufacture of fireworks, rubber, fluorescent paints, glass and porcelain.