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Essential, explosive sodium is a soft, silvery alkali metal that roils in water, releasing clouds of hydrogen gas that fan its yellow flames. It reacts with most elements, and is naturally found only in compounds, such as sodium chloride, or common salt. Ancient Egyptians knew sodium from natron, a mix of salts prized for cleaning, personal hygiene, and preservation, particularly in mummification. Humphry Davy first isolated the element from caustic soda in 1807, naming it sodium; Jakob Berzelius preferred natrium, hence its symbol (Na). As a metal, liquid sodium cools nuclear reactors, and sodium-vapor lamps bathe streets at night in yellow, monochromatic light.

Learn how the mix of saltwater and freshwater in the San Francisco Bay affects its diverse ecosystems with John Largier, professor of coastal oceanography at the University of California, Davis.

Exploratorium staff member Earl Stirling demonstrates the amazing "Pyrograph", an artwork refined over four years. Like a fiery version of the museum���s classic Drawing Board, Stirling���s "Pyrograph" swings a pendulum over a sandy cauldron, tracing out oscillating patterns in colorful fire. This mesmerizing piece evokes both the Foucault pendulum and Dante���s Inferno.

Watch as the best teachers on the planet battle it out for the title of Iron Science Teacher. In this zany competition teachers will have ten minutes to create a science activity. Tee off with this week���s ���secret��� ingredient-salt!