In 1806, Humphry Davy decomposed potash and soda, employing a voltaic pile of approximately 250 cells, showing that these substances were respectively the oxides of potassium and sodium, which metals previously had been unknown. Employing a battery of 2,000 elements of a voltaic pile and charcoal enclosed in a vacuum, Davy gave the first public demonstration of the electric arc lamp in 1809.[7]