Samples of cobalt, c 1890.
© Science Museum / Science & Society Picture Library
Cobalt, atomic number 27 in the periodic table, is a hard, grey naturally magnetic metal of low strength and little electric conductivity (though it does become more conductive in higher temperatures). It is a fairly rare element, making up only 0.003 percent of the Earth's crust, and is not often found in its pure form in nature - it usually occurs in compounds bonded to arsenic and sulphur. Cobalt was discovered in 1730 by the Swedish chemist Georg Brandt (1694-1768). These samples are from a collection of chemical elements bequeathed to the Science Museum, London, by Prince Louis Lucien Bonaparte (1813-1891) the younger brother of Napoleon I.