Caesium is the chemical element with atomic number 55. A soft, silvery-gold alkali metal with a melting point of 28 °C (83 °F), it is one of only five metals that are liquid at or near room temperature. It has physical and chemical properties similar to those of rubidium and potassium. The metal is extremely reactive and pyrophoric, reacting with water even at −116 °C (−177 °F). It is the least electronegative element with stable isotopes, of which it has only one, caesium-133. Caesium is mined mostly from pollucite, while the radioisotopes, especially caesium-137, are extracted from waste produced by nuclear reactors. German chemists Robert Bunsen and Gustav Kirchhoff discovered caesium in 1860 by flame spectroscopy. The first small-scale applications for caesium have been as a "getter" in vacuum tubes and in photoelectric cells. In 1967, a specific frequency from the emission spectrum of caesium-133 was chosen for use in the definition of the second by the International System of Units. Since then, caesium has been widely used in atomic clocks. Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids. It has a range of applications in the production of electricity, in electronics, and in chemistry. The radioisotope caesium-137 is used in medical applications, industrial gauges, and hydrology.
Read the rest of this article: <http://en.wikipedia.org/wiki/Caesium> _______________________________ Today's selected anniversaries: 1777: El Pueblo de San José de Guadalupe, the first civil settlement in the Spanish colony of Alta California, was founded as a farming community. <http://en.wikipedia.org/wiki/San_Jose%2C_California> 1781: The crew of the overcrowded British slave ship Zong killed 133 African slaves by dumping them into the sea in order to claim insurance. <http://en.wikipedia.org/wiki/Zong_Massacre> 1890: The Diet of Japan (pictured in session), a bicameral legislature modelled after both the German Reichstag and the British Westminster system, first met after the Meiji Constitution went into effect. <http://en.wikipedia.org/wiki/Diet_of_Japan> 1899: FC Barcelona, one of the most successful clubs in Spanish football, was founded by Swiss football pioneer Joan Gamper. <http://en.wikipedia.org/wiki/FC_Barcelona> 1947: The United Nations General Assembly voted to approve the Partition Plan for Palestine, a plan to resolve the Arab–Israeli conflict in the British Mandate of Palestine by separating the territory into Jewish and Arab states. <http://en.wikipedia.org/wiki/United_Nations_Partition_Plan_for_Palestine> _____________________________ Wiktionary's word of the day: languish (v): 1. To lose strength and become weak; to be in a state of weakness or sickness. 2. To pine away in longing for something; to have low spirits, especially from love <http://en.wiktionary.org/wiki/languish> ___________________________ Wikiquote quote of the day: Far away in the sunshine are my highest aspirations. I may not reach them, but I can look up and see their beauty, believe in them, and try to follow where they lead. --Louisa May Alcott <http://en.wikiquote.org/wiki/Louisa_May_Alcott> _______________________________________________ Wikipedia Daily Article mailing list. To unsubscribe, visit: https://lists.wikimedia.org/mailman/listinfo/daily-article-l Questions or comments? Contact [email protected]
