Radium seventh of a gram of radium. One kilogram of the Earth's crust contains about 900 picograms of radium, and one liter of sea water contains about 89 femtograms of radium. Radium was discovered by Marie Sklodowska-Curie and her husband Pierre Curie on 21 December 1898, in a uraninite (pitchblende) sample. While studying the mineral earlier, the Curies removed uranium from it and found that the remaining material was still radioactive. They separated out an element similar to bismuth from pitchblende in July 1898, that turned out to be polonium. They then separated out a radioactive mixture consisting mostly of two
Polonium dichloride by dehalogenation of polonium tetrachloride, PoCl. Methods for dehalogenating PoCl include thermal decomposition at 300 °C, reduction of cold, slightly moist PoCl by sulfur dioxide; and heating PoCl in a stream of carbon monoxide or hydrogen sulfide at 150 °C. PoCl dissolves in dilute hydrochloric acid to give a pink solution, which autoxidises to Po(IV). PoCl is rapidly oxidised by hydrogen peroxide or chlorine water. Addition of potassium hydroxide to the pink solution results in a dark brown precipitate – possibly hydrated PoO or Po(OH) – which is rapidly oxidised to Po(IV). With dilute nitric acid, PoCl forms a dark