(France) Discovered in 1939 by Mlle. Marguerite Perey of the Curie Institute, Paris.Francium, the heaviest known member of the alkali metals series, occurs as a result of analpha disintegration of actinium. It can also be made by artificially bombarding thoriumwith protons. While it occurs naturally in uranium minerals, there is probably less thanan ounce of francium at any time in the total crust of the earth. It has the highestequivalent weight of any element, and is the most unstable of the first 101 elements ofthe periodic system. Thirty-three isotopes of francium are recognized. The longest lived223Fr (Ac, K), a daughter of 227Ac, has a half-life of 22 min. This is the only isotope offrancium occurring in nature. Because all known isotopes of francium are highly unstable,knowledge of the chemical properties of this element comes from radiochemical techniques.No weighable quantity of the element has been prepared or isolated. The chemicalproperties of francium most resemble cesium.