It's Elemental: Potassium - Basic physical and historical information. ChemicalElements.com: Potassium - Basic information, atomic structure, and isotopes. EnvironmentalChemistry.com: Potassium - Atomic structure, chemical and physical properties, and table of nuclides. Lenntech: Potassium - Physical data, chemical properties, and health effects. Wikipedia: Potassium - Properties of the element, including its history, applications, and characteristics. Radiochemistry of Potassium - Full text of the monograph by William T. Mullins and G. W. Leddicotte (Oak Ridge National Laboratory, Oak Ridge, Tennessee). WebElements: Potassium - Extensive information on history, uses, occurrence, compounds, and properties of the element.