Caesium chloride, polarised light micrograph. Caesium was first discovered in mineral water. The non-radioactive caesium chloride has a wide range of applications. It is used to improve the efficiency of solar cell technology and electrically conductive glass. It is also used in the brewing industry. The radioactive form of the salt, Caesium-137, made by enriching Caesium with ions, is used in nuclear medicine to treat cancers. One common use of caesium chloride is in buoyant density centrifugation for separating strands of DNA (deoxyribonucleic acid). Magnification: x70 when printed 10 centimetres wide.