Water fluoridation
Health and dental organizations worldwide have endorsed its safety and effectiveness. Its use began in 1945, following studies of children in a region where higher levels of fluoride occur naturally in the water. Further research showed that moderate fluoridation prevents tooth decay.
History of fluorine
Moissan also constructed special apparatus—5m long platinum tubes with fluorite windows—to determine the slight yellow color of fluorine gas. (The gas appears transparent in small tubes or when allowed to escape. The color observation was not repeated until the 1980s, when his result was confirmed.)