Fluorine

a widely distributed them i cal element, one of the reputed halogens, which was known only in a combined state, until De Moi an in 1887 isolated it as a colorle gas, that attacks almost every substance and is the most active element known. [ts most abundant compound is ealcie fluoride, which exists in the mineral kingdom not only as a a but forms an e ential part of the bones and teeth of animals.