Period 3 element in 1810, who named it chlorine, from the Greek word χλωρος (chlōros), meaning "green-yellow." Chlorine is a component of various compounds, including table salt. It is the second most abundant halogen and 21st most abundant chemical element in Earth's crust. The great oxidizing potential of chlorine led it to its bleaching and disinfectant uses, as well as uses of an essential reagent in the chemical industry. As a common disinfectant, chlorine compounds are used in swimming pools to keep them clean and sanitary. In the upper atmosphere, chlorine-containing molecules such as chlorofluorocarbons have been implicated in ozone depletion. "Argon" (symbol
Westward the Course of Empire Takes Its Way in the Rocky Mountains" that was part of the 1898 Trans-Mississippi Issue, and reprinted a century later. A Currier and Ives print from 1868 uses the same title and theme for a very different print, showing a railroad crossing a new settlement as the train goes west. A and a stereograph by Alexander Gardner, both of an 1867 end-of-track frontier construction train, were titled "Westward The Course of Empire Takes Its Way". David Foster Wallace named one of his short stories "Westward the Course of Empire Takes Its Way" in his 1989 collection "Girl with Curious Hair". Early revisions of