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 imperial iconography and is regarded as a symbol of American exceptionalism and the realization of Manifest Destiny, ultimately leading to the evolution of the American Empire. The painting takes its inspiration from the closing lines of George Berkeley's "Verses on the Prospect of Planting Arts and Learning in America: <poem> Westward the course of empire takes its way; The first four Acts already past, A fifth shall close the Drama with the day; Time's noblest offspring is the last. </poem> The imagery of the pilgrim gesturing on a high rock is very similar to the 5 cent postage stamp, "Fremont