Manufacturers produce chlorine from the electrolysis of seawater. The process separates sodium chloride, commonly known as table salt. While chlorine is an element, the gas readily combines with other elements to form salts, and elemental chlorine does not exist naturally on earth.
The discovery of chlorine gas was an accident that occurred in 1774, when a Swedish pharmacist dropped hydrochloric acid on manganese dioxide, producing a greenish yellow gas. Sir Humphrey Davy recognized chlorine as an element in 1810. The chlorine compound NaOCl was used in the fabric industry by the late 18th century as bleach.
During the 19th century, chlorine was added to public water systems as a disinfectant, improving the lives and health of many people. Chlorine compounds help to kill bacteria, and hospitals first used bleach to disinfect areas in the 1850s, improving the quality of care for patients.
Manufacturers often release chlorine gas into the atmosphere as a part of the manufacturing process. In 2003, a single magnesium-manufacturing plant that converted magnesium chloride into magnesium metal released 90 percent of the chlorine gas pollution in the United States. Too much chlorine can have deadly results, as in a 1915 accident in France where deadly chlorine gas, which is heavier than air, killed thousands of victims.