Chlorine was discovered in 1774 and named in 1810. It is a yellow-green gas that is heavier than air and has a pungent odor. Chlorine is widely used for water purification and in household cleaning products. Exposure to chlorine can irritate the skin, eyes, and respiratory system, and cause coughing, chest pain, and fluid in the lungs. If exposed, quickly leave the area, remove clothing, and wash the entire body with soap and water. Seek medical help immediately.