I. Chlorine (KLOHR-een): Cl on the table of elements, in the halogen family; extremely reactive, strips color from whatever it touches, heavier than air; discovered by Carl Wilhelm Scheele in 1774 when he poured hydrochloric acid over pyrolusite (which resembles a lava rock) and, surprise, a yellow-green gas smoke evaporated, filling Scheele’s nostrils with the bright-white smell of bleach. Chlorine was put to use in the cleaning industry for deodorizing and disinfecting; also used to clean human wounds. Then it …