[Gk. chloros, light green.] One of the non-metallic elements, discovered by Scheele in 1774. It is prepared from common salt by the action of sulphuric acid on manganese dioxide. It is a transparent gas of a greenish-yellow color, which does not occur free in nature. United with the metals sodium, potassium, and magnesium , it forms the chief salts of sea-water. Chlorine is a powerful bleaching agent, and this action depends upon the power which it possesses of combining with the hydrogen of water, and so setting free the oxygen.