Chlorine, discovered by Scheele in 1774, is a greenish gas, irrespirable, and when incautiously inhaled producing injurious irritant effects. It has a peculiar odor; is very soluble in cold water; it bleaches all vegetable colors, and is a powerful disinfectant; under a pressure of six atmospheres at 32° F. the gas becomes a yellow liquid of sp. gr. 1.33. It may be prepared from any metallic chloride (as common salt), but is directed by the Pharmacopoeia to be made from hydrochloric acid by the agency of manganese oxide, the oxygen of which combines with the hydrogen of the acid, and sets free chlorine on the application of heat: 4HCl + MnO2 =MnCl2+2H1O+Cl2.