Discovered : 1774 by C.W. Scheele Isolated in Uppsala, Sweden Origin : The name is derived from the Greek ‘chloros’, meaning pale green. Description : A yellowy-green dense gas with a choking smell. It is very poisonous and was used as a weapon during the First World War. The gas is made on a large scale from salt (sodium chloride) and is used in the manufacture of chlorite bleach and PVC plastic, and to purify drinking water and to disinfect swimming pools. Our daily intake is about 6 grammes (a fifth of an ounce), mainly as salt, but we could manage with half this amount. Image : Hazard warning.