Chlorine is a greenish-yellow gas which is toxic and corrosive. It irritates and can damage the respiratory system and the eyes. Used carefully and in suitable amounts, it disinfects drinking water and keeps swimming pools clean. Chlorine chemistry is used to make thousands of products, from plastic foams to contact lenses. Even when not part of the finished item, it is vital in many production processes – for example, titanium is purified using chlorine.