In its “normal” state, chlorine is a greenish yellow gas, but at -34°C it turns to a liquid. It is the eleventh most common element in the earth’s crust and is widespread in nature. Chlorine is a key building block of modern chemistry and used in three principal ways: direct use (e.g. to disinfect water); as a raw material for chlorine-containing products (e.g. plastics, pharmaceuticals, pesticides) and as an intermediate to manufacture non-chlorinated products (eg polycarbonates and polyurethanes).