Chlorine is more than just a chemical used in swimming pools. This poisonous green gas is the great enabling element of the chemicals industry, used in creating your clothes, computer chips, medicines and flooring. Justin Rowlatt travels to Thurrock to tour the chlor-alkali plant of Industrial Chemicals Ltd with chief chemist David Compton, as he discovers the brutal process of extracting chlorine from the most mundane of raw materials - table salt. We hear from regular contributor Professor Andrea Sella of University College London who explains the many uses of chlorine. Finally Laurence Knight speaks to Mike Smith, an expert in the chlorine market from consultants IHS, about why the bursting of Spain's property bubble might put up the price of soap there.