Mercury is a heavy liquid metal that can be extracted easily by heating cinnabar, a red ore (mercury sulfide). Mercury is known to be dangerous in all its forms, and use is now confined to industry in the manufacture of chlorine and sodium hydroxide, . Some is still used to treat seed corn to make it resistant to fungus disease, and in street lighting, dental amalgam and electrical apparatus. Older uses - in thermometers, in felt production and as a de-worming powder .Mercury is widespread in the environment - every mouthful of food we eat contains a little. Our daily intake is about 0.01 milligramme (about a 0.3 grammes in a lifetime), and this we can cope with easily. However, one form of mercury - methylmercury - is particularly dangerous.