"Gold! Gold! Gold! Gold!" wrote the poet Thomas Hood. "Bright and yellow, hard and cold." When the word "gold" comes to your mind the first thing you think about is jewelry, money, treasure and luxury. Gold is soft yellow metal. Its chemical symbol is Au, from the Latin word, Aurum. Gold is one of the heaviest chemical elements. It is 19 times heavier than water.

Unlike most metals, gold does not tarnish in the air. It remains bright and shiny indefinitely. People first valued gold for this special quality.

Gold is one of the least chemically active metals. It only reacts with few acids; it does not dissolve in aqua regia, or a mixture of hydrochloric acid and nitric acid, although neither attacks it alone. Gold also dissolves in a solution of potassium cyanide or sodium cyanide, chloride, fluorine, bromine, and iodine are elements that combine with gold in...