I've read a little bit about it. One of those Time-Life "Mysteries of the Unknown" books.
Alchemy was practiced in various forms throughout the world. The Western style of it seems to have its roots in Ancient Egypt. (Where people actually liked to make gold impure by adding other metals to it, such as iron and copper, to create diffrent "colors" of gold).
Originally, it was an attempt to transform less valuable metals into gold for purely material reasons, then it became a mystic pursuit... it got tied into Medieval Christianity a bit... People involved with it thought that if they could transform lead into gold, that they could transform their base souls into spiritual perfection or some such thing like that. They saw the turning of lesser metals into gold as metaphor for and being linked to transforming the spirit into something pure and pleasing to God.
There was also a branch of Alchemy where people tried to create life... It was thought by some, that with the right combination of ingredients and such, that someone could make a miniature person, called a Hommonculus.
There was a kind of Alchemy in the East, too, but one not concerned with gold. This kind of alchemy was a search for immortality... people trying to find serums and materials that would make people immortal.