Check out this interesting article in the NY Times titled Transforming the Alchemists
Alchemy was very big in the 16th and 17th centuries but has gotten a bad rap because of a small minority of crazies who used to practice it. (And these folks are the ones you read about - turning lead into gold etc...) However there is now a new appreciation for the practice of alchemy and how important it really was to the development of modern chemistry.
Possibly made mad by the mercury they were sniffing, some actually made some scientific advances. Take Paracelsus for example: He analyzed urine and detected disorders that could be cured by alchemy. (Of course modern scientists think that this guy was actually trying to find a Christian alternative to pagan natural philosphy aka "science".)
Famous alchemists include Sir Issac Newton who thought gravity was an occult force. (Doesn't everyone?) Please check the link above for more on this fascinating subject.