True alchemy is the purification of the soul, reaching the ultimate goal of reuniting with God after moving from sphere to sphere in you're development. If you're wondering how to turn lead into gold, sorry it's not possible. Gold is on the periodic table, it's a base element so you cant make it anyway even with magic, sorry.
I think Deepsea may have meant more along the lines of using herbs and the mixing of potions and stuff. It's not my specialty, but I think that's what some people label as alchemy. Sorry I can't be more helpful with this.
Are you talking about the medieval theory of turning common metals into gold and silver? That doesn't actually work but the metaphorical meaning on alchemy about transforming your sould into something purer does.