Philosopher's Stone was, with the Elixir of Life, the object of the search of the mediæval alchemists. Their theory regarded gold as the most perfect metal, all others being removed from it by various stages of imperfection, and they sought an amalgam of pure sulphur and pure mercury, which, being more perfect still than gold, would transmute the baser metals into the nobler.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Philosophe * Philosophism, French