Philosophers stone

The Philosopher's Stone was the (theoretical) perfect catalyst that was the goal of medieval alchemy. The theory went that there existed such a substance (not necessarily a "stone" per se, but generally conceived in powder-form) that could be added to *any* chemical reaction that would catalyse the reaction (ie make it work quicker and with greater efficiency), and yet not be expended itself. Thus it could be used forever and in anything.