Experiment for the philosopher's stone with 5500 litres of Urine

Hennig Brand was a German pharmacist and alchemist in 16th Century. Like other alchemists of the time, Brand searched for the "philosopher's stone", a substance which supposedly transformed base metals (like lead) into gold. Like many before him, he was interested in water and tried combining it with various other materials, in hundreds of combinations.

The Alchemist Discovering Phosphorus depicting Hennig Brand discovering phosphorus

Around 1669 he heated residues from boiled-down urine on his furnace until the retort was red hot, where all of a sudden glowing fumes filled it and liquid dripped out, bursting into flames. He could catch the liquid in a jar and cover it, where it solidified and continued to give off a pale-green glow. What he collected was phosphorus, which he named from the Greek word for "light-bearing" or "light-bearer."

Phosphorus must have been awe-inspiring to an alchemist: it was a product of man, and seeming to glow with a "life force" that did not diminish over time (and did not need re-exposure to light like the previously discovered Bologna Stone). Brand kept his discovery secret, as alchemists of the time did, and worked with the phosphorus trying unsuccessfully to use it to produce gold.

Brand's process yielded far less phosphorus than it could have done. The salt part he discarded contained most of the phosphate. He used about 5,500 litres of urine to produce just 120 grams of phosphorus. If he had ground up the entire residue he could have got many times more than this (1 litre of adult human urine contains about 1.4g of phosphorus salts, which amounts to around 0.11 grams of pure white phosphorus).

His recipe was:

  • Boil urine to reduce it to a thick syrup.
  • Heat until a red oil distills up from it, and draw that off.
  • Allow the remainder to cool, where it consists of a black spongy upper part and a salty lower part.
  • Discard the salt, mix the red oil back into the black material.
  • Heat that mixture strongly for 16 hours.
  • First white fumes come off, then an oil, then phosphorus.
  • The phosphorus may be passed into cold water to solidify.

The chemical reaction Brand stumbled on was as follows. Urine contains phosphates PO43−, as sodium phosphate (i.e. with Na+) in the form of microcosmic salt, and various carbon-based organics. Under strong heat the oxygen atoms from the phosphate react with carbon to produce carbon monoxide CO, leaving elemental phosphorus P, which comes off as a gas. Phosphorus condenses to a liquid below about 280°C and then solidifies (to the white phosphorus allotrope) below about 44°C (depending on purity). This same essential reaction is still used today (but with mined phosphate ores, coke for carbon, and electric furnaces).

The Squared Circle: an alchemical symbol (17th century) illustrating the interplay of the four elements of matter (earth, fire, water, air) symbolising the philosophers' stone

The philosophers' stone

The philosophers' stone was the central symbol of the mystical terminology of alchemy, symbolizing perfection at its finest, enlightenment, and heavenly bliss. Efforts to discover the philosophers' stone were known as the Magnum Opus ("Great Work"). The English philosopher Sir Thomas Browne in his spiritual testament "Religio Medici" (1643) identified the religious aspect of the quest for the philosopher's Stone when declaring: "The smattering I have of the Philosophers stone, (which is something more than the perfect exaltation of gold) hath taught me a great deal of Divinity."