Phosphorus

Phosphorus has something of a smelly history. Phosphorus—which was the 13th known element and the first element discovered after ancient times—was first isolated from human urine by German alchemist Hennig Brand in 1669. Brand wasn’t trying to discover a new element, but rather to produce the philosopher’s stone, a mythical substance that was thought to turn base metals like copper, lead, and zinc into gold.

Brand let the urine evaporate and then heated the red-hot residue, producing a phosphorus vapor that he then condensed in water. This process yielded white phosphorus, which, although incapable of producing gold, glowed in the dark and could be used as a fire starter. Brand named the substance phosphorus mirabilis, which means “miraculous light-bearer.”

In the 18th century, chemists discovered that bone ash also contains phosphorus. In the 19th century, bird and bat guano became important sources of phosphorus, which by that point had become a key ingredient in fertilizers. Today, most of the world’s phosphorus comes not from urine, bone, or guano, but from phosphate rock, which was first used to produce phosphorus in 1850. The process of making phosphorus has gotten a lot more pleasant!

Phosphorus exists in at least four allotropes, or forms, that have wildly different qualities and that are denoted by color. White phosphorus is soft and waxy, and it looks a little like brie cheese. But you wouldn’t want to eat white phosphorus; this allotrope is toxic. White phosphorus is also the most reactive of phosphorus allotropes, and it is highly flammable. It can even ignite spontaneously! In the presence of oxygen, white phosphorus glows in the dark.

Red phosphorus is stabler than white phosphorus, although it’s more reactive than the other allotropes, capable of igniting at a relatively low temperature (around 300 °C). Violet phosphorus is still more stable than red phosphorus, but not as stable as black phosphorus. Black phosphorus is like graphite in terms of similar atomic structure and electrical conductivity.

White phosphorus was first used to make matches. However, white phosphorus is toxic, which is why, beginning in the early 1900s, laws were enacted mandating use of the much less toxic red phosphorus instead. White phosphorus’ terrific flammability is why it has been used in weapons like firebombs and smoke grenades, and in tracer bullets.

The biggest use of phosphorus is in fertilizer, with up to 75 percent of phosphorus being used in this way. Phosphorus can also be used as a preservative, in steel production, and light-emitting diodes (LEDs). In the form of phosphoric acid, phosphorus is used to give certain foods and drinks a pleasantly bitter taste. If you’ve ever had Coca-Cola, you’ve consumed phosphoric acid!

Phosphorus can join with oxygen to form phosphate (PO₄³⁻), which is used in fertilizers. Phosphate also makes many salts that are commonly found in nature, and it can be used in special kinds of glass, like the ones used in sodium vapor lamps. Phosphoric acid (H₃PO₄) is used in everything from fertilizers to food preservatives, anti-rust chemicals, aluminum etching, and semiconductor manufacturing. Trisodium phosphate is an important cleaning agent that’s also used to remove minerals from water.

Some organophosphorus compounds—that is, compounds with a phosphorus-carbon bond—are used in pest controls and insecticides. These compounds can be extremely toxic. The nerve agent sarin is an organophosphorus compound. While some forms of phosphorus are highly flammable, certain phosphorus compounds are useful as flame retardants. Calcium phosphates are present in bones and tooth enamel.

Scientists have found 22 phosphorus isotopes, ranging from phosphorus-26 to phosporus-47. But only phosphorus-31 is stable (non-radioactive). The longest-lived phosphorus radioisotope, phosphorus-33, has a half-life of 25 days. The least-stable isotope, phosohorus-47, has a half-life of 2 milliseconds!

Today, most phosphorus comes from phosphate rock (although some still comes from guano). Phosphate rock is a kind of sedimentary rock with lots of phosphorus-bearing minerals inside. China, Mexico, and Morocco are the world’s top phosphorus producers.