White phosphorus (P4) is a form of the element phosphorus. It is colorless and transparent when pure; most commonly, however, it appears as a waxy white solid, while commercial versions are usually yellow (and known as "yellow phosphorus.") It is insoluble in water, and is thus usually kept submerged. It ignites spontaneously on contact with oxygen, burning with a dull-yellow flame to P4O10 and producing large quantities of thick, white smoke. The isolation of white phosphorus is usually accomplished by heating a phosphate with sand and carbon in an electric furnace,1 which is highly energy intensive. White phosphorus does not occur naturally (for obvious reasons - poof.)
White phosphorus is used as an ingredient for phosphoric acid, which is highly useful in industry. This acid (and other phosphorus-based chemicals) are used to make fertilizers, food additives, and cleaning compounds, among other things. Pure white phosphorus is used in small quantities in some rat and roach poisons and in fireworks; it was once used to make matches, but has since been replaced by a less toxic compound.
White phosphorus has numerous military applications, as well. It is luminous in darkness, which makes it useful for "tracer" bullets. In addition, white phosphorus (WP, or "Willy Pete") artillery shells, grenades, and mortar rounds have seen regular use by military forces since WWII. These typically consist of a small explosive charge and a quantity of the chemical. The smoke produced by these rounds is useful for concealment of friendly troop movements. In addition, the detonator (and impact, for ballistic weapons) spreads flaming WP particles throughout the target area, with devastating effect. Troops in WWII feared this weapon, with good reason: the shellburst was followed by
"...a snowstorm of small, white particles that floated down upon us. We looked in amazement, and eyes filled with instant terror. Where the particles landed on shirts and trousers they sizzled and burned. White phosphorus! We brushed our clothing frantically, pushed shirt collars up. If any of the stuff touched the skin, it could inflict a horrible burn, increasing in intensity as it burrowed into a man's flesh...
"Another shell. Another missile from hell. Fiery snow! I remember thinking that if the shelling kept up for long it would be more than most men could endure. There was nowhere to hide, no place that was safe." - Lt. Robert Weiss
Wounds from these weapons were indeed horriffic; particles produce a "necrotic area, with a yellowish color and characteristic garliclike odor." Furthermore, the WP particles are lipid-soluble, which causes the substance to permeate the wound and prevent healing, and WP smoke is highly toxic, causing long-term liver and kidney damage. American troops in WWII and Vietnam regularly used WP shells and grenades to clear enemy fortifications and machine gun nests.
White phosphorous can constitute a serious environmental risk, although until recently it was thought not to persist. WP from manufacturing, chemical spills, and particles from munitions can find their way into water and soil; as it is not water soluble it can persist for some time in damp soil and tends to concentrate in sensitive wetlands, although it does not appear to move very deeply into soil. It also concentrates somewhat in the flesh of fish which consume errant particles, as well as in waterfowl.
One of the greatest cases of white phosphorus contamination occurred in Eagle River Flats, a salt marsh on the grounds of Fort Richardson, Alaska. Large quantities of phosphorus from artillery shells found its way into the marsh's shallow pools and sediment, causing numerous fatalities among the area's duck and swan populations. The area was declared a Superfund site and the cleanup appears to be progressing well. The army in particular has become far more careful about disposing of obsolete WP rounds; originally, they were simply detonated, burned, or dumped into the ocean. In 1989, Crane Army Ammunition Activity opened a conversion facility that can recycle up to 6 tons of WP ordnance a day, turning it into useful phosphoric acid and metals for re-use.
12Ca3(PO4)2 + 6SiO2 + 10C (1500deg C) -> 6CaSiO3 + 10CO + P4.
Agency for Toxic Substance and Disease Registry, "Toxicological profile for white phosphorus." http://www.atsdr.cdc.gov/toxprofiles/tp103.html
"Crane Army Ammunition Activity, Best Practice: White Phosphorus Conversion," Best Manufacturing Practices, http://www.bmpcoe.org/bestpractices/internal/caaa/caaa_10.html
"Eagle River Flats," Army Corps of Engineers, http://www.crrel.usace.army.mil/erf/
"Excerpt from CBRNE - Incendiary Agents, White Phosphorus," eMedicine, http://www.emedicine.com/emerg/byname/cbrne---incendiary-agents-white-phosphorus.htm
"Phosphorus" entry in Webelements.com database, http://www.webelements.com/webelements/elements/text/P/key.html
Weiss, Robert, Enemy North, South, East, West. Strawberry Hill Press, Portland, 1998.