in a flare stack. in the 1840s, world phosphate production turned to the mining of tropical island deposits formed from bird and bat guano (see also guano islands act). these became an important source of phosphates for fertiliser in the latter half of the 19th century. phosphate rock phosphate rock, which usually contains calcium phosphate, was first used in 1850 to make phosphorus, and following the introduction of the electric arc furnace by james burgess readman in 1888 (patented 1889), elemental phosphorus production switched from the bone-ash heating, to electric arc production from phosphate rock. after the depletion of world guano sources about the same time, mineral phosphates became the major source of phosphate fertiliser production. phosphate rock production greatly increased after world war ii, and remains the primary global source of phosphorus and phosphorus chemicals today. see the article on peak phosphorus for more information on the history and present state of phosphate mining. phosphate rock remains a feedstock in the fertiliser industry, where it is treated with sulfuric acid to produce various "superphosphate" fertiliser products. incendiaries white phosphorus was first made commercially in the 19th century for the match industry. this used bone ash for a phosphate source, as described above. the bone-ash process became obsolete when the submerged-arc furnace for phosphorus production was introduced to reduce phosphate rock. the electric furnace method allowed production to increase to the point where phosphorus could be used in weapons of war. in world war i, it was used in incendiaries, smoke screens and tracer bullets. a special incendiary bullet was developed to shoot at hydrogen-filled zeppelins over britain (hydrogen being highly flammable). during world war ii, molotov cocktails made of phosphorus dissolved in petrol were distributed in britain to specially selected civilians within the british resistance operation, for defence; and phosphorus incendiary bombs were used in war on a large scale. burning phosphorus is difficult to extinguish and if it splashes onto human skin it has horrific effects. early matches used white phosphorus in their composition, which was dangerous due to its toxicity. murders, suicides and accidental poisonings resulted from its use. (an apocryphal tale tells of a woman attempting to murder her husband with white phosphorus in his food, which was detected by the stew's giving off luminous steam). in addition, exposure to the vapours gave match workers a severe necrosis of the bones of the jaw, known as "phossy jaw". when a safe process for manufacturing red phosphorus was discovered, with its far lower flammability and toxicity, laws were enacted, under the berne convention (1906), requiring its adoption as a safer alternative for match manufacture. the toxicity of white phosphorus led to discontinuation of its use in matches. the allies used phosphorus incendiary bombs in world war ii to destroy hamburg, the place where the "miraculous bearer of light" was first discovered. production mining of phosphate rock in nauru main article: peak phosphorus in 2017, the usgs estimated 68 billion tons of world reserves, where reserve figures refer to the amount assumed recoverable at current market prices; 0.261 billion tons were mined in 2016. critical to contemporary agriculture, its annual demand is rising nearly twice as fast as the growth of the human population. the production of phosphorus may have peaked before 2011 and some scientists predict reserves will be depleted in before the end of the 21st century." phosphorus comprises about 0.1% by mass of the average rock, and consequently, the earth's supply is vast, though dilute. wet process most phosphorus-bearing material is for agriculture fertilisers. in this case where the standards of purity are modest, phosphorus is obtained from phosphate rock by what is called the "wet process." the minerals are treated with sulfuric acid to give phosphoric acid. phosphoric acid is then neutralized to give various phosphate salts, which comprise fertilizers. in the wet process, phosphorus does not undergo redox. about five tons of phosphogypsum waste are generated per ton of phosphoric acid production. annually, the estimated generation of phosphogypsum worldwide is 100 to 280 mt. thermal process for the use of phosphorus in drugs, detergents, and foodstuff, the standards of purity are high, which led to the development of the thermal process. in this process, phosphate minerals are converted to white phosphorus, which can be purified by distillation. the white phosphorus is then oxidised to phosphoric acid and subsequently neutralised with a base to give phosphate salts. the thermal process is conducted in a submerged-arc furnace which is energy intensive. presently, about 1,000,000 short tons (910,000 t) of elemental phosphorus is produced annually. calcium phosphate (phosphate rock), mostly mined in florida and north africa, can be heated to 1,200–1,500 °c with sand, which is mostly sio2, and coke to produce p4. the p4 product, being volatile, is readily isolated: 4 ca5(po4)3f + 18 sio2 + 30 c → 3 p4 + 30 co + 18 casio3 + 2 caf2 2 ca3(po4)2 + 6 sio2 + 10 c → 6 casio3 + 10 co + p4 side products from the thermal process include ferrophosphorus, a crude form of fe2p, resulting from iron impurities in the mineral precursors. the silicate slag is a useful construction material. the fluoride is sometimes recovered for use in water fluoridation. more problematic is a "mud" containing significant amounts of white phosphorus. production of white phosphorus is conducted in large facilities in part because it is energy intensive. the white phosphorus is transported in molten form. some major accidents have occurred during transportation. historical routes historically, before the development of mineral-based extractions, white phosphorus was isolated on an industrial scale from bone ash. in this process, the tricalcium phosphate in bone ash is converted to monocalcium phosphate with sulfuric acid: ca3(po4)2 + 2 h2so4 → ca(h2po4)2 + 2 caso4 monocalcium phosphate is then dehydrated to the corresponding metaphosphate: ca(h2po4)2 → ca(po3)2 + 2 h2o when ignited to a white heat (~1300c) with charcoal, calcium metaphosphate yields two-thirds of its weight of white phosphorus while one-third of the phosphorus remains in the residue as calcium orthophosphate: 3 ca(po3)2 + 10 c → ca3(po4)2 + 10 co + p4 applications flame retardant phosphorus compounds are used as flame retardants. flame -retardant materials and coatings are being developed that are both phosphorus and bio-based. food additive phosphorus is an essential mineral for humans listed in the dietary reference intake (dri). food-grade phosphoric acid (additive e338) is used to acidify foods and beverages such as various colas and jams, providing a tangy or sour taste. the phosphoric acid also serves as a preservative. soft drinks containing phosphoric acid, which would include coca-cola, are sometimes called phosphate sodas or phosphates. phosphoric acid in soft drinks has the potential to cause dental erosion. phosphoric acid also has the potential to contribute to the formation of kidney stones, especially in those who have had kidney stones previously. fertiliser main article: fertiliser phosphorus is an essential plant nutrient (the most often limiting nutrient, after nitrogen), and the bulk of all phosphorus production is in concentrated phosphoric acids for agriculture fertilisers, containing as much as 70% to 75% p2o5. that led to large increase in phosphate (po43−) production in the second half of the 20th century. artificial phosphate fertilisation is necessary because phosphorus is essential to all living organisms; it is involved in energy transfers, strength of root and stems, photosynthesis, the expansion of plant roots, formation of seeds and flowers, and other important factors effecting overall plant health and genetics. natural phosphorus-bearing compounds are mostly inaccessible to plants because of the low solubility and mobility in soil. most phosphorus is very stable in the soil minerals or organic matter of the soil. even when phosphorus is added in manure or fertilizer it can become fixed in the soil. therefore, the natural cycle of phosphorus is very slow. some of the fixed phosphorus is released again over time, sustaining wild plant growth, however, more is needed to sustain intensive cultivation of crops. fertiliser is often in the form of superphosphate of lime, a mixture of calcium dihydrogen phosphate (ca(h2po4)2), and calcium sulfate dihydrate (caso4·2h2o) produced reacting sulfuric acid and water with calcium phosphate. processing phosphate minerals with sulfuric acid for obtaining fertiliser is so important to the global economy that this is the primary industrial market for sulfuric acid and the greatest industrial use of elemental sulfur. widely used compoundsuse ca(h2po4)2·h2obaking powder and fertilisers cahpo4·2h2oanimal food additive, toothpowder h3po4manufacture of phosphate fertilisers pcl3manufacture of pocl3 and pesticides pocl3manufacture of plasticiser p4s10manufacturing of additives and pesticides na5p3o10detergents organophosphorus white phosphorus is widely used to make organophosphorus compounds through intermediate phosphorus chlorides and two phosphorus sulfides, phosphorus pentasulfide and phosphorus sesquisulfide. organophosphorus compounds have many applications, including in plasticisers, flame retardants, pesticides, extraction agents, nerve agents and water treatment. metallurgical aspects phosphorus is also an important component in steel production, in the making of phosphor bronze, and in many other related products. phosphorus is added to metallic copper during its smelting process to react with oxygen present as an impurity in copper and to produce phosphorus-containing copper (cuofp) alloys with a higher hydrogen embrittlement resistance than normal copper. phosphate conversion coating is a chemical treatment applied to steel parts to improve their corrosion resistance. matches match striking surface made of a mixture of red phosphorus, glue and ground glass. the glass powder is used to increase the friction. the first striking match with a phosphorus head was invented by charles sauria in 1830. these matches (and subsequent modifications) were made with heads of white phosphorus, an oxygen-releasing compound (potassium chlorate, lead dioxide, or sometimes nitrate), and a binder. they were poisonous to the workers in manufacture, sensitive to storage conditions, toxic if ingested, and hazardous when accidentally ignited on a rough surface. production in several countries was banned between 1872 and 1925. the international berne convention, ratified in 1906, prohibited the use of white phosphorus in matches. in consequence, phosphorous matches were gradually replaced by safer alternatives. around 1900 french chemists henri sévène and emile david cahen invented the modern strike-anywhere match, wherein the white phosphorus was replaced by phosphorus sesquisulfide (p4s3), a non-toxic and non-pyrophoric compound that ignites under friction. for a time these safer strike-anywhere matches were quite popular but in the long run they were superseded by the modern safety match. safety matches are very difficult to ignite on any surface other than a special striker strip. the strip contains non-toxic red phosphorus and the match head potassium chlorate, an oxygen-releasing compound. when struck, small amounts of abrasion from match head and striker strip are mixed intimately to make a small quantity of armstrong's mixture, a very touch sensitive composition. the fine powder ignites immediately and provides the initial spark to set off the match head. safety matches separate the two components of the ignition mixture until the match is struck. this is the key safety advantage as it prevents accidental ignition. nonetheless, safety matches, invented in 1844 by gustaf erik pasch and market ready by the 1860s, didn't gain consumer acceptance until the prohibition of white phosphorus. using a dedicated striker strip was considered clumsy. water softening sodium tripolyphosphate made from phosphoric acid is used in laundry detergents in some countries, but banned for this use in others. this compound softens the water to enhance the performance of the detergents and to prevent pipe/boiler tube corrosion. miscellaneous phosphates are used to make special glasses for sodium lamps. bone-ash, calcium phosphate, is used in the production of fine china. phosphoric acid made from elemental phosphorus is used in food applications such as soft drinks, and as a starting point for food grade phosphates. these include mono-calcium phosphate for baking powder and sodium tripolyphosphate. phosphates are used to improve the characteristics of processed meat and cheese, and in toothpaste. white phosphorus, called "wp" (slang term "willie peter") is used in military applications as incendiary bombs, for smoke-screening as smoke pots and smoke bombs, and in tracer ammunition. it is also a part of an obsolete m34 white phosphorus us hand grenade. this multipurpose grenade was mostly used for signaling, smoke screens, and inflammation; it could also cause severe burns and had a psychological impact on the enemy. military uses of white phosphorus are constrained by international law. 32p and 33p are used as radioactive tracers in biochemical laboratories.