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PHOSPHATES

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Originally appearing in Volume V21, Page 476 of the 1911 Encyclopedia Britannica.
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PHOSPHATES , in See also:

chemistry, the name given to salts of phosphoric See also:acid. As stated under See also:PHOSPHORUS, phosphoric See also:oxide, P2O5, combines with See also:water in three proportions to See also:form See also:H2O•P2O5 or HPO3, metaphosphoric acid; 2H2O•P205 or H4P2O7, pyrophosphoric acid; and 3H2O•P206 or H3PO4, orthophosphoric or See also:ordinary phosphoric acid. These acids each give origin to several See also:series of salts, those of ordinary phosphoric acid being the most important, and, in addition, are widely distributed in the See also:mineral See also:kingdom (see below under Mineral Phosphates). Orthophosphoric acid, H3PO4, a tribasic acid, is obtained by boiling a See also:solution of the pentoxide in water; by oxidizing red phosphorus with nitric acid, or yellow phosphorus under the See also:surface of water by See also:bromine or See also:iodine; and also by decomposing a mineral phosphate with sulphuric acid. It usually forms a thin See also:syrup which on concentration in a vacuum over sulphuric acid deposits hard, transparent, rhombic prisms which melt at 41.70. On See also:long See also:heating the syrup is partially converted into pyro - phosphoric and metaphosphoric acids, but on adding water and boiling the ortho-acid is re-formed. It gives origin to three classes of salts: M'H2PO4 or M"H4P203; M'2HPO4 or M"HPO4, M'3PO4, M"3P208 or M"'PO4, wherein M',M",M"' denote a mono-, di-, and tri-valent See also:metal. The first set may be called monometallic, the second dimetallic, and the third trimetallic salts. Per-acid salts of, the alkalis, e.g. (K,Na,NH4)H5(PO4)2, are also known; these may be regarded as composed of a monometallic phosphate with phosphoric acid, thus M'H2PO4 H3PO4. The three See also:principal 3AgP03+3H2O=Ag3PO4+2H3PO4. On heating with an oxide or carbonate they yield a trimetallic orthophosphate, See also:carbon dioxide being evolved in the latter See also:case.

Metaphosphoric acid can be distinguished from the other two acids by its See also:

power of coagulating albumen, and by not being precipitated by mag- nesium and ammonium chlorides in the presence of See also:ammonia. (C. E.*) Mineral Phosphates.—Those varieties of native See also:calcium phosphate which are not distinctly crystallized, like See also:apatite (q.v.), but occur in fibrous, compact or earthy masses, often nodular, and more or less impure, are included under the See also:general See also:term See also:phosphorite. The name seems to have been given originally to the See also:Spanish phosphorite, probably because it phosphoresced when heated. This mineral, known as See also:Estremadura phosphate, occurs at Logrossan and See also:Caceres, where it forms an important See also:deposit in See also:clay-See also:slate. It may contain from 55 to 62 % of calcium phosphate, with about 7% of See also:magnesium phosphate. A some-what similar mineral, forming a fibrous incrustation, with a mammillary surface, and containing about 9% of calcium carbonate, is known as staffelite, a name given by A. See also:Stein in 1866 from the locality Staffel, in the valley of the See also:Lower See also:Lahn, where (as also in the valley of its tributary the See also:Dill) large deposits of phosphorite occur. Dahllite is a See also:Norwegian phosphorite, containing calcium carbonate, named in 1888 by W. C. See also:Brogger and H. Backstrom after the Norwegian geologists T. and J.

Dahll. Osteolite is a See also:

white earthy phosphorite occurring in the clefts of basaltic rocks, named in 1851 by J. C. Bromeis from the See also:Greek oarEov, See also:bone. Phosphorite, when occurring in large deposits, is a mineral of much economic value for See also:conversion into the superphosphate largely used as a fertilizing See also:agent. Many of the impure sub-stances thus utilized are not strictly phosphorite, but pass under such names as " See also:rock-phosphate," or, when nodular, as " coprolite " (q.v.), even if not of true coprolitic origin. The ultimate source of these mineral phosphates may be referred in most cases to the apatite widely distributed in crystalline rocks. Being soluble in water containing carbonic acid or organic acids it may be readily removed in solution, and may thus furnish See also:plants and animals with the phosphates required in their structures. On the decay of these structures the phosphates are returned to the inorganic See also:world, thus completing the See also:cycle. There are three See also:sources of phosphates which are of importance geologically. They occur (a) in crystalline igneous and metamorphic rocks as an See also:original constituent, (b) in See also:veins associated with igneous rocks, and (c) in sedimentary rocks either as organic fragments or in secondary concretionary forms. The first mode of occurrence is of little significance practically, for the crystalline rocks generally contain too little phosphate to be valuable, though occasionally an igneous rock may contain enough apatite to form an inferior fertilizing agent, e.g. the See also:trachyte of Cabo de Gata in See also:south-See also:east See also:Spain, which contains 12—15% of phosphoric acid.

In many deposits of See also:

iron ores found in connexion with igneous or metamorphic rocks small quantities of phosphate occur. The See also:Swedish, Norwegian, See also:Ontario and See also:Michigan mines yield ores of this See also:kind; and though none of them can be profitably worked as a source of phosphate, yet on reducing the ore it may be retained in the slags, and thus rendered available for See also:agriculture. Another See also:group of phosphatic deposits connected with igneous rocks comprises the apatite veins of south See also:Norway, See also:Ottawa and other districts in See also:Canada. These are of pneumatolytic origin (see See also:PNEUMATOLYSIS), and have been formed by the See also:action of vapours emanating from cooling bodies of basic eruptive rock. Veins of this type occur at Oedegarden in Norway and Dundret in See also:Lapland. From 1500 to 3500 tons of apatite are obtained yearly in Norway from these veins. In Ontario apatite has been worked for a long See also:time in deposits of similar nature. The See also:total output of Canada in 1907 was only 68o tons. The phosphatic rocks which occur among the sedimentary strata are the principal sources of phosphates for See also:commerce and agriculture. They are found in formations of all ages from the See also:Cambrian to those which are accumulating at the See also:present See also:day. Of the latter the best known is See also:guano (see See also:MANURES and MANURING). Where guano-beds are exposed to See also:rain their soluble constituents are removed and the insoluble matters See also:left behind.

The soluble phosphates washed out of the guano may become fixed by entering into See also:

combination with the elements of the rock beneath. Many of the oceanic islets are composed of See also:coral See also:limestone, which in this See also:groups differ remarkably in their behaviour towards indicators. The monometallic salts are strongly acid, the dimetallic are neutral or faintly alkaline, whilst the soluble trimetallic salts are strongly alkaline. The monometallic salts of the alkalis and alkaline earths may be obtained in crystal form, but those of the heavy metals are only See also:stable when in solution. The soluble trimetallic salts are decomposed by carbonic acid into a dimetallic See also:salt and an acid carbonate. All soluble orthophosphates give with See also:silver nitrate a characteristic yellow precipitate of silver phosphate, Ag3PO4, soluble in ammonia and in nitric acid. Since the reaction with the acid salts is attended by liberation of nitric acid: NaH2PO4+3AgNO3=Ag3PO4+NaNO3 +2HNO3, Na2HPO4+3AgNO3=Ag3PO4+2NaNO3+HNO3, it is necessary to neutralize the nitric acid if the See also:complete precipitation of the phosphoric acid be desired. The three series also differ when heated: the trimetallic salts, containing fixed bases are unaltered, whilst the mono- and dimetallic salts yield See also:meta- and pyrophosphates respectively. If the heating be with See also:charcoal, the trimetallic salts of the alkalis and alkaline earths are unaltered, whilst the mono- and di-salts give See also:free phosphorus and a trimetallic salt. Other precipitants of phosphoric acid or its salts in solution are: ammonium molybdate in nitric acid, which gives on heating a See also:canary-yellow precipitate of ammonium phosphomolybdate, 12[See also:MoOd (NH4)3PO4, insoluble in acids but readily soluble in ammonia; magnesium chloride, ammonium chloride and ammonia, which give on See also:standing in a warm See also:place a white crystalline precipitate of magnesium ammonium phosphate, Mg(NH4)PO4.6H20, which is soluble in acids but highly insoluble in ammonia solutions, and on heating to redness gives magnesium pyrophosphate, Mg2P2O7; uranic nitrate and ferric chloride, which give a yellowish-white precipitate, soluble in hydrochloric acid and ammonia, but insoluble in acetic acid; mercurous nitrate which gives a white precipitate, soluble in nitric acid, and See also:bismuth nitrate which gives a white precipitate, insoluble in nitric acid. Pyrophosphoric acid, H4P207, is a tetrabasic acid which may be regarded as derived by eliminating a See also:molecule of water between two molecules of ordinary phosphoric acid; its constitution may therefore be written (HO)20P.O.PO(OH)2. It may be obtained as a glassy See also:mass, indistinguishable from metaphosphoric acid, by heating phosphoric acid to 215 When boiled with water it forms the ortho-acid, and when heated to redness the meta-acid.

After neutralization, it gives a white precipitate with silver nitrate. Being a tetrabasic acid it can form four classes of salts; for example, the four solium salts Na4P2O7, Na3HP2O7, Na2H2P2O7, NaH3P2O7 are known. The most important is the normal salt, Na4P2O7, which is readily obtained by heating disodium orthophosphate, Na2HPO4. It forms See also:

monoclinic prisms (with IoH2O) which are permanent in See also:air. All soluble pyrophosphates when boiled with water for a long time are converted into orthophosphates. Meta phosphoric acid, HPO3, is a monobasic acid which may be regarded as derived from orthophosphoric acid by the See also:abstraction of one molecule of water, thus H3PO4—H2O=HP'03; its constitution is therefore (HO)PO2. The acid is formed by dissolving phosphorus pentoxide in See also:cold water, or by strongly heating orthophosphoric acid. It forms a colourless vitreous mass, hence its name " glacial phosphoric acid." It is readily soluble in water, the solution being gradually transformed into the orthoacid, a reaction which proceeds much more rapidly on boiling. Although the acid is monobasic, salts of polymeric forms exist of the types (MPO3),,, where n may be 1, 2, 3, 4, 6. They may be obtained by heating a monometallic orthophosphate of a fixed See also:base, or a dimetallic orthophosphate of one fixed and one volatile base, e.g. microcosmic salt: MH2PO4=MPO3+H20, (NH4) NaHPO4= NaPO3+NH3+HDO; they may also be obtained by acting with phosphorus pentoxide on trimetallic orthophosphates: Na3PO4+P203=3NaPO3. The salts are usually non-crystalline and fusible. On boiling their solutions they yield orthophosphates, whilst those of the heavy metals on boiling with water give a trimetallic orthophosphate and orthophosphoric acid: way becomes phosphatized; others are igneous, consisting of ^ trachyte or See also:basalt, and these rocks are also phosphatized on their surfaces but are not so valuable, inasmuch as the presence of iron or alumina in any quantity renders them unsuited for the preparation of artificial manures.

The leached guanos and phosphatized rocks, which are grouped with them for commercial purposes, have been obtained in See also:

great quantities in many islands of the Pacific Ocean (such as See also:Baker, Howland, See also:Jarvis and McKean Islands) between long. 150° to 18o° W. and See also:lat. 10° N. to to° S. In the See also:West Indies from See also:Venezuela to the See also:Bahamas and in the Caribbean See also:Sea many islands yield supplies of leached guanos; the following are important in this respect: See also:Sombrero, Navassa, Aves, Aruba, Curacoa. See also:Christmas See also:Island has been a great source of phosphates of this type; also Jaluit Island in the Maldive See also:Archipelago, Banaba or Ocean Island, and Nauru or Pleasant Island. On Christmas Island the phosphate has been quarried to depths of too ft. To these leached guanos and phosphatized limestones the name sombrerite has been given. It has been estimated that 500,000 tons of phosphate were obtained in Aruba, t,000,000 tons from Curacoa since the deposits were discovered in 187o, and Christmas Island in 1907 yielded 290,000 tons. In the older formations the phosphates tend to become more and more mineralized by chemical processes. In whatever form they were originally deposited they often suffer complete or partial solution and are redeposited as concretionary lumps and nodules, often called See also:coprolites. The " Challenger " and other oceanographic expeditions have shown that on the bottom of the deep sea concretions of phosphate are now gathering around the dead bodies of fishes lying in the oozes; consequently the formation of the concretions may have been carried on simultaneously with the deposition of the strata in which they occur. Important deposits of mineral phosphates are now worked on a large See also:scale in the See also:United States, the See also:annual yield far surpassing that of any other See also:part of the world.

The most active operations are carried on in See also:

Florida, where the phosphate was first worked in 1887 in the form of pebbles in the gravels of See also:Peace See also:river. Then followed the See also:discovery of " hard rock-phosphate," a massive mineral, often having cavities lined with nearly pure phosphorite. Other kinds not distinctly hard and consisting of less See also:rich phosphatic limestone, are known as " soft phosphate ": those found as smooth pebbles of variable See also:colour are called " See also:land pebble-phosphate," whilst the pebbles of the river-beds and old river-valleys, usually of dark colour, are distinguished as " river pebble-phosphate." The land pebble is worked in central South Florida; the hard rock chiefly between See also:Albion and See also:Bay See also:City. In South Carolina, where there are important deposits of phosphate, formerly more productive than at present, the " land rock " is worked near See also:Charleston, and the " river rock "in the Coosaw river and other streams near See also:Beaufort. The phosphate beds contain See also:Eocene fossils derived from the underlying strata and many fragments of See also:Pleistocene See also:vertebrata such as See also:mastodon, See also:elephant, See also:stag, See also:horse, See also:pig, &c. The phosphate occurs as lumps varying greatly in See also:size, scattered through a See also:sand or clay; they often contain phosphatized Eocene fossils (See also:Mollusca, &c.). Sometimes the phosphate is found at the surface, but generally it is covered by alluvial sands and See also:clays. Phosphate See also:mining began in South Carolina in 1868, and for twenty years that See also:state was the principal producer. Then the Florida deposits began to be worked. In 1892 the phosphates of See also:Tennessee, derived from Ordovician limestones, came into the See also:market. From See also:North Carolina, See also:Alabama and See also:Pennsylvania, also,.phosphates have been obtained but only in comparatively small quantities. In 1900 mining for phosphates was commenced in See also:Arkansas.

In 1908 Florida produced 1,673,651 tons of phosphate valued at 11 million dollars. All the other states together produce less phosphate than Florida, and among them Tennessee takes the first place with an output of 403,180 tons. See also:

Algeria contains important deposits of phosphorite, especially near See also:Tebessa and at See also:Tocqueville in the See also:province of See also:Constantine. Near See also:Jebel Kouif, on the frontier between Algeria and See also:Tunis, there are phosphate workings, as also in Tunis, at Gafsa. The deposits belong to the Lower Eocene, where it rests unconformably upon the Cretaceous. The See also:joint See also:production of Tunis and Algeria in 1907 was not less than a million tons. Phosphates occur also in See also:Egypt, in the See also:desert east of Keneh and in the Dakla See also:oasis in the Libyan desert. See also:France is rich in mineral phosphates, the See also:chief deposits being the departments of the Pas-de-See also:Calais, See also:Somme, See also:Aisne, See also:Oise in and See also:Meuse, in the north-east, and another group in the departments of See also:Lot, See also:Tarn-et-See also:Garonne and See also:Aveyron, in the south-west: phosphates occur also in the See also:Pyrenees. The deposits near See also:Caylus and in See also:Quercy occupy fissures and pockets in See also:Jurassic• limestone, and have yielded a remarkable assemblage of the See also:relics of See also:Tertiary mammals and other fossils. Phosphates occur in See also:Belgium, especially near See also:Mons, and these, like those of north-east France, are principally in the Upper See also:Chalk. Two varieties of phosphate rock are recognized in these districts, viz. the phosphatic chalk and the phosphate sand, the latter resulting from the decomposition of the former. Large and valuable deposits of the sand have been obtained in sinks and depressions on the surface of the chalk.

The production is on the whole diminishing in Belgium (18o,000 tons in 1907), but in France it is still large (375,000 tons in 1907). In the Lahn See also:

district of See also:Nassau (See also:Germany) there are phosphate beds in Devonian rocks. The deposits were rich but irregular and See also:local, and were much worked from 1866 to 1884, but are no longer of economic importance. In See also:northern Estremadura in Spain and Alemtezo in See also:Portugal there are vein deposits of phosphate of See also:lime. As much as 200,000 tons of phosphate have been raised in these provinces, but in 1906 the total production of Spain was only 1300 tons. Large deposits of phosphate occur in See also:Russia, and those in the neighbourhood of Kertch have attracted some See also:attention; it is said that the Cretaceous rocks between the See also:rivers See also:Dniester and See also:Volga contain very large supplies of phosphate, though probably of See also:low grade. Phosphatic nodules and concretions, with phosphatized fossils and their casts, occur at various See also:geological horizons in Great See also:Britain. Bands of See also:black nodules, highly phosphatic, are found at the See also:top of the See also:Bala limestone in North See also:Wales; beds of concretions occur in the Jurassic series; and important deposits are known in the Cretaceous strata, especially in the Lower See also:Greensand and at the base of the See also:Gault. The Lower Greensand phosphates have been worked, under the name of " coprolites," at Potton in See also:Bedfordshire and at Upware and Wicken in See also:Cambridgeshire. The See also:Cambridge Greensand, rich in phosphatic nodules, occurs at the base of the Chalk See also:Marl. The chalk occasionally becomes phosphatized, as at Taplow (Bucks) and See also:Lewes (See also:Sussex). At the base of the Red See also:Crag in East Anglia, and occasionally at the base of the other See also:Pliocene Crags, there is a " nodule See also:bed, consisting of phosphatic nodules, with rolled See also:teeth and bones, which were formerly worked as " coprolites " for the preparation of artificial manure.

See also:

Professor R. J. See also:Strutt has found that phosphatized nodules and bones are rich in radioactive constituents, and has brought this into relation with their geological See also:age. (J. S. F.; F. W.

End of Article: PHOSPHATES

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