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by Vincenzo Cascariolo, a cobbler of Bologna, in about 1602. This was followed by the discovery of a number of other substances which become luminous either after exposure to light or on heating, or by attrition, and to which the general name of “ phosphori ” (from M: and ¢6pos, bringing light) was given. Among these may be mentioned Homberg’s phosphorus (calcium chloride), John Canton’s phosphorus (calcium sulphide) and Balduin’s phosphorus (calcium nitrate). Of late years it has been found convenient to limit the strict meaning of the word “ phosphorescence ” to the case of bodies which, after exposure to light, become self-luminous (even if only for a fraction of a second). The general term “luminescence” has been proposed by E. Wiedemann to include all cases in which bodies give ofi light not due to ignition. This general term embraces several subdivisions. Thus, fluorescence (q.v.) and phosphorescence are included under the same heading, “photoluminescence,” being distinguished from each other only by the fact that fluorescent bodies emit their characteristic light only while under the influence of the exciting illumination, while phosphorescent bodies are luminous for an appreciable time after the exciting light is cut ofl.

Pl'msphorescence, in its restricted meaning as above explained, is most strikingly exhibited by the artificial sulphides of calcium, strontium and barium. If any of these substances is exposed for some time to daylight, or, better, to direct sunlight, or to the light of the electric arc, it will shine for hours in the dark with a soft coloured li ht. The colour depends not only on the nature of the substance, ut also on its physical condition, and on its tem rature durin insolation, that is, exposure to the sun's rays. hus the phosp crescent light emitted by calcium sulphide may be orangeyellow, yellow, green or violet, according to the method of preparation and the materials used. Balmain's luminous paint, a preparation of calcium sulphide, shines with a white light. The colour also depends on the temperature during exposure to light. Thus A. E. Becquerel found that the light given by a specimen of strontium sulphide changed from violet to blue, green, yellow and orange, as t e temperature during the correspondin previous insolation was 20°, 40°, 70°, 100° or 200° C. The uration of

hos horescence varies greatly with different substances. it may at or days or for only a fraction of a second.

As in the case of fluorescent bodies, the li ht produced by phos~ phorescent substances consists commonly o rays less refrangible than those of the exciting light. Thus the ultra-violet portion of the spectrum is usuall the most eflicient in exciting rays belongin to the visible part 0 the spectrum. V. Klatt and Ph. Lenar (Wied. Ann., l889, xxxviii. 90), have shown that the phos horescence of calcium sulphide and other phosphori depends on t e resence of minute quantities of other substances, such as copper, ismuth and manganese. The maximum intensity of phosphorescent light is obtained when a certain definite roportion of the impurity is present, and the intensity is diminishedlif this proportion is increased.

it appears likely that when a phosphorescent body is exposed to light, the energy of the li ht is stored up in some kind of strain energy, and that the phosphorescent light is given out during a more or less slow recovery from this state of strain. Klatt and Lenard have shown that the sulphides of the alkaline earths lose the property of phosphorescing when subjected to heavy pressure. Many fluorescent solutions become briefly phosphorescent when rendered solid by gelatin.

When the duration of phosphorescence is brief, some mechanical device becomes necessa to detect it. The earliest and bestknown instrument for this purpose is Becquerel's phosphoroscope. It consists essentially of a shallow drum, in whose ends two eccentric holes, exactly 0 posite one another, are cut. Inside it are fixed two e ual meta disks, attached perpendicularl to an axis, and divid into the same number of sectors, the a ternate sectors of each being cut out. One of these disks is close to one end of the drum, the other to the opposite end, and the sectors are so arranged that, when the disks are made to rotate, the hole in one end is open while that in the other is closed, and vice versa. If the eye be placed near one hole, and a ray of sunlight be admitted by the other, it is obvious that while the sun shines on an object inside the drum the aperture next the eye is closed, and vice versa. If the disks be made to revolve with reat velocity by means of a train of toothed wheels the object wil be presented to the eye almost instantly after it has been exposed to sunlight, and these presentations succeed one another so rapidly as to produce a sense of continuous vision. By means of this apparatus we can test with considerable accurac the duration of the phenomenon after the light has been cut 0 . For this purpose we require to know merely the number of sectors in the disks and the rate at which they are turned.

Thermoluminesccnce.—Some bodies which do not emit light at ordinary temperatures in a dark room begin to do so if they are heated to a temperature below a visible red heat. In the case of

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chlorophane, a variety of fluor-spar, the heat of the hand is sufliciemv Many yellow diamonds exhibit this form of luminescence. lt has been shown, however, that a previous exposure to light is always necessary. Sir James Dewar found that if ammonium platinoc anide, Balmain‘s paint and some other substances are cooled to t e temperature of liquid- air and exposed to light, they do not phosphoresce, but as soon as they are allowed to warm up to the ordinary temperature they emit a brilliant light. On the other hand, some bodies, such as gelatin, celluloid, paraffin and ivory, are phosphorescent at very low temperatures, but lose the property at ordinary temperatures.

Triboluminescence (from rplflew, to rub) is luminescence excited by friction, percussion, cleavage or such mechanical means. Calcium chloride, prepared at a red heat, exhibits this property. If sugar is broken in the dark, or two crystals of quartz rubbed together, or a piece of mica cleft, a flash of light is seen, but this is probabl of electrical origin. Closely allied to this form of luminescence IS crystalloluminescence, a p osphorescent light seen when some substances crystallize from solution or after fusion. This roperty is exhibited by arsenious acid when crystallizing from so ution in hydrochloric acid.

Chemiluminescence is the name given to those cases in which chemical action produces light without any great rise of temperature. Phosphorus exposed to most air in a dark room shines with a soft light due to slow oxidation. Decaying wood and other vegetable substances often exhibit the same property.

Electroluminescmce is luminescence due to electrical causes. Many gases are phosphorescent for a short time after an electric discharge has been passed through them, and some solid substances, especially diamonds and rubies, are strongly phosphorescent when eXposed to kathode rays in a vacuum tube.

See generally, Winkelmann, Handbuch der Physik, Bd. vi. (1806); E. Becquerel, La Lumiere (1867). (j. R. .)

Phosphorcscence in Zoology.

The emission of light by living substance is a widespread occurrence, and is part of the general metabolism by which the potential energy introduced as food is transformed into kinetic energy and appears in the form of movement, heat, electricity and light. In many cases it is probably an accidental byproduct, and like the heat radiated by living tissues, is not necessarily of use to the organism. But in other cases the capacity to produce light is awakened on stimulation, as when the wind ripples the surface of the sea, or when the water is disturbed by the blade of an oar. It has been suggested that the response to the stimulus may be protective, and that enemies are frightened by the flash of light. In luminous insects and deep-sea fish the power of emitting light appears to have a special significance, and very elaborate mechanisms have been developed. The pale glow of phosphorescence has a certain resemblance to the light emitted by phosphorus, and it was an early suggestion that the phenomenon in living organisms was due to that substance. Phosphorus, however, and its luminous compounds are deadly poisons to all living tissues, and never occur in them in the course of natural metabolism, and the phosphorescence of life cannot therefore be assigned to the oxidation of phosphorus. On the other hand, it is certainly the result of a process of oxidation, as the emission of light continues only in the presence of oxygen. J. H. Fabre showed in 185 5 that the luminous fungus, Agaricus, discharges more carbonic acid when it is emitting light, and Max Schultze in 186 5 showed that in insects the luminous cells are closely associated with the tracheae, and that during phosphorescence they withdraw oxygen from them. In 1880 B. Radziszewski showed that many fats, ethereal oils and alcohols emit light when slowly combined with oxygen in alkaline fluids at appropriate temperatures. Probably the phosphorescence of organisms is due to a' similar process acting on the many fats, oils and similar substances found in living cells. The colour varies much in diflerent organisms; green has been observed in the glow-sworm, fire-flies, brittle-stars, centipedes and annelids; blue in the Italian fire-fly (Luciola italica); blue and light green are the predominant colours in the phosphorescence of marine organisms, but red and lilac have also been observed. The Lantern-Fly (Fulgora nyorhynchus) is said to have a purple light, and E. H. Giglioli has recorded that an individual Apjmuiicularia appeared first red, and then blue, and then green. P. Panceri, chiefly in the case of 8011):, and S. P. Langley and F. W. Very in the case of Pyrophorus, have investigated the light spectroscopically, and found that it consisted of a continuous band without separate bright lines. The solar spectrum extends farther both towards the violet and the red ends, but is less intense in the green when equal luminosities are compared.

Many of the bacteria of putrefaction are hosphorescent, and the light emitted by dead fish or molluscs or esh is probably due in every case to the presence of these. Under the miscroscope, the individual bacteria appear as shining points of light. The phosphorescence of decaying wood is due to the presence of the m celium of Agan'cus melleus, and various other species of A garicu: ave been found to be luminous. The great displays of phosphorescence in sea-water are usually due to the presence of very large numbers of small luminous organisms, either protozoa or protophyta. Of these Noctiluca miliaris and species of Peridim'um and Pyrocystis are the most frequent, the two former near land and the latter in mid-ocean.

In higher animals the phosphorescence tends to be limited to special parts of the body which may form elaborate and highly specialized luminous organs. Many coelenterates show the beginning of such localization; in medusae the whole surface ma be luminous, but the light is brighter along the radial canals, in t e ovaries, or in the marginal sense-organs. In Pennatulids each polyp has eight luminous bands on the outer surface of the digestive cavity. Some Chaetopods (Chaetoptems and Tamoftenls) have luminous organs at the bases of the lateral processes 0 the bod Pymsoma, a colonial pela ic ascidian, is responsible for some of t e most striking displa s of phosphorescence in tropical seas; it has two small patches 0 cells at the base of each inhalent tube which on stimulation discharge light, and the luminosity has been observed to spread through the colon from the point of irritation.

Amongst the rustacea, many pelagic Copepods are phosphorescent. W. Giesbrecht has shown that the light is produced by a fluid secreted by certain dermal glands. A similar fluid in other Copepods hardens to form a protective case, and it may be that the display of light is in such cases an accidental by-product. Glands in the labrum of the Ostracod P ocypris and on the maxillae of the Mysid Gnathaphausia similary roduce a luminous secretion. in the Euphausiacea, on the other liand, phosphorescence is produced by elaborate luminous or ans which are situated on the thoracic appendages and the ab omen, and which were at first believed to be ocular organs. The deep-sea Decapod Crustaceans belonging to many families are luminous. A. Alcock observed that in some of the dee ~sea prawns a luminous secretion was discharged at the bases of t e antennae, but in most cases the luminous or ns are numerous eye-like structures on the limbs and body.

he rock-boring mollusc, Pholas, which Pliny knew to be phosphorescent, has luminous organs along the anterior border of the mantle, two small triangular atches at the entrance of the anterior si hon, and two long paralle cords within the siphon. The cells ofp these organs have (peculiar, ranulated contents. W. E. Hoyle, in his presidential ad ress to t e Zoological Section of the British Association in 1907, brought together observations on the occurrence of luminous organs in no less than thirty-three species of Cephalopods. In Heteroteuthis, Sepiala and Russia the light is produced b the secretion of a glandular organ on the ventral side of the ody behind the funnel. The secretion glows through the transparent wall with a greenish colour, but, at least in the case of Heteroteuthis, continues to glow after being e'ected into the water. in most cases the luminous organs are nong andular and may be simple, or possess not only a generator but a reflector, lens and diaphragm. The different organs shine with different coloured li hts, and as the Cephalopods are for the most part inhabitants of the depths of the sea, it has been suggested that they serve as recognition marks.

Some centipedes (mg. Geophaus electricus and G. phosphorus) are luminous, and, if a lowed to crawl over the hand, are stated to leave a luminous trail. Amongst insects, elaborate luminous organs are developed in several cases. The abdomen of a Ceylonese May-fly (Telegzmodes) is luminous. The so-called New Zealand “ glow-worm " is the larva of the fly Boletophila luminosa, and some

nats have been observed to be luminous, although the suggestion .is that in their case disease is present and the light emanates from phosphorescent bacteria. An ant (Orya) and a poduran (Anuro

horus) are occasionally luminous. The so-called lantern flies are

omoptera allied to the Cicadas, and the supposed luminous organ is a huge projection of the front of the head, regarding the luminosity of which there is some doubt. The glow-worms and true fire-flies are beetles. Eggs, larvae and adults are in some cases luminous. The organs consist of a pale transparent superficial layer which

ives the light, and a deeper layer which may act as a reflector. They are in close connexion with the tracheae and the light is produced by the oxidation of a substance formed under the influence of the nervous system, and probably some kind of anic fat. in the females the phosphorescence IS probably a sexua lure; in the males its function is unknown.

Phosphorescent organs known as photophores are characteristic structures in many of the deep-sea Teleostome fishes, and have been developed in widely different families (Stomiah'dae, Scopzlidaz.

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Halasauridae and Anomalojn'dae), whilst numerous sim le luminous organs have been detected in many species of Selachii. The number, distribution and complexity of the organs vary much in different fish. They are most frequent on the sides and ventral surface of the anterior part of the body and the head, and may extend to the tail. The simpler forms are generally arranged in rows, sometimes metamerically distributed; the more complex organs are larger and less numerous. In Opostomias micrianus there is a large organ on a median barbel hanging down from the chin, others be ow the eyes, and one on the elongated first ray of the pectoral fin. ln Swrnoptyx diaphana there is one on the lower jaw, and in many species one or two below the eyes. The luminous organs appear to be specialized skin lands which secrete a fluid that becomes luminous on slow oxi ation. The essential part of the organ remains a collection of gland cells, but in the more complex types there are blood vessels and nerves, a protecting membrane, an iris-like dia hragm, a reflector and lens. As the distribution and probably the colour of the light varies with the species, these organs may serve as recognition marks. They may also attract prey, and from their association with the eyes in such a position as to send light downwards and forwards it is probable that in the higher types they are used by the fish actually as lanterns in the dark abysses of the sea. (P. C. M.)

PHOSPHORITE, in mineralogy, the name given to impure massive apatite (q.v.; see also PHOSPHATES).

PHOSPHORUS (Gr. 4:85, light, ¢épew, to bear), the name originally given to any substance which possessed the property of phosphorescence (q.v.), 11¢. the power of shining in the dark, but now generally restricted to a non-metallic element, which was first known as Phosphorus mirabilis or igneus. This element is very widely distributed in nature in combination, but is never found free. In the mineral kingdom it is exceptionally abundant, forming large deposits of phosphates (q.v.). It is also necessary to animal and vegetable life (see MANURE). It occurs in the urine, blood, tissues, and bones of animals, calcium phosphate forming about 58% of bones, which owe their rigidity to its presence.

The element appears to have been first obtained in 1669 by Brand of Hamburg; Krath bought his secret and in 1677 exhibited specimens in England, where it created an immense sensation. Its preparation was assiduously sought for, and Kunckel in 1678 and Boyle in 1680 succeeded in obtaining it by the same process as was discovered by Brand, 1'.e. by evaporating urine to dryness and distilling the residue with sand. This method was generally adopted until 177 5, when Scheele prepared it from bones, which had been shown by Gahn in 1769 to contain calcium phosphate. Scheele treated bone ash with nitric acid, precipitated the calcium as sulphate, filtered, evaporated and distilled the residue with charcoal. ' Nicolas and Pelletier improved the process by decomposing the bone-ash directly with sulphuric acid; whilst Fourcroy and Vauquelin introduced further economies. In modern practice degreased bones (see GELATIN), or bone-ash which has lost its virtue as a filtering medium, &c., or a mineral phosphate is treated with sufficient sulphuric acid to precipitate all the calcium, the calcium sulphate filtered off, and the filtrate concentrated, mixed with charcoal, coke or sawdust and dried in a muffle furnace. The product is then distilled from Stourbridge clay retorts, arranged in a galley furnace, previously heated to a red heat. ' The temperature is now raised to a white heat, and the product led by malleable iron pipes into condensing troughs containing water, when it condenses. The chemical reactions are as follows: the treatment of the calcium phosphate with the acid gives phosphoric acid, H3P04, which at a red heat loses water to give metaphosphoric acid, HP03; this at a white heat reacts with carbon to give hydrogen, carbon monoxide and phosphorus, thus: 2HPO;+

Electrothermal processes are also employed. Calcium phos~ phate, mixed with sand and carbon, is fed into an electric furnace, provided with a closely fitting cover with an outlet leading to a condenser. At the temperature of the furnace the silica (sand) attacks the calcium phosphate, forming silicate, and setting free phosphorus pentoxide, which is attacked by the carbon, forming phosphorus and carbon monoxide. As phosphorus boils at 290° C. (5 54° F.), it is produced in the form of vapour, which, mingled with carbon monoxide, passes to the condenser, where it is condensed. It is then cast under water. The calcium silicate remains in the furnace in the form of a liquid slag, which may be run 05, so that the action is practically continuous. Kaolin may with advantage be used in addition to or in part substitution for sand, because the double silicate thus formed is more fusible than the single silicate of lime. The alternating current is generally used, the action not being electrolytic. One of the special advantages of the electrical over the older process is that the distilling vessels have a longer life, owing to the fact that they are not externally heated, and so subjected to a relatively high temperature when in contact with the corrosive slag formed in the process. The Readman-Parker process (see Jour. Soc. Chem. Ind, 1891, x. 445) appears to be very generally adopted. Readman, experimenting with a Cowles furnace in Stafl'ordshire in 1888, patented his process, and in the same year Parker and Robinson, working independently, patented a similar one. The two inventors then cooperated, an experimental plant was run successfully, and the patents were taken over by the leading manufacturers. With the object of obtaining a valuable by-product in place of the slag produced in this furnace, several patentees (mg. Hilbert and Frank, Billaudot, Bradley and Jacobs, and others) have sought to combine the manufacture of calcium carbide and phosphorus by using only calcium phosphate and carbon, efiecting direct reduction by carbon at a high temperature.

The crude phosphorus is purified by melting under water and then filtering through animal black and afterwards through chamois leather, or by treating it, when molten, with chromic acid or a mixture of potassium bichromate and sulphuric acid; this causes the impurities to rise to the surface as a scum which can be skimmed off. It is usually sent on the market in the form of sticks, which were at one time prepared by sucking the molten material up glass tubes; but the.dangers to the workmen and other disadvantages of this method have led to its replacement by a continuous process, in which the phosphorus leaves the melting-pot for a pipe surrounded by water, in which it solidifies and can be removed as a continuous rod.

Properties—When perfectly pure phosphorus is a white, trans~ parent, waxy solid, but as usually prepared it is yellowish owing to the presence of the allotropic “ red phosphorus,” J. Boeseken (Abs. Jour. Chem. 800., 1907, ii. 343, 760) prepares perfectly pure phosphorus by heating the crude product with chromic acid solution, washing and drying in a vacuum, first at 40", then at 80°. It remains colourless in vacuum tubesin the dark, but on exposure it rapidly turns yellow. At 2 5° to 30° C. it is soft and flexible, but it hardens when strongly cooled, and can then only be cut with difficulty. The fracture is distinctly crystalline; large crystals, either regular dodecahedra or octahedra, may be obtained by crystallization from carbon bisulphide, sulphur chloride, &c., or by sublimation. It is a non-conductor of electricity. Its density at 0° is 1836; this regularly diminishes up to the melting-point, 44'3°, when a sudden drop occurs. Molten phosphorus is a viscid, oily, highly refractive liquid, which may be supercooled '10 32° before solidification. It boils at 290°, forming a colourless vapour which just about the boiling-point corresponds in density to tetratomic molecules, P4; at 15oo° to 1700°, however, Biltz and Meyer detected dissociation into P1 molecules. Beckmann obtained P4 molecules from the boiling-point of carbon bisulphide solutions, and Hertz arrived at the same conclusion from the lowering f the freezing-point in benzene solution; E. Paterno and asini, however, detected dissociation. Phosphorus is nearly insoluble in water, but dissolves in carbon bisulphide, sulphur chloride, benzene and oil of turpentine.

The element is highly inflammable, taking fire in air at 34° and burning with a bright white flame and forming dense white clouds of the pentoxide; in perfectly dry air or oxygen, however, . it may be distilled unchanged, H. B. Baker showing that a trace of water vapour was necessary for combination to occur. When exposed to the air a stick of phosphorus undergoes slow combustion, which is revealed by a greenish-white phosphorescence when the stick is viewed in the dark. This phenomenon was

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minutely studied by Boyle, who found that solutions in some essential oils (oil of cloves) showed the same character, whilst in others (oils of mace, and aniseed) there was no phosphorescence. He also noticed a strong garlic-like odour, which we now know to be due to ozone. Frederick Slare noticed that the luminosity increased when the air was rarefied, an observation confirmed by Hawksbee and Homberg, and which was possibly the basis of Berzelius's theory that the luminosity depended on the volatility of the element and not on the presence of oxygen. Lampadius, however, showed that there was no phosphorescence in a Torricellian vacuum; and other experimenters proved that oxygen was essential to the process. It depends on the partial pressure of the oxygen and also on temperature. In compressed air at ordinary temperature there is no glowing, but it may be brought about by heating. Again, in oxygen under ordinary conditions there is no phosphorescence, but if the gas be heated to 25° glowing occurs, as is also the case if the pressure be diminished or the gas diluted. It is also remarkable that many gases and vapours, e.g. Cl, Br, I,NH;, N10, N01, H15, 802, C5,, CH4, C¢H4, inhibit the phosphorescence.

The theory of this action is not settled. It is certain that the formation of hydrogen peroxide and ozone accompany the glowing, and in 1848 Schonbein tried to demonstrate that it depended on the ozone. E. Jungfleisch (Comptes rcndus, 1905, 140, p. 444) suggested that it is due to the combustion of an oxide more volatile than phosphorus, a view which appears to be supported by the observations of Scharfl (Zeit. phyrilz. Chem, 1908, 62, p. 178) and of L. and E. Bloch (Comptes rendus, 1908, 147, P- 842)

The element combines directly with the halogens, sulphur and selenium, and most of the metals burn in its vapour forming phosphides. When finely divided it decomposes water giving hydrogen phosphide; it also reduces sulphurous and sulphuric acids, and when boiled with water gives phosphine and hypophosphorous acid; when slowly oxidized under water it yields hypophosphoric acid.

Altotropic Phosphorus—Several allotropic forms of phosphorus have been described, and in recent years much work has been done towards settling their identities. When the ordinary form immersed in water is exposed to light, it gradually loses its transparency and becomes coated with a thin film. This substance was regarded as an allotrope, but since it is not produced in non-aerated water it is probably an oxide. More important is the so-called “ red phosphorus,” which is produced by heating yellow phosphorus to about 2 30° for 24 hours in an inert atmosphere, or in closed vessels to 300°, when the change is effected in a few minutes. E. Kopp in 1844 and B. C. Brodie in 1853 showed that a trace of iodine also expedited the change. The same form is also produced by submitting ordinary phosphorus to the silent electric discharge, to sunlight or the ultraviolet light. Since this form does not inflame until heated to above 350°, it is manufactured in large quantities for consumption in the match industry. The process consistsin heating yellow phosphorus in iron pots provided with air-tight lids, which, however, bear a long pipe open to the air. A small quantity of the phosphorus combines with the oxygen in the vessel, and after this the operation is practically conducted in an atmosphere of nitrogen with the additional safety from any risk of explosion. The product is ground under water, and any unchanged yellow form is eliminated by boiling with caustic soda, the product being then washed and dried and finally packed in tin boxes. The red variety is remarkably different from the yellow. It is a dark red microcrystalline powder, insoluble in carbon bisulphide, oil of turpentine, &c., and having a density of 2-2. It is stable to air and light, and does not combine with oxygen until heated, to above 350° in air or 260° in oxygen, forming the pentoxide. It is also non-poisonous. When heated in a vacuum to 530° it sublimes, and on condensation forms microscopic needles.

Hittorf’s phosphorus is another crystalline allotrope formed by heating phosphorus with lead in a sealed tube to redness, and removing the lead by boiling the product with nitric and hydrochloric acid. It is also obtained by heating red phosphorus under pressure to 580°. It forms a lustrous, nearly black crystalline mass, composed of minute rhombohedra. G. E. Linck and P. Moller (Ben, 1908, 41, p. 1404) have aflirmed that the product of the first process always contains lead. E. Cohen and J. Olie, Jun. (Abs. Jour. Chem. Soc., 1909, ii. 998) regard red phosphorus as a solid solution of the white in Hittorf’s, but this is contradicted by A. Stock (Ben, 1909, 42, p. 4510), who points out that ordinary red phosphorus melts at 605°—610°, whilst Hittorf’s melts at 620°; moreover, the latter is less reactive than the former at high temperatures. Another form was obtained by R. Schenck (Zeit. Elektroehem, 1905, ii. 117) as a scarlet amorphous powder by deposition of solutions of phosphorus in the tri-iodide, tribromide or sulphide (P453). It phosphoresces in ozone, but not in air, and is nonpoisonous; from its solution in alcoholic potash acids precipitate the hydride PulHfi, and when heated it is transformed into the red modification. It has been used in combination with potassium chlorate as a 'composition for matches to strike on any surface. Finally a black phosphorus was described by Thénard as formed by rapidly-cooling melted phosphorus.

Phosphine (fphosphoretted hydrogen), PH;, a gas formed in the gutrefaction 0 organic matter containing hosphorus, was obtained y Gengembre (Crell’s Ann., 1789, i. 450 by the action of potash upon phosphorus, the gas so prepared being spontaneously inflammable. Some time later Davy, by heating phosphorous acid, obtained a phosphoretted hydrogen which was not spontaneously inflammable. T ese gases were considered to be distinct until Le Verrier (Ann. shim. phys, 1835 [2], 60, p. 174) showed that the inflammability of Gengembre's phosphine was due to small quantities of liquid phosphoretted h drogen, P,H4. Phosphine may be prepared by the decomposition oly calcium phosphide with water (P2114 being formed simultaneously); by the decomposition of phosphorous and hypophosphorous acids when strongly heated; and by the action of solutions of the caustic alkalis on phosphorus: Pi+3NaOH+3H10= PH1+3NaH1POg hydrogen and EH; are produced at the same time, and the gas may be freed from the latter substance b passing into a hydrochloric acid solution of cuprous chloride an heating the solution, when ure phosphine is liberated (Riban, Comples rendus, 58, p. 581). he pure gas may also be obtained by heating phosphonium iodide with caustic potash (A. W. Hofmann, Ben, 1871, 4, p. 200); by the decomposition of crystalline calcium phosphide or of aluminium phosphide with water (H. Moissan, Bull. soc. china, 1899 (3), 21, p. 926; Matignon, Comptes rendus, 1900, 130, p. d1391); and by the reduction of phosphorous acid with nascent y rogen.

It is a colourless, extremely poisonous gas, possessing a characteristic offensive smell, resembling that of rotting fish. It becomes liquid at -90° C., and solid at -1 3° C.‘ (K. Olszewski, Mortals, 1866, 7, p. 371). It is only slightly so uble in water, but is readily soluble “1 solutions of copper sulphate, hypochlorous acid, and acid solutions of cuprous chloride. It burns with a brightly luminous flame, and is spontaneously inflammable at about 100° C. When mixed with oxy en it combines explosively if the mixture be under dimims ed ressure, and is violently decomposed by the halogens. It is aso decomposed when heated with sulphur or with most metals, in the latter case with the liberation of hydrogen and formation of phosphide of the metal. It combines with the halide derivatives of boron and silicon to form, e.g. Pris-2BR, 2PHrSiCli (Besson, Comptes rendus, 1890, 110, 80, pp. 240, 516; 18131, 1 1i, p. 8), with the halogen acids to form (phosphonium salts, P X ( =C ,Br,l), and with sodammonium an potassammonium to form PH-iNa, Pl-ng (Joannis, Complex rendus, 1894, 119, p. 557). It oxidizes slowly in air, and is a reducing agent. It decomposes when heated, hydrogen and red phos horus being formed.

Liquid Phaéphoretted Hydrogen, Pg} 4, first obtained by P. Thénard (Camptes ren us, 1844, 18, p. 652) by decomposing calcium phosphide with warm water, the products of reaction being then passed through a U tube surrounded by a freezing mixture (see also L. Gattermann, Ben, 1890, 23, p. 1174). It is a colourless liquid which boils at 57°-58 C It is insoluble in water, but soluble in

It is very unstable, being readily decomposed By passing the products of the decom sition of ranular calcium ch oride, the

alcohol and ether. by heat or light.

calcium phosphide with water over PgH ives a new hydride, PHI-ls an phosphine, the former being an o ourless, canary-yellow, amorphous powder. When heated in a vacuum it evolves phos hine, and leaves an orange-red residue (if a second new hydride, iii: (A. Stc8>ck3 \V. Biittcher, and W.

en er, Ben, I 09, 42, p. 2839, 284 ,2 53 .

Sglid Phosplgiretted I-Fydrogen, P4 3, first obtained b Le Verrier (lac. cit.),is formed by the action of phosphorus trichlori e on gaseous phosphine (Besson, Campus rendus, 111, p. 972); by the action of water on phos horus di-iodide and by the decomposition of calcium phosphide with hot concentrated hydrochloric acid. It is a yellow

solid, which is insoluble in water. It burns when heated to about 200° C. Oxidizing agents decompose it with great violence. When warmed with alcoholic potash it yields gaseous phosphine, hydrogen and a hypophosphite. It reduces silver salts.

Phosphom'um Salts—The chloride, PHCI, was obtained as a crystalline solid by Ogier (Comptes rendus, 1879, 89, p. 705) by combining phosphine and hydrochloric acid gas under a pressure of from 14—20 atmospheres; it can also be obtained at “30° to —35° C. under ordinary atmos heric pressure. It crystallizes in large transparent cubes, but rapi ly dissociates into its constituents on exposure.

he bromide, PHiBr, was first obtained by H. Rose (Pogg. Ame, 1832, 24, p. 151) from phosphine and hydrobromic acid; it also results when osphorus is heated with hydrobromic acid to 100120” C. in sea ed tubes (Damoiseau, Bull. sac. china, 1881, 35, p. 49). 1t crystallizes in colourless cubes, is deliquescent, and often inflames spontaneously on exposure to air. It is readily decomposed by water

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chim. phys, 1814, 91, I4). is usually obtained by the action of water on a mixture 0 Iphosphorus and iodine (A. W. Hofmann. Ben, 1373, 6, p. 286). t is also prepared by the action of iodine on gaseous Cphosphine, or by heating amorphous hosphorus with concentrate hydriodic acid solution to 160° C. t crystallizes in large cubes and sublimes readily. It is a strong reducin agent. Water and the caustic alkalis readily decompose it with li ration of phosphine and the formation of iodides or b driodic acid. It is also decomposed by carbonyl chloride (Besson, ac. 617.). 4PHQI+8COCIQ=16HC1+SCO+P2I|+2P,

Just as the amines are derived from ammonia, so from phosphine are derived the primary, secondary and tertiary organic phosphines by the exchange of hydrogen for alkyl groups, and corres nding to the phosphonium salts there exists a series of organic p osphonium bases. The primary and secondary phosphines are produced when the alkyl iodides are heated with phosphonium iodide and zinc oxide to 150° C. (A. W. Hofmann, Ben, 1871, g, p. 30, 605). thus: 2 R1 + 2 PH41+ ZnO = 2 R'PHQ‘HI + ni: + ,O, 231 + PHJ + ZnO = Rg'PH'HI + ang + H10. The reaction mlxture on treatment with water yields the rimary hosphine, the secondary phosphine being then liberated rom its ydriodide b caustic soda. The tertiary phosphines, discovered by L. Thénard (.ompws rendus, 1845, 21, p. 144; 1847, 25, . 892), are formed (together with the quaternary hosphonium sa ts) b heatin alkyl iodides with phos honium iodi e to 15o—180° C.: P il+3 H,l= P(CH;);HI +3H ;P(CH,);HI + CH;I = P(CH;)iI + HI (see also Fireman, Ben, 1897, 30, p. 1088). They are also formed by the interaction of phosphorus trichloride and zinc alk ’ls (Cahours and Hofmann, Arm, 1857, 104, p. 1): 2PCl=+3 Zn (C,Hi),=3ZnCl,+ 2P(C¢H6)l.

The primary and secondary phosphines are colourless compounds, and with the exception of methyl phosphine are liquid at ordinary temperature. They possess an unpleasant odour, fume on eXposure to air, show a neutral reaction, but combine with acids to form salts. They oxidize very rapidly on exposure, in many cases being spontaneously inflammable. On oxidation with nitric acid the rimary compounds give monoalkyl hos hinic acids, R-PO(O :, the secondary yielding dialkyl p osp inic acids, R;PO(OH). The primary phosphines are very weak bases, their salts with acids

eing readily decom sed by water. The tertiary phosphines are characterized by their readiness to pass into derivatives containing pentavalent phosphorus, and consequentl they form addition compounds with sul hur, carbon bisulphide, chlorine, bromine, the alogen acids an the alkyl halides with eat readiness. On oxidation they yield phosphine oxides, RIP' . The quatemary phosphonium salts resemble the corres onding nitrogen compounds hey are stable towards aqueous al alis, but on digestion with moist silver oxide yield the phosphonium hcydroxides, which are stronger bases than the caustic alkalis. They it'fer from the 0 nic ammonium hydroxides in their behaviour when heated, ’ie + .

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The alkyl phosphinic acids are colourless crystalline com unds which are easily soluble in water and alcohol. They yiel); two series of salts, viz. RHM-PO, and RMaPO; (M =metal). The dialkyl phosphinic acids are also colourless compounds, the majority of which are insoluble in water. They yield 0113/ one series of salts.

Oxides—Phosphorus forms three well-define oxides, P405, P104 and P105; two others, P40 and P20, have been described.

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Phosphorus subaxide, P40, is said to be formed, mixed with the other oxides, when the element is burnt in a limited supply of air or in ure oxygen under reduced pressure (E. Jungfleisch, Abs. Jour. hem. Soc, 1907, ii. 761), and also when a solution of phosphorus in the trichloride or tribromide is exposed to light. It is a yellow or red powder which becomes dark red on heating; it is stable in air, and can be heated to 300° without decomposition. Its existence, however, has been denied by A. Stock (Abs. Jour. Chem. Soc., 1910, ii. 121). The oxide P20 was obtained by Besson (Campus rendus, 1897, 124, p. 763; 1901, pp. 132, 1556) by heating a mixture of phosphonium bromide and phosphorus oxychloride in sealed tubes to 50°.

Phos horus oxide, PtOQ, discovered by Sage in 1777, is a roduct of the imited combustion of phosphorus in air. It may conveniently prepared by passing a rapid current of air over burning phosphorus contained in a combustion tube, and condensing the product in a metal condenser, from which it may be removed by

eating the condenser to 50°—-60° (Thorpe and Tutton, Jour.

Chem. Soc, 1890, pp. 545, 632; 1891, p. 1019). Jungfleisch has obtained it by carrying out the combustion with oxygen under reduced ressure, or diluted with an inert as. It forms crystals, apparent y monoclinic, which melt at 22-5 to a clear, colourless, mobile li uid 0f boiling-point 173-1°. Its specific gravity is 2-135 at 21°. Vapour ensity and cryoscopic determinations point to the double formula, P406. It is comparatively stable up to 200°, but when heated in a sealed tube to 410° it gives phosphorus and the tetroxide P,O. It is unaffected by ight when pure, but if phosphorus be present, even in minute quantity, it turns yellow and ultimately dark red. It oxidizes on exposure to air to the pentoxide, and with a brilliant inflammation when thrown into oxygen at 0°—60°. It slowly reacts with cold water to form phosphorous aci ; but with hot water it is ener etically decomposed, givin much red phosphorus or the suboxide in formed With an explosive evolution of spontaneouzly inflammablep 0s horetted hydrogen;phoe horic acid is also form . With dilute alkalis phosphites are slowly ormed, but with concentrated solutions the decomposition follows the same course as with hot water. With chlorine it gives phosphoryl and “ metaphosSheryl " chlorides, the action being accompanied with a greenish

ame; bromine gives phosphorus pentabromide and pentoxide which interact to give phosphoryl and “ metaphosphoryl " bromides; iodine ives phosphorus di-iodide, P114, and pentoxide, P105; whilst hydrochloric acid gives phosphorus trichloride and phosphorous acid, which interact to form free phosphorus, phosphoric acid and hydrochloric acid. It combines Violently with sulphur at 160° to form phosphorus sul hoxide, P4054, which forms highly lustrous tetragonal plates (a ter sublimation), melting at 102 and boilin at 295°; it is decomposed by water into sulphuretted hydrogen an metaphosphoric acid, the latter changing on standing into orthophosphoric acid. Sulphur trioxide and sul huric acid oxidize phosphorus oxide, giving the pentoxide and su phur dioxide, whilst sulphur chloride, S,Cl,, gives phosphoryl and thiophosphoryl chlorides, free sulphur and sulphur dioxide. Ammonia also reacts immediately, giving phosphorus diamide, P(OH)(NH1)1, and the corresponding ammonium salt. Phosphorous oxide is very poisonous, and is responsible for the caries set u in the jaws of those employed in the phos horus industries (see below). It is probable, however, that pure p osphorous oxide vapour is odourless, and the odour of phosphorus as ordinarily perceived is that of a. mixture of the oxide with ozone.

Phosphorus Ielroxide, P10 was obtained by Thorpe and Tutton by heating the product of the limited combustion of phosphorus in menu as a sublimate of transparent, highly lustrous,orthorhombic crystals. They are highly deliquescent, and form with water a mixture of phosphorous and phosphoric acids: P20¢+3HQO=H3POj+ H;PO,. The vapour density at about 1400° is 230, Le. slightly less than that required by P501; (West, Jour. Chem. 800., 1 02, p. 9231).

Phosphoric oxide, or phosphorus pentoxide, RON, ormed w en phosphorus is burned in an excess of air or oxygen, or from dry phosphorus and oxygen at atmospheric pressure (Jun fleiseh, loc. cit), was examined by Boyle and named “ flowers of p osphorus " by Marggraf in 1740. It is a soft, flocculent powder, which on sublimation forms transparent, monoclinic crystals. It is extremely deliquescent, hissing when thrown into water, with which it combines to form phosphoric acid. it is reduced when heated with carbon to phosphorus, carbon monoxide being formed simultaneously. Its va ur density at 1400“ ints to the double formula (West, Jour. hem. $00., 1896, p. 154?.0

Oxyacids.——Phosphorus forms several oxyacids: hypo hosphorous acid, H,PO,, and hypophosphoric acid, H430, or H,P ;, of which the anhydrides are unknown; phosphorous acid, HlPOh derived from P0,; monoperphosphoric acid, HIPOQ; peyhosphoric acid, H4P10'; and meta-, pyr0-, and ortho-phosphoric aci 5, derived from P4010, for which see PHOSPHATES.

Hypophosphorous acid. HP(OH)¢. discovered by Dulong in 1816, and obtained crystalline by Thomson in 1874 (Ben, 7, p. 994), is pre red in the form of its barium salt by warming phosphorus wit baryta water, removing the excess of baryta by carbon dioxide, and crystallizing the filtrate. The acid may be prepared by evaporating in a vacuum the solution obtained by decomposing the barium 53 t with the equivalent amount of sulphuric acid. The acid forms a white crystalline mass, melting at 17-4° and having a strong acid

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reaction. Exposure to air gives phosphorous and phosphoric acids, and on heating it gives phosp inc and phosphoric ac1d. characteristic reaction is the formation of a red precipitate of cuprous hydride, Cuzl'h, when heated with copper sulphate solution to 60°. It is a monobasic acid forming salts which are permanent in air, but which are gradually oxidized in aqueous solution. On heating they yield phosphine and leave a residue of pyro hos hate, or a mixture of meta- and pyrophos hates, with a little p osp orus. They react as reducing agents. 11 boiling with caustic potash thgy evolve hydrogen, ielding a phosphate. hosphorous acid, PeIOH)“ discovered by Davy in 1812, may be

obtained by dissolvin its anhydride, P406, in cold water; by immersing sticks of osphorus in a solution of copper sulphate contained in a well-c osed flask, filtering from the copper sulphide and precipitating the sulphuric acid simultaneously formed by baryta water, and concentrating the solution in vacuo; or by passing chlorine into melted phosphorus covered with water, the

rst formed phosphorus trichloride being decomposed by the water into phosphorous and hydrochloric acids. It may also be repared by leading a current of dry air into phosphorus trichlori e at 60° and passing the va urs into water at 0°, the c stals thus formed being drained, was ed with ice-cold water and ried in a vacuum. The crystals melt at 70°. The acid is very deliquescent, and oxidizes on exposure to air to phosphoric acid. It decomposes on heating into phosphine and phosphoric acid. It is an energetic reducing agent; for example, when boiled with co per sulphate metallic copper is precipitated and hydrogen evolve . Although nominally tri asic the commonest metallic salts are dlbasic. O nic ethers, however, are known in which one, two and three of t e hydrogen atoms are substituted (Michaelis and Becker, Born, 1897, 30, p. 1003). The metallic phosphites are stable both dry and in solution; when strongly heated they evolve hydrogen and yield a pyrophosphate, or, especiallg with the heavy metals, they give hydrogen and a mixture of p osphide and yrophosphate.

Hypophosphoric and, £10, or H,PO., discovered by Salzer in 1877 among the oxidation products of phosphorus by moist air, may be prepared by oxidizing phosphorus in' an aqueous solution of cop r nitrate, or by oxidizmg sticks of phos horus under water, neutra izing with sodium carbonate, forming the cad salt and decomposing this with sul huretted hydrogen (J. Cavalier and E. Cornee, Abs. Jour. Chem. oc., 1910, ii. 31). The aqueous solution may be boiled without decomposition, but on concentration it yields phosphorous and hosphoric acids. Deliquescent, rectangular tablets of H4P1062 10 separate out on concentrating a solution in a vacuum, which on drying further give the acid, which melts at 55°, and decomposes suddenly when heated to 70° into phosphorous and meta hosphoric acids with a certain amount of hydrogen phosphide. he solution is stable to oxidizing agents such as dilute hydrogen peroxide and chlorine, but is oxidized by potassium permanganate to hosphoric acid; it does not reduce salts of the

eavy metals. \ ith silver nitrate it gives a white recipitate, Aginot. The sodium salt, NaiP,O.-10H¢O, forms monoc inic prisms and in solution is strongly alkaline; the acid salt, Na,HP,O,-9H,O, forms monoclinic tablets. The formula of the acid is not quite definite. Cryoscopic measurements on the sodium salt points to the double formula, but the organic esters appear to be derived from HgPOg (see A. Rosenheim and M. Pritze, Ben, 1908, 41, 2708; E. Cornee, Abs. Jour. Chem. Soc., 1910, ii. 121).

Monoperphosphoric and rphosphoric acids, HIPOE and H,P,O;, were obtained by J. Schmi lin and P. Massini (Ben, 1910, 43, 1162). The first is formed when 30% hydrogen peroxide reacts with phosphorus pentoxide or meta- or pyrophosphoric acids at low temperatures and the mixture diluted with ice-cold water. The solution is strongly oxidizing, even converting manganous salts to perman

ganates in the cold, a pro rty not ssessed by monopersulphuric acid. Perphosphoric aci is form when pyrophosphoric acid is treated wit a large excess of hydrogen peroxide.

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