Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/853

PHOSPHORUS 817 dried and then sent out in bottles or canisters like any ordinary chemical preparation. It is not at all affected by even moist air, nor by aerated water, hence it is neither phosphorescent nor poisonous. When heated in air to about 260 C. it begins to pass into the ordinary modification and consequently burns, readily enough, into the same phosphoric acid P.,0 D as ordinary phosphorus does. But its combustion-heat amounts to only 5070 Centigrade- units per unit -weight of fuel as against the 5953 units produced in the combustion of ordinary phosphorus. The balance of 883 units is the equivalent of the surplus of energy contained in the yellow as compared with the red modification. This accounts for the relative chemical inertness of the latter. The specific gravity of red phosphorus is 2 089 to 2 106 at 17 C. ; its electric conduct ive power is about 000,000,1 of that of silver wire (Matthiesen). It is used in making safety-matches. Metallic Phosphorus. This, discovered by Hittorf, is obtained by heating ordinary phosphorus with lead in sealed -up tubes to redness for forty hours. After removal of the lead by nitric acid metallic phosphorus remains, partly in the shape of dark re splendent plates, partly in the form of microscopic rhombohedra. It requires a temperature of 358 to be converted into ordinary phosphorus-vapour. The specific gravity is 2 34 at 15 C. Direction of Phosphorus. The detection of (ord. ) phosphorus in medico-legal cases offers no difficulty as long as the phosphorus has not disappeared by oxidation. In the case of a mass of food or the contents of a stomach the first step is to spread out the mass on a plate and view it in the dark. A very small admixture of phosphorus becomes visible by its phosphorescence. Failing this, the mass is distilled with water from out of a glass flask connected with a glass Liebig s condenser in a dark room. The minutest trace of phosphorus suffices to impart phosphorescence to the vapours at some stage of the distillation. Should this second test fail we must search for phosphorous acid, which may be there as a product of the oxidation of phosphorus originally present as such. To test for phosphoric acid would be of no use, as salts of this acid are present in all animal and vegetable juices and tissues. Phosphorous acid, if present, can be detected by treating the mass, in a properly constructed gas-evolution appa ratus, with pure hydrochloric acid and zinc. The hydrogen gas evolved must be purified by passing it over pieces of solid caustic potash, and made to stream out of a narrow platinum nozzle. If the reagents are pure and phosphorous acid is absent the gas burns with a colourless flame, which remains so even when depressed by means of a porcelain plate ; in the presence of phos phorous acid the gas contains phosphuretted hydrogen, which causes the flame of the gas to exhibit a green core, at least when depressed by means of a porcelain plate. The test is very delicate, but in interpreting a positive result it must be remembered that it applies likewise to hypophosphorous acid, and that certain salts of this acid are recognized medicinal agents. Of all phosphorus compounds ortho- phosphates are the com monest, and they can be detected by the tests given below under "Phosphates." All other phosphorus compounds, when fused with carbonate of alkali and nitre, or heated in sealed -up tubes with strong nitric acid to a sufficient temperature, are changed so that the phosphorus assumes the form of ortho -phosphoric acid, which is easily detected. Either of the two operations named (by the mere action of the alkali or of the acid qua acid) converts what may be present of meta- phosphoric or pyro - phosphoric into ortho-phosphoric acid. Phosphor-Bronze,. This name has been given to a class of useful metallic substances produced by the chemical union of either pure copper or of copper alloys with phosphorus. Most commercial copper is contaminated with a small proportion of its own sub- oxide, which, in the case of an otherwise pure metal, detracts from its tenacity and plasticity ; and all ordinary bronze is subject to a similar contamination, because, whatever kind of copper may have been used in making it, the tin is sure to suffer partial oxidation, and some of this oxide, as Montefiori-Levi and Kiinzel found, remains diffused throughout the casting, and diminishes its homo geneity and solidity. Experience shows that both in the case of copper and bronze the oxygen present as metallic oxide can be re moved by introduction into the fused metal of a judiciously limited proportion of phosphorus, which takes out the oxygen (and itself) into the slag s phosphate, and thus produces a purely metallic and consequently superior metal. A small excess of phosphorus in either case effects further improvement. A phosphor-copper con taining O l to 5 per cent, of the non- metallic element has all the plasticity of the pure metal coupled with higher degrees of hard ness and solidity. An alloy of from O o to 2 per cent, gives good castings, because, unlike the pure metal, it does not form blisters on solidifying. In the case of phosphorized bronze the presence of somewhat more than O o per cent, of phosphorus (in the finished alloy) produces a warmer tone of colour (more gold-like than that of the plain alloy), a finer grain (similar to that of steel), a higher degree of elasticity, and a higher breaking-strain. The latter may be more than double that of the corresponding plain bronze. By increasing or diminishing the proportion of phosphorus the mechan ical properties of a phosphor-bronze can be modified at will, within wide limits. By its fine colour and its perfect fluidity when molten it lends itself particularly well for the casting of artistic or orna mental articles. The introduction of phosphorus into the metal is best effected by fusing it with the proper proportion of a rich phosphor-copper, A phosphor-copper containing about 9 per cent, of phosphorus can be produced as follows. A kind of potential phosphorus ("phosphorus mass") is made by mixing superphos phate of lime with 20 per cent, of charcoal, and dehydrating the mixture at a dull red heat. Six hundred parts of this mass are mixed with 975 of copper-turnings and 75 of charcoal, and kept at copper-fusion heat for sixteen hours within a graphite crucible. The phosphor-copper is obtained in the form of detached granules, which are picked out, re-fused, and cast out into cast-iron moulds. Phosphor-bronze has only come to be popularly known during the last decade or two ; but as early as 1848 A. & H. Parkes of Bir mingham took out a patent for phosphoriferous metallic alloys. Phosphuretted Hydrogens. Of these three are known, namely, (1) phosphine, a gas of the composition and specific gravity PH 3 , (2) a volatile liquid of the composition and vapour-density P._>H 4 , and (3) a yellow solid of the probable composition P 4 H 2 . The liquid compound (No. 2) at once takes fire when it comes into contact with air, and a small admixture of its vapour to any inflam mable gas, such as coal-gas, renders the latter self-inflammable. The most important and best known of the three hydrides is phosphine, PH 3 . This gas is formed when (syrupy) phosphorous acid is heated thus, 4PH 3 3 = 3PH 3 4 + PH 3 ; also when phos phorus is being dissolved in hot solutions of caustic potash, soda, or baryta, 4P + 3(KHO + H,0) = 3PH a KO a + PH 3 ; Hype phos phite. also by the action of water on the phosphides of highly basilous metals. The gas evolved by any of these processes is impure ; that obtained by the second or third invariably includes vapour of PsH,,, and consequently is self -inflammable. Pure phosphine can be obtained only by decomposing solid iodide of phosphonium with concentrated caustic potash -ley in a suitable gas -evolution bottle previously filled with hydrogen to avoid explosions. It is a colour less gas, smelling intensely like putrid fish, and very poisonous. It is slightly soluble in water, and takes fire in air only beyond 100 C. It may be mixed with pure oxygen without change ; but when the mixture is suddenly expanded it explodes violently. Notwith standing its analogy to ammonia (NH 3 ), phosphine is only very feebly basic. It unites with gaseous hydriodic or hydrobromic acid into solid phosphonium salts PH 4 (I or Br) ; but these are both decomposed by water into the respective acids and phosphine. Pure phosphine is little known ; chemists are more familiar with the (impure) gas which is evolved when " phosphide of calcium " is thrown into water, and which, containing vapour of P U H 4 , at once catches fire when it bubbles out of the water into the air, with formation of steam and a smoke of meta -phosphoric acid, which latter, in a still atmosphere, assumes the form of an exquisite vortex-ring. During the last decade or so this reaction has come to be pretty extensively utilized in navigation for producing a light on the surface of the sea at night, in case of accidents, and for other purposes. A British patent for this useful application of phosphide of calcium was granted (as No. 1828) to the agent of Silas and Pegot Ogier of Paris on the 8th of August 1859, but allowed to lapse in 1863, to be subsequently wrought by others. The manufacture of the phosphide is now (1884) being chiefly carried on by one firm (in Warrington, England), and through the courtesy of their chemist, Mr W. G. Johnston, the writer is enabled to give the following details. The preparation of the phosphide is effected within a crucible standing on a support within a furnace, and divided by a perforated false bottom into two compartments. The lower is charged with pieces of phos phorus, the upper, up to the closely-fitting lid, with fragments of quicklime. The firing is conducted so that the lime is red hot before the phosphorus, through the radiation and conduction of the heat applied above, begins to volatilize. A charge yielding 20 lb of product is finished in from five to eight hours. The reaction is very complex, but it is easy to see through its general course ; part of the phosphorus deoxidizes lime with formation of P 2 5 , which unites with other lime into phosphate, and of calcium, which combines with other phosphorus into phosphides. Of the latter, PCa seems to predominate, and consequently the product, when thrown into water, should yield chiefly the hydride P;>H 4 ; but this latter very readily breaks up into phosphine and solid hydride P 2 H. The crude phosphide forms a brown stone- like mass, which must at once be secured in air-tight receptacles. But most of it is immediately worked up into " lights " of various kinds, of which the "life-buoy light" may be selected as an example. It consists of a cylindrical tinned-iron box, the upper half of which is taken up by an inverted hollow box, which serves as a float when the light is in the water. The lower half contains XVIII. 103