Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/528

Rh 516 CHEMISTRY [COMPOUNDS OP Temperature of formation. Sp. gr. at 0&quot; C. 2-148 2-19 2-293 Heat of oxidation per gramme. 5592 units. 5570 above 5272 5222 5272 265 360 500 580 (fused) ? 580 (crystalline) 2 34 Hydrogen, except in the nascent state, appears to be without action on phosphorus. Oxygen forms the two oxides P 2 O 3 and P 2 5. Chlorine, bromine, and iodine enter directly into reaction with ordinary phosphorus, the combination being attended with inflammation ; red phos phorus also enters into reaction with these elements at ordinary temperatures, and heat is developed, although to a much less extent. When sulphur and ordinary phos phorus are melted together, combination takes place with great violence, and the experiment of bringing the two bodies together is attended with much danger. If dis solved in carbon disulphids, they are without action upon each other. Red phosphorus readily enters into reaction with sulphur when a mixture of the two substances is gently warmed, and although much heat is developed by their combination, the reaction is not explosively violent. Selenium also unites with phosphorus when the two are heated together nearly to the boiling point of the latter. Most metals combine with phosphorus when they are heated in its vapour, or when it is thrown upon them whilst they are in a state of ignition. Compounds of Phosphorus with Hydrogen. Three of these compounds are known, viz., phosphine or phosphoretted hydrogen gas, PH 3, and a liquid and a solid hydrogen phosphide. Phosphine is obtained in a pure state by decomposing phosphonium iodide by a solution of potassium or sodium hydroxide : PH 4 I + KHO - PH 3 + KI + H 2 O. It is a colour less gas, possessing a most intolerable garlic-like odour ; it is sparingly soluble in water, the solution being neutral to test paper. Phosphine is extremely inflammable, igniting at a temperature a little above 100 C. ; contact with a drop of fuming nitric acid, or with chlorine or bromine, also causes it to inflame. A mixture of the gas with oxy gen standing over water is gradually absorbed, and phos phorous acid produced. It is a powerful reducing agent, withdrawing oxygen with great readiness from bodies like nitric oxide, sulphur dioxide, and sulphuric acid. It pre cipitates many metallic salts, the precipitate in most cases consisting either of metallic phosphide, as in the case of copper, or of reduced metal, as in the case of gold and silver. It combines with hydriodic acid, forming phos phonium iodide, PH 4 I, and with hydrobromic acid forming phosphonium bromide, PH 4 Br, but not with hydrochloric acid or other acids ; these salts are crystalline bodies, which are decomposed by water into phosphine and hydriodic or hydrobromic acid. Phosphine mixed with more or less hydrogen is obtained by the action of water on the calcium phosphide, prepared by heating phosphorus with lime ; by heating phosphorus with a solution of an alkaline hydroxide 3Ca(OH) 2 + 8P + 60H 2 = 2PH 3 + 3Ca(PH 2 O 2 ) 2 ; Calcium hydroxide. Calcium hypophosphite. and when phosphorous, or hypophosphorous, acid is heated 2H 3 P0 2 = PH 3 Rypophosphorous acid. H 3 PO 4. Phosphoric acid. 4HPO 2 = PH 3 3H 3 P0 4. Phosphoric acid. Phosphorous add. The gas obtained by the first and second methods is spon taneously inflammable, owing to the presence of liquid hydrogen phosphide, which may be separated by passing the gas through a U-tube cooled by a mixture of ice and salt. Liquid hydrogen phosphide probably has the com position P 2 H 4 ; by contact with various substances, and especially by hydrochloric acid, and by exposure to light, it is converted into phosphine and a yellowish solid hydrogen phosphide, supposed to have the composition P 2 H or P 4 H 2 - Compounds of Phosphorus with the Halogens. A gaseous phosphorus pentafluoride may be obtained by the action of phosphorus pentachloride on arsenic tri- fluoride: 5AsF 3 + 3PC1 5 = 3PF 5 + 5AsCl 3. It is not de composed by the passage of electric sparks, even when mixed with oxygen or hydrogen. Two chlorides of phosphorus are produced by the action of chlorine on phosphorus, a liquid trichloride, PC1 3, and a solid penta chloride, PC1 5. Bromine in like manner forms a liquid tribromide, PBr 3, and a solid pentabromide, PBr 5. Bro mine also combines with phosphorus trichloride, forming the chlorobromide PCl 3 Br 2, and this compound is capable of combining with further quantities of bromine, forming the compounds PCl 3 Br 2. Br 2 and PCl 3 Br 2. 3Br 2 ; all these chlorobromides of phosphorus are crystalline bodies. Iodine forms the two iodides PI 3 and P 2 I 4, which are both crystalline. Phosphorus trichloride boils at 70 C., and the tri bromide is also volatile without decomposition, but the remaining chlorine and bromine compounds of phosphorus are decomposed by heat into the trihaloid compounds and halogen: PC1 5 = PC1 3 + C1 2. The iodides are also decom posed by heat, apparently into iodine and amorphous phos phorus. The haloid compounds of phosphorus are all readily decomposed by water. The pentachloride and penta bromide are first converted into the oxychloride and oxy- bromide, two of the atoms of halogen being displaced by a single atom of oxygen and by the continued action of water these compounds are converted into phosphoric acid ; thus POBr 3 + 3H 2 = PO 4 H 3 + 3HBr. The behaviour of the trihaloid compounds of phosphorus is analogous to that of the oxychloride and oxybromide, phosphorous acid being produced PI 3 -f-3H 2 = P0 3 H 3 + 3HI. The compounds containing more than five atoms of halogen behave as mixtures of the pentahaloid compounds with halogens that is to say, they furnish the products of the decomposition by water of the pentahaloid compound, and also the free halogen. The iodide of phosphorus, P 2 I 4, is peculiar in its behaviour with water ; it is stated that when it is decomposed by a small quantity of water only phos phorous and hypophosphorous acids are formed P 2 I 4 + 5 H 2 O = H 3 P0 3 + H 3 P0 2 + 4HI ; but that when a large quantity of water is employed, a- yellow insoluble substance of the composition P 5 H 3 O is produced, the reaction taking place in the manner repre sented by the equation 6P L 24H 9 O = + 3P0 4 H 3 Phosphoric acid. h PO 2 H 3 Hypophos phorous acid. 24HI. 3P0 3 H 3 Phosphorous acid. Oxides of Phosphorus. The combustion of phosphorus in air produces both phosphorous and phosphoric anhydrides, P 2 3 and P 2 O 5 ; the latter may be readily obtained by burning phosphorus