Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/531

Rh THOSPHORTJS.] CHEMISTRY 519 and that both are liquid compounds. The sulphides P 4 S 3 , PjSg, and P 2 S 5 may be crystallized from their solutions in carbon disulphide ; they all exhibit acid properties, dis solving readily in solutions of the metallic sulphides, form ing salts of sulpho-acids of phosphorus, which have been little studied, however, on account of their instability. They also dissolve in solutions of the alkaline hydroxides and carbonates, forming salts of oxysulpho-acids of phos phorus ; but these are also very unstable bodies, and readily decompose in contact with water. The sulphides of phosphorus are readily decomposed by water alone, their sulphur being displaced by oxygen and corresponding oxy- acids of phosphorus produced, the sulphur being separated as hydrogen sulphide; thus P 2 S 3 + 6H 2 O = 3H 2 S + 2H 3 PO 3. By heating amorphous phosphorus with selenium in various proportions, the selenides P 4 Se, P 2 Se, P 2 Se 3, and P 2 Se 5 are produced. They resemble the corresponding sulphides, and also exhibit acid characters, combining with metallic selenides to form salts of seleniophosphoric acids, which are even less stable than the corresponding sulpho- salts. Oxy- and Sulpho-Haloid Compounds of Phosphorus. We have already pointed out that phosphorus peutachlo- ride and bromide are converted by water into phosphorus oxychloride, POC1 3, and phosphorus oxybromide, POBr 3. Phosphorus oxychloride may also be obtained by the direct combination of phosphorus trichloride with oxygen, being produced on passing oxygen through the boiling trichlo ride ; it is a colourless mobile liquid at ordinary tempera tures, but solidifies on cooling to a mass of crystals, which melt at 2 C. ; it boils at 110 C. The oxybromide is a similar compound; its crystals melt at 46 C., and it boils at 195 C. The oxides of phosphorus do not combine with the halo gens, but by the action of nitric peroxide on phosphorus trichloride an oxychloride of phosphorus is formed, which bears the same relation to pyrophosphoric acid that phos phorus oxychloride or phosphoric chloride bears to phos phoric acid 4PC1 3 + 3X 2 4 = 2P 2 3 C1 4 + 2NO + 4NOC1. Pyrophosphoric chloride, as this compound may be termed, is a colourless liquid, which boils between 210 and 215 C., but decomposes partially into phosphoric chloride and phosphoric anhydride : 3P 2 O 3 C1 4 = 4POC1 3 + P 2 O 5. It is immediately decomposed by water, producing hydrochloric and phosphoric acids. Phosphorus sulphochloride or sulphophosphoric chloride, PSC1 3, and sulphophosphoric bromide, PSBr 3 , are obtained on heating phosphorus trichloride and tribromide with sulphur, and by the action of hydrogen sulphide on the pentachloride and pentabromide of phosphorus: PC1 3 + H 2 S = PSC1 3 + 2HC1. The sulphochloride is an oily liquid, having an intensely pungent odour, and boils at 126 C. The sulphobromide crystallizes; it is partially decomposed on distillation into sulphur and the compound PSBr 3, PBr 3. They are only slowly decomposed by water, the sulpho bromide even forming a crystalline hydrate with water, PSBr 3, H 2 ; the decomposition of the sulphochloride is represented by the following equations PSC1 3 +H 9 =POC1 3 +H 2 S POC1 3 + 3H 2 = P0 4 H 3 + 3HC1. The sulphobromide apparently is first converted into rnono- sulphophosphoric acid : PSBr 3 + 3H 2 = PS0 3 H 3 + 3HBr, which is then resolved partly into sulphur and phosphorous acid, and partly, by the action of the water, into phos phoric acid and hydrogen sulphide. Phosphorus sulpho chloride behaves in a similar manner when heated with a solution of sodium hydroxide ; thus PSC1 3 + GNaOH = FS0 3 Na 3 + 3NaCl + 3H 2. A sulphopyrophosphoric bromide, P 2 S 3 Br 4, correspond ing to pyrophosphoric chloride, is formed by directly com bining bromine with the sulphide P2S 3. It is an oily liquid, which cannot be distilled, being resolved by heat into phosphorus pentasulphide and phosphoric bromide : 3P 2 S 3 Br 4 = P 2 S 5 + 4PSBr 3. Constitution of the Phosphorus Compounds. The formulae of the two chlorides and of the tetriodide of phosphorus may be given in illustration of the con stitution of the compounds cf phosphorus with monad elements Cl ci p a ci Cl p Cl I p I I p I ci a Phosphorus pentachloride. Phosphorus trichloride. Phosphorus pentachloride. Phosphorus tetriodide. The two oxychlorides of phosphorus are represented by the following formulae, the corresponding bromine and sulphur compounds, of course, being similarly constituted: Cl Cl Cl Cl P Cl

O=P P=O Cl Cl Phosphoric chloride. Pyrophosphoric chloride. The constitution of the oxides is expressed by the for mulas O O / 0=P P=0 P P / O O Phosphorous anhydride. Phosphoric anhydride. Similar formulae are assigned to the corresponding sul phides. Hypophosphorous, phosphorous, and phosphoric acids may be regarded as derived from the compound POH 3, or phosphine oxide, by the displacement of one, two, and three atoms of hydrogen by the monad radicle OH ; although this compound is not known at present, analogous bodies are readily obtained on oxidizing the substituted phosphines formed by displacing the hydrogen in phosphine by positive monad compound radicles, such as methyl, CH 3 00 O H P H H P H

II

H Hyppl los ph r ous Phosphorous acid. acid. H P H H Phosphoric acid. The relation of meta- and pyrophosphoric acid to phos phoric acid will be evident from the following formulas O O II 0=P O H Uetaphosphoric acid. H P H O H P H II O Pyrophosphoric acid.