Halogens with Phosphorus. 349 



rullas* ; yet I did not find the same occur with the pentabro- 

 mide ; nor was the pentachloride itself affected by a stream 

 of hydrobromic acidf, even when heated. The proto-com- 

 pounds of oxygen and sulphur with hydrogen act somewhat 

 differently : the hydrogen enters into combination with the 

 two atoms of the halogen that are more easily removable, and 

 leaves the oxygen or sulphur in combination with the phos- 

 phorus compound. These substances in the chlorine series 

 are the oxychloride of phosphorus described by WurtzJ, 

 having the composition PCI3 Og, and the sulphochloride of 

 phosphorus discovered by Serullas§, bearing the formula 

 P CI3 Sg. In order to produce this oxygen compound, the 

 action of the water must be moderated, or a secondary trans- 

 formation into phosphoric and hydrochloric acids will take 

 place. This may be effected either by throwing the white 

 crystals of pentachloride of phosphorus into water, when they 

 are instantly converted into the liquid oxychloride, and imme- 

 diately afterwards drawing off the supernatant fluid ; or, with 

 greater ease, by exposing the solid chloride to the moisture 

 of the atmosphere until the conversion is complete, hydro- 

 chloric acid being constantly evolved. A compound strictly 

 analogous to this, may be obtained from the pentabromide of 

 phosphorus by either of the two processes. The latter is of 

 course preferable. 



Oxyhromide of Phosphorus. — When pentabromide of phos- 

 phorus is entirely decomposed by a moist atmosphere, there 

 remains in the vessel a reddish liquid of a sticky consistency. 

 This must be gently heated to expel hydrobromic acid, of 

 which it contains a large quantity ; and then, upon distillation 

 at about 180° C, a heavy vapour passes over, condensing into 

 a colourless liquid of high specific gravity. It does not mix 

 with water, but is slowly resolved by it into phosphoric acid 

 and hydrobromic acid. It is soluble in oil of turpentine and 

 in aether, and is also dissolved by strong sulphuric acid, from 

 which it may be precipitated by water, unchanged, but soon 

 suffering, of course, a secondary decomposition. Nitric acid 

 destroys it violently with evolution of bromine. Bromine 

 added to it reproduces momentarily the yellow crystals of 



* Ann. de Chim. et de Phys., xxxviii. 322. 



\ Hydriodic or hydrobromic acid in a gaseous condition may be conve- 

 niently prepared by the action of iodine or bromine on hyposulphite of soda 

 moistened with a little water. The reaction will be evident from the equa- 

 tion — 



NaO,S2 02+HO+Br=NaO,S03+S+HBr. 



In the case of iodine it is necessary to apply heat. 



X Ann. de Ch. et de Phys., 3rd ser. xx. 472. § Ibid. xlii. 25. 



