1876.] 



Phosphorus Peniafluoride. 



123 



Phosphorus peutafluoride is a colourless gas : it is incombustible and 

 extinguishes flame ; it is absolutely irrespirable even when largely diluted 

 with air ; it fumes strongly in moist air, and is rapidly decomposed 

 by water, forming hydrofluoric and phosphoric acids. As it is nearly 4| 

 times heavier than air, it may be collected by downward displacement, 

 and may be poured from vessel to vessel. It may be preserved in glass 

 vessels over dry mercury for some time without much alteration ; but its 

 volume very gradually diminishes, and the glass after prolonged contact 

 with the gas is found to be slightly corroded. 



An attempt was made to liquefy the gas by compressing it in an 

 Oersted's apparatus as arranged to show the condensation of the more 

 readily liqueflable gases. Under a pressure of 12 atmospheres (which 

 was the highest pressure the apparatus would safely bear) it showed no 

 signs of change. When compared with the same initial volume of air, 

 no deviation from Boyle's law was observed sufliciently marked to warrant 

 the belief that the' gas under this pressure was anywhere near its point 

 of condensation. 



Phosphorus peutafluoride experiences no apparent change on the ^Jas- 

 sage of induction-sparks, either when pure or when mixed with oxygen 

 or hydrogen. The character of the light emitted during the discharge 

 is under investigation ; the spectrum which it affords is exceedingly 

 complicated. 



Phosphorus peutafluoride combines immediately with ammonia-gas, 

 forming a white solid body of the composition 2Prg.5]N"H3. ^^^^ 

 readily absorbed by an aqueous solution of ammonia, and the liquid on 

 concentration yields a crystalUne deposit consisting of a mixture of am- 

 monium dihydrogen phosphate, NH^ H., PO^, and acid ammonium fluoride, 

 NH^P.HF. 



Wurtz has conclusively shown that phosphorus pentachloride can 

 actually exist in the gaseous state under diminished pressure and between 

 certain narrow limits of temperature. On the other hand, the author 

 has given reasons, derived from considerations of specific volume, for the 

 supposition that phosphorus oxychloride, POCI3, and phosphorus thio- 

 chloride, P8CI3 (bodies which are frequently adduced to show its penta- 

 dicity), are in reality derivatives of triad phosphorus*. 



The existence of the gaseous peutafluoride, taken in conjunction witn 

 the fact that it is perfectly stable, even at very high temperatures, is of 

 great interest theoretically, inasmuch as this body unequivocally indicates 

 the pentadicity of phosphorus. 



* " Eesearches upon the Specific Voliiines of Liquids. — I Oil the Atomic Value oi 

 Phoephorus," Proc. Eoy. Soc. xxiii. p. 364. 



K 2 



