Phosphonium Chloride, PH₄Cl

Phosphonium Chloride, PH₄Cl, is formed when the component gases are mixed under a pressure of about 20 atmospheres. Under atmospheric pressures it can only exist at temperatures below about -25° C. It can be melted under pressure at +28.5° C. (Other determinations gave 25° C. and 26° C.)

The change of volume on melting is very great, being about +0.73 c.c./gram at +40° C. The critical volume is 3.5 c.c./gram. The critical temperature is given as 50° to 51° C., 48° C., 48.8° to 50.1° C., 49.1° C., and the critical pressure as 80 to 90 atm., 96 atm., 74.2 to 75.0 atm. and 72.7 atm. The heat of formation of 1 mol of gaseous PH₄Cl is +16.4 Cals.; that of the solid is +43.4 Cals., and therefore the heat of sublimation is +27.0 Cals. The dissociation pressures have also been investigated.