Triple point violet phosphorus, liquid

The vapour pressure of fused violet phosphorus has also been determined by Smits and Bokhorst not only at temperatures above the triple point for solid—liquid— vapour, but also at temperatures considerably below this. The values found are contained in the following table —... 

In this figure FD represents the conditions of equilibrium of the univariant system, violet phosphorus and vapour, which ends at D, the triple point for solid—liquid— vapour, or the melting-point of violet phosphorus under the pressure of its own vapour. This point,... 

Vapour Pressure.—The determination of the values given below was beset with considerable difficulty, especially that of securing inner equilibrium in the solid phase. The curve lies below that of liquid phosphorus, which is unstable with respect to the violet (and red) forms up to the melting-point, 589-5°, of violet phosphorus. The pressure at this triple point is 43-1 atm., while that calculated from the thermodynamical equations (v. infra) is 42-9 atm. 

This triple point is the point of intersection of the three univariant systems solid— vapour (curve FD), liquid— vapour (curve DE), solid— liquid (curve DI). The values of the vapour pressures of solid and of liquid violet phosphorus are given in the tables on pp. 60 and 61. The curve DE will end abruptly at the critical point of liquid phosphorus. The critical temperature was found by W. A. Wahl to lie at 695° C. and from the course of the vapour-pressure curve, Smits and Bokhorst have calculated that at this temperature the pressure (critical pressure) would be 82 2 atm. According to Marckwald and Helmholz, the critical temperature is 720 6 . 

---