98 | 
For the critical quantities of PH, Lrpuc and SACERDOTE *) found 
what follows: 
. i; = 52,5" and Pi = 64 atm. 
If the 6 is calculated from this, we find: 
bh = 0,002330. 
According to vaN peR Waars’ new views “The volume of the 
molecules and the volume of the component atoms” *) hydrogen presents 
the peculiarity that the 6 of a hydrogen atom in a compound is 
much smaller than in the hydrogen molecule; it amounts viz. to 
0.000362 instead of 0.000825, from which follows that for the 
3 hydrogen atoms in PH,, 0,001086 must be taken. We then get: 
0.002330—0.001086 = 0.001244 
for the h-value of the phosphorus atom, from which follows: 
0,005304 
0,001244 — 
for the size of the phosphorus molecule at the critical temperature 
and pressure of the liquid violet phosphorus. 
This result already points to a small association, for on an average 
the phosphorus molecule is greater than 1. 
4,26 
4. Caleulation of the factor f of Vax per Waars’ vapour tension 
formula. 
Finally we have also calculated the value of the factor f from 
the empirical vapour tension equation of VAN DER WAALS. 
Ts, 
— AE geen (5 — 1) 
DE ~. JR 
When we consider the pressures at two different temperatures, 
then it follows from this relation that 
0,4348 (T,InP,—T,InP,) 
See ROE 
1 rd 2 
. from which it-appears that f is graphically to be derived from the 
line that represents 7'/n P as function of 7. Over a range of tem- 
perature of 200°, viz. from 500° to 700°, 7'{p P increases from 
2388 to 4332, so by 1944. 
From this follows that: 
_ 0,4848 X 1944 __ 
An Ee 
4,221. 
1) C.R. 125, 397 1897). 
2) These Proc. Vol. XVI. p. 880. 
