980 
the coexisting colourless liquid phase is certainly considerably smaller 
than that between violet phosphorus and its vapour, which also 
follows from the molecular heat of melting, for which we found, 
as was stated above, 15,877 K. Cal. from the mol. sublimation heat 
and evaporation heat. 
B. Size of the phosphorus molecule. 
As we published some time ago’) we succeeded in determining 
the vapour tension line of liquid phosphorus between 504° and 634?. 
On that occasion we showed at the same time that when 7’ ln P 
is represented as function of 7, a perfectly straight line is formed 
as a proof that here too the Q from the equation: 
= Aes 
Tin P= — R + C1 
is no appreciable function of the temperature. 
Now lately Want *) determined the critical temperature of liquid 
violet phosphorus in a quartz tube, and found for it the temperature 
695°. As now the line for 7’ P as function of 7, appeared to 
be a straight line from 504° to 634°, it was perfectly justifiable to 
prolong this line to 695°, hence to read the value of 7'/nP at 
T = 695° + 273° = 968° by extrapolation, and derive from this the 
value of P, hence of the critical pressure. In this way 4284 was 
found for 7'/n P, from which follows P, = 83.56 atm. 
Now that we know the critical data for the liquid violet phosphorus 
it is of importance to inquire what can be derived from these data 
about the size of the phosphorus molecule. 
For this purpose we calculate the 4 value by the aid of VAN DER 
Waats’ relation : 
“5, sll aaa GE 
78218 Bp 2828.85.6 
or 
b = 0,005304. 
When we now assume the 5 to be an additive quantity we can 
find the 4 of a phosphorus atom e.g. from the h-value of e.g. PH,, 
and when we then divide the 4 value of the phosphorus molecule 
by this value, we find the number of atoms of phosphorus present 
in the molecule. 
1) These Proc. Vol XVI. p. 1174. 
2) Meddelanden Fran Finska Kemistsamfundet 1913, 3. 
