962 
which satisfy the following values of the critical constants 
pr == 33.49 atm, and 7, = 125.°96 K 3) 
(Or= Ti —Tfoc=— 147.°13 C. in Kelvin-degrees) 
The circumstance, that the observations do not agree very well with 
the formula, finds its explanation, at least partly, in the fact, that 
the critical point falls a little outside the extrapolated vapour-pressure 
curve. The same fact occurs with the vapour-pressure curves of 
argon (CROMMELIN) *), ether (Ramsay and Yocng) *), isopentane (Youn) *) 
normal octane (Youne) *), carbon disulphide (BaTTELLt) ®) in contrast 
with what is found with the great majority of vapour-pressure curves 
of other substances, with regard to the critical point. 
A systematic inquiry into the cause of these deviations would be 
very desirable. 
In conclusion I wish to thank Prof. H. KAMERLINGH ONNES most 
heartily for the continued interest shown in my work. 
Chemistry. — “On the vapour pressure lines of the system phos- 
phorus.’ TI. By Prof. A. Smits and S. C. BokHorst. (Com- 
municated by Prof. J. D. vaN DER Waats). 
(Communicated in the meeting of December 30, 1914). 
I. Determinations of the vapour pressure of the violet phosphorus. 
In the preliminary investigation about the vapour tension of the 
violet phosphorus we found a vapour pressure line with a discontinuity 
at about 450°, which result seemed to confirm the existence of a 
transition point found by Jormors ®) at + 460. | 
To get further certainty about the existence or non-existence of 
this transition point, it had to be examined whether really two 
branches intersecting each other, could be realized here. For this 
purpose it would be necessary to determine also a part of the 
metastable prolongations on either side of the transition point, and 
keeping this end in view we undertook the definitive investigation. 
The preliminary experiments were made with a preparation N°. 1, 
which was obtained by heating pure white phosphorus with 0,1 °/, 
Iodium at + 300° for 24 hours. This preparation was hard and 
1) Comm. 1450. 
2) C. A. CROMMELIN,' Proc. May 1910 and Oct. 1913, Comm. 115 and 138c 
and Dissertation Leiden 1910. 
8) W. Ramsay and S. Youne, Phil. Trans A 178, (1887) p. 57. 
4) S. Youne, Proc. phys. Soc. 1894/1895 p. 602. 
5) S. Youne, Journ. Chem. Soc. 77 (1900) p. 1145. 
) 
) A. Barrett, Mem. d. Ac. di Torino, (2) 41 I (1890) and 42 I (1891). 
) GC. r 149, 287 (1909); 151, 382 (1910). 
a 
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