996 
After this heating the phosphorus was once more extracted in the 
way deseribed above, and finally dried, after which we could again 
proceed to the vapour pressure determination. 
„As the evaporation in question must give rise to a disturbance 
of the internal equilibrium of the black phosphorus, the method of 
investigation was now this that we immediately heated to such 
a high temperature that on the ground of the investigation of the 
violet phosphorus we can expect the setting in of the internal equi- 
librium within a comparatively short time. 
The result was as follows: 
| Vapour t 
ension in atmospheres 
Temperature | ————_— 
Black P Violet P 
566° | 28.7 (constant) | 28 ') 
580 | 38.8 | 36 
Hence it follows from this that the vapour tension of black P at 
566°, with only a difference of 0,7 atm., tallied with that of the 
violet P, but we thought the preparation had not yet been sufficiently 
freed from volatile kerosene residues, for at higher temperature the 
pressure rose slowly, and at 580° the pressure was already 2,8 
atmospheres higher than that of the violet P. A correction for the 
pressure could not be applied, because the apparatus burst, so that 
the pressure of the remainder of the gas at lower temperature could 
not be determined. 
To expel the kerosene more completely another quantity of black 
phosphorus was heated at 300° in the way described, for three days, 
and then again, just as the preceding preparation, purified and dried. 
The vapour tension determination of this preparation gave the 
following result: 
Vapour tension in atmospheres 
Temperature |— esi 
| Black P Violet P 
| | 
515° | 8.5 LEE 10.5 
552 | 21.8 (constant) | 21.0 
At 515° the pressure was still rising after + 30 minutes’ heating, 
probably on account of the internal equilibrium not yet having set 
1) Read from the vapour tension-line of the violet phosphorus. 
