993 
Violet phosphorus‘), however, was not converted to black phos- 
phorus under the same circumstances. 
That we had to do here with a new modification became probable 
first on account of the high spec. gravity of the substance, viz. 2,69, 
the spec. gravity of violet phosphorus varying between 2.21 and 
2.34 according to our measurements, and secondly because black P 
possesses electric conductivity, whereas violet P is an isolator for 
electricity. 
To ascertain the place of black P with regard to the violet 
condition of phosphorus, BRIDGMAN determined the vapour tension at 
a few temperatures, according to a method of Hirrore’s*), which 
comes to this that a small weighed quantity of phosphorus is pumped 
into a vacuum, and is then heated in a sealed vessel of known 
capacity at a definite temperature, till the space is filled with the 
vapour, which is saturate with respect to the solid phosphorus. Then 
the vessel is quickly taken out of the bath of constant temperature, 
and cooled exposed to the air. Under these circumstances the vapour 
condenses to white phosphorus, which can then be determined by 
treating the contents of the vessel with CS,, and weighing the white 
phosphorus or the remaining quantity of the original form. We then 
find the vapour tension by making an assumption about the size of 
the phosphorus molecule in the gas-phase at the temperature of 
investigation, and at a pressure equal to that of the saturate vapour. 
On the ground of the investigations by Srock, Gipson, and Stam *) 
BRIDGMAN assumed P,. 
Violet and black phosphorus were examined in this way at the 
boiling temperature of mercury and of sulphur with the following 
result: 
Black P Violet P 
Temperature vapour tension vapour tension 
in cm. Hg. in cm. Hg. 
gbi le 2.3 5.2 
443.7 | — 132 
45.2 | 58.5 — 
It follows, therefore, from this table that the vapour tension of 
black P was found lower than that of violet P. 
1) Bripeman writes red phosphorus, but as what is meant here is phosphorus 
which is almost in internal equilibrium, we write violet phosphorus. 
2) Pogg. Ann. 126, 193 (1865). 
3) Ber. 45 3527 (1912). 
64* 
