Chemistry. — "On Black Phosphorus" . II. By Prof. A. Smits, 

 G. Meyer, and R. Th Beck. (Communicated by Prof. 

 S. Hoogewerff). 



(Communicated in the meeting of June 30, 1917). 



As was already communicated before, our researches carried out 

 with Bridgman's black phosphorus have corroborated the supposition 

 that this new form of phosphorus is always metastable under the 

 vapour pressure. 



That this is the case at the triple point temperature of the black 

 phosphorus, is beyond doubt, for it appeared that the black phos- 

 phorus melts ± 2° lower than the violet phosphorus, hence at 

 =b 587.5°. The vapour tension determinations, however, gave results 

 which, though this did not seem })robable, pointed to the possibility 

 that below ± 560° the black phosphorus, and above that tempera- 

 ture the violet phosphorus would possess the smallest vapour tension, 

 or in other words that there exists a transition point between black 

 and violet P at 560°. This conclusion seemed, however, by no 

 means necessary, as the results could also be explained by a too 

 slow establishment of the internal equilibrium at temperatures under 

 ± 560°. 



To ascertain whether the black phosphorus under 568° is really 

 stable, the following experiments were made. Equal quantities of 

 violet and black P were heated with 1 "/o Iodine in a tube of glass 

 that melts with difïiculty in vacuum 13 days in succession in a bath 

 of KNO3— NaNO. at ± 480°. 



Then the tube was quickly taken out of the bath, the contents 

 extracted with CS^ etc. and then the specific weight is determined 

 according to the susj)ension method. It then appeared that almost 

 everything had been changed into a substance with a specific weight 

 2.3, some particles still possessing the spec, weight 2.7. Accordingly 

 it already follows from this that 560° is no transition temperature, 

 for at 480° the black P was still converted into the violet phos- 

 phorus and was therefore metastable ^). 



In the following experiment the proportion between black and 



^) Without contact with violet P we liave not been able to convert the black 

 P into violet P. Even after 4 hours' heating of black P with 1 0/^ I at 580° not 

 the slightest change had occurred. 



