1000 
city of heating was too great to obtain a setting in of tbe internal 
equilibrium, we heated slowly in the final definitive experiment 
mentioned here, and the bath was kept at + 580° for half an hour. 
Then we made the temperature rise exceedingly slowly. 
We then observed that in tube 5 with blaek phosphorus + iodine 
melting made its appearance first, viz. at + 587,5°, whereas in the 
tube c‚ filled with violet phosphorus with iodine melting was observed 
at 589,5°. In tube a, which contained black phosphorus without 
iodine, melting did not make its appearance before 598°. 
When this had been ascertained, the bath was brought back to 
+ 588° as soon as possible. Only +1, of the black phosphorus in 
tube a had then been melted. Our purpose was to examine whether 
the black phosphorus withont iodine would exhibit complete melting 
on continued heating at the same temperature as the black phos- 
phorus + a trace of iodine. This experiment showed that this was 
actually the case, and that after + an hour’s heating at 588° the 
black phosphorus had completely melted to a colourless liquid. This 
experiment was repeated with the same result. 
Accordingly the investigation described here yielded the result 
that the black phosphorus melts at + 2° lower temperature than 
the violet phosphorus; thus the proof has been furnished that the 
violet phosphorus as was to be expected, appears at higher 
temperatures at least as the stable modification. 
§ 5. Explanation of the behaviour of the black phosphorus. 
It is now the question how the phenomenon is then to be ac- 
counted for that the black phosphorus, which we suppose for the 
present the metastable modification, under vapour tension shows an 
initial vapour tension lower than that of the unary violet modifica- 
tion. It seems absurd that a metastable state of an element or a 
compound can have a lower vapour tension than the stable state, 
and this would really be impossible when we had to do with a 
substance built up of one kind of molecules or atoms, but when an 
element or a compound is complex, this is very well possible, but 
only for a metastable state not being in internal equilibrium. 
To make this clear we shall suppose the system phosphorus to 
be built up of two kinds of molecules, « and 3, and the P, X-section 
of the pseudo system to have a shape as indicated in fig. 3 at a 
temperature of 200°. 
The internal equilibrium in the vapour at different pressures is 
indicated by the line Gy, Gu. 
At G, this line meets the line Gd of the pseudobinary system, 
