979 
centration, the greater will be the chemical transformation of one 
phase into another. It follows from this that the sublimation heat, 
the evaporation heat of the liquid and the melting heat will consist 
for a greater part of a chemical heat as the coexisting phases differ 
more in concentration. The quantities of heat found above are of 
importance in this respect, because they confirm this view in the 
most convincing way. 
According to the theory of allotropy the difference in concentra: 
tion between the solid violet phosphorus and the vapour is greatest, 
and that between the liquid phosphorus and the vapour smallest. 
This tallies perfectly with the colour of the phases; the vapour 
phase is always colourless, just as the liquid phase. 
The evaporation of the solid phosphorus and the melting of the 
solid phosphorus will therefore be processes which are accompanied 
with a strong chemical conversion, whereas this reaction is probably 
only slight during the evaporation of the liquid. 
The found values for the three mentioned quantities of heat 
confirm this perfectly, and the exceedingly high values for the mol. 
sublimation heat and the mol. melting heat prove that the heat 
effect is for the greater part a chemical heat. The sublimation heat 
of the violet phosphorus is even so great that it is of the order of 
magnitude of the sublimation heat of NH,Cl, which amounts to 
37.9 K. Cal., and in which the dissociation heat is included. 
For the difference of energy between white and violet phosphorus 
per gram-atom the following has been found: 
Pie eg Roter + 44 cal. a 
If we now assume for a moment, what certainly is not far from 
the truth, that this heat effect is entirely a chemical heat, and if 
we. further assume that these two phases differ almost as much 
from each other in concentration as the violet phosphorus and its 
vapour, then a chemical heat of about 4 x 4,4 K. Cal. will be in- 
cluded in the mol. sublimation heat. If we subtract this heat effect 
from the molecular sublimation heat, we keep for the physical heat 
25,8 —-17,6 = 8.2 K. Cal.; this is a heat effect that lies already 
much nearer the sublimation heats of other comparable substances 
in which a chemical heat is also included, but a much smaller one 
than for the violet phosphorus. The mol. sublimation heat of SO, 
e.g. amounts to 11,79 K. Cal.’). 
The difference in concentration between violet phosphorus and 
1) GrRAN, Ann. Chim. phys. (7) 30, 203 (1903). 
2) C. R. 90, 1511 (1880). 
65* 
