1340 
stable melting point under tbe vapour pressure appears. This takes 
place in D’; of course two more metastable internal equilibrium 
lines of the unary system must start from this triple point, viz. the 
o 
metastable melting-point line D’E’ for the coexistence Sy, + Ly and 
the sublimation line of the first solid modification D’A, which is 
metastable as far as the point B, and refers to the coexistence Sy’ + Gy. 
That here in this P,T-projection the theory of allotropy has been 
applied, appears from this that the four three-phase lines meeting 
in the pseudo-binary system in the quadruple point e,, are indi- 
cated by S.,+L+G, Se,+L-+G, S.,,+5s,,+G and S.,,+S,,+L, 
in which the index M is used to state emphatically that the solid 
substance here is a muived crystal phase. If this were not the 
case this P.T-projection would quite agree with that given by 
SCHOEVERS!), but then it would be in conflict with the theory of 
allotropy. 
The P,T-projection discussed here is in itself exceedingly little 
suitable for an illustration of the theory, because as I already 
remarked, it quite hides the most important factor, the difference in 
concentration of the different phases. Accordingly this figure will 
only be used here to indicate which P,X-sections of the spacial 
figure are in consideration. 
3. (P,N)r-sections of the spacial figure. 
The (P,X)yp-sections, just as the (T,X)p-sections can of course be 
derived from the ¢,x-lines. The only difference that appears is this that 
p 
mn 
di =—ndt + vdp 
follows from the equation: 
and that therefore at constant pressure the &lines descend on increase 
of temperature, at least when is positive, while 
el HEN 
gem 
which means that the &-lines ascend with increase of pressure at 
constant temperature. 
As, however, in the derivation we have only to do with the 
relative displacement of the S-lines, this is of secondary importance, 
and we need not enter info a special discussion of the thermo- 
dynamic derivation of the P,X)y-sections. 
1) Thesis for the doctorate, Amsterdam 1907. 
