718 
(Ieey=GtL-+S. Curve gt terminates in the point ¢: the melting- 
point of ice under its Own vapour-pressure, consequently the triple- 
point: water + vapour + ice. Curve ga terminates in the melting- 
point a of the salt JS. 
Fig. 4. 
We find in fig.4, besides the ?,7-diagram, also the concentration- 
diagram; as ice and watervapour have the same composition, in 
this the points / and G coincide. 
We find in fig. 4 besides the curves (M), (1), (S), (J) and (G) 
also the triplepoint ¢ of the water. Three curves start from this 
triplepoint; fr is the evaporationcurve (equilibrium : water + vapour); 
ts is the meltingcurve of the ice (equilibrium: ice + water); fg is 
the sublimationeurve of the ice (equilibrium : ice + vapour). This. 
sublimationcurve fq of the ice is, therefore, at the same time the 
singular curve (/) = Ice + G of the binary system. 
This (J/)-curve is bidirectionable, for the invariant point g of 
course cannot be a terminating-point of this curve; at the one side 
of the point q it coincides with the singular curve (5) —/ce 4 GH L, 
at the other side of the point g with the singular curve (£) = /ce + 
+G+S. 
The reaction /cee+ SZ L may occur between the phases of 
curve (G)= Ice + SH L; consequently curve (G) is the common 
melting-curve of ice and salt S. Im general it proceeds upwards 
starting from the point q fairly parallel to the P-axis. When at the 
reaction Zce + SL the volume increases, then it goes starting 
from g towards higher temperatures; when the volume decreases, 
it goes towards lower temperatures. In fig. 4 we have assumed that 
it proceeds, just as the melting-line fs of the ice, starting from q 
towards lower temperatures. 
It follows from fig. 3 that in fig. 4 curve ga must be situated 
