468 Proceedings of the Royal Society of Edinburgh. [Sess. 
isothermal A B, the temperature being supposed to be below the triple-point, 
between A and a the isothermal is unique. At the point a , corresponding 
to the normal freezing-point pressure, the isothermal splits. The normal 
path is abef~B. Between a and b solidification occurs; between b and e 
the solid expands. At e the solid evaporates, the normal sublimation point 
A v B 
having been reached ; at / evaporation is complete, and from / to B the 
vapour expands uniquely. But, at a, in the absence of nucleation for 
solidification, the liquid course is continued to c, where the normal vaporisa- 
tion pressure of the liquid is reached. Vaporisation then proceeds till d , a 
point on the vapour region of the isothermal, is reached; and the two 
courses rejoin at /. 
In the Case of water-substance, the experiments of Ramsay and Young, 
