Freezing-points, Boiling-points, and Solubilities. 407 



Since the solubility (or the concentrations of the dissolved 



dry 

 substance) decreases above and below T/3, at /3, where ^ =0 



on the one hand, and on the other hand on the freezing-point 

 curve the concentrations always increase with the decrease ofT, 

 and on the boiling-point curve the concentrations always in- 

 crease with the increase of T, we have the general result for all 

 non-volatile substances that the solubility and the freezing-point 

 curves as well as the solubility and the boiling-point curves must 

 ahcays cut each other. 



Fig. 2 gives an illustration o£ this. At the point T /? which 

 is common to the solubility and freezing-point curves,, the 



Fiff. 2. 



) /C£ Tr, Pa # £ water y ' 



'absolute ,0 



6v 



T ( Tempera tures) 



dissolved substance in its solid state, the solid solvent, the 

 saturated solution (and vapour) are in equilibrium. At 

 the point T ///? where the solubility and boiling-point curves 

 intersect, the dissolved substance in its solid state, the saturated 

 solution and its vapour are in equilibrium. Points T y and 

 T //y are the freezing-point and boiling-point of the saturated 

 solution in the presence o£ an excess of the dissolved substance 

 in the solid state, and are as characteristic as the freezing- 

 point and boiling-point of the pure solvent. The points T, and 

 T //; are the only points where the concentration of the 

 solubility and of the freezing-point curves as well as the 

 concentration of the solubility and of the boiling-point curves 

 are the same. 



It is evident that, once having the points T, and T //; , we 

 can connect with each other the concentrations of the solu- 

 bility, freezing-point and boiling-point curves, t\w latent 



2E 2 



