40(J Dr. Merer Wilderman on the Connexion between 



of equation (A) it follows that the solubility curves should 

 be of the form shown in fig. 1 : i. e., the curve must, first 

 increase, starting at the lower 



Fig. 1. 



temperature asymptotically to 



the abscissa of temperatures, 

 then have a point of inflexion 

 (a), reach a maximum (/3), 

 then again decrease, having 

 then another point of inflexion (y), approaching at higher 

 temperatures again asymptotically the abscissa. The solu- 

 bility curve must thus decrease above and below the tempe- 

 rature belonging to /3. 



In the next place we have from van't HofFs thermo- 

 dynamic deductions the following relations for the freezing- 

 point curve, where the solidified solvent and the solutions of 



,.«. • • T1 • (T -T)N.X 



dinerent concentrations are in equilibrium, n= — ^ a — 



for non-electrolytes, and n= ^ ° .m 2 ^ or electrolytes, 



where n is the number of molecules dissolved, N the number 

 of molecules of the solvent, A the latent heat of melting, 

 which is also a function of temperature. T is the freezing- 

 point of the pure solvent. T is the freezing-point of the 

 given solution. This law,, which holds good strictly for 

 dilute solutions, becomes for several reasons more complicated 

 in the case of more concentrated solutionsc But even in 

 very_ concentrated solutions, so far as experience goes, the 

 greater the concentration of the solution, the lower is its 

 freezing-temperature. 



In the third place we have to consider the boiling-point curve,. 

 where the solvent or solutions and their vapour are in equili- 

 brium. Attention should again be restricted to solutions of 

 non- volatile substances. Here we have the following thermo- 

 dynamic relations existing between the concentrations of the 

 solutions, and the rise of boiling-point, analogous to that for 



(T— T X )N I 

 freezing-point (Arrhenius) n— - — b ; 9 — -for non-electrolytes 



(T— T 7 )jN./ ^ 1o- 



and n= v — T /2 — for electrolytes, where T</is the boiling- 



point of the pure solvent, I is the latent heat of evaporation, 

 which is also a function of temperature. This equation holds 

 good for dilute solutions, and becomes more complicated for 

 more concentrated solutions. But in case of non-volatile sub- 

 stances in solution, e\en for the most concentrated solutions, 

 the greater the concentration of the solution the higher is its 

 boiling-point. 



