Freezing-points, Boiling-points, and Solubilities. 417 



T , T</, X, I are the same for the same solvent, are different 

 for different solvents, and the freezing-point and boiling-point 

 curves are (for non-electrolytes) in the same solvent inde- 

 pendent of the nature of the dissolved substance. On the 

 contrary, q, T /} T /// are characteristic of both, of the solvent 

 as well as of the dissolved substance. Each substance in 

 solution has in every solvent its own solubility curve. 



B. In a similar manner to the above figure 2, the 

 figure 3 may be formed, representing, instead of con- 

 centrations, the vapour-pressures of three curves at different 

 temperatures. 



Fig. 3. 

 Vapour £#£ssw?£S_ _ _ Tp'&fa /^G/ ^r/v/s gwrr£T,'„ 



— -1 \- o fa jrrjTk*KMTWKi) 



T — absolute represents the vapour -pressure curve of ice, 

 T -T o ' that of pure water, T', T", T 7// , V fn , &c. are the 

 vapour-pressure curves of the unsaturated solutions. Since 

 the vapour- pressures of an aqueous solution are known to be 

 smaller than that of pure water, i, e. the vapour-pressure curve 

 of a solution runs below that of water, Gruldberg drew from 

 this as early as 1870 (C. B,. lxx.p. 1349) the conclusion that the 

 freezing-points of the solution must be below that of the pure 

 solvent. It is evident that in the same way we may show that 

 the boiling-point of the solution must be higher than that of 

 the pure solvent. As at the boiling-point the pure solvent 

 and the solution have a vapour-pressure equal to that of the 

 given atmospheric pressure, we have to draw a line T '— T /y> 

 from the ordinate Tq' (say for 760 mm.) parallel to the ab- 

 scissa; T / --T /// is to represent the vapour-pressure curve 

 belonging to the concentrations of the solubility curve, which 

 for different substances will have a different form. As the 

 curve of the saturated solutions meets with the curve of 

 boiling-points the curve T, T /y/ will intersect the whole series 

 of rjv rjv/ ? T ,„ T „„ &0>j gtarti for the S0 l ur i 01i h av i n o- the 



