﻿Surface-Tension and Osmotic Pressure of Solutions. *2<s;-> 



expected that the laws deducible theoretically for the surface- 

 tensions of such solutions can be proven more rigorously 

 than they can in the case of such concentrated solutions for 

 the allied phenomena of solution, such as lowering of vapour- 

 pressure and depression of freezing-point. 



It will be better to tabulate the results that may be expected 

 to follow in case surface-tension is as closely connected, as 

 here suggested, with osmotic pressure and the other solution 

 phenomena, before discussing them. 



(1) The surface-tensions of all solutions, obeying the other 

 solution laws, should be higher than those of the solvents. 



(2) For solutions of the same substance in the same solvent, 

 the surface-tension, after correcting for dissociation, should 

 increase directly as the concentration within certain limits of 

 concentration, that is to say, within the same limits as those 

 within which osmotic pressure obeys the gas law. 



(3) For solutions of different substances in the same 

 solvent, after correcting for dissociation, the differences in 

 surface-tension between solution and solvent should be the 

 same for equi-molecular solutions of these different substances. 



(4) For equi-molecular solutions of either the same sub- 

 stance or different substances in different solvents, after cor- 

 rection for different amounts of dissociation in the different 

 solvents, the differences in surface-tension in each case be- 

 tween the solvent and its solution must be equal, no matter 

 how the surface-tensions of the different solvents may vary. 



The only exception to the first law seems to be that of 

 solutions of liquids, themselves possessing surface-tensions of 

 their own, in water and in other liquids ; in all such cases 

 the surface-tension lies between the surface-tension of the 

 components. But this is not a real exception : such solu- 

 tions do not obey the vapour-pressure law either ; the vapour- 

 pressure of a solution of alcohol in water is not lower, but 

 higher than that of pure water. On the other hand, all salt- 

 solutions, both in water and other solvents, have a surface- 

 tension higher than that of the solvent. 



With regard to the second law, Quincke* found, although 

 working with concentrated solutions, that the increase in 

 surface-tension is very nearly directly proportional to the 

 concentration of the solution, and this result is confirmed by 

 Volkmannf. 



Upon the third law the experimental evidence varies. 

 Quincke J and the earlier experimenters state the law that 



* Pbgg. Ann. clx. pp. 337, 560. 



t Wied. Ann. xvii. p. 353 (1882); xxviii. p. 135 (1886). 



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