﻿284 Surf ace-Tension and Osmotic Pressure of Solutions. 



the increase in surface-tension is the same for equi-equivalent 

 not equi-normal solutions as the law here described requires; 

 but their results were uncorrected for dissociation, and besides 

 do not agree very closely with the law given by these ob- 

 servers, when so corrected (by dividing the increase in each 

 case by the corresponding value of Arrhenius's coefficient of 

 dissociation i) ; they agree almost as closely with one law as I 

 the other, and cannot be said to agree with either. 



In considering this point of variance, it ought to be remem- 

 bered that the experiments quoted were carried out with 

 concentrated solutions ; for which analogy teaches us, from a 

 consideration of the irregularities shown in depression of 

 freezing-point and vapour-pressure under like conditions, no 

 close agreement can be expected ; and besides the quantity 

 to be measured, viz. a small variation in surface-tension, is 

 infinitely more difficult to obtain accurately than the corre- 

 sponding quantities which are measured in freezing-point 

 and boiEng-point determinations, that is to say, than small 

 differences in temperature. 



In the case of dilute solutions these differences would 

 become so small as to be impossible to measure with any 

 approach to accuracy, so that from experimental difficulties 

 this deduction cannot be tested with certainty. 



Goldstein *, in a recent paper, states a law which, though 

 expressed differently, is practically the same as the third 

 deduction here given, viz.:— In solutions of equal percentage 

 concentration the difference in capillary rise is proportional, 

 after correction for dissociation, to the molecular weight. 

 But as there is no account whatever taken of the densities of 

 the solutions, and the correction for dissociation is made by 

 multiplying the observed difference in capillary rise by i, 

 Arrhenius's Coefficient of Dissociation, instead of, as all 

 reasoning and analogy show ought to be done, dividing by 

 that factor, it does not seem to me that much reliance can be 

 placed on the result. 



The results given by Quincke for solutions of chlorides in 

 water and alcohol are, when corrected for dissociation, in 

 remarkably close agreement with the fourth deduction stated 

 above. 



Quincke's f figures give as the increase in surface-tension 

 of a normal solution of lithium chloride in water, 1*534: dynes 

 per centimetre, and for a normal solution of the same salt in 



* Zeitschrift fur physikalische Chemie, t. p. 233 (1890). 

 + Pog-g. Ann. clx. p. 560. 



