374 Mr. A. Frumkin on the 



reasoning. Thus the term TF is o£ importance i£ the double 

 layer is built up by the same ions whose concentration 

 determines the value of the potential difference, but so far 

 as we are dealing with pure mercury its influence is pro- 

 bably very small. In fact, along nearly the whole o£ the 

 electrocapillary curve the mercuiy concentration in the 

 solution is very low as compared with the concentration of 

 other ions. If we suppose with Krueger that the anomalies 

 of the electrocapillary curves of anorganic electrolytes are 

 due to the adsorption of mercury, we must assume that salts 

 of mercury are much more adsorbed at the mercury surface 

 than any other known substances. Thus, the addition of 

 w/100 KI to n/i Na 2 S0 4 lowers the surface-tension which 

 corresponds to -^ = 0*6 volt by 5 per cent. To produce such 

 a lowering effect, a very active substance like amyl alcohol 

 ought to be present at a concentration as high as M/10, 

 whereas the corresponding concentration of mercury in the 

 solution, as we may easily calculate with the help of Nernst's 

 formula from the experimental data of Abegg and Sherill*, 

 is 10 ~ 16 . Therefore it seems to me reasonable to admit that 

 the lowering effect is not caused by the mercury salts, but 

 by the KI (viz. by I'), whose concentration is high enough. 



Krueger quotes in favour of his theory that the anomaly 

 of the electrocapillary curves increases with increasing- 

 stability of the corresponding complex salts, i. e. with the 

 concentration of mercury in the solution at constant 

 potential; but it is easy to show that this relation does not 

 hold. In fact, the stability of complex salts increases in 

 the following order: nitrates, sulphates, iodides, cyanides, 

 whereas the maximum surface-tension of normal solutions 

 are: KN0 3 , 98*95 ; K 2 S0 4 , 100*17; KI, 94'0 ; KON, 96*6. 



In the following we will make the probable assumption 

 that the adsorbability of mercury salts is a quantity of the 

 same order of magnitude as that of other substances and 

 neglect the term r Hg F. Equation (4) becomes then identical 

 with the classical equatiom (1) 



&- ' (1) 



where 



6 == (1 Anions ~~ 1 Cations)! 1 • 



In equation (1) 6 is a function of i|r, whose form is deter- 

 mined by the composition of the solution. 



In particular, the value of ty which makes e zero may 

 vary between very wide limits (0*2 v.-l v.). 



* Abegg's Handbuch der anorganischen Chemie, Bd. ii. Abt. 2, p. 648. 



