ADSORPTION POTENTIALS AND ELECTROKINETIC PHENOMENA 267 



(e) CrCls in faintly acidified water +59 



CrCls Same + 1/1000 M K3Fe(CN)6 +2 



CrCls Same + 1/50 M K3Fe(CN)6 -20 



(f) CrCU in 1/1000 N HCl +86 



CrCls Same + 1/2000 M K4Fe(CN)6 +1.5 



These experiments show the effect of various polyvalent ions. 

 As seen in (d), as long as a wall remains negatively charged, even 

 polyvalent negative ions are without effect. But the same ions 

 exercise, even in low concentrations, a strongly diminishing effect 

 upon the potential of a positively charged wall, as in (e) and (f); 

 while in greater concentration they can even reverse the sign of the 

 charge, as in (e). This activity rises markedly with the valence. 

 Bivalent ions are more effective than univalent, and trivalent ions 

 have a greater effect than the bivalent. The effect of the valence of 

 the anions is also noticeable in experiment (a), where the anion is 

 added not in the form of a neutral salt, but as a constituent of the 

 acid itself, for HCl and HNO3 show the same activity, while 

 H2SO4 greatly reduces the potential. 



The cations behave in an exactly corresponding manner: they 

 exert an influence only upon a negatively charged wall. For example : 



CrCls in faintly acidified water +43 



CrCU Same + 1/1000 M MgCU +43 



CrCls 1/1000 A^KOH -76 



CrCls Same + 1/1000 M MgCU -10 



AI2O3 1/500 N NaOH -85 



AI2O3 Same + 1/500 A^ Ca(N03) 2 -18 



AI2O3 in faintly acidified water +41 



AI2O3 Same + 1/500 AT Ca(N03)2 +41.5 



Mn203 in faintly alkaline water —40 



Mn203 Same + 1/500 A" Ba(N03)2 +18 



Carborundum 1/500 A KOH -60 



Carborundum Same + 1/1000 A La (NO3) 3 -0.7 



The example with the Mn203 shows that the bivalent Ba-ion can 

 even reverse the charge. The same could be demonstrated to an 

 even greater extent by A1+++ or La+++, but these are so insoluble in 



