622 



in that research secondary influences come to the fore ; pei-liaps the 

 powerful electric field in which the measurements are executed is 

 not without influence on the capillary itself. Only the quadrivalent 

 Th---ion was capable of causing a charge reversal. 



The results obtained here are in harmony with the general theore- 

 tical points of view. The electric double layer in the capillary, in 

 the case of pure water consists of 'OH-ions at the side of the glass 

 wall and 'H-ions at the side of the liquid in consequence of the 

 selective ion adsorption of the glass wall which always adsorbs the 

 'OH-ion more strongly. From the electrolyte solutions the cations are 

 absorbed more eagerly than the anions so that the charge gets lowered. 

 If this adsorption for KCl, BaCl^ and AlClj, is such that solutions of 

 the same molecular concentration are absorbed about equally, it is 

 conceivable that the three times more active Al---ion requires a much 

 lesser concentration than the K'-ion in order to attain an equal 

 potential reduction. 



If once the capillaiy is charged reversely the adsorption of the 

 Cl'-ion, which carries a charge now opposite to that of the capillary, 

 seems to predominate. The positive charge now soon attains (at 3 (i mol.) 

 a maximum value, and than decreases, but only slowly, because the 

 discharging ion is univalent here. 



In agreement with the theory are also the resulls of Riety ^), for 

 instance that the salt of a heavy metal has a slrongei* discharging 

 action than that of a lighter one (Cu and Zn, at least in the small 

 concentrations). A cation of a heavy metal is known to be adsorbed 

 more strongly than that of a light one.'') 



Moreover, the behaviour in the case of CuSO^ and of Cu(N03)2 is 

 in agreement with investigations as to the adsorbability of those salts =*). 

 The influence of the anions is also observable in Riétv's results and 

 appears to have an effect corresponding with that in the case of 

 AICI3 just described. 



The question whether the organic cations also behave according to 

 the theoretical expectations is being considered. Several other solutions 

 of electrolytes in water as well as in mixed solvents ^) will be 

 investigated. 



Utrecht, June 1914. van 't Royv- Laboratory. 



1) 1. c. 



2) MoRAwiTz, Koll. Beih. 1, 301 (UJIO). 



'^) Freundlich and Schucht, Z. f. physik. Chem. 85. 641 (1913). 

 ^) Of these have also already been measured a few scries in connexion with 

 the researches of Kruyt and van Duin, Koll. Beih. 5, 269 (1914). 



