ADSORPTION POTENTIALS AND ELECTROKINETIC PHENOMENA 265 



In general, the acidoid theory still shows a total lack of any values 

 which would determine or define the relative strength of the acidoid 

 or basoid properties in the sense in which the dissociation constant 

 defines the strength of the various true acids and bases. In this 

 latter case such a scale of measurement was made available by the 

 possibilitj' of applying the mass-law. This possibihty is lacking in 

 the case of acidoids and basoids. And yet it appears to be a quite 

 soluble problem for the future, to find the means of extending the 

 definition of the acidic and basic character of substances so as to in- 

 clude cases bordering upon the state of molecular dispersion. 



All that is valid for sohd walls is entirely applicable to any par- 

 ticles suspended in water and to colloidal solutions. And thus the 

 electric charge phenomena of colloidal solutions are rendered com- 

 pletely analogous to the dissociation phenomena of electrolytes in 

 true solution. The laws of dissociation hence appear as a limiting 

 case for the condition where the dissolved electrolyte approaches 

 molecular dispersion. On the other hand, the electric charge phe- 

 nomena in a colloidal solution appear as a limiting case for an elec- 

 trolyte solution in which the dissolved electrolyte become more 

 coarsely dispersed and finally acquires the character of a solid 'Svall." 



78. A consideration of the other ions 



The above simple approximate method of explanation was made 

 possible, as in the case of theory of electrolytic dissociation, by the 

 auxihary assumption which ascribed an exceptional position to the 

 H- and OH-ions. Just as in that case we assumed that the salts of 

 acids and bases are always completely dissociated, or, in effect, non- 

 existent, so in this case we assume provisionally that a wall alwaj^'s 

 adsorbs only H- and OH-ions, but no Na- or Cl-ions, for instance. 

 The extremely shght adsorbability of NaCl on charcoal (see page 234) 

 in contrast to NaOH or HCl, indicates that such an assumption must 

 be justifiable in reaching an approximated general law. In order to 

 complete the scope of this law it is again necessary to drop these sim- 

 plifying assumptions and to reconsider it in the fight of the adsor- 

 ability of the other ionic species. It is to be expected that the in- 

 fluence of any ionic species is the more pronounced, the greater its 

 adsorbabihty, and hence the more effectively it can compete with 

 the H- or OH-ions. Accordingly, the common univalent ions, which 

 are poorly adsorbed, have also the least influence upon the electric 



