ADSORPTION POTENTIALS AND ELECTROKINETIC PHENOMENA 269 



colloids that we shall discuss its contributions in greater detail in the 

 following volume on colloids. For the present we shall only point 

 out some instructive examples of the reversal of the sign of the 

 charge. R. Hober^^ estabhshed the fact that the ordinarily nega- 

 tively charged blood corpuscles become easily positively charged 

 under the influence of trivalent ions. But since their charge is also 

 reversed by H-ions, they are, therefore, of ampholytoid nature.^^ 

 Putter^'^ found that bacteria in colloid-free aqueous suspension are 

 always negatively charged, even in a most acid medium; and yet 

 their charge is reversed by A1+++. But in the presence of peptone 

 bacteria become also positively charged by means of high H+- 

 concentrations. 



79. Summary of the theory of formation of the electric charge on 



walls or diaphragms 



The electric charging of a wall towards a solution depends upon the 

 differences of adsorbability of the various ions. The charge of the 

 adsorbed ion is imparted to the wall. The serial sequence of adsorb- 

 abihty of the ions is the same as can be found with charcoal by 

 chemical analysis. Since the H- and OH-ions are particularly strongly 

 adsorbable, the formation of the charge can be approximately ex- 

 plained, in the absence of polj^alent or organic ions, in terms of the 

 difference between the adsorbabilities of the H- and OH-ions alone. 

 On closer consideration the other ions must also be taken into account. 

 The serial sequence of the anions is probably the same for all ad- 

 sorbents, as for example (arranged in order of increasing adsorb- 

 abihty) : 



CI- I- SCN- OH- 

 and similarly it is also the same for the cations, namely in the order: 



Na+ Ca + + A1 + + + H + 



But the absolute extent to which anions on the one hand and 

 cations on the other are adsorbed by any adsorbent is quite different 



3^ R. Hober, Pfliigers Arch. f. d. ges. Physiol. 101, 627 (1904) ; 102, 196 (1904). 

 " L. Michaelis and Takahashi, Bioch. Zeitschr. 29, 439 (1910); Calvin B. 

 Coulter, Journ. of Gen. Physiol. 3, 309 (1921). 



" E. Putter, Zeitschr. f. Immunitatsforsch. u. exp. Therap., 32, 538 (1921). 



