﻿the Adsorption of Ions. 327 



sowohl auf Adsorption des gebildeten Kaliumstannats wie 

 audi daraut' zUruckt'iihren sein, das Kaliumhydrat mit 

 den Oberflachenmolekeulen der Zinnsaureprimarteilchen in 

 Reaktion tritt, wobei diese von der Oberflache der Primar- 

 teilehen festgehalten werden." 



The view suggested bv the writer to account for the ad- 

 sorption of a common ion, leads one to expect that ions 

 which can displace one of the constituent ions in the crystal 

 lattice should also be adsorbed. Marc {Z. Phys. Chem. lxxxi. 

 p. 641 (1913)) has observed that crystalline adsorbents adsorb 

 crystalloids to any marked degree only when they can form 

 mixed crystals with them and are isomorphous with them. 

 Paneth and Horrowitz (Physik. Zeitsch. xv. p. 924 (1914)) 

 have noticed that oc the radio elements those only will be 

 adsorbed that can form insoluble salts with the common 

 ion of the adsorbent and can also form mixed crystals with 

 the adsorbent. This kind of adsorption is somewhat different 

 from the type we have considered for, as Paneth has pointed 

 out in his case, an actual interpenetration of the two non- 

 common ions is occurring in the crystal lattice. Thus 

 radium is taken up by barium sulphate giving out to the 

 solution barium ions in exchange. Such an interchange will 

 not impart a charge to the surface. 



Attention may also be drawn to the explanation advanced 

 by Bradford (Biochem. J. x. p. 169 (1916) ; xi. p. 14 (1917)) 

 to account for zonal precipitations, first siudied by Liese- 

 gang. Bradford thinks that the adsorption of a constituent 

 ion is responsible for their formation. From the numerous 

 instances given aboA r e, this conception seems to be quite 

 plausible. It is probable that other factors have also an 

 influence on the process (Hatschek, Brit. Assoc. Rep. p. 24 

 (1918)). 



II. The Variation of the Density of the Electric Charge 

 with the Concentration of an Electrolyte. 



In the previous paper the particular case when the charge 

 o£ the surface is due to strong chemical adsorption of ions of 

 one kind and when the added electrolytes have not any ions,, 

 subject to the cheniical affinity of the surface atoms, has been 

 fully treated. In this case it was assumed that the number 

 or! ions adsorbed at the surface by chemical affinity remains 

 constant. The experimental data of Elissafoff on glass 

 and quartz agree well with equations deduced from these 

 assumptions, on the basis of the theory of electrical 

 adsorption. 



