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XXIX. The Adsorption of Jons. By Jnanendra Nath 

 MuKHERJEE, D.Sc, Professor of Physical Chemistry in 

 the University of Calcutta*. 



IN a paper in the Transactions of the Faraday Society 

 (Far. Soc. Disc. Oct. 1921) an attempt has been made to 

 define the nature of the adsorption of ions to which the 

 origin and the neutralization of: the charge oE a colloidal 

 particle are due. The origin of the charge was assumed to 

 be due to the adsorption of ions by the atoms in the surface 

 as a result of their chemical affinity. 



It was pointed out that the adsorption of one kind of ions 

 will impart a charge to the surface, in virtue of which ions 

 of opposite sign will be drawn near the surface. In the 

 liquid there remains an equivalent amount of ions. of opposite 

 sign. The electrical energy will be a minimum when these 

 ious are held near the surface so that the distance between 

 the oppositely charged ions has the minimum value possible 

 under the conditions, and they will be held opposite to the 

 ions chemically adsorbed. An "ion'' so held will not be 

 " free" to move if its kinetic energy is less than " W " the 

 energy required to separate the ion from the oppositely 

 charged surface. The number of such "bound " ions deter- 

 mines the diminution in the charge of the surface. When 

 the concentration of ions of opposite charge in the liquid is 

 small the number of ions "held" to the surface by electrical 

 attraction will be small. 



If the chemically adsorbed ions have a valency equal to 

 " N l5 " and if " N 2 " is the valency of the oppositely charged 

 ions in the liquid in contact with the surface, then 



Ni.Xs.E 2 

 vv ~ D.a ' w 



where E = the electronic charge, x = the distance between 

 the centres of the ions at the position of minimum distance, 

 and " D " is the dielectric constant of water. 



Depending on the concentration of the oppositely charged 

 ions in the liquid near the surface, at any instant a certain 

 number of the " chemically adsorbed " ions are " covered " 

 by ions of opposite charge. In the liquid near the surface 

 there are always a number of free ions equivalent in amount 

 to the " uncovered" chemically adsorbed ions on the surface. 

 The total amount of ions of opposite sign both " bound" and 



* Communicated by Prof. F. G. Donnan, F.R.S. 

 Phil Mag, Scr. 6. Vol. 44. No. 260. Aug. 1922. Y 



