Colloidchemistry. — "Researches on the Nature of the So-Called 

 Adsorpdve Power of Finely-Divided Carbon." I. The Binding 

 of Water by Animal Carbon. By Dr. J. R. Katz. (Communi- 

 cated by Prof. A. F. Holleman). 



(Communicated at the meeting of June 30, 1923). 



I. Introduction. 



The power of fine!)' liivided carbon to bind all kinds of substances 

 is evidently in connection with the degree of fineness of division; 

 for in not finely divided condition the carbon does not show this 

 property. At present the phenomenon is almost universally considered 

 as a typical example of real surface adsorption, i.e. as the acciunnlation 

 of a substance in the boundary layer simply in consequence of the 

 surface-forces. 



This surface adsorption is generally considered as in sharp contrast 

 with the formation of a solid solution. In the latter case the bound 

 substance is not only found in the boundary layer solid-liquid, but 

 through diffusion it gradually penetrates between the molecules of 

 the solid substance, so that finally the principal quantity of the 

 absorbed substance is not found in the boundary layer, but 

 homogeneously distributed throughout the solid body. 



A clear realization of the questions that can be solved by 

 experiments on the nature of this binding to carbon only dates 

 from tiie time of physical chemistry. Bancroft ') and others have 

 considered the possibility that the substances would have been 

 absorbed by the carbon in solid solution ; but the further development 

 of this thought failed on account of the form of the binding-isotherm. 

 If we had to do with a solid solution, — this was the opinion 

 some twenty years ago — the laws of Henry and Nernst must be 

 valid, hence the quantity of absorbed substance must be in direct 

 ratio to the concentration of the vapour and liquid phase, with 

 which it is in equilibrium. A curve is, however, obtained which is 

 almost horizontal at first, and which then turns its convex side 

 downward. This might be explained by the assumption that the 

 absorbed substance dissociates in the carbon into many (e.g. four 



1) The Phase Rule. 



