242 HYDROGEN ION CONCENTRATION 



cant amount of such would remain in the boundary layer. Other- 

 wise aniline behaves as a chemically indifferent substance, and there 

 is nothing in the way of OH-ions accumulating in the surface layer 

 in accord with Gibbs' theory. It could then be stated that anihne 

 not dissolved in water is of the character of a very weak acidoid. 

 No matter what nomenclature is adopted, instances will be met with 

 which are not adequately provided for. Such cases are disposed of 

 by our "extended" definitions. The most exact of the sciences, 

 mathematics, furnishes ample illustrations of this. Thus the defini- 

 tion: "a — b is the sum of the terms + a and — b" is an instructive 

 example. For, according to the original definition of a sum, a — b 

 is no sum at all, but its exact opposite, a difference. Likewise, we 

 shall have to accept the idea, that aniline may either be a base or an 

 acidoid, according to the conditions and to the point of view. 



Whether or not the acidoid- or basoid-nature of a substance varies 

 as its true chemical acidic or basic character, depends upon the 

 relative intensity of the acidic or basic character. The very weak 

 base aniline is thus an acidoid, while the much stronger base A1(0H)3 

 is a basoid in respect to pure water. Hence only substances with a 

 very pronounced basic character can behave as basoids, and that 

 is why basoids occur relatively much more rarely than acidoids. 

 And most of these are basoids only towards a neutral or acid solution, 

 for most of them chemically are ampholytoids possessing an iso- 

 electric point, as, for example, AI2O3, Fe203, ZnO, and other similar 

 substances. 



68. The equivalent adsorption of ions of a salt by charcoal; the 

 neutralization effect of charcoal 



The property of the H-ions of being more strongly adsorbed by 

 charcoal than the other cations leads to the following consequence. 

 A solution containing any number of ionic species and whose reaction 

 is acid never becomes more acid in reaction on being shaken with 

 charcoal. On the contrary it becomes less acid. An alkaUne solution 

 behaves in a reverse manner under these conditions, becoming less 

 alkaline,^ Thus, as a matter of rule, any solution on being treated with 

 charcoal approaches neutrality, and the reaction of a neutral solution 

 never becomes markedly acid or alkaline on treatment with charcoal. 



9 W. Loffler and K. Spiro, Helvet. chim. Acta 2, 417 (1918) and 2, 533 (1919). 



