SURFACES 27 



that the distribution of arsenious acid between iron hydroxid gel and 

 water follows the equation 



adsorbed 



2 ._ = 0.631. 



c (free) * 



Were we to believe that the arsenious acid went into solid solution in 

 iron hydroxid gel we should have to conclude that the arsenious acid 

 had a molecular weight one-fifth as large in iron hydroxid gel as in 

 water. From other observations, however, we know that arsenious 

 acid in water breaks up into simple molecules so that the assumption 

 that it dissolves in iron hydroxid gel is untenable. 



The following statements will show that many conditions may 

 modify the course of the adsorption curve and such cases, according 

 to L. MICHAELIS, are best called abnormal adsorption. 



A substance may, for instance, as the result of swelling, absorb 

 more water than the substance dissolved and thereby simulate a nega- 

 tive adsorption. Thus, B. HERZOG and ADLER* found that talcum 

 powder adsorbed from sugar or albumin solution more water than 

 sugar or albumin so that as a result, the solution appeared to be more 

 concentrated at the end than at the beginning of the experiment. 



The great concentration which adsorbed substances cause in the 

 dispersed phase may be associated with changes in its condition; 

 for instance, it may be thrown down as a solid. It has been ob- 

 served, that charcoal which has been shaken with a solution of 

 anilin dye shows the greenish metallic shimmer and the dichroism 

 of the solid dye; albumin may coagulate at interfaces. Pro- 

 found changes may accompany these variations of condition. This 

 may be shown by the following examples, the so-called basic anilin 

 dyes are salts consisting of a strong acid (usually hydrochloric 

 acid) and a weak color base. The aqueous solution undergoes 

 strong hydrolytic dissociation; the free color base shows a more or 

 less colloidal character and is always strongly adsorbed. H. FREUND- 

 LICH and G. LOSEV * showed that the color bases adsorbed by char- 

 coal from new f uchsin and crystal violet were changed at the surface 

 of the charcoal, and substances with entirely different properties 

 were formed; probably they were the insoluble substances which 

 A. VON BAEYER had previously prepared separately. In the case 

 of the basic dyes, these chemically changed substances form the color 

 on the textile fiber. 



Now we must recall that pure adsorption is a condition of equilib- 

 rium changeable with the concentration of the dissolved substance. 

 There can be no balance if a substance is removed from the solution 



