28 COLLOIDS IN BIOLOGY AND MEDICINE 



and thus made insoluble (irreversible) as in the above-mentioned ex- 

 ample of the basic dyes. As dye stuff becomes insoluble, the char- 

 coal or fibers must adsorb more dye and the process will continue 

 until all the dye is adsorbed from the solution. In the case in ques- 

 tion, the process is prematurely ended because of the concentration 

 of the HC1 hydrolytically separated, which to a certain degree ex- 

 ercises a solvent action on the colored condensation product. WILH. 

 OSTWALD * has called attention to the fact that in solutions which 

 are hydrolytically split into fatty acids and free alkali, there is a 

 marked displacement of the adsorption balance. This occurs in 

 washing. The fatty acids are adsorbed by the fabric and the skin; 

 to accomplish this, there must occur in the solution a further hydroly- 

 sis, i.e., a splitting off of alkali. In other cases the dissolved sub- 

 stances may be completely removed from solution, e.g., albumin 

 from urine (by charcoal, silicic acid or mastic emulsion, as adsorb- 

 ents). 



If we try to determine the adsorption curves for the phenomena 

 just described (especially the fixation of dyes), we shall find that the 

 curve might be mistaken for that of an irreversible chemical process. 



Still more peculiar are the curves which W. BILTZ and H. STEINER * 

 obtained for the adsorption of night blue and Victoria blue by 

 cotton, and H. FREUNDLICH * 3 for the adsorption of strychnine salts 

 by charcoal or arsenic trisulphid, as well as G. DREYER and J. 

 SHOLTO * for the adsorption of agglutinins by bacteria. In these 

 cases less substance was taken up by the adsorbent from the con- 

 centrated solutions than from those of medium concentration. 



The explanation of a phenomenon of this kind was given by A. 

 LOTTERMOSER,* who observed with A. ROTHE that amorphous silver 

 iodid adsorbed less potassium iodid from highly concentrated solu- 

 tions than from solutions of medium concentration. The process is 

 influenced by the fact that high concentrations of KI precipitate 

 Agl, and make it partially assume the crystallin form. In this in- 

 stance the cause is a diminution of surface; in the other cases, above 

 described, there is a strong probability of a diminution of surface, 

 especially with the agglutination of bacteria. 



Hitherto it has been tacitly assumed that there is no affinity be- 

 tween adsorbents and dissolved substance. This occurs, though only 

 in a few exceptional cases. Thus B. S. G. HEDIN * 4 has shown that 

 certain enzymes (trypsin and rennin) are irreversibly adsorbed from 

 water, but they may be displaced by other substances (casein, serum, 

 grape sugar). L. MICHAELIS demonstrated that__acid kaolin could 

 adsorb only basic or amphoteric dyes, while basic clay could adsorb 

 only acid dyes. Similar experiments have been performed by various 



