COLLOIDS. 29 



solved bodies, and for this reason the adsorbed substance lowers the 

 surface tension of the solid-fluid, and indeed, the more the greater con- 

 centration in which it occurs. That especially carbon and colloid sub- 

 stances are adsorption bodies lies in the fact that they have an especially 

 large surface due to their finely divided state or porosity, which there- 

 fore, cet. par., must give them a great surface energy. 



That proteins, on precipitation, carry down other bodies with avidity 

 is well known; inorganic hydrogels also take up dissolved substances 

 with energy. The curves obtained for the latter process by VAN BEM- 

 MELEN l show a close analogy with the characteristic curves for the 

 adsorption compounds. It often occurs that the body taken up homo- 

 geneously saturates the hydrogel, in which case = k, and a sort of 



C2 



solid solution is the result. In certain cases, undoubtedly, chemical 

 combinations with quite positive conditions are formed. 



The precipitation of colloids by electrolytes has also been discussed 

 by FREUNDLiCH 2 from the standpoint of the adsorption hypothesis. 

 Thus, for the precipitation ability of an electrolyte, the electric charge 

 of the precipitating ion comes first into consideration and secondly, the 

 ability of the precipitating colloid to adsorb the same. According to 

 MOORE and ROAF S the salts of the red corpuscles are retained as adsorp- 

 tion compounds (adsorpates) by the proteins. 



Thus far only the adsorption of crystalloids has been considered. 

 Colloids are also taken up by solid substances or by other colloids. Still in 

 these cases the conditions are more complicated than in the above- 

 mentioned adsorption phenomena, as the combinations formed are in special 

 cases irreversible or gradually become irreversible. It is well known that 

 carbon takes up colloidal colored substances, and we have numerous exam- 

 ples of the combination of dissolved colloids with solid colloids in technology. 

 BiLTz 4 has been able to show that many dyeing processes are to be 

 considered as adsorption phenomena, and later FREUNDLICH and LOSEV 5 

 have measured the adsorption of basic and acid pigments by carbon 

 and also by fibers (wool, silk, cotton), and have shown the correspondence 

 of the two processes. With the basic pigments, which were used as 

 salts, a splitting occurred into a pigment base, which was taken up by 

 the fibers as well as by carbon, and an acid which quantitatively remained 

 behind. This is similar to the cleavage which precipitating electrolytes 

 undergo in the precipitation of the suspension colloids (see page 26). 



Zeitschr. anorg. Chem., 23, 111, 321 (1900). 



2 Zeitschr. f. Chem. u. Ind. d. Koll., 1, 321 (1907). 



3 Bioch. Journ., 3, 55 (1908). 



*Ber. d. d. chem. Gesellsch., 37, 1766 (1904); 38, 2963, 2973, 4143 (1905). 

 5 Zeitschr. f. physik. Chem., 59, 284 (1907). 



