236 HYDROGEN ION CONCENTRATION 



The most striking aspect of these series is the relation to the elec- 

 tromotive tension series, the nobler the metal the more easily are its 

 ions adsorbed. Also the valence has a certain influence. The higher 

 oxidation forms of the ions (Fe+++, Hg++) are exceptionally strongly 

 adsorbable, as well as the salts of certain organic bases and acids, 

 such as the dyes, quinine, etc. Among the halogen anions the dis- 

 charge tension increases with increasing atomic weight. No demon- 

 strable difference in the adsorbabihties of the different alkali metal 

 cations was observed. This fact was also confirmed by Hartleben.^ 



The relative adsorption of the salts, as it was also shown for non- 

 electrolytes, increases with the decreasing concentration of their 

 solutions. Table 37, taken from the cited article by Rona and 

 Michaelis, shows the results obtained by using 0.1 equivalent normal 

 solutions of the different salts and by employing 15 g. of the same 

 land of charcoal (Merck's blood charcoal) per 100 cc. of solution. 

 The figures represent the per cent of the original salt content re- 

 moved from solution by adsorption."* 



66. The exceptional position of the H- and OH-ions 



At this juncture also our attention is especially attracted to the 

 H- and OH-ions; they assume an exceptional position and belong 

 to the most strongly adsorbable ions. Only the ions of the "noblest" 

 metals, a few polyvalent (Fe+++) and some organic ions rival the 

 H-ions, and only the most easily adsorbed acid dye ions compare 

 with the OH-ions. In this connection an analogy to the chemical 

 combinations among ions suggests itself. In aqueous solutions most 

 ions combine among themselves but to a very slight extent, i.e., 

 most salts are "strong" highly dissociated electrolytes. Only among 

 the acids and bases are there countless weak electrolytes. This means 

 that the H- and OH-ions bind other ions more firmly than all other 

 ions. In an exactly similar way, the H-ion is more firmly bound 

 by charcoal than the other cations and OH-ion more firmly bound 

 than the other anions. To be sure, it is impossible to effect the 



3 Hans Hartleben, Bioch. Zeitschr. 115, 46 (1921). 



* The figures in the original article were recalculated in the following man- 

 ner. From the given data of the rough analyses a correction for the water 

 content of the charcoal (30 per cent) was applied. Furthermore, all concen- 

 trations were recalculated into terms of normal equivalents, for some of the 

 original data were given in terms of molarity. 



