ADSORPTION POTENTIALS AND ELECTROKINETIC PHENOMENA 243 



Exactly in the same way the reaction of any aqueous solution may 

 be made to approach neutrality by the addition of a true ampholyte 

 whose isoelectric point lies in the vicinity of neutrality. Hence it 

 follows that in an aqueous solution of a neutral salt, or even of a salt of 

 an organic dye, equivalent amounts of anions and cations are ad-, 

 sorbed, i.e., the salt molecule is adsorbed as a whole. Michaelis and 

 Rona^'' designated this phenomenon as the equivalent ionic adsorption 

 of salts, and established the fact that no hydrolytic cleavage of salts 

 takes place in the process of adsorption on charcoal. The second 

 observation stated above, to the effect that an acid or alkaline solu- 

 tion approaches neutrality on treatment with charcoal could have 

 been deduced from these observations of Michaelis and Rona, but 

 was not recognized by them at the time. It was found experimen- 

 tally by Loffler and Spiro,^ and this phenomenon can be designated 

 as the neutralization effect of charcoal.^°'' 



69. Other adsorbents 



Charcoal possesses the pecuharity of not itself yielding any ions to 

 a solution. As soon as an adsorbent contains ionogenic radicals, it 

 must be taken into account that the adsorbent itself may show a 



>« Michaelis and Rona, Bioch. Zeitschr. 94, 225; 97, 57; 102, 268 (1920). 



1"" It developed later that the above described amphylotoid nature of char- 

 coal is not a general property but is rather peculiar to certain varieties or 

 preparations of charcoal. It seems to have little to do with the mineral im- 

 purities, but to depend much more upon the organic material from which the 

 charcoal is prepared, and above all upon the temperature at which the carbon- 

 ization is carried out. It now appears that with rising temperature of charring 

 all charcoals tend to reach a single definite limiting state. This fact was first 

 brought out by Miller and Bartell (Jour. Amer. Chem. Soc, 44, 1866 (1922)) 

 with highly heated (activated) ash free charcoal from sugar. This charcoal is 

 not of ampholytoid character. For it adsorbs HCl but to a slight extent, does 

 not adsorb NaOH at all, while neutral salts are adsorbed by it in such a manner 

 that a trace of acid is adsorbed, leaving a slightlj' alkaline solution, the adsorp- 

 tion being thus a hydrolytic one. 



On the other hand blood charcoal which had not been activated by thorough 

 heating will yield all the adsorption phenomena described in this section (I . 

 Ogawa, Biochem. Zeitschr., 172, 249 (1926jj. No recognizable differences 

 were observed in the elementary analyses of the different charcoal prepara- 

 tions before and after activation, making it probable that the changes occur 

 only in the ultimate crystal structure of the substance, in spite of the fact 

 that the x-ray diagrams obtained by the method of Debye and Scherrer show 

 no differences between the two states. 



