260 



HYDROGEN ION CONCENTRATION 



to occur in general at the neutral reaction. To be sure, for a few 

 substances, such as charcoal and gelatin, the reversal at neutrality 

 was to a certain extent confirmed. But a large series of substances 

 was found which at ever so strong an acid reaction showed no positive 

 charge, but which at most showed an abohtion of their original 

 negative charge, as for instance, cellulose, collodion, agar, kaolin, 

 also retort-charcoal belongs to this group, according to Bethe and 

 Toropoff. Even the point of reversal of the charge of gelatin (i.e., 



TABLE 39 



gelatinized collodion membranes as used by Jacques Loeb ^^ or mem- 

 branes of congealed gelatin) proved to be not at exact neutraUty but 

 rather at that pH which the present author^^ had previously found 

 by electrophoresis experiments to be the isoelectric point of gelatin. 



Table 39 shows some of the results obtained by Glixelli.^^ He 

 found at first a few substances which, as most of Perrin's substances 

 did, showed a reversal of their charge on passing from an acid to an 



^' Jacques Loeb, Journ. of gen. phj^siol. 2, 225 (1920). 



32 L. Michaelis and W. Grineff, Bioch. Zeitschr. 41, 373 (1912). 



