58 AMPHOTERIC COLLOIDS. 



SUMMARY. 



1. It has been shown in this paper that while non-ionized gelatin 

 may exist in gelatin solutions on both sides of the isoelectric point 

 (which Hes for gelatin at a hydrogen ion concentration of Cjj= 2.10~* 

 or pH = 4.7), gelatin, when it ionizes, can only exist as an anion on the 

 less acid side of its isoelectric point (pH >4.7), as a cation only on the 

 more acid side of its isoelectric point (pH<4.7). At the isoelectric 

 point gelatin can dissociate practically neither as anion nor as cation. 



2. When gelatin has been transformed into sodium gelatinate by 

 treating it for some time with m/32 NaOH, and when it is subsequently 

 treated with HCl, the gelatin shows on the more acid side of the iso- 

 electric point effects of the acid treatment only ; while the effects of the 

 alkali treatment disappear completely, showing that the negative 

 gelatin ions formed by the previous treatment with alkali can no 

 longer exist in a solution with a pH<4.7. When gelatin is first 

 treated with acid and afterwards with alkali on the alkaline side 

 of the isoelectric point only the effects of the alkali treatment are 

 noticeable. 



3. On the acid side of the isoelectric point amphoteric electrolytes 

 can only combine with the anions of neutral salts, on the less acid side 

 of their isoelectric point only with cations; and at the isoelectric 

 point neither with the anion nor cation of a neutral salt. This har- 

 monizes with the statement made in the first paragraph, and the 

 experimental results on the effect of neutral salts on gelatin published 

 in the writer's previous papers. 



4. The reason for this influence of the hydrogen ion concentration 

 on the stability of the two forms of ionization possible for an ampho- 

 teric electrolyte is at present unknown. We might think of the possi- 

 bility of changes in the configuration or constitution of the gelatin 

 molecule whereby ionized gelatin can exist only as an anion on the 

 alkaline side and as a cation on the acid side of its isoelectric point. 



5. The literature of colloid chemistry contains numerous state- 

 ments which if true would mean that the anions of neutral salts act 

 on gelatin on the alkahne side of the isoelectric point, e.g. the alleged 

 elTect of the Hofmeister series of anions on the swelling and osmotic 

 pressure of common gelatin in neutral solutions, and the statement 



