110 THEORY OF COLLOIDAL BEHAVIOR 



no influence on the viscosity, osmotic pressure, or P.D. of protein 

 solutions at the isoelectric point. This prerequisite of the 

 Donnan theory was also fulfilled. 



In his book on "Applied Colloid Chemistry" Bancroft makes 

 the following comment on the writer's experiments on the Hof- 

 meister series. 



"Under the conditions of the experiments Loeb found that on the acid 

 side of the isoelectric point only anions of neutral salts are taken up and on 

 the alkaline side of the isoelectric point only cations. Since the Hofmeister 

 series calls for an effect due to both ions of a neutral salt on the swelling of 

 gelatine, Loeb concludes that the Hofmeister series is a delusion and a snare. 

 This does not follow at all. Loeb is working at such extreme dilutions that 

 the specific effects of all ions but hydrogen and hydroxyl ions are practically 

 negligible. In acid solutions only anions are taken up and in alkaline 

 solutions only cations. Loeb recognizes the specific effect of iodine ions over 

 chlorine ions in causing the liquefaction of gelatine; but he considers that 

 liquefaction stands in no necessary relation to swelling, an assumption which 

 will be shared by few. With higher salt concentrations Loeb will undoubt- 

 edly get entirely different results." 1 



The answer to this comment is that when Bancroft wrote it he 

 had not read the writer's later papers dealing with the Hof- 

 meister series. A glance at Figs. 27, 29, 30, 31, 33, 35, 46, and 60 

 will show that salt solutions up to grammolecular concentration 

 were used without any indication of the validity of the Hof- 

 meister series being found. Bancroft will surely not maintain 

 that solutions of neutral salts up to molecular concentration are 

 so dilute that the effects of all ions except the hydrogen and 

 hydroxyl ions are practically negligible. 



The writer's statement that the liquefaction of solid gelatin 

 stands in no necessary relation to swelling is correct, since higher 

 concentrations of acids or of salts like CaCl 2 diminish the swelling 

 of gelatin while they increase its solubility (see Chap. XIV). 

 This is due to the fact that swelling and solution of solid gelatin 

 in the presence of acid are functions of different variables, swell- 

 ing in acid depending on the Donnan equilibrium, while the solu- 

 tion of gelatin depends on the same forces which are responsible 

 for the solution of ordinary crystalloids in water (probably 

 secondary valency forces). 



The belief in the validity of the Hofmeister series has given rise 



1 BANCROFT, W. D., "Applied Colloid Chemistry," New York and London, 

 1921, pp. 255-256. 



