JACQUES LOEB 745 



increasing with an increase in the concentration of Na4Fe(CN)6 

 until the concentration of m/4,096 is reached where the p.d. between 

 solid gelatin and Na4Fe(CN)6 solution is 22 millivolts, the gelatin 

 having the negative charge. Upon increasing the concentration of 

 Na4Fe(CN)6 beyond m/4,096 the p.d. diminished again until it 

 became 1 millivolt when the concentration of Na4Fe(CN)6 was m/8 

 (Table II). 



The next step was to find whether solutions of CaCl2 of pH 4.7 

 also give a positive charge to isoelectric gelatin and whether solutions 

 of Na2S04 give a negative charge. Table III shows that both of 

 these salts, as well as NaCl, have only a depressing effect on the 

 potential of isoelectric gelatin but cause no increase of p.d. in low 

 concentration. 



There is, however, a slight difference between the action of the 

 three salts. While in the case of Na2S04 gelatin becomes slightly 

 negative in concentrations beyond m/512, this does not happen in 

 the case of NaCl and CaClo. The negative charge is, however, so 

 small that it would not be wise to attribute much importance to this 

 fact. The important fact is that solutions of LaCls and Na4Fe(CN)6 

 of pH 4.7 have a similar influence on isoelectric gelatin to that of 

 acids and alkalies respectively, while this effect cannot be demon- 

 strated in the case of NaCl, CaCl2, or Na2S04. This would be 

 intelligible on the basis of the assumption that the electrostatic at- 

 traction of Na,Cl, SO4, and Ca ions is not sufficient to cause the forma- 

 tion of any considerable quantity of ionizable gelatin salts when react- 

 ing with isoelectric gelatin; at least not in the concentrations of salts 

 used in this experiment. If this surmise is correct, we must consider 

 the fact that the electrostatic attraction of an ion is a function of at 

 least two variables; namely, the number of charges and the radius. 

 If this is taken into consideration it is not to be expected that all 

 divalent ions should be as inactive as Ca or SO4. 



II. 



If the influence of LaCls and Na4Fe(CN)6 on the p.d. of solid 

 isoelectric gelatin is due to ionization of the protein and the estab- 

 lishment of a Donnan equilibrium as a consequence of this ionization, 

 this should betray itself also in the osmotic pressure of mixtures of 



