DAVID I. HITCHCOCK 



611 



was found that the solubility of edestin in acid or alkali was less than 

 0.45 gm. in 100 cc. for a broad zone around the isoelectric point, from 

 about pH 5 to pH 9. Table IX gives the results of a few measure- 

 ments that were made with 0.45 per cent sodium edestinate in sodium 

 hydroxide. Both inside and outside solutions were protected from 

 the CO2 of the air by soda-lime tubes. 



These results show that the prediction of the theory was confirmed, 

 for the pH outside is now greater than the pH inside, and the sign of 

 both observed and calculated p.d. is opposite to that obtained with 

 the acid solutions. Moreover, the agreement between observed and 

 calculated p.d. is close enough to show that the Donnan theory applies 

 quantitatively on the alkaline side of the isoelectric point of edestin. 



TABLE IX. 

 P.D. atid Osmotic Pressure of 0.45 Per Cent Sodium Edestinate. 



pH inside 



pH outside 



Observed p.d., millivolts 



Calculated p.d., millivolts 



Observed osmotic pressure, mm. 



10.96 

 11.05 

 -6.0 

 -6.0 

 45 



IV. 



Osmotic Pressure. 



The similarity between the depressing effect of salt on the osmotic 

 pressure and on the p.d. in the case of gelatin chloride has been pointed 

 out by Loeb.^ That the same resemblance exists in the case of edestin 

 chloride is shown by the results in Tables II to V, and by a comparison 

 of Fig, 7 with Fig. 4. Since the abscissae in Fig. 7 represent equivalent 

 concentrations of salt with respect to chloride ion, and the points ob- 

 tained with the three chlorides all fall on the same curve, it is evident 

 that it is again only the anion that is effective in depressing the 

 osmotic pressure of a solution in which the protein ion is positive. The 

 nature or valence of the cation seems to have no effect. These re- 

 sults are in contradiction to the theory that the effect of a salt on such 

 colloidal properties of protein solutions is due to the adsorption of 

 both ions of the salt, but are in complete accord with the results of 



