604 COLLOIDAL BEHAVIOR OF EDESTIN 



evident that the edestin must be combined with these strong alkalies 

 in chemically equivalent proportions. 



It should be pointed out that these titration experiments with edes- 

 tin and acids or bases are completely analogous to those previously 

 obtained by Loeb^ with gelatin, casein, and egg albumin, and that they 

 are in complete agreement with the idea that proteins are ampho- 

 teric electrolytes, reacting chemically and stoichiometrically with 

 acids and bases. 



HI. 



Membrane Potentials. 



Loeb^-'-^" showed that when a solution of gelatin or egg albumin in 

 dilute acid was separated by a collodion membrane from an aqueous 

 solution of the same acid, containing no protein, a difference in 

 electrical potential existed between the two solutions. Moreover, 

 he found it possible to calculate the magnitude of the potential differ- 

 ence with considerable accuracy from the hydrogen ion concentrations 

 of the two solutions, on the basis of Donnan's theory,^ according to 

 which, for 25°C., 



X 



p.D. = 59 log — millivolts (1) 



y 



where x represents the hydrogen concentration of the outside solution 

 and y that of the inside solution. He showed also that the presence 

 of increasing concentrations of a neutral salt decreased the p.d., the 

 decrease being dependent on the concentration and valence of the 

 anion. 



Experiments were carried out to determine whether similar results 

 could be obtained with edestin. Solutions were prepared containing 

 0.45 gm. of edestin in 100 cc. of HCl of concentration sufficient to 

 give a pH of 3, and containing varying concentrations of Na2S04, 

 NaCl, CaCl2, or LaCU. These were placed in 50 cc. collodion bags 

 fitted with rubber stoppers and manometer tubes, and the bags were 

 suspended in beakers of HCl of pH 3, which had been made up to 



8 Loeb, J., /. Gen. Physiol., 1920-21, iii, 557. 



9 Loeb, J., /. Gen. Physiol., 1920-21, iii, 667. 

 "> Loeb, J., J. Gen. Physiol, 1921-22, iv, 351. 



