618 



P.D. NEAR THE ISOELECTRIC POINT 



with these solutions of gelatin in buffer solutions as described in pre- 

 vious papers. The bags were put into beakers containing 350 cc. 

 of identical solutions of m/100 Na acetate and 1 m acetic acid as those 

 inside the bags, except that the 350 cc. outside solutions contained 

 no gelatin. The temperature was 24°C. After 24 hours the osmotic 

 pressure, the p.d. between inside and outside solutions, and the pH 

 of the inside and outside solutions were measured. From the value 

 pH inside minus pH outside the p.d. was calculated, and Table I 

 shows that the p.d. thus calculated agrees with the observed p.d. 

 The rest of the table needs no explanation. 



TABLE I. 



Influence of pH on p.d. of Solutions of Gelatin Acetate in the Presence of Buffer 



Solution. 



Similar results were obtained, in the case of solutions of edestin, 

 by Dr. Hitchcock, whose paper appears simultaneously with this 

 note.^ 



SUMMARY and CONCLUSIONS. 



1 . It had been noticed in the previous experiments on the influence 

 of the hydrogen ion concentration on the p.d. between protein solu- 

 tions inside a collodion bag and aqueous solutions free from protein 

 that the agreement between the observed values and the values cal- 

 culated on the basis of Donnan's theory was not satisfactory near the 



3 Hitchcock, D. I., /. Gen. Physiol, 1921-22, iv, 597. 



