THE ELIMINATION OF DISCREPANCIES BETWEEN 

 OBSERVED AND CALCULATED P.D. OF PRO- 

 TEIN SOLUTIONS NEAR THE ISOELEC- 

 TRIC POINT WITH THE AID OF 

 BUFFER SOLUTIONS. 



By JACQUES LOEB. 

 {From the Laboratories of The Rockefeller Institute for Medical Research.) 



(Received for publication, March 30, 1922.) 



The writer has shown in a series of papers^ that the p.d. observed 

 between a solution of gelatin chloride or albumin chloride inside a 

 collodion bag and an outside solution free from gelatin could be cal- 

 culated from the difference in the hydrogen ion concentration between 

 the inside and outside solutions. The agreement between the ob- 

 served and calculated values was perfect when the solution contained 

 a neutral salt or when the hydrogen ion concentration of the solution 

 was not too close to that of the isoelectric point; the agreement was, 

 however, less satisfactory when the pH was near that of the isoelectric 

 point of gelatin, i.e., near pH 4.7, and no salts were present.^ The 

 source of this disagreement seemed to lie in the inaccuracy in the meas- 

 urement of the pH of the aqueous solution free from gelatin (the out- 

 side solution) at a pH between 4.0 and 7.0. If this surmise was cor- 

 rect, the disagreement in that region of hydrogen ion concentrations 

 should be caused to disappear by the use of a buffer solution inside 

 and outside. 



1 per cent solutions of isoelectric gelatin were made up in m/100 Na 

 acetate solutions containing varying amounts of 1 m acetic acid so 

 that the pH of the gelatin solution varied (at the end of the experi- 

 ment) between 4.65 {i.e., practically isoelectric gelatin) and 3.34 

 (Table I.) Collodion bags, of a content of about 50 cc, were filled 



I Locb, J., /. Gen. Physiol, 1920-21, iii, 667; 1921-22, iv, 351. 

 * Loeb, J., Proteins and the theory of colloidal behavior, New York and London, 

 1922, 138, 156. 



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