THE MECHANISM BY WHICH TRIVALENT AND 



TETRAVALENT IONS PRODUCE AN ELECTRICAL 



CHARGE ON ISOELECTRIC PROTEIN. 



By JACQUES LOEB. 



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



(Received for publication, May 4, 1922.) 

 I. 



Experiments on anomalous osmosis recently published^ suggest 

 that isolectric gelatin assumes a negative charge when a solution of a 

 salt with tetravalent anion, e.g. Na4Fe(CN)6, is added; and that 

 isoelectric gelatin assumes a positive charge when a salt with a 

 trivalent cation, e.g. LaCls, is added. In these experiments special 

 care was taken that the pH of the solutions was that of the isoelectric 

 point of gelatin; i.e., pH 4.7. CaCl2, Na2S04, and NaCl had appar- 

 ently no such effect on the charge of isoelectric gelatin. 



The question arose whether it was possible to support this sug- 

 gestion by direct measurements of the p.d. between isoelectric solid 

 gelatin and the surrounding salt solution of pH 4.7; and if this was 

 the case what was the reason for this peculiar action of trivalent and 

 tetravalent ions. 



The method of the experiments was as follows: Doses of 1 gm. of 

 powdered gelatin (going through mesh 30 but not through 60) were 

 rendered isoelectric in the way described in previous publications. 

 They were then put for 2 hours at 15°C. into 200 cc. of solutions of 

 LaCls of different concentration, all of pH 4.7. In this time equihb- 

 rium was practically established between the gel and the outside 

 LaCls solution. The suspension was then transferred into cylinders 

 and the gelatin granules allowed to settle (at 15°C.). The su- 

 pernatant liquid and the solid gelatin granules were then separated 

 by filtration, the solid gelatin granules were melted by wanning, 

 poured into cylinders with two glass tubes attached (as described in 



1 Locb, ].,J. Gen. Physiol, 1921-22, iv, 463. 



741 



