JACQUES LOEB 749 



III. 



While all this seems clear, there remains the possibility that the 

 effects of LaCls and of Na4Fe(CN)6 on the p.d. and osmotic pressure 

 of isoelectric gelatin are due to a different kind of ionization from 

 that assumed above. When a solution of LaCls of pH 4.7 is added 

 to a gelatin solution of the same pH, the solution becomes more acid; 

 and when a solution of Na4Fe(CN)6 of pH 4.7 is added to a solution 

 of isoelectric gelatin, the solution becomes more alkaline. A solu- 

 tion of LaCls of pH 4.7 makes, therefore, isoelectric gelatin more 

 acid and this should lead to a formation of gelatin chloride, without 

 the necessity of assuming the formation of a complex gelatin-La 

 cation; while solutions of Na4Fe(CN)6 of pH 4.7 make isoelectric 

 gelatin more alkaline and this should lead to a fonnation of Na 

 gelatinate. To test this possibility 1 per cent solutions of nearly 

 isoelectric gelatin (pH 4.85) were made up in various concen- 

 trations of LaCls of pH 4.7 and the pH was determined electro- 

 metrically (Table VI). 



According to Table V the highest p.d. is reached in LaCls-gelatin 

 mixtures at a concentration of LaCls of m/8,192; such a solution 

 influences the pH of the gelatin solution too little to account for the 

 P.D. of 8.0 millivolts, since near the isoelectric point the difference 

 between pH inside and outside is almost zero. 



It was then attempted to repeat the experiments on the influ- 

 ence of Ce(N03)3 on the p.d. and osmotic pressure of solutions 

 of isoelectric gelatin in buffer solutions, but these experiments failed 

 since the addition of the salt contained in the buffer solution in 

 itself sufficed to suppress the p.d. to be expected. 



To reach a decision the following experiments were made. 



1 per cent solutions of isoelectric gelatin were prepared and to some 

 solutions was added HCl to others NaOH so that the pH values ob- 

 tained were approximately 3.5, 4.0, 4.4, 4.7, 5.0, and 5.5. These 

 gelatin solutions were made up in solutions of different salts of the 

 same pH. In this way it was possible to ascertain the influence of 

 these salts on the pH of the gelatin solution (Table VII). 



The P.D. between these gelatin solutions inside the collodion bags 

 and the outside aqueous solutions of the same salt and originally 



