JACQUES LOEB 



747 



These experiments confirm the conclusion reached in connection 

 with the experiments on the charge of solid gelatin that salts with 

 trivalent cations or tetravalent anions ionize isoelectric gelatin and 

 thereby set up a Donnan equilibrium; while salts of the type of 

 CaCl2 or Na2S04 or NaCl do not act this way. 



In the experiments just described it seemed advisable to measure 

 also the influence of different salt solutions of pH 4.7 on the p.d. 

 between solutions of isoelectric gelatin inside the collodion bag and 

 the outside aqueous solution free from gelatin but also of pH 4.7. 

 These measurements were taken at the end of the experiments after 



TABLE IV. 



Influence of Salt Solutions of pll 4.7 on the Osmotic Pressure {in Mm. IhO) 

 of 1 Per Cent Solutions of Isoelectric Gelatin. 



Concentration. 



Na4Fe(CN)6 



NaaSOi 



NaCl 



LiCl 



MgCh 



CaCU 



LaCU 



CeCNO,),... 



osmotic equilibrium was established. The figures show that the 

 addition of little LaCla or Ce(N03)3 increases the p.d. across the 

 membrane until a ma.ximum is reached at a concentration near 

 m/8,192 or m/4,096 and that the p.d. drops again with a further in- 

 crease in the concentration of the salt. The gelatin is positively 

 charged, showing that the gelatin forms cations. Na4Fe(CN)8 

 acts similarly except that gelatin is negatively charged. NaCl, 

 LiCl, Na^SO^, MgCle, and CaCU create no potential ditTerence; or 

 in other words, they cause no ionization of isoelectric gelatin. These 

 results agree with the results obtained with solid gelatin and they 

 agree also with the results obtained in the experiments on anomalous 

 osmosis (Table V). 



