746 CHARGE OF ISOELECTRIC PROTEIN BY IONS 



isoelectric gelatin in solutions of LaCls or Na4Fe(CN)6 of pH 4.7. 

 The osmotic pressure of 1 gm. of isoelectric gelatin in 100 cc. of solu- 

 tion should at first increase with the concentration of LaCls or Na4Fe 

 (CN)6 until a maximum is reached, and the osmotic pressure should 

 then drop again if the concentration of these two salts is increased 

 beyond this point. On the other hand, NaCl, LiCl, MgCla, CaCl2, 

 or Na2S04 should have either no such effect, or it should be 

 considerably smaller. 



A stock solution of concentrated isoelectric gelatin was prepared 

 and so diluted that 1 gm. (by dry weight) of such isoelectric gelatin 

 was contained in 100 cc. of H2O or various concentrations of the salts 

 mentioned, all of a pH of 4.7. Collodion bags of a volume of about 

 50 cc. were filled with these gelatin solutions. Each bag was put into 

 a beaker containing 350 cc. of a solution of the same salt and the same 

 concentration as that in which the gelatin was dissolved. These 

 350 cc. of outside solutions were free from gelatin but had the same 

 pH as the salt solution inside the bag; namely, 4.7. The osmotic 

 pressure was measured in the way previously described and the final 

 measurements were made after 18 or 20 hours. The temperature 

 was kept constant, in some cases at 24°, but generally at 27°C. 

 The higher temperature was chosen to prevent the gelatin from 

 setting to a gel too quickly; i.e., before osmotic equilibrium between 

 the gelatin solution and the outside solution was established. Iso- 

 electric gelatin is rather insoluble but becomes more soluble if 

 salt is added. We shall discuss this more fully in a later part of this 

 paper. 



The results of these experiments are given in Table IV. From this 

 table it is clear that the addition of LaCla and Ce(N03)3 or Na4Fe 

 (CN)6 acts on the osmotic pressure of 1 per cent solutions of iso- 

 electric gelatin in a similar way as the addition of acid or alkali, 

 inasmuch as the addition of little LaCls or Ce(N03)3 or Na4Fe(CN)6 

 raises the osmotic pressure until a maximum is reached at a concen- 

 tration of m/2,048 for LaCla and of m/4,096 for Na4Fe(CN)6; while 

 the addition of more LaCls or Ce(N03)3 or Na4Fe(CN)6 depresses 

 the osmotic pressure. None of the other salts used, NaCl, LiCl, 

 MgCl2, CaCl2, or Na2S04, acted in this way. There was possibly a 

 slight rise when the concentration of these latter salts became very 

 high. 



