504 AMPHOTEKIC COLLOmS. IV 



SUMMARY. 



1. A method is given by which the amount of equivalents of metal 

 in combination with 1 gm. of a 1 per cent gelatin solution previously 

 treated with an alkali can be ascertained when the excess of alkali is 

 washed away and the pH is determined. The curves of metal equiv- 

 alent in combination with 1 gm. of gelatin previously treated with 

 different concentrations of LiOH, NaOH, KOH, NH4OH, Ca(0H)2, 

 and Ba(0H)2 were ascertained and plotted as ordinates, with the pH 

 of the solution as abscissae, and were found to be identical. This 

 proves that twice as many univalent as bivalent cations combine with 

 the same mass of gelatin, as was to be expected. 



2. The osmotic pressure of 1 per cent solutions of metal gelatinates 

 with univalent and bivalent cation was measured. The curves for 

 the osmotic pressure of 1 per cent solution of gelatin salts of Li, Na, 

 K, and NH4 were found to be identical when plotted for pH as ab- 

 scissae, tending towards the same maximum of a pressure of about 

 325 mm. of the gelatin solution (for pH about 7.9). The correspond- 

 ing curves for Ca and Ba gelatinate were also found to be identical but 

 different from the preceding ones, tending towards a maximum pres- 

 sure of about 125 mm. for pH about 7.0 or above. The ratio of maxi 

 mal osmotic pressure for the two groups of gelatin salts is therefore 

 about as 1 : 3 after the necessary corrections have been made. 



3. When the conductivities of these solutions are plotted as 

 ordinates against the pH as abscissas, the curves for the conductivities 

 of Li, Na, Ca, and Ba gelatinate are almost identical (for the same pH), 

 while the curves for the conductivities of K and NH4 gelatinate are 

 only little higher. 



4. The curves for the viscosity and swelling of Ba (or Ca) and Na 

 gelatinate are approximately parallel to those for osmotic pressure. 



5. The practical identity or close proximity of the conductivities of 

 metal gelatinates with univalent and bivalent metal excludes the pos- 

 sibiHty that the differences observed in the osmotic pressure, viscosity, 

 and swelling between metal gelatinates with univalent and bivalent 

 metal are determined by differences in the degree of ionization (and 

 a possible hydratation of the protein ions). 



6. Another, as yet tentative, explanation is suggested. 



