488 



AMPHOTERIC COLLOmS. IV 



etc., of a definite concentration, varying from m/4 to m/8192 at 15°C. 

 During this perfusion the powdered gelatin was sufficiently stirred to 

 allow intimate contact between all the gelatin particles and the alkali, 

 and then after all the excess of alkali had been allowed to drain off 

 the mass on the filter was washed once with 25 cc. of H2O at 5° and 



3Z5 



300 



275 



£50 



225 



200 



175 



150 



125 



100 



75 



50 



25 







3 



2 



pM 4.8 51 5.4 5.7 6.0 63 6.6 69 72 75 78 8.1 

 Li OH 



Figs. 2 to 7. Curves for osmotic pressure (in terms of mm. of a 1 per cent gelatin 



/ io,ooo \ 



solution) and conductivity 



of a 1 per cent gelatin solution first rendered 



y ohms / 



isoelectric and then treated with concentrations of an alkali, e.g. NaOH, varying 

 from m/8 to m/8192 to cause a varying proportion of the gelatin to form a metal 

 gelatinate. Abscissae represent pH of the solution after dialysis; ordinatcs of 

 upper curve, osmotic pressure, and of lower curve, conductivity of the solution 

 found at different pH. Curves for the osmotic pressures for gelatin salts with 

 univalent ion, Li, Na, K, and NH4 (Figs. 2 to 5) are ahke and high, reaching a 

 maximum of about 325 mm. Curves for the osmotic pressures of salts with bi- 

 valent metals, Ca and Ba, are very much lower than those for metal gelatinates 

 with univalent metal, reaching a maximum of only 125 mm. Curves for conduc- 

 tivity are almost identical for both types of gelatin salts. 



