44 



AMPHOTERIC COLLOIDS. 



nCl concentration ^ ft ^ 1^ I^ ^z 1^3 iVa A & "." 

 pH 3.2 M id 42 45 5.^ 15 6.1 6.6 6.7 71 



Fig. 1. HCl curves. 

 Curves of the conductiv- 

 ity, osmotic pressure, 

 swelling, and alcohol num- 

 ber of gelatin previously 

 treated with various con- 

 centrations of HCl and 

 then freed from excess of 

 HCl by washing with 

 water. On the axis of ab- 

 scissae are the logarithms 

 of the HCl concentration 

 used, and under each con- 

 centration is the pH of the 

 1 per cent gelatin solution 

 in H2O (made from the 

 washed gelatin) . The or- 

 dinates are the values for 

 conductivity, osmotic pres- 

 sure, swelling, and alcohol 

 number for the gelatin. 

 In the region of the iso- 

 electric point (pH = 4.7) 

 all the curves have a min- 

 imum. On the left of this 

 point gelatin exists in the 

 form of gelatin chloride 

 (with high ionization), the 

 curves rising more rapidly 

 than on the right of the 

 isoelectric point where the 

 gelatin exists in the form 

 of common gelatin which 

 dissociates as a ver}'^ weak 

 acid. All four curves are 

 nearly parallel. 



