138 



THEORY OF COLLOIDAL BEHAVIOR 



This is indeed the case and the 

 turning point lies, as was ex- 

 pected, at the isoelectric point. 



The experiments with Na 

 gelatinate demand more rigid 

 precautions than those with 

 gelatin chloride. It is neces- 

 sary to prevent the CO 2 of 

 the air from diffusing into 

 the alkaline solutions and 

 therefore the outside solution 

 was put into stoppered bot- 

 tles connected with the outside 

 air by glass tubes filled with 

 soda lime. On account of the 

 CO 2 error the pH measure- 

 ments near the isoelectric point 

 are unreliable and only when 

 the pH is above 7.0 is it pos- 

 sible to get reliable results. 

 The main facts demanded by 

 the theory can, however, be 

 demonstrated. The first fact 

 is the proof that the sign of 

 charge of the Na gelatinate 

 solution is the reverse of that 

 of a gelatin chloride solution. 



Collodion bags of a vol- 

 ume of about 50 c.c. were 

 filled with solutions of Na 

 gelatinate containing 1 gm. 

 of originally isoelectric gelatin 

 and varying amounts of 0.1 N 

 NaOH in 100 c.c. solution. 

 The collodion bags were dip- 

 ped into flasks containing 500 

 c.c. of aqueous solutions of 

 NaOH of various concentra- 

 tions and free from gelatin. 



