356 ELECTRICAL CHARGES OF COLLOIDAL PARTICLES 



gelatinate (inside solution). As a consequence the pH in the outside 

 solution should be higher than in the inside solution, and the value 

 pH inside minus pH outside should become negative when the inside 

 solution is Na gelatinate. This is the reason why powdered particles 

 of Na gelatinate must assume a negative charge. In the case of a 

 gelatin chloride solution the value pH inside minus pH outside is 

 positive and this explains why powdered particles of gelatin chloride 

 are positively charged. 



We will now show that when we separate a solution of Na gelatinate 

 from a watery solution by a collodion membrane and allow both 

 solutions to reach or approach equilibrium, the value pH inside minus 

 pH outside actually becomes negative. 



//. The Electrical Charge of Na Gelatinate. 



It is necessary to prevent the CO2 of the air from diffusing into the 

 solutions of Na gelatinate, and therefore the outside solution was put 

 into stoppered bottles connected with the outside air by glass tubes 

 filled with soda lime. The pH measurements were less certain than 

 in the experiments with acid on account of the CO2 error. There 

 may be other experimental shortcomings, e.g., the slowness of the 

 establishment of the Donnan equilibrium between inside and outside 

 solutions near the isoelectric point. 



Collodion bags of a volume of about 50 cc. were filled with solutions 

 of Na gelatinate containing 1 gm. of originally isoelectric gelatin and 

 varying amounts of 0.1 N NaOH in 100 cc. solution. The collodion 

 bags were dipped into flasks containing 500 cc. of aqueous solutions 

 of NaOH of various concentrations and free from gelatin. The 

 flasks were sealed, communicating with the air only through tubes 

 filled with soda lime, as stated. The collodion bags containing the 

 gelatin were closed by a rubber stopper perforated by a glass tube 

 which served as a manometer. The experiment lasted 6 hours at a 

 temperature of 24°C. The results of the experiments are given in 

 Table I. The upper horizontal row gives the number of cc. of 0.1 N 

 NaOH originally in 100 cc. of the gelatin solution; the second row 

 gives the original concentration of NaOH in the outside aqueous 

 solution free from gelatin; the third row gives the osmotic pressure 

 in millimeters HoO after 6 hours. The next row gives the pH inside 



