THE ELECTRICAL CHARGES OF MICELLA 157 



electric point is accompanied by a change in the sign of the value 

 (pH inside micellae minus pH outside). 



One gram of powdered gelatin of grain size between mesh 30 

 and 60, rendered isoelectric, was put into each of a series of 

 closed flasks containing 350 c.c. of distilled water with varying 

 quantities of 0.1 N HC1 or NaOH per 100 c.c. (see Table XXV). 

 The temperature was 20C. After 4 hours the powdered gelatin 

 was separated from its supernatant liquid by filtration, the gela- 

 tin was melted and the pH of the melted gelatin and of the outside 

 solution (filtrate) were measured. The gelatin was then solidi- 

 fied and the P.D. between the solid gelatin and the filtrate (out- 

 side solution) determined, as described. The results of the 

 experiments are given in Table XXV. The first row gives the 

 number of cubic centimeters of 0.1 N HC1 or NaOH contained 

 originally in 100 c.c. outside solution. The next row gives the 

 relative volume of the solid mass of gelatin, i.e., the degree of 

 swelling. The rest of the table needs no explanation. It is 

 obvious that pH inside minus pH outside is positive as long as the 

 pH of the gelatin is on the acid side of the isoelectric point, while 

 it is negative when the gelatin is on the alkaline side of the iso- 

 electric point. The turning point is approximately at the iso- 

 electric point, but the measurements near the isoelectric point 

 are obviously vitiated by experimental errors and possibly by 

 some other factor, so that we cannot demonstrate more by the 

 experiment than that suspended particles of solid metal gelatinate 

 have the opposite sign of charge to that of the micellae of gelatin 

 chloride, and that this difference is accompanied by a reversal of 

 the sign of the value of pH inside minus pH outside, which is 

 positive in the case of gelatin chloride and negative in the case 

 of Na gelatinate. It may also be pointed out that the minimum 

 of swelling (volume) coincides with the minimum of P.D. 



5. THE INFLUENCE OF SALTS ON THE CHARGE OF SUSPENDED 

 PARTICLES OF GELATIN 



The most important fact which a theory of the electrical charge 

 of colloidal micellse is expected to explain is the annihilation of 

 these charges by neutral salts. Those who believe in the adsorp- 

 tion theory assume that both ions of a neutral salt are adsorbed 



