THE ELECTRICAL CHARGES OF MICELLA 153 



cohesion between the protein ions themselves. The formation of 

 a micella depends upon these cohesive forces between the protein 

 ions (or parts of these ions) becoming stronger than the attractive 

 forces between the protein molecules and the molecules of water. 

 The nondiffusibility of the protein ions of the micella must give 

 rise to the establishment of a Donnan equilibrium between the 

 micella and the surrounding liquid, and this equilibrium must 

 give rise to the electrical charge of the micella. The only ques- 

 tion is how far the agreement between Donnan's theory and the 

 observed charge goes in the case of true micellae. To test this we 

 used suspensions of particles of powdered gelatin in water. If it 

 can be shown, first, that these particles assume electrical charges 

 when suspended in water, second, that these charges vary in the 

 usual way with pH and the presence of salts, and third, that these 

 charges can be derived from the Donnan equilibrium, the theory 

 of these charges as well as the theory of the stability of colloidal 

 suspensions can be put on an exact scientific basis. 



The method of these experiments was as follows: Powdered 

 particles of isoelectric gelatin were put into a solution of acid or 

 alkali at a temperature of 20C. and allowed to remain there for a 

 number of hours to allow a complete or approximate equilibrium 

 to be established between the inside of the micellae and the outside 

 solution. 1 The temperature must not be above 20, since other- 

 wise the granules of gelatin will dissolve too rapidly. After a 

 number of hours the suspended particles were separated from 

 the outside solution by filtration, the gelatin was melted and put 

 into vessels with two bent tubes (see Fig. 42). After the gelatin 

 had set to a gel (by cooling) the P.D. between the solid gel and 

 the outside solution (filtrate) was determined with the electro- 

 meter. The P.D. was that of the following cell: 



calomel 

 electrode 



saturated 

 KC1 



outside 

 watery 

 solution 



solid gel 



saturated 

 KC1 



calomel 

 electrode 



Everything else being symmetrical the P.D. measured was that 

 between the suspended particles of gelatin (solid gel) and the 

 outside solution with which the gelatin micellae had been in 

 complete or approximate equilibrium. 



1 LOEB, J., J. Gen. Physiol, vol. 4, p. 351, 1921-22. 



