764 TRIVALENT AND TETRAVALENT IONS 



The addition of 0.02 cc. of 0.1 n HCl prevented coagulation but 

 the solution was opaque showing that only when the micellae were 

 comparatively large did they assume electrical charges; owing to 

 the fact that the concentration of albumin ions was small com- 

 pared with that of non-ionized protein. These charges sufficed, 

 however, to prevent the further coalescence of the large micellae. 

 When the solutions contained 0.03 cc. of 0.1 n HCl the relative 

 concentration of ionized protein was increased and hence the 

 micellae remained smaller; the solution was no longer opaque but 

 opalescent. With the addition of 0.04 cc. of 0.1 n HCl the solution 

 became very transparent, showing only slight opalescence. With 

 the increasing concentration of ionized protein the average num- 

 ber of molecules in a micella was considerably diminished, and 

 this small size of the average micellae manifested itself in the 

 greater transparency of the solution. With a still greater con- 

 centration of HCl the average size of the micellae diminished still 

 further and the solution became as clear as water. 



When, however, the concentration of HCl was increased beyond 

 a certain limit, the p.d. between the micellae and solution was 

 diminished again on account of the depressing effect of the CI ions 

 demanded by Donnan's theory. When 100 cc. of 1 per cent solu- 

 tion of originally isoelectric albumin contained 30 cc. of n HCl, 

 the protein coagulated at a temperature of 66°C. In this case all 

 the protein was practically ionized but the p.d. between the micellae 

 and the liquid was nevertheless depressed to zero on acccount of 

 the high concentration of CI ions. 



By measuring the concentration of salt required to precipitate 

 crystalline egg albumin from a 1 per cent solution in water of pH 

 3.0 at a temperature of 70°C. we can show that the forces pre- 

 venting heat coagulation in this case are the electrical charges of 

 the micellae, since the concentration of salt required to cause 

 precipitation is of the order of M/8 or below, and since sulfates are 

 more efficient than chlorides. 



The fact that ionization of protein prevents heat coagulation of 

 albumin can be used to find out whether other electrolytes than 

 acids or alkalies are able to produce ionization of isoelectric egg 



