210 ELECTROCHEMISTRY 



then the dissociation of H+ ions must be inhibited and that of 

 OH' ions encouraged by the presence of an excess of H + ions, 

 while that of OH' must be inhibited and of H + ions encouraged 

 by an excess of OH' ions, and a reaction must exist at which 

 H+ and OH' are split off in exactly equal quantities so that the 

 salt is "isoelectric," i.e., wanders equally in both directions in an 

 electric field. A simple calculation suffices (53) to show that if 

 the mode of dissociation of the protein is actually that repre- 

 sented by the above formulae, then the number of protein ions 

 in a solution of proteins must attain a minimum in solutions in 

 which it is "isoelectric." 



A number of observations, to which more detailed reference 

 will be made in a later chapter, tend to establish the fact that the 

 viscosity of protein solutions is in the greater proportion attributa- 

 ble to its ions, and that, consequently, when the ionization of a 

 protein is at a minimum the viscosity of its solution will tend 

 to a minimum also. 



Applying these considerations, and also employing direct obser- 

 vation of the movement of the protein in an electric field, Michaelis 

 and co-workers (40) (41) (42) (43) (44) (45) have endeavored 

 to ascertain the hydrogen ion concentration of the solution in 

 which egg-albumin is isoelectric. 



In the light of the view which I have developed concerning 

 the mode of formation and dissociation of the protein salts a 

 somewhat different interpretation must be placed upon these 

 results. A glance at the figure on p. 185 will show that if the 

 protein is soluble in the free condition and uncombined with 

 bases or acids it must, if it is ionized at all, migrate equally in 

 both directions through the solution under the influence of an 

 electric current, reacting at the electrodes as follows : 



(Anode) 2 HOOC.R.N^ = 2 HOOC.R.NH 2 + 2 

 I 

 OH 



(Cathode) H 2 N.R.COH + H 2 O = H 2 N.R.COOH + H 2 



containing 45 X 10~ 5 equivalents of HC1 per gram at 30 degrees equals 80.1 X 

 10~ 5 reciprocal ohms. Sum of these conductivities equals 118.1 X 10~ 6 recip- 

 rocal ohms. Conductivity of a mixture containing the two salts in the above 

 concentrations at 30 degrees equals 108.5 X 10~ 5 reciprocal ohms. 



