IN ISO-ELECTRIC REACTION 51 



equally clear that, owing to the almost complete combination 

 with the acid which occurs, the free H- ions, over a wide range 

 preserve a low concentration, which fluctuates only between 

 narrow limits. 



On account of the differing valency of the negative groups 

 present, and of the newly-formed positive albumin ions, points 

 which are apparently iso-electric appear when considerable 

 combination with acid occurs. These points have many pro- 

 perties in common with the true iso-electric points found by 

 using hydrion regulators, but they must be clearly distinguished 

 therefrom. The main difference between the two cases lies in 

 the fact that the first three points (a, b, c) are merged into a 

 single point when regulators are used, whereas with strong 

 acids they lie wide .apart. Nevertheless, the difference must 

 not be considered absolute. With regulator mixtures, which 

 greatly reduce the ionisation of the acid employed, the forma- 

 tion of polyvalent albumin ions is largely prevented. Conse- 

 quently there is to some extent a satisfactory agreement 

 between the properties of albumin and those required by the 

 theory of Michaelis, which holds strictly only for amphoytes of 

 simple structure.* 



S. P. L. Sorensenf has quite recently made use of the rule 

 that the quantities of acid or base required to make a solution 

 iso-electric are independent of the concentration of ampholyte 

 as a means of determining the iso-electric H- ion concentration. 

 To this end a concentration of H- ion was sought which remained 

 unaltered on addition of any arbitrary quantity of amphoteric 

 electrolyte. A close examination of Sorensen's conditions of 

 work is necessary in order to test how far his results can be 

 reconciled with the quite contradictory ones obtained in the 

 case of strong acids. Sorensen used for his experiments egg 



* From this point of view, the importance of the fact that slight 

 variations in the behaviour of the components of the buffer mixture 

 produce small divergences from the point of change of the properties of 

 the protein is brought out. These variations show a certain conformity 

 to those larger differences shown when strong acids are used. Moreover, 

 the hydrion concentration which causes minimum viscosity is regularly 

 slightly greater than that at which the precipitation by alcohol shows a 

 maximum. 



f Zeitsch. physiol. Chem., 1918, 103, 192. See also A. Hasselbalch, 

 Biochem. Zeitsch., 1916, 78, 129. 



4-2 



