26 ELECTRIC CHARGE ON NATURAL SOLUBLE 



Table 4. 

 (Valid for N/ioo and more dilute solutions.] 



* From the dissociation equation of water C TT . x C___, = K (K = 



H OH w w 



0-58 X io- 14 at 1 8). 



The proteins, as we have emphasised above, are amphoteric 

 electrolytes, behaving both as acids and as bases. They have 

 both an acid dissociation constant K a and a basic dissociation con- 

 stant K&, or, should they be poly-basic acids or poly-acid bases, 

 more than one dissociation constant of each kind. We will not 

 here discuss the observations so far made, but these show that 

 if certain conditions for the determination of the iso-electric 

 reaction are observed, a single mean constant K a can be taken 

 as an index of the acid strength of the protein, and similarly 

 K ft as a measure of the basic character, without encountering 

 any difficulty. 



This effect is in complete accordance with the general be- 

 haviour of polyvalent acids or bases which dissociate in several 

 stages ; for, as a rule, the first stage is large compared with the 

 later ones, as indicated by the greatest development of H- or 

 OH' ions. 



Most of the natural proteins that have been studied, whether 

 simple or compound (albumin, globulin, glutin, casein, haemo- 

 globin), show a stronger acid than basic character. As, there- 

 fore, the dissociation into hydrion predominates, so does the 

 electro-negative character of the colloidal portion of the protein, 

 as is shown by the marked anodic migration of the pure natural 

 substance. It can be predicted from the fact that these proteins 

 are built up of amino-acids, which themselves are more acid 



