LAWS OF ELECTROLYTIC DISSOCIATION 



73 



TABLE 15 



Glycocoll, ka 



Glycocoll, kb 



Glycylglycocoll, ka 

 Glycylglycocoll, kb 



Temperature 



25° 



17.5° 



18° 



25° 



17.5° 



18° 



25° 



18° 



25° 



18° 



Observer* 



Winkelblech 



Michaelis and Rona 



Dernby 



Winkelblech 



Michaelis and Rona 



Dernby 



Euler 



Dernby 



Euler 



Dernby 



* Winkelblech, Zeitschr. f. physikal. Chem., 46, 546 (1901). 

 Michaelis and Rona, Biochem. Zeitschr. 49, 248 (1913). 

 Dernby, Cpt. rend, des travaux du lab. de Carlsberg. 11, 265 (1916). 

 H. Euler, Hofmeisters Beitr. 7, 1 (1906). 



19. Amphoteric ions 



Bredig pointed out that one of the ionization forms of an ampho- 

 lyte of the general type NH2-R-COO must be an amphoteric ion 

 ("Zwitter-Ion") which is positively as well as negatively charged, 

 such as -""NHs-R-COO". This molecular species may also be 

 conceived of as an inner salt formation arising between the COOH- 

 and the NH2-groups. Thus, for instance, 



CH3COOH + NHs;:^ CH3COO- + NH4 + 



In the same manner we may assume that the salt arising from the 

 internal salt-formation of the amino-acid dissociates electrolytically 

 and produces the ion -"-NHs-R-COO". It is not possible to 

 demonstrate the existence of this molecular species by the usual 

 method of demonstrating ions, i.e., the migration in one direction in 

 an electric current, for this amphoteric ion is electrically neutral. 

 Besides, it is undoubtedly present in extremely small amounts. 

 Furthermore, an amino-acid being the salt of so weak an acid and so 

 weak a base always hydrolyses to a great extent, and the product 

 of hydrolysis of the amphoteric ion is the usual form of the amino- 

 acid. Just as the hydrolysis product of ammonium acetate is 

 ammonia and acetic acid, or, 



NH4+ -f CHaCOO-;^ NH3 + CH3COOH 



;v 



S) 



0« A^ 



<1 





-•01 



