LAWS OF ELECTROLYTIC DISSOCIATION 67 



denote, as always, the apparent dissociation constants. Thus our 

 original equation remains correct, and the contingent deviations 

 from the directly determined isoelectric point and from that calcu- 

 lated from the dissociation constants will have to be explained in 

 some other way. 



Latest developments in the theory of ampholyte dissociation 



The most marked advance in the theory of dissociation is based 

 upon a contribution by Bjerrum,^^^ and its important forerunner 

 being an article by Adams. '^"^ Accordingly it is no longer correct 

 to state the ampholyte ions (Zwitter-Ionen) are present only in 

 extremely small amounts. For the aliphatic amino-acids it seems 

 to hold true that in their "undissociated" state they are present 

 almost entirely as amphoteric ions +NH3— R— C00~, while the 

 amount of the molecular species NH2 — R — COOH must be consid- 

 ered as being negligible. Isoelectric glycocoll is to a certain extent 

 an inner salt between the NH2- and the COOH-groups which is 

 completely dissociated, in analogy with ammonium acetate consisting 

 in solution entirely of NH4+ and CHaCOO^-ions. Upon the ad- 

 dition of acid to a solution of glycocoll, the ionization of the R — 

 COO~-group is suppressed, and there are formed +NH3CH2COOH- 

 ions (just as with ammonium acetate NH4+ + CH3COOH would be 

 formed). Upon adding alkali, the ionization of the ammonium- 

 group is suppressed, and the formation of NH2— CH2 — COO~-ions 

 occur (analogously to the reaction of ammonium acetate + alkali 

 -> NH3 + CH3COO-). 



ka, hitherto designated as the acid dissociation constant, relates 

 to a process involving the ammonium group, and kb, hitherto desig- 

 nated as the basic dissociation constant, relates to a process involving 

 the COO-group. The following method of presentation^^*= appears 

 to be the simplest : 



We shall consider as the undissociated form the molecular species 

 +NH3 — CH2 — COOH, on the grounds that this ion contains the 

 greatest number of atoms, and because all other forms of glycocoll 

 may be conceived to arise by the process of splitting off H-ions from 



38a N. Bjerrum, Zts. physik. Chem. 104, 147 (1923). 



38b E. Q. Adam.s, J. Amer. Chem. Soc, 38, 1503 (1906). 



38c L. Michaelis and M. Mizutani, Zts. physik. Chem. 116, 152 (1925). 



