1904] 



Theory of Amphoteric Electrolytes. 



157 



must be constant.* From this hydrated form we may assume the 

 ions to be derived. If the substance acts as base the ions produced 

 are NH 3 .CH2.COOH + and OH~ ; if it acts as acid the ions are H + 

 and OH.NH3.CH0.COO ~, or the corresponding anhydrous ion 

 NH2.CH0.COO - . Ionisation of the internal salt would, of course, give 

 rise to the same positive and negative ions of the glycine as those 

 just mentioned. As a matter of fact, according to the dissociation 

 theory, all of these ions must exist together in aqueous solution of 

 glycine, and we shall now proceed to develope the appropriate 

 equilibrium equations. 



In general an amphoteric electrolyte H.X.OH will form the ions 

 H + , OH - , H.X + , and X.OH~, the unionised portion being either the 

 hydrous form H.X.OH or the anhydrous form X. Let the active 

 masses of the various substances for equilibrium be represented as 

 under : — 



H+ OH- XOH- HX+ HXOH X 



a b c d e f 



For equilibrium between the various positive and negative ions in 

 pairs we have 



ab = K ... (5), ac = k' a e ... (6), bd = k' b e ... (7), cd = Qf 2 ... (8). 



Here we assume for the moment that the combination of the ions 

 c and d gives rise to the anhydrous form X, in order to show from 

 the ionic equations that e is proportional to /, as has already been 

 deduced from a consideration of the unionised substances alone. 

 Multiplying (6) and (7) together we obtain 



abed = Jc'cJc'ie 2 , 



or, substituting from (5) and (8), 



KQP = k' a k' b e 2 , 



i.e., the ratio of e to / is constant, the magnitudes k' a , k' b , iTand Q being 

 all invariable. This result, that the relative proportions of the hydrous 

 and anhydrous forms are independent of the dilution, has already been 

 deduced in another way by Bredig.f 



Seeing now that the total unionised substance is always proportional 

 to e, we may rewrite equations (6) and (7) in the form 



ac = k a u (6ft), bd = k b u (7a), 



in which n represents the active mass of the total unionised solute. 

 The constants k a and k b are, of course, different from k' a and k' b , and 

 represent the dissociation constants accessible to measurement from 

 hydrolysis experiments or the like. 



* Compare Walker, ' Jour. Chem. Soe./ vol; 83, p. 182 (1903). 

 t Loe. ext. 



