J 311 



Tn the work of Michaelts attention is drawn to the fact, that a 

 representation of the imdissooiated part of an amphoteric eleclrol^'te 

 as a function of the //-ion concentration, taking as abscissae the 

 values of pH, instead of those of the //-ion concentration itself, 

 presents the advantage of prociucing curves of far nioie characteristic 

 type. 



His "rest-curves" are derived as foUows: 



Calling {A) tlie total concentration of the amphoteric electrolyte, 

 f.4+) that of the kation, {A ) thai of the anion, the concentration 

 of the undissociated rest {x) is: 



According (o the law of mass action we have in the solution the 

 two equations of equilibi'ium : 



{A-^){OH) -=h{x) 

 {A ){H) =ka{x). 



Therefore 



from which 



(,,.) = (A) — (x) — ^ (^) — ^. 







{H) {OH) 



{x) 

 The undissociated fraction o^ — becomes 



{A) 



1 



^ {H) {ÖH) 



For (he -«ake of comparison the curves, drawn by Michaki-is for 

 different values of the dissociation-constants /„ and //,, are reproduced 

 in Figure 4. 



The resemblance of our diagram of ui-ease activity in to these 

 curves is obvious. 



It is to be borne in mind, however, that the relative dimensions 

 of pij and () are, of course, arbitrary in these figures. 



Evidently, at least with decreasing /;//, where the experiments 

 could be pushed farther than on the other side, in tends not to zero, 

 but to a value of about 18. 



The interpretation of these i-esults is therefore as follows: 



Urease is an amphoteric electrolyte, whose activity is greatest 

 when undissociated. When the asymptote, to which ni ap[)roaches, 



85* 



