LAWS OF ELECTROLYTIC DISSOCIATION 



71 



(see figure 8) depends upon the same value. Tiie sharply defined 

 minima of the aminobenzoic acids corresponds to 



p-aminobenzoic acid ka X kb = 3 X 10~'^ 



??i-aminobenzoic acid ka X kb = 2 X 10~^^ 



On the other hand, it has long been known that such ampholytes 

 as tyrosine and arsenious acid have quite poorly defined (flat) 

 maxima. These are soluble in strong acids and bases but quite 

 insoluble in the wide intermediate range of reaction. No sharply 

 defined optimum in relation to the pH of solution is to be found in 

 this case, and the small order of the corresponding values of the 

 dissociation constants products is to be noted: 



Tyrosine ka X kb = 1 X IQ-^o 



Arsenious acid ka X kb = 6 X 10"^* 



Employing the above method Michaelis and Davidsohn obtained 

 the following values: 



o-Aminobenzoic acid. 

 m-Aminobenzoic acid 

 Aspartic acid 



1.21 X 10-5 

 1.63 X 10-5 

 1.5 X 10-" 



2.33 X 10-12 

 1.22 X 10-" 

 1.2 X 10-12 



I calc. 



1.7 X 10-" 



8.8 X 10-5 

 8.7 X 10-" 



I found 



1.6 X 10-" 

 6.3 x'lO-5 

 9.3 x'lO-" 



It may he of interest to compare the results obtained by various in- 

 vestigator's, partly for varying temperatures {table 15). 



The agreement among the above figures is quite good, especially 

 when they are reduced to the same temperature. The uncertain- 

 ties which existed formerly in regard to some of the figures were 

 due to the fact that the influences of salt concentration had not been 

 properly understood and corrected for. With due consideration 

 for some of the newer principles the lack of agreement among some 

 of the older figures will disappear. This applies to all dissociation 

 constants, and not only to those of the ampholytes. 



Of all of the above ampholytes only arginine, lysine and his- 

 tidine have (in their second stage of dissociation) larger kb values 

 than those of ka; the isoelectric point of only these ampholytes is 

 at an alkaline reaction. 



