H. ECKWEILER, H. M. NO YES, AND K. G. FALK 303 



acids. The vertical differences between the two curves also show the 

 extent of base-combining property or enol-lactim tautomerism. 



The method of plotting pH values against the amounts of acid and 

 alkali added is also open to question, but it appears to be the best 

 method which is available. Placing the emphasis on the hydrogen ion 

 concentration gives a one-sided chemical perspective, especially for 

 the alkaline solutions. The suggestion of Wherry^^ to use pH 7.0 

 as the zero point and to calculate values from this as a logarithmic 

 function is not practicable as indicated by Clark.^^ The suggestion 

 may be made to determine a zero point for each substance, this point 

 to be identical with the isoelectric point, and to measure acidity and 

 alkalinity from this point logarithmically in terms similar to the pH 

 scale. This would fix a characteristic property for each substance 

 as the starting point. The practical difficulty lies in the determina- 

 tion of the isoelectric point, as its experimental measurement is prob- 

 ably the least accurate point of most titration curves. 



The general chemical nature of amphoteric electrolytes will be taken 

 up briefly here. These substances, depending upon conditions, ion- 

 ize or react as salts in which the complex ampholyte component acts 

 as the positive constituent or as the negative constituent. Loeb^' 

 has recently pointed out clearly and convincingly, and has presented 

 considerable experimental evidence to show, that the positive ampho- 

 lyte ion (of gelatin, for example) is fundamentally different from the 

 same ampholyte as negative ion. The relative acidity and alkalinity 

 of the solution govern these changes, the ionization taking the 

 different courses in more acid or more alkaline solutions (the tran- 

 sition point will be taken up presently) . In order to account for the 

 different processes of ionization, it appears to be necessary to assume 

 that the molecule (unionized) is different in the two cases. In order 

 to ionize so that the complex is part of the cation, the molecule must 

 possess a structure different from that of the molecule which ionizes 

 with the complex as part of the anion. This difference in structure 

 may be due to an isomeric rearrangement, possibly tautomeric, to a 

 difference in the action of the solvent involving hydration, or to some 



17 Wherry, E. T., /. Washington Acad. Sc, 1919, ix, 305. 



18 Clark,2 p. 28. 



19 Loeb, J., /. Gen. Physiol., 1918-19, i, 39, 237, 363, 483, 559; 1919-20, ii, 87. 



