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Scientific Proceedings (129) 



that the velocity of this reaction varies inversely as (hydrogen 

 ion concentration)^ 2 and further that it becomes of appreciable 

 magnitude on shaking vigorously in air when the reaction is more 

 alkaline than about P H 7.8. Apparently hydroquinone will not 

 absorb oxygen until the alkalinity is sufficient to cause phenolic 

 ionization through salt formation. 



In order to get more definite information on the stability 

 of the quinhydrone electrode potentials to air over a wide range 

 of P H , we have carried out careful parallel electrometric titra- 

 tions at 25° C. of 0.2 molar hydrochloric acid, acetic acid, po- 

 tassium acid phosphate and borate buffer mixtures with 0.2 

 molar caustic soda, using in one case the hydrogen electrode 

 and in the other the quinhydrone electrode in the presence of 

 air. We have directed particular attention to the point in the 

 alkaline range at which the quinhydrone electrode first begins to 

 give values that are different from those given by the hydrogen 

 electrode. 



The result of these experiments, some of which are repre- 

 sented graphically in the figure, may be summarized as fol- 

 lows : 



1. The quinhydrone electrode furnishes an admirably simple 

 and rapid way of determining the end points and titration curves 

 of acids that are stronger than monopotassium phosphate; i.e., 

 having values of K 2 greater than 10" 7 . The method should be 

 valuable in determining the ionization constants of unsaturated 

 acids. 



2. The divergence between the hydrogen electrode and the 

 quinhydrone electrode values is negligible up to P H 8.0. 



3. Since the quinhydrone electrode is a one phase system 

 and therefore attains electrode equilibrium promptly, it can be 

 used for the determination of electrometric end points by con- 

 tinuing the titration curve beyond P H 8, provided that one works 

 rapidly and avoids undue shaking in air. See boric acid curve 

 for concordance beyond P H 8.0. 



We are extending these investigations to the substituted hydro- 

 quinone-quinone systems with the object of choosing appro- 

 priate electrode materials for more alkaline ranges and particular- 

 ly for the determination of the reaction of oxygenated blood. 



