METHODS FOR THE ELECTROMETRIC DETERMI- 

 NATION OF THE CONCENTRATION OF HYDRO- 

 GEN IONS IN BIOLOGICAL FLUIDS 



K. A. HASSELBALCH 

 (Finsen Institute j Copenhagen, Denmark) 



(WITH PL ATE 3) 



The great importance of the reaction of the medium in many 

 biological processes has long been appreciated and has led to a series 

 of more or less successful endeavors to measure its degree. It is 

 only within the most recent years, hovvever, that the methods of 

 measurement have been so far perfected as to enable us to say that 

 the "true reaction" of biological fluids can now be measured with 

 sufficient accuracy for most purposes. 



This is due, in the first instance, to the insight into the nature 

 of the question which has been derived from the electrolytic dis- 

 sociation theory : the " true reaction " of a liquid is not determined 

 by its concentration of free acid or alkali, but by its concentration 

 of hydrogen and hydroxyl ions — or, practically speaking, by the 

 concentration of hydrogen ions alone, for the product of the two 

 is a constant. Since the dissociation of acid or base in a liquid, and 

 thereby also its hydrogen-ion concentration, is in many respects 

 dependent on the nature of the dissolved substances, the true reac- 

 tion of the liquid cannot be determined by merely measuring the 

 quantity of alkali or acid that must be added to a certain quantity 

 of the liquid in order to effect a particular change of color in the 

 indicator used. As is now known, such a titration shows only that, 

 at the moment, a certain hydrogen-ion concentration, to which the 

 indicator reacts, has been reached, the original hydrogen-ion con- 

 centration of the liquid remaining unknown. 



Thus, the determination of the true reaction of a liquid requires 

 some procedure by which the concentration of the hydrogen ion is 



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