﻿THE MEASUREMENT OF OXIDATION POTENTIAL AND 

 ITS SIGNIFICANCE IN THE STUDY OF 

 OXIDASES 



(with two figures) 

 In the course of a series of investigations on the role of plant 

 oxidases, the writer has found it necessary to follow with accuracy 

 the progress of various oxidation reactions. The best method of 

 accomplishing this is found undoubtedly in the measurement of 

 the oxidation potential of the solutions entering into the reactions. 

 Since this method has never been employed in the study of biological 

 processes, and has only a limited use in physical chemistry, a 

 description of the apparatus as modified by the writer may be of 

 interest. 



According to electro-chemical conceptions, oxidation is the 

 process of taking on positive charges of electricity or the giving 

 up of negative charges of electricity. Hence if we have a measure 

 of the tendency of a substance to take on or give up electrical 

 charges, we may determine the oxidizability of that substance. 



If we consider a hydrogen electrode, that is, a strip of indiffer- 

 ent metal, such as platinum, platinized to increase its surface and 

 charged with hydrogen gas, dipping into a solution containing 

 hydrogen ions, we see that there will be a potential difference 

 between the electrode and the solution. The hydrogen on the 

 electrode will give up to the solution positively charged hydrogen 

 ions until equilibrium with osmotic pressure of the hydrogen ions 

 in solution is reached. If two such electrodes dip into solutions 

 containing hydrogen ions at different concentrations connected by 

 a liquid (as through a siphon), the potential of the cell is equal 

 to the algebraic sum of the two single potentials, and is expressed 

 by the formula 



