308 Prof. A. J. Ewart. Comparative Study of Oxidation by 



H 2 2 , but no other oxidase reaction. At five months it produced a weak 

 decomposition of H 2 2 but no other oxidase reaction. At the eighth month 

 the decomposition of H 2 2 became practically imperceptible. In this case, by 

 gradual attenuation, the same oxidase became first a " peroxidase " and 

 finally a pure " katalase." 



Paraphenyknediamine Test for Oxidase. 



As is well known, this substance forms an exceedingly sensitive test for 

 oxidases, and goes through a remarkable series of colour changes under 

 their action. The full series of colour changes is green, then blue, then 

 brown, then violet, darkening, and in strong solutions forming a black 

 precipitate, but according to circumstances, or if the oxidase action is very 

 intense or very feeble, one or more of these changes may be omitted or 

 modified. The chief objections to the reagent are the readiness with which 

 decomposition or oxidation takes place naturally and its excessive sensitivity. 

 Grass* recommends tbe use of the tartrate of paraphenylenediamine (ursol 

 tartrate). This dissolves readily in water, and a pinch of tbe dry salt can 

 be dissolved in water for each test. Any colour change in the clear solution- 

 is readily perceptible, and there is no alcohol present to interfere with the 

 reaction. Further the dry tartrate keeps indefinitely. It is, however, not so 

 sensitive and responds more slowly. On the other hand, it will often give 

 ■a full colour series, where the alcoholic solution of paraphenylenediamine 

 gives a single colour change only, which, when slow, may be confused with 

 its natural slow darkening on exposure to air. 



Neither alcoholic paraphenylenediamine nor the tartrate respond to all 

 •oxidising agents. Thus nitric acid appears if anything to exercise a 

 reducing rather than an oxidising action. It does not produce any colour 

 .sequence, and if a little dilute nitric acid is added to potato pulp turned 

 green or blue by ursol tartrate and peroxide of hydrogen, the pulp imme- 

 diately becomes pale in colour. 



The reactions with those metallic salts capable of turning guaiacuin blue 

 •are of interest. 



Silver nitrate forms a grey precipitate, slowly darkening, with alcoholic 

 paraphenylenediamine, but in the presence of hydrogen peroxide the colour 

 sequence, green, brown, ruby, violet is given, and the same is given with 

 silver nitrate and ursol tartrate, whereas in the presence of hydrogen peroxide 

 the change is from green to brown only. Ferric chloride gives the full colour 

 sequence (green, brown, violet, or purple) with alcoholic paraphenylenediamine, 



* 'Biologie der Enzyme,' 1912. 



