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



oxidation is, in part at least, a direct one and hydrogen peroxide diminishes 

 the oxidising action. If hydrogen peroxide is added to very dilute potassium 

 permanganate, a colourless liquid is formed and the evolution of oxygen soon 

 ceases. With stronger solutions the liquid is hrown, and contains an oxide 

 capable of continuous oxidase and katalase action. 



The Tables show further that chromium and iron can act as oxidases when 

 present in the form of acids. 



In general a feeble oxidase acts feebly on all the substances tested, and the 

 order of sensitivity to oxidases is : guaiacum, ursol tartrate, pyrogallol, 

 hydroquinone, gallic acid, gallotannic acid, tyrosin. There are, however, 

 various exceptions. Thus chromium chloride and manganese chloride give 

 a blue with guaiacum, and copper sulphate does the same in the presence of 

 H 2 2 , but all three give direct oxidase reactions with ursol tartrate, 

 pyrogallol, etc. Where there is a strong tendency to precipitation between 

 the oxidase and oxidant as in the case of lead acetate or of ferric chloride 

 and hydroquinone, the oxidase action may be retarded or prevented. In the 

 case of potassium phosphate the feeble oxidase properties are evidently due 

 to the phosphoric acid and not to the potassium. Further, the chlorides, 

 nitrates or sulphates of the same metal are not necessarily equally powerful 

 oxidases, chlorides apparently surpassing sulphates (see copper) and nitrates 

 chlorides. Thus cobalt chloride shows no oxidase properties with or without 

 H 2 2 . Cobalt nitrate slowly browns pyrogallol and hydroquinone in the 

 presence of H 2 2 but is inactive to guaiacum, ursol tartrate, and tannic acid. 



Lead nitrate shows no oxidase action, whereas lead acetate exhibits a 

 peroxidase action. Yellow potassium chromate has similar oxidase properties 

 to potassium bichromate except that it causes tannic acid to brown rapidly 

 in the absence of H 2 2 , probably owing to the alkaline nature of the basic 

 chromate. 



The Nature of Oxidases. 



The fact that certain plant oxidases contain oxidase metals, such as 

 manganese in laccase, has long been known and certain oxidases, as for 

 instance, tobacco oxidase, can be boiled without being destroyed. Woods* 

 considers that this is due to the oxidase existing as a zymogen from which 

 on cooling the oxidase is reproduced. The supply of zymogen can, however, 

 hardly be unlimited, and, since the boiling can be repeated more than once 

 without destroying the oxidase, it must itself be resistant to heat. 



According to Bach and Chodatf the oxidases form three distinct groups of 

 ferments, namely : — 



* 1 Bull. U.S. Dept. Agric.,' vol. 18, p. 17. 

 t 'Biochem. Centralbl.,'" 1903, p. 141. 



