THE CHEMICAL PROCESSES IN PLANT RESPIRATION 105 



properties of peroxides. Contrary to the opinion of Traube, 

 Bach considers the direct formation of various organic peroxides 

 to be possible. Thus the latter process can take place without 

 an intermediate formation of hydrogen peroxide and even with 

 the complete exclusion of water. A. Engler^ also proposed this 

 theory entirely independently of Bach. 



According to Bach-Engler, certain substances called autox- 

 idators can fiz atmospheric oxygen directly. This process may 

 be expressed by the following schematic equation : 



A + O2 = AOo, 

 e.g. H + H + Oo = H0O2. 



This reaction is often made possible by the separation of the 

 autoxidator A from a molecular complex through the interven- 

 tion of certain substances (pseudo-autoxidators). Thus e.g.: 



Zn + 2H0O = Zn(0H).2 + H + H (see above) 



The moloxides formed by the autoxidation then decompose 

 while they bind half of the absorbed oxygen to remaining mole- 

 cules or atoms of the autoxidator as is the case in the combus- 

 tion of hydrogen. 



(I) H + H + O2 = H0O2 



(II) H + H + H2O2 - 2H2O. 



It is evident that one-half of the hydrogen is oxidised to water 

 by atmospheric oxygen but that the other half is oxidised by 

 the oxygen of hydrogen peroxide. The moloxides formed by 

 the autoxidation are always more powerful mediums of oxida- 

 tion than molecular oxygen of the atmosphere. Consequently 

 not only surplus quantities of the autoxidator but also other 

 substances are oxidised by moloxides. In this the velocities 

 of the respective reactions play a guiding role. Thus the 

 oxidation of indigo white along with the autoxidation of triethyl 

 phosphine or benzaldehyde may be represented by the fol- 

 lowing reactions: 



> Engler, A. und Wild. Ber. d. chem. Ges. 30: 1669. 1897; Engler und Weissberg. 

 fbid. 31 : 3055. 1898; 33: 1097. 1900; Krit. Studien iiber die Vorgange d. Autoxydation. 

 1904; Engler und Herzog. Z. f. physiol. Chem. 59: 327. 1909; Engler. Z. f. Elektro- 

 chem. 18: 945. 1912; and others. 



