I04 PLANT RESPIRATION 



benzaldehyde leads to the formation of labile peroxides, in 

 connection with which a whole molecule of oxygen is absorbed 

 and so no dissociation of oxygen occurs. On the strength of 

 these results the dissociation theory is also to be considered too 

 weak to hold. 



The theory of peroxide formation developed by Traube,^ out 

 of which later grew the modern theories of Bach-Engler and von 

 Wi eland, proved more fruitful. Traube assumed that in all 

 autoxidations hydrogen peroxide is first formed and finally 

 there occurs the fixation of a whole molecule of oxygen and the 

 formation of organic peroxides. Thus Traube- proved that 

 not only slow oxidation of hydrogen but also the combustion of 

 hydrogen in the flame depends on the formation of hydrogen 

 peroxide.^ The oxidation of metallic zinc in alkaline solution 

 is also accompanied, according to Traube's statements,"* by an 

 intermediate formation of hydrogen peroxide. 



(I) Zn + 2H2O = Zn(0H)2 + 2H 



(II) 2H + Oo = H2O2 



(III) Zn + H.Oo = Zn(0H)2. 



Traube assumed that all autoxidations are possible only in the 

 presence of water, since hydrogen peroxide can be formed only 

 under this condition. The Traube theory was then remodelled 

 by Bach and Engler. Bach^ assumes that in processes of autox- 

 idation the oxygen is active only in the form of unsaturated 

 molecules — O — O — . Fixation of two atoms of oxygen always 

 occurs by the formation of so-called moloxides which possess the 



'Traube, M. Ber. d. chem. Ges. 15: 222, 659, 2491. 1882; 16: 123, 463. 1883; 18: 

 1877, 1887, 1890, 1894. 1885; 19: iiii. 1886; 26: 1471. 1894- 



^Traube, M. Ber. d. chem. Ges. 18: 1897. 1885; ig: iiii. i886; Engler. Ibid. 33: 

 1 109. 1900. 



' In my laboratories this reaction is used as a lecture demonstration. A long rubber tube 

 is attached by one end to a hydrogen generator and the other end is fitted with a finely 

 drawn-out glass tube. The hydrogen is passed through the tube and lighted as it escapes 

 from the capillary opening. In this way there is obtained a slender flame with which a deep, 

 narrow hole is bored in a block of ice. In this the flame is frequently extinguished by melting 

 water and must be relighted with a burner kept nearby. Part of the intermediate products 

 of the hydrogen combustion are retained in the hole in the ice by rapid cooling before they 

 are destroyed, and are collected with the water in a tumbler set beneath the hole. In this 

 water the presence of hydrogen peroxide may then be demonstrated by the release of iodine 

 from potassium iodide or by other specific reactions. Cf. Engler. Ber. d. chem. Ges. 33 ; 

 1109. 1900. 



•Traube, M. Ber. d. chem. Ges. 26: 1471. 1894- 



6 Bach, A. Compt. rend. 124: 951. 1897; Monit. sci. (IV) 11: 479. 1897; Arch. sci. 

 phys. et nat. (IV) 35: 240. 1913- 



