28 
These experiments afford quantitative proof of the peroxide theory 
of oxidation. 
A similar case has been studied by Bamberger ( 34 ), who showed 
that when an aqueous solution of phenylhydroxylamin is exposed 
to the air it is oxidized to nitrosobenzene with the formation of hy- 
drogen peroxide, thus: 
c 6 h 5 nhoh + o 2 = c 6 h 5 no + h 2 o 2 . 
Thus three grams of phenylhydroxylamin in 40 grams of water 
yield, after treatment with a current of air for seventy hours, 2.5 
grams of azoxybenzene. 
Finally, during the last ten or twelve years Engler and his co- 
workers ( 164 > 165 ) have done a great deal to extend the peroxide theory 
of oxidation. According to these authors every oxidation consists 
CD 
primarily in the union of molecular oxygen with the substance under- 
going the oxidation, and that, contrary to Traube, the primary product 
of the aut oxidation is not necessarily hydrogen peroxide but a per- 
oxide of the substance undergoing oxidation. Thus when rubidium 
burns in air it is converted quantitatively into rubidium peroxide — 
Rb + 0 2 = Rb0 2 , 
and, as shown by Baeyer and Villiger ( 33 ), when benz aldehyde is ex- 
posed to oxygen or air it is first converted into benzoyl-hydrogen 
peroxide, thus: 
c 6 h 5 cho + o 2 = C 6 H 5 CO.O.OH. 
Engler and his coworkers have also pointed out that hydrogen per- 
oxide, so frequently encountered in processes of autoxidation, may be 
produced in several entirely different ways; first, as the primary 
product of the autoxidation- — as, for example, the burning of hydrogen 
or by the action of oxygen on the hydrogen liberated at the cathode 
during electrolysis, or in the oxidation of substances like indigo-white 
and hydrazobenzene, which contain labile hydrogen atoms, thus: 
H- 
H- 
+ 
-O 
-O 
=h 2 0 2 , 
and 
IkiIcL 2 -f0 2 — Iti A H 2 0 2 ; 
or, as Traube pointed out, it may result from any autoxidation in 
which water is essential to the oxidation; thus: 
Zn + ho] t H + ° 2 = Zn(0H) 2 + HA - 
According to Engler, the true autoxidator in such processes is the 
hydrogen ion, while he looks upon the zinc as the pseudo-autoxidator. 
Secondly, as pointed out by Engler, hydrogen peroxide is frequently 
