18 
bly, in the luminous zone of flames and combustible gases, and also in 
the flame of burning alcohol. Similarly it was observed by Yon 
Helmholtz ( 207 ) a that Wurster’s paper is colored blue in the neighbor- 
hood of a glowing platinum spiral, pointing to the presence of active 
oxygen in the surrounding atmosphere. 
It has also been shown by Elster and Geitel ( 158 ) that the electrifi- 
cation of gases is brought about by glowing bodies. They ( 159 ’ 160, 161, 
162 ) likewise observed that air in which moist phosphorus is oxidizing 
conducts the electric current, while ozone does not conduct it. Hence 
they conclude that this conduction is accomplished by ions, or split 
oxygen molecules, and that the production of ozone must result from 
the previous splitting of the oxygen molecule. That ozone differs 
essentially in its conduct from atomic oxygen is also indicated by the 
fact that ozone itself has no effect on the steam jet, whereas decom- 
posing ozone, like decomposing oxygen, affects it most actively. ( See 
also Y on Helmholtz and Richarz ( 208 ), pp. 194-195, and also Meissner 
It is evident, therefore, from these observations and others of 
similar import, that the dissociation of oxygen, whereby active or 
ionic oxygen is produced under a great variety of conditions, had been 
recognized for some time before it was employed by Yan’t Hoff in 
explanation of oxygen activation. In reality the idea that in oxygen 
gas we have an equilibrium represented by the equation, O 2 ^20, 
dates from the time of Clausius. On the other hand, we are indebted 
to Yan’t Hoff and his coworkers ( 214, 236 ), especially to Ewan ( 169 ), for 
experimental proof that in the oxidation of acetic aldehyde the 
velocity of the reaction is as indicated by the above equation, propor- 
tional to the square root of the oxygen pressure, and to Yan’t Hoff 
himself for experimental proof than an atom of oxygen is rendered 
active for every two atoms of phosphorus oxidized, irrespective of the 
nature of the acid of phosphorus produced. 
The fact that oxygen can distribute itself equally between two 
oxidizable substances, one of which is autoxidizable, while the other 
is not, is supported by a vast amount of experimental evidence, all of 
which, to a degree at least, supports Ahrn't Hoff’s hypothesis. Thus, 
to take an actual case studied by Jorissen ( 234 ’ 235, 236 )' 131.5 milligrams 
of tri-ethyl phosphine were found to require 17.8 milligrams of oxygen 
to completely oxidize it in the sense of this equation, 
(C 2 H 5 ) 3 P + O = (C 2 H 5 ) 3 PO, 
whereas when this same amount of this compound was oxidized in 
the presence of 2 grams of sodium indigo-sulfonate, 35.3 milligrams 
of oxygen were consumed, or approximately twice as much. Similar 
results were obtained by this observer with propionic and benzalde- 
hydes. ( See also Yan’t Hoff ( 215 ). 
a See also Gorup-Besanez ( 196 ). 
