15 
no means a new one, nor clid it originate with Van’t Hoff. As a 
matter of fact, it had been promulgated by Clausius ( 119 > 120 ’ 121 ) upon 
theoretical grounds and as affording a simple explanation of the dif- 
ferences between active and common oxygen, as early as 1857 to 
1863, and has since been employed by other physicists (among them 
Schuster, Yon Helmholtz, Richarz, Thomson, and others), as affording 
a simple explanation of the phenomena observed in the electrification 
of gases, including oxygen, and in the condensation of aqueous vapor 
in the steam jet as the result of the oxidation of various substances 
in close proximity thereto. Thus Clausius ( 119 ) in a communication 
entitled “Ueber die Art der Bewegung, welche wir Warme nennen , 11 
had put forward the suggestion that in common oxygen the atoms 
are not detached, but combined in twos to form molecules, a conclu- 
sion which also derived support from the views of Gerhardt on the 
constitution of gaseous molecules. He reached the conclusion there- 
fore that the active oxygen which common oxygen sometimes con- 
tains and which at this time was not distinguished from ozone, con- 
sists not of atoms combined in pairs, but of single atoms distributed 
among the molecules of the element in its ordinary form, and in a 
later communication on the difference between active and common 
oxygen ( m ) this author reiterates the view that common oxygen 
consists of paired atoms, and active oxygen of unpaired atoms, and 
further that the two atoms which go to form ordinary oxygen are in 
oppositely electrified states. Hence, according to Clausius, the 
molecule of ordinary oxygen is diatomic, containing one electro- 
positive and one electro-negative atom. On the other hand, active 
oxygen consists of unpaired atoms which may exist either free or 
loosely bound together (lose gebunden). If electro-negative, these 
atoms form ozone; if electro-positive, antozone. 
Long afterwards it was pointed out by Schuster ( 392 ) in connec- 
tion with his investigations on the electrification of gases that the 
passage of electricity from one molecule to another in a gas is always 
accompanied by an interchange of atoms composing the molecule. 
According to this author, physicists of the Faraday-Maxwell school 
had long considered it probable that the conduction of electricity 
through gases is due to something similar to the electrolytic conduc- 
tion in solutions, or, in other words, to the migration of ions under 
the influence of the current. 
Similarly, according to Von Helmholtz and Richarz ( 208 ) the inter- 
esting phenomena observed during the electrification of a steam jet 
and the influence of certain chemical reactions on condensation occur- 
ring in the jet, can only be explained on the supposition that molec- 
ular oxygen or the gaseous substances in the immediate vicinity of the 
jet are dissociated to a greater or less extent into free atoms or ions, 
or into molecular groups containing free valences, and that these are 
