152 
The Lines of Discovery in the 
[March, 
have shown to be in reality only oxygen in a peculiarly 
modified form, &c.” . . . . 
The hypothesis herein stated, that ozone is tnatomic 
oxygen, necessarily involved the assumption of such a cor- 
responding difference in density, and other physical proper- 
ties, — differences admitting of exadt quantitative proof 01 
disproof. Such were the experimental difficulties in the 
wav, however, that it was not until i860 that an investiga- 
tion was made into the volumetric relations of ozone to 
oxygen. The experiments of Professors Andrews and i ait 
then resulted in establishing that when perfeftly pure and 
dry oxygen is converted into ozone, under the influence of 
the silent eledtric discharge, it becomes more dense, the 
amount of contradlion being proportional to the quantity of 
ozone produced ; also that when ozone thus condensed is 
exposed for a short time to a temperature of 270° to 300 it 
expands to its original volume. That the increase in density 
was exadtly proportional to the amount of ozone formed 
was proven by an analysis of the contracted gas by means 
of potassium iodide. The amount of iodine in every case 
set free was precisely equivalent to the weight of a volume 
of oxygen equivalent to the volume of the contraction which 
the oxygen had experienced in the process of ozonation. 
The same laws were demonstrated to hold good with regard 
to electrolytic ozone, not only by these authors (i860), but 
also by Von Babo and Claus and by Soret (1863). 
Andrews and Tait found great difficulty in reconciling the 
theory of the allotropism of ozone with their expeuments, 
inasmuch as the oxidation of a body like mercury, potas- 
sium iodide, &c., was effected without any diminution in 
the volume of the contrafted gas. In other words, the 
density of the allotropic oxygen concerned in this oxidation 
was apparently infinite. They sought therefore to explain 
the origin of ozone by the assumption of a decomposition ot 
Butrin 1861 Odling put forth the interpretation that ozone 
was a compound of oxygen with oxygen, the combination 
being attended by a contraction. Hence if one portion ot 
the combined or contracted oxygen were absorbed by an 
oxidisable body, the other portion would be set free and by 
its liberation might expand to the initial volume. He like- 
wise suggested that this contraftion might consist in the 
condensation of three volumes of oxygen into two volumes, 
not because this ratio was the only one which would explain 
the volume and density relations, so far as then known, bu 
because, on the hypothesis of the dual nature of oxygen, 
