128 
DE. AXDEEWS AXD PEOFESSOE TAIT OX THE 
in an allotropic form, it is necessaiy to assume that its density immensely exceeds that 
of any known gas or vapour ; being, as we have seen, according to the first and second 
series of experiments (§§ 3 and 4), from fifty to sixty times that of oxygen, and accord- 
ing to the third series (§4) absolutely infinite. Even the former results would make 
it only six times less dense than the metal lithium, and would place it rather in the 
class of solid or liquid bodies than of gaseous. The question may then be fairly pro- 
posed, — Can this singular body, at common temperatures, be actually a solid or h'quid 
substance, whose particles, in an extremely fine state of subdivision, are suspended in 
the oxygen with which it is always mixed 1 This question will scarcely, we think, admit 
of an affirmative answer. Not only does ozone, mixed as usual with oxygen, pass through 
several U-tubes containing fragments of pumice moistened with sulphuric acid, but it 
exhibits its characteristic reactions when left for many hom's in tubes of this kind. 
Besides, there is not the slightest cloud \isible in a tube filled uith ovygen, even when 
one-twelfth of the gas has been converted into ozone, nor does any deposit appear after 
long standing. 
Ozone may be formed under conditions which exclude the possibihty of its containing, 
as a constituent, any element except oxygen, or the elements of oxygen, if that body 
should hereafter be shown to be compound. As has been before stated, om expeiiments 
may be reconciled with the allotropic view and an ordinary density, but still one greater 
than that of oxygen, if we assume that when ozone comes into contact with such sub- 
stances as iodine, or solutions of iodide of potassium, one portion of it, retaining the 
gaseous form, is changed back into common oxygen, while the remainder enters into 
combination ; and that these are so related to one another, that the expansion due to 
the former is exactly equal to the contraction arising from the latter. AVe do not, how- 
ever, consider this supposition to be by any means probable, nor can it be easily recon- 
ciled with the results (§ 3) obtained when mercury acts on ozone. 
If we consider the conditions under which ozone is formed, we shall find them to be 
different from those which produce allotropic modifications in other cases. Such 
elements, for example, as phosphorus or sulphur, are modified by the action of heat, 
and not by the electrical discharge. It is true, at the same time, that the destruction 
of ozone, or, on the allotropic view, its reconversion into oxygen, by exposure to a tem- 
perature of 270° C., is apparently analogous to that action of heat whereby common 
phosphorus is converted into the red variety. 
Without rejecting the allotropic constitution of ozone, although the results of our 
volumetric experiments are certainly difficult to reconcile with it, it may not be unin- 
structive to consider whether the facts already known admit of a different explanation. 
As ozone is formed from pure and dry oxygen by the electrical discharge, if it is not an 
allotropic form of oxygen, the latter must be either a mechanical mixture of two or more 
gases, or it must be a compound gas. It is perhaps scarcely necessary to consider the 
former hypothesis, according to which, oxygen, in its ordinary state, would be a mecha- 
nical mixture, as atmospheric air is a mixtine of nitrogen and oxygen. The contraction, 
