VOLUTVIETEIC EELATIONS OF OZONE. 
121 
The agi’eement in the results of these experiments, made with solutions of iodide of 
potassium so widely differing, is very remarkable. We ought also to observe that direct 
experiments, performed with great care, showed that the iodine set free by the ozone in 
the primary vessel did not affect the tension of the vapour of the solution. 
Taking the mean of the above numbers, the density of ozone, as compared with that 
of oxygen, must be expressed, on the alio tropic hypothesis, by about the number 60 ; 
in other words, ozone must be a gas only about six times lighter than the metal lithium. 
If the small differences in the fifth column be due, wholly or in part, to accidental 
causes, which is far from improbable, a still higher number must, on the same hypo- 
thesis, be taken to express the density of ozone. 
In the last series of experiments, the amount of iodine set free in the solution of 
iodide of potassium was determined by analysis, and the weight of oxygen deduced 
therefi'om compared with the weight of oxygen, calculated from the volumetric change 
which had occurred in the formation of the ozone. 
We shall describe these experiments with some detail, particularly as the methods 
employed will be found applicable to other cases of gas analysis, where small changes 
in a given volume of gas have to be estimated. 
Before filling it with oxygen, a sealed capsule containing a solution of iodide of potas- 
sium was introduced into the primary vessel, while the auxiliary contained the dry gas 
only. The silent discharge was passed through the former, and the contraction care- 
fully observed. The capsule was then broken, and the solution agitated in the primary 
vessel for a few seconds. The siphon tube was next cut off, and the liquid carefully 
washed out and analysed by means of a weak solution of sulphurous' acid, the exact 
strength of which had been immediately before determined by observing the amount 
required to decolorize a solution containing a known weight of iodine. 
In some of the experiments the solution of iodide of potassium was slightly acidu- 
lated, in the others it was neutral. In the latter case it was acidulated before being 
analysed. The results were the same, whether the solution was taken in the neutral 
or in the acid state. For, although oxygen gas acts upon an acid solution of iodide of 
potassium, the action requires time, and the contact in this case was only continued for 
a few seconds*. 
The formula by which we calculated the results of these experiments may be thus 
investigated. 
Lety*, ^(fig. 1) be the mean level of the acid in the legs of the siphon tube ; e the 
levels at any time, t being the temperature, and 11 the barometric pressure corrected for 
* Baijmebt has objected on this ground to some of the experiments in a former communication made by 
one of us to the Society. AYe have foimd that, in the circumstances in which those experiments were per- 
formed, about one-twentieth of the effect was due to this cause ; but as the oxygen acting on the solution 
of iodide of potassium set free its equivalent of iodine, the equality of the numbers given in that paper could 
not he disturbed by this action. AYe have, since that time, by additional experiments, fully confirmed the 
statement that no water is produced in the destruction of electrolytic ozone by heat. 
