DR. ANDREWS ON THE CONSTITUTION AND PROPERTIES OF OZONE. 
11 
spark, and nothing is easier than to convert the whole of a given volume of oxygen 
into ozone in presence of a solution of iodide of potassium. The next step in the 
inquiry was therefore to ascertain whether ozone derived from electrolysis, from the 
action of the electrical spark, and from the oxidation of phosphorus, exhibited a per- 
fect identity in all its properties. 
One of the most remarkable properties of ozone is its destruction by heat, or rather 
its conversion by heat into ordinary oxygen. To ascertain the temperature at which 
this change occurs, the vessel D, fig. 4, was placed in a bath of mercury, and the gas 
examined as it escaped, without previously passing it through the rest of the apparatus. 
On heating the mercurial bath, the amount of ozone, as determined by its action on 
iodide of potassium paper*, did not notably diminish till the temperature attained 
230° C. It still continued, however, very intense till the thermometer rose to 235°. 
Between that point and 240° the ozone reactions entirely disappeared, when the ozone 
was in a very dilute state ; but when more concentrated, slight traces of ozone could 
still be discovered, which no doubt would have also disappeared if the current of 
gas had been passed very slowly. Time is in fact an element in this action. Even 
at the temperature of 100° C. ozone is slowly destroyed. Two similar tubes were 
filled, at the same time, and by the same process, with ozone diluted as usual with 
oxygen, and afterwards hermetically sealed. One of these tubes was maintained 
for three hours in a vapour bath at 100°C., the other was not exposed to heat. On 
examining both tubes at the end of the time, it was found that the ozone in the tube 
which had been exposed to heat was perceptibly less than in the other. I have no 
doubt that, even at the common temperature of the air, ozone preserved in an herme- 
tically sealed glass tube would gradually change into common oxygen. I made an 
experiment of this kind two or three years ago, which resulted in the disappearance 
of the ozone, but I do not remember the source from which the ozone was derived, 
nor what precautions were taken to dry the gas. 
On the other hand, ozone brought directly into contact with the vapour of water 
at the boiling-point is instantly destroyed. 
To obtain a continuous stream of ozone from the action of the electrical spark, a 
current of pure oxygen gas, obtained from the decomposition of the chlorate of 
potassa, and purified and dried by passing through tubes containing hydrate of 
potassa and sulphuric acid, was exposed to a rapid succession of electrical sparks. 
To obtain a sufficient stream of electricity, an electrical machine, firmly screwed 
down to the floor of the apartment, was connected by a belt with a heavy cast-iron 
wheel, 40 inches in diameter, contained in a frame which was also firmly secured to 
the floor. By this arrangement, the machine could be worked for any length of time 
* Bibulous paper which has been dipped into a solution of iodide of potassium of moderate strength and 
afterwards allowed to dry, hut still retaining its hygrometric moisture, is the most convenient test of ozone. 
If it be exposed to a continuous current of dry air, it should be removed from time to time and its hygrometric 
moisture restored. 
