82 R. THRELFALL AND FLORENCE MARTIN. 
bubble of oxygen on reaching the exhausted tube was therefore 
reduced in pressure over the range of instability. After six 
hours, no change having taken place in the potassium iodide 
solution, the apparatus was filled with oxygen at atmospheric 
pressure and left for several hours. This experiment was repeated 
during three days, that is to say the oxygen was passing through 
the apparatus at a pressure of 0.25 mm. for 17-5 hours altogether. 
At the end of this time, no trace of the ozone reaction being 
observable, it was considered advisable to ascertain whether if a 
very small proportion of the oxygen passing through had become 
converted into ozone—so minute a quantity, at so low a pressure, 
would affect the test solution. With this object, the wires of the 
ozoniser were now joined up, and it was found that in one minute 
a faint yellow colouring of the solution, slight but distinctly 
visible, occurred. Evidently, therefore, twenty bubbles of elec- 
trically ozonised oxygen produce more effect than 21,000 bubbles 
of oxygen which has been simply subjected to the effects of low 
pressure, And even if the experiment described above is not 
considered to prove, with sufficient conclusiveness, that low 
pressure alone has no power to cause the formation of ozone in 
oxygen, it must at least be admitted that the ozone so formed is 
less than y¢55 of the quantity produced by an ozoniser in the 
ordinary way in the same volume of oxygen, and as this can 
scarcely exceed 57% of the whole volume, the ozone formed by 
lowering the pressure cannot be so much as 005% of the volume 
of oxygen present. 
We must not neglect to state that our curiosity in this matter 
was stimulated to the experimenting point by a letter from our 
friend, Mr. W. Sutherland, of Melbourne, who considered, oD 
grounds based on the kinetic theory of gases, that allotropi¢ 
oxygen of some kind would most likely be found at about the 
pressure we employed. The soiling of Sprengel pumps, however, 
as well as the experiments of Baly and Ramsay, had previously 
led us, independently, to infer the possibility of a production of 
active oxygen under the conditions we have mentioned. 
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