45 8 SCIENCE PROGRESS 



even when present with other gases, hydrogen peroxide can 

 also be distinguished by the following separate tests. A solution 

 of titanium sulphate in sulphuric acid is coloured yellow by traces 

 of hydrogen peroxide, and this property forms a distinguishing 

 test for this compound. 



In the case of ozone, however, it was not found possible to 

 characterise this gas when present together with the others. An 

 estimation could probably be made in presence of the first two 

 gases, if very dilute, by a method of elimination. For this 

 purpose, a determination could be made of the sum of the three 

 gases by absorbing in acidified potassium iodide, and then 

 deducting the quantity of hydrogen and nitrogen peroxide as 

 determined separately. 



In the measurements made in the present work, it was found 

 that nitrogen and hydrogen peroxide are not present at high 

 altitudes to any detectable extent, so that the problem of the 

 estimation of ozone was considerably simplified. The manner of 

 applying these reagents to atmospheric tests is described below. 



Part 3. The Action of Ultra-violet Light on Air 



It is now a well-established fact that ozone is formed by the 

 action of ultra-violet light on oxygen or on air, and that if 

 initially above a certain concentration, exposure to the same 

 light causes a decomposition of ozone into oxygen. In either of 

 these reactions, the same stationary state is finally reached, 

 representing an equilibrium value, when no further change in 

 the concentration of the ozone results. 



It has been found that the actual value of this equilibrium 

 quantity varies with the nature of the light, and with the tempera- 

 ture and pressure of the gas. At a reduced pressure, for 

 instance, the rate of formation of ozone is decreased, and the rate 

 of its decomposition increased, so that the final equilibrium is 

 represented by a smaller value. 



Photochemical investigations have shown that light which is 

 effective in causing the production of ozone from oxygen is 

 limited to the region of the spectrum of wave-length below 

 200 /u/i. This corresponds to the observed fact that an absorption 

 point of light by oxygen occurs at 193 fifj. and below. It has 

 similarly been found that rays which are effective in causing the 

 decomposition of ozone lie in the range of wave-length between 





