OZONE IN THE UPPER ATMOSPHERE 457 



place in this reaction, and a comparison made with those brought 

 about by oxides of nitrogen and hydrogen peroxide. It was 

 found that in the case of ozone, in accordance with the operation 

 of mass action, an important influence is exerted on the nature 

 of the products by the quantity of gas circulated and also for a 

 given amount of ozone, by the concentration per unit volume. 

 Thus with very dilute gas, and at temperatures above the 

 freezing point, — 24 , the formation of free iodine and hypoiodite 

 results, while with a more concentrated gas, and in all cases 

 with the solidified reagent, in addition to these products, 

 potassium iodate is formed directly. An estimation of the 

 products formed in the first case can readily be made by titrating 

 the solution with standardised sodium thiosulphate solution 

 until the yellow colour of the iodine is removed, iand in the 

 second case, the iodate can be estimated afterwards by acidifying, 

 when decomposition into iodide and free iodine occurs, and this 

 last is then estimated as before. 



On comparing the above reactions with those given by 

 hydrogen peroxide, it was found in this latter case that potassium 

 hypoiodite and free iodine are formed to a limited extent, but no 

 iodate. The reaction is not quantitative since the hypoiodite 

 formed, when above a certain concentration, reacts with hydrogen 

 peroxide with evolution of oxygen. Nitrogen peroxide was 

 found to react with potassium iodide under all conditions to 

 give mainly iodate together with some free iodine. With this 

 last gas a very characteristic property was shown, which enabled 

 the detection of minute traces of this gas. If in the potassium 

 iodide solution which had been exposed to oxides of nitrogen, 

 the free iodine, which was liberated after acidifying, was removed 

 by titration with sodium thiosulphate, then, on standing in air, 

 a further liberation of iodine developed with a velocity depending 

 on the total amount of the oxides of nitrogen originally absorbed. 

 This change is brought about through the catalytic influence of 

 the nitrous acid formed in absorbing oxygen from the air and 

 then undergoing reduction by the potassium iodide with libera- 

 tion of iodine. This reaction enables an approximate deter- 

 mination to be made of these oxides when present in quantities 

 too small to estimate by direct titration. The method thus 

 resolves itself into a measurement of the rate at which the 

 reagent after acidifying liberates iodine when exposed to air. 

 While this reaction is characteristic for oxides of nitrogen 



