1867.] 



Evidence of Ozone in the Atmosphere, 



63 



XIII. " On tlie Identity of tlie Body in tlie Atmospliere Avliicli 

 decomposes Iodide of Potassium mtli Ozone.'''' By Thomas 

 Andrews, M.D., F.B.S. Eeceiyed June 20, 1867. 



It was assumed for many years, cMefly on tlie authority of Schoubeiu, 

 that the body in the atmosphere which colours iodide-of-potassium 

 paper is identical with ozone ; but this identity has of late been called 

 in question, and as the subject is one of considerable importance, I 

 submitted it lately to a careful investigation, the results of which I beg 

 to lay briefly before the Society. The only property of ozone, hitherto 

 recognized as belonging to the body in the atmosphere, is that of setting 

 free the iodine in iodide of potassium ; but as other substances, such as 

 nitric acid and chlorine, which may possibly exist in the atmosphere, 

 have the same property, no certain conclusion could be drawn from 

 this fact alone. 



One of the most striking properties of ozone is its power of oxidizing 

 mercury, and few experiments are more striking than that of aUowiug 

 some bubbles of electrolytic oxygen to j)lay over the surface of one or 

 two pounds of mercury. The metal instantly loses its lustre, its mo- 

 bility, and its convexity of surface, and when moved about it adheres in 

 thin mirror-like films to the sides of the containing glass vessel. The 

 body in the atmosphere acts in the same way upon pure mercury ; but, 

 from the very minute quantity of it which is at any time present, the 

 experiment requires some care in order that the efiect may be observed. 

 On passing a stream of atmospheric air, which gave the usual reactions 

 with test-paper, for some hours over the surface of mercury in aU-tube, 

 the metal was distinctly oxidized at the end at which the air first came 

 into contact with it. 



This experiment, however, cannot be considered conclusive, as mercury 

 will tarnish and lose its mobility under the influence of many bodies 

 besides ozone. 



It is well known that all ozone reactions disappear when ozone 

 is passed through a tube containing pellets of dry peroxide of man- 

 ganese, or other body of the same class. The same thiug occurs with 

 the substance supposed to be ozone in the atmosphere. About SO litres 

 of atmospheric air were drawn, at a uniform rate, through a tube con- 

 taining peroxide of manganese, and afterwards made to play upon very 

 delicate test-paper. Not the slightest coloration occurred, although the 

 same paper was distinctly afiected when 10 litres of the same air, with- 

 out the interposition of the manganese tube, were passed over it. 



But the action of heat furnishes the most unequivocal proof of the iden- 

 tity of the body in the atmosphere with ozone. In a former communi- 

 cation (Phil. Trans, for 185G, p. 12) I sliowed that ozone, whether ob- 

 tained by electrolysis or by the action of the electrical brush upon oxy- 

 gen, is quickly destroyed at the temperature of 237° C. An apparatus 



