ATMOSPHERIC OZONE. I53 



plants; and if plants emit ozone, as is believed by some agricultural chemists, 

 they would have within themselves the power to partially supply the nitrogen 

 which they require. The large leafed plants, according to this view, should be 

 better able to supply themselves with these needed compounds ; and, seemingly to 

 substantiate this view, it has been observed in agricultural practice that these same 

 plants, with massive foliage, although they contain a larger amount of nitrogen, 

 do not impoverish the soil as do the fine-leafed cereals. Further, the presence in 

 the atmosphere of such a vigorous oxidizing agent would destroy such organic 

 matters as prevade the air; and epidemic diseases would be rarer, in proportion 

 as the ozone increased in the air. But, being irrespirable from its great activity, 

 throat diseases would proportionately increase. 



These considerations were sufficient to direct the greatest attention to atmos- 

 pheric conditions in this respect. The usual test for ozone in the air has been 

 the well-known iodide-of-potassium starch-papers. The ozone oxidizes the potas- 

 sium and sets free the iodine, which then reacts upon the starch, giving a blue 

 which varies in intensity with the proportion of ozone present. This color is 

 compared with a scale of varying tints, and the corresponding number read off. 

 It was known that other substances, such as nitrous acid and hydric-peroxide, 

 have the power to thus react with this test ; and that ozone would act only in the 

 presence of moisture. The influence of the latter seems not to have been given 

 its true importance. The former objection was met by the fact that peroxide of 

 hydrogen was not known to exist in the air, even in minute quantity ; and it was 

 supposed to have been demonstrated that it gives the reaction only when concen- 

 trated. The papers were blued under conditions when it could not have been 

 due to nitrous acid. But later and more satisfactory investigations have shown 

 that hydric superoxide does exist in the air, and that in sufficient quantity to react 

 with the above test. The reliability of this test for estimating any oxidizing prin- 

 ciple in the atmosphere, has been shown by observing that the hygroscopic char- 

 acter of the paper used, although the same formula be followed in preparing the 

 reagent, so far influences the reaction' that test papers from different sources, ex 

 posed together, give widely different results. ' The results with the same paper 

 vary with the humidity, and seem to have little other value than is possessed in 

 common by crude chemical hygrometers. Nor are the other tests which haVe 

 hitherto been trusted, decisive between ozone and these other oxidizers. So that 

 the existence of ozone as a usual constituent of the atmosphere, has been rend- 

 ered quite problematical. Thallium papers, however, are not influenced by 

 moisture, and seem to furnish a reliable means of estimating the oxidizing prin. 

 ciple present in the air ; and it seems, in general, to be peroxide of hydrogen. 



Do these uncertainties regarding the existence of ozone in the atmosphere, 

 overthrow all the conclusions drawn from its supposed abundance ? Does the 

 untrustworthiness of the conclusions based upon carefully conducted experiments 

 show the folly of trusting scientific "facts" and of accepting the theories founded 

 upon them? To the latter the answer is an emphatic no; to the former, in one 



