162 Prof. B. Moore. The Formation of Nitrites from 



correspondence between the amount of nitrites and nitrates in air and rain- 

 water and the prevalence of thunderstorms, such as must undoubtedly exist, 

 were the energy of the lightning discharge the main cause of the production 

 of nitrites and nitrates in the air. 



Rain collected in the course of the present experiments when there had 

 been no recent thunder was found to contain nearly as much nitrite (about 

 0'5 part per million) as rain caught in a thunderstorm, and, as has been 

 shown by Ilosvay (5), the morning dew contains nitrites. Also, although the 

 amounts of nitrites and nitrates present at any given time in the air are 

 small, the amounts abstracted by condensing aqueous vapour and falling as 

 rain or condensing as dew on the surfaces of leaves and ground in the course 

 of the year is enormous, and this would appear to demand some uniformly 

 distributed and more constantly acting source of energy, such as sunlight, 

 rather than be dependent upon fortuitous electrical discharges. 



These nitrites of the rain and dew form one of the chief supplies of nitro- 

 genous nutrition for plants and animals supported by soil not artificially 

 enriched with nitrogenous manure ; the experiments given below indicate 

 that there is also a probable aerial uptake of nitrites by the green leaves. 



A source of much error and confusion in estimating the so-called " active " 

 oxygen of air, rain, or dew by different observers at meteorological stations 

 has been the use of test-papers, impregnated with starch and iodides, which 

 were moistened and exposed to air and indicated, by the rapidity of develop- 

 ment of a blue colour, the degree of " active " oxygen in air. This " active " 

 oxygen was assumed to be present mainly as ozone or hydrogen peroxide 

 without more proof, but this liberation of iodine from iodides is accomplished 

 quite as readily by nitrogen tri- or tetr-oxide as by ozone or hydrogen 

 peroxide. All the more recent researches (7) indicate that ozone and 

 hydrogen peroxide are absent from the air at the earth's surface, and the 

 important purifying and bleaching reactions hitherto ascribed to them must 

 now be transferred to the intermediate oxides of nitrogen. At high dilutions, 

 such as are shown below to occur under atmospheric conditions, the odours of 

 ozone and that of the oxides of nitrogen are indistinguishable. 



The present experiments show that air, rain, and dew invariably contain a 

 mixture of nitrites and nitrates, and that on keeping the nitrites pass over 

 into nitrates, but by insolation this process is reversed, and nitrites are 

 formed from nitrates. 



The test used was Ilosvay's modification of the diazo-reactions discovered 

 by Griess, yielding compounds deeply coloured even at high dilutions ; one 

 of the best of these reactions for the purpose is that in which solutions of 

 sulphanilic acid and «-naphthylamine in acetic acid are added to the water 



