76 FORMATION OF NITRITES FROM NITRATES 



rootlets of plants from the soil can be converted into the more 

 reactive nitrites in the green leaf with absorption of solar energy ; 

 simultaneously, non-nitrogenous organic bodies are being built 

 up in the same situation, which suggests that by interaction under 

 the influence of light protein synthesis as well as carbohydrate may 

 occur in the green leaf. 



The presence of nitrites and nitrates in rain and dew indicates 

 their occurrence in atmospheric air, and this was ultimately proven 

 in a series of experiments which showed that the main portion of the 

 oxidised nitrogen from air is found in water, after bubbling air 

 through it, as nitrate and not as nitrite. 



Great care is required in order to give a rigorous proof of this, 

 because the condition of the absorbed substances from the air may 

 be modified in the act of collection if light be not carefully excluded, 

 and nitrate from the air be changed by insolation into nitrite. This 

 fact first emerged from a series of experiments intended to study the 

 relative amounts of nitrite in air by day and by night, when appar- 

 ently the interesting result was obtained that there was practically 

 no nitrite in night air, but a considerable amount in day air. Just 

 then the effect of light in converting nitrates into nitrites was learnt, 

 and a repetition of the experiment was made, using a blackened 

 bottle with distilled water as absorbent. This distilled water had 

 been twice distilled, and was so free from nitrate that it gave no 

 Griess-Ilosvay reaction even after prolonged exposure to ultra-violet 

 light. The result now obtained was that, whether the air were 

 bubbled through by day or by night, only a very slight reaction for 

 nitrites was obtained ; but on now exposing to sunlight this distilled 

 water through which air had been bubbled in darkness, whether by 

 day or by night, a strong reaction was obtained in each case, 

 showing that oxidised nitrogen is present always in air both by day 

 and by night. 



It is not possible to conclude that the relative amounts of nitrate 

 and nitrite in bubbled air give an indication of the relative amounts 

 of the two oxides of nitrogen in the air, for if the absorption be 

 attempted in the presence of light there will be a reduction to nitrite, 

 and if in darkness the great volume of oxygen simultaneously 

 bubbled through may have oxidised nitrite to nitrate, so that there 

 is a labile equilibrium between a given degree of light exposure and 

 nitrates, nitrites, and oxygen. 



Researches are called for to determine the earlier stages of 



