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



nitrite to nitrate, so that there is a labile equilibrium between a given degree 

 of light exposure and nitrates, nitrites, and oxygen. 



Attempts are at prqsent being made to follow up the earlier stages of 

 nitrogen fixation from the atmosphere. The light of the sun in the upper 

 strata of the atmosphere, where the ultra-violet has not yet been absorbed, 

 must produce vast amounts of ozone, and these disappear as the earth's 

 surface is approached ; in so disappearing, the ozone may oxidise nitrogen and 

 give nitrites and nitrates. Whatever their source, these nitrites are most 

 reactive with organic substances and destructive to micro-organisms, and 

 many of the natural bleaching, deodorising, and sterilising activities in air 

 and water which have been hitherto ascribed to ozone and hydrogen 

 peroxide are more probably due to nitrites. 



Summary. 



Dilute solutions of nitrates exposed either to sunlight or to a source of 

 light rich in light-energy of short wave-length (such as light from mercury 

 vapour arc enclosed in silica) undergo conversion of nitrate into nitrite. 



There is an uptake of chemical energy in this reaction transformed from 

 light-energy as in formation of organic carbon compounds in foliage leaves ; 

 it is to be added to the^ relatively' small number of endothermic reactions 

 known to be induced by light. 



Interposition of a layer of glass between source of hght and solution of 

 nitrate greatly slows the reaction, showing that the most effective rays are 

 those of short length. 



When green leaves are immersed in nitrate solution, comparatively little 

 nitrite accumulates, indicating that nitrites are rapidly absorbed by the green 

 leaf. Nitrates taken up by plants from soil would, in presence of sunlight, be 

 changed to nitrites, which are much more reactive than nitrates. This 

 indicates that the early stages of synthesis of nitrogenous compounds are 

 carried out in the green leaf and aided by sunlight. 



Eain-water collected for considerable time contains no nitrites, all having 

 been oxidised to nitrates, but if exposed to bright sunlight or ultra-violet 

 light for a few hours a strong reaction for nitrites is always obtained. 



Freshly collected rain-water or dew always contains a mixture of nitrites 

 and nitrates, as shown by the nitrite test appearing without any previous 

 treatment of the water and the great enhancement of this on exposure to 

 strong illumination. 



Air bubbled through nitrite- and nitrate-free distilled water gives a mixed 

 reaction afterwards when the water is tested for nitrites and nitrates, showing 

 presence of both forms of oxides of nitrogen in air. 



