164 Prof. B, Moore. The Formation of Nitrites from 



equilibrium with water, the aqueous solution will contain three volumes of 

 gaseous carbon dioxide in 10,000 volumes of water. That is, in 10 litres of 

 water there will be dissolved 3 c.c. of carbon dioxide. Now, since 44 grm. 

 of carbon dioxide gas measure at normal temperature and pressure 

 22,000 c.c, this means that 3 c.c. of carbon dioxide weigh approximately 

 6 mgrm. ; 6 mgrm. of carbon dioxide in 10 litres, therefore, represents a 

 concentration of 6 parts in 10,000,000 parts of water. It is the carbon in 

 the carbon dioxide which is utilised in formation of the organic carbon com- 

 pounds of the plant, and this stands to carbon dioxide in the relationship 

 of 12 to 44, so that the concentration of assimilable carbon becomes reduced 

 to about 1 part by weight in 6,000,000 parts of water. 



So far as nitrogen assimilation is concerned, the amount of nitrogen 

 required by plants is not on the average more than about 5 per cent, of the 

 required carbon assimilation, so that, other factors, such as coefficients of 

 distribution between air and water, being taken as equal, a concentration of 

 nitrites or nitrates in the atmosphere or cell-sap about equivalent to 1 part of 

 nitrogen in 120,000,000 parts of water ought to supply sufficient for assimi- 

 lative purposes. 



In a series of twenty experiments it was shown that both rain and dew 

 invariably contain nitrites, but these slowly diminish, so that water drawn 

 from a reservoir by a service tap gives a quite negative result when tested 

 by the diazo-reaction for nitrites. If, however, another portion of this same 

 sample of water be exposed, either in the open or within a transparent quartz 

 container, to sunlight or an artificial source of light rich in short wave- 

 lengths,* in one or two hours a strong reaction is given for nitrites. In this 

 manner, by testing water before and after exposure, the presence and 

 relative amounts of nitrite and nitrate may be determined. Similar changes, 

 only greatly diminished quantitatively, are obtained when the exposures are 

 made in glass vessels, showing that it is the ultra-violet waves which are 

 most potent. That this result is due to conversion of nitrates into nitrites, 



* At the time the experiments on the action of rays from the quartz mercury arc light 

 upon nitrates were made it was thought they were original, but since the paper was 

 written two references have been discovered to experiments made by observers in 

 France, who have approached the subject from quite a different standpoint. The first 

 observer, M. Lombard, 'Comptes Eendus Acad, des Sciences,' vol. 150, p. 227 (1910), 

 found that when tap-water or dilute solutions of nitrates were exposed to this source of 

 light nitrites were formed. This was later confirmed by D. Berthelot and H. Gaudechon, 

 'Comptes Rendus Acad, des Sciences,' vol. 152, p. 522 (1911), but neither communication 

 speaks of the importance in nature of this change, or shows it occurs with sunlight, or 

 draws attention to the occurrence in green leaves, and the activation thereby produced. 

 Attention is mainly directed to the cause of the sterilisation of water by exposure to 

 ultra-violet light. 



