THE SOURCES OP THE XITROGEX OF VEGETATIOX, ETC. 497 



bottle containing only pure water. The latter also, at the termination of the experi- 

 ment, failed to give evidence of even traces of nitric acid. 



At the termination of the experiment, the contents of each of the eleven bottles were 

 also examined. A portion was exhausted with water, and the extract concentrated by 

 boiling, after the addition of permanganate of potash to destroy the organic matter. 

 The excess of permanganic acid was removed by carbonate of lead, and the clear solu- 

 tion filtered off from the precipitate. Each solution so obtained was tested for nitric 

 acid ; but in no case, excepting that of the garden soil, was there any indication of its 

 presence. An examination of the original garden soil showed that it contained nitric 

 acid before being subjected to the action of the Ozone. 



Owing to the negative character of the above results, it is not necessary to describe 

 the apparatus, and the circumstances of the experiments, in any more detail, which would 

 have been desirable had the results been of a positive kind. 



We are, however, by no means prepared to infer, from the evidence just adduced, that 

 under no circumstances in nature is it possible for Ozone to transform nitrogenous com- 

 pounds of the ammonia class, or the nascent nitrogen evolved during decomposition, 

 into oxides of Nitrogen. We would not say that it may not be possible for Ozone to 

 form such compounds when in connexion with non-nitrogenous bodies or porous sub- 

 stances permeated with gaseous Nitrogen, or even in the atmosphere. Nor are we pre- 

 pared to maintain that the nitric acid in soils is not in part due to some of these causes. 

 These questions will require much further investigation before they can be satisfactorily 

 settled. To some of them we shall refer again presently. 



But we wish particularly to call attention to the fact that, in the experiments just 

 referred to, there was a very much larger quantity of Ozone, acting upon organic matter, 

 soil, &c, in a very wide range of circumstances, and for a much longer period of time, 

 than was involved in our experiments on the question of the assimilation of free Nitro- 

 gen by plants. Yet there was no appreciable quantity of nitric acid formed. It may 

 therefore be concluded that there will be no error introduced into the results of the 

 experiments on the question of the assimilation of free Nitrogen by plants themselves, 

 arising from the action of Ozone upon free Nitrogen under the circumstances of the 

 experiments, and so providing to the plants an unaccounted supply of combined 

 Nitrogen. 



D. — Evolution of free Nitrogen in the decomposition of Nitrogenous organic compounds. 

 Two obvious methods of investigating the question, whether or not free Nitrogen is 

 given off in the decomposition of nitrogenous organic matter, present themselves. 



1. To allow the organic matter to decompose under circumstances in which any free 

 Nitrogen that may be evolved can be collected and estimated. 



2. To allow the organic matter to decompose under circumstances in which the total 

 amount of the compounds of Nitrogen formed in the process can be estimated — the loss 

 of Nitrogen then representing the free Nitrogen evolved. 



3 y2 



