244 ProGeedings of the Royal Irish Academy. 



whicii consisted in placing different portions of the same mixtures in 

 similar bottles, some of which, were surrounded with black cloth or 

 velvet to exclude light, whilst others were left uncovered, and all of 

 them were suffered to remain open or uncorked. On examination 

 after a few days there was but little difference as to the amount ^ of 

 nitrification that had taken place in each — indeed in some of my ex- 

 periments it had progressed to a greater extent in the uncovered than 

 in the covered bottles ; and in all made on this subject (except those 

 to determine this point as to the necessity or not of darkness), 

 the mixtures were left exposed to the light, and some to the full 

 influence of strong sunshine, yet still a considerable amount of nitrifi- 

 cation took place in each. Besides, in nature much of the nitrates 

 Avhich. occur in the surface soils of different localities must have been 

 formed under the influence of more or less daylight; all of which 

 facts, I conceive, are more or less opposed to the necessity of darkness 

 in this process. 



Another point which has not, I believe, been clearly established, 

 at least as regards nitriflcation occurring in water containing organic 

 matters, is the necessity of having a certain amount of air or free 

 oxygen to carry on the process ; this I have proved in the following 

 very simple manner: — To water which had been kept boiling for some 

 time to expel its contained air, I added a small quantity of freshly 

 voided urine (the proportion employed being about one part of urine 

 to sixteen parts of water, such a mixture having been proved to be 

 very suitable for nitrification), and then repeated the boiling to ensure 

 the removal, as far as possible, of any dissolved air. Several bottles 

 which had been kept immersed in the boiling mixture were then 

 filled completely with it, corked, and sealed with sealing-wax, to 

 prevent the access of air. Some, however, of them containing this 

 mixture were left open for comparison. After leaving the bottles for 

 a day or two in the same place, I first examined the open ones for 

 nitrites, and when the test indicated the abundant formation of those 

 salts, I opened one of those sealed, when not a trace of nitrites was 

 discoverable in its contents; the remaining sealed ones were opened at 

 different periods subsequently, with the same results. Other compa- 

 rative experiments were made, where the temperature of the mixtures 

 was artificially kept at a heat very favourable to nitrification, but, in 

 every instance whore the access of air had been excluded, no trace of 

 nitrites could be detected — clearly proving the necessity of more or 

 less air or free oxygen for their formation. But the amount neces- 

 sary to commence, at least, the process is small, for I found where 



^ In ascertaining the amount of nitrification, the indigo process as described by 

 Sutton in his " Volumetric Analysis " was employed, wMch served for the deter- 

 mination of the nitrites and nitrates collectively ; and though it may not be quite so 

 accurate as some other methods, Avas sufficiently so for this pui-pose, as it Avas only 

 the comparative amounts of nitrites and nitrates formed under the different circiyii- 

 stances of the experiments that I wanted to determine. 



