246 Dr. H. Chick. The Process of Nitrification L^P 1 '- 1> 



seem to show that loss of ammonia goes hand in hand with production of 

 oxidised nitrogen. 



Tables Ia (Vienna) and Ib (Munich) give a clear idea of the general 

 progress of the oxidation of nitrogen. They are compiled from analyses 

 made from time to time, and while the times given for the later stages are 

 approximate, those for the first stage are exact, being based on almost daily 

 tests. 



The Nitrite Stage. — After the first appearance of oxidised nitrogen in the 

 filtrates, nitrification went ahead, and, in the case of the tall filter, five days 

 later there was nitrous nitrogen in the filtrate about equal in amount to the 

 total nitrogen going on. The two stages in which nitrification occurs were 

 well separated in time, and show very distinctly, first, the production of 

 nitrites in quantity without nitrates, and finally the complete oxidation to 

 nitrates, nitrites being absent. For example, in the case of the tall filter, 

 five weeks after having been started (Table II, analyses 10 and 11) the 

 sewage contained 17 parts ammoniacal and albuminoid nitrogen, which in 

 the filtrate was reduced to 1*5 parts, while 10 parts nitrogen were 

 present as nitrites, nitrates being altogether absent. Three days later a 

 similar result was obtained (analyses 14 and 15), eight weeks later nitrates 

 were being formed in small amount, and an analysis of the filtrate made four 

 months after starting (analysis 21) showed a complete oxidation of the 

 nitrogen, nitrates being present in quantity unaccompanied by nitrites. In 

 the case of the short filter the process was much slower, for an analysis 

 made after four months showed production in the filtrates of nitrites only 

 (analysis 23). This comparative lack of efficiency may be referred to the 

 lower temperature* of the short filter, for an analysis on the same date of 

 the liquid from No. 1 tap of the tall filter, 50 cm. from the top (Table III, 

 6 and 7) showed the presence of nitrates in abundance, and only traces of 

 nitrites. 



* An exactly parallel fact was noticed with regard to the time of the first appearance of 

 oxidised nitrogen in these two filters. Strictly speaking, the top section of the tall filter 

 should have been exactly comparable with the short filter, and the only possible 

 explanation is that, as the first division of the latter filter stood 150 cm. higher in the 

 room, the discrepancy was due to a temperature difference. Regular observations of 

 temperature had been made by means of the thermometers in the filters, and the higher 

 position in the room was found to be constantly from T5° to 2 - 5° C. higher than the lower 

 one, the temperature of the interior of the filters differing hardly at all from that of the 

 surrounding air. This explanation is confirmed by the results of the Munich experiment, 

 where all the six filters were arranged so that their tops, and not their bottoms, were on 

 one level ; hence the first divisions of all were at a similar temperature, and it was found 

 that the first oxidation of nitrogen was observed after the same period in all the three 

 filters of each set. 



