1905.] with reference to the Purification of Seivage. 



249 



met with failure. Cows' urine diluted only 1 in 50, and containing about 

 30 parts ammoniacal nitrogen per 100,000, was put through the medium 

 filter for about a fortnight, and also at a later date through all three filters, 

 but it was found that they were incapable of oxidising so concentrated 

 a liquid, and the quality of the filtrates deteriorated (ef. Table IV). 



Throughout the history of these filters there was a considerable loss of 

 total nitrogen from the sewage while filtering through, but it was Specially 

 noticeable during the period when the diluted urine was being treated, when 

 in some cases not much more than half the original nitrogen was present in 

 the filtrate (Table II, analyses 33 to 36). This loss is doubtless due to an 

 escape of free nitrogen, set free possibly by decomposition of ammonium 

 nitrite, a very probable iutermediate product in the nitrification of ammonia 

 (NH4NO2 = 2HjO + N2). This loss of nitrogen was not so marked in the 

 case of the Vienna filters (Table II, analyses 1 to 23), though it occurred later 

 to some extent. These differences are probably due to the absence or 

 presence in quantity of the organisms involved. 



The Munich continuous filters in their later history, and they were worked 

 for about a year, possessed an efficiency rarely met with in large scale filters, 

 showing that this type can give excellent results in the absence of much 

 suspended matter.* The larger filters could not be considered to be heavily 

 worked, but the short filter, which had a capacity of two litres and treated 

 four litres of sewage daily, approximated more nearly to a practical installa- 

 tion. It oxidised daily about 0'5 gramme nitrogen, and this result must be 

 considered extremely satisfactory when the high nitrogenous concentration 

 of this special sewage (14 to 20 parts of ammoniacal nitrogen per 100,000 

 instead of the 3 to 8 parts usual in ordinary sewage) is kept in mind. The 

 quantities of nitrate appearing in the filtrates from these filters have rarely, 

 if ever, been obtained in practice on the large scale. 



S ec tion 1 1 . — Ba eter iolog icat Ii 1 vest iga tio as. 



Enumeration of Nitrifying Bacteria in the Filtrates. — It was thought 

 worth while to attempt to count the numbers of nitrifying bacteriaf present 

 in the filtrates from the filters, as it was conceivable that such enumerations 

 might furnish a bacteriological criterion of the qualitj- of sewage effluents. 



The practical utility of this procedure is, however, diminished by its 



* This can be removed in practice by a preliminary screening or septic tank treatment. 



+ The recent -work of O. C. Frye (' Report of Eoy. Com. on Sewage Disposal,' vol. 2, 

 1902, p. 9) has experimentally verified the view which has been generally held, though 

 doubted in some quarters, that all the nitrification taking place in sewage filters is the 

 work of living organisms, and none of it purely chemical. 



