680 



PROCEEDINGS OF SECTION I. 



Table XI. — Table showing Percentage Reduction in Organic Matter 

 Effected in Tanks and Filters, Separately and Combined. 



Balmoral Outfall. 



INCUBATOR TEST. 



All the above final effluents were examined by the incubator test 

 carried out thus. The oxygen absorbed in three minutes from acid 

 permanganate, at room temperature, was estimated in the fresh 

 samples. A bottlefull of the same was then placed in an incubator at 

 37° centigrade, and kept there for one week. At the end of the period 

 the bottle was removed, allowed to cool, and the oxygen absorbed in 

 three minutes again estimated. Further, any decomposition as indi- 

 cated by smell was observed, and also the general appearance of the 

 effluent, whether turbid or otherwise. 



In general it may be said that none of the effluents showed any 

 physical signs of decomposition ; but on estimating the oxygen 

 absorbed it was found that the North Sydney effluents invariably showed 

 an increase, sometimes considerable. As in view of the physical condition 

 of the effluent after incubation it appeared highly improbable that 

 this increase was due to the presence of easily oxidised products of 

 decomposition, an estimate was made of the amount of nitrites after 

 incubation. It was then found that coinci dentally with an increase 

 in the oxygen absorbed there was an increase of nitrites. 



In the report of the present English Royal Commission on Sewage 

 Disposal, McGowan recommends that allowance should be made for 

 the nitrites found in the effluent after incubation. This does not appear 



