VENTILATION OF SEWERS AND DRAINS. 159 
off like a skin. That this is due to the aerating effect of the air 
drawn into the sewer is beyond a doubt. 
The men who have to work in the sewers quite appreciate the 
benefits of the supply of air, as prior to the spray being fixed, 
working in the sewer was not only uncomfortable, but owing to 
the stagnation of the air it was dangerous to keep them too long 
init. The air currents were tested with the spray not working, 
and the results show that, although tests were made every two 
chains and at every manhole, there was not sufficient air move- 
ment to start the instrument; what little movement there was, 
was in the direction of the flow—this simply meant stagnation. 
When the spray was turned on, the currents registered as before 
stated. 
The Board of Water Supply and Sewerage have lately brought 
this system into use on a larger scale. The water from Busby’s 
Bore was turned into the Bondi outfall for flushing purposes and 
the officer in charge of the ventilating work conceived the idea of 
utilizing this water for ventilating purposes as well as flushing. 
This was done by discharging the water at a higher level through 
a Six inch pipe with a cone at the bottom; the cone is attached 
to a spindle which admits of the annular aperture being adjusted 
to suit the pressure. 
The arrangement is simple and the work done is extremely 
satisfactory, far exceeding my expectations. The quantity of 
air drawn into the sewer by the falling water was 183,458 
cubic feet per hour, or 4,402,992 cubic feet per day representing 
36°74 tons of oxygen passed into the sewer. The effect of this 
abundant supply of air is felt for nearly a mile eastwards and 
for some distance westwards. The power here practically 
costs nothing. The Board has under experiment a scheme for 
extracting the air from the sewers by water power, the arrange- 
ments are only ofa tentative character, but the results so far shew 
that the work can be done efficiently and economically. I should 
have stated that the measured velocities of the air currents when 
the spray was working varied from 9,600 lineal feet per hour to 
