VENTILATION OF SEWERS AND DRAINS. 151 
materials, &c. ; shafts were sunk and built up at intervals, these 
were not carried to the surface and were therefore, as a means 
of ventilation, useless. An attempt was made to cut off the house 
drain from the main sewer by means of cast iron flap traps—these- 
became rusted at the joints and either prevented the sewage pass- 
ing from the houses, or permitted the gas to pass freely through 
the house drain into the houses. 
The monument in Hyde Park was erected with the view of 
ventilating a section of the system, viz., Pitt, Castlereagh, and 
Elizabeth Streets sewers, these were supposed to be connected with 
the sewer in Bathurst Street for the purposes of circulation. It 
would appear that this shaft was erected as an experiment, because 
although other sections of the drainage works were carried out, 
no other shafts were erected. The shaft has been lately under 
observation as to the limit of effect as regards the sewers con- 
nected with it. These results are so far unsatisfactory when 
relying on natural forces only for creating a draught. The shaft 
would at certain times in the year act as an exhaust, while in 
others as an induct. 
The only means by which the sewers appeared to be ventilated 
was by means of gully shafts and rainwater pipes from buildings. 
The gully shafts after a while became a nuisance on account of 
the sewer air being expelled by the forces before referred to. 
The gullies were then trapped, consequently greater pressure was 
thrown on the house drains and rainwater pipes. The outlet. 
of the main outfalls being tide locked twice during the twenty- 
four hours, and a rise of temperature taking place, the result 
of the direct connection with houses can be imagined. The sewer 
gas cannot be bottled up, it will force its way somewhere. 
Where? Into the street, no, the shafts were closed down; through 
the gullies, no, they were trapped; into the dwellings, yes; because 
the line of least resistance in this case was the house drain. Com- 
pare the resistance of old fittings such as bell traps, D traps with 
the pressure brought to bear on them by a rise of temperature or 
surcharging of the sewer. Then again, the hopper head of the 
