president's address SECTION H. 161 



connected to the main or lateral drain without a trap. The 

 lateral drain may be ventilated by means of a cowl at one 

 end forcing" air downwards, and an open pipe at the other for 

 discharging the diluted gases into the atmosphere. 



Manholes about every 1000 feet to the main sewers provide 

 a supply of fresh air, and assist in the discharge of sewer gas. 



The ventilation of large sewers is by no means a simple 

 matter, and there appears to be no better method than 

 providing gas checks and a drop in the gradient at every 

 manhole, so as to ensure as far as possible the discharge or 

 supply of air at every manhole. The omission of the trap in 

 the house drain at its junction with the main sewer facilitates 

 ventilation, and is perfectly safe if the sewers are properly 

 designed, constructed, and maintained, but it may be in some 

 cases dangerous to omit the trap. The house fixtures are 

 trapped from the house drain, so that the dilute sewer air is 

 discharged above the roof only, and is not at all likely to 

 force the house traps. The movement of air in the sewers 

 depends upon differences in temperature between the air 

 outside and inside the sewer, also upon barometric changes, 

 effect of wind blowing across the outlets connected with the 

 sewer, the effect of heat on the soil pipe ventilator, and the 

 fluctuations in the flow of sewage. 



. I will now direct your attention to a few examples illustrating 

 the subject so far as I have considered it. The City of 

 Adelaide Avas the first in Australia to adopt a complete 

 system of sewerage, which was designed and carried out by 

 Mr. Oswald Brown, M. Inst. C.E., on the partially separate 

 system. The Hon. Dr. Allan Campbell pointed out in a 

 paper read before this Association in Sydney that the 

 ventilation of the Adelaide sewers was defective, and he 

 suggested the omission of the trap 'between the house drain 

 and the main drain, so as to make better use of the soil pipe 

 ventilators. I had some doubts at the time the paper was 

 read, but I now concur with Dr. Campbell. Before the 

 sewerage system was in operation in Adelaide it was the 

 most unhealthy city in Australia, whereas now it is the 

 cleanest and one of the healthiest. The sewerage of 

 Sydney lias been fully described in my paper read before this 

 Association in Sydney, " History of Civil Engineering in New 

 South Wales." I will now only briefly refer to it. There 

 are three main divisions. The Northern Section, draining 

 five thousand three hundred acres, discharging by means of 

 an intercepting sewer at a point on the ocean cliffs, about 3| 



