VENTILATION OF SEWERS AND DRAINS. 153 
The main sewers and existing city system were transferred to 
the Board by Act of Parliament on 18th December, 1882. The 
Board proceeded without delay to deal with the ventilating of 
the sewers under their control. It was found heye, as in other 
countries, that ventilation by open grids in the centre of the road- 
way was a failure, and considering the conditions of some of the 
suburbs, the streets being in some cases not twenty feet wide, 
the existence of an open grating in direct communication with 
the sewer could not be otherwise than dangerous to the health of 
the residents. Numerous complaints were received, and on investi- 
gation it was found that in almost every case the nuisance arose 
from a man or lamp hole. ‘The first section operated upon was 
the Borough of Darlington and portion of the Borough of Redfern 
the population being about 10,000. 
A few shafts were erected at first with the view of utilizing the 
man holes as inducts or air feeds, but the result was extremely un- 
satisfactory. It was found that owing to the spaces between the 
bars of grids becoming choked with horse manure, detritus, &c., 
the quantity of air passed through was extremely small. It 
appeared clear to me that if the gratings were to be used as 
adjuncts to ventilation it would be at a high cost for maintenance. 
In lieu of the gratings, specially made and tested induct cowls 
were attached to shafts at certain points, and a large volume of 
pure air was forced into the sewers. This system of aérating the 
sewers was tried in England with success. <A description by Mr. 
Strachan, A.M.1.c.E., of Chelsea, appeared in the Minutes of Pro- 
ceedings of the Institute of Civil Engineers; it wasa small instal- 
lation, but there does not appear any record whether the system 
has been generally adopted. The method is a combination of the 
“plenum” and “‘vacuum” systems, the advantages being purer air 
than that which would be obtained from surface feeds and a con- 
siderable saving in maintenance. 
Where the Borough sewers join the City sewers the former are 
locked off by specially constructed gas check chambers, and air is 
thrown in or exhausted in the reverse side of the valve as required, 
