NORTH SYDNEY AND DOUBLE BAY SEWERAGE SCHEMES. XV. 



iormed. The joint is effected by placing neat cement into grooves 

 round each end, and so forming a dowel or tongue. 



Under some circumstances the cheapness and speed with which 

 such work can be done renders a great saving of money and time 

 possible, as against the ordinary brick and concrete sewer. In 

 the South Mosman branch the discharging capacity of the 

 sewer did not require it to be over 2 ft. 5 in. by 1 ft. 9 in., and 

 the " Monier " construction enabled the sewer to be built that 

 «ize, whereas if the ordinary section had been adopted — concrete 

 and brickwork — the smallest size which could be constructed 

 with advantage is 3 ft. 3 in. by 2 ft. 2 in. 



A steel arch will carry the sewer, which is in the form of a 

 rivetted steel tube over the head of Mosman's Bay, and other 

 aqueducts are to be built where depressions have to be crossed. 



Another branch sewer, the first section of which tenders will 

 be called for in the course of a few weeks, will be constructed to 

 -drain the northern or Middle Harbour side of Mosman. This 

 will join the main sewer near its outfall. 



The South Willoughby branchy 70 chains in length, is now 

 being constructed, and, like the Mosman branch, will be an oval 

 sewer in tunnel through rock. Here, also, a " Monier " pipe 

 2 ft. 5 in. by 1 ft. 9 in. is being used, and the remarks made as 

 to the South Mosman branch apply in this case. 



The work of reticulation, which has in the main been con- 

 structed by the Metropolitan Water and Sewerage Board, has now 

 been finished over a portion of North Sydney, and a large 

 population is already served by the system in that borough. 

 With the completion of the branches to the other suburbs the 

 whole of the area will be similarly connected. 



TREATMENT WORKS. 



The original method and site of sewage disposal has been 

 practically adhered to, and briefly the process in operation is as 

 follows. After the sewage has passed through screens, to remove 

 the larger floating solids (which are afterwards burnt), it is treated 

 with lime to facilitate precipitation of the suspended matters in 

 the settling tanks. After settlement has taken place, the clearer 



