XVIII. J. G. S. PURVIS. 



The filtering material in this tank consists of Nepean gravel 

 graded upwards every foot from about 4 inch gauge to that of the 

 size of a pea. The filtering material in the contact beds consists 

 of coal in two cases, and coke in the others, graded from 3 inches 

 to 1 inch. It was found impossible to adhere absolutely to the 

 eight hour cycles with an uniform rate of flow, on account of the 

 interstitial spaces in the coke beds exceeding those of the coal, 

 the excess amounting to as much as 30%. 



The main carrier was tapped by a 4 inch cast iron pipe provided 

 with a screw-down stop valve. This entered the bottom of the 

 cultivation tank just underneath the false bottom, thus causing 

 the sewage to pass upwards through the filtering material. The 

 main cultivation tank is 25 feet 3 inches long by 9 feet by 5 feet 

 1 J inch deep, and has an estimated net capacity of 3,636 gallons. 



On the 24th January of this year the rate of flow was carefully 

 measured, so as to give as near as possible the eight hour cycles. 

 The contact beds are each 10 feet by 6 feet by 4 feet deep. The 

 holding capacity of the beds filled with coal was found to be 475*6 

 gallons, and each of them took 1 hour 42f minutes to fill The 

 holding capacity of the tanks filled with coke was found to be 

 622 A gallons, and each of them took 2 hours 13 J minutes to fill. 

 From these figures it will be seen that the voids in the coal filling 

 is 33%, and in the coke filling 43 5%, and that the rate of flow is 

 4*66 gallons per minute or 626,300 gallons per acre per diem. 



This is hardly a fair way of making a comparison as the depth 

 of the tanks is not admitted as a function, but when such is 

 admitted it will be found that 3*16 gallons of sewage are purified 

 (to a degree to be afterwards stated) per cubic foot of gross tank 

 capacity per twenty-four hours, and that -316 cubic feet of gross 

 tank capacity is required per gallon per capita for this particular 

 degree of purification. The flow of sewage through this installa- 

 tion was started in November 1st, 1900. On December 3rd of 

 the same year, Mr. Doherty of the Health Board under directions 

 of Mr. Hamlet, Government Analyst, commenced his analyses, 

 and on March 26th 1901, reported as follows: — 



