26 WILLIAM M. HAMLET. 



by Scott-Moncrieff, as well as the closed septic tank of Cameron, 

 reducing the experiments to the last stage of simplicity. Two 

 plain open rectangular brick-lined tanks, twenty-two feet six 

 inches long, ten feet eight inches wide, and twelve feet deep, 

 giving a superficial area of gf 3 of an acre each. A third tank, 

 of similar shape and area, but six feet in depth, was also employed 

 to note differences in efficiency caused by depth. Laid on the 

 bottom of these tanks were parallel series of loosely-jointed drain 

 pipes to assist in drawing off the effluent. Walnut-sized fragments 

 of common gas-coke are placed in the tanks to the depths of four 

 and six feet respectively. 



When thus ready, the coke beds are filled with screened sewage, 

 the screening intercepting some curious and miscellaneous items 

 of the wealth of the absent minded citizen, such as tobacco pipes, 

 purses (empty), brushes, combs, and Dr. Clowes even mentions 

 ' wedding rings.' Seven minutes are allowed for the filling of the 

 tank, then comes a resting period of three hours. The word 'rest' 

 is here but a relative term, for it is really a period of great 

 bacterial activity. The outflow afterwards extends over one hour, 

 the bed remaining eight hours empty in order to aerate itself. The 

 tank is again filled and the sequence continued, one million gallons 

 per acre per day being the working capacity of the system. 



Later experiments made with thirteen feet beds show no appre- 

 ciable advantages over the six feet of coke. Here then we have 

 an intermittent process for the treatment of sewage of undoubted 

 simplicity: crude sewage is screened and flowed into a tank con- 

 taining some four or six feet of coke, in pieces of the size of walnuts, 

 submerged for three hours, and just allowed to flow out again. 

 And what are the results ? Clowes measures the degree of puri- 

 fication attained by this process by finding the amount of oxygen 

 required tc oxidise the putrescible organic matter ; first in the 

 raw sewage, and then in the effluent. The results show that over 

 fifty per cent, of purification takes place. His figures show that 

 51-30 per cent. 1 of the putrescible organic matter is dealt with, so 

 that an effluent is obtained pure enough to support fish life. 



1 Tn allowing a longer period of time for the fermentation, results as 

 high as eighty-six per cent, have been obtained by Clowes. 



