XC. ABSTRACT OF PROCEEDINGS. 



gases will escape at the crowns of the corrugations and 

 break the surface slime which is the true filtering medium. 

 Dealing with rapid filtration as practiced in America, he 

 says — that where attempts have been made to filter very 

 turbid waters in ordinary sand filter beds even when pre- 

 liminary coagulation and sedimentation have been used, 

 the cost of scraping filters has been so high as to lead to 

 the abandonment of the system. The successful working 

 of rapid filtration depends upon the efficiency of the pre- 

 liminary coagulation and sedimentation. It is necessary 

 that the coagulant be added in exact proportion to the 

 quantity of water to be treated, and that it be thoroughly 

 mixed with the water. As regards sedimentation, some 

 American engineers say that the time allowed should not 

 be less than 12 hours ; 48 hours is recommended when the 

 cost of construction is low, but 24 hours is a fair allowance. 



The results obtained by the mechanical filtration plant 

 at Broken Hill shew that 62°/° of the bacteria present in the 

 raw water as well as all the higher forms of plant and 

 animal life are removed. After heavy rains the raw water 

 is very turbid and carries in suspension a large amount of 

 clayey matter, more in the form of a solution than a solid 

 in suspension. At these times 10 grains of coagulant per 

 gallon of water was hardly sufficient to obtain a clear 

 effluent. Generally after subsidence the water was first 

 treated with 2 grains of sulphate of alumina per gallon and 

 then with a solution of lime equal to 1 in 400 of raw water. 

 After describing the apparatus he gave tables illustrating 

 the physical and chemical character of raw water, the 

 effluent from the working filter and the effluent from the 

 mechanical plant. 



W. M. Hamlet, f.i.c, f.c.s., said that the trend of public 

 opinion was all in the direction of obtaining pure water 

 supplies and more particularly in the case of country towns; 



