ABSTRACT OP PROCEEDINGS. XC111. 



from 260 to 760 parts per million, and the albuminoid from 

 '16 to *30 parts per million, although since then the pro- 

 portion had been greatly increased. 



To deal with the question by means of subsiding reservoirs 

 would have been too costly, and ordinary sand filters would 

 have been of very little use on account of the large amount 

 of fine clay in suspension. Rapid mechanical filters having 

 been adopted, the process was to bring the water from the 

 pumping station into a subsiding reservoir which held one 

 hour's supply. In the tank are copper plates. In the 

 filters of which there are four, the medium is quartz, nothing 

 larger than would pass a 144 mesh sieve and nothing smaller 

 than would remain on 1,600 mesh. The filters work very 

 well so long as the solids are not excessive, but when they 

 amounted to 1,000 per million they gave trouble ; when 

 they filter at the rate of about 50 cubic feet per hour a 

 good effluent is obtained. Working at this rate the filters 

 had to be cleansed about once every 2 or 6 days, which 

 operation takes about 15 minutes, with an expenditure of 

 about 20,000 gallons of water. Using about \ to 2 grains 

 of coagulant we get a reduction in the albuminoid ammonia 

 of about 55 per cent, and in bacteria of about 62 per cent. 

 He exhibited a diagram shewing the curves of purification 

 for quartz and sand respectively, which are practically 

 identical. The deposit of clay on the quartz in the filters 

 is very considerable, and sometimes the machinery employed 

 for raking the filters is unable to break it up, and the 

 question of cleansing by the aid of forced air is now being 

 considered. He thought that mechanical filters for Sydney 

 Water Supply would be a mistake, the sand filters have 

 been proved to be efficient in operation and cheap in main- 

 tenance. 



Mr. Ohas. W. Smith, m. inst. c.e., said that the subject of 

 water filtration has been so thoroughly threshed out by 



