ABSTRACT OF PROCEEDINGS. XCVll. 



Frankland, and is clearly illustrated by the diagram plotted 

 from his figures, a study of the diagram shews that although 

 the top film intercepts the majority of the passing organisms 

 a great number manage to pass through, and are intercepted 

 by the underlying sand. The curves appear to demonstrate 

 that result s are not improved beyond a depth of 600 mm. 

 or about 2 feet, and that the existence of a more open 

 stratum below the sand in the shape of gravel is deleterious 

 to the effluent. It is reasonable to suppose that the nature 

 of the water and of the sand would be important factors in 

 determining the depth of media, but experiments seem to 

 shew that given a sufficient depth to ensure the stability 

 of the film, the depth of the sand need not vary so greatly 

 as appears to be the practise in English waterworks. 



The cost of filtration of water is of such importance from 

 an economic standpoint that some trouble has been taken 

 to gather evidence concerning it. Mr. Price Williams, 

 m. inst. c.b., i n a paper read before the Institution of Civil 

 Engineers two years ago, gives the cost of filtration on sand 

 beds for the past 30 years to 8 of the London water com- 

 panies, and from those figures a diagram has been prepared; 

 it embraces the period 1871 to 1901 ; the average cost 

 during the period referred to is 6/6 per million gallons or 

 5*51 per cent, of all charges of maintenance. Now if the 

 experience of London is applied to the Sydney Water Supply 

 and the amount of water consumed in 1901-2 is dealt with, 

 the cost of filtration calculated by the percentage of all 

 charges as given above would be 8/3f per million gallons. 



Mr. Loxley Meggitt, f..i.c, in seconding the vote of 

 thanks to the author, said that although not an expert on 

 water filtration he had carried out experiments in connec- 

 tion with the purification of sewage from factories, and he 

 thought it strange that work on similar lines had not been 

 done in regard to the purification of water. 



