340 MODERN METHODS OF WATER PURIFICATION. 



contact surfaces, removing- suspended matter and bacteria to a 

 considerable extent before they reach the sand and oxidium. 

 In another example of Candy's filters at Brede Pumping Sta- 

 tion, Hastings, there are 3 inches of sand at the top and at 

 the bottom, all the rest being polarite. 



The water to be filtered is admitted into the cylinders under 

 pressure, varying in different works according to local require- 

 ments, or local ideas of what is most suitable, and is automati- 

 cally sprayed in contact with air under pressure, whereby 

 atmospheric oxygen is driven into the water, which thus passes 

 under pressure down through the 5 feet of the filtering 

 material. Some samples of water which I saw came out from 

 the filters exposed to so much pressure that they were practi- 

 cally aerated waters when they emerged. Pressure gives 

 oxidation; it also drives bacteria through. 



The filters are cleansed by reversal of the flow passing 

 through the layers. Under a considerable pressure filtered 

 water is passed upwards, washing out the interstices of the 

 material and carrying away the impurities. The length of time 

 occupied in cleaning operations is from 5 to 15 minutes, and 

 it is a very simple matter, merely opening and closing valves. 

 There are no mechanical arrangements in the way of rakes and 

 agitators, only water flushing is used, and the amount of water 

 used in washing the Candy filters that I saw was very much 

 less than in other methods inspected; for instance, instead of 

 the practical minimum of 3 per cent, of the filtered water being 

 required for filter washing in the American or Jewell filtration, 

 and at times more than that, it is only one-half of i per cent., 

 i.e.. about one-sixth of the amount, or even less than that in 

 some of the installations that I saw. The washing operation 

 takes about 10 minutes, and is done when needed : in some 

 cases every two or three days. In one installation where it 

 had been at work for years it was washed only once a week, 

 and it had given complete satisfaction. I saw a number of 

 Candy filters, and will quote some of the results attained, which 

 were in some cases most eminently satisfactory and highly 

 praised to me by the Water Engineers or Town Surveyors of 

 various places. 



In Harrogate they have had excellent results. Mr. Dixon, 

 the Water Engineer there, states that "the analytical results 

 show that the water from the Candy filters is cleaner and better 

 filtered than the water from our best sand beds." A portion 

 of the water is still filtered in Harrogate by the old sand filters, 

 so they are able to compare them, and he stated that the Cor- 

 poration of Harrogate considered they obtained a higher puri- 

 fication from a bacteriological point of view from the Candy 

 filters than from the sand filters, especially during frost. That 

 is the opinion of a man well qualified to judge, because he had 

 experience of the two systems together to guide him. At the 

 same time also the working expenses of the Candy he found 

 were roundly half, or less than that of the sand filters. For 

 such an experienced opinion as Mr. Dixon's one has great 

 respect, but it must be stated that the water is gathered from 

 moorlands, and though very discoloured and deep ])rown in 



