August 1, 1902.] 



SCIENCE. 



169 



cibJe substances from the sewage and 

 gives a product that can be emptied into a 

 stream without causing offense. On the 

 other hand, the construction is costly. 

 There is much difficulty experienced in 

 automatically converting the liquid into 

 spray, chiefly through clogging of the holes 

 in the distributer, and being obliged to heat 

 the sewage in winter, which must be done, 

 makes the cost of treatment very large. 



A form of continuous Alter that has 

 attracted much attention in England dur- 

 ing the past year is the Stoddart filter. 



This is essentially only a heap of coarse 

 coke or hard cinder, diameter two to three 

 inches, placed on a cement floor which has 

 a fall of one inch in three feet from the 

 center to the collecting drains which sur- 

 round, but are entirely outside, the filter. 

 As no liquid can remain in the filter no 

 walls are necessary and the side of the 

 filter can be made of large pieces of the 

 filling material, with a slight batten to in- 

 crease solidity. The essential points of the 

 filter are the slope of floor, the collecting 

 drains and the coarseness of the filling ma- 

 terial, free from all small particles. 



The method of distribution is patented 

 by Mr. Stoddart, and is one of the most 

 essential parts of the filter. In principle it 

 is very simple. It is made of zinc or gal- 

 vanized iron, and consists of a number of 

 perforated gutters, eleven in each section, 

 two inches wide and one and a half inches 

 deep, arranged at right angles to the supply 

 channel. The perforations are cut in dia- 

 mond shape at intervals along the upper 

 edges of the gutters. On the under surface 

 of the gutters are a number of small points, 

 360 to the square yard. The distributer 

 rests upon the margin of the supply chan- 

 nel and upon suitable supports at the fur- 

 ther end, and must be perfectly level to 

 secure equal distribution. The clarified 

 sewage flows from the supply channel into 

 the gutters and over the gutters through 



the diamond-shaped perforations, and falls 

 from the small points in a series of drops. 



A filter such as described, and six feet 

 deep, Mr. Stoddart claims will treat septic 

 tank or clarified sewage at the very high 

 rate of five million gallons per acre. 



A number of small plants have been built 

 at different places in England, and experi- 

 mental plants are now being tried at Man- 

 chester and Leeds. Opinions differ greatly 

 as to the amount of purification that can 

 be obtained by this form of continuous filter 

 when run at the high rate of five million 

 gallons per acre. I think, however, it is 

 true that when the filter is in perfect run- 

 ning order, this method will purify sewage 

 at a higher rate than any form of filter yet 

 devised. The trouble is to keep the filter 

 in perfect running order ; if any solid mat- 

 ter lodges in the channels of the trays, or if 

 the trays are not kept perfectly level, the 

 distribution becomes uneven, and the suc- 

 cessful working of the process depends on 

 the even distribution of the sewage on the 

 filter. To keep the channels free from sedi- 

 ment, and the plates from buckling, even 

 if this is possible, must require constant 

 attention. Further, in this process, there 

 is no provision for heating the sewage in 

 winter, and, in my opinion, in cold weather 

 the whole filter would become one mass of 

 ice, practically stopping bacterial action. 



By far the most interesting exijeriment 

 on continuous filtration that is now being 

 tried is the one at Salford, Eng. In this 

 city a plant has been just constructed by 

 Mr. Jos. Corbett, Borough Engineer, which 

 is to treat from eight to sixteen million gal- 

 lons of crude sewage per day. The sewage 

 is first to be subjected to chemical treat- 

 ment, to remove the suspended matter, and 

 the clarified sewage is to be distributed 

 continuously, in the form of spray on the 

 filter bed. 



This bed is 500 feet long, 510 feet wide, 

 10 feet deep, and filled with cinders passed 



