MODERN METHODS OF WATER PURIFICATION. 333 



largest, newest and best installations and naming them Ameri- 

 can mechanical filters, it is to be understood that one is 

 describing what is usually called the Jewell filter by non- 

 Americans — Columbus, New Orleans, Hackensack and Little 

 Falls are examples of the newer development of the Jewell 

 filters. Raw water is admitted from the river through a 5- 

 foot 6-inch steel pipe into a concrete stand pipe, and there it 

 receives its mixture with the coagulant. In the w'orks visited 

 sulphate of alumina is the coagulant used, but sulphate of iron 

 is used in some w^orks. The water next passes slowly through 

 the coagulating basins, taking some 12 to 18 hours — baffled 

 in some cases — and here subsidence takes place. The water 

 is removed from near the surface, and delivered to the filters. 

 In the works I am keeping before me as a mental picture 

 there w^ere 32 of these filters. These filters were of reinforced 

 concrete, no wooden or steel filters being used in the con- 

 struction. After going through the filters the water passes 

 into the clear w^ater basin. A few remarks on the various 

 steps to make the working plain now follow. 



The alum is run down chutes into the dissolving tanks, 

 where a saturated solution is prepared. From these the water 

 next goes through cement pipes to the mixing tanks. These 

 are concrete tanks, holding about 25,000 gallons, where the 

 saturated solution of alum is diluted to the desired degree. 

 " Blowers " in the tank keep the solution uniform. All pipes, 

 valves and fittings are made of " hard rubber " to prevent 

 corroding action of alum.* There are mechanical arrange- 

 ments to secure even head to the llow of alum solution, and 

 also devices to control the proportion of solution reaching the 

 raw water. One way in which alteration in the rate of flow 

 of coagulant into the water is communicated to those in charge 

 is by the automatic ringing of a gong by means of a float in 

 the orifice tank. The water now passes through the coagulat- 

 ing and subsidence basin, entering from near the bottom ^nd 

 passing diagonally upward through the basin, which it leaves 

 near the top. Tlie sulphate of alumina is decomposed and a 

 floculent, gelatinous precipitate of aluminic hydrate is formed. 

 The suspended substances, bacteria and organic matter are 

 entangled and aggregated, carried down through the water, 

 and the greater part of them are deposited on the bottom of 

 the coagulation and subsidence basin. From these basins the 

 clarified water passes to the filters, where, in passing, it is 

 strained, and the remaining coagulated particles including 

 bacteria are removed. A few^ minutes after a filter is put into 

 operation, a thin gelatinous layer is formed on the top of the 

 sand of the filter. 



The filters are rectangular, built of continuous reinforced 

 concrete, each filter practically a monolith. There were ^2 

 such at Little Falls works, each filter capable of filtering" 

 1,000,000 gallons per day at " normal " rate, through a filter 

 area of 24 feet by 15 feet. 



* I made a note at the time that perhaps it would be possible to apply 

 rubber solution to the parts in our settling pools, etc., at Mazel's Poort that 

 are so much incrustated by the precipitant used in our water purification. 



