FILTER 



voluminous works include Guy 

 Patin, Sa Vie et Sa Correspondance, 

 1862; Histoire de la Litterature 

 Anglaise, crowned by the Academy, 

 1883; Nos Grand-Peres, 1887; 

 Profils Anglais, 1893 ; Merimee et 

 ses Amis, 1894; Le Theatre An- 

 glais, 1896, Eng. trans. F. Whyte, 

 1897 ; Prosper Merimee, 1898 ; De 

 Dumas a Rostand, 1898 ; and La 

 Caricature en Angleterre, 1902. 



His son, Louis Napoleon George 

 Filon (b. 1875), a mathematician, 

 was appointed professor of mathe- 

 matics and mechanics in the uni- 

 versity of London, 1912. He 

 served in the army and on the air 

 board during the Great War. 



Filter (late Lat. filtrum, felt). 

 Mechanism designed to act as a very 

 fine strainer and to arrest solid 

 suspended matter, even down to 

 germs and microbes where potable 

 water is in question. 



The filter bed ordinarily used by 

 water companies is formed either 

 of bricks or paving slabs laid in 

 cement or, more generally now, of 

 fine concrete finished with a layer 

 of asphalt or bitumen, the aim 

 being to secure a water-tight sur- 

 face. The floor will not be laid 

 level but will slope a little from the 

 sides towards the middle or to one 

 end, where the arrangements for 

 withdrawing the water will be 

 placed. On this floor will be laid 

 j either coarse gravel to a thickness 

 of about 6 ins., or two layers of 

 bricks or pipes, the lower one 

 having the bricks spaced an inch 

 or so apart, and the upper one 

 having them placed close against 

 one another. Upon the latter will 

 be spread fine gravel to the depth 

 of about 6 ins., and over this a mass 

 of clean, sharp sand to a depth 

 of from 2 ft. to 4 ft. This combi- 

 nation of bricks, gravel, and sand 

 constitutes a filter bed. The term 

 is peculiarly appropriate, as no 

 part of this formation may be the 

 real filtering medium, which will 

 be formed usually by the fine 

 deposit which the water itself 

 gradually lays on the surface of 

 the filter bed. 



When the filter has been working 

 for some time a film of mud, pro- 

 duced by the life-processes of in- 

 numerable bacteria, which destroy 

 organic matter and are an essential 

 feature of the filter, forms on the 

 sand, and the filter is then in its 

 most efficient condition. The rate 

 of filtration should not exceed 

 about one gallon per sq. ft. of bed 

 per hour. In the U.S.A. the 

 mechanical or pressure filter is 

 much used. The water, dosed with 

 a minute proportion of alum, which 

 precipitates clay and organic matter 

 almost instantaneously, is forced 

 through large metal containers al- 



31 47 



FILTER PRESS 



most filled with 

 sand. The rate 

 of filtration is up 

 to 100 times 

 higher than that 

 of a gravity filter. 

 The best forms 

 of household 

 filter are those 

 in which unglazed 

 porcelain or 

 biscuit china is 

 the filtering 

 medium. Microbes 



Filter. Multiple filters and raw water reservoir at 



Accra, Gold Coast Colony. Above, filter bed as used 



in London waterworks, under construction. The three 



depths of loose pipes, gravel, and sand are visible 



cannot pass through or into such 

 material, and water itself perco- 

 lates so slowly at low pressure that 

 a filter of this kind should, if 

 possible, be attached directly to a 

 tap connected with the main. 



To use a neglected filter may be 

 more dangerous than not using one 

 at all, as a foul filter provides an 

 ideal breeding-place for injurious 

 microbes. See Water Supply. 



Filter Press. Appliance much 

 used in a variety of industries, 

 including the manufacture of 

 chemicals, dyes, sugar, paints and 

 colours, pottery, yeast, starch, and 

 many pharmaceutical preparations. 

 To some limited extent it is also 

 used in the treatment of sewage. 



Its construction and operation 

 are best explained by the aid of a 

 diagram as appended. A, A' are 

 two frames, of cast iron usually, 

 though sometimes they are made 

 of wood and occasionally of special 

 metals lead, brass, and even gold. 

 These are filter plates. B is a frame 

 corresponding generally to A, A', 

 and prepared so that it may make 

 perfectly water-tight joints with 

 them at a, a, a, a, but with 

 the centre hollow. This is the 

 " cake " plate. A series of these 

 plates, alternating as shown, are 

 placed in a frame which is provided 

 with gear by which all the plates 

 may be pressed tightly up against 

 one another, a " press " being thus 

 constituted. Over each of the 

 filter plates is placed a filter cloth, 

 C, C', or double cloths may be used, 

 one being fine and the other coarse. 



The centre of 

 the filter plate is 

 grooved all over 

 on each side, so 

 that the filter cloth 

 lies against or 

 upon the grooved 

 surface. The 

 liquor to be fil- 

 tered is introduced 

 at D (the position 

 shown is conven- 

 tional for simplici- 

 ty of illustration) 

 and at once fills the whole of the 

 hollow space of the cake plate ; the 

 liquid passes through the filter cloth 

 into the grooves on the surface of 

 the filter plate and is led by those 

 grooves into the vent E (conven- 

 tional posi- 

 tion) at the 

 bottom of 

 the plate, 

 whence it es- 

 capes. As the 

 process goes 

 on the hollow 

 space of the 

 cake plate 

 gradually fills 

 with solid ma- 

 terial filtered 

 out of the 

 liquid which 

 has passed 

 through the 

 cloth, until in 

 time this space 

 is closed with a 

 firm, com- 

 pacted mass 

 through which 

 it is difficult or 

 impossible to 

 force any more 

 liquid. The 

 press is then 

 opened, the 

 plates drawn 

 apart, the 

 "cake" re- 

 moved, the 

 filter cloths 

 cleaned or 

 replaced 



Filter Press. For 

 explanation see text 



