▪ I. filter, n.
(ˈfɪltə(r))
Forms: 5–9 filtre, (6 fylter, -ture), 6– filter. Also 7 philter.
[ME. filtre, a. OF. filtre, ad. med.L. filtrum: see felt]
† 1. = felt n. Also a piece of felt. Obs.
| c 1400 Mandeville (Roxb.) xxvi. 125 Þan es he sette apon a blak filtre, with þe whilk þai lift him vppe and settez him in his trone. Ibid. xxxiv. 152 Þai dwell all in tentez made of blakk filtre. |
2. a. A piece of felt, woollen cloth, paper, or other substance, through which liquids are passed to free them from matter held in suspension.
Now only with reference to chemical manipulation, where the filter is usually of unsized paper.
| 1563 T. Gale Antidot. ii. 76 b, Distill them by a fylture or thorowe a lyttle bagge, or by a peece of clothe. 1683 Pettus Fleta Min. i. (1686) 214 Dissolve the Vitriol and purify it through a Filtre. 1769 Lane in Phil. Trans. LIX. 220 The clear liquor being decanted, the remainder was passed through a filter. 1812 Sir H. Davy Chem. Philos. 285 The whole is then to be poured upon a filtre of cloth. 1846 J. Baxter Libr. Pract. Agric. (ed. 4) I. 53 Collected on a filter, washed and dried. |
b. ‘A twist of thread’ (or a strip of cloth) ‘of which one end is dipped in the liquor to be defecated, and the other hangs below the bottom of the vessel, so that the liquor drips from it’ (J.).
Obs. exc. in
capillary filter.
| 1559 Morwyng Euonym. 75 Distillacion by a filter, or a list of wollen cloth. 1660 Boyle New Exp. Phys. Mech. xxxv. 263 We resolved, instead of a List of Cotton, or the like Filtre, to make use of a Siphon of Glass. 1727–41 in Chambers Cycl. 1874 Knight Dict. Mech. I. 455/2 Capillary-filter, a simple mode of freeing water of its larger impurities by means of a cord of loose fiber. |
c. In wider sense: Any contrivance for freeing liquids from suspended impurities;
esp. an apparatus consisting of a vessel in which the liquid is made to pass through a stratum of sand, charcoal, or some porous substance.
| 1791 J. Peacock Patent No. 1844 The filters will be cleansed by drawing out the head or body of water or fluid. 1834 S. Bagshaw Patent No. 6708 An improved filter for water or other liquids. 1872 Baker Nile Tribut. xx. 339 Nevertheless the natives had scraped small holes in the sand, as filters. 1879 A. B. MacDowall in Encycl. Brit. (ed. 9) IX. 167/2 The filter was occasionally cleaned with an exhausting and condensing pump. |
d. transf. and
fig.| 1605 Timme Quersit. i. v. 20 The common salt..passing thro' the philter of the earth. 1802 Paley Nat. Theol. xii. (1803) 241 This natural filter [the bills of a duck]. 1840 Alison Hist. Europe (1850) VIII. l. §39. 159 The whole information..was strained through the imperial filters. 1873 Tristram Moab xii. 228 A heavy conversation of ponderous compliments passed through the dragoman filter. |
3. a. A contrivance for arresting dust, smoke, disease-germs, etc. in the air which is breathed.
| 1874 Knight Dict. Mech. s.vv. Filter, Air-filter. |
b. Photogr. A screen to cut out rays which interfere with correct colour-rendering;
= colour-filter (see
colour n.1 18).
| 1900, 1902 [see colour n.1 18]. 1912 E. J. Wall Dict. Photogr. (ed. 9) 335 Most makers of orthochromatic..plates also supply filters specially adapted for use with their plates. 1948 [see colour n.1 18]. 1958 M. L. Hall Newnes' Compl. Amat. Photogr. viii. 97 Light filters are transparent, coloured discs which are attached to the camera lens for the purpose of modifying the colour quality of the light transmitted but which do not otherwise affect the image formed by the lens. |
c. In a cigarette: a pad of absorbent material fitted at the unlit end to purify the smoke. Also, a cigarette so fitted.
| 1908 Lancet 21 Mar. 907/2 A pad of cotton wool is inserted into the paper casing of these cigarettes, which effectually prevents dust and shreds of tobacco entering the mouth, besides which a large proportion of the objectionable oils formed during smoking is arrested in the wool filter. 1958 Amer. Speech XXXIII. 147 A new cellulose fiber for..cigarette filters. 1963 N. Freeling Gun before Butter ii. 96 Yes, I do smoke but only filters. |
d. Radiology and
Nuclear Sci. A sheet or block of material inserted in the path of a beam of X-radiation or elementary particles in order to reduce the intensity of radiation of certain wavelengths or energies.
| 1917 Arthur & Muir Man. Pract. X-Ray Work (ed. 2) x. 313 For skin treatment it is well to use a weak filter—such as thick paper—which will absorb the softest rays which..might otherwise produce dangerous over-effects. 1957 Encycl. Brit. XVIII. 898/1 In some of the work for which X-rays are used, the quality or penetrating ability of the radiation is expressed..in terms of its absorbability in filters of standard composition and thickness. 1969 G. E. Bacon Neutron Physics x. 127 We can..use a sufficiently thick block of graphite as a filter which..removes all neutrons with a wavelength greater than 0·67 nm. |
e. Electronics. A passive circuit that attenuates all signals except those within one or more frequency bands.
| 1920 Radio Rev. July 505 By a combination of the two types of filter only currents between the two frequency limits are transmitted. 1922, etc. [see band n.2 14]. 1938 F. E. Terman Fund. Radio x. 267 The pulsating voltage delivered by the rectifier output can be smoothed into a steady direct-current voltage..by being passed through an electrical network called a filter, which ordinarily consists of series inductances and shunt condensers. 1955 G. M. Glasford Fund. Telev. Engin. xvii. 581 There must be employed in the video section a 4·5-Mc rejection filter to remove the audio carrier and its sidebands from the video signal. 1959 Engineering 30 Jan. 153/3 A conventional voltage doubler serves as the high voltage rectifier, with sufficient capacitance employed in the filter to reduce the r.m.s. ripple to 0.5 per cent. |
4. A material for filtering.
rare.
| 1823 J. Badcock Dom. Amusem. 26 The burning it over and over again..produces a better filtre than at first. 1870 Tyndall in Nature 27 Jan. 341 This [cotton-wool] was the filter used by Schrœder in his experiments on spontaneous generation. |
5. attrib. and
Comb., as
filter-shop; also
filter aid, any substance added to a liquid or to a filtering medium in order to improve filtration by preventing the formation of an impervious filter cake;
filter-arrow, a device forming part of a traffic signal (
cf. filter v. 3 b);
filter-bed, a pond or tank with a false bottom covered with sand or gravel, serving as a large filter; also
fig.;
filter cake, the insoluble residue deposited on a filter; so
filter-caked adj.;
filter circuit Electronics = 3 e above;
filter condenser Electronics, a capacitor forming one of the chief elements in a filter circuit;
filter factor: see
factor n. 7 c;
filter-faucet (see
quot.);
filter-feeder, an animal that obtains its nourishment by means of filter-feeding;
filter-feeding vbl. n., the filtering and ingestion of nutrient matter suspended in water; also as
adj.;
filter-paper, porous paper to be used for filtering;
filter-passer, a filter-passing ‘organism’,
esp. a virus;
filter-passing a., not retained by a filter,
esp. by one that does retain bacteria;
filter-press, (
a) a filter in which the liquid is forced through by pressure; (
b) a machine for extracting oil from fish;
filter reactor Electronics, a reactor forming one of the chief elements in a filter circuit;
filter shot Photogr., a photograph taken through a colour-filter;
filter tip = 3 c above; hence
filter-tipped a.,
filter-tipping vbl. n.| 1946 Dickey & Bryden Theory & Pract. Filtration iii. 47 A precoat and/or a *filter aid are often necessary, to prevent the deposited particles from being carried..into the interstices of the filter medium, or filter cake. 1951 Kirk & Othmer Encycl. Chem. Technol. VI. 510 Materials such as kieselguhr or diatomite, asbestos fibres,..and sawdust flour are examples of materials used as filter aids. 1963 Times 24 May p. xiv/1 (Advt.), Filteraids and chemicals to purify most pipe-borne liquids. |
| 1965 Priestley & Wisdom Good Driving xi. 77 A *filter-arrow allowing left-turning vehicles to proceed. |
| 1874 Knight Dict. Mech. I. 846/2 *Filter-bed, a settling pond whose bottom is a filter. 1885 Weekly Notes 7 Feb. 24/2 The water..was filtered through filterbeds on their premises. 1892 Pall Mall G. 25 May 2/1 All that is known here of the Transvaal..comes through the political filter-beds of Cape Town. |
| 1912 Mining & Engin. World 20 Apr. 863/3 In forming a *filter cake with any material there is a certain point where the rate of filtration begins to drop off very rapidly due to the resistance offered by the cake. 1967 Filtration & Separation IV. 471 Most filter cakes show some degree of compressibility. |
| 1956 K. Imhoff et al. Disposal of Sewage xii. 202 The *filter-caked sludge may be dried finally by heat and sold as fertilizer. |
| 1920 Radio Rev. July 505 A number of special *filter circuits designed with the object of allowing certain frequencies to pass and cutting out others. 1962 A. Nisbett Technique Sound Studio iv. 82 Correction of a whole range of faults, such as noise, distortion, and unsatisfactory frequency response, is often attempted by means of filter circuits. |
| 1922 A. F. Collins Book of Wireless Telegraph & Telephone iii. iv. 197 Connect the filter reactor and the *filter condensers to the mid-taps of the filament secondaries. 1951 S. Deutsch Theory & Design Telev. Receivers xii. 406 The size of the various filter condensers is determined by consideration of tolerable ripple. |
| 1921 *Filter factor [see factor n. 7 c]. 1958 M. L. Hall Newnes' Compl. Amat. Photogr. vii. 98 Filters reduce the light transmitted to form the image and require a compensating exposure increase; with certain very pale filters..this filter factor is..small enough to be ignored... The increase is specified as a multiplying factor. |
| 1874 Knight Dict. Mech. I. 846/2 *Filter-faucet, one having a chamber containing sand, sponge, or other material to arrest impurities. |
| 1928 Trans. R. Soc. Edin. LV. i. 235 Besides being a *filter feeder, Hemimysis also feeds from large solid masses of food. 1959 A. Hardy Fish & Fisheries v. 109 The most elaborately developed suspension-feeders are the bivalve (lamellibranch) molluscs. They are filter-feeders. Their gills have been enormously enlarged..as sieving devices to collect the fine particles of food from the water which is propelled through them by cilia. |
| 1931 Trans. R. Soc. Edin. LVI. iii. 537 A study of the feeding mechanisms and physiology of digestion in Polychaetes has..been begun, choosing a *filter-feeding form as a starting point. 1963 R. P. Dales Annelids 11 With loss of motility we find more selective methods of feeding, this evolution culminating in the filter-feeding fan or feather-duster worms. |
| 1849 D. Campbell Inorg. Chem. 18 A few grains of recently-heated spongy platinum, in a small piece of *filter paper. 1892 Photogr. Ann. II. 109 Dried on pure filter paper. |
| 1913 J. McFadyean in XVIIth Internat. Congress Med. IV. i. 50 The term ‘*filter passers’ has been adopted..as the preferable name for the micro⁓organisms which..were..called the ultra-visible or invisible viruses. 1919 Nature 6 Nov. 210/2 The infective agents of the common exanthemata..are at some period of their life-history so small as to be included amongst the ‘filter-passers’. 1946 Nature 21 Sept. 398/1 Bacteria, filter-passers, viruses, protozoan and metazoan parasites or fungi. |
| 1915 Lancet 4 Dec. 1241/2 Attempts were made to demonstrate the presence of non-pathogenic *filter-passing viruses. 1930 Morning Post 24 Nov. 3 ‘Ultra⁓microscopic’ or ‘filter passing’ virus. 1947 Auden Age of Anxiety (1948) v. 107 No filter-passing Virus invade. 1957 G. E. Hutchinson Treat. Limnol. I. vi. 385 They give the percentage effect of suspended or retained and dissolved or filter-passing material on the absorption. |
| 1889 Pall Mall G. 2 May 7/1 The sludge is next forced into a *filter press. |
| 1922 A. F. Collins Book of Wireless Telegraph & Telephone iii. iv. 194 The purpose of a *filter reactor is to smooth out the pulsating direct current after it is produced by the rectifier tube. |
| 1842 Dickens Amer. Notes II. iv. 112, I have seen water like it at the *Filter shops. |
| 1951 J. B. Priestley Festival at Farbridge i. iii. 126 We got some lovely *filter and scrim shots. |
| 1932 Daily Mail 12 Oct. 8/4 (Advt.), The *Filter Tip that holds throat irritants in check. 1953 Wall St. Jrnl. 1 Oct. 1/4 The work on a filter-tip cigaret began early in 1951. The company was seeking a non-mineral material to filter the smoke and finally decided upon a highly purified alpha cellulose tip. 1957 New Yorker 23 Nov. 100/2 When I ran out of American filter-tips, I chose the nearest equivalent I could find—a Bulgarian make. 1957 Times 28 Dec. 4/2 A substantial increase in the sales of filter-tip cigarettes was a common feature of tobacco sales in Britain and the United States in 1957. |
| 1954 Newsweek 16 Aug. 72/3 The American Tobacco Co...brought out a *filter-tipped version of Herbert Tareyton, its king-size and cork-tipped brand. |
| 1954 Wall St. Jrnl. 18 Nov. 10/2 American Machine Foundry Co. has developed a new method of applying filter tips to cigarets which it claims ‘renders obsolete all other *filter tipping devices currently used in the tobacco industry’. |
▪ II. filter, v. (
ˈfɪltə(r))
Forms: 7
fylter, 7–9
filtre, 6–
filter. Also 6
philter.
[ad. mod.L. filtrāre, f. filtrum filter n. Cf. F. filtrer.] 1. a. trans. To pass (a liquid) through a filter, or some porous medium, for the purpose of removing solid particles or impurities. Also with
off. Also
absol.| 1576 G. Baker Jewell of Health i. i. 2 The dropping caused by a Lyste, or piece of Woollen cloth..which maner of dooing the Chymistes name Fyltring. 1594 Plat Jewell-ho., Chim. Concl. 23 Some use to filter this Lee divers times. 1605 Timme Quersit. i. ix. 36 They dissolue many times, they fylter, and coagulate. 1671 Grew Anat. Plants i. i. §31 The Sap..not being filtred through so fine a Cotton. 1747 Wesley Prim. Physic (1762) 86 Filtre the Tincture thro' Paper. 1784 Cowper Task ii. 507 Sages strove In vain to filter off a crystal draught Pure from the lees. 1812–6 J. Smith Panorama Sc. & Art II. 355 Putrid and stinking water may be rendered sweet by filtering it through charcoal-powder. 1838 T. Thomson Chem. Org. Bodies 200 We then filter, washing the blue-coloured sulphate of lime remaining on the filter till it becomes red. 1853 A. Soyer Pantroph. 27 The liquid was several times filtered. |
b. transf. and
fig.| 1830 Gen. P. Thompson Exerc. (1842) I. 291 The Chamber of Deputies, though filtered through every process which policy could invent. 1856 Emerson Eng. Traits, First Visit Wks. (Bohn) II. 5 The passage would no doubt strike you more in the quotation than in the original, for I have filtered it. 1885 Manch. Exam. 10 Jan. 5/3 At present his instructions to counsel are filtered through a solicitor. 1892 Pall Mall G. 4 May 1/3 Each of these images is ‘filtered’ through a colour screen. |
c. Said of the filtering material.
| 1854 Woodward Mollusea (1856) 37 The sea-weed filters the salt-water. 1882 Watts Dict. Chem. II. 648 Paper which filters slowly may be improved in quality by this treatment. |
d. Electronics. To pass (an electrical signal, etc.) through a filter (
filter n. 3 e) as a means of removing or attenuating components of undesired frequencies or undue prominence. Also with
out: to select or remove (a component of a signal) by means of a filter.
| 1921 B. Leggett Wireless Telegr. xiii. 399 Zenneck has proposed..to filter out and utilise this harmonic by means of a tuned circuit. 1937 W. G. Dow Fund. Engin. Electronics xxi. 487 The greater the number of anodes, the smaller is the ripple to be filtered out. 1959 Zimmermann & Mason Electronic Circuit Theory iv. 130 The effects of a poorly filtered power supply on an audio system can be heard directly in the form of an objectionable hum. |
2. To cause (a liquid) to pass drop by drop, or slowly, through a porous medium (now only in
pass.); also,
† to give forth through the pores, exude.
rare.
| 1583 Stanyhurst æneis iii. (Arb.) 71 The tre..of swart blud filtred abundance. 1644 Digby Two Treat. i. xx. 183 That streame [of atoms]..clymbing and filtring it selfe along the stones streame. 1860 Maury Phys. Geog. Sea x. §466 Rivers..some of which are filtered through soils..which yield one kind of salts. |
3. a. intr. To pass as through a filter; to percolate; also with
away,
down.
Cf. F.
filtrer, used
refl. and intr. in this sense.
| 1798 W. Blair Soldier's Friend 100 The water..will filter through the sand. 1864 Marsh Man & Nature 438 A stratum of snow..causes almost all the water that composes it to filter down into the earth. 1882 Vines Sachs' Bot. 687 Water will filter through the cell-walls into the cavities of the wood. |
| transf. and fig. 1821 Clare Vill. Minstr. I. 207 The sunbeams, filtering small, Freckling through the branches fall. 1868 Yates Rock Ahead ii. iii, A perpetual stream of..people..would filter..through her..drawing-rooms. 1944 Times 29 Apr. 3/3 Here the enemy succeeded in temporarily filtering through our lines. 1958 Hayward & Harari tr. Pasternak's Dr. Zhivago ii. viii. 231 Although the station area was cordoned off..passengers for the local trains had managed, in some unaccountable way, to ‘filter through’ (as we would say now). 1969 Listener 27 Feb. 281/2 Meanwhile foreign literature (Ibsen and Chekhov notably) and painting (the Post-Impressionist Exhibition) were slowly filtering in. 1971 Daily Tel. 16 June 11/5 Hints..of an upsurge in Government spending on new by-passes..have filtered out with unusually effective timing. |
b. spec. Of road vehicles: to join another line of traffic at a road junction,
usu. by deviating from the main stream which is held up by traffic lights.
| 1928 Traffic Signals to be used by Police & Drivers of Vehicles (H.M.S.O.) ii. 10 At road junctions, when one stream of traffic has been halted, constables should, so far as may be safe or practicable, permit drivers who wish to do so to turn to the left and so filter into the cross stream of moving traffic. 1937 V. Woolf Years 334 He filtered slowly round the corner. 1971 A.A. Continental Handbk. 396 Some crossroads have traffic lights with a flashing yellow arrow which allows drivers to filter off in the direction of the arrow. |
4. a. To obtain by filtering. Also
transf. rare.
| 1794 Pearson in Phil. Trans. LXXXIV. 387 The liquid filtered from these solutions had a sweetish and bitterish taste. 1845 Darwin Voy. Nat. i. (1879) 5 Fine dust, which appeared to have been filtered from the wind by the gauze of the vane at the mast-head. |
b. to filter out (
trans.): to separate or prevent the passage of by, or as by, filtering.
| 1908 [see scratch n. 6 b]. 1917 G. W. C. Kaye X Rays (ed. 2) ix. 116 By filtering out the soft rays from the primary beam by the use of a suitable screen, the polarisation can be doubled. 1921, 1937 [see 1 d above]. 1927 Davis & Kaye Acoustics of Buildings i. 7 In suitable circumstances it is possible to filter out undesired harmonics. 1936 Discovery July 224/1 These [stops] change the tone-colour..the original note produced being deliberately made very rich in overtones, which in turn are filtered out as required. 1951 Kirk & Othmer Encycl. Chem. Technol. VI. 516 The sand acts as the filter medium and filters out suspended solids. 1961 G. Millerson Technique Telev. Proa. iii. 43 Sound reproduction begins to lose crispness as higher audio notes are filtered out. 1965 N. Chomsky Aspects of Theory of Syntax 224 An extraneous factor..filters out certain latent intepretations provided by the deep structures. 1967 M. Frayn Towards End of Morning viii. 151 He seemed unaware of the noise Damian was making. Bob's head ached..at the effort of filtering the adult conversation out from it. 1971 Daily Tel. 4 Mar. 3/3 Continued flights..could reduce the ozone layer that filters out cancer-producing ultra-violet rays. |
Hence
ˈfiltered,
ˈfiltering ppl. adjs. Also
ˈfilterer, that which filters or serves as a filter.
| 1727 Bailey vol. II, Filtered, strained through a Paper, Cloth, etc. 1794 Schmeisser in Phil. Trans. LXXXIV. 421 The remaining filtered liquor was saturated with purified pot-ash. 1809 J. F. Archbold Patent No. 3225 It [sea water] is passed through a filterer. 1821 Clare Vill. Minstr. II. 162, I love to watch thy [an hour-glass's] filtering burthen pass. 1830 Tennyson Ode to Memory iv, The filtered tribute of the rough woodland. 1853 A. Soyer Pantroph. 412 Eight barrels of filtered water. 1859 Cornwallis New World I. 38 The stretcher might have been directly under this water filterer. |
▪ III. filter var. form of
felter v.,
philtre.