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 sb. Also a piece of felt. Obs.
c. 1400. Maundev. (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. Þat dwell all in tentez made of blakk filtre.
2. 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, Antidotarie, 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, fair and clear.
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, trans. The Treasure of Euonymus, 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, such as cotton candle-wick.
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, and thus they were satisfied with this poisonous fluid.
1879. A. B. MacDowall, in Encycl. Brit. (ed. 9), IX. 167/2. The filter was occasionally cleaned with an exhausting and condensing pump, which sucked up water rapidly through the filtering material and then sent it back with force, washing out the dirt.
d. transf. and fig.
1605. Timme, Quersit., I. v. 20. The common salte, and that which is of the sea, passing through the philter of the earth, and boyled and digested with the heates of the bowels of the same earth, doth participate of the nature of fixed and firme salt.
1802. Paley, Nat. Theol., xii. (1803), 241. What more artificial, or more commodious instrument [the bill] of selection, could have been given to it [the duck], than this natural filter?
1840. Alison, Hist. Europe (1850), VIII. i. § 39. 159. Under the active administration and vigilant police of the empire, these powers were so constantly and rigorously exercised, that not only was the whole information on political subjects or public affairs, which was permitted to reach the people, strained through the Imperial filters, but all passages were expunged from every work which had a tendency, however remote, to nourish independent sentiments, or foster a feeling of discontent with the existing government.
1873. Tristram, Moab, xii. 228–9. A heavy conversation of ponderous compliments passed through the dragoman filter.
3. A contrivance for arresting dust, smoke, disease-germs, etc. in the air which is breathed.
1874. Knight, Dict. Mech., s.vv. Filter, Air-filter.
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-bed, a pond or tank with a false bottom covered with sand or gravel, serving as a large filter; also fig.; filter-faucet (see quot.); filter-paper, porous paper to be used for filtering; filter-press, (a) a filter in which the liquid is forced through by pressure; (b) a machine for extracting oil from fish.
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.
1874. Knight, Dict. Mech., I. 846/2. *Filter-faucet. One having a chamber containing sand, sponge, or other material to arrest impurities in water.
1889. Pall Mall G., 2 May, 7/1. The sludge is next forced into a *filter press.
1842. Dickens, Amer. Notes, II. iv. 112. I have seen water like it at the *Filter shops.
