Cooley's Cyclopaedia of Practical Receipts Volume I Part 239

=FILARIA SANGUINIS HOMINIS.= In 1872, Dr T. R. Lewis, in examining microscopically the blood and urine of some of his patients in India, discovered a worm enveloped in an extremely delicate tube, closed at both ends, within which it could either elongate or shorten itself. This parasite (called from its princ.i.p.al habitat the _Filaria Sanguinis Hominis_) is about 1/75th of an inch in length, and about 1/35000th of an inch in diameter. When removed from the body with a small quant.i.ty of blood, it is described as being in a state of incessant motion, unceasingly coiling and uncoiling itself, las.h.i.+ng the blood-corpuscles in all directions, and insinuating itself between them.

The worms are said, when first taken from the body, to present a translucent appearance; the larger specimens, however, frequently exhibit an aggregation of granules towards the junction of the lower and middle half. Occasionally a bright spot, suggestive of a mouth, is seen at the thicker extremity. It is stated that they continue active from six to thirty hours. Mr Lewis does not believe they are able to perforate the tissues.

"These parasites," says Mr Lewis, "are so persistently ubiquitous, as to be obtained day after day by simply p.r.i.c.king any portion of the body, even to the tips of the fingers and toes of both hands and both feet of one and the same person, with a finely pointed needle. On one occasion six excellent specimens were obtained in a single drop of blood by merely p.r.i.c.king the lobule of the ear."

Dr Lewis estimates, from the number of the Filaria found in one drop of the blood of one patient, that his body must have contained more than 140,000. The presence of these creatures in the blood is believed to be the cause of chylous urine, which is a very common disease in the East. It seems probable they gain admission into the body from being present in drinking water.

=FIL'BERT.= _Syn._ FILBERD. The fruit of the cultivated hazel or nut-tree (_Corylus Avellana_). Filberts are distinguished from common nuts by their lengthened figure and larger size. The best are imported from Spain.

=FILES.= The manufactures of these articles do not come within the limits of this work. It may, however, be useful to mention that FILES, FLOATS, and RASPS, which "cut dull" from age, dirt, or being much worn, are greatly improved by being kept wet, immersed in water for some hours, or even for a day or two.

Mr Ernest Spon recommends the following method for renovating files:--The file to be first cleansed from all foreign matter, and then dipped in a solution of one part of nitric acid, three parts of sulphuric acid, and seven parts of water; the time of immersion will be according to the extent the file has been worn, and the fineness of the teeth, varying from five seconds to five minutes. On taking it out of the mixture, wash in water, then dip in milk of lime, wash off the lime, dry by a gentle heat, rub over equal parts of olive oil and turpentine, and finally brush over with powdered c.o.ke.

=FIL'TER.= _Syn._ FILTRUM, L. An instrument or apparatus for straining or filtering liquids.

=FIL'TERING POWDERS.= _Prep._ 1. Fuller's earth washed, dried without heat, and reduced to coa.r.s.e powder.

2. Pipe clay or potter's clay, as the last. Both the above are used to filter and bleach oils.

3. Clay or fuller's earth, 1 part; fine siliceous sand, 2 parts; the two are separately washed, after which they are drained, and mixed together, and dried as before. Used for GLUTINOUS OILS.

4. Granulated animal charcoal, sifted and fanned from the dust. Used to filter and bleach SYRUPS and VEGETABLE SOLUTIONS.

_Obs._ Filtering powders are prepared of several degrees of coa.r.s.eness, and should be chosen with reference to the degree of fluidity of the liquid to be filtered through them. In no case should they be reduced to fine powder, as not only is the process of filtration thereby rendered unnecessarily tedious, but in some cases (as when charcoal dust is mixed with glutinous vegetable solutions and syrups) the filtrate carries off a portion of the powder, which can afterwards be separated from it only with considerable difficulty. See CHARCOAL, FILTRATION, OIL, &c.

=FILTRA'TION.= _Syn._ FILTRATIO, L. The separation of liquids from substances mechanically suspended in them, by pa.s.sing them through media having pores sufficiently fine to retain or keep back the solid matter.

Filtration is one of the most common and useful of the chemico-mechanical operations of the arts, and its successful performance in an economical and expeditious manner is therefore a matter of the highest importance in the laboratory, and, indeed, in almost every branch of human skill and industry, in which liquids are employed. Simple in principle, and apparently easily performed, it is, nevertheless, one of those operations which require no less of care than of tact and experience to conduct it with certainty and success. The losses sustained in the laboratory, by defective manipulation in this particular, often exceed those arising from ignorance and accidents in every other department conducted in it.

Filtration is generally resorted to for the purpose of freeing liquids from feculence, dirt, and other foreign matter, and for obtaining them in a clear or transparent state; but, in some cases, it has for its object the collection of the suspended substances, as precipitates, &c., and in others both these intentions are combined. The word 'filtration' is absolutely synonymous with 'straining,' but in the language of the laboratory it is usually applied to the operation of rendering liquids transparent, or nearly so, by pa.s.sing them through fine media, as filtering paper, sand, and the like; whilst the term 'straining' is employed to designate the mere separation of the grosser portion, by means of coa.r.s.e media, flannel, horsehair cloth, &c., through which they flow with considerable rapidity. Filtration is distinguished from 'clarification' by its mere mechanical action, whereas the latter operates by depuration, or the subsidence of the suspended substances or faeces, arising from their gravity being naturally greater than the fluid with which they are mixed, or being rendered so by the application of heat, or by the addition of some foreign substance.

The apparatus, vessels, or media, employed for filtration, are called 'FILTERS,' and are technically distinguished from 'STRAINERS' by the superior fineness of their pores.

Both strainers and filters act on the same principles as the common sieve on powders; they all, in like manner, retain or hold back the coa.r.s.er matter, and permit the liquid or smaller and more attenuated particles to pa.s.s through. The term 'medium' (pleural 'media') is applied to the substance or substances through the pores of which the liquid percolates.

[Ill.u.s.tration: FIG. 1.]

The form of filters, and the substances of which they are composed, are various, and depend upon the nature of the liquids for which they are intended. On the small scale, funnels of tin, zinc, copper, wedgwood-ware, earthenware, gla.s.s, or porcelain, are commonly employed as the containing vessels. (See _engr._) The filtering medium may be any substance of a sufficiently spongy or porous nature to allow of the free percolation of the liquid, and whose pores are, at the same time, sufficiently small to render it limpid or transparent. Unsized paper, flannel, linen, calico, cotton wool, felt, sand, coa.r.s.ely powdered charcoal, porous stone, or earthenware, and numerous other substances of a similar kind, are employed for this purpose.

[Ill.u.s.tration: FIG. 2.]

For many liquids that filter easily, and in which the suspended matter is of a coa.r.s.e and porous nature, it is often sufficient merely to place a little cotton wool or tow, or a small piece of sponge, in neck of the funnel, as at (_a_, fig. 1) in the above engr.; but such an apparatus, from the small extent of the filtering surface, acts either slowly or imperfectly, and soon gets choked up. Filters of unsized paper are well suited for all liquids that are not of a corrosive or viscid nature, and are universally employed for filtering small quant.i.ties of liquids in the laboratory. A piece of the paper is taken of a size proportionate to the quant.i.ty of the liquid to be filtered, and is first doubled from corner to corner into a triangle (see _engr. a_), which is again doubled into a smaller triangle _b_, and the angular portion of the margin being rounded off with a pair of scissors _c_, it const.i.tutes a paper cone, which is placed on a funnel of proportionate capacity, and is then nearly filled with the liquid. A piece of paper so cut, when laid flat upon the table, should be nearly circular. Filtering paper is now sold ready cut in circles of various sizes, which simply require doubling for use. Another method of forming a paper filter, preferred by some persons, is to double the paper once, as above, and then to fold it in a similar way to a fan, observing so to open it and lay it on the funnel that a sufficient interval be left between the two to permit of the free pa.s.sage of the filtered liquid on its descent towards the receiver. The 'plaited filter,'

as thus formed, is exceedingly useful for general purposes; it exposes the entire surface of the paper to the liquid, and allows filtration to proceed more rapidly than a 'plain filter' does. (See Fig. 3.)

[Ill.u.s.tration: FIG. 3.]

Mr Rother takes objection to the ordinary plain paper filter employed in the laboratory, because of the superfluous fold which in two thicknesses lies under one half of the extended surface of the filter. He says the interposition of these two extra layers compels the liquid to pa.s.s through three thicknesses of paper on the half side of the extended filter, whilst the other half side presents only a single thickness. It is evident that the two hidden layers are a very appreciable impediment to the current, aside from the more important fact that the liquid will traverse this side less rapidly than the other, and thus occasion an imperfect was.h.i.+ng of the precipitate, or at least prolong the operation beyond reasonable limits.

Recognising these objections to the old filter, Mr Rother has invented a very simple modification of the plain filter which, whilst saving 50 per cent. of the paper, he states, removes all the defects of the old form.

This new filter practically presents but a single thickness of paper to penetrate, at the same time preserving an even surface, equal in all other advantages to the plain filter.

The filtrations are said to be more rapid than with the usual form, and the absence of the superfluous half sheet admits of more rapid drying.

To make the new filter:--Cut the circular disk of filtering paper in two through the line of its diameter, take either half disk, and fold it across the line of the radius, then turn down the double edge of the cut side and fold it over several times--finally, run a hard smooth surface along the seam thus produced, to compress it, and spread the finished filter into an appropriate funnel, first moistening it with water before the liquid to be filtered is poured in.

In reference to funnels, it may be remarked that those employed for filtering rapidly should be deeply ribbed on the inside, or small rods of wood or gla.s.s, or pieces of straw, or quills, should be placed between them and the paper. The neck or tubular part of the funnel should, in like manner, be deeply ribbed or fluted on the outside, to permit of the free pa.s.sage of the air, when it is placed in a narrow-mouthed bottle or receiver. When this is not the case, filtration proceeds but slowly, and the filtered liquid is apt to be driven up the outside of the neck of the funnel by the confined air, and to be continually hissing and flowing over the mouth of the vessel. The breadth of a funnel, to filter well, should be about three fourths its height, reckoning from the throat (_a_). When deeper, the paper is liable to be continually ruptured, from the pressure of the superinc.u.mbent fluid; and when shallower, filtration proceeds slowly, and an unnecessarily large surface of the liquid is exposed to the atmosphere, and is lost by evaporation. To lessen this as much as possible, the upper edge of the gla.s.s is frequently ground perfectly smooth, and a piece of smooth plate-gla.s.s is laid thereon. When paper filters are of large dimensions, or employed for aqueous fluids that rapidly soften the texture of the paper, or for collecting heavy powders, or metallic precipitates, it is usual to support them on linen or calico, to prevent them breaking. This is best done by folding the cloth up with the paper, and cutting the filter out of the two, in the same way as would be done with doubled paper, observing so to place it in the funnel that the paper and calico may remain close together, especially towards the bottom.

[Ill.u.s.tration]

The filtration of small quant.i.ties of liquid, as in chemical experiments, may often be conveniently performed by merely placing the paper on the circular top of a recipient (see _engr._), or on a ring of gla.s.s or earthenware laid on the top of any suitable vessel. A filter of this kind that will hold one fluid ounce will filter many ounces of some liquids in an hour.

Good filtering paper should contain no soluble matter, and should not give more than 1/250 to 1/230 of its weight of ashes. The soluble matter may be removed by was.h.i.+ng it, first, with very dilute hydrochloric acid, and secondly, with distilled water.

The 'Munktell' Swedish filtering paper[301] is composed of flax fibres very much crushed and broken, and owes its value to the broken pieces of the fibres filling up the pores, and thus preventing solids from pa.s.sing through the paper. Rhenish filtering paper is also made from flax, but in consequence of the more perfect condition of its fibres, is more porous than Munktell's, and therefore inferior to it for filtering purposes.

Another kind of Rhenish paper, also of flax, in which the fibres are much torn, is manufactured and is said to be a useful article, and to allow the rapid pa.s.sage of fluids through it. The white filtering papers of English make have a small quant.i.ty of cotton mixed with the flax; and the fibres are much torn and crushed; hence they make serviceable filters.

[Footnote 301: Dr F. Mohr says that Swedish filtering paper is now undeserving its traditional reputation, and that it contains soluble alumina.]

The grey, circular cut filtering paper of varying sizes, of foreign make, as well as the grey sheet filtering paper of Dutch and English manufacture, contains a large quant.i.ty of wool, much of which is coloured; as well as jute and esparto gra.s.s, both of these latter in an unbleached state. The amount of ash in the Munktell paper has of late increased in quality.[302]

[Footnote 302: Greenish.]

[Ill.u.s.tration]

For filtering a larger quant.i.ty of a liquid than can be conveniently managed with a funnel, and also for substances that are either too viscid or too much loaded with feculence to allow them to pa.s.s freely through paper, conical bags made of flannel, felt, tweeled cotton cloth or Canton flannel, linen or calico, and suspended to iron-hooks by rings or tapes, are commonly employed. The first two of the above substances are preferable for saccharine, mucilaginous, and acidulous liquors; the third for oily ones; and the remainder for tinctures, weak alkaline lyes, and similar solutions. These bags have the disadvantage of sucking up a considerable quant.i.ty of the fluid poured into them, and are therefore objectionable, except for large quant.i.ties, or when they are to be continued in actual use as filters for some time. On the large scale, a number of them are usually worked together, and are generally enclosed in cases to prevent evaporation, and to exclude dirt from the filtered liquor that trickles down their sides. These arrangements will be noticed further on.

[Ill.u.s.tration]

A simple mode of filtering aqueous fluids, which are not injured by exposure to the air, is to draw them off from one vessel to another, by means of a number of threads of loosely twisted cotton or worsted, arranged in the form of a syphon. (See _engr._) The little cotton rope at once performs the operations of decantation and filtration. This method is often convenient for sucking off the water from a small quant.i.ty of a precipitate.

For fuller information on the subject of laboratory filtration, the reader is referred to the following papers (which are too long for quotation here) in 'The Chemical News':--

"On a New Mode of Filtration," by J. B. Cooke, May 30th, 1873; "Filtering Apparatus," by John F. Kerr, February 6th, 1874; "Implements for Filtration," by P. Casamajor, July 23rd, 1875, and 30th, 1875; Ibid, by W.

Jago, February 4th, 1876; "On Rapid Filtration," by E. C. H. Hildebrand, August 11th, 1876; also to 'Journal of the Chemical Society,' for papers on:--"Simple Suction arrangement for Rapid Filtering," by C. Holthof, vol.

x.x.xii, part 2, p. 508; "Employment of Compressed Air on Filtering Solutions," by W. Leube, vol. x.x.xii, part 1, p. 270.

When solid substances, as porous stone or earthenware, are used as the media for filtrations, vessels of metal, wood, or stone-ware, are employed to contain them and the supernatant liquid. In these cases the filtering medium is usually arranged as a shelf or diaphragm, and divides the vessel into two compartments; the upper one being intended to contain the dirty liquid, and the under one to receive the same when filtered. Such an apparatus is set in operation by merely filling the upper chamber, and may at any time be readily cleared out by reversing it, and pa.s.sing clean water through it in an opposite direction. Small arrangements of this kind, intended to be screwed on to the water supply-pipe by either end, and which answer the purpose intended in the most satisfactory manner, have been manufactured and vended under the name of 'REVERSIBLE' or 'SELF-CLEANING FILTERS,' When pulverulent substances, as sand, coa.r.s.ely powdered charcoal, &c., are employed, a similar arrangement is followed; but in this case the shelf or diaphragm must consist of any convenient substance pierced with numerous holes, over which must be placed, first a stratum of coa.r.s.e pebbles, next some of a finer description, and on this a proper quant.i.ty of the sand, charcoal, or other medium. Over the whole should be placed another layer of pebbles, or a board or plate of metal or earthenware, pierced with a number of holes, to allow the liquid to be poured into the filter without disturbing its arrangement. Apparatus of this kind, of a permanent description, and arranged for filtering large quant.i.ties of liquids, are properly denominated 'FILTERING MACHINES,'

Among the liquids usually submitted to filtration, the following may be mentioned as the princ.i.p.al--water, oils, syrups, tinctures, vegetable juices, infusions, and decoctions.

The filtration of water may now be considered. The water of our wells is presented by nature ready filtered to the hand of man, and often exhibits an admirable degree of transparency and purity. It acquires this state by percolating through the mineral strata of the earth, which deprives it of the organic matter it derives from the soil and subsoil, but, at the same time, it dissolves a portion of the saline and earthy media through which it pa.s.ses, and hence acquires that peculiar 'hardness' which is constantly found in spring water. On the large scale, this natural system of filtration has been imitated by some of the commercial companies that supply our cities and towns with water. Extensive beds of sand and gravel have been employed, with variable success, as the filtering media; and were it not that filters gradually lose their porosity by the acc.u.mulation of the retained matter in their pores, such a method would be excellent.

But the great expense of such filters precludes the possibility of frequently cleaning or renewing them, by which means they can alone be kept in an efficient state.

A filter which possesses the advantages of being easily and cheaply cleaned when dirty, and which frees water from mechanical impurities with immense rapidity, may be formed by placing a stratum of sponge between two perforated metallic plates, united by a central screw, and arranged in such a manner as to permit of the sponge being compressed to any required degree. Water, under gentle pressure, flows with such rapidity through the pores of compressed sponge, that it is said that a few square feet of this substance will perfectly filter several millions of gallons of water daily. This method of filtration has been made the subject of a patent, and has been favorably noticed by the legislature.

A few barrels or hogsheads of water may be easily filtered daily, by the arrangement represented in the engraving.

[Ill.u.s.tration:

_A._ A common water-pipe or c.o.c.k.