Hardening of files

—This is the last and most important part of file making. Whatever may be the quality of the steel, or however excellent the workmanship, if it is not well hardened all the labour is lost. Three things are strictly to be observed in hardening; first, to prepare the file on the surface, so as to prevent it from being oxidated by the atmosphere when the file is red hot, which effect would not only take off the sharpne of the tooth, but render the whole surface so rough that the file would, in a little time, become clogged with the substance it had to work. Secondly, the heat ought to be very uniformly red throughout, and the water in which it is quenched, fresh and cold, for the purpose of giving it the proper degree of hardne . Lastly, the manner of immersion is of great importance, to prevent the files from warping, which in long thin files is very difficult. The first object is accomplished by laying a substance upon the file, which when it fuses, forms as it were, a varnish upon the surface, defending the metal from the action of the oxygen of the air. Formerly the proce consisted in first coating the surface of the file with ale grounds, and then covering it over with pulverized common salt, (muriate of soda.) After this coating became dry, the files were heated red hot, and hardened; after this, the surface was lightly brushed over with the dust of cokes, when it appeared white and metallic, as if it had not been heated. This proce has lately been improved, at least so far as relates to the economy of the salt, which from the quantity used, and the increased thickne , had become a serious object. Those who use the improved method are now consuming about one fourth the quantity of salt used in the old method. The proce consists in di olving the salt in water to saturation, which is about three pounds to the gallon, and stiffening it with ale grounds, or with the cheapest kind of flour, such as that of beans, to about the consistence of thick cream. The files require to be dipped only into this substance, and immediately heated and hardened. The grounds or the flour are of no other use, than to give the ma consistence, and by that means to allow a larger quantity of salt to be laid upon the surface. In this method, the salt forms immediately a firm coating. As soon as the water is evaporated, the whole of it becomes fused upon the file. In the old method the dry salt was so loosely attached to the file, that the greatest part of it was rubbed off into the fire, and was sublimed up the chimney, without producing any effect. The carbonaceous matter of the ale grounds is supposed to have some effect in giving hardne to the file, by combining with the steel, and rendering it more highly carbonated. It will be found, however, upon experiment, that vegetable carbon does not combine with iron, with sufficient facility to produce any effect, in the short space of time a file is heating, for the purpose of hardening. Some file makers are in the habit of using the coal of burnt leather, which doubtle produces some effect; but the carbon is generally so ill prepared for the purpose, and the time of its operation so short, as to render the result inconsiderable. Animal carbon, when properly prepared and mixed, with the above hardening composition, is capable of giving hardne to the surface even of an iron file. This carbonaceous matter may be readily obtained from any of the soft parts of animals, or from blood. For this purpose, however, the refuse of shoemakers and curriers is the most convenient. After the volatile parts have been distilled over, from an iron still, a bright shining coal is left behind, which, when reduced to powder, is fit to mix with the salt. Let about equal parts, by bulk, of this powder, and muriate of soda be ground together, and brought to the consistence of cream, by the addition of water. Or mix the powdered carbon with a saturated solution of the salt, till it become of the above consistence. Files which are intended to be very hard, should be covered with this composition, previous to hardening. All files intended to file iron or steel, particularly saw files, should be hardened with the aid of this mixture, in preference to that with the flour or grounds. Indeed, it is probable, that the carbonaceous powder might be used by itself, in point of economy, since the ammonia or hartshorn, obtained by distillation, would be of such value as to render the coal of no expense. By means of this method the files made of iron, which, in itself, is unsusceptible of hardening, acquire a superficial hardne sufficient for any file whatever. Such files may, at the same time, be bent into any form; and, in consequence, are particularly useful for sculptors and die-sinkers. The next point to be considered is the best method of heating the file for hardening. For this purpose a fire, similar to the common smiths’ fire, is generally employed. The file is held in a pair of tongs by the tang, and introduced into the fire, consisting of very small cokes, pushing it more or le into the fire for the purpose of heating it regularly. It must frequently be withdrawn with the view of observing that it is not too hot in any part. When it is uniformly heated, from the tang to the point, of a cherry red colour, it is fit to quench in the water. At present an oven, formed of fire-bricks, is used for the larger files, into which the blast of the bellows is directed, being open at one end, for the purpose of introducing the files and the fuel. Near to the top of the oven are placed two cro bars, on which a few files are placed, to be partially heating. In the hardening of heavy files, this contrivance affords a considerable saving, in point of time, while it permits them also to be more uniformly and thoroughly heated. After the file is properly heated for the purpose of hardening, in order to produce the greatest po ible hardne , it should be cooled as soon as po ible. The most common method of effecting this is by quenching it in the coldest water. Some file-makers have been in the habit of putting different substances in their water, with a view to increase its hardening property. The addition of sulphuric acid to the water was long held a great secret in the hardening of saw files. After all, however, it will be found, that clear spring water, free from animal and vegetable matter, and as cold as po ible, is the best calculated for hardening files of every description. In quenching the files in water, some caution must be observed. All files, except the half-round, should be immersed perpendicularly, as quickly as po ible, so that the upper part shall not cool. This management prevents the file from warping. The half-round file must be quenched in the same steady manner; but, at the same time that it is kept perpendicular to the surface of the water, it must be moved a little horizontally, in the direction of the round side, otherwise it will become crooked backwards. After the files are hardened, they are brushed over with water, and powdered cokes, when the surface becomes perfectly clean and metallic. They ought also to be washed well in two or three clean waters, for the purpose of carrying off all the salt, which, if allowed to remain, will be liable to rust the file. They should moreover be dipped into lime-water, and rapidly dried before the fire, after being oiled with olive oil, containing a little oil of turpentine, while still warm. They are then finished. FILLIGREE ( Filigrane , Fr.; Filigran , or Feine Drahtgeflecht , Germ.); is, as the last term justly expre es it, intertwisted fine wire, used for ornamenting gold and silver trinkets. The wire is seldom drawn round, but generally flat or angular; and soldered by gold or silver solder with borax and the blowpipe. The Italian word, filigrana , is compounded of filum and granum , or granular net-work; because the Italians, who first introduced this style of work, placed small beads upon it. FILTRATION (Eng. and Fr.; Filtriren , Germ.), is a proce purely mechanical, for separating a liquid from the undi olved particles floating in it, which liquid may be either the useful part, as in vegetable infusions, or of no use, as the washings of mineral precipitates. The filtering substance may consist of any porous matter in a solid, foliated, or pulverulent form; as porous earthen ware, unsized paper, cloth of many kinds, or sand. The white blotting paper sold by the stationers answers extremely well for filters in chemical experiments, provided it be previously washed with dilute muriatic acid, to remove some lime and iron that are generally present in it. Filter papers are first cut square, and then folded twice diagonally into the shape of a cornet, having the angular parts rounded off. Or the piece of paper being cut into a circle, may be folded fan-like from the centre, with the folds placed exteriorly, and turned out sharp by the pre ure of the finger and thumb, to keep intervals between the paper and the funnel into which it is fitted, to favour the percolation. The diameter of the funnel should be about three-fourths of its height, measured from the neck to the edge. If it be more divergent, the slope will be too small for the ready efflux of the fluid. A filter covered with the sediment is most conveniently washed by spouting water upon it with a little syringe. A small camel’s-hair paint brush is much employed for collecting and turning over the contents in their soft state. Agitation or vibration is of singular efficacy in quickening percolation, as it displaces the particles of the moistened powders, and opens up the pores which had become closed. Instead of a funnel, a cylindrical ve el may be employed, having its perforated bottom covered with a disc of filtering powder folded up at the edges, and made tight there by a wire ring. Linen or calico is used for weak alkaline liquors; and flannels, twilled woollen cloth, or felt-stuff for weak acid ones. These filter bags are often made conical like a fool’s cap, and have their mouths supported by a wooden or metallic hoop. Cotton wool put loose into the neck of a funnel answers well for filtering oils upon the small scale. In the large way, oil is filtered in conical woollen bags, or in a cask with many conical tubes in its bottom, filled with tow or cotton wool. Stronger acid and alkaline liquors must be filtered through a layer of pounded gla , quartz, clean sand, or bruised charcoal. The alcarrhazas are a porous biscuit of stone ware made in Spain, which are convenient for filtering water, as also the porous filtering stone of Teneriffe, largely imported into England at one time, but now superseded in a great measure by the artificial filters patented under many forms, consisting e entially of strata of gravel, sand, and charcoal powder. It is convenient to render the filter self-acting, by accommodating the supply of liquid to the rate of percolation, so that the pre ure upon the porous surface may be always equally great. Upon the small scale, the lamp-fountain or bird’s-gla form so generally used for lamps, will be found to answer. IMG:4147767755307473660_illo0468a.png:Filtration apparatus Fig. 386. represents a gla bottle A , partly filled with the fluid to be filtered, supported in the ring of a chemical stand, and having its mouth inverted into the same liquor in the filter funnel. It is obvious, that whenever this liquor by filtration falls below the lip of the bottle, air will enter into it, let down a fresh supply to feed the filter, and keep the funnel regularly charged. If larger quantities are to be operated upon, the following apparatus may be employed. Fig. 387. A B is a metallic ve el which may be made air-tight; C is the under pipe provided with a stopcock R , for letting down the liquor into the filter a b . The upper pipe t , through which the fluid is poured by means of the funnel E , has also a stopcock which opens or shuts, at the same time, the small side tube u t , through which, during the entrance of the fluid, the air is let off from the receiver. A gla tube g , shows the level of the liquor in the body of the apparatus. In using it, the cock R must be first closed, and the cock S must be opened to fill the receiver. Then the filter is set a going, by re-opening the cock R , so as to keep the fluid in the filter upon a level with the opening of the tube C . Both these pieces of apparatus are e entially the same. IMG:4147767755307473660_illo0468b.png: In many manufactures, self-acting filters are fed by the plumber’s common contrivance of a ball-cock in which the sinking and rising of the ball, within certain limits, serves to open or shut off the supply of liquor, as it may be required or not. Dumont has adopted this expedient for his system of filtering syrup through a stratum of granularly ground animal charcoal or bone-black. Fig. 388. is a front view of this apparatus with 4 filters C ; and fig. 389. is a cro section. The framework B supports the cistern A , in which the syrup is contained. From it the liquor flows through the stop-cock b , and the connection-tube a , into the common pipe c , which communicates, by the short branch tubes e , with each of the four filters. The end of the branch tube, which is inside of the filter tub, is provided with a stopcock d f , whose opening, and thereby the efflux of the liquor from the cistern through the tube a , is regulated by means of the float-ball g . Upon the brickwork D the filter tub stands, furnished at h with a false bottom of zinc or copper pierced with fine holes; besides which, higher up at i there is another such plate of metal furnished with a strong handle k , by which it may be removed, when the bone-black needs to be changed. In the intervening space l , the granular coal is placed. o is the cover of the filter tub, with a handle also for lifting it. One portion of it may be raised by a hinge, when it is desired to inspect the progre of the filtration within. m m is a slender vertical tube, forming a communication between the bottom part h , and the upper portion of the filter, to admit of the easy escape of the air from that space, and from among the bone-black as the syrup descends; otherwise the filtration could not go on. p is the stopcock through which the fluid collected in the space under h is let off from time to time into the common pipe q , fig. 388. r is a trickling channel or groove lying parallel to the tube q , and in which, by means of a tube s , inserted at pleasure, the syrup is drawn off in case of its flowing in a turbid state, when it must be returned over the surface of the charcoal. The celerity with which any fluid pa es through the filter depends, 1. upon the porosity of the filtering substance; 2. upon the pre ure exercised upon it; and 3. upon the extent of the filtering surface. Fine powders in a liquor somewhat glutinous, or closely compacted, admit of much slower filtration than those which are coarse and free; and the former ought, therefore, to be spread in a thinner stratum and over a more extensive surface than the latter, for equal effect; a principle well exemplified in the working of Dumont’s apparatus, just described. IMG:4147767755307473660_illo0468c.png:Filtration apparatus In many cases filtration may be accelerated by the increase of hydrostatic or pneumatic pre ure. This happens when we close the top of a filtering cylinder, and connect it by a pipe with a cistern of fluid placed upon a higher level. The pre ure of the air may be rendered operative also either by withdrawing it partially from a close ve el, into which the bottom of the filter enters, or by increasing its density over the top of the liquor to be filtered. Either the air pump or steam may be employed to create a partial void in the receiver beneath the filter. In like manner, a forcing pump or steam may be employed to exert pre ure upon the surface of the filtering liquor. A common syphon may, on the same principle, be made a good pre ure filter, by making its upper leg trumpet-shaped, covering the orifice with filter paper or cloth, and filling the whole with liquor, the lower leg being of such length so as to create considerable pre ure by the difference of hydrostatic level. This apparatus is very convenient either on the small or great scale, for filtering off a clear fluid from a light muddy sediment. The pre ure of the atmosphere may be elegantly applied to common filters, by the apparatus represented in fig. 390. , which is merely a funnel inclosed within a gasometer. The case A B bears an annular hollow ve el a b , filled with water, in which receiver the cylindrical gasometer d , e , f , i , is immersed. The filter funnel C is secured at its upper edge to the inner surface of the annular ve el a b . In consequence of the pre ure of the gasometer regulated by the weight g , upon the air inclosed within it, the liquid is equally pre ed, and the water in the annular space rises to a corresponding height on the outer surface of the gasometer, as shown in the figure. Were the apparatus made of sheet iron, the annular space might be charged with mercury. In general, relatively to the application of pre ure to filters, it may be remarked, that it cannot be pushed very far, without the chance of deranging the apparatus, or rendering the filtered liquor muddy. The enlargement of the surface is, generally speaking, the safest and most efficacious plan of increasing the rapidity of filtration, especially for liquids of a glutinous nature. This expedient is well illustrated in the creased bag filter now in use in most of the sugar refineries of London. See Sugar . In many cases it is convenient so to construct the filtering apparatus, as that the liquid shall not descend, but mount by hydrostatic pre ure. This method has two advantages: 1. that without much expensive apparatus, any desired degree of hydrostatic pre ure may be given, as also that the liquid may be forced up through several filtering surfaces placed alongside of each other; 2. that the object of filtering, which is to separate the particles floating in the fluid without disturbing the sediment, may be perfectly attained, and thus very foul liquids be cleared without greatly soiling the filtering surface. IMG:4147767755307473660_illo0470b.png:Water purifier Such a construction is peculiarly applicable to the purification of water, either alone, or combined with the downwards plan of filtration. Of the former variety an example is shown in fig. 391. The wooden or zinc conical ve el is provided with two perforated bottoms or sieves e e , betwixt which the filtering substance is packed. Over this, for the formation of the space h h , there is a third shelf, with a hole in its middle, through which the tube d b is pa ed, so as to be water tight. This places the upper open part of the apparatus in communication with the lowest space a . From the compartment h h a small air tube l runs upwards. The filtering substance consists at bottom of pebbles, in the middle of gravel, and at the top of fine sand, which may be mixed with coarsely ground bone-black, or covered with a layer of the same. The water to be filtered being poured into the cistern at top, fills through the tube b d the inferior compartment a , from which the hydrostatic pre ure forces the water upward through the perforated shelf, and the filtering materials. The pure water collects in the space h h , while the air escapes by the small tube l , as the liquid enters. The stopcock i serves to draw off the filtered water. As the motion of the fluid in the filter is slow, the particles suspended in it have time to subside by their own gravity; hence there collects over the upper shelf at d , as well as over the under one at a , a precipitate or deposit which may be washed out of the latter cavity by means of the stopcock m . IMG:4147767755307473660_illo0470a.png:Upand down-flow filter As an example of an upwards and downwards filter, fig. 392. may be exhibited. A B C D is a wooden or metallic cistern furnished with the perforated shelf c d near its under part, upon which a vertical partition is fixed through the axis of the ve el. A semicircular perforated shelf is placed at a , and a second similar one at b . These horizontal shelves rest upon brackets in the sides of the cisterns, so that they may be readily lifted out. The space G is filled with coarse sand, J with moderately fine, and H with very fine. The foul water is poured into the chamber E , and pre es through G J H and into the space F ; whence it may be drawn by the stopcock f . IMG:4147767755307473660_illo0470c.png:Filtration apparatus Fig. 393. represents in section a filtering apparatus consisting of two concentric chambers; the interior being destined for downwards filtration, and the exterior for upwards. Within the larger cistern A , a smaller one B is placed concentrically, with its under part, and is left open from distance to distance, to make a communication between the interior cavity and the exterior annular space. These cavities are filled to the marked height with sand and gravel. The inner cylindrical space has fine sand below, then sharper sand with granular charcoal, next coarse sand, and lastly gravel. The annular space has in like manner fine sand below. The foul water is introduced by the pipe E , the orifice at whose end is acted upon by a ball-cock with its lever a ; whereby the water is kept always at the same level in the inner ve el. The water sinks through the sand strata of the middle ve el, pa es outwards at its bottom into the annular space, thence up through the sand in it, and collecting above it, is let off by the stopcock on the pipe b . When a muddy deposit forms after some time, it may be easily cleared out. The cord e , running over the pulleys f f , being drawn tight, the ball lever will shut up the valve. The stopcock d made fast to the conducting tube E must then be opened, so that the water now overflows into the annular space at A ; the tube c , in communication with the inner space B , being opened by taking out the stopper h . The water thereby percolates through the sand strata in the reverse direction of its usual course, so as to clear away the impurities in the space B , and to discharge them by the pipe c h . An apparatus of this kind of moderate size is capable of filtering a great body of water. It should be constructed for that purpose of masonry; but upon a small scale it may be made of stone-ware. IMG:4147767755307473660_illo0471.png:Filtration apparatus A convenient apparatus for filtering oil upwards is represented in fig. 394. g is an oil cask, in which the impure parts of the oil have accumulated over the bottom. Immediately above this, a pipe a is let in, which communicates with an elevated water cistern n . f is the filter, (placed on the lid of the cask) furnished with two perforated shelves, one at e and another at d ; which divide the interior of the filter into three compartments. Into the lower space immediately over the shelf e , the tube b , furnished with a stopcock enters, to establish a communication with the cask; the middle cavity e is filled with coarsely ground charcoal or other filtering materials; and the upper one has an eduction pipe l . When the stopcocks of the tubes a and b are opened, the water pa es from the cistern into the oil cask, occupies from its density always the lowest place, and pre es the oil upwards, without mixing the two liquids; whereby first the upper and purer portion of the oil is forced through tube b into the filter, and thence out through the pipe l . When the fouler oil follows, it deposits its impurities in the space under the partition c , which may from time to time be drawn off through the stopcock k , while the purer oil is pre ed upwards through the filter. In this way the different strata of oil in the cask may be filtered off in succe ion, and kept separate, if found nece ary for sale or use, without running any risk of mixing up the muddy matter with what is clear. According to the height of the water cistern n , will be the pre ure, and of course the filtering force. When the filter gets choked with dirt, it may be easily re-charged with fresh materials. In filtering caustic alkaline lyes through linen or quartz, it is proper to exclude the free contact of air; which is done by inclosing the upper ve el, and attaching a pipe of communication between its cover, and the shoulder of the lower ve el, or recipient of the lyes. In proportion as these flow down, they will displace their bulk of air, and drive it into the top of the upper ve el above the foul lyes. Many modifications of the above described apparatus are now on sale in this country; but certainly the neatest, most economical, and effective means of transforming the water of a stagnant muddy pool, into that of a crystalline fountain, is afforded by the Royal Patent Filters of George Robins.