Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

te women, commonly known by the name of whites. See MEDICINE, and LEUCORRHEA. FLUORIC ACID. See FLUORIC SPAR. FLUORIC SPAR, (acide fluorique, French; fluss spathsuure, Germ.). In the Transactions of the Academy of Sciences at Berlin for 1763, is contained a memoir by Margraaf on fluor spar. This able chemist found that when the above mineral was distilled with sulphuric acid a volatile acid vapour was disengaged, which deposited a white earth on coming into contact with water; he also remarked that the retort in which the distillation was carried on was corroded and worn into holes by the proThree years after, Schee'e published a valuable essay on the same subject, in which he proved that fluor spar consisted of lime combined with a peculiar acid, many of the properties of which were investigated by him with great success. Priestley then took up the subject, confining his attention for the most part to the action of fluoric acid in the state of gas. Since the date of these last experiments but few additions have been made to our knowledge of this acid and its various combinations.

cess.

The distinguishing property of fluoric acid is that when dry and in the state of gass it readily combines with silex, and still retains its elastic form: hence arises the peculiar and almost insurmountable difficulty of obtaining this substance in a state of purity.

Fluoric acid is procured from fluor spar: for this purpose a quantity of the mineral being reduced to a fine powder is to be mixed in a thick glass retort with an equal weight of concentrated sulphuric acid: upon the application of a gentle heat the sulphuric acid will combine with the calcareous base of the spar, and fluoric gass will at the same time be liberated, and may be received in the mercurial pneumatic apparatus in the usual way. If the heat applied to the retort is somewhat considerable, and the gass is rapidly produced, the retort will give way in the space of a minute or two, being eaten into holes by the action of the acid; if the process is conducted cautiously and at as low a temperature as possible, the retort may be made to last a considerable while longer. The gass thus procured, while confined over mercury, is perfectly colourless and transparent; it has a pungent suffocating odour like muriatic acid, produces immediate death to animals which are immersed in it, extinguishes the flame of a candle after having previously tinged its flame of a green colour, and changes certain vegetable blues to red. Its specific gravity is considerably greater than that of atmospheric air, but has not yet been ascertained with any accuracy. If this gass is mixed with atmospheric air, a white vapour similar to but more copious than that occasioned by the muriatie acid gass in the same circumstances is the result; this appearance is partly occasioned by the combination of the acid with the moisture of the air, but principally by the deposition of silex, which takes place at the same time. The earth is in like

manner deposited if the gass is received in water, and this experiment, according to the circumstances under which the acid is disengaged, exhibits a variety of singular and interesting appearances. As soon as a bubble of gass pusses from the beak of the retort into the water it is immediately diminished in size from the absorption of a portion of the acid, and the whole would be taken up if the globule did not instantly become coated with the earth deposited by that part of the acid which is absorbed, for the earthy film being interposed between the gass and the water prevents any further combination till the bubble reaches the surface of the water, where it bursts. If this is performed in a jar full of water inverted over mercury, and care is taken to prevent the gass from being mixed with atmospheric air, the whole of the gass is absorbed, and the silex, in proportion as it is deposited, diffuses itself through the liquor, which thus at length acquires a gelatinous consistence: when in this state, the greater part of the earth may be separated by putting the whole in a piece of linen and squeezing it. The acid liquor thus procured being again inverted over mercury, will absorb an additional quantity of gass, and by thus treating it three or four times successively, a strong fuming acid liquor may be obtained, consisting principally of Huoric acid and water, but still holding in solution a portion of silex, and probably also alkali, from the decomposition of the glass of the retort. If this saturated liquor is mixed with a few drops of fluat of silver, a slight precipitate of cornea takes place, and the fluoric acid is thus separated from a small portion of muriatic acid, which, when prepared in the foregoing manner, it is always found to contain. From the liquor thus purified a considerable quantity of Anoric acid pure gass may be obtained by heating it almost to ebullition in a retort, and receiving the product in mercury. This gass appears to consist merely of fluoric acid, saturated with as much water as it can hold in an elastic state, and at a moderately cool temperature seems to have no action on glass. It combines readily with water without depositing in any earth, and bas an astringent acidulous tastė. A candle immersed in it is extinguished without any previous change in the colour of the flame: it combines with ammoniacal gass, forming a white cloud: it dissolves camphor, and is taken up in large quantity by oil of turpentine, to which it communicates an orange colour and a pungent acid odour. If kept for some time in a bottle of soft glass it acts upon it though slightly, on which account it is a useful precaution before putting the acid in, to line the bottle with a thin coating of a mixture of oil and wax. It has been proposed by some chemists, as a method of obtaining pure liquid fluoric acid, to make use of a leaden retort and receiver; in which case the fluor spar being previously reduced to an exceedingly fine powder, is to be mixed in the retort with an equal weight of strong sulphuric acid; the application of a gentle heat, not exceeding that o!

boiling water, will force into the receiver a large quantity of acid gass, where it combines to saturation with water, and thus produces liquid fluoric acid. In this process, provided the spar selected was free from quartz, there is indeed no deposition of silex, but a very notable proportion of lead is volatilized, and remains for the most part dissolved in the liquor, which, on this account, is by no means so pure as the acid produced by Dr. Priestley's

method.

Fluoric acid has not yet been decomposed, its base therefore is wholly unknown, and it is only from analogy that chemists suppose it to contain oxygen. A remarkable difference between the fluoric and muriatic acid is that the latter is incapable of becoming oxygenated: it will neither unite with oxygen in the state of gass nor when digested with manganese. Fluoric acid combines with the alkalies and alkaline earths, with alumine and siles, and with the metallic oxyds; the metals in a reguline state appear to have no affinity for dry Дuoric acid, but when liquid it will dissolve iron, zine, copper, and arsenic, hydrogen being at the same time disengaged. The order of its affinities is as follows: lime, barytes, strontian, magnesia, potash, soda, ammonia, alumine, and silex.

The only use to which fluoric acid has been applied is engraving on glass. It appears from Beckman that this was first practised by an artist of Nuremberg, in the year 1670, who prepared his etching liquor by digesting together nitrous acid and finely powdered fluor spar for several hours on a warm sand bath, and then using the clear liquor as aquafortis is employed by the copper-plate engravers. But the knowlege and application of this liquor was confined to a few German artists, till, after the discoveries of Scheele and Priestley, the fluoric acid in a pure state was used for the same purpose by various ingenious artists in England and France. Puymaurin found the liquid acid prepared in leaden vessels according to Scheele's process to answer very well for this purpose in warm weather, but by cold its activity is so much impaired as to produce little effect even in three or four days. The gasseous acid however is much more efficacious; and being at the same time sufficiently manageable with proper care, merits the preference. To engrave on glass, select a piece of plate glass of the requisite size, cover it with hard engraver's wax, and with a needle or other suitable instrument trace the intended design as in common etching, observing that every stroke passes quite through the wax to the surface of the glass; which may be ascertained by placing the plate on a sloping frame like a portable reading-desk, in which situation the hght will shine through wherever the wax is removed. When the etching is completed, lay the plate with the engraved side downwards ou a frame, in a box lined with strong sheet lead or thick tin foil, and place on the bottom of the box a few leaden cups containing a

mixture of one part of very fine pulverized fluor spar and two parts of sulphuric acid: then close the lid of the box, and place it on a stove, or in any other convenient situation where it may be exposed to as high a heat as it can bear without risking the melting of the wax : fluoric acid gass will be copiously disengaged, and in a short time (from one hour to three, according to circumstances) the plate will be found sufficiently corroded. See FLUOR.

FLURRY. s. 1. A gust of wind; a hasty blast (Swift). 2. Hurry; a violent commotion.

To FLUSH. v. n. (fluysen, Dutch.) 1. To flow with violence (Mortimer). 2. To come in haste (Ben Jonson). 3. To glow in the skin (Collier). . 4. To shine suddenly: obsolete (Spenser).

To FLUSH. v. a. 1. To colour; to redden (Addison). 2. To elate; to elevate (Atterbu.). FLUSH. a. 1. Fresh; full of vigour (Cleave.). 2. Affluent; abounding (Arbuthnot).

FLUSH. S. 1. Afflux; sudden impulse; violent flow (Rogers). 2. Cards all of a sort.

FLUSHING, a handsome, strong, and considerable town in Zealand, and in the island of Walcheren, with a good harbour, and a great foreign trade. It was put into the hands of queen Elizabeth as a security for the money she advanced. It is one of the three places which Charles V. advised Philip II. to preserve with care. It is four miles S. W. of Middleburg. Lon. 3. 35 E. Lat. 51.29 N. This town was taken, in August, 1809, by the English under the command of earl Chatham.

To FLUSTER. v. a. (from To flush.) To make hot and rosy with drinking (Shakspeare).

FLU'STRA. Horn-wrack. In zoology, a genus of the class vermes, order zoophyta. Animal, a polype proceeding from porous cells; stem fixed, foliaceous, membranaceous, consisting of numerous rows of cells united together and woven like a mat. Eighteen species; inhabitants of the European or Mediterranean seas; one or two of the Indian and Atlantic; eight found on the British coasts; adhering to fuci or other submarine substances.

F. chartacea may serve as an example. This, as its name evinces, is papyraceous, or of a thin semitransparent texture, like fine paper; of a very light straw colour, with cells on both sides: the tops of the branches sometimes digitated, sometimes irregularly divided, and truncate like the edge of an axe: the cells are ob long-square. It is found on the British shores, adhering to sea-wrack, shells, and rocks.

FLUTE, a musical instrument, the most simple of those which are played by the breath impelled from the lips. The common fute, or flute a bec, is a tube about eighteen inches in length and one in diameter; it has eight holes along the side, and the end is formed like a beak, to apply the lips to. The German Alute consists of a tube formed of several joints or pieces screwed into each other, with holes disposed along the side, like those of the

common flute. It is stopped at the upper end, and furnished with moveable brass or silver keys, which, by opening and closing certain holes, serve to temper the tones to the various flats and sharps. In playing this instrument the performer applies his under lip to a hole about two inches and a half from the upper extremity, while the fingers, by their action on the holes and keys, accommodate the tones to the notes of the composition.

FLUTES, or FLUTINGS, in architecture, channels or cavities running perpendicularly along the shaft of a column or pilister. They are chiefly affected in the Ionic order, in which they had their first rise; though they are also used in all the richer orders, as the Corinthian or Composite; but rarely in the Doric; and scarce ever in the Tuscan. Their number is usually twenty-four, though in the Doric it is only twenty. Each flute is hollowed exactly in a quadrant of a circle. Between the flutes are little spaces that separate them, called by Vitruvius, stric, and by us, lists; though in the Doric, the flutes are frequently made to join each other, without any intermediate space at all, the list being sharpened off to a thin edge, which forms a part of each flute.

[blocks in formation]

FLUX, s. (fluxus, Latin.) 1. The act of flowing; passage (Digby). 2. The state of passing away and giving place to others (Bro.). 3. Any flow or issue of matter (Arbuthnot). 4. Dysentery disease in which the bowels are excoriated and bleed; bloody flux (Hali faa). 5. Excrement; that which falls from bodies (Shakspeare). 6. Concourse; confluence (Shakspeare). 7. The state of being melted. 8. That which mingled with the body makes it melt.

FLUX AND REFLUX OF THE SEA. See TIDES.

FLUX (fluss, Gernian), in chemistry, any substance which is added to another to assist its fusion when heat is applied. Thus alkali is a flux for flint, as when mixed with it in due proportion, and heated, it causes it to melt into the compound called glass.

The term flux is almost exclusively, in che

mistry, applied to those substances, often sad line mixtures, that are added to minerals or metallic ores to assist in the process of reduction.

White flux is made simply by mixing equal parts of tartar or cream of tartar and nitre, and deflagrating them in a clean crucible. The nitrous acid burns the carbonaceous part of the tartar, and the mixed alkalies of the nitre and tartar alone remain. This flux is, there. fore, little else than a pure subcarbonat of potash. The mixture of these substances before deflagration is called crude flux. But of all the saline reducing substances that most frequently employed is Mack flux. This is made by deflagrating in a large crucible a mixture of one part of nitre and two of tartar; and differs from the former in containing, besides carbonat of potash, a quantity of charcoal of the tartar, which there has not been nitre enough to consume. It therefore both assists in the fusion of ores by its alkaline ingredient, and oxygenates, and reduces them to the metallic state by means of its carbon.

In making this last flux, the materials, previously well mixed, should be thrown by small quantities into a red-hot crucible, and loosely covered after each projection; and as soon as the last portion is deflagrated, it should be removed from the fire, and kept in well-closed bottles to prevent the deliquescence of the alkali. Bergman however uses the term flux in a much more extensive sense; and intends by it not only substances useful in the reduction of metals, but substances capable of analyzing by the blowpipe saline, earthy, or inflammable matters. The fluxes recommended by him for this purpose are the following.

1. The phosphoric acid, or rather the microcosmic salt, as it is called, which contains that acid partly saturated with mineral, partly with amnionia, and loaded besides with much water. This salt, when exposed to the flame, boils and foams violently, with a continual crackling noise, until the water and ammonia have flown off: afterwards it is less agitated, sending forth something like black scoria arising from the burned gelatinous part: these, however, are soon dispelled, and exhibit a pellucid sphericle encompassed by a beautiful green cloud, which is occasioned by the de flagration of the phosphorus, arising from the extrication of the acid by means of the inflammable matter. The clear globule which remains, upon the removal of the flame, continues longer soft than that formed by borax, and therefore is more fit for the addition of the matter to be dissolved. The ammonia is expelled by the fire; therefore an excess of acid remains in what is left behind, which readily attracts moisture in a cool place. 2. Soda, when put upon charcoal, melts superficially, penetrates the charcoal with a crackling noise, and then disappears. In the spoon it yields a permanent and pellucid sphericle, as long as it is kept fluid by the blue apex of the flame, but when the heat is diminished, it becomes

[ocr errors]

It at

paque, and assumes a milky colour. Licks several earthy matters, particularly those of the siliceous kind, but cannot be employed on charcoal. 3. Crystallized borax, exposed to the flame urged by the blowpipe, or charcoal, first becomes opaque, white, and excessively swelled, with various protuberances, or branches proceeding out from it. When the water is expelled, it easily collects itself into a mass, which, when well fused, yields a transparent sphericle, retaining its transparency even after cooling. If calcined borax be employed, the clear sphericle is obtained the

sooner.

Having provided every thing necessary, the following directions are next to be attended to. 1. A common tallow candle, not too thick, is generally preferable to a wax candle, or to a Lamp. The snuff must not be cut too short, as the wick should bend towards the object. 2. The weaker exterior flame must first be directed upon the object, until its effects are discovered after which the interior flame must be applied. 3. We must observe with attention whether the matter decrepitates, splits, swells, vegetates, boils, &c. 4. The piece exposed to the flame should scarcely ever exceed the size of a pepper-corn, but ought always to be large enough to be taken up by the forceps. 5. A small piece should be added separately to each of the fluxes; concerning which it must be observed whether it dissolves wholly or only in part; whether this is effected with or without effervescence, quickly or slowly; whether the mass is divided into a powder, or gradually and externally corroded; with what colour the glass is tinged, and whether it becomes opaque er remains pellucid.

Having given these directions, M. Bergman proceeds next to consider the subjects proper to be examined by the blowpipe. These he divides into four classes: 1. Saline; 2. Earthy; 3. Inflammable; and 4. Metallic. As the subject, however, is treated at considerable length, we shall refer the reader to M. Bergman's writings, and confine ourselves in this place to what he has advanced concerning the last of these subjects, namely, metallic substances.

The perfect metals, when calcined (oxygenated) in the moist way, recover their former nature by simple fusion. The imperfect metals are calcined by fire, especially by the exterior flame; and then, in order to their being reduced, indispensably require the contact of an inflammable substance. With respect to finsibility, the two extremes are mercury and platina; the former being scarcely ever seen in a solid form, and the latter almost as difficult of fusion. The metals, therefore, may be ranked in this order, according to their degrees of fusibility. 1. Mercury; 2. Tin; 3. Bismuth; 4. Lead; 5. Zinc; 6. Antimony; 7. Silver; 8. Gold; 9. Arsenic; 10. Cobalt; 11. Nickel; 12. Irou; 13. Manganese; 14. Platinum. The last two do not yield to the blowpipe, and indeed forged iron does not melt without difficulty; but cast iron perfectly. Metals in fusion affect a globuluar form, and

easily roll off the charcoal, especially when of the size of a grain of pepper. Smaller pieces, therefore, ought either to be used, or they should rest in hollows made in the charcoal. On their first melting they assume a polished surface, an appearance always retained by the perfect metals; but the imperfect are soon obscured by a pellicle formed of the calx (oxide) of the metal. The colours communicated by the calces vary according to the nature of the metal from which the calx is produced. Some of the calces easily recover their metallic form by simple exposure to flame upon the charcoal; others are reduced in this way with more difficulty; and some not at all. The reduced calces of the volatile metals immediately fly off from the charcoal. In the spoon they exhibit globules; but it is very difficult to prevent them from being first dissipated by the blast.

The metals are taken up by the fluxes; but as soda yields an opaque spherule, it is not to be made use of. Globules of borax dissolve and melt any metallic calx; and, unless too much loaded with it, appear pellucid and coloured. A piece of metal calcined in flux produces the same effect, but more slowly. A portion of the calx generally recovers its metallic form, and floats on the melted matter like one or more excrescences.

The calces of the perfect metals are reduced by borax in the spoon, and adhere to it at the point of contact, and there only. The microcosmic salt acts like borax, but does not reduce the metals. It attacks them more powerfully on account of its acid nature; at the same time it preserves the spherical form, and therefore is adapted in a peculiar manner to the investigation of metals.

The tinge communicated to the flux frequently varies, being different in the fused and in the cooled globule; for some of the dissolved calces, while fused, show no colour, but acquire one while cooling; but others, on the contrary, have a much more intense colour while in the state of fluidity. Should the transparency be injured by too great a concentration of colour, the globule, on compressing it with the forceps, or drawing it out into a thread, will exhibit a thin and transparent mass; but if the opacity arises from supersaturation, more flux must be added; and as the fluxes attract the metals with unequal forces, the latter precipitate one another.

Metals when mineralized by acids have the properties of metallic salts; when mineralized by carbonic acid, they possess the properties of calces, that volatile substance being easily expelled without any effervescence; but when combined with sulphur they possess properties of a peculiar kind. They may then be melted, or even calcined upon the charcoal, as also in a golden or silver spoon. The volatile parts are distinguished by the smell or smoke; the fixed residua, by the particles reduced or precipitated upon iron, or from the tinge of the fluxes.

Gold in its metallic state fuses on the charcoal, and is the only metal which remains un

changed. It may be oxygenated in the moist way by solution in aqua regia; but to calcine it also by fire, we must pursue the following method: To a globule of microcosmic salt, let there be added a small piece of solid gold, of gold leaf, purple mineral, or, which is best of all, of the crystalline salt formed by a solution of gold in aqua regia containing sea-salt. Let this again be melted, and added while yet sott to turbith mineral, which will immediately grow red on the contact. The fusion being afterwards repeated, a vehement effervescence arises; and when this is considerably diminished, let the blast be stopped for a few moments, again begun, and so continued until almost all the bubbles disappear. After this the spherule, on cooling, assumes a ruby colour; but if this does not happen, let it be just made soft by the exterior flame, and upon hardening, this tinge generally appears. Should the process fail at first, owing to some minute circumstances which cannot be described, it will succeed on the second or third trial. The rubycoloured globule, when compressed by the for. ceps while hot, frequently becomes blue; by sudden fusion is generally assumes an opal colour, which by refraction appears blue, and by reflection of a brown red. If further urged by the fire it loses all colour, and appears like water; but the redness may be reproduced several times by the addition of turbith mineral. The flux is reddened in the same manner by the addition of tin instead of turbith; but it has a yellowish hue, and more easily becomes opaque; while the redness communicated by turbith mineral has a purple tinge, and quite resembles a ruby. Borax produces the same phenomena, but more rarely; and in all cases the slightest variation in the management of the fire will make the experiment fail entirely.

The ruby colour may also be produced by copper; whence a doubt may arise, whether it is the gold or the remains of the copper that produce this effect. M. Bergman thinks it probable that both may contribute towards it, especially as copper is often found to contain gold.

This precious metal cannot directly be mineralized by sulphur: but by the medium of iron is sometimes formed into a golden pyrites. Here, however, the quantity of gold is so small, that a globule can scarcely be extracted from it by the blowpipe.

Grains of native platinum are not affected by the blowpipe, either alone or mixed with fluxes; which, however, are frequently tinged green by it: but platinum, precipitated from aqua regia by vegetable or volatile alkali, is reduced by microcosmic salt to a small malleable globule. Our author has been able to unite seven or eight of these into a malleable mass; but more of them produced only a brittle one. Platinum scarcely loses all its iron, unless reduced to very thin fusion.

Silver in its metallic state easily melts, and resists calcination. Silver leaf fastened by means of the breath, or a solution of borax, may casily be fixed on it by the flame, and

through the glass it appears of a gold colour; but care must be taken not to crack the glass. Calcined silver precipitated from nitrous acid by nixed alkali is easily reduced. The microcosmic acid dissolves it speedily and copiously; but on cooling it becomes opaque, and of a whitish yellow, which is also sometimes the case with leaf-silver. Copper is discovered by a green colour, and sometimes by that of a ruby, unless we choose rather to inpute that to gold. The globules can scarcely be obtained pellucid, unless the quantity of calx is very small; but a longer fusion is necessary to produce an opacity with borax. The globule, loaded with dissolved silver during the time of its fusion in the spoon, covers a piece of copper with silver, and becomes itself of a pellucid green: autimony quickly takes away the milky opacity of dissolved luna cornea, and separates the silver in distinct grains. Cobalt, and most of the other metals, likewise, precipitate silver on the same principles as in the moist way, viz. by a double elective attraction. This metal, when mineralized by marine and vitriolic acids, yields a natural luna cornea, which produces a number of small metallic globules on the charcoal: it dissolves in microcosmic salt, and renders it opaque, and is reduced, partially at least, by borax. Sulphurated silver, called also the glassy ore of that metal, fused upon charcoal, easily parts with the sulphur it contains: so that a polished globule is often produced, which, if necessary, may be depurated by borax. The silver may also be precipitated by the addition of copper, iron, or manganese. When arsenic makes part of the compound, as in the red ore of ar-enic, it must first be freed from the sulphur by gentle roasting, and finally entirely depurated by borax. It decrepitates in the fire at first.

Copper, together with sulphur and arsenic mixed with silver, called the white ore of silver, yields a regulus having the same alloy.

Galena, which is an ore of lead containing sulphur and silver, is to be freed in the same manner from the sulphur; after which the lead is gradually dissipated by alternately melting and cooling, or is separated in a cupel from the galena by means of the flame. Bergman has not been able to precipitate the silver distinct from the lead, but the whole mass becomes malicable; and the same is true of tin, but the mass becomes more brittle.

Pure mercury flies off from the charcoal with a moderate heat, the fixed heterogeneous matters remaining behind. When calcined, it is easily reduced and dissipated, and the fluxes take it up with effervescence; but it is soon totally driven off. When mineralized by sulphur, it liquefies upon the charcoal, burt Swith a blue flanie, smokes, and gradually disappears; but, on exposing cinnabar to the fire on a polished piece of copper, the mercurial globules are fixed upon it all round,

Lead in its metallic state readily melts, and continues to retain a metallic splendour for some time. By a more intense heat it boils and smokes, forming a yellow circle upon the

« ΠροηγούμενηΣυνέχεια »