Page:Cyclopaedia, Chambers - Supplement, Volume 1.djvu/739

 FLU

Of the bivalve frefh water {hells, we have the following (pe- cks. Of the chama kind we have five. i. The white chama. 2. The red fpotted chama. 3. The blackifh brown chama. 4. The grey chama, and 5. The common dwarf chama.

Of the mufcle kind we have fix fpecies. I. The brown fpot- ted mufcle, 1. The blackifh brown mufcle. 3. The oblong mufcle. 4. The large light mufcle, 5. The long prickly mufcle, and 6. The white mufcle.

Of the fe&en kind we have only one fpecies, that is, the white pedten.

Of the multivalve clafs, there is not one known fpecies. The reducing the feveral fpecies to their proper genera is eafy from a remembrance of the characters of each genus of the marine fhells. The hmpet is a flat fhell elevated into a fort of cone at the fummit. Of the fnail kind, if the mouth be round, the fhell is a true limax; when it is femicircular, the fhell is a nerita ; and when it is oval or depreffed, and the clavicle is long, it is then a trochus. The turbo or fcrew-fhell, is known by its long and flender figure. The buccina are long fhaped, and have a tail, and their mouth is narrow ; and the dolia are of a fomewhat globofe figure. The cornu ammonis, and the umbilicated fnail are often confounded together by thofe who obferve their external refemblance among the frefh water fhells; but they are in reality fufficiently different, the cor- nu ammonis being marked on the outfide with circular ridges, and divided on the infide into feveral feparate cells like the common foflil kinds ; whereas the umbilicated fnail is of an even external furface, and has only one cavity within. The fnail alfo has its mouth placed toward one fide, the cornu ammonis in the middle : there are other differences, but thefe are fuf- ficient for the diftin&ion. The chama? are known by their roundifh figure ; the mufcles by being oblong ; and the peclen is known by its ears and its ftriae. Hift. Nat. Eclair, p. 372. FLUX, (Cycl.) in medicine. The Biftiop of Cloyne in his re- flections on tar-water, fays he has known a bloody-Flux of lung continuance, after divers medicines had been trieu in vain, cured by tar-water. But what he takes to be the moil fpeedy and effeclual remedy in a bloody-Flux, is a clyfter of an ounce of common brown rofin, diflblved over a fire in two ounces of oil, and added to a pint of broth, which not long fince he had frequent occafion of trying, when that diftemper was epide- mical. Nor can he fay, that any to whom he advifed it, mifcarried. See Tar water, &c. FLUXES, in metallurgy, are whatever can caufe a body other- wife not at all, or hardly fufible by fire, to melt. The mod powerful of thefe, are glafs of lead, and the alka- line and neutral faits. Thefe are principally ufed by affayers, when they would work minerals in a fmall quantity; but when large quantities of minerals are to be wrought on, it is feldom poflible to ufe Fluxes of this kind to any advantage, be- caufe of their prices. In thefe cafes, inftead of thefe ex pen five Fluxes, they ufe fuch ftones as are vitrified by a gentle fire, or the fcorias made of the fame ftones when melted, which al- ways ferves their purpofes much better ; for the oftner thefe ftones have been expofed to the fire, the more eafily are they put in fufion: the reafon of which feems to be, that the alka- line fait proceeding from the fuel of the fire, adheres to the fcorise ; and thefe added in large quantities to the reft of the metals in great operations, caufe the faid ores to melt, which are otherwife made refractory by the calcarious and incom- buftible ftones and earths mixed with them. The melting of gold and filver, and of their calxes is great- ly promoted by glafs of lead, alkaline falts, &c. but when gold and filver in the fufion itfelf, are to be purged from other metals and femimetals, it is proper to ufe nitre only ; or if not fo, nitre muft be always mixed with the other falts; for the femimetals and the four lefs perfedf. metals are deftroyed by nitre.

In this operation, nitre by its detonation with their fulphurs is in part alkalifed, and by the help of a gentle fire, turns their calxes into a vitrious and much attenuated fcorias. From hence, the reason is plain, why gold and filver, when made brittle, are readily reftored to their malleability by nitre : for the femimetals, and among the metals, lead, and tin, moft of all communicate this fault to gold and filver; but thefe being changed as before obferved by nitre, are then rejected by gold, and filver in a fimple fufion, fo that they can no lon- ger mix with thefe metals, unlefs they are themfelves firft again reduced to their metallic ftate ; and there Ubeiide thefe, no other body that can be mixed with filver and gold to ren- der them brittle, unlefs crude charcoal happening to fall into the veffel, wherein thofe metals are melted, mould impreg- nate them with fomething arftnical, there being fbme aifenic contained in coals of this kind; as has been demonftrated by Stahl and Hoffman.

The lefs perfect metals, and the femimetals melt more eafily by adding falts to them, than of themfelves ; they always however, lofe a great deal of their fubflance by this means, and this is more particularly the cafe, in regard to copper and iron. To amend this, it is neceflary to add feme kind of fat

F L IT

body, which prevents the deftrudtion, and even reduces the metals already deftroyed; and this is the more neceflary, when the calxes prepared either by burning, or by a detonation with nitre, are to be reduced.

The moft proper AW on thefe occafions is, that ufually known among metallurgifts, under the name of tile black Flux pan- der, and is thus prepared.

Take of common nitre one part, of crude tartar thoroughly dried, two or three parts; make them feparately into very fine powder, then grind them well together, and afterward, put them into an earthen pot, narrow at the orifice, not glazed within, and of capacity three times larger than the powder will take up; put this into a gentle fire, and as f.or. as the mafs begins to flame with fome noife, fhut the orifice of the veffel with a tile; after the detonation is over, you will find in the veflel a black oily alkaline fait, which is very eafily fufible in the fire, and is called the black flux ; keep it in a dry warm place, and in a veflel clofely fliut, to prevent its growing moift.

Tartar being burnt either alone in veffels clofely flint, or de- tonated; with nitre, is very readily alkalized ; and thus retains a coniiderable quantity of the oil which it contains in great abundance, and which is fixed enough to remain with it, af- ter this operation ; and for this reafon if very eafily becomes a reducing Flux, which on account of its alkaline falts, diflblves earths and ftones, and changes them into an imperfeft kind of giafs by a moderate melting fire; but the oil being ol a more fixed nature, ftill remains concealed therein, and is of great ufe both to pieferve metals from being deftroyed, and to re- duce filch as have been deftroyed already. It the pot in which this Flux powder is made be glez'd within, and pai t of the glazing comes off, and mixes with the Flux, and melts with it, it is again reduced to lead, and may thus difappoint the artificer; for this ciuft of glazing is given to earthen veffels by lead or litharge.

Another caution is alfo neceflary ; wl ich is, that all Fluxes muft be kept and ufed very drv, for moid falts foam very much ; and when the operations are made in clofe veffels, if the fire is quickly increafed. not being able to get rid of the moifture, the veffels will Iplit and break. Befide the black, affayers aie alfo very fond of a white Flux powder, which is prepared only of equal parti of nitre and tar- tar detonated in the fame manner. Foi in this cafe the oil of the tartar is almoft entirely confirmed by the abundance of the nitre, and the remaining mafs becomes a whitifh or a(h coloured fait ; which is alfo more powerfully alkaline, and fnarp than the foregoing. This Flux is very efficacious in the diflolvmg of ftones, and earths; but for want of its oil is of a lels redufiive virtue, and deftroys the metal, when the fire is continued a little longer than is required. Flux powders ate of great il-rvice alfo to reduce metals out of their refpedtive calxes, and to free them from the ('ones in which they are embodied; but when the refractory calx of i- ron is to be reduced by a great and long failing fire, thefe Fluxes being greatly attenuated, tho' confined in clofe veffels, part from their oily principle, and their alkaline fall re- maining, begin to corrode and confume the veffels of what matter loeier they are made, and finally make their way thro' them and get out. The firft of theie ac.-idents is preveined by adding coal duft, which will never paitwnh its oil, without the help of a free air ; and the others by an admixture of com- mon gluts, made of a due mixture t f flints and fixed alk ili. For this is fuflicientlv fufible, and readily melts with ihe fluxes, and by its vifcidity, in fome lort coagulates, ind holds the fait of the Flux together, and prevents it from >o eafily corroding the veffels.

Many artificers arM to compofe a great variety of Fluxes with the dfferent proportions and combinations of the alkaline and neutral falts ; nay fome are tor having as many Fluxes, as there are ores of metals; but thefe fimples ores will be found on trial more ufel'ul, as well as more ealily prepared, than ma- ny of the laboured compofitions, which inc.eafe the number, not the virtue of the things employed. The skilful will eafi- ly make from thefe the flight neceflary variations. Liamer> Art. rtff. p. 48, 52.

The great fecret in making and improving Fluxes for the ores of metals, is not only to find fuch ingredients as will be of ef- ficacy to feparate the metal ahead) ripei.ed in the ore, but even to mature and ripen the yet immature part of it in ihe fire ; and fomething of this kind we a, prebend might be ef- fected, as there is great reafon to believe, that certain Fluxes will obtain a much larger yield of metals from certain ores than other Fluxes in common uie, tho* efleemed of the belt, and perhaps of the deareft kind : thus clean iron filings will often do more than borax; but as the fcales and ruff, oi iron have commonly been ufed under the name of iron in Fluxes, few operators know the value of pure iron in that intention, and many advantages are now obtained by mixing one ore with another of the fame denomination, and with the fla^s or recrements of metals in the way of a Flux. The Fluxes for the ores of metals feem in general reducible to

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