Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/24

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, tincture gives it a tendency to blacknels, of any degree of deep red that is dented.

A blue colour may be given alfo to Marble by diffolving turnibi in a lixivium of lime and urine, or in the volatile fpi- rit of urine ; but this has always a tendency to purple, whe- ther made by the one or the other of thefe ways. A better blue* and ufed in an eafier manner, is furnifhed by the ca- nary turnfol, a fubftance well known among the dyers : This needs only to be difiolved in water, and drawn on the place with a pencil ; '.his penetrates very deep into the Marble, and the colour may be encrcafed by drawing the pencil wet- ted afrefti feveral times over the fame lines. This colour is fnbjea to fpread and diffufe itfelf irregularly ; but it may be kept in regular bounds, by circumfcribing its lines with beds of wax, or any other fuch fubitance. It is to be obferved, that this colour fhould always be laid on cold, and no heat given even afterwards to the Marble ; and one great advan- tage of this colour is, that it is therefore eafily added to Mar- hies already ftained with any other colours, and it is a very beautiful tinge* and lafts a long time. Mem. Acad. Par. 1732.

Marble Colour. To give this variegated colour to glafs is a very eafy operation : There needs no more than to put cryftal frit into a pot in the furnace, and to work it before it has ftood the ufual time to purify in the fire. Neri's Art ot Glafs, p. 99.

Marble Wood, a name given by the people of fome parts of America to the lignum rhodium, orrofe-wood, from the heart of the tree being fometimes variegated like Marble.

MARBLED {CycL) — Marbled China IFare, a name given by many to a (pedes of porcelain, or China-ware which iecms to be full of cemented flaws. It is called by the Chinefe, who are very fond of it, tfou tchi.

It is generally plain white, fometimes blue, and has exactly the appearance of a piece of China which had been firft: broken, and then had all the pieces cemented in their places again, and covered with the original varnifh. The manner of preparing it is eafy, and might be imitated with us. In- ftead of the common varnifh of the China-ware, which is made of what they call oil of ftone and oil of fern mixed to- gether. They cover this with a fimple thing made only of a fort of coarfe agates, calcined to a white powder, and ieparated from the grofler parts by means of water, after long grinding in mortars. When the powder has been thus prepared, it is left moift, or in form of a fort of cream, with the laft water that is fufFered to remain in it, and this is ufed as the varnifh. Our cryftal would ferve fully as well as thefe coarfe agates, and the method of preparation is perfectly eafy. Obf. fur les Cout. de PAfie.

The occafion of the fingular appearance of this fort of Porce- lain is, that the varnifh never fpreads evenly, but runs into ridges and veins. Thefe often run naturally into a fort of mofaic work, which can fcarce be taken for the effect of chance. If the marbled China be defired blue, they firft give it a general coat of this colour, by dipping the vellel into a blue varnifh ; and when this is thoroughly dry, they add an- other coat of this agate oil,

MARCASITE, {Cycl.) in natural hiltory, a name ufed in a very vague fenfe by many writers upon foflils, but reftrain'd by Dr. Hill to be the name of a peculiar genus of foflils, the characters of which are, that they are compound inflamma- ble metallic bodies, naturally conftituting whole ftrata ; of a folid and firm fubftance, of an obfeurely and irregularly fo- liaceous ftructure, and of a bright glittering appearance, very freely and readily giving fire with fteel, not fermenting with acid menftruums, and when put into the fire, yielding a deep blue flame, and finally calcining into a purple powder. Though the natural difpofition of thefe boclies be to form whole ftrata, and that they are moil ufually found in this firate, yet they are at times found in loofe mafles, as many, even of the ftones of ftrata, at times are. They are fubject alfo, by their frequent admixtuie with adventitious matter, the ores of metals, and other foflife bodies, to fuch various external appearances, that their varieties are almoft innumerable, and molt of them are very beautiful : But tho' thefe accidental differences are fo very numerous, the genuine fpecies are very few, the naturalift allowing only three. Thefe are, 1. The bright filver-colour'd Marcafite. 2. The bright gold-co!our'd Marcafite. And 3. The pale heavy dead white Marcafite. The firft fpecies ufually conititutes ftrata of great extent, and of about a foot in thicknefs ; very often much lefs, but fcarce ever much more : It is compofed of a number of fo- liaceous flakes, not regularly difpoied, but oddly contorted and waved, and often folding round one another \ though fome- times this ftructure is lefs diftinct, and the whole feems run into one folid mafs. Its colour is extremely bright, very like iilver, but more glittering. This is its common and its more pure Hate ; but it is liable to a vaft number of varieties. Sometimes it contains a large quantity of the ore of lead or tin, and very often a dulky brown ferrugineous matter is in- timately mixed with it ; at other times many of the angular and regularly figured phlogonias are immerfed in it, and feem to make a part of its very ftructure ; and fometimes where it has room, its conftitucnt flakes rife on its furface in feveral conjunct feries, and form a very elegant foliaceous top to it. Nor is this all the difference of appearance it puts on; for very often, where there has not been a fufficient quantity of

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it to form itfelf into any figure alone, it is found depofitod til fpecks, or fiat cakes, of a more or lefs complex, but always. of a flaky ftructure, on ftones or ores of various kinds ; and frequently, beiide its native filvery white, it has all the rain- bow-colours on its different parts, as differently turned to the light. Hill's Hift. of Fofi: p. 609.

The golden Marcafite is a more beautiful fubftance than the former : It is of a lefs firm or compact ftructure than the others, and is ufually found in very long but very thin ftrata, and is of an extremely bright and glittering appearance* and is fometimes found in large and mif-fhapen nodules, or loofe mafles. It is liable to all the accidental varieties that the former is, and in many of them makes a very elegant ap- pearance. The third, or dead white kind, is the hardeft and heavieft of all. It is, in its more ufual and natural ap- pearance, of much lefs beauty than the former kinds, but it is, like them, fubject to various accidents, under fome of which its makes a very gay and fplendid appearance. It, like the reft, fometimes forms compleat ftrata, fometimes de- tach'd nodules ; but its molt ufual appearance is in the hori- zontal cavities of other ftrata ; in thefe it often forms a fort of baftard ftratum of many yards continuance, and frequently of very confiderable thicknefs, for it almoft always fills up the whole vacuity, and that fo clofely as feldom to leave room for any foliaceous fhoots at its furface, or protuberances at its edges, but forms a plain mafs like that of a metal melted and poured into the place. It is of the fmootheft furface of all the Marcafites, and is fomewhat foft to the touch, and in' colour refembles tarnifhed pewter.

This is its common appearance, but it fometimes {hews itfelf like the reft in fmall patches on the furfaces of ftones, and is there often very beautifully foliated ; it is liable alfo to all the accidents of the other kinds.

The Marcafites are all found In great plenty in the Englifh and German mines. Devonfhire and Cornwall afford vaft quantities of them ; and very beautiful ones are found in Derbyfhire. They often contain the feveral metals, but the quantity of fulphur has yet baffled all the attempts that have been made to work them to advantage. Hill, Hift. of Foil", p. 610.

Avifenna mentions four kinds of Marcafite; the golden, the filvery, the brafly, and the iron Marcafite. He does not pretend that the two firft contain really the metals whofe names they bear, but fays they are fo called from their likenefs in colour, and that they are thought by fome to poiTefs, in part, their virtues. Diofcorides mentions only one kind, that is, the brafly pyrites or Marcafite. This is, of all others, the moft common ; and the preference is given by this author to fuch of it as is of a bright brafs colour, and fuch as, when ftruck againft fteel, yields the Iargeft fparks. This is the kind called by Avifenna and Serapio, Marcafita ■nuhafi, and it is called by the Perfians, hagiar alruxenavi, that is, the ftone of light or brightnefs, there being a very vivid and fparkling luftre in this ftone when newly broken. The antients ufed to calcine it, and then made it an ingre- dient in their feveral compofitions for difeafes of the eyes. The calcining it renders it a fort of colcothar of vitriol, for the fulphureous parts burn away in the operation, and leave only the caput mortuum of the vitriol behind ; fome have fup- pofed it called lapis lucis, from its reftoring light to the eyes ; but this is a very far fetch'd etymology.

The firft opinion of the world, in regard to this flittering fubftance, was, that it was almoft all gold or filver, accord- ding to the colour : But the error of this opinion being foon difcovered by trials, there grew another contrary one, that Marcafite never contained any metal at all. This is, in ge- neral, true of our Marcafites^ but it is not to be extended into a general rule for thofe of all the world. The fearchers after royal mines are not to throw away all thefe fubftances as ufe- lefs, whercverthey find them. For Alonfo Barba, a very great judge of thefe things, and himfelf very converfant in mines, allures us, that the Marcafites of the mines of Montferrat en los chicas contain ufually one half filver : And in the mines of Potoft there is great plenty of a Marcafite, in which there is embodied a large quantity of the black filver ore, well known there, and efteemed one of the richeft kinds, except the na- tive filver. They always are glad to find this Marcafite vein, it being efteemed a proof, that the black ore is very rich in filver. They make the fame fort of obfervation in regard to orpiment and gold, that they do in regard to Marcafite and filver; that the orpiment ufually contains itfelf fome o-old, and is a certain fign that there is gold in the neighbourhood wherever it is found. Alonfo Barba dc Met. MARCH, (Cycl,) in military affairs, is in general the fteps made in marching, or the moving of a body of men from one place to another.

But the beat of the drum, when the foldicrs are upon March, or beginning to march, is like-wife called the March. It ia likewife a word of command, when a battalion is to alter its difpofition.

To march is to move from one place to another. The orders being given the evening before a March, that the drums beat at a certain hour, the foldiers are then ready drawn up at their ftandards and colours, in fuuadrons, or battalions, ready to begin their march,

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