Page:Cyclopaedia, Chambers - Volume 1.djvu/617

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DUG

Ductus Taucreaticw, a little Canal arifing from the 'pancreas, and opening into the 'Duodenum, ferving to dif- charge the Pancteatic juice into the Intefiines. See Pan- creas, and Pancreatic Juice.

This Z>»S being firft difcover'd by Virtfimgitl, is fre- quently call'd Z)ublus Virtfiingianus.

Ductus Salivates, the excretory Tubes of the Salival Glands ; ferving to difcharge the fecreted Saliva into the j^louth. See Salival 2)uEts.

Ductus Lachrymales, the excretory Veffels of the Glan- AuU Lachrymales, ferving for the Effufion of Tears. See Lachrymal 2)iiSs.

Ductus Alimentalh, a Name that accurate Anatomiit, Dr. Tyfin, gives the Gula, Stomach, and Intefiines ; all which" make but one continued Canal, or Ztefi. This Dud he makes the proper Charafleriftic of an Animal.

Ductus Urinaruis, the fame as the Urethra. See Ure- thra. Ductus Umbilicalis. Sec Funiculus Uvibilicalis. Ductus ChyliflrmA h f as % gm <£ iora6im. Ductus Ron f ems, i See Thoracic y Duffi. Ductus I'horaciciis. See Thoracic 2)ubJ. The thoracic tDutl, Dr. Wharton affures us, was obfer- ved by 'Barthol. Eufiachio in 1 5CT3 ; but its Life, and Com- munication with the Receptaculum Chyli, was unknown. And hence "Pecquet, a Phyiician of ' "Dieppe, is commonly fuppofed to have firft difcover'd it in 1651 - whence its Denomination Z)utJus PecquctiamtS : Tho' the Defcription he gives of its Infcrtion is faulty. Van Home confounds it with the Receptaculum, or as he calls it, Ciftema Chyli.

DUCTILITY, in Phyficks, a Property of certain Bodies, whereby they become capable of being beaten, prefs'd, drawn, or ftretch'd forth, without breaking ; Or, whereby they are capable of great Alterations in their Figure, and Dimcnfions; and of lofing in one Way, as they gain in another. See Mat- ter, Body, &c.

Such are Metals, which being urg'd by the Hammer, gain in Length and Breadth what they lofe in Thicknefs 5 or be- ing drawn into Wiar through Iron, grow longer as they be- come ilenderer. See Metal.

Such, alfo, are Gums, Glues, Reims, and fome other Bo- dies, which, tho 1 not malleable, yet may be denominated 2)utlile, in as much as when foften'd by Water, Fire, or fome other Menftruum, they may be drawn into Threads. See Malleable.

So that we have two Gaffes o^DnBile Eodies. The one Hard, and the other Soft : Each of which we Jhall beftow fome Confiderations upon.

The Caufe of "Dutiiiity is very oblcure ; as depending in oreat Meafure on Hardnefs, than which there is nothing in Nature we know lefs of. 'Tis true, we ufually account for Hardnefs from the Force of Attraction between the Par- ticles of the hard Body ; and for 1)uc7ility from the Particles of the ductile Body, being, as it were, joynted, and entangled within each other. See Hap.dness, Cohtesion, £SV. 1 Inftead of fanciful Hypothefes to account for IjitBilhy ; we fhall here entertain the Reader with fome truly amazing Circumftances and Phenomena thereof.

One of the Properties of Gold, is to be the moft ductile of all Bodies. See Gold.

Of this, the Gold-beaters, and Gold Wiar-drawers, furnifti us with abundant Proof. Fa. Merfenne, Monfr. Rohazdt, Dr. Halley, &c. have made Computations thereof: But they trufted to the Reports of the Workmen. Monfr. Reaumur, in the Memoir e$ de VAcademie Roy ale des Sciences An.i-j 13. took a furer Way : He made the Experiment himfelf. A Angle Grain of Gold, he found, even in the common Gold- Leafs, us'd in moft of our Gildings, is extended into ^6 and a half, fquare Inches ; and an Ounce of Gold, which in Form of a Cube is not half an Inch cither high, broad, or long, is beat under the Hammer into a Surface of 1415" and a half fquare Feet : An Extent almoft double what could be done 90 Years ago. In Fa. Merfennes time, it was deem'd pro- digious, that an Ounce of Gold mould form itfoo Leaves ; which together only made a Surface of 105 fquare Feet. See GoLV-Beating.

But the Detention of Gold under the Hammer (how con- siderable foever) is nothing to that it undergoes in the Draw- ing Iron. There are Gold-Leaves, in fome Parts, fcarce j 6oooo Part of an Inch thick ; but ^ oooo Part of an Inch is a no- table Thicknefs, in Companion of that of the Gold fpun on Silk in our Gold-Thread.

To conceive this prodigious "Ductility, it is ncceffary, to have fome Idea of the Manner wherein the Wiar-drawers proceed. The Wiar, and Thread we commonly call Gold- Thread, &c. which every body knows is only Silver-Wiar gilt, or cover'd over with Gold, is drawn from a large Ingot of Silver, ufually about 30 Pound Weight. This they round into a Cylinder, or Roll, about an Inch and a half in Dia- meter, and 22 Inches long; and cover it over with the Leaves

prepared by the Gold-beater, laying one over another, till the Cover is a good deal thicker than that in our ordinary Gilding. And yet even then 'tis very thin ; as will be eafi- ly conceiv'd from the Quantity of Gold that goes to gild the 30 Pound of Silver. Two Ounces, ordinarily, do the Bu- finefs ; and frequently little more than one. In effect, the full Thicknefs oftheGoldon the Ingot rarely exceeds '"•*■ or ~ oo Part, and fomctimes not 7 000 Part of an Inch.

But this thin Coat of Gold mult be yet much thinner : The Ingot is fucceflively drawn through the Holes of feve- ral Irons each lefs than other, till it be as fine, or finer than a Hair. Every new Hole leflens its Diameter ; but it gains in Length what it lofes in Thicknefs, and of Confequence in- creafes in Surface. Yet the Gold {till covers it; h follows the Silver in all its Exteniion ; and never leaves the minu- teft Part bare, not even to the Microfcope. Yet, how in- conceivable muft it be attenuated while the Ingot is drawn into a Thread, whofe Diameter is 51000 times lefs than that of the Ingot.

Mr. Reaumur, by ex a £1 weighing, and rigorous Calcula- tion, found, that one Ounce ot" the Thread was 3232 Feet long, and the whole Ingot 1KJ3520 Feet, 'Paris Meafure, or 96 French Leagues ; equal to 1264400 Englijh Feet, or 240 Miles Englift ; An Extent which far furpalfes what Fa. Merfenne, Furetiere, Dr. Halley, &c. ever dreamt of.

Merfenne fays, that half an Ounce of the Thread is 100 Toifcs, or Fathoms long;' on which footing, an Ounce would only be 1200 Foot: whereas Monfr. Reaumur finds it 3232. Dr. Halley makes 6 Foot of the Wiar one Grain in Weight, and one Grain of the Gold, 98 Yards, and confequently the ten thoufandth Part of a Grain above one Third of an Inch. The Diameter of the Wiar he found one iSfi'th Part of an Inch ; and the Thicknefs of the Gold one 154500th Part of an Inch. But this, too, comes fhort of Monfr. Reaumur : For on this Principle, the Ounce of. Wiar would only be 2i5"So Feet.

But the Ingot is not yet got to its full Length. The greateft Part of our Gold-Thread is fpun, or wound on Silk 5 and before they fpin it, they flat it, by pafling it between two Rolls, or Wheels of exceedingly polifh'd Steel ; which Wheels, in flatting it, lengthen it by above one Seventh. So that our 240 Miles are now got to 274. The Breadth, now, of thefe Lamince, or Plates, Monfr. Reaumur finds, is only one 8th of a Line, or one ptfth of an Inch, and theirThicknefs one 3072th. The Ounce of Gold, then, is here extended to a Surface of 1190 fquare Feet ; whereas, the utmoft the Gold-beaters can do, we have obferved, is, to extend it to 146 fquare Feet.

But the Gold, thus exceedingly extended, how thin mud: it be? From Monfr. Reamnur's Calculus it is found to be one 175000th of a Line, or one 2100000th of an Inch; which is fcarce one 13th of the Thicknefs of Dr. Halley's Gold. But he adds, that this fuppofes the Thicknefs of the Gold every where equal ; which is noways probable : For in beat- ing the Gold-leaves, whatever Care they can bellow, 'tis im- poiTible to beat 'em equally. This we eafily find by the greater Opacity of fome Parts than others. And where the Leaf is thicker!, it will gild the Wiar the tkickeft.

Monfr. Reaumur computing what the Thicknefs of the Gold mult be where thinneft, finds it only one 3150000th of an Inch. But what is the one 3150000th Part of an Inch? Yet this is not the utmoft 'Dutliliry of Gold : For inftead of two Ounces of Gold to the Ingot, which we have here computed upon, a fingle one might have been ufed ; And then the Thicknefs of the Gold, in the thinneft Places, would only be the <J3oooooth Part of an Inch.

And yet, as thin as the Plates are, they might be made twice as thin, yet ftill be gilt; by only prefling 'em more be- tween the Wheels, they are extended to double the Breadth, and proportionably in Length. So that their Thicknefs at laft will be reduced to one thirteenth, or fourteenth Mil- lionth Part of an Inch.

Yet with this amazing Thinnefs of the Gold, 'tis ftill a perfecl: Cover for the Silver. The beft Eye, nor even the beft Microfcope, cannot difcovcr the leaft Chafm, or Difconti- nuity. There is not an Aperture to admit Alcohol of Wine, the fubtileft Fluid in Nature, nor even Light it felf. Add, that if a Piece of this Gold-Thread, or Gold-plate, be laid to diffolve in Aqua fortis, the Silver will be ail excavated, or eat out, and the Gold left entire in little Tubules.

As to the Dutfility of Soft Bodies, it is not yet earned to that Pitch. The Reader, however, mull not be furpmed, that among the ductile Bodies of this Clafs, we gave the firft Place to the meft brittle of all others, Glafs. We all know, that when well penetrated with the Heat of the Fire, the Workmen can figure, and manage it like foit Wax. But what is moft remarkable," is, that it may be drawn, or fpun out into Threads exceedingly fine, and lon S-

Our ordinary Spinners don't form their Threads of Silk, Flax, or the like, with half the Bate, and Expeduion. as the Glafs-Spinners do Threads of this brittle Matter. We have^