DUCT 
may be drawn into threads. Some bodies are dudtile 
both when they are hot and cold, and in all circum- 
ftances: fitch are metals, and efpecially gold and lilver; 
other bodies are dudtile only when they have a certain 
degree of heat; fitch as glafs and wax ; others again are 
ductile only when cold, and brittle when hot ; as feme 
kinds of iron, viz. thofe called by workmen redfhot, as 
all'o bra'fs, and fome metallic alloys. 
The caufe of dud'tility is very obfeure; as depending 
much on hardnefs, a quality whole nature we know but 
little about. It is true, it is ufual to account for hard- 
nefs from the force of attradfion betw een the particles of 
the hard body ; and for dudtility, from the particles of 
the dudtile body being, as it were jointed, and entangled 
with each other. But without dwelling on any fanciful 
liypothefes about dudtility, we may inform ourfelves of 
fome truly amazing circumdances and phenomena of it, 
in the inftances of gold, glafs, fpider’s webs, See. oblerv- 
ing, however, that the dudtility of metals decreafes in the 
following order: gold, lilver, copper, iron, tin, lead. 
Gold is faid to be the molt dudtile of all bodies; of 
which the gold-beaters and gold-wire-drawers furnifh us 
with abundant proofs. Merlenne, Robault, Dr. Halley, 
&c. have made computations of it ; but they trufled to 
the reports of the workmen. M. Reaumur, in the Me- 
moires de l'Academic Royale des Sciences, anno 1713, took a 
furer way ; he made the experiment himfelf. A fingle 
grain of gold, he found, even in the common gold-leaf, 
ufed in molt of our gildings, is extended into thirty-lix 
and a half (quare inches; and an ounce of gold, which, 
in form of a cube, is not half an inch either high, broad, 
or long, is beat under the hammer into a furface of 146 
and a half Iquare feet; an extent almolt double to what 
could be done in former times. In Merfenne’s time, it 
was deemed prodigious, that an ounce of gold Ihould form 
1600 leaves ; which, together, only made a furface of 105 
fquare feet. But the didenfion of gold under the ham¬ 
mer (how confiderable foever) is nothing to that which 
it undergoes in the drawing-iron. There are gold leaves 
in fome parts fcarcely the -3^5*050 P art an hich thick ; 
but -jeoVoo P art of an inch is a confiderable thicknefs, in 
compariion of that of the gold fpun on filk in our gold 
thread. To conceive this prodigious ductility, it is ne- 
ceffary to have fome idea of the manner in which the 
wire-drawers proceed. The wire and thread we com¬ 
monly call gold-thread, Sec. (which is only filver-wire 
gilt, or covered over with gold,) is drawn from a large 
ingot of filver, ufually about thirty pounds weight. This 
they round into a cylinder, or roll, about an inch and a 
half in diameter, and twenty-two inches long, and cover 
it 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, it is 
very thin ; as will be ealily conceived from the quantity 
of gold that goes to gild the thirty pounds of filver : two 
ounces ordinarily do the bufmefs; and, frequently, little 
more than one. In effect, the foil thicknefs of the gold 
on the ingot rarely exceeds or part; and fome- 
times not -j-^oo P art °f an inch. But this thin coat of 
gold muff be yet vadly thinner : the ingot is fucceffively 
drawn through the holes of feveral irons, each fmaller 
than the other, till it be as fine or finer than a hair. 
Every new hole lelfens its diameter ; but it gains in 
length what it lofes in thicknefs; and, of’confequence, 
increafes in furface : yet the gold dill covers it; it fol¬ 
lows the filver in all its extenfion, and never leaves the 
minuteft part bare, not even to the microfcope. Yet, 
how inconceivably mud it be attenuated while the ingot 
is drawn into a thread, whofe diameter is 9000 times lefs 
than that of the ingot. 
M. Reaumur, by exadb weighing, and rigorous calcu¬ 
lation, found, that one ounce of the thread was 3232 feet 
long ; and the whole ingot 1,163,520 feet, Paris meafure, 
or ninety-fix French leagues; equal to 1,264,406 Eng! ilh 
feetj or 240 miles Englilh j an extent which far furpaifes 
I L I T Y. 107 
what Merfenne, Furetiefe, Dr. Halley, Sec. ever dreamt 
of. Merfenne fays, that half an ounce of the thread is 
100 toifes, or fathoms long; on which footing, an ounce 
would only be 1200 feet; whereas M. Reaumur finds it 
3232. Dr. Halley makes fix feet of the wire one grain 
in weight, and one grain of the gold ninety-eight yards; 
and, con-fequently, the ten thoufandth part of a grain, 
above one-third of an inch. The diameter of the wire 
lie found one-i86th part of an inch ; and the thicknefs of 
the gold one-154,500th part of an inch. But this, too, 
comes fiiort of M. Reaumur; for, on this principle, the 
ounce of wire would only be 2680 feet. But the ingot 
is not yet extended to its full length. The greated part 
of our gold-thread is fpun, or wound on filk; and, be¬ 
fore it is Ipun, they flat it, by palling it between two 
rolls, or wheels of exceedingly well polilbed fteel; which 
wheels, in flatting it, lengthen it by above one-feventh. 
So that out 240 miles are brought to 274. The breadth, 
now, of thele laminae, or plates, M. Reaumur finds, is 
only one-eighth of a line, or one-ninety-fixth of an inch ; 
and their thicknefs one-3072d. The ounce of gold, then, 
is here extended to a furface of 1190 Iquare feet; whereas 
the utmofi the gold-beaters can do, we have obferved, is 
to extend it to 146 fquare feet. But the gold, thus ex¬ 
ceedingly extended, how thin muft it be! From M. Reau¬ 
mur’s calculus, it is found to be one-175,oooth of a line, 
or one-2,100,000th of an inch ; which is fcarcely o: e-thir¬ 
teenth of the thicknefs of Dr. Halley’s gold. But, he 
adds, that this fuppofes the thicknefs of the gold every 
where equal, which is no ways probable ; for in beating 
the gold-leaves, whatever care they can bellow, it is im- 
pollible to extend them equally. This we ealily find, by 
the greater opacity of fome parts than others ; for, where 
the leaf is thicked, it will gild the wire the thickeft. 
M. Reaumur, computing what the thicknefs of the 
gold mult be where thinneft, finds it only one-3,150,000th 
part of an inch. But what is the one-3,150,000th part of 
an inch ? Yet this is not' the utmoll ductility of gold ; 
for, inllead 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 thin¬ 
ned places, would only be the 6,300,000th part of an inch. 
And yet, as thin as the plates are, they might be made 
twice as thin, yet Hill be gilt; by only prefling them more 
between the flatter’s wheels, they are extended to double 
the breadth and proportionably in length. So that their 
thicknefs, at laft, will be reduced to one-thirteen or four¬ 
teen millionth part of an inch. Yet, with this amazing 
thinnefs of the gold, it is Hill a perfect cover for the fil- 
ver: the belt eye, or even the belt microfcope, cannot 
djfcover the lead chafm, or difeontinuity. There is not 
an aperture to admit alcohol of wine, the fubtiled fluid 
in nature, or even light itfelf, unlefs it be owing to cracks 
occafioned by repeated drokes of the hammer. And, if. 
a piece of this gold-thread, or gold-plate, be laid to dif- 
folve in aquafortis, the filver will be all excavated, or 
eat out, and the gold left entire, in little tubules. It 
Ihould be obferved, that gold, when it has been druck 
for fome time by a hammer, or violently compreffed, as 
by gold-wire-drawers, becomes more hard, eiadic, and 
did - , and lefs dudtile, fo that it is apt to be cracked or 
torn : the fame thing happens to the other metals by per- 
cuOion and compredion. But dudtility and tradtability 
may be redored to metals in that date, by annealing them, 
or making them red-hot. Gold feems to be more affect¬ 
ed by percuffion and annealing, than any other meta'lSi- 
As to the dudlility of foft bodies, it is not yet carried 
to that pitch. The reader, howdvef, mud not be fur- 
prifed that, among the dudtile bodies of this clafs, we 
give the fird place to the mod brittle of all other, glafs. 
We all know that, when w'ell penetrated with the heat 
of the fire, the workmen can figure and manage glafs like 
foft wax ; but, what is mod remarkable, it may be drawn, 
or fpun out into threads, exceedingly fine and-long. Our 
ordinary fpinners do not form their, threads'o'ffijk, flax,, 
